Lasting mantle scars lead to perennial plate tectonics

PubMed Central

Heron, Philip J.; Pysklywec, Russell N.; Stephenson, Randell

2016-01-01

Mid-ocean ridges, transform faults, subduction and continental collisions form the conventional theory of plate tectonics to explain non-rigid behaviour at plate boundaries. However, the theory does not explain directly the processes involved in intraplate deformation and seismicity. Recently, damage structures in the lithosphere have been linked to the origin of plate tectonics. Despite seismological imaging suggesting that inherited mantle lithosphere heterogeneities are ubiquitous, their plate tectonic role is rarely considered. Here we show that deep lithospheric anomalies can dominate shallow geological features in activating tectonics in plate interiors. In numerical experiments, we found that structures frozen into the mantle lithosphere through plate tectonic processes can behave as quasi-plate boundaries reactivated under far-field compressional forcing. Intraplate locations where proto-lithospheric plates have been scarred by earlier suturing could be regions where latent plate boundaries remain, and where plate tectonics processes are expressed as a ‘perennial' phenomenon. PMID:27282541

Seafloor spreading on the Southeast Indian Ridge over the last one million years: a test of the Capricorn plate hypothesis

NASA Astrophysics Data System (ADS)

Conder, James A.; Forsyth, Donald W.

2001-05-01

Plate motions in the Indian Ocean are inconsistent with a rigid Indo-Australian plate. An equatorial, diffuse boundary dividing the plate into separate Indian and Australian plates significantly improves the fit of kinematic plate models to the spreading rates, transform azimuths, and earthquake slip vectors on the spreading center boundaries. An additional boundary, further dividing the Australian plate into Australian and Capricorn plates has been proposed to account for much of the remaining inconsistency and the pattern of intraplate earthquakes [J.-Y. Royer, R.G. Gordon, Science 277 (1997) 1268-1274]. The proposed boundary is ˜2000 km wide where it intersects the Southeast Indian Ridge. Several recent geophysical cruises to the Southeast Indian Ridge, including a cruise within the proposed boundary, provide many new data for investigating the validity of the Capricorn plate model. These new observations strongly support the hypothesis that the Capricorn plate exists. Statistical tests of the data from the Southeast Indian Ridge alone are not sufficient to confirm it, but motion about the Rodriguez Triple Junction (RTJ) suggests some non-rigidity in the Antarctica-Australia-Somalia circuit. Inferred deformation with enforced closure about the RTJ leads to an estimate of plate motion consistent with the Capricorn plate model. However, the diffuse Capricorn-Australia boundary does not extend south of the St. Paul Fracture Zone, 800 km narrower than the previously proposed boundary.

Nonlinear Radiation Heat Transfer Effects in the Natural Convective Boundary Layer Flow of Nanofluid Past a Vertical Plate: A Numerical Study

PubMed Central

Mustafa, Meraj; Mushtaq, Ammar; Hayat, Tasawar; Ahmad, Bashir

2014-01-01

The problem of natural convective boundary layer flow of nanofluid past a vertical plate is discussed in the presence of nonlinear radiative heat flux. The effects of magnetic field, Joule heating and viscous dissipation are also taken into consideration. The governing partial differential equations are transformed into a system of coupled nonlinear ordinary differential equations via similarity transformations and then solved numerically using the Runge–Kutta fourth-fifth order method with shooting technique. The results reveal an existence of point of inflection for the temperature distribution for sufficiently large wall to ambient temperature ratio. Temperature and thermal boundary layer thickness increase as Brownian motion and thermophoretic effects intensify. Moreover temperature increases and heat transfer from the plate decreases with an increase in the radiation parameter. PMID:25251242

An updated digital model of plate boundaries

NASA Astrophysics Data System (ADS)

Bird, Peter

2003-03-01

A global set of present plate boundaries on the Earth is presented in digital form. Most come from sources in the literature. A few boundaries are newly interpreted from topography, volcanism, and/or seismicity, taking into account relative plate velocities from magnetic anomalies, moment tensor solutions, and/or geodesy. In addition to the 14 large plates whose motion was described by the NUVEL-1A poles (Africa, Antarctica, Arabia, Australia, Caribbean, Cocos, Eurasia, India, Juan de Fuca, Nazca, North America, Pacific, Philippine Sea, South America), model PB2002 includes 38 small plates (Okhotsk, Amur, Yangtze, Okinawa, Sunda, Burma, Molucca Sea, Banda Sea, Timor, Birds Head, Maoke, Caroline, Mariana, North Bismarck, Manus, South Bismarck, Solomon Sea, Woodlark, New Hebrides, Conway Reef, Balmoral Reef, Futuna, Niuafo'ou, Tonga, Kermadec, Rivera, Galapagos, Easter, Juan Fernandez, Panama, North Andes, Altiplano, Shetland, Scotia, Sandwich, Aegean Sea, Anatolia, Somalia), for a total of 52 plates. No attempt is made to divide the Alps-Persia-Tibet mountain belt, the Philippine Islands, the Peruvian Andes, the Sierras Pampeanas, or the California-Nevada zone of dextral transtension into plates; instead, they are designated as "orogens" in which this plate model is not expected to be accurate. The cumulative-number/area distribution for this model follows a power law for plates with areas between 0.002 and 1 steradian. Departure from this scaling at the small-plate end suggests that future work is very likely to define more very small plates within the orogens. The model is presented in four digital files: a set of plate boundary segments; a set of plate outlines; a set of outlines of the orogens; and a table of characteristics of each digitization step along plate boundaries, including estimated relative velocity vector and classification into one of 7 types (continental convergence zone, continental transform fault, continental rift, oceanic spreading ridge, oceanic transform fault, oceanic convergent boundary, subduction zone). Total length, mean velocity, and total rate of area production/destruction are computed for each class; the global rate of area production and destruction is 0.108 m2/s, which is higher than in previous models because of the incorporation of back-arc spreading.

An eddy-viscosity treatment of the unsteady turbulent boundary layer on a flat plate in an expansion tube

NASA Technical Reports Server (NTRS)

Gupta, R. N.; Trimpi, R. L.

1974-01-01

An analysis is presented for the relaxation of a turbulent boundary layer on a semiinfinite flat plate after passage of a shock wave and a trailing driver gas-driven gas interface. The problem has special application to expansion tube flows. The flow-governing equations have been transformed into the Lamcrocco variables. The numerical results indicate that a fully turbulent boundary layer relaxes faster to the final steady-state values of heat transfer and skin-friction than a fully laminar boundary layer.

Unsteady boundary layer flow and heat transfer of a Casson fluid past an oscillating vertical plate with Newtonian heating.

PubMed

Hussanan, Abid; Zuki Salleh, Mohd; Tahar, Razman Mat; Khan, Ilyas

2014-01-01

In this paper, the heat transfer effect on the unsteady boundary layer flow of a Casson fluid past an infinite oscillating vertical plate with Newtonian heating is investigated. The governing equations are transformed to a systems of linear partial differential equations using appropriate non-dimensional variables. The resulting equations are solved analytically by using the Laplace transform method and the expressions for velocity and temperature are obtained. They satisfy all imposed initial and boundary conditions and reduce to some well-known solutions for Newtonian fluids. Numerical results for velocity, temperature, skin friction and Nusselt number are shown in various graphs and discussed for embedded flow parameters. It is found that velocity decreases as Casson parameters increases and thermal boundary layer thickness increases with increasing Newtonian heating parameter.

A Plate Tectonic Model for the Neoproterozoic with Evolving Plate Boundaries

NASA Astrophysics Data System (ADS)

Merdith, Andrew; Collins, Alan; Williams, Simon; Pisarevsky, Sergei; Müller, Dietmar

2017-04-01

The Neoproterozoic was dominated by the formation of the supercontinent Rodinia, its break-up and the subsequent amalgamation of Gondwana, during which, the planet experienced large climatic variations and the emergence of complex life. Here we present a topological plate model of the Neoproterozoic based on a synthesis of available geological and palaeomagnetic data. Subduction zones, which are well preserved in the geological record, are used as a proxy for convergent margins; evidence for mid-ocean ridges and transform motion is less clearly preserved, though passive margins are used as a proxy for spreading centres, and evidence for strike-slip motions are used to model transform boundaries. We find that the model presented here only predicts 70% of the total length of subduction active today, though it models similar lengths of both transform and divergent boundaries, suggesting that we have produced a conservative model and are probably underestimating the amount of subduction. Where evidence for convergent, divergent or transform motion is not preserved, we interpret the locations of plate boundaries based on the relative motions of cratonic crust as suggested through either palaeomagnetic data or the geological record. Using GPlates, we tie these boundaries together to generate a plate model that depicts the motion of tectonic plates through the Neoproterozoic. We omit India and South China from Rodinia completely, due to long-lived subduction preserved on margins of India and conflicting palaeomagnetic data for the Cryogenian, but tie them together due to similar Tonian aged accretionary patterns along their respective (present-day) north-western and northern margins, such that these two cratons act as a "lonely wanderer" for much of the Neoproterozoic, and form their own tectonic plate. We also introduce a Tonian-Cryogenian aged rotation of the Congo-São Francisco Craton relative to Rodinia to better fit palaeomagnetic data and account for thick passive margin sediments along its southern margin during the Tonian. The model depicts a sequential breakup of Rodinia, with Australia-Antarctica rifting first ( 800 Ma), Congo-São Francisco (and the Sahara Metacraton) second ( 750 Ma) and Kalahari third (700 Ma). Amazonia and West Africa rift later with the opening of the Iapetus Ocean from 600 Ma. We expect that this global model will assist in the development of future regional models for the Neoproterozoic, and that the production of this full-plate topological reconstruction will facilitate the investigation of controls on other earth systems, such as the possible role of volcanism on initiation of the Cryogenian, or the nature of mantle convection in the Neoproterozoic.

An Examination of Seismicity Linking the Solomon Islands and Vanuatu Subduction Zones

NASA Astrophysics Data System (ADS)

Neely, J. S.; Furlong, K. P.

2015-12-01

The Solomon Islands-Vanuatu composite subduction zone represents a tectonically complex region along the Pacific-Australia plate boundary in the southwest Pacific Ocean. Here the Australia plate subducts under the Pacific plate in two segments: the South Solomon Trench and the Vanuatu Trench. The two subducting sections are offset by a 200 km long, transform fault - the San Cristobal Trough (SCT) - which acts as a Subduction-Transform Edge Propagator (STEP) fault. The subducting segments have experienced much more frequent and larger seismic events than the STEP fault. The northern Vanuatu trench hosted a M8.0 earthquake in 2013. In 2014, at the juncture of the western terminus of the SCT and the southern South Solomon Trench, two earthquakes (M7.4 and M7.6) occurred with disparate mechanisms (dominantly thrust and strike-slip respectively), which we interpret to indicate the tearing of the Australia plate as its northern section subducts and southern section translates along the SCT. During the 2013-2014 timeframe, little seismic activity occurred along the STEP fault. However, in May 2015, three M6.8-6.9 strike-slip events occurred in rapid succession as the STEP fault ruptured east to west. These recent events share similarities with a 1993 strike-slip STEP sequence on the SCT. Analysis of the 1993 and 2015 STEP earthquake sequences provides constraints on the plate boundary geometry of this major transform fault. Preliminary research suggests that plate motion along the STEP fault is partitioned between larger east-west oriented strike-slip events and smaller north-south thrust earthquakes. Additionally, the differences in seismic activity between the subducting slabs and the STEP fault can provide insights into how stress is transferred along the plate boundary and the mechanisms by which that stress is released.

Lithosperic rheology controls on oceanic spreading patterns

NASA Astrophysics Data System (ADS)

Gerya, T.

2012-04-01

Mid-ocean ridges sectioned by transform faults represent one of the most prominent surface expressions of terrestrial plate tectonics. A fundamental long standing problem of plate tectonics is how and why ridge-transform spreading patterns are formed and maintained. On the one hand, geometrical correspondence between mid-ocean ridges and respective rifted margins apparently suggests that many oceanic transform faults are inherited structures that persisted throughout the entire history of oceanic spreading. On the other hand, data from incipient oceanic spreading regions show that transform faults are not directly inherited from transverse rift structures and start to develop as or after oceanic spreading nucleate. Based on self-consistent 3D thermomechanical numerical model of oceanic spreading we demonstrate that only limited range of oceanic lithosphere rheologies can reproduce natural spreading patterns. In particular, spontaneous formation and long-term stability of orthogonal ridge-transform spreading pattern requires visco-brittle/plastic rheology of plates with strong dynamic weakening of spontaneously forming faults. Our, numerical models of incipient oceanic spreading demonstrate that one or several oceanic transform faults can form gradually within broad non-transform accommodation zones connecting initially offset spreading centers. Orientation of transform faults and spreading centers changes exponentially with time as the result of new oceanic crust growth. The resulting orthogonal ridge-transform system is established within few millions of years after the beginning of oceanic spreading. By its fundamental physical origin, this system is a crustal growth pattern governed by space accommodation and not a plate breakup pattern governed by stress distribution. It is demonstrated that the characteristic extension-parallel orientation of oceanic transform faults can be obtained from space accommodation criteria as a steady state orientation of a strike-slip fault sustaining in between simultaneously growing offset crustal segments. Numerical models also suggest that transform faults can develop at single straight ridge as the result of dynamical instability of constructive plate boundaries caused by weakening of forming brittle/plastic fractures. Boundary instability from asymmetric plate growth can spontaneously start in alternate directions along successive ridge sections; the resultant curved ridges become transform faults within a few million years. Offsets along the transform faults change continuously with time by asymmetric plate growth and discontinuously by ridge jumps. Degree of asymmetric plate accretion increases with increasing degree of brittle/plastic weakening. It is also strongly dependent on the brittle/plastic yielding criterion and is notably reduced in models with pressure-dependent brittle/plastic plate strength compared to models with pressure-independent strength.

Deformation of the Pacific/North America plate boundary at Queen Charlotte Fault: The possible role of rheology

USGS Publications Warehouse

ten Brink, Uri S.; Miller, Nathaniel; Andrews, Brian; Brothers, Daniel; Haeussler, Peter J.

2018-01-01

The Pacific/North America (PA/NA) plate boundary between Vancouver Island and Alaska is similar to the PA/NA boundary in California in its kinematic history and the rate and azimuth of current relative motion, yet their deformation styles are distinct. The California plate boundary shows a broad zone of parallel strike slip and thrust faults and folds, whereas the 49‐mm/yr PA/NA relative plate motion in Canada and Alaska is centered on a single, narrow, continuous ~900‐km‐long fault, the Queen Charlotte Fault (QCF). Using gravity analysis, we propose that this plate boundary is centered on the continent/ocean boundary (COB), an unusual location for continental transform faults because plate boundaries typically localize within the continental lithosphere, which is weaker. Because the COB is a boundary between materials of contrasting elastic properties, once a fault is established there, it will probably remain stable. We propose that deformation progressively shifted to the COB in the wake of Yakutat terrane's northward motion along the margin. Minor convergence across the plate boundary is probably accommodated by fault reactivation on Pacific crust and by an eastward dipping QCF. Underthrusting of Pacific slab under Haida Gwaii occurs at convergence angles >14°–15° and may have been responsible for the emergence of the archipelago. The calculated slab entry dip (5°–8°) suggests that the slab probably does not extend into the asthenosphere. The PA/NA plate boundary at the QCF can serve as a structurally simple site to investigate the impact of rheology and composition on crustal deformation and the initiation of slab underthrusting.

Seismicity of the Earth 1900-2012 Sumatra and vicinity

USGS Publications Warehouse

Hayes, Gavin P.; Bernardino, Melissa; Dannemann, Fransiska; Smoczyk, Gregory; Briggs, Richard W.; Benz, Harley M.; Furlong, Kevin P.; Villaseñor, Antonio

2013-01-01

The plate boundary southwest of Sumatra is part of a long tectonic collision zone that extends over 8,000 km from Papua, New Guinea, in the east to the Himalayan front in the west. The Sumatra-Andaman part of the collision zone forms a subduction zone plate boundary, which accommodates convergence between the Indo-Australia and Sunda plates. This convergence is responsible for the intense seismicity in Sumatra. The Sumatra Fault, a major transform structure that bisects Sumatra, accommodates the northwest-increasing lateral component of relative plate motion. Most strain accumulation and release between the two plates occurs along the Sunda megathrust. The increasingly oblique convergence moving northwest is accommodated by crustal seismicity along several transform and normal faults, including the Sumatra Fault. Plate-boundary related deformation is also not restricted to the subduction zone and overriding plate: the Indo-Australian plate actually comprises two somewhat independent plates (India and Australia) that are joined along a broad, actively deforming region that produces seismicity up to several hundred kilometers west of the trench. This deformation is exemplified by the recent April 2012 earthquake sequence, which includes the April 11 M 8.6 and M 8.2 strike-slip events and their subsequent aftershocks. Since 2004, much of the Sunda megathrust between the northern Andaman Islands and Enggano Island, a distance of more than 2,000 km, has ruptured in a series of large subduction zone earthquakes—most rupturing the plate boundary south of Banda Aceh. These events include the great M 9.1 earthquake of December 26, 2004; the M 8.6 Nias Island earthquake of March 28, 2005; and two earthquakes on September 12, 2007, of M 8.5 and M 7.9. On October 25, 2010, a M 7.8 on the shallow portion of the megathrust to the west of the Mentawai Islands caused a substantial tsunami on the west coast of those islands.

Lithospheric strength variations as a control on new plate boundaries: examples from the northern Red Sea region

NASA Astrophysics Data System (ADS)

Steckler, Michael S.; ten Brink, Uri S.

1986-08-01

The complex plate boundary between Arabia and Africa at the northern end of the Red Sea includes the Gulf of Suez rift and the Gulf of Aqaba—Dead Sea transform. Geologic evidence indicates that during the earliest phase of rifting the Red Sea propagated NNW towards the Mediterranean Sea creating the Gulf of Suez. Subsequently, the majority of the relative movement between the plates shifted eastward to the Dead Sea transform. We propose that an increase in the strength of the lithosphere across the Mediterranean continental margin acted as a barrier to the propagation of the rift. A new plate boundary, the Dead Sea transform formed along a zone of minimum strength. We present an analysis of lithospheric strength variations across the Mediterranean continental margin. The main factors controlling these variations are the geotherm, crustal thickness and composition, and sediment thickness. The analysis predicts a characteristic strength profile at continental margins which consists of a marked increase in strength seaward of the hinge zone and a strength minimum landward of the hinge zone. This strength profile also favors the creation of thin continental slivers such as the Levant west of the Dead Sea transform and the continental promontory containing Socotra Island at the mouth of the Gulf of Aden. Calculations of strength variations based on changes of crustal thickness, geotherm and sediment thickness can be extended to other geologic settings as well. They can explain the location of rerifting events at intracratonic basins, of backarc basins and of major continental strike-slip zones.

Observations of Displacement-driven Maturation along a Subduction-Transform Edge Propagator Fault

NASA Astrophysics Data System (ADS)

Neely, J. S.; Furlong, K. P.

2016-12-01

The Solomon Islands-Vanuatu composite subduction zone represents a tectonically complex region along the Pacific-Australia plate boundary in the southwest Pacific Ocean. Here the Australia plate subducts under the Pacific plate in two parts - the Solomon Trench and the Vanuatu Trench - with the two segments separated by a transform fault produced by a tear in the approaching Australia plate. As a result of the Australia plate tearing, the two subducting sections are offset by the 280 km long San Cristobal Trough (SCT) transform fault, which acts as a Subduction-Transform Edge Propagator (STEP) fault. The formation of this transform fault provides an opportunity to study the evolution of a newly created transform plate boundary. As distance from the tear increases, both the magnitude and frequency of earthquakes along the transform increase reflecting the coalescence of fault segments into a through-going structure. Over the past few decades, there have been several instances of larger magnitude earthquakes migrating westward along the STEP through a rapid succession of events. A recent May 2015 sequence of MW 6.8, MW 6.9, and MW 6.8 earthquakes followed this pattern, with an east to west migration over three days. However, neither this 2015 sequence, nor a previous 1993 progression, ruptured into or nucleated a large earthquake within the region near the tear. SCT sequence termination outside the region of the newly formed fault occurs even though Coulomb Failure Stress analyses reveal that the tear end of the SCT is positively loaded for failure by the earthquake sequence. Changing seismicity patterns along the SCT are also mapped by b-value variations that correspond to the rupture patterns of these propagating sequences. These seismicity pattern changes along the SCT reveal a fault maturation process with strain localization driven by cumulative slip corresponding to approximately 80-100 km of displacement.

MHD Forced Convective Laminar Boundary Layer Flow from a Convectively Heated Moving Vertical Plate with Radiation and Transpiration Effect

PubMed Central

Uddin, Md. Jashim; Khan, Waqar A.; Ismail, A. I. Md.

2013-01-01

A two-dimensional steady forced convective flow of a Newtonian fluid past a convectively heated permeable vertically moving plate in the presence of a variable magnetic field and radiation effect has been investigated numerically. The plate moves either in assisting or opposing direction to the free stream. The plate and free stream velocities are considered to be proportional to whilst the magnetic field and mass transfer velocity are taken to be proportional to where is the distance along the plate from the leading edge of the plate. Instead of using existing similarity transformations, we use a linear group of transformations to transform the governing equations into similarity equations with relevant boundary conditions. Numerical solutions of the similarity equations are presented to show the effects of the controlling parameters on the dimensionless velocity, temperature and concentration profiles as well as on the friction factor, rate of heat and mass transfer. It is found that the rate of heat transfer elevates with the mass transfer velocity, convective heat transfer, Prandtl number, velocity ratio and the magnetic field parameters. It is also found that the rate of mass transfer enhances with the mass transfer velocity, velocity ratio, power law index and the Schmidt number, whilst it suppresses with the magnetic field parameter. Our results are compared with the results existing in the open literature. The comparisons are satisfactory. PMID:23741295

Evidence of displacement-driven maturation along the San Cristobal Trough transform plate boundary

NASA Astrophysics Data System (ADS)

Neely, James S.; Furlong, Kevin P.

2018-03-01

The San Cristobal Trough (SCT), formed by the tearing of the Australia plate as it subducts under the Pacific plate near the Solomon Islands, provides an opportunity to study the transform boundary development process. Recent seismicity (2013-2016) along the 280 km long SCT, known as a Subduction-Transform Edge Propagator (STEP) fault, highlights the tearing process and ongoing development of the plate boundary. The region's earthquakes reveal two key characteristics. First, earthquakes at the western terminus of the SCT, which we interpret to indicate the Australia plate tearing, display disparate fault geometries. These events demonstrate that plate tearing is accommodated via multiple intersecting planes rather than a single through-going fault. Second, the SCT hosts sequences of Mw ∼7 strike-slip earthquakes that migrate westward through a rapid succession of events. Sequences in 1993 and 2015 both began along the eastern SCT and propagated west, but neither progression ruptured into or nucleated a large earthquake within the region near the tear. Utilizing b-value and Coulomb Failure Stress analyses, we examine these along-strike variations in the SCT's seismicity. b-Values are highest along the youngest, western end of the SCT and decrease with increasing distance from the tear. This trend may reflect increasing strain localization with increasing displacement. Coulomb Failure Stress analyses indicate that the stress conditions were conducive to continued western propagation of the 1993 and 2015 sequences suggesting that the unruptured western SCT may have fault geometries or properties that inhibit continued rupture. Our results indicate a displacement-driven fault maturation process. The multi-plane Australia plate tearing likely creates a western SCT with diffuse strain accommodated along a network of disorganized faults. After ∼90 km of cumulative displacement (∼900,000 yr of plate motion), strain localizes and faults align, allowing the SCT to host large earthquakes.

Geodynamic environments of ultra-slow spreading

NASA Astrophysics Data System (ADS)

Kokhan, Andrey; Dubinin, Evgeny

2015-04-01

Ultra-slow spreading is clearly distinguished as an outstanding type of crustal accretion by recent studies. Spreading ridges with ultra-slow velocities of extension are studied rather well. But ultra-slow spreading is characteristic feature of not only spreading ridges, it can be observed also on convergent and transform plate boundaries. Ultra-slow spreading is observed now or could have been observed in the past in the following geodynamic environments on divergent plate boundaries: 1. On spreading ridges with ultra-slow spreading, both modern (f.e. Gakkel, South-West Indian, Aden spreading center) and ceased (Labrador spreading center, Aegir ridge); 2. During transition from continental rifting to early stages of oceanic spreading (all spreading ridges during incipient stages of their formation); 3. During incipient stages of formation of spreading ridges on oceanic crust as a result of ridge jumps and reorganization of plate boundaries (f.e. Mathematicians rise and East Pacific rise); 4. During propagation of spreading ridge into the continental crust under influence of hotspot (Aden spreading center and Afar triple junction), under presence of strike-slip faults preceding propagation (possibly, rift zone of California Bay). Ultra-slow spreading is observed now or could have been observed in the past in the following geodynamic environments on transform plate boundaries: 1. In transit zones between two "typical" spreading ridges (f.e. Knipovich ridge); 2. In semi strike-slip/extension zones on the oceanic crust (f.e. American-Antarctic ridge); 3. In the zones of local extension in regional strike-slip areas in pull-apart basins along transform boundaries (Cayman trough, pull-apart basins of the southern border of Scotia plate). Ultra-slow spreading is observed now or could have been observed in the past in the following geodynamic environments on convergent plate boundaries: 1. During back-arc rifting on the stage of transition into back-arc spreading (central part of Bransfield rift); 2. During back-arc inter-subduction spreading (Ayu trough, northern Fiji basin), 3. During diffuse back-arc spreading (area on the south-eastern border of Scotia sea), 4. During back-arc spreading under splitting of island arc (northern extremity of Mariana trough). Each of the geodynamic environments is characterized by peculiar topographic, geological and geophysical features forming under the same spreading velocities. Development of ultra-slow spreading in each of these environments results in formation of peculiar extension sedimentary basins.

The Role of Oceanic Transform Faults in Seafloor Spreading: A Global Perspective From Seismic Anisotropy

NASA Astrophysics Data System (ADS)

Eakin, Caroline M.; Rychert, Catherine A.; Harmon, Nicholas

2018-02-01

Mantle anisotropy beneath mid-ocean ridges and oceanic transforms is key to our understanding of seafloor spreading and underlying dynamics of divergent plate boundaries. Observations are sparse, however, given the remoteness of the oceans and the difficulties of seismic instrumentation. To overcome this, we utilize the global distribution of seismicity along transform faults to measure shear wave splitting of over 550 direct S phases recorded at 56 carefully selected seismic stations worldwide. Applying this source-side splitting technique allows for characterization of the upper mantle seismic anisotropy, and therefore the pattern of mantle flow, directly beneath seismically active transform faults. The majority of the results (60%) return nulls (no splitting), while the non-null measurements display clear azimuthal dependency. This is best simply explained by anisotropy with a near vertical symmetry axis, consistent with mantle upwelling beneath oceanic transforms as suggested by numerical models. It appears therefore that the long-term stability of seafloor spreading may be associated with widespread mantle upwelling beneath the transforms creating warm and weak faults that localize strain to the plate boundary.

Gas Metal Arc Welding Process Modeling and Prediction of Weld Microstructure in MIL A46100 Armor-Grade Martensitic Steel

DTIC Science & Technology

2013-06-01

acicular/Widmanstatten ferrite (a version of ferrite possessing an acicular/ lenticular - plate morphology which grows into the untransformed aus- tenite...boundary regions which have been transformed into allotriomorphic ferrite, as well as lenticular -shaped Widmanstatten plates advancing from the

The angular velocity of Nubia relative to Somalia and the location of the Nubia-Somalia-Antarctica triple junction

NASA Astrophysics Data System (ADS)

Horner-Johnson, Benjamin C.; Gordon, Richard G.; Cowles, Sara M.; Argus, Donald F.

2005-07-01

A new analysis of geologically current plate motion across the Southwest Indian ridge (SWIR) and of the current location of the Nubia-Antarctica-Somalia triple junction is presented. Spreading rates averaged over the past 3.2 Myr are estimated from 103 well-distributed, nearly ridge-perpendicular profiles that cross the SWIR. All available bathymetric data are evaluated to estimate the azimuths and uncertainties of transform faults; six are estimated from multibeam data and 12 from precision depth recorder (PDR) data. If both the Nubian and Somalian component plates are internally rigid near the SWIR and if the Nubia-Somalia boundary is narrow where it intersects the SWIR, that intersection lies between ~26°E and ~32°E. Thus, the boundary is either along the spreading ridge segment just west of the Andrew Bain transform fault complex (ABTFC) or along some of the transform fault complex itself. These limits are narrower than and contained within limits of ~24°E to ~33°E previously found by Lemaux et al. from an analysis of the locations of magnetic anomaly 5. The data are consistent with a narrow boundary, but also consistent with a diffuse boundary as wide as ~700 km. The new Nubia-Somalia pole of rotation lies ~10° north of the Bouvet triple junction, which places it far to the southwest of southern Africa. The new angular velocity determined only from data along the SWIR indicates displacement rates of Somalia relative to Nubia of 3.6 +/- 0.5 mm yr-1 (95 per cent confidence limits) towards 176° (S04° E) between Somalia and Nubia near the SWIR, and of 8.3 +/- 1.9 mm yr-1 (95 per cent confidence limits) towards 121° (S59° E) near Afar. The new Nubia-Somalia angular velocity differs significantly from the Nubia-Somalia angular velocity estimated from Gulf of Aden and Red sea data. This significant difference has three main alternative explanations: (i) that the plate motion data have substantial unmodelled systematic errors, (ii) that the Nubian component plate is not a single rigid plate, or (iii) that the Somalian component plate is not a single rigid plate. We tentatively prefer the third explanation given the geographical distribution of earthquakes within the African composite plate relative to the inferred location of the Nubia-Somalia boundary along the SWIR.

Current Plate Motion Across the Southwest Indian Ridge: Implications for the Diffuse Oceanic Plate Boundary Between Nubia and Somalia

NASA Astrophysics Data System (ADS)

Horner-Johnson, B. C.; Cowles, S. M.; Gordon, R. G.; Argus, D. F.

2001-12-01

Prior studies of plate motion data along the Southwest Indian Ridge (SWIR) have produced results that conflict in detail. Chu & Gordon [1999], from an analysis of 59 spreading rates averaged over 3 Myr and of the azimuths of active transform faults, found that the data are most consistent with a diffuse Nubia-Somalia plate boundary where it intersects the SWIR. When they solve for the best-fitting hypothetical narrow boundary, they find that it lies near 37° E, east of the Prince Edward fracture zone. They find a Nubia-Somalia pole of rotation near the east coast of South Africa. In contrast, Lemaux, Gordon, and Royer [2001], from an analysis of 237 crossings of marine magnetic anomaly 5 (11 Ma), find that most of the motion is accommodated in a narrow zone, most likely along the ``inactive'' trace of the Andrew Bain fracture zone complex (ABFZC), which intersects the SWIR near 32° E. They find a pole well to the west of, and probably to the southwest of, the pole of rotation found by Chu & Gordon. Their pole indicates mainly strike-slip motion along the ``inactive'' ABFZC. To resolve these conflicting results, we determined a new greatly expanded and spatially much denser set of 243 spreading rates and analyzed available bathymetric data of active transform faults along the SWIR. The data show that the African oceanic lithosphere spreading away from the SWIR cannot simply be two plates divided by a single narrow boundary. Our interpretation of the data is as follows. Near the SWIR, there is a diffuse boundary with a western limit near the ABFZC and an eastern limit near 63.5° E. Slip is partitioned in this wide boundary. Somewhere near the ABFZC (most likely the ABFZC itself) is a concentrated locus of right-lateral shearing parallel to the ABFZC whereas contraction perpendicular to the ABFZC is accommodated east of the ABFZC, perhaps over a very broad zone.

Seismicity of the Earth 1900-2010 eastern margin of the Australia plate

USGS Publications Warehouse

Benz, Harley M.; Herman, Matthew; Tarr, Arthur C.; Hayes, Gavin P.; Furlong, Kevin P.; Villaseñor, Antonio; Dart, Richard L.; Rhea, Susan

2011-01-01

The eastern margin of the Australia plate is one of the most seismically active areas of the world due to high rates of convergence between the Australia and Pacific plates. In the region of New Zealand, the 3,000 km long Australia-Pacific plate boundary extends from south of Macquarie Island to the southern Kermadec Island chain. It includes an oceanic transform (the Macquarie Ridge), two oppositely verging subduction zones (Puysegur and Hikurangi), and a transpressive continental transform, the Alpine Fault through South Island, New Zealand. Since 1900, there have been 15 M7.5+ earthquakes recorded near New Zealand. Nine of these, and the four largest, occurred along or near the Macquarie Ridge, including the 1989 M8.2 event on the ridge itself, and the 2004 M8.1 event 200 km to the west of the plate boundary, reflecting intraplate deformation. The largest recorded earthquake in New Zealand itself was the 1931 M7.8 Hawke's Bay earthquake, which killed 256 people. The last M7.5+ earthquake along the Alpine Fault was 170 years ago; studies of the faults' strain accumulation suggest that similar events are likely to occur again.

Present-day kinematics of the Danakil block (southern Red Sea-Afar) constrained by GPS

NASA Astrophysics Data System (ADS)

Ladron de Guevara, R.; Jonsson, S.; Ruch, J.; Doubre, C.; Reilinger, R. E.; Ogubazghi, G.; Floyd, M.; Vasyura-Bathke, H.

2017-12-01

The rifting of the Arabian plate from the Nubian and Somalian plates is primarily accommodated by seismic and magmatic activity along two rift arms of the Afar triple junction (the Red Sea and Gulf of Aden rifts). The spatial distribution of active deformation in the Afar region have been constrained with geodetic observations. However, the plate boundary configuration in which this deformation occurs is still not fully understood. South of 17°N, the Red Sea rift is composed of two parallel and overlapping rift branches separated by the Danakil block. The distribution of the extension across these two overlapping rifts, their potential connection through a transform fault zone and the counterclockwise rotation of the Danakil block have not yet been fully resolved. Here we analyze new GPS observations from the Danakil block, the Gulf of Zula area (Eritrea) and Afar (Ethiopia) together with previous geodetic survey data to better constrain the plate kinematics and active deformation of the region. The new data has been collected in 2016 and add up to 5 years to the existing geodetic observations (going back to 2000). Our improved GPS velocity field shows differences with previously modeled GPS velocities, suggesting that the rate and rotation of the Danakil block need to be updated. The new velocity field also shows that the plate-boundary strain is accommodated by broad deformation zones rather than across sharp boundaries between tectonic blocks. To better determine the spatial distribution of the strain, we first implement a rigid block model to constrain the overall regional plate kinematics and to isolate the plate-boundary deformation at the western boundary of the Danakil block. We then study whether the recent southern Red Sea rifting events have caused detectable changes in observed GPS velocities and if the observations can be used to constrain the scale of this offshore rift activity. Finally, we investigate different geometries of transform faults that might connect the two overlapping branches of the southern Red Sea rift in the Gulf of Zula region.

Links Between Clay Dehydration and Plate Boundary Earthquakes Along the Costa Rica Subduction Megathrust

NASA Astrophysics Data System (ADS)

Lauer, R. M.; Saffer, D. M.; Harris, R. N.

2016-12-01

The transformation of smectite to illite is one leading hypothesis to explain the upper transition from stable aseismic slip to seismogenesis along subduction megathrusts, through its influence on both fluid pressure and fault zone frictional properties. Here, we document a well-defined spatial correlation between plate boundary seismicity and smectite transformation at the Costa Rican subduction zone, consistent with the idea that clay transformation and associated silica deposition condition the fault for locking and stick-slip behavior. Previous efforts to explore this relationship have been impeded by a lack of studies that precisely locate seismicity at margins where the thermal structure is well-constrained. We take advantage of new results from Costa Rica that together provide a clear view of both seismicity and thermal conditions on the Middle-America megathrust. These results allow a thorough evaluation of the links between smectite dehydration and fault-slip behavior. We simulate smectite transformation using a kinetic model to assess reaction progress and quantify fluid production at the plate boundary, along 16-transects that span a 500-km length along strike. We find that large (Mw≥7.0) earthquakes are located down-dip of peak fluid production and in regions where the reaction is >50% complete. The earthquake ruptures, however, extend up-dip into the zone of peak reaction. We suggest that silica cementation that accompanies the reaction promotes lithification, embrittlement, and slip-weakening behavior that together enable the initiation of unstable slip, which can then propagate updip into fluid-rich and weak regions of the megathrust that coincide with the peak dehydration window.

On the Enigmatic Birth of the Pacific Plate within the Panthalassa Ocean

NASA Astrophysics Data System (ADS)

Boschman, L.; Van Hinsbergen, D. J. J.

2016-12-01

The oceanic Pacific Plate started forming in Early Jurassic time within the vast Panthalassa Ocean that surrounded the supercontinent Pangea and contains the oldest lithosphere that can directly constrain the geodynamic history of the circum-Pangean Earth. Here, we show that the geometry of the oldest marine magnetic anomalies of the Pacific Plate attests of a unique plate kinematic event that sparked the plate's birth in virtually a point location, surrounded by the Izanagi, Farallon and Phoenix Plates. We reconstruct the unstable triple junction that caused the plate reorganization leading to the birth of the Pacific Plate and present a model of the plate tectonic configuration that preconditioned this event. We show that a stable, but migrating triple junction involving the gradual cessation of intra-oceanic Panthalassa subduction culminated in the formation of an unstable transform-transform-transform triple junction. The consequent plate boundary reorganization resulted in the formation of a stable triangular three-ridge system from which the nascent Pacific Plate expanded. We link the birth of the Pacific Plate to the regional termination of intra-Panthalassa subduction. Remnants thereof have been identified in the deep lower mantle of which the locations may provide paleolongitudinal control on the absolute location of the early Pacific Plate. Our results constitute an essential step in unraveling the plate tectonic evolution of `Thalassa Incognita' comprising the comprehensive Panthalassa Ocean surrounding Pangea.

On the enigmatic birth of the Pacific Plate within the Panthalassa Ocean.

PubMed

Boschman, Lydian M; van Hinsbergen, Douwe J J

2016-07-01

The oceanic Pacific Plate started forming in Early Jurassic time within the vast Panthalassa Ocean that surrounded the supercontinent Pangea, and contains the oldest lithosphere that can directly constrain the geodynamic history of the circum-Pangean Earth. We show that the geometry of the oldest marine magnetic anomalies of the Pacific Plate attests to a unique plate kinematic event that sparked the plate's birth at virtually a point location, surrounded by the Izanagi, Farallon, and Phoenix Plates. We reconstruct the unstable triple junction that caused the plate reorganization, which led to the birth of the Pacific Plate, and present a model of the plate tectonic configuration that preconditioned this event. We show that a stable but migrating triple junction involving the gradual cessation of intraoceanic Panthalassa subduction culminated in the formation of an unstable transform-transform-transform triple junction. The consequent plate boundary reorganization resulted in the formation of a stable triangular three-ridge system from which the nascent Pacific Plate expanded. We link the birth of the Pacific Plate to the regional termination of intra-Panthalassa subduction. Remnants thereof have been identified in the deep lower mantle of which the locations may provide paleolongitudinal control on the absolute location of the early Pacific Plate. Our results constitute an essential step in unraveling the plate tectonic evolution of "Thalassa Incognita" that comprises the comprehensive Panthalassa Ocean surrounding Pangea.

Seismic imaging of deep low-velocity zone beneath the Dead Sea basin and transform fault: Implications for strain localization and crustal rigidity

USGS Publications Warehouse

ten Brink, Uri S.; Al-Zoubi, A. S.; Flores, C.H.; Rotstein, Y.; Qabbani, I.; Harder, S.H.; Keller, Gordon R.

2006-01-01

New seismic observations from the Dead Sea basin (DSB), a large pull-apart basin along the Dead Sea transform (DST) plate boundary, show a low velocity zone extending to a depth of 18 km under the basin. The lower crust and Moho are not perturbed. These observations are incompatible with the current view of mid-crustal strength at low temperatures and with support of the basin's negative load by a rigid elastic plate. Strain softening in the middle crust is invoked to explain the isostatic compensation and the rapid subsidence of the basin during the Pleistocene. Whether the deformation is influenced by the presence of fluids and by a long history of seismic activity on the DST, and what the exact softening mechanism is, remain open questions. The uplift surrounding the DST also appears to be an upper crustal phenomenon but its relationship to a mid-crustal strength minimum is less clear. The shear deformation associated with the transform plate boundary motion appears, on the other hand, to cut throughout the entire crust. Copyright 2006 by the American Geophysical Union.

On the enigmatic birth of the Pacific Plate within the Panthalassa Ocean

PubMed Central

Boschman, Lydian M.; van Hinsbergen, Douwe J. J.

2016-01-01

The oceanic Pacific Plate started forming in Early Jurassic time within the vast Panthalassa Ocean that surrounded the supercontinent Pangea, and contains the oldest lithosphere that can directly constrain the geodynamic history of the circum-Pangean Earth. We show that the geometry of the oldest marine magnetic anomalies of the Pacific Plate attests to a unique plate kinematic event that sparked the plate’s birth at virtually a point location, surrounded by the Izanagi, Farallon, and Phoenix Plates. We reconstruct the unstable triple junction that caused the plate reorganization, which led to the birth of the Pacific Plate, and present a model of the plate tectonic configuration that preconditioned this event. We show that a stable but migrating triple junction involving the gradual cessation of intraoceanic Panthalassa subduction culminated in the formation of an unstable transform-transform-transform triple junction. The consequent plate boundary reorganization resulted in the formation of a stable triangular three-ridge system from which the nascent Pacific Plate expanded. We link the birth of the Pacific Plate to the regional termination of intra-Panthalassa subduction. Remnants thereof have been identified in the deep lower mantle of which the locations may provide paleolongitudinal control on the absolute location of the early Pacific Plate. Our results constitute an essential step in unraveling the plate tectonic evolution of “Thalassa Incognita” that comprises the comprehensive Panthalassa Ocean surrounding Pangea. PMID:29713683

Measurements of strain at plate boundaries using space based geodetic techniques

NASA Technical Reports Server (NTRS)

Robaudo, Stefano; Harrison, Christopher G. A.

1993-01-01

We have used the space based geodetic techniques of Satellite Laser Ranging (SLR) and VLBI to study strain along subduction and transform plate boundaries and have interpreted the results using a simple elastic dislocation model. Six stations located behind island arcs were analyzed as representative of subduction zones while 13 sites located on either side of the San Andreas fault were used for the transcurrent zones. The length deformation scale was then calculated for both tectonic margins by fitting the relative strain to an exponentially decreasing function of distance from the plate boundary. Results show that space-based data for the transcurrent boundary along the San Andreas fault help to define better the deformation length scale in the area while fitting nicely the elastic half-space earth model. For subduction type bonndaries the analysis indicates that there is no single scale length which uniquely describes the deformation. This is mainly due to the difference in subduction characteristics for the different areas.

The Implications of Strike-Slip Earthquake Source Properties on the Transform Boundary Development Process

NASA Astrophysics Data System (ADS)

Neely, J. S.; Huang, Y.; Furlong, K.

2017-12-01

Subduction-Transform Edge Propagator (STEP) faults, produced by the tearing of a subducting plate, allow us to study the development of a transform plate boundary and improve our understanding of both long-term geologic processes and short-term seismic hazards. The 280 km long San Cristobal Trough (SCT), formed by the tearing of the Australia plate as it subducts under the Pacific plate near the Solomon and Vanuatu subduction zones, shows along-strike variations in earthquake behaviors. The segment of the SCT closest to the tear rarely hosts earthquakes > Mw 6, whereas the SCT sections more than 80 - 100 km from the tear experience Mw7 earthquakes with repeated rupture along the same segments. To understand the effect of cumulative displacement on SCT seismicity, we analyze b-values, centroid-time delays and corner frequencies of the SCT earthquakes. We use the spectral ratio method based on Empirical Green's Functions (eGfs) to isolate source effects from propagation and site effects. We find high b-values along the SCT closest to the tear with values decreasing with distance before finally increasing again towards the far end of the SCT. Centroid time-delays for the Mw 7 strike-slip earthquakes increase with distance from the tear, but corner frequency estimates for a recent sequence of Mw 7 earthquakes are approximately equal, indicating a growing complexity in earthquake behavior with distance from the tear due to a displacement-driven transform boundary development process (see figure). The increasing complexity possibly stems from the earthquakes along the eastern SCT rupturing through multiple asperities resulting in multiple moment pulses. If not for the bounding Vanuatu subduction zone at the far end of the SCT, the eastern SCT section, which has experienced the most displacement, might be capable of hosting larger earthquakes. When assessing the seismic hazard of other STEP faults, cumulative fault displacement should be considered a key input in determining potential earthquake size.

Scaling and spatial complementarity of tectonic earthquake swarms

NASA Astrophysics Data System (ADS)

Passarelli, Luigi; Rivalta, Eleonora; Jónsson, Sigurjón; Hensch, Martin; Metzger, Sabrina; Jakobsdóttir, Steinunn S.; Maccaferri, Francesco; Corbi, Fabio; Dahm, Torsten

2018-01-01

Tectonic earthquake swarms (TES) often coincide with aseismic slip and sometimes precede damaging earthquakes. In spite of recent progress in understanding the significance and properties of TES at plate boundaries, their mechanics and scaling are still largely uncertain. Here we evaluate several TES that occurred during the past 20 years on a transform plate boundary in North Iceland. We show that the swarms complement each other spatially with later swarms discouraged from fault segments activated by earlier swarms, which suggests efficient strain release and aseismic slip. The fault area illuminated by earthquakes during swarms may be more representative of the total moment release than the cumulative moment of the swarm earthquakes. We use these findings and other published results from a variety of tectonic settings to discuss general scaling properties for TES. The results indicate that the importance of TES in releasing tectonic strain at plate boundaries may have been underestimated.

Heat Transfer Analysis for Stationary Boundary Layer Slip Flow of a Power-Law Fluid in a Darcy Porous Medium with Plate Suction/Injection

PubMed Central

Aziz, Asim; Ali, Yasir; Aziz, Taha; Siddique, J. I.

2015-01-01

In this paper, we investigate the slip effects on the boundary layer flow and heat transfer characteristics of a power-law fluid past a porous flat plate embedded in the Darcy type porous medium. The nonlinear coupled system of partial differential equations governing the flow and heat transfer of a power-law fluid is transformed into a system of nonlinear coupled ordinary differential equations by applying a suitable similarity transformation. The resulting system of ordinary differential equations is solved numerically using Matlab bvp4c solver. Numerical results are presented in the form of graphs and the effects of the power-law index, velocity and thermal slip parameters, permeability parameter, suction/injection parameter on the velocity and temperature profiles are examined. PMID:26407162

Oblique collision and accretion of the Netherlands Leeward Antilles island arc: A structural analysis of the Caribbean-South American plate boundary zone

NASA Astrophysics Data System (ADS)

Beardsley, Amanda Gail

2007-12-01

The Netherlands Leeward Antilles volcanic island arc is an ideal natural laboratory to study the evolution of the Caribbean-South American plate boundary. The Leeward Antilles islands (Aruba, Curacao, and Bonaire) are located offshore western Venezuela, within the obliquely convergent diffuse plate boundary zone. Outcrop analysis, microthermometry, and 2D marine seismic reflection data provide evidence of three generations of regional deformation since the Late Cretaceous. Outcrop analysis of structural features, including faults, joints, and veins, characterizes the kinematic history of the islands. Fluid inclusion analysis of quartz and calcite veins coupled with apatite fission-track dating provides the island exhumation history. Finally, marine reflection seismic data processing and interpretation of newly acquired data elucidates offshore structures to integrate with our onshore results. The oldest regional deformation, resulting in both ductile (D1) and brittle (F 1) structures, is attributed to displacement partitioning along the arcuate Caribbean plate boundary. Associated crustal thinning initiated island exhumation, at a rate of 0.18 km/my, from a maximum burial depth of 6 km in the Late Cretaceous (˜89 Ma). Coeval with D1/F1 deformation and exhumation, stretching of the island arc resulted in extensive basin rifting that separated the island blocks. At ˜55 Ma, a change in the relative motion of the Caribbean plate altered plate boundary dynamics. Displacement along the right-lateral Caribbean transform fault and Oca - San Sebastian - El Pilar strike-slip fault system created a wrench tectonic regime within the diffuse plate boundary zone. A second generation of brittle structures (F2) developed while the islands were at a maximum burial depth of 2 km during the Paleocene/Eocene. Since ˜45 Ma, continued motion along the strike-slip fault systems and oblique plate convergence resulted in the youngest generation of structural features (F3). Regional tectonics control the ongoing steady-state exhumation of the islands at a rate of 0.04 km/my. Most recently, the northeast escape of the Maracaibo block also drives deformation within the diffuse plate boundary zone. Overall, the Caribbean-South American plate boundary geometry has evolved with diachronous deformation, from west to east, accompanied by 135° of clockwise block rotation during collision and accretion of the Leeward Antilles since the Late Cretaceous.

Florida: A Jurassic transform plate boundary

USGS Publications Warehouse

Klitgord, Kim D.; Popenoe, Peter; Schouten, Hans

1984-01-01

Magnetic, gravity, seismic, and deep drill hole data integrated with plate tectonic reconstructions substantiate the existence of a transform plate boundary across southern Florida during the Jurassic. On the basis of this integrated suite of data the pre-Cretaceous Florida-Bahamas region can be divided into the pre-Jurassic North American plate, Jurassic marginal rift basins, and a broad Jurassic transform zone including stranded blocks of pre-Mesozoic continental crust. Major tectonic units include the Suwannee basin in northern Florida containing Paleozoic sedimentary rocks, a central Florida basement complex of Paleozoic age crystalline rock, the west Florida platform composed of stranded blocks of continental crust, the south Georgia rift containing Triassic sedimentary rocks which overlie block-faulted Suwannee basin sedimentary rocks, the Late Triassic-Jurassic age Apalachicola rift basin, and the Jurassic age south Florida, Bahamas, and Blake Plateau marginal rift basins. The major tectonic units are bounded by basement hinge zones and fracture zones (FZ). The basement hinge zone represents the block-faulted edge of the North American plate, separating Paleozoic and older crustal rocks from Jurassic rifted crust beneath the marginal basins. Fracture zones separate Mesozoic marginal sedimentary basins and include the Blake Spur FZ, Jacksonville FZ, Bahamas FZ, and Cuba FZ, bounding the Blake Plateau, Bahamas, south Florida, and southeastern Gulf of Mexico basins. The Bahamas FZ is the most important of all these features because its northwest extension coincides with the Gulf basin marginal fault zone, forming the southern edge of the North American plate during the Jurassic. The limited space between the North American and the South American/African plates requires that the Jurassic transform zone, connecting the Central Atlantic and the Gulf of Mexico spreading systems, was located between the Bahamas and Cuba FZ's in the region of southern Florida. Our plate reconstructions combined with chronostratigraphic and lithostratigraphic information for the Gulf of Mexico, southern Florida, and the Bahamas indicate that the gulf was sealed off from the Atlantic waters until Callovian time by an elevated Florida-Bahamas region. Restricted influx of waters started in Callovian as a plate reorganization, and increased plate separation between North America and South America/Africa produced waterways into the Gulf of Mexico from the Pacific and possibly from the Atlantic.

MHD Free Convective Boundary Layer Flow of a Nanofluid past a Flat Vertical Plate with Newtonian Heating Boundary Condition

PubMed Central

Uddin, Mohammed J.; Khan, Waqar A.; Ismail, Ahmed I.

2012-01-01

Steady two dimensional MHD laminar free convective boundary layer flows of an electrically conducting Newtonian nanofluid over a solid stationary vertical plate in a quiescent fluid taking into account the Newtonian heating boundary condition is investigated numerically. A magnetic field can be used to control the motion of an electrically conducting fluid in micro/nano scale systems used for transportation of fluid. The transport equations along with the boundary conditions are first converted into dimensionless form and then using linear group of transformations, the similarity governing equations are developed. The transformed equations are solved numerically using the Runge-Kutta-Fehlberg fourth-fifth order method with shooting technique. The effects of different controlling parameters, namely, Lewis number, Prandtl number, buoyancy ratio, thermophoresis, Brownian motion, magnetic field and Newtonian heating on the flow and heat transfer are investigated. The numerical results for the dimensionless axial velocity, temperature and nanoparticle volume fraction as well as the reduced Nusselt and Sherwood number have been presented graphically and discussed. It is found that the rate of heat and mass transfer increase as Newtonian heating parameter increases. The dimensionless velocity and temperature distributions increase with the increase of Newtonian heating parameter. The results of the reduced heat transfer rate is compared for convective heating boundary condition and found an excellent agreement. PMID:23166688

Unsteady heat-flux measurements of second-mode instability waves in a hypersonic flat-plate boundary layer

NASA Astrophysics Data System (ADS)

Kegerise, Michael A.; Rufer, Shann J.

2016-08-01

In this paper, we report on the application of the atomic layer thermopile (ALTP) heat-flux sensor to the measurement of laminar-to-turbulent transition in a hypersonic flat-plate boundary layer. The centerline of the flat-plate model was instrumented with a streamwise array of ALTP sensors, and the flat-plate model was exposed to a Mach 6 freestream over a range of unit Reynolds numbers. Here, we observed an unstable band of frequencies that are associated with second-mode instability waves in the laminar boundary layer that forms on the flat-plate surface. The measured frequencies, group velocities, phase speeds, and wavelengths of these instability waves are consistent with data previously reported in the literature. Heat flux time series, and the Morlet wavelet transforms of them, revealed the wave-packet nature of the second-mode instability waves. In addition, a laser-based radiative heating system was used to measure the frequency response functions (FRF) of the ALTP sensors used in the wind tunnel test. These measurements were used to assess the stability of the sensor FRFs over time and to correct spectral estimates for any attenuation caused by the finite sensor bandwidth.

Double Diffusive Magnetohydrodynamic (MHD) Mixed Convective Slip Flow along a Radiating Moving Vertical Flat Plate with Convective Boundary Condition

PubMed Central

Rashidi, Mohammad M.; Kavyani, Neda; Abelman, Shirley; Uddin, Mohammed J.; Freidoonimehr, Navid

2014-01-01

In this study combined heat and mass transfer by mixed convective flow along a moving vertical flat plate with hydrodynamic slip and thermal convective boundary condition is investigated. Using similarity variables, the governing nonlinear partial differential equations are converted into a system of coupled nonlinear ordinary differential equations. The transformed equations are then solved using a semi-numerical/analytical method called the differential transform method and results are compared with numerical results. Close agreement is found between the present method and the numerical method. Effects of the controlling parameters, including convective heat transfer, magnetic field, buoyancy ratio, hydrodynamic slip, mixed convective, Prandtl number and Schmidt number are investigated on the dimensionless velocity, temperature and concentration profiles. In addition effects of different parameters on the skin friction factor, , local Nusselt number, , and local Sherwood number are shown and explained through tables. PMID:25343360

Crustal deformation and volcanism at active plate boundaries

NASA Astrophysics Data System (ADS)

Geirsson, Halldor

Most of Earth's volcanoes are located near active tectonic plate boundaries, where the tectonic plates move relative to each other resulting in deformation. Likewise, subsurface magma movement and pressure changes in magmatic systems can cause measurable deformation of the Earth's surface. The study of the shape of Earth and therefore studies of surface deformation is called geodesy. Modern geodetic techniques allow precise measurements (˜1 mm accuracy) of deformation of tectonic and magmatic systems. Because of the spatial correlation between tectonic boundaries and volcanism, the tectonic and volcanic deformation signals can become intertwined. Thus it is often important to study both tectonic and volcanic deformation processes simultaneously, when one is trying to study one of the systems individually. In this thesis, I present research on crustal deformation and magmatic processes at active plate boundaries. The study areas cover divergent and transform plate boundaries in south Iceland and convergent and transform plate boundaries in Central America, specifically Nicaragua and El Salvador. The study is composed of four main chapters: two of the chapters focus on the magma plumbing system of Hekla volcano, Iceland and the plate boundary in south Iceland; one chapter focuses on shallow controls of explosive volcanism at Telica volcano, Nicaragua; and the fourth chapter focuses on co- and post-seismic deformation from a Mw = 7.3 earthquake which occurred offshore El Salvador in 2012. Hekla volcano is located at the intersection of a transform zone and a rift zone in Iceland and thus is affected by a combination of shear and extensional strains, in addition to co-seismic and co-rifting deformation. The inter-eruptive deformation signal from Hekla is subtle, as observed by a decade (2000-2010) of GPS data in south Iceland. A simultaneous inversion of this data for parameters describing the geometry and source characteristics of the magma chamber at Hekla, and geometry and secular rates across the plate boundary segments, reveals a deep magma chamber under Hekla and gives a geodetic estimate of the current location of the North-America Eurasian plate boundary in south Iceland. Different geometries were tested for Hekla's magma chamber: spherical, horizontally elongated ellipsoidal, and pipe-like magma chambers. The data could not reliably distinguish the actual geometry; however, all three models indicate magma accumulation near the Moho (˜20-25 km) under Hekla. The February -- March 2000 eruption of Hekla gave another opportunity to image the magmatic system. In Chapter 5, I used co-eruptive GPS and InSAR displacements, borehole strain, and tilt measurements to jointly invert for co-eruptive deformation associated with the 2000 eruption and found a depth of approximately 20 km for the magma chamber, in accordance with my previous results. Telica is a highly seismically active volcano in Nicaragua. The seismicity is mostly of shallow (<2 km deep) origin, and shows a high variability in terms of the number of seismic events per time unit. The highest rates exceed one earthquake per minute averaged over 24 hours, but overall trends in seismic activity, as observed since 1993, do not have an obvious correlation with eruptive activity. This variability causes difficulties for hazard monitoring of Telica. Telica erupted in a small (VEI 2) explosive eruption in 2011. Eruptions of this style and size seem to occur on decadal time scales at Telica. In Chapter 3, I used an extensive multidisciplinary data set consisting of seismic and GPS data, multivariate ash analysis, SO2 measurements, fumarole temperatures, and visual observations, to show that the eruption was essentially an amagmatic eruption of hydrothermally altered materials from the conduit, and that short-term sealing of hydrothermal pathways led to temporary pressure build-up, resulting in the explosions. No significant crustal deformation was detected before or during the eruption, in accordance with low (<2 km) plume heights and small (<105 m3) eruptive volumes. The primary signal observed in the 10-site continuous GPS geodetic network on and near Telica is shear on the Caribbean plate -- fore-arc plate boundary, which our measurements show crosses Telica. Thus, like at Hekla volcano, Iceland, it is important for volcano geodesy to consider the plate boundary deformation within volcanic arcs in geodetic studies of volcanoes. The August 27, 2012 Mw = 7.3 earthquake offshore El Salvador was the largest event to rupture this segment of the subduction interface for at least 95 years. The earthquake ruptured shallow (<20 km depth) parts of the subduction zone. Co-seismic deformation, as observed on land, was less than 2 cm, and was exceeded by post-seismic deformation within the first year after the earthquake, signifying low coupling on the subduction zone offshore El Salvador and Nicaragua.

An Alternative Estimate of the Motion of the Capricorn Plate

NASA Astrophysics Data System (ADS)

Burris, S. G.; Gordon, R. G.

2013-12-01

Diffuse plate boundaries cover ~15% of Earth's surface and can exceed 1000 km in across-strike width. Deforming oceanic lithosphere in the equatorial Indian Ocean accommodates the motion between the India and Capricorn plates and serves as their mutual diffuse plate boundary. This deforming lithosphere lies between the Central Indian Ridge to the west and the Sumatra trench to the east; the plates diverge to the west of ≈74°E and converge to the east of it. Many data have shown that the pole of rotation between the India and Capricorn plates lies within this diffuse plate boundary [1,2]. Surprisingly, however, the recently estimated angular velocity in the MORVEL global set of angular velocities [3] places this pole of rotation north of prior poles by several degrees, and north of the diffuse plate boundary. The motion between the India and Capricorn plates can only be estimated indirectly by differencing the motion of the India plate relative to the Somalia plate, on the one hand, and the motion of the Capricorn plate relative to Somalia plate, on the other. While the MORVEL India-Somalia angular velocity is similar to prior estimates, the MORVEL Capricorn-Somalia pole of rotation lies northwest of its predecessors. The difference is not caused by new transform azimuth data incorporated into MORVEL or by the new application of a correction to spreading rates for outward displacement. Instead the difference appears to be caused by a few anomalous spreading rates near the northern end of the Capricorn-Somalia plate boundary along the Central Indian Ridge. Rejecting these data leads to consistency with prior results. Implications for the motion of the Capricorn plate relative to Australia will be discussed. [1] DeMets, C., R. G. Gordon, and J.-Y. Royer, 2005. Motion between the Indian, Capricorn, and Somalian plates since 20 Ma: implications for the timing and magnitude of distributed deformation in the equatorial Indian ocean, Geophys. J. Int., 161, 445-468. [2] Gordon, R. G., Royer, J.-Y., and D. F. Argus, 2008. Space geodetic test of kinematic models for the Indo-Australian composite plate, Geology, 36, 827-830, doi: 10.1130/G25089A.1. [3] DeMets, C., Gordon, R. G., & Argus, D. F., 2010. Geologically current plate motions, Geophys. J. Int., 181, 1-80, doi: 10.1111/j.1365-246X.2009.04491.x.

Geodetic estimates of fault slip rates in the San Francisco Bay area

USGS Publications Warehouse

Savage, J.C.; Svarc, J.L.; Prescott, W.H.

1999-01-01

Bourne et al. [1998] have suggested that the interseismic velocity profile at the surface across a transform plate boundary is a replica of the secular velocity profile at depth in the plastosphere. On the other hand, in the viscoelastic coupling model the shape of the interseismic surface velocity profile is a consequence of plastosphere relaxation following the previous rupture of the faults that make up the plate boundary and is not directly related to the secular flow in the plastosphere. The two models appear to be incompatible. If the plate boundary is composed of several subparallel faults and the interseismic surface velocity profile across the boundary known, each model predicts the secular slip rates on the faults which make up the boundary. As suggested by Bourne et al., the models can then be tested by comparing the predicted secular slip rates to those estimated from long-term offsets inferred from geology. Here we apply that test to the secular slip rates predicted for the principal faults (San Andreas, San Gregorio, Hayward, Calaveras, Rodgers Creek, Green Valley and Greenville faults) in the San Andreas fault system in the San Francisco Bay area. The estimates from the two models generally agree with one another and to a lesser extent with the geologic estimate. Because the viscoelastic coupling model has been equally successful in estimating secular slip rates on the various fault strands at a diffuse plate boundary, the success of the model of Bourne et al. [1998] in doing the same thing should not be taken as proof that the interseismic velocity profile across the plate boundary at the surface is a replica of the velocity profile at depth in the plastosphere.

An analytical study of the free and forced vibration response of a ribbed plate with free boundary conditions

NASA Astrophysics Data System (ADS)

Lin, Tian Ran; Zhang, Kai

2018-05-01

An analytical study to predict the vibration response of a ribbed plate with free boundary conditions is presented. The analytical solution was derived using a double cosine integral transform technique and then utilized to study the free and forced vibration of the ribbed plate, as well as the effect of the rib on the modal response of the uniform plate. It is shown that in addition to the three zero-frequency rigid body modes of the plate, the vibration modes of the uniform plate can be classified into four mode groups according to the symmetric properties of the plate with respect to the two orthogonal middle lines parallel to the plate edges. The four mode groups correspond to a double symmetric group, a double anti-symmetric group and two symmetric/anti-symmetric groups. Whilst the inclusion of the rib to the plate is shown to cause distortion to the distribution of vibration modes, most modes can still be traced back to the original modes of the uniform plate. Both the mass and stiffness of the rib are shown to affect the modal vibration of the uniform plate, whereby a dominant effect from the rib mass leads to a decrease in the modal frequency of the plate, whereas a dominant effect from the rib stiffness leads to an increase in plate modal frequency. When the stiffened rib behaves as an effective boundary to the plate vibration, an original plate mode becomes a pair of degenerate modes, whereby one mode has a higher frequency and the other mode has a lower frequency than that of the original mode.

Seismicity of the Earth 1900-2010 Mexico and vicinity

USGS Publications Warehouse

Rhea, Susan; Dart, Richard L.; Villaseñor, Antonio; Hayes, Gavin P.; Tarr, Arthur C.; Furlong, Kevin P.; Benz, Harley M.

2011-01-01

Mexico, located in one of the world's most seismically active regions, lies on three large tectonic plates: the North American plate, Pacific plate, and Cocos plate. The relative motion of these tectonic plates causes frequent earthquakes and active volcanism and mountain building. Mexico's most seismically active region is in southern Mexico where the Cocos plate is subducting northwestward beneath Mexico creating the deep Middle America trench. The Gulf of California, which extends from approximately the northern terminus of the Middle America trench to the U.S.-Mexico border, overlies the plate boundary between the Pacific and North American plates where the Pacific plate is moving northwestward relative to the North American plate. This region of transform faulting is the southern extension of the well-known San Andreas Fault system.

Present-Day Kinematics of the Dead Sea Transform and Internal Deformation within the Sinai and Arabian Plates

NASA Astrophysics Data System (ADS)

Gomez, F. G.; Yassminh, R.; Cochran, W. J.; Reilinger, R. E.; Barazangi, M.

2015-12-01

An updated GPS velocity field along the Dead Sea Fault (DSF) provides a basis for assessing off-transform strain within the Sinai and Arabian plates along entire length of this left-lateral, continental transform. As one of the main tectonic elements in the eastern Mediterranean region, an improved kinematic view of the DSF elucidates the broader understanding of the regional tectonic framework, as well as contributes to refining the earthquake hazard assessment. Reconciling short-term (geodetic) measurements of crustal strain with neotectonic data on fault movements can yield insight into the mechanical and rheological properties of crustal deformation associated with transform tectonics. In addition to regional continuous GPS stations, this study assembles results from campaign GPS networks in Syria, Lebanon, and Jordan spanning more than a decade. 1-sigma uncertainties on velocities range from less than 0.4 mm/yr (continuous stations and older GPS survey sites) to about 1.0 mm/yr (newer survey sites). Analyses using elastic block models suggest slip rates of 4.0 - 5.0 mm/yr along the southern and central DSF and slip rates of 2.0 - 3.0 mm/yr along the northern DSF, and fault locking depths also vary along strike of the transform. Furthermore, the spatial distribution of GPS observations permits analyzing residual strains within the adjacent plates, after plate boundary strain is removed. A key observation is horizontal stretching within the Sinai plate, which may be related to pull by the subducted slab of the Sinai plate. Within the Arabian plate, areas of horizontal stretching generally correlate with locations of Quaternary volcanism.

Role of Transtension in Rifting at the Pacific-North America Plate Boundary

NASA Astrophysics Data System (ADS)

Stock, J. M.

2011-12-01

Transtensional plate motion can be accommodated either in a localized zone of transtensional rifting or over a broader region. Broader zones of deformation can be classified either as diffuse deformation or strain partitioning (one or more major strike-slip shear zones geographically offset from a region of a extensional faulting). The Pacific-North America plate boundary in southwestern North America was transtensional during much of its history and has exhibited the full range of these behaviors at different spatial scales and in different locations, as recorded by fault motions and paleomagnetic rotations. Here we focus on the northern Gulf of California part of the plate boundary (Upper and Lower Delfin basin segments), which has been in a zone of transtensional Pacific-North America plate boundary motion ever since the middle Miocene demise of adjacent Farallon-derived microplates. Prior to the middle Miocene, during the time of microplate activity, this sector of North America experienced basin-and-range normal faults (core complexes) in Sonora. However there is no evidence of continued extensional faulting nor of a Gulf-related topographic depression until after ca 12 Ma when a major ignimbrite (Tuff of San Felipe/ Ignimbrite of Hermosillo) was deposited across the entire region of the future Gulf of California rift in this sector. After 12 Ma, faults disrupted this marker bed in eastern Baja California and western Sonora, and some major NNW-striking right-lateral faults are inferred to have developed near the Sonoran coast causing offset of some of the volcanic facies. However, there are major tectonic rotations of the volcanic rocks in NE Baja California between 12 and 6 Ma, suggesting that the plate boundary motion was still occurring over a broad region. By contrast, after about 6 Ma, diminished rotations in latest Miocene and Pliocene volcanic rocks, as well as fault slip histories, show that plate boundary deformation became localized to a narrower transtensional zone of long offset strike-slip faults and intervening basins (the modern Gulf of California basin and transform fault system). Within and adjacent to this zone the fault patterns continued to evolve, with new plate boundary strike-slip faults breaking into previously intact blocks of continent. These new strike-slip faults were not accompanied by any widespread zones of tectonic rotation. This suggests that if widespread rotations are occurring, plate boundary transtension has not yet localized and the strike-slip faults are not yet accommodating most of the plate boundary slip. The cessation of widespread and significant vertical axis rotations could indicate strain localization and the increasing importance of throughgoing strike-slip faults (a precursor to fully oceanic rifting) along a transtensional plate boundary.

Stress intensity factors of composite orthotropic plates containing periodic buffer strips

NASA Technical Reports Server (NTRS)

Delale, F.; Erdogan, F.

1978-01-01

The fracture problem of laminated plates which consist of bonded orthotropic layers is studied. The fields equations for an elastic orthotropic body are transformed to give the displacement and stress expressions for each layer or strip. The unknown functions in these expressions are found by satisfying the remaining boundary and continuity conditions. A system of singular integral equations is obtained from the mixed boundary conditions. The singular behavior around the crack tip and at the bimaterial interface is studied. The stress intensity factors are computed for various material combinations and various crack geometries. The results are discussed and are compared with those for isotropic materials.

Microstructural evolution of AZ31 magnesium alloy subjected to sliding friction treatment

NASA Astrophysics Data System (ADS)

Zhang, Wei; Lu, Jinwen; Huo, Wangtu; Zhang, Yusheng; Wei, Q.

2018-06-01

Microstructural evolution and grain refinement mechanism in AZ31 magnesium alloy subjected to sliding friction treatment were investigated by means of transmission electron microscopy. The process of grain refinement was found to involve the following stages: (I) coarse grains were divided into fine twin plates through mechanical twinning; then the twin plates were transformed to lamellae with the accumulation of residual dislocations at the twin boundaries; (II) the lamellae were separated into subgrains with increasing grain boundary misorientation and evolution of high angle boundaries into random boundaries by continuous dynamic recrystallisation (cDRX); (III) the formation of nanograins. The mechanisms for the final stage, the formation of nanograins, can be classified into three types: (i) cDRX; (ii) discontinuous dynamic recrystallisation (dDRX); (iii) a combined mechanism of prior shear-band and subsequent dDRX. Stored strain energy plays an important role in determining deformation mechanisms during plastic deformation.

Hydrodynamic and Thermal Slip Effect on Double-Diffusive Free Convective Boundary Layer Flow of a Nanofluid Past a Flat Vertical Plate in the Moving Free Stream

PubMed Central

Khan, Waqar A.; Uddin, Md Jashim; Ismail, A. I. Md.

2013-01-01

The effects of hydrodynamic and thermal slip boundary conditions on the double-diffusive free convective flow of a nanofluid along a semi-infinite flat solid vertical plate are investigated numerically. It is assumed that free stream is moving. The governing boundary layer equations are non-dimensionalized and transformed into a system of nonlinear, coupled similarity equations. The effects of the controlling parameters on the dimensionless velocity, temperature, solute and nanofluid concentration as well as on the reduced Nusselt number, reduced Sherwood number and the reduced nanoparticle Sherwood number are investigated and presented graphically. To the best of our knowledge, the effects of hydrodynamic and thermal slip boundary conditions have not been investigated yet. It is found that the reduced local Nusselt, local solute and the local nanofluid Sherwood numbers increase with hydrodynamic slip and decrease with thermal slip parameters. PMID:23533566

Features on Venus generated by plate boundary processes

NASA Technical Reports Server (NTRS)

Mckenzie, Dan; Ford, Peter G.; Johnson, Catherine; Parsons, Barry; Sandwell, David; Saunders, Stephen; Solomon, Sean C.

1992-01-01

Various observations suggest that there are processes on Venus that produce features similar to those associated with plate boundaries on earth. Synthetic aperture radar images of Venus, taken with a radar whose wavelength is 12.6 cm, are compared with GLORIA images of active plate boundaries, obtained with a sound source whose wavelength is 23 cm. Features similar to transform faults and to abyssal hills on slow and fast spreading ridges can be recognized within the Artemis region of Venus but are not clearly visible elsewhere. The composition of the basalts measured by the Venera 13 and 14 and the Vega 2 spacecraft corresponds to that expected from adiabatic decompression, like that which occurs beneath spreading ridges on earth. Structures that resemble trenches are widespread on Venus and show the same curvature and asymmetry as they do on earth. These observations suggest that the same simple geophysical models that have been so successfully used to understand the tectonics of earth can also be applied to Venus.

Owen Fracture Zone: The Arabia-India plate boundary unveiled

NASA Astrophysics Data System (ADS)

Fournier, M.; Chamot-Rooke, N.; Rodriguez, M.; Huchon, P.; Petit, C.; Beslier, M. O.; Zaragosi, S.

2011-02-01

We surveyed the Owen Fracture Zone at the boundary between the Arabia and India plates in the NW Indian Ocean using a high-resolution multibeam echo-sounder (Owen cruise, 2009) for search of active faults. Bathymetric data reveal a previously unrecognized submarine fault scarp system running for over 800 km between the Sheba Ridge in the Gulf of Aden and the Makran subduction zone. The primary plate boundary structure is not the bathymetrically high Owen Ridge, but is instead a series of clearly delineated strike-slip fault segments separated by several releasing and restraining bends. Despite an abundant sedimentary supply by the Indus River flowing from the Himalaya, fault scarps are not obscured by recent deposits and can be followed over hundreds of kilometres, pointing to very active tectonics. The total strike-slip displacement of the fault system is 10-12 km, indicating that it has been active for the past ~ 3 to 6 Ma if its current rate of motion of 3 ± 1 mm yr- 1 has remained stable. We describe the geometry of this recent fault system, including a major pull-apart basin at the latitude 20°N, and we show that it closely follows an arc of small circle centred on the Arabia-India pole of rotation, as expected for a transform plate boundary.

A new plate tectonic concept for the eastern-most Mediterranean

NASA Astrophysics Data System (ADS)

Huebscher, C.; McGrandle, A.; Scaife, G.; Spoors, R.; Stieglitz, T.

2012-04-01

Owing to the seismogenic faults bordering the Levant-Sinai realm and the discovery of giant gas reservoirs in the marine Levant Basin the scientific interest in this tectonically complex setting increased in recent years. Here we provide a new model for the Levant Basin architecture and adjacent plate boundaries emphasizing the importance of industrial seismic data for frontier research in earth science. PSDM seismics, residual gravity and depth to basement maps give a clear line of evidence that the Levant Basin, formerly considered as a single tectonic entity, is divided into two different domains. Highly stretched continental crust in the southern domain is separated from deeper and presumably Tethyan oceanic crust in the north. A transform continuing from southwest Cyprus to the Carmel Fault in northern Israel is considered as the boundary. If this interpretation holds, the Carmel-Cyprus Transform represents a yet unknown continent-ocean boundary in the eastern Mediterranean, thus adding new constrains for the Mediterranean plate tectonic puzzle. The Eratosthenes Seamount, considered as the spearhead of incipient continental collision in the eastern Mediterranean, is interpreted as a carbonate platform that developed above a volcanic basement. NW-SE trending strike-slip faults are abundant in the entire Levant region. Since this trend also shapes the topography of the Levant hinterland including Quaternary deposits their recent tectonic activity is quite likely. Thus, our study supports previous studies which attributed the evolution of submarine canyons and Holocene triggering of mass failures not only to salt tectonics or depositional processes, but also to active plate-tectonics.

Variable Viscosity Effects on Time Dependent Magnetic Nanofluid Flow past a Stretchable Rotating Plate

NASA Astrophysics Data System (ADS)

Ram, Paras; Joshi, Vimal Kumar; Sharma, Kushal; Walia, Mittu; Yadav, Nisha

2016-01-01

An attempt has been made to describe the effects of geothermal viscosity with viscous dissipation on the three dimensional time dependent boundary layer flow of magnetic nanofluids due to a stretchable rotating plate in the presence of a porous medium. The modelled governing time dependent equations are transformed a from boundary value problem to an initial value problem, and thereafter solved by a fourth order Runge-Kutta method in MATLAB with a shooting technique for the initial guess. The influences of mixed temperature, depth dependent viscosity, and the rotation strength parameter on the flow field and temperature field generated on the plate surface are investigated. The derived results show direct impact in the problems of heat transfer in high speed computer disks (Herrero et al. [1]) and turbine rotor systems (Owen and Rogers [2]).

Geophysics and Tectonic Development of the Caroline Basin.

DTIC Science & Technology

1983-05-01

three diverse (shallow and intermediate depth ) epicenters scattered along the eastern margin of the Caroline Basin, one mech- anism determination has been...between the plates could conceivably change to a relative left-lateral motion of the Pacific Plate along a transform boundary. Again there is no...Sea Drilling Project, southwest Pacific structures : Geotimes, v. 18, P. 18-21. Scientific Staff, 1978, Leg 60 ends in Guam: Geotimes, v. 23, p. 19-23

Cenozoic deformation from the Yakutat-North American collision to the eastern margin of the Northern Canadian Cordillera

NASA Astrophysics Data System (ADS)

Enkelmann, E.

2017-12-01

The western margin of the Northern Cordillera of North America is dominated by transform motion of the Yakutat microplate along the Fairweather fault system. In southeast Alaska the transform boundary changes to convergence and the oblique collision of the buoyant Yakutat microplate formed the St. Elias Mountains. One of the outstanding questions in understanding the St. Elias orogeny is how stress from the plate boundary has been transferred inboard and distributed strain in the North American plate. The timing, amount, and spatial pattern of deformation and rock exhumation have been studied using multiple thermochronology methods. Together the data reveal that Late Cenozoic deformation inboard of the Fairweather Fault and the colliding Yakutat plate corner at the St. Elias syntaxis was spatially very limited, resulting in rock exhumation within a <30 km-wide corridor north and northeast of the plate boundary. The data from this inboard region, located in Yukon and northern British Columbia, record Late Cretaceous-Early Eocene cooling associated with Cordilleran deformation, and Paleocene-Eocene cooling due to spreading-ridge subduction. In contrast, the region west of the St. Elias syntaxis is dominated by convergence, which resulted in significant Cenozoic deformation in southeastern and southern Alaska. In the St. Elias orogen itself, most of the Late Cenozoic deformation and exhumation occurs within the Yakutat microplate and its Cenozoic sedimentary cover that composes the fold-thrust belt. The efficient interaction between tectonic uplift and glacial erosion resulted in rapid exhumation (>1 km/Myr) and extreme rates (4 km/Myr) that are localized at the syntaxis region and have shifted southward over the past 10 Myr. Far-field deformation reaches more than 500 km to the northwest of the convergent margin and caused mountain building in south-central Alaska. Deformation to the northeast is unclear. New thermochronology data from the eastern margin of the Northern Canadian Cordillera (Northwest Territory) reveal exhumation during the Oligocene to early Miocene. At this time, transform motion was already dominating the plate margin in the west. The post-Cordilleran deformation at the eastern front may thus be related to mantle convection and/or stresses associated with the North Atlantic opening.

Formation and Elimination of Transform Faults on the Reykjanes Ridge

NASA Astrophysics Data System (ADS)

Martinez, Fernando; Hey, Richard

2017-04-01

The Reykjanes Ridge is a type-setting for examining processes that form and eliminate transform faults because it has undergone these events systematically within the Iceland gradient in hot-spot influence. A Paleogene change in plate motion led to the abrupt segmentation of the originally linear axis into a stair-step ridge-transform configuration. Its subsequent evolution diachronously and systematically eliminated the just-formed offsets re-establishing the original linear geometry of the ridge over the mantle, although now spreading obliquely. During segmented stages accreted crust was thinner and during unsegmented stages southward pointing V-shaped crustal ridges formed. Although mantle plume effects have been invoked to explain the changes in segmentation and crustal features, we propose that plate boundary processes can account for these changes [Martinez & Hey, EPSL, 2017]. Fragmentation of the axis was a mechanical effect of an abrupt change in plate opening direction, as observed in other areas, and did not require mantle plume temperature changes. Reassembly of the fragmented axis to its original linear configuration was controlled by a deep damp melting regime that persisted in a linear configuration following the abrupt change in opening direction. Whereas the shallow and stronger mantle of the dry melting regime broke up into a segmented plate boundary, the persistent deep linear damp melting regime guided reassembly of the ridge axis back to its original configuration by inducing asymmetric spreading of individual ridge segments. Effects of segmentation on mantle upwelling explain crustal thickness changes between segmented and unsegmented phases of spreading without mantle temperature changes. Buoyant upwelling instabilities propagate along the long linear deep melting regime driven by regional gradients in mantle properties away from Iceland. Once segmentation is eliminated, these propagating upwelling instabilities lead to crustal thickness variations forming the V-shaped ridges on the Reykjanes Ridge flanks, without requiring actual rapid radial mantle plume flow or temperature variations. Our study indicates that the Reykjanes Ridge can be used to study how plate boundary processes within a regional gradient in mantle properties lead to a range of effects on lithospheric segmentation, melt production and crustal accretion.

Seismotectonics of the Lwandle-Nubia plate boundary between South Africa and the Southwest Indian Ridge

NASA Astrophysics Data System (ADS)

Hartnady, Chris; Okal, Emile; Calais, Eric; Stamps, Sarah; Saria, Elifuraha

2013-04-01

The Lwandle (LW) plate shares a boundary with the Nubia (NU) plate, extending from a diffuse triple junction with the Rovuma plate in Southern Mozambique to a triple junction with the Antarctic plate along a segment of the Southwest Indian Ridge (SWIR). The LW-NU boundary terminates in the ~750 km-long, complex transform of the Andrew Bain Fracture Zone (ABFZ), but its exact locus is still unclear. Recent works locate it along the eastern boundary of the submarine Mozambique Ridge, parallel to the pre-existing, oceanic transform-fault fabric. However, an early concept of the LW block ('ambiguous region' of Hartnady, 1990, Fig. 2) indicates a more westerly trajectory in the north that includes parts of South Africa, with a southerly extension across old oceanic crust of the submarine Natal Valley and Transkei Basin. This proposed boundary is marked by several, aligned epicentres of moderate to strong earthquakes (1941, 1942, 1956, 1969, 1972, 1975, 1981 and 1989). Our re-examination of seismographic records from the 1975 'intraplate' earthquake (-37.62°N, 30.98°E, mb5.0), in the oceanic crust of the distal Transkei Basin, shows a thrust-faulting focal mechanism along a nodal plane striking N272°E. The largest (ML4.2) of a series of three small earthquakes in the Natal Valley in 2009, close to a zone of recent seafloor deformation mapped in 1992, has similar first-motion patterns at Southern African seismograph stations. When the 1975 slip-vector result (N173°E) is combined with a normal-faulting slip vector (N078°E) from a 1986 onland earthquake (-30.53°N, 28.84°E, mb5.0) near the Lesotho-KZN border, and both are incorporated into the wider data-set previously used to solve for East African Rift kinematics, they produce a LW-NU rotation pole that is located south of Africa, near the Agulhas Plateau, and approximately 950 km from the Natal Valley deformation zone. The modeled low rate of right-lateral, LW-NU slip (~0.50-0.75 mm/yr) across this LW-NU boundary segment suggests that the 1972, 1981 and nearby 2009 earthquakes are instances of a 'long aftershock sequence' in the source zone of the 1850 'i-Nyikima' event, which was felt over a very wide region of the Eastern Cape Colony, and the adjacent territories of British Kaffraria and Pondoland. This remarkable historic shaking appears to have been caused by a great (Mw8.0+), oceanic event along a segment of the LW-NU boundary, resembling the 1942 SWIR event along the ABFZ and the recent (2012 March 11) North Indian Ocean events along the incipient boundary between the Indian and Australian plates. This new interpretation has implications for the re-assessment of seismic and submarine-landslide (tsunami) hazard along the SE continental margin of South Africa. Reference Hartnady CJH (1990). Seismicity and plate boundary evolution in southeastern Africa. S. Afr. J. Geol. 93, 473 484.

Unsteady Heat-Flux Measurements of Second-Mode Instability Waves in a Hypersonic Boundary Layer

NASA Technical Reports Server (NTRS)

Kergerise, Michael A.; Rufer, Shann J.

2016-01-01

In this paper we report on the application of the atomic layer thermopile (ALTP) heat- flux sensor to the measurement of laminar-to-turbulent transition in a hypersonic flat plate boundary layer. The centerline of the flat-plate model was instrumented with a streamwise array of ALTP sensors and the flat-plate model was exposed to a Mach 6 freestream over a range of unit Reynolds numbers. Here, we observed an unstable band of frequencies that are associated with second-mode instability waves in the laminar boundary layer that forms on the flat-plate surface. The measured frequencies, group velocities, phase speeds, and wavelengths of these instability waves are in agreement with data previously reported in the literature. Heat flux time series, and the Morlet-wavelet transforms of them, revealed the wave-packet nature of the second-mode instability waves. In addition, a laser-based radiative heating system was developed to measure the frequency response functions (FRF) of the ALTP sensors used in the wind tunnel test. These measurements were used to assess the stability of the sensor FRFs over time and to correct spectral estimates for any attenuation caused by the finite sensor bandwidth.

Relaxation of an unsteady turbulent boundary layer on a flat plate in an expansion tube

NASA Technical Reports Server (NTRS)

Gurta, R. N.; Trimpi, R. L.

1974-01-01

An analysis is presented for the relaxation of a turbulent boundary layer on a semi-infinite flat plate after passage of a shock wave and a trailing driver gas-driven gas interface. The problem has special application to expansion-tube flows. The flow-governing equations have been transformed into the Crocco variables, and a time-similar solution is presented in terms of the dimensionless distance-time variable alpha and the dimensionless velocity variable beta. An eddy-viscosity model, similar to that of time-steady boundary layers, is applied to the inner and outer regions of the boundary layer. A turbulent Prandtl number equal to the molecular Prandtl number is used to relate the turbulent heat flux to the eddy viscosity. The numerical results, obtained by using the Gauss-Seidel line-relaxation method, indicate that a fully turbulent boundary layer relaxes faster to the final steady-state values of heat transfer and skin friction than a laminar boundary layer. The results also give a fairly good estimate of the local skin friction and heat transfer for near steady-flow conditions.

Philippine Sea Plate inception, evolution, and consumption with special emphasis on the early stages of Izu-Bonin-Mariana subduction

NASA Astrophysics Data System (ADS)

Lallemand, Serge

2016-12-01

We compiled the most relevant data acquired throughout the Philippine Sea Plate (PSP) from the early expeditions to the most recent. We also analyzed the various explanatory models in light of this updated dataset. The following main conclusions are discussed in this study. (1) The Izanagi slab detachment beneath the East Asia margin around 60-55 Ma likely triggered the Oki-Daito plume occurrence, Mesozoic proto-PSP splitting, shortening and then failure across the paleo-transform boundary between the proto-PSP and the Pacific Plate, Izu-Bonin-Mariana subduction initiation and ultimately PSP inception. (2) The initial splitting phase of the composite proto-PSP under the plume influence at ˜54-48 Ma led to the formation of the long-lived West Philippine Basin and short-lived oceanic basins, part of whose crust has been ambiguously called "fore-arc basalts" (FABs). (3) Shortening across the paleo-transform boundary evolved into thrusting within the Pacific Plate at ˜52-50 Ma, allowing it to subduct beneath the newly formed PSP, which was composed of an alternance of thick Mesozoic terranes and thin oceanic lithosphere. (4) The first magmas rising from the shallow mantle corner, after being hydrated by the subducting Pacific crust beneath the young oceanic crust near the upper plate spreading centers at ˜49-48 Ma were boninites. Both the so-called FABs and the boninites formed at a significant distance from the incipient trench, not in a fore-arc position as previously claimed. The magmas erupted for 15 m.y. in some places, probably near the intersections between back-arc spreading centers and the arc. (5) As the Pacific crust reached greater depths and the oceanic basins cooled and thickened at ˜44-45 Ma, the composition of the lavas evolved into high-Mg andesites and then arc tholeiites and calc-alkaline andesites. (6) Tectonic erosion processes removed about 150-200 km of frontal margin during the Neogene, consuming most or all of the Pacific ophiolite initially accreted to the PSP. The result was exposure of the FABs, boninites, and early volcanics that are near the trench today. (7) Serpentinite mud volcanoes observed in the Mariana fore-arc may have formed above the remnants of the paleo-transform boundary between the proto-PSP and the Pacific Plate.

Double diffusive magnetohydrodynamic (MHD) mixed convective slip flow along a radiating moving vertical flat plate with convective boundary condition.

PubMed

Rashidi, Mohammad M; Kavyani, Neda; Abelman, Shirley; Uddin, Mohammed J; Freidoonimehr, Navid

2014-01-01

In this study combined heat and mass transfer by mixed convective flow along a moving vertical flat plate with hydrodynamic slip and thermal convective boundary condition is investigated. Using similarity variables, the governing nonlinear partial differential equations are converted into a system of coupled nonlinear ordinary differential equations. The transformed equations are then solved using a semi-numerical/analytical method called the differential transform method and results are compared with numerical results. Close agreement is found between the present method and the numerical method. Effects of the controlling parameters, including convective heat transfer, magnetic field, buoyancy ratio, hydrodynamic slip, mixed convective, Prandtl number and Schmidt number are investigated on the dimensionless velocity, temperature and concentration profiles. In addition effects of different parameters on the skin friction factor, [Formula: see text], local Nusselt number, [Formula: see text], and local Sherwood number [Formula: see text] are shown and explained through tables.

Localizing sources of acoustic emission during the martensitic transformation

NASA Astrophysics Data System (ADS)

Niemann, R.; Kopeček, J.; Heczko, O.; Romberg, J.; Schultz, L.; Fähler, S.; Vives, E.; Mañosa, L.; Planes, A.

2014-06-01

Acoustic avalanches are a general feature of solids under stress, e.g., evoked by external compression or arising from internal processes like martensitic phase transformations. From integral measurements, it is usually concluded that nucleation, phase boundary pinning, or interface incompatibilities during this first-order phase transition all may generate acoustic emission. This paper studies the local sources of acoustic emission to enlight the microscopic mechanisms. From two-dimensional spatially resolved acoustic emission measurement and simultaneous optical observation of the surface, we can identify microstructural events at the phase boundary that lead to acoustic emission. A resolution in the 100-μm range was reached for the location of acoustic emission sources on a coarse-grained Ni-Mn-Ga polycrystal. Both, the acoustic activity and the size distribution of the microstructural transformation events, exhibit power-law behavior. The origin of the acoustic emission are elastically incompatible areas, such as differently oriented martensitic plates that meet each other, lamellae growing up to grain boundaries, and grain boundaries in proximity to transforming grains. Using this result, we propose a model to explain the decrease of the critical exponent under a mechanical stress or magnetic field.

Crustal deformation in great California earthquake cycles

NASA Technical Reports Server (NTRS)

Li, Victor C.; Rice, James R.

1986-01-01

Periodic crustal deformation associated with repeated strike slip earthquakes is computed for the following model: A depth L (less than or similiar to H) extending downward from the Earth's surface at a transform boundary between uniform elastic lithospheric plates of thickness H is locked between earthquakes. It slips an amount consistent with remote plate velocity V sub pl after each lapse of earthquake cycle time T sub cy. Lower portions of the fault zone at the boundary slip continuously so as to maintain constant resistive shear stress. The plates are coupled at their base to a Maxwellian viscoelastic asthenosphere through which steady deep seated mantle motions, compatible with plate velocity, are transmitted to the surface plates. The coupling is described approximately through a generalized Elsasser model. It is argued that the model gives a more realistic physical description of tectonic loading, including the time dependence of deep slip and crustal stress build up throughout the earthquake cycle, than do simpler kinematic models in which loading is represented as imposed uniform dislocation slip on the fault below the locked zone.

New Evidence for Quaternary Strain Partitioning Along the Queen Charlotte Fault System, Southeastern Alaska

NASA Astrophysics Data System (ADS)

Walton, M. A. L.; Miller, N. C.; Brothers, D. S.; Kluesner, J.; Haeussler, P. J.; Conrad, J. E.; Andrews, B. D.; Ten Brink, U. S.

2017-12-01

The Queen Charlotte Fault (QCF) is a fast-moving ( 53 mm/yr) transform plate boundary fault separating the Pacific Plate from the North American Plate along western Canada and southeastern Alaska. New high-resolution bathymetric data along the fault show that the QCF main trace accommodates nearly all strike-slip plate motion along a single narrow deformation zone, though questions remain about how and where smaller amounts of oblique convergence are accommodated along-strike. Obliquity and convergence rates are highest in the south, where the 2012 Haida Gwaii, British Columbia MW 7.8 thrust earthquake was likely caused by Pacific underthrusting. In the north, where obliquity is lower, aftershocks from the 2013 Craig, Alaska MW 7.5 strike-slip earthquake also indicate active convergent deformation on the Pacific (west) side of the plate boundary. Off-fault structures previously mapped in legacy crustal-scale seismic profiles may therefore be accommodating part of the lesser amounts of Quaternary convergence north of Haida Gwaii. Between 2015 and 2017, the USGS acquired more than 8,000 line-km of offshore high-resolution multichannel seismic (MCS) data along the QCF to better understand plate boundary deformation. The new MCS data show evidence for Quaternary deformation associated with a series of elongate ridges located within 30 km of the QCF main trace on the Pacific side. These ridges are anticlinal structures flanked by growth faults, with recent deformation and active fluid flow characterized by seafloor scarps and seabed gas seeps at ridge crests. Structural and morphological evidence for contractional deformation decreases northward along the fault, consistent with a decrease in Pacific-North America obliquity along the plate boundary. Preliminary interpretations suggest that plate boundary transpression may be partitioned into distinctive structural domains, in which convergent stress is accommodated by margin-parallel thrust faulting, folding, and ridge formation within the Pacific Plate, with strike-slip faulting localized to the primary trace of the QCF. Contractional structures may be occupying zones of pre-existing crustal weakness and/or re-activated fabrics in the oceanic crust, possibly explaining strain partitioning behavior in areas with a low convergence angle (<15°).

Overview of the Kinematics of the Salton Trough and Northern Gulf of California

NASA Astrophysics Data System (ADS)

Stock, J. M.

2016-12-01

In the Salton Trough and Northern Gulf of California, transtensional rifting is leading to full continental plate breakup, as a major continental block is being transferred to an oceanic plate. Since at least 6 Ma this region has taken up most of the plate boundary slip between the Pacific and North America plates at this latitude. We review the structural history of plate separation, as constrained by many recent studies of present and past fault configurations, seismicity, and basin development as seen from geology and geophysics. Modern activity in the USA is dominated by NW-striking strike-slip faults (San Andreas, San Jacinto, Elsinore), and subsidiary NE-striking faults. There is an equally broad zone in Mexico (faults from the Mexicali Valley to the Colorado River Delta and bounding the Laguna Salada basin), including active low-angle detachment faults. In both areas, shifts in fault activity are indicated by buried faults and exhumed or buried earlier basin strata. Seismicity defines 3 basin segments in the N Gulf: Consag-Wagner, Upper Delfin, and Lower Delfin, but localization is incomplete. These basins occupy a broad zone of modern deformation, lacking single transform faults, although major strike-slip faults formed in the surrounding continental area. The off-boundary deformation on the western side of the plate boundary has changed with time, as seen by Holocene and Quaternary faults controlling modern basins in the Gulf Extensional Province of NE Baja California, and stranded Pliocene continental and marine basin strata in subaerial fault blocks. The eastern side of the plate boundary, in the shallow northeastern Gulf, contains major NW-striking faults that may have dominated the earlier (latest Miocene-early Pliocene) kinematics. The Sonoran coastal plain likely buries additional older faults and basin sequences; further studies here are needed to refine models of the earlier structural development of this sector. Despite > 250 km of plate separation, and production of new crustal area in these segments of the plate boundary, the deformation is not considered to be fully localized because some occurs outside the region of new crustal formation. Similar scenarios may need to be considered when evaluating continent-ocean transitions in other rift systems.

Transform migration and vertical tectonics at the Romanche fracture zone, equatorial Atlantic

NASA Astrophysics Data System (ADS)

Bonatti, E.; Ligi, M.; Gasperini, L.; Peyve, A.; Raznitsin, Y.; Chen, Y. J.

1994-11-01

The Romanche transform offsets the Mid-Atlantic Ridge (MAR) axis by about 950 km in the equatorial Atlantic. Multibeam and high-resolution multichannel seismic reflection surveys as well as rock sampling were carried out on the eastern part of the transform with the R/V Akademik Strakhov as part of the Russian-Italian Mid-Atlantic Ridge Project (PRIMAR). Morphobathymetric data show the existence on the northern side of the transform of a major 800-km-long aseismic valley oriented 10 deg to 15 deg from the active valley; it disappears about 150 km from the western MAR segment. The aseismic valley marks probably the former location of the Romanche transform ('PaleoRomanche') that was active up to roughly 8-10 Ma, when the transform boundary migrated to its present position. A temporary microplate developed during the migration and reorientation of the transform. This microplate changed its sense of motion as it was transferred from the South American to the African plate. Evaluation of the seismic reflection data as well as study of samples of carbonates, ventifact basaltic pebbles and gabbroic, peridotitic and basaltic rocks recovered at different sites on the transverse ridge, suggest that (1) the summit of the transverse ridge was above sea level at and before about 5 Ma; (2) the transverse ridge subsided since then at an average rate 1 order of magnitude faster than the predicted thermal contraction rate; its summit was flattened by erosion at sea level during subsidence; (3) the transverse ridge is an uplifted sliver of lithosphere and not a volcanic constructional feature; and (4) transtensional and transpressional tectonics have affected the transverse ridge. Uplift may have been caused primarily by thrust faulting induced by transpression related to the oblique impact of the lithospheric plate against the former (PaleoRomanche) and the younger transform boundaries, before and during the transition to the present boundary. After migration of the transform boundary to its present position, transpression was replaced by transtension and by subsidence of the transverse ridge. An aseismic axial rift valley impacting against the transform valley about 80 km west of the present RTI suggests eastward ridge jumping and probably followed transform migration. Localized transtension or transpression due to bends in the orientation of the transform may have caused intense although localized vertical movements, such as those that formed an ultradeep (greater than 7800 m) pull-apart basin along the transform valley.

The effects of magnetohydrodynamic and radiation on flow of second grade fluid past an infinite inclined plate in porous medium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ismail, Zulkhibri; Khan, Ilyas; Nasir, Nadirah Mohd

2015-02-03

An analysis of the exact solutions of second grade fluid problem for unsteady magnetohydrodynamic (MHD) flows past an infinite inclined plate in a porous medium is presented. It is assumed that the bounding infinite inclined plate has a constant temperature with radiation effects. Based on Boussinesq approximation the expressions for dimensionless velocity, temperature and concentration are obtained by using Laplace transform method. The derived solutions satisfying the involved differential equations, and all the boundary and initial conditions. The influence of various parameters on the velocity has been illustrated graphically and analyzed.

Passive recording of an active transform, an example from the Levant continental margin and the Dead Sea Fault

NASA Astrophysics Data System (ADS)

Lang, Guy; Lazar, Michael; Schattner, Uri

2017-04-01

Transform faults accommodate lateral motion between two adjacent plates. Records of plate motion and consequent boundary development on land is, at times, scarce and limited to structures along the fault axis. Investigation of a passive continental margin adjacent to the plate boundary might broaden the scope and provide estimates for its structural development. To examine this hypothesis, we analyzed depth and time migrated 3D seismic data together with four boreholes located along the southern Levant continental margin, ca. 100 Km from the continental Dead Sea fault (DSF). The analysis focus on the Plio-Pleistocene sequence, a key period in the development of the DSF. It includes formation of structural maps, stacking pattern investigation and calculation of sedimentation rates based on decompacted 3D depth data. These, in turn, enabled the reconstruction of margin development. This includes Messinian-earliest Zanclean NNE-SSW sinistral strike-slip faulting followed by Zanclean-Late Gelasian syn-depositional folding striking in the same direction. Abrupt change is marked by the Top Gelasian surface that shows indications of regional mass slumping. Successive Mid-Late Pleistocene progradation marks a basinward shift of the depocenter. Progradation controls margin sedimentation rates during the mid-late Pleistocene. These were found to increase throughout the whole Plio-Pleistocene, in contrast to reported sediment discharge from the Nile, which was shown to decrease after the Gelasian. Correlations to onshore findings, suggest that the continental margin records strain localization on the DSF during the Pliocene-Gelasian. This trend peaked at 1.8 Ma when short wavelength strain ceased along the margin, and differential subsidence commenced basinwards. This is attributed to consequent deepening of the DSF plate boundary.

Tectonic interpretation of the Andrew Bain transform fault: Southwest Indian Ocean

NASA Astrophysics Data System (ADS)

Sclater, John G.; Grindlay, Nancy R.; Madsen, John A.; Rommevaux-Jestin, Celine

2005-09-01

Between 25°E and 35°E, a suite of four transform faults, Du Toit, Andrew Bain, Marion, and Prince Edward, offsets the Southwest Indian Ridge (SWIR) left laterally 1230 km. The Andrew Bain, the largest, has a length of 750 km and a maximum transform domain width of 120 km. We show that, currently, the Nubia/Somalia plate boundary intersects the SWIR east of the Prince Edward, placing the Andrew Bain on the Nubia/Antarctica plate boundary. However, the overall trend of its transform domain lies 10° clockwise of the predicted direction of motion for this boundary. We use four transform-parallel multibeam and magnetic anomaly profiles, together with relocated earthquakes and focal mechanism solutions, to characterize the morphology and tectonics of the Andrew Bain. Starting at the southwestern ridge-transform intersection, the relocated epicenters follow a 450-km-long, 20-km-wide, 6-km-deep western valley. They cross the transform domain within a series of deep overlapping basins bounded by steep inward dipping arcuate scarps. Eight strike-slip and three dip-slip focal mechanism solutions lie within these basins. The earthquakes can be traced to the northeastern ridge-transform intersection via a straight, 100-km-long, 10-km-wide, 4.5-km-deep eastern valley. A striking set of seismically inactive NE-SW trending en echelon ridges and valleys, lying to the south of the overlapping basins, dominates the eastern central section of the transform domain. We interpret the deep overlapping basins as two pull-apart features connected by a strike-slip basin that have created a relay zone similar to those observed on continental transforms. This transform relay zone connects three closely spaced overlapping transform faults in the southwest to a single transform fault in the northeast. The existence of the transform relay zone accounts for the difference between the observed and predicted trend of the Andrew Bain transform domain. We speculate that between 20 and 3.2 Ma, an oblique accretionary zone jumping successively northward created the en echelon ridges and valleys in the eastern central portion of the domain. The style of accretion changed to that of a transform relay zone, during a final northward jump, at 3.2 Ma.

Geomorphic Evolution and Slip rate Measurements of the Noushki Segment , Chaman Fault Zone, Pakistan

NASA Astrophysics Data System (ADS)

Abubakar, Y.; Khan, S. D.; Owen, L. A.; Khan, A.

2012-12-01

The Nushki segment of the Chaman fault system is unique in its nature as it records both the imprints of oblique convergence along the western Indian Plate boundary as well as the deformation along the Makran subduction zone. The left-lateral Chaman transform zone has evolved from a subduction zone along the Arabian-Eurasian collision complex to a strike-slip fault system since the collision of the Indian Plate with the Eurasia. The geodetically and geologically constrained displacement rates along the Chaman fault varies from about 18 mm/yr to about 35 mm/yr respectively throughout its total length of ~ 860 km. Two major hypothesis has been proposed by workers for these variations; i) Variations in rates of elastic strain accumulation along the plate boundary and, ii) strain partitioning along the plate boundary. Morphotectonic analysis is a very useful tool in investigations of spatial variations in tectonic activities both regionally and locally. This work uses morphotectonic analysis to investigate the degree of variations in active tectonic deformation, which can be directly related to elastic strain accumulation and other kinematics in the western boundary of the plate margin. Geomorphic mapping was carried out using remotely sensed data. ASTER and RADAR data were used in establishing Quaternary stratigraphy and measurement of geomorphic indices such as stream length gradient index, valley floor width to height ratio and, river/stream longitudinal profile within the study area. High resolution satellite images (e.g., IKONOS imagery) and 30m ASTER DEMs were employed to measure displacement recorded by landforms along individual strands of the fault. Results from geomorphic analysis shows three distinct levels of tectonic deformation. Areas showing high levels of tectonic deformation are characterized by displaced fan surfaces, deflected streams and beheaded streams. Terrestrial Cosmogenic nuclide surface exposure dating of the displaced landforms is being carried out to calculate slip-rates. Slip-rates estimation along this segment of this plate boundary will help in understanding of tectonic evolution of this plate boundary and seismic activity in the region.

Strike-slip earthquakes in the oceanic lithosphere: Observations of exceptionally high apparent stress

USGS Publications Warehouse

Choy, George; McGarr, A.

2002-01-01

The radiated energies, ES, and seismic moments, M0, for 942 globally distributed earthquakes that occurred between 1987 to 1998 are examined to find the earthquakes with the highest apparent stresses (τa=μES/M0, where μ is the modulus of rigidity). The globally averaged τa for shallow earthquakes in all tectonic environments and seismic regions is 0.3 MPa. However, the subset of 49 earthquakes with the highest apparent stresses (τa greater than about 5.0 MPa) is dominated almost exclusively by strike-slip earthquakes that occur in oceanic environments. These earthquakes are all located in the depth range 7–29 km in the upper mantle of the young oceanic lithosphere. Many of these events occur near plate-boundary triple junctions where there appear to be high rates of intraplate deformation. Indeed, the small rapidly deforming Gorda Plate accounts for 10 of the 49 high-τa events. The depth distribution of τa, which shows peak values somewhat greater than 25 MPa in the depth range 20–25 km, suggests that upper bounds on this parameter are a result of the strength of the oceanic lithosphere. A recently proposed envelope for apparent stress, derived by taking 6 per cent of the strength inferred from laboratory experiments for young (less than 30 Ma) deforming oceanic lithosphere, agrees well with the upper-bound envelope of apparent stresses over the depth range 5–30 km. The corresponding depth-dependent shear strength for young oceanic lithosphere attains a peak value of about 575 MPa at a depth of 21 km and then diminishes rapidly as the depth increases. In addition to their high apparent stresses, which suggest that the strength of the young oceanic lithosphere is highest in the depth range 10–30 km, our set of high-τa earthquakes show other features that constrain the nature of the forces that cause interplate motion. First, our set of events is divided roughly equally between intraplate and transform faulting with similar depth distributions of τa for the two types. Secondly, many of the intraplate events have focal mechanisms with the T-axes that are normal to the nearest ridge crest or subduction zone and P-axes that are normal to the proximate transform fault. These observations suggest that forces associated with the reorganization of plate boundaries play an important role in causing high-τa earthquakes inside oceanic plates. Extant transform boundaries may be misaligned with current plate motion. To accommodate current plate motion, the pre-existing plate boundaries would have to be subjected to large horizontal transform push forces. A notable example of this is the triple junction near which the second large aftershock of the 1992 April Cape Mendocino, California, sequence occurred. Alternatively, subduction zone resistance may be enhanced by the collision of a buoyant lithosphere, a process that also markedly increases the horizontal stress. A notable example of this is the Aleutian Trench near which large events occurred in the Gulf of Alaska in late 1987 and the 1998 March Balleny Sea M= 8.2 earthquake within the Antarctic Plate.

Extension and transtension in the plate boundary zone of the northeastern Caribbean

DOE Office of Scientific and Technical Information (OSTI.GOV)

Speed, R.C.; Larue, D.K.

1991-03-01

The authors propose that the Caribbean (Ca)-North American (NA) plate boundary zone (pbz) from the Puerto Rico Trench to the Venezuelan Basin from Mona Canyon east has been in left-transtension over the last 15-20 ma. A boundary-normal component of extension occurs throughout the pbz and is a principal cause of the Puerto Rico Trench. Such extension is due to WNW velocity of NA-Ca and the northward pullaway of NA from its S-dipping slab, which is below Puerto Rico. Strike slip motion may be taken up among terranes in the pbz by rigid CCW rotation and by oblique slip at theirmore » boundaries. Rotation of the largest terrane, Puerto Rico-Virgin Islands (PRVI), has caused such major structures as the Muertos thrust and Anegada Passage. The model implies NA-Ca velocity estimated from Cayman transforms is more accurate than that from slip vectors from seisms in the NA slab.« less

Quadratic Convective Flow of a Micropolar Fluid along an Inclined Plate in a Non-Darcy Porous Medium with Convective Boundary Condition

NASA Astrophysics Data System (ADS)

RamReddy, Ch.; Naveen, P.; Srinivasacharya, D.

2017-06-01

The objective of the present study is to investigate the effect of nonlinear variation of density with temperature and concentration on the mixed convective flow of a micropolar fluid over an inclined flat plate in a non-Darcy porous medium in the presence of the convective boundary condition. In order to analyze all the essential features, the governing non-dimensional partial differential equations are transformed into a system of ordinary differential equations using a local non-similarity procedure and then the resulting boundary value problem is solved using a successive linearisation method (SLM). By insisting the comparison between vertical, horizontal and inclined plates, the physical quantities of the flow and its characteristics are exhibited graphically and quantitatively with various parameters. An increase in the micropolar parameter and non-Darcy parameter tend to increase the skin friction and the reverse change is observed in wall couple stress, mass and heat transfer rates. The influence of the nonlinear concentration parameter is more prominent on all the physical characteristics of the present model, compared with that of nonlinear temperature parameter.

Structural analysis and martensitic transformation in equiatomic HfPd alloy

NASA Astrophysics Data System (ADS)

Hisada, S.; Matsuda, M.; Takashima, K.; Yamabe-Mitarai, Y.

2018-02-01

We investigated the crystal structure and the martensitic transformation in equiatomic HfPd alloy. The analysis of the crystal structure by electron diffraction and Rietveld refinement using X-ray diffraction data indicates that the space group of the martensitic phase is Cmcm, and the lattice parameters are a = 0.329 nm, b = 1.021 nm, and c = 0.438 nm. Martensitic variants are composed of the plate-like morphology of several hundred nm, and the boundaries between the variants have (021)Cmcm twin relations. This (021)Cmcm twin boundary seems to be sharp without ledge and steps. Differential scanning calorimetry measurement indicates that each martensitic transformation temperature is determined to be Ms = 819 K, Mf = 794 K, As = 928 K, and Af = 954 K. Based on the dimension change using a thermo-mechanical analyzer, the expansion and shrinkage of the sample occurred with the forward and reverse martensitic transformation, respectively.

Lithospheric strength in the active boundary between the Pacific Plate and Baja California microplate constrained from lower crustal and upper mantle xenoliths

NASA Astrophysics Data System (ADS)

Chatzaras, Vasileios; van der Werf, Thomas; Kriegsman, Leo M.; Kronenberg, Andreas; Tikoff, Basil; Drury, Martyn R.

2017-04-01

The lower crust is the most poorly understood of the lithospheric layers in terms of its rheology, particularly at active plate boundaries. We studied naturally deformed lower crustal xenoliths within an active plate boundary, in order to link their microstructures and rheological parameters to the well-defined active tectonic context. The Baja California shear zone (BCSZ), located at the western boundary of the Baja California microplate, comprises the active boundary accommodating the relative motion between the Pacific plate and Baja California microplate. The basalts of the Holocene San Quintin volcanic field carry lower crustal and upper mantle xenoliths, which sample the Baja California microplate lithosphere in the vicinity of the BCSZ. The lower crustal xenoliths range from undeformed gabbros to granoblastic two-pyroxene granulites. Two-pyroxene geothermometry shows that the granulites equilibrated at temperatures of 690-920 oC. Phase equilibria (P-T pseudosections using Perple_X) indicate that symplectites with intergrown pyroxenes, plagioclase, olivine and spinel formed at 3.6-5.4 kbar, following decompression from pressures exceeding 6 kbar. FTIR spectroscopy shows that the water content of plagioclase varies among the analyzed xenoliths; plagioclase is relatively dry in two xenoliths while one xenolith contains hydrated plagioclase grains. Microstructural observations and analysis of the crystallographic texture provide evidence for deformation of plagioclase by a combination of dislocation creep and grain boundary sliding. To constrain the strength of the lower crust and upper mantle near the BCSZ we estimated the differential stress using plagioclase and olivine grain size paleopiezomtery, respectively. Differential stress estimates for plagioclase range from 10 to 32 MPa and for olivine are 30 MPa. Thus the active microplate boundary records elevated crustal temperatures, heterogeneous levels of hydration, and low strength in both the lower crust and upper mantle. To further investigate the relative strength of the two lithospheric layers, we calculated the strain rate of plagioclase in granulites and the strain rate of olivine in lherzolites using experimental flow laws. These flow laws predict that plagioclase deforms at higher strain rates than olivine. Our data provide constraints on the viscosity structure of active transform plate boundaries and insights on how rheological processes in the lithosphere may change during plate boundary evolution.

The influence of finite cavities on the sound insulation of double-plate structures.

PubMed

Brunskog, Jonas

2005-06-01

Lightweight walls are often designed as frameworks of studs with plates on each side--a double-plate structure. The studs constitute boundaries for the cavities, thereby both affecting the sound transmission directly by short-circuiting the plates, and indirectly by disturbing the sound field between the plates. The paper presents a deterministic prediction model for airborne sound insulation including both effects of the studs. A spatial transform technique is used, taking advantage of the periodicity. The acoustic field inside the cavities is expanded by means of cosine-series. The transmission coefficient (angle-dependent and diffuse) and transmission loss are studied. Numerical examples are presented and comparisons with measurement are performed. The result indicates that a reasonably good agreement between theory and measurement can be achieved.

Triple Junction Reorganizations: A Mechanism for the Initiation of the Great Pacific Fractures Zones

NASA Astrophysics Data System (ADS)

Pockalny, R. A.; Larson, R. L.; Grindlay, N. R.

2001-12-01

There are two general explanations for the initiation of oceanic transform faults that eventually evolve into fracture zones: transforms inherited from continental break-up and transforms acquired in response to a change in plate motions. These models are sufficient to explain the fracture zones in oceans formed by continental break-up. However, neither model accounts for the initiation of the large-offset, great Pacific fracture zones that characterized the Pacific-Farallon plate boundary prior to 25 Ma. Primarily, these models are unable to explain why the initial age of these fracture zones becomes progressively younger from the Mendocino fracture zone (\\~{ } 160 Ma) southward down to the Resolution FZ (\\~{ }84 Ma). We propose a new transform initiation mechanism for the great Pacific fracture zones, which is intimately tied to tectonic processes at triple junctions and directly related to the growth of the Pacific Plate. Recently acquired multibeam bathymetry and marine geophysics data collected along Pandora's Escarpment in the southwestern Pacific have identified the escarpment as the trace of the Pacific-Farallon-Phoenix triple junction on the Pacific Plate. Regional changes in the trend of the triple junction trace between 84-121 Ma roughly coincide with the initiation of the Marquesas, Austral and Resolution fracture zones. Bathymetry and backscatter data from the projected intersections of these fracture zones with the triple junction trace identify several anomalous structures that suggest tectonic reorganizations of the triple junction. We believe this reorganization created the initial transform fault(s) that ultimately became the large-offset, great Pacific fracture zones. Several possible mechanisms for initiating the transform faults are explored including microplate formation, ridge-tip propagation, and spontaneous transform fault formation.

Geodynamical simulation of the RRF triple junction

NASA Astrophysics Data System (ADS)

Wang, Z.; Wei, D.; Liu, M.; Shi, Y.; Wang, S.

2017-12-01

Triple junction is the point at which three plate boundaries meet. Three plates at the triple junction form a complex geological tectonics, which is a natural laboratory to study the interactions of plates. This work studies a special triple junction, the oceanic transform fault intersects the collinear ridges with different-spreading rates, which is free of influence of ridge-transform faults and nearby hotspots. First, we build 3-D numerical model of this triple junction used to calculate the stead-state velocity and temperature fields resulting from advective and conductive heat transfer. We discuss in detail the influence of the velocity and temperature fields of the triple junction from viscosity, spreading rate of the ridge. The two sides of the oceanic transform fault are different sensitivities to the two factors. And, the influence of the velocity mainly occurs within 200km of the triple junction. Then, we modify the model by adding a ridge-transform fault to above model and directly use the velocity structure of the Macquarie triple junction. The simulation results show that the temperature at both sides of the oceanic transform fault decreases gradually from the triple junction, but the temperature difference between the two sides is a constant about 200°. And, there is little effect of upwelling velocity away from the triple junction 100km. The model results are compared with observational data. The heat flux and thermal topography along the oceanic transform fault of this model are consistent with the observed data of the Macquarie triple junction. The earthquakes are strike slip distributed along the oceanic transform fault. Their depths are also consistent with the zone of maximum shear stress. This work can help us to understand the interactions of plates of triple junctions and help us with the foundation for the future study of triple junctions.

Jeffrey fluid effect on free convective over a vertically inclined plate with magnetic field: A numerical approach

NASA Astrophysics Data System (ADS)

Rao, J. Anand; Raju, R. Srinivasa; Bucchaiah, C. D.

2018-05-01

In this work, the effect of magnetohydrodynamic natural or free convective of an incompressible, viscous and electrically conducting non-newtonian Jeffrey fluid over a semi-infinite vertically inclined permeable moving plate embedded in a porous medium in the presence of heat absorption, heat and mass transfer. By using non-dimensional quantities, the fundamental governing non-linear partial differential equations are transformed into linear partial differential equations and these equations together with associated boundary conditions are solved numerically by using versatile, extensively validated, variational finite element method. The sway of important key parameters on hydrodynamic, thermal and concentration boundary layers are examined in detail and the results are shown graphically. Finally the results are compared with the works published previously and found to be excellent agreement.

Evolution of the Gorda Escarpment, San Andreas fault and Mendocino triple junction from multichannel seismic data collected across the northern Vizcaino block, offshore northern California

USGS Publications Warehouse

Godfrey, N.J.; Meltzer, A.S.; Klemperer, S.L.; Trehu, A.M.; Leitner, B.; Clarke, S.H.; Ondrus, A.

1998-01-01

The Gorda Escarpment is a north facing scarp immediately south of the Mendocino transform fault (the Gorda/Juan de Fuca-Pacific plate boundary) between 126??W and the Mendocino triple junction. It elevates the seafloor at the northern edge of the Vizcaino block, part of the Pacific plate, ??? 1.5 km above the seafloor of the Gorda/Juan de Fuca plate to the north. Stratigraphy interpreted from multichannel seismic data across and close to the Gorda Escarpment suggests that the escarpment is a relatively recent pop-up feature caused by north-south compression across the plate boundary. Close to 126??W. the Vizcaino block acoustic basement shallows and is overlain by sediments that thin north toward the Gorda Escarpment. These sediments are tilted south and truncated at the seafloor. By contrast, in a localized region at the eastern end of the Gorda Escarpment, close to the Mendocino triple junction, the top of acoustic basement dips north and is overlain by a 2-km-thick wedge of pre-11 Ma sedimentary rocks that thickens north, toward the Gorda Escarpment. This wedge of sediments is restricted to the northeast corner of the Vizcaino block. Unless the wedge of sediments was a preexisting feature on the Vizcaino block before it was transferred from the North American to the Pacific plate, the strong spatial correlation between the sedimentary wedge and the triple junction suggests the entire Vizcaino block, with the San Andreas at its eastern boundary, has been part of the Pacific plate since significantly before 11 Ma.

Present-day plate motions

NASA Technical Reports Server (NTRS)

Minster, J. B.; Jordan, T. H.

1977-01-01

A data set comprising 110 spreading rates, 78 transform fault azimuths and 142 earthquake slip vectors was inverted to yield a new instantaneous plate motion model, designated RM2. The mean averaging interval for the relative motion data was reduced to less than 3 My. A detailed comparison of RM2 with angular velocity vectors which best fit the data along individual plate boundaries indicates that RM2 performs close to optimally in most regions, with several notable exceptions. On the other hand, a previous estimate (RM1) failed to satisfy an extensive set of new data collected in the South Atlantic Ocean. It is shown that RM1 incorrectly predicts the plate kinematics in the South Atlantic because the presently available data are inconsistent with the plate geometry assumed in deriving RM1. It is demonstrated that this inconsistency can be remedied by postulating the existence of internal deformation with the Indian plate, although alternate explanations are possible.

Reaction-induced rheological weakening enables oceanic plate subduction.

PubMed

Hirauchi, Ken-Ichi; Fukushima, Kumi; Kido, Masanori; Muto, Jun; Okamoto, Atsushi

2016-08-26

Earth is the only terrestrial planet in our solar system where an oceanic plate subducts beneath an overriding plate. Although the initiation of plate subduction requires extremely weak boundaries between strong plates, the way in which oceanic mantle rheologically weakens remains unknown. Here we show that shear-enhanced hydration reactions contribute to the generation and maintenance of weak mantle shear zones at mid-lithospheric depths. High-pressure friction experiments on peridotite gouge reveal that in the presence of hydrothermal water, increasing strain and reactions lead to an order-of-magnitude reduction in strength. The rate of deformation is controlled by pressure-solution-accommodated frictional sliding on weak hydrous phyllosilicate (talc), providing a mechanism for the 'cutoff' of the high peak strength at the brittle-plastic transition. Our findings suggest that infiltration of seawater into transform faults with long lengths and low slip rates is an important controlling factor on the initiation of plate tectonics on terrestrial planets.

Group solution for unsteady free-convection flow from a vertical moving plate subjected to constant heat flux

NASA Astrophysics Data System (ADS)

Kassem, M.

2006-03-01

The problem of heat and mass transfer in an unsteady free-convection flow over a continuous moving vertical sheet in an ambient fluid is investigated for constant heat flux using the group theoretical method. The nonlinear coupled partial differential equation governing the flow and the boundary conditions are transformed to a system of ordinary differential equations with appropriate boundary conditions. The obtained ordinary differential equations are solved numerically using the shooting method. The effect of Prandlt number on the velocity and temperature of the boundary-layer is plotted in curves. A comparison with previous work is presented.

Is There Really A North American Plate?

NASA Astrophysics Data System (ADS)

Krill, A.

2011-12-01

Lithospheric plates are typically identified from earthquake epicenters and evidence such as GPS movements. But no evidence indicates a plate boundary between the North American and South American Plates. Some plate maps show them separated by a transform boundary, but it is only a fracture zone. Other maps show an "undefined plate boundary" or put no boundary between these two plates (check Google images). Early plate maps showed a single large American Plate, quite narrow east of the Caribbean Plate (Le Pichon 1968, Morgan 1968). The North and South American Plates became established by the leading textbook Earth (Press & Siever 1974). On their map, from a Scientific American article by John Dewey (1972), these new plates were separated by an "uncertain plate boundary." The reasons for postulating a North American Plate were probably more psychological than geological. Each of the other continents of the world had its own plate, and North American geologists naturally wanted theirs. Similarly, European geographers used to view Europe as its own continent. A single large plate should again be hypothesized. But the term American Plate would now be ambiguous ("Which plate, North or South?") Perhaps future textbook authors could call it the "Two-American Plate." Textbook authors ultimately decide such global-tectonic matters. I became aware of textbook authors' opinions and influence from my research into the history of Alfred Wegener's continental drift (see Fixists vs. Mobilists by Krill 2011). Leading textbook author Charles Schuchert realized that continental drift would abolish his cherished paleogeographic models of large east-west continents (Eria, Gondwana) and small oceans (Poseiden, Nereis). He and his junior coauthors conspired to keep drift evidence out of their textbooks, from the 1934-editions until the 1969-editions (Physical Geology by Longwell et al. 1969, Historical Geology by Dunbar & Waage 1969). Their textbooks ruled in America. Textbooks elsewhere, such as S.J. Shand (1933), E.B. Bailey (1939), and Arthur Holmes (1944), presented continental drift as a working hypothesis that could elegantly solve important geological problems. Americans were preconditioned to dislike continental drift theory, ever since James Dwight Dana taught in his Manual of Geology (1863...1895) that North America was the type continent of the world, and that it had stood alone since earliest time. Such beliefs sometimes trump geologic evidence. As noted by Stephen Jay Gould (1999) Sigmund Freud had much insight into the psychology of scientific revolutions: they involve a scientific development that shows humans to have lesser status than previously perceived. In the Copernican revolution (geocentrism vs. heliocentrism) humans no longer inhabited the center of the universe. In the Darwinian revolution (creationism vs. evolutionism) humans were no longer uniquely created. In the Wegenerian revolution (fixism vs. mobilism) North America was no longer uniquely created; it was just other fragment from Pangaea. North American geologists were pleased when Press & Siever gave them their own lithospheric plate. Being a global-tectonic killjoy, I would like to take away that small consolation as well. Or at least pose the question: Is there really a North American Plate?

Formation of an Oceanic Transform Fault During Continental Rifting

NASA Astrophysics Data System (ADS)

Illsley-Kemp, F.; Bull, J. M.; Keir, D.; Gerya, T.; Pagli, C.; Gernon, T.; Ayele, A.; Goitom, B.; Hammond, J. O. S.; Kendall, J. M.

2017-12-01

We integrate evidence from surface faults, geodetic measurements, local seismicity, and 3D numerical modelling of the subaerial Afar continental rift to show that an oceanic-style transform fault is forming during the final stages of continental breakup. Transform faults are a fundamental tenet of plate tectonics, connecting offset extensional segments of mid-ocean ridges, and are vital in palaeotectonic reconstructions of passive margins. The current consensus is that transform faults initiate after the onset of seafloor spreading. However this inference has been difficult to test given the lack of observations of transform fault formation. We present the first direct observation of transform fault initiation, and shed unprecedented light on their formation mechanisms. We demonstrate that they originate during late-stage continental rifting, earlier in the rifting cycle than previously thought. Our results have important implications for reconstructing the breakup history of the continents. Palaeotectonic reconstructions that use transform fault terminations as an indicator of the continent-ocean boundary may have placed the continent-ocean boundary landward of its true location. This will have led to an overestimation of the age of continental breakup of between 8-18 Myr. Our results therefore have significant implications for studies that rely on accurate dating of continental breakup events.

Similarity solutions for unsteady free-convection flow from a continuous moving vertical surface

NASA Astrophysics Data System (ADS)

Abd-El-Malek, Mina B.; Kassem, Magda M.; Mekky, Mohammad L.

2004-03-01

The transformation group theoretic approach is applied to present an analysis of the problem of unsteady free convection flow over a continuous moving vertical sheet in an ambient fluid. The thermal boundary layer induced within a vertical semi-infinite layer of Boussinseq fluid by a constant heated bounding plate. The application of two-parameter groups reduces the number of independent variables by two, and consequently the system of governing partial differential equations with the boundary conditions reduces to a system of ordinary differential equations with appropriate boundary conditions. The obtained ordinary differential equations are solved analytically for the temperature and numerically for the velocity using the shooting method. Effect of Prandtl number on the thermal boundary-layer and velocity boundary-layer are studied and plotted in curves.

Baseline-Subtraction-Free (BSF) Damage-Scattered Wave Extraction for Stiffened Isotropic Plates

NASA Technical Reports Server (NTRS)

He, Jiaze; Leser, Patrick E.; Leser, William P.

2017-01-01

Lamb waves enable long distance inspection of structures for health monitoring purposes. However, this capability is diminished when applied to complex structures where damage-scattered waves are often buried by scattering from various structural components or boundaries in the time-space domain. Here, a baseline-subtraction-free (BSF) inspection concept based on the Radon transform (RT) is proposed to identify and separate these scattered waves from those scattered by damage. The received time-space domain signals can be converted into the Radon domain, in which the scattered signals from structural components are suppressed into relatively small regions such that damage-scattered signals can be identified and extracted. In this study, a piezoelectric wafer and a linear scan via laser Doppler vibrometer (LDV) were used to excite and acquire the Lamb-wave signals in an aluminum plate with multiple stiffeners. Linear and inverse linear Radon transform algorithms were applied to the direct measurements. The results demonstrate the effectiveness of the Radon transform as a reliable extraction tool for damage-scattered waves in a stiffened aluminum plate and also suggest the possibility of generalizing this technique for application to a wide variety of complex, large-area structures.

Stress Rotation Across the Cascadia Megathrust Requires a Weak Subduction Plate Boundary at Seismogenic Depths

NASA Astrophysics Data System (ADS)

Li, D.; McGuire, J. J.; Liu, Y.; Hardebeck, J.

2017-12-01

Despite the great effort spent investigating subduction zones, there are very limited constraints on the stress state on the plate boundary fault at the depth of megathrust earthquakes. Here we utilize a focal mechanism dataset, including observations from the Cascadia Initiative ocean bottom seismograph experiment, to constrain the stress orientations. We present a high-resolution inversion for the principal stress orientations both above and below the thrust interface in the southern Cascadia Subduction zone. The distinctive stresses above and below the interface require a significant stress rotation within 10 km of the plate boundary. To quantify the implications of this rotation for the strength of the plate boundary, we designed an inversion that solves for the absolute stress tensors in a three-layer model subject to assumptions about the strength of the subducting mantle. Our approach utilizes the continuous traction boundary conditions between layers as well as the observed principal stress orientations and the relative magnitude ratios in the crust and subducting mantle as constraints. Our results indicate that the shear stress on the plate boundary fault is likely no more than about 50 MPa at 20 km depth. Regardless of the assumed upper mantle strength, we infer a relatively weak megathrust fault with an effective friction coefficient of 0 to 0.2 at seismogenic depths. The central question for the Cascadia subduction zone is why it remains seismically quiet despite the 300+ years of stress accumulation since the last megathrust earthquake. For example, we also document that no thrust earthquakes were recorded by the 2-year Cascadia Initiative expedition down to magnitude 2.0, despite the stress perturbation generated by a nearby Mw5.7 earthquake on Jan 28th, 2015, on the Mendocino Transform fault. To help answer that question, we provide a new and fundamental constraint on the absolute level of stress accumulation to date in the current seismic cycle. Our technique for evaluating the absolute level of stress in subduction zones can be applied at a number of regions around the globe as datasets improve.

Barriers to the Migration of Interphase Boundaries.

DTIC Science & Technology

1984-01-06

and G.W. Lorimer, "Considerations on a Martensitic Mechanism for the F.C.C.->B.C.C. Transformation in a Cu-0.33 W/O Cr Alloy ," Scripta Met., 9, 533...Plate-Shaped Precipitates in Aluminum- Copper and Aluminum-Gold Alloys ’ by Y.H. Chen and R.D. Doherty," Scripta Met., 11, 731 (1977). 19. H.I. Aaronson...34A Re-examination of the Thermodynamics of the Proeutectoid Ferrite Transformation in Fe-C Alloys ," Met. V" Trans., 9A, 999 (1978). 24. J.M. Rigsbee

The frequency-domain method of calculation for the pulsed electromagnetic field in a conductive ferromagnetic plate

NASA Astrophysics Data System (ADS)

Nosov, G. V.; Kuleshova, E. O.; Lefebvre, S.; Plyusnin, A. A.; Tokmashev, D. M.

2017-02-01

The technique for parameters determination of magnetic skin effect on ferromagnetic plate at a specified pulse of magnetic field intensity on the plate surface is proposed. It is based on a frequency-domain method and could be applied for a pulsing transformer, a dynamoelectric pulse generator and a commutating inductor that contains an imbricated core. Due to this technique, such plate parameters as specific heat loss energy, the average power of this energy and the plate temperature raise, the magnetic flux attenuation factor and the plate q-factor could be calculated. These parameters depend on the steel type, the amplitude, the rms value, the duration and the form of the magnetic field intensity impulse on the plate surface. The plate thickness is defined by the value of the flux attenuation factor and the plate q-factor that should be maximal. The reliability of the proposed technique is built on a common frequency-domain usage applicable for pulse transient study under zero boundary conditions of the electric circuit and the conformity of obtained results with the sinusoidal steady-state mode.

Analysis of unsteady compressible viscous layers

NASA Technical Reports Server (NTRS)

Power, G. D.; Verdon, J. M.; Kousen, K. A.

1990-01-01

The development of an analysis to predict the unsteady compressible flows in blade boundary layers and wakes is presented. The equations that govern the flows in these regions are transformed using an unsteady turbulent generalization of the Levy-Lees transformation. The transformed equations are solved using a finite difference technique in which the solution proceeds by marching in time and in the streamwise direction. Both laminar and turbulent flows are studied, the latter using algebraic turbulence and transition models. Laminar solutions for a flat plate are shown to approach classical asymptotic results for both high and low frequency unsteady motions. Turbulent flat-plate results are in qualitative agreement with previous predictions and measurements. Finally, the numerical technique is also applied to the stator and rotor of a low-speed turbine stage to determine unsteady effects on surface heating. The results compare reasonably well with measured heat transfer data and indicate that nonlinear effects have minimal impact on the mean and unsteady components of the flow.

Fluid flow and heat transfer of carbon nanotubes along a flat plate with Navier slip boundary

NASA Astrophysics Data System (ADS)

Khan, W. A.; Khan, Z. H.; Rahi, M.

2014-06-01

Homogeneous flow model is used to study the flow and heat transfer of carbon nanotubes (CNTs) along a flat plate subjected to Navier slip and uniform heat flux boundary conditions. This is the first paper on the flow and heat transfer of CNTs along a flat plate. Two types of CNTs, namely, single- and multi-wall CNTs are used with water, kerosene or engine oil as base fluids. The empirical correlations are used for the thermophysical properties of CNTs in terms of the solid volume fraction of CNTs. For the effective thermal conductivity of CNTs, Xue (Phys B Condens Matter 368:302-307, 2005) model has been used and the results are compared with the existing theoretical models. The governing partial differential equations and boundary conditions are converted into a set of nonlinear ordinary differential equations using suitable similarity transformations. These equations are solved numerically using a very efficient finite difference method with shooting scheme. The effects of the governing parameters on the dimensionless velocity, temperature, skin friction, and Nusselt numbers are investigated and presented in graphical and tabular forms. The numerical results of skin friction and Nusselt numbers are compared with the available data for special cases and are found in good agreement.

Using shape contexts method for registration of contra lateral breasts in thermal images.

PubMed

Etehadtavakol, Mahnaz; Ng, Eddie Yin-Kwee; Gheissari, Niloofar

2014-12-10

To achieve symmetric boundaries for left and right breasts boundaries in thermal images by registration. The proposed method for registration consists of two steps. In the first step, shape context, an approach as presented by Belongie and Malik was applied for registration of two breast boundaries. The shape context is an approach to measure shape similarity. Two sets of finite sample points from shape contours of two breasts are then presented. Consequently, the correspondences between the two shapes are found. By finding correspondences, the sample point which has the most similar shape context is obtained. In this study, a line up transformation which maps one shape onto the other has been estimated in order to complete shape. The used of a thin plate spline permitted good estimation of a plane transformation which has capability to map unselective points from one shape onto the other. The obtained aligning transformation of boundaries points has been applied successfully to map the two breasts interior points. Some of advantages for using shape context method in this work are as follows: (1) no special land marks or key points are needed; (2) it is tolerant to all common shape deformation; and (3) although it is uncomplicated and straightforward to use, it gives remarkably powerful descriptor for point sets significantly upgrading point set registration. Results are very promising. The proposed algorithm was implemented for 32 cases. Boundary registration is done perfectly for 28 cases. We used shape contexts method that is simple and easy to implement to achieve symmetric boundaries for left and right breasts boundaries in thermal images.

Numerical simulation of present day tectonic stress across the Indian subcontinent

NASA Astrophysics Data System (ADS)

Yadav, R.; Tiwari, V. M.

2018-04-01

In situ measurements of maximum horizontal stress (S Hmax) in the Indian subcontinent are limited and do not present regional trends of intraplate stress orientation. The observed orientations of S Hmax vary considerably and often differ from the plate velocity direction. We have simulated orientation and magnitude of S Hmax through finite element modeling incorporating heterogeneities in elastic property of the Indian continent and plain stress approximation to understand the variability of S Hmax. Four different scenarios are tested in simulation: (1) homogeneous plate with fixed plate boundary (2) homogeneous plate with boundary forces (3) heterogeneous plate with fixed boundary (4) heterogeneous plate with boundary forces. The estimated orientation and magnitude of S Hmax with a heterogeneous plate with boundary forces in the Himalayan region and an eastern plate boundary comprising the Indo-Burmese arc and Andaman subduction zone are consistent with measured maximum horizontal stress. This study suggests that plate boundary force varies along the northern Indian plate margin and also provides a constraint on the intraplate stress field in the Indian subcontinent.

Reaction-induced rheological weakening enables oceanic plate subduction

PubMed Central

Hirauchi, Ken-ichi; Fukushima, Kumi; Kido, Masanori; Muto, Jun; Okamoto, Atsushi

2016-01-01

Earth is the only terrestrial planet in our solar system where an oceanic plate subducts beneath an overriding plate. Although the initiation of plate subduction requires extremely weak boundaries between strong plates, the way in which oceanic mantle rheologically weakens remains unknown. Here we show that shear-enhanced hydration reactions contribute to the generation and maintenance of weak mantle shear zones at mid-lithospheric depths. High-pressure friction experiments on peridotite gouge reveal that in the presence of hydrothermal water, increasing strain and reactions lead to an order-of-magnitude reduction in strength. The rate of deformation is controlled by pressure-solution-accommodated frictional sliding on weak hydrous phyllosilicate (talc), providing a mechanism for the ‘cutoff' of the high peak strength at the brittle-plastic transition. Our findings suggest that infiltration of seawater into transform faults with long lengths and low slip rates is an important controlling factor on the initiation of plate tectonics on terrestrial planets. PMID:27562366

Spatial Analysis of Gravity Data in the California, Nevada, and Utah (US)

NASA Astrophysics Data System (ADS)

Ferani, NA; Hartantyo, E.; Niasari, SW

2018-04-01

The geological condition of western North America is very complex because of the encounter of three major plates namely North America, Juan de Fuca, and Pacific Plate. The process of Juan de Fuca subduction and Pacific transform against North America plate created many mountains and produced Great Basin that we can see extending across California, Nevada, and Utah. The varied natural condition causes the varied value of gravity anomaly distribution. Using Topex free-air anomaly analyzed with second vertical derivative (SVD), we can analyze the fracture structures that occur in the Great Basin. The results show that the maximal SVD anomaly value is higher than the minimal SVD anomaly value at the western and eastern border of Great Basin. This explains that the two of Great Basin border are normal faults with trend direction NW-SE in the western boundary and NE-SW trending in the eastern boundary. This research result corresponds with the high seismicity data along the fault. Through this research, we can know that topex free-air anomaly data can be used to determine the type and trend of fault on a regional scale.

Mixed convection boundary layer flow over a moving vertical flat plate in an external fluid flow with viscous dissipation effect.

PubMed

Bachok, Norfifah; Ishak, Anuar; Pop, Ioan

2013-01-01

The steady boundary layer flow of a viscous and incompressible fluid over a moving vertical flat plate in an external moving fluid with viscous dissipation is theoretically investigated. Using appropriate similarity variables, the governing system of partial differential equations is transformed into a system of ordinary (similarity) differential equations, which is then solved numerically using a Maple software. Results for the skin friction or shear stress coefficient, local Nusselt number, velocity and temperature profiles are presented for different values of the governing parameters. It is found that the set of the similarity equations has unique solutions, dual solutions or no solutions, depending on the values of the mixed convection parameter, the velocity ratio parameter and the Eckert number. The Eckert number significantly affects the surface shear stress as well as the heat transfer rate at the surface.

Elastic interactions of a fatigue crack with a micro-defect by the mixed boundary integral equation method

NASA Technical Reports Server (NTRS)

Lua, Yuan J.; Liu, Wing K.; Belytschko, Ted

1993-01-01

In this paper, the mixed boundary integral equation method is developed to study the elastic interactions of a fatigue crack and a micro-defect such as a void, a rigid inclusion or a transformation inclusion. The method of pseudo-tractions is employed to study the effect of a transformation inclusion. An enriched element which incorporates the mixed-mode stress intensity factors is applied to characterize the singularity at a moving crack tip. In order to evaluate the accuracy of the numerical procedure, the analysis of a crack emanating from a circular hole in a finite plate is performed and the results are compared with the available numerical solution. The effects of various micro-defects on the crack path and fatigue life are investigated. The results agree with the experimental observations.

Tear geometry at active STEPs: an analogue model approach

NASA Astrophysics Data System (ADS)

Broerse, Taco; Sokoutis, Dimitrios; Willingshofer, Ernst; Govers, Rob

2017-04-01

At the lateral end of a subduction zone, tearing of lithosphere is the result of subduction of oceanic lithosphere while adjacent buoyant continental lithosphere stays at the surface. The location of lithospheric tearing is called a Subduction-Transform-Edge-Propagator (STEP), which continuously extends the plate boundary between overriding plate and continental lithosphere. One of our areas of interest is the southern Caribbean where Atlantic lithosphere subducts below the Caribbean plate. Mantle tomography suggests a clear southern edge of the Lesser Antilles slab, which makes the boundary between the Caribbean and South America a clear STEP candidate. At the surface, the San Sebastián/El Pilar fault zone forms the plate boundary between the Caribbean and South America and the active STEP is located near Trinidad. For the deeper part of the damage/shear zone, some information is available from a recent 3D gravity study: significant lateral variability in densities of the lithospheric mantle to the south of the STEP fault zone. The low-density zone may result from higher sub-crustal temperatures, such as would arise from an asthenospheric window resulting from detachment. Interpreted in this way, the mantle part of the damage zone may be 200-250 km wide. So, while the location of the plate boundary at the surface is relatively well resolved, little is known about the deeper continuation of the active STEP in the mantle lithosphere. We study the evolution of the tearing process at a STEP using analogue models. In our models we use silicone putty (lithosphere) and glucose (asthenosphere). Solely gravitational forces resulting from density differences between oceanic lithosphere and asthenosphere drive our model. Lithospheric tearing commences after subduction has initiated. The geometry of the tear varies with the rheology of the lithosphere and asthenosphere, particularly Newtonian versus power-law. We investigate the dependence on model parameters of the width of the tearing zone and the depth at which tearing occurs.

Control of boundary layer transition location and plate vibration in the presence of an external acoustic field

NASA Technical Reports Server (NTRS)

Maestrello, L.; Grosveld, F. W.

1991-01-01

The experiment is aimed at controlling the boundary layer transition location and the plate vibration when excited by a flow and an upstream sound source. Sound has been found to affect the flow at the leading edge and the response of a flexible plate in a boundary layer. Because the sound induces early transition, the panel vibration is acoustically coupled to the turbulent boundary layer by the upstream radiation. Localized surface heating at the leading edge delays the transition location downstream of the flexible plate. The response of the plate excited by a turbulent boundary layer (without sound) shows that the plate is forced to vibrate at different frequencies and with different amplitudes as the flow velocity changes indicating that the plate is driven by the convective waves of the boundary layer. The acoustic disturbances induced by the upstream sound dominate the response of the plate when the boundary layer is either turbulent or laminar. Active vibration control was used to reduce the sound induced displacement amplitude of the plate.

Kinematics of the Southwestern Caribbean from New Geodetic Observations

NASA Astrophysics Data System (ADS)

Ruiz, G.; La Femina, P. C.; Tapia, A.; Camacho, E.; Chichaco, E.; Mora-Paez, H.; Geirsson, H.

2014-12-01

The interaction of the Caribbean, Cocos, Nazca, and South American plates has resulted in a complex plate boundary zone and the formation of second order tectonic blocks (e.g., the North Andean, Choco and Central America Fore Arc blocks). The Panama Region [PR], which is bounded by these plates and blocks, has been interpreted and modeled as a single tectonic block or deformed plate boundary. Previous research has defined the main boundaries: 1) The Caribbean plate subducts beneath the isthmus along the North Panama Deformed Belt, 2) The Nazca plate converges at very high obliquity with the PR and motion is assumed along a left lateral transform fault and the South Panama Deformed Belt, 3) The collision of PR with NW South America (i.e., the N. Andean and Choco blocks) has resulted in the Eastern Panama Deformed Belt, and 4) collision of the Cocos Ridge in the west is accommodated by crustal shortening, Central American Fore Arc translation and deformation across the Central Costa Rican Deformed Belt. In addition, there are several models that suggest internal deformation of this region by cross-isthmus strike-slip faults. Recent GPS observations for the PR indicates movement to the northeast relative to a stable Caribbean plate at rates of 6.9±4.0 - 7.8±4.8 mm a-1 from southern Costa Rica to eastern Panama, respectively (Kobayashi et al., 2014 and references therein). However, the GPS network did not have enough spatial density to estimate elastic strain accumulation across these faults. Recent installation and expansion of geodetic networks in southwestern Caribbean (i.e., Costa Rica, Panama, and Colombia) combined with geological and geophysical observations provide a new input to investigate crustal deformation processes in this complex tectonic setting, specifically related to the PR. We use new and existing GPS data to calculate a new velocity field for the region and to investigate the kinematics of the PR, including elastic strain accumulation on the major plate boundaries. Expanding our GPS observations within these proposed small blocks could allow us to solve for Euler vectors and calculate their rotation, strain accumulation and slip rates on the major fault systems. Our results combined with the local seismicity could help authorities to reduce uncertainties in seismic risk evaluations.

A bottom-driven mechanism for distributed faulting in the Gulf of California rift

NASA Astrophysics Data System (ADS)

Persaud, Patricia; Tan, Eh; Contreras, Juan; Lavier, Luc

2017-11-01

Observations of active faulting in the continent-ocean transition of the Northern Gulf of California show multiple oblique-slip faults distributed in a 200 × 70 km2 area developed some time after a westward relocation of the plate boundary at 2 Ma. In contrast, north and south of this broad pull-apart structure, major transform faults accommodate Pacific-North America plate motion. Here we propose that the mechanism for distributed brittle deformation results from the boundary conditions present in the Northern Gulf, where basal shear is distributed between the Cerro Prieto strike-slip fault (southernmost fault of the San Andreas fault system) and the Ballenas Transform Fault. We hypothesize that in oblique-extensional settings whether deformation is partitioned in a few dip-slip and strike-slip faults, or in numerous oblique-slip faults may depend on (1) bottom-driven, distributed extension and shear deformation of the lower crust or upper mantle, and (2) the rift obliquity. To test this idea, we explore the effects of bottom-driven shear on the deformation of a brittle elastic-plastic layer with the help of pseudo-three dimensional numerical models that include side forces. Strain localization results when the basal shear abruptly increases in a step-function manner while oblique-slip on numerous faults dominates when basal shear is distributed. We further explore how the style of faulting varies with obliquity and demonstrate that the style of delocalized faulting observed in the Northern Gulf of California is reproduced in models with an obliquity of 0.7 and distributed basal shear boundary conditions, consistent with the interpreted obliquity and boundary conditions of the study area.

Lower crustal flow and the role of shear in basin subsidence: An example from the Dead Sea basin

USGS Publications Warehouse

Al-Zoubi, A.; ten Brink, Uri S.

2002-01-01

We interpret large-scale subsidence (5–6 km depth) with little attendant brittle deformation in the southern Dead Sea basin, a large pull-apart basin along the Dead Sea transform plate boundary, to indicate lower crustal thinning due to lower crustal flow. Along-axis flow within the lower crust could be induced by the reduction of overburden pressure in the central Dead Sea basin, where brittle extensional deformation is observed. Using a channel flow approximation, we estimate that lower crustal flow would occur within the time frame of basin subsidence if the viscosity is ≤7×1019–1×1021 Pa s, a value compatible with the normal heat flow in the region. Lower crustal viscosity due to the strain rate associated with basin extension is estimated to be similar to or smaller than the viscosity required for a channel flow. However, the viscosity under the basin may be reduced to 5×1017–5×1019 Pa s by the enhanced strain rate due to lateral shear along the transform plate boundary. Thus, lower crustal flow facilitated by shear may be a viable mechanism to enlarge basins and modify other topographic features even in the absence of underlying thermal anomalies.

An equivalent network representation of a clamped bimorph piezoelectric micromachined ultrasonic transducer with circular and annular electrodes using matrix manipulation techniques.

PubMed

Sammoura, Firas; Smyth, Katherine; Kim, Sang-Gook

2013-09-01

An electric circuit model for a clamped circular bimorph piezoelectric micromachined ultrasonic transducer (pMUT) was developed for the first time. The pMUT consisted of two piezoelectric layers sandwiched between three thin electrodes. The top and bottom electrodes were separated into central and annular electrodes by a small gap. While the middle electrode was grounded, the central and annular electrodes were biased with two independent voltage sources. The strain mismatch between the piezoelectric layers caused the plate to vibrate and transmit a pressure wave, whereas the received echo generated electric charges resulting from plate deformation. The clamped pMUT plate was separated into a circular and an annular plate, and the respective electromechanical transformation matrices were derived. The force and velocity vectors were properly selected using Hamilton's principle and the necessary boundary conditions were invoked. The electromechanical transformation matrix for the clamped circular pMUT was deduced using simple matrix manipulation techniques. The pMUT performance under three biasing schemes was elaborated: 1) central electrode only, 2) central and annular electrodes with voltages of the same magnitude and polarity, and 3) central and annular electrodes with voltages of the same magnitude and opposite polarity. The circuit parameters of the pMUT were extracted for each biasing scheme, including the transformer ratio, the clamped electric impedance, and the open-circuit mechanical impedance. Each pMUT scheme was characterized under different acoustic loadings using the theoretically developed model, which was verified with finite element modeling (FEM) simulation. The electrode size was optimized to maximize the electromechanical transformer ratio. As such, the developed model could provide more insight into the design, optimization, and characterization of pMUTs and allow for performance comparison with their cMUT counterparts.

Anomalous Buckling Characteristics of Laminated Metal-Matrix Composite Plates with Central Square Holes

NASA Technical Reports Server (NTRS)

Ko, William L.

1998-01-01

Compressive buckling analysis was performed on metal-matrix composite (MMC) plates with central square holes. The MMC plates have varying aspect ratios and hole sizes and are supported under different boundary conditions. The finite-element structural analysis method was used to study the effects of plate boundary conditions, plate aspect ratio, hole size, and the composite stacking sequence on the compressive buckling strengths of the perforated MMC plates. Studies show that by increasing the hole sizes, compressive buckling strengths of the perforated MMC plates could be considerably increased under certain boundary conditions and aspect ratios ("anomalous" buckling behavior); and that the plate buckling mode could be symmetrical or antisymmetrical, depending on the plate boundary conditions, aspect ratio, and the hole size. For same-sized plates with same-sized holes, the compressive buckling strengths of the perforated MMC plates with [90/0/0/90]2 lamination could be as much as 10 percent higher or lower than those of the [45/- 45/- 45/45]2 laminations, depending on the plate boundary conditions, plate aspect ratios, and the hole size. Clamping the plate edges induces far stronger "anomalous" buckling behavior (enhancing compressive buckling strengths at increasing hole sizes) of the perforated MMC plates than simply supporting the plate edges.

Oceanic transform faults: how and why do they form? (Invited)

NASA Astrophysics Data System (ADS)

Gerya, T.

2013-12-01

Oceanic transform faults at mid-ocean ridges are often considered to be the direct product of plate breakup process (cf. review by Gerya, 2012). In contrast, recent 3D thermomechanical numerical models suggest that transform faults are plate growth structures, which develop gradually on a timescale of few millions years (Gerya, 2010, 2013a,b). Four subsequent stages are predicted for the transition from rifting to spreading (Gerya, 2013b): (1) crustal rifting, (2) multiple spreading centers nucleation and propagation, (3) proto-transform faults initiation and rotation and (4) mature ridge-transform spreading. Geometry of the mature ridge-transform system is governed by geometrical requirements for simultaneous accretion and displacement of new plate material within two offset spreading centers connected by a sustaining rheologically weak transform fault. According to these requirements, the characteristic spreading-parallel orientation of oceanic transform faults is the only thermomechanically consistent steady state orientation. Comparison of modeling results with the Woodlark Basin suggests that the development of this incipient spreading region (Taylor et al., 2009) closely matches numerical predictions (Gerya, 2013b). Model reproduces well characteristic 'rounded' contours of the spreading centers as well as the presence of a remnant of the broken continental crustal bridge observed in the Woodlark basin. Similarly to the model, the Moresby (proto)transform terminates in the oceanic rather than in the continental crust. Transform margins and truncated tip of one spreading center present in the model are documented in nature. In addition, numerical experiments suggest that transform faults can develop gradually at mature linear mid-ocean ridges as the result of dynamical instability (Gerya, 2010). Boundary instability from asymmetric plate growth can spontaneously start in alternate directions along successive ridge sections; the resultant curved ridges become transform faults. Offsets along the transform faults change continuously with time by asymmetric plate growth and discontinuously by ridge jumps. The ridge instability is governed by rheological weakening of active fault structures. The instability is most efficient for slow to intermediate spreading rates, whereas ultraslow and (ultra)fast spreading rates tend to destabilize transform faults (Gerya, 2010; Püthe and Gerya, 2013) References Gerya, T. (2010) Dynamical instability produces transform faults at mid-ocean ridges. Science, 329, 1047-1050. Gerya, T. (2012) Origin and models of oceanic transform faults. Tectonophys., 522-523, 34-56 Gerya, T.V. (2013a) Three-dimensional thermomechanical modeling of oceanic spreading initiation and evolution. Phys. Earth Planet. Interiors, 214, 35-52. Gerya, T.V. (2013b) Initiation of transform faults at rifted continental margins: 3D petrological-thermomechanical modeling and comparison to the Woodlark Basin. Petrology, 21, 1-10. Püthe, C., Gerya, T.V. (2013) Dependence of mid-ocean ridge morphology on spreading rate in numerical 3-D models. Gondwana Res., DOI: http://dx.doi.org/10.1016/j.gr.2013.04.005 Taylor, B., Goodliffe, A., Martinez, F. (2009) Initiation of transform faults at rifted continental margins. Comptes Rendus Geosci., 341, 428-438.

Composite and Component Plates, Plate Non-rigidity, and the Steadiness of Plate Motion From Marine Geophysical and Space Geodetic Data

NASA Astrophysics Data System (ADS)

Gordon, R. G.; Argus, D. F.; DeMets, C.

2017-12-01

Plate tectonic theory has evolved since its birth 50 years ago. In particular, we now recognize that some of the originally proposed plates such as the Indo-Australia plate, the Africa plate, and the America plate are what we term "composite" plates—entities that contain no traditionally defined narrow plate boundaries, but are composed of multiple approximately rigid regions, which we term "component" plates, separated by diffuse plate boundaries. The best example of a composite plate is the Indo-Australia composite plate, which consists of the India, Capricorn, Australia, and Macquarie component plates and multiple intervening diffuse oceanic plate boundaries. The poles of relative rotation between component plates tend to lie in their mutual diffuse plate boundary. Outside of diffuse boundaries, plate rigidity has proven to be an excellent approximation, but the non-closure of some plate circuits indicates that stable plate interiors have a small but significant non-rigidity that may add up to 1 to 2 mm/a across any individual plate and may be partly due to horizontal thermal contraction of oceanic lithosphere. The greatest observational challenge to plate rigidity is posed by the Pacific-Cocos-Nazca plate circuit, which fails closure by 15 ±4 mm/a. The most rapid deformation of the plates observed with space geodesy is generated by solid Earth's viscous response to unloading of the late Pleistocene ice sheets. Differences between different realizations of global plate velocities from space geodesy appear in some cases to be due to differing assumptions about the motion of the geocenter, which affects estimated plate relative angular velocities and estimated vertical motion at geodetic sites. Comparison of space geodetic and marine geophysical plate motion rates and directions has demonstrated that plate motion is nearly steady, which allows plate boundary conditions to be applied to inter-seismic strain accumulation due to locking of specific faults. In detail it appears, however, that plate velocities over the past few decades have in several cases been significantly different from plate motions averaged over geologic time. Some of the largest changes have been decreases in rates across convergent plate boundaries: Nazca-South America and the velocities of Nubia, Arabia, and India relative to Eurasia.

A bottom-driven mechanism for distributed faulting: Insights from the Gulf of California Rift

NASA Astrophysics Data System (ADS)

Persaud, P.; Tan, E.; Choi, E.; Contreras, J.; Lavier, L. L.

2017-12-01

The Gulf of California is a young oblique rift that displays a variation in rifting style along strike. Despite the rapid localization of strain in the Gulf at 6 Ma, the northern rift segment has the characteristics of a wide rift, with broadly distributed extensional strain and small gradients in topography and crustal thinning. Observations of active faulting in the continent-ocean transition of the Northern Gulf show multiple oblique-slip faults distributed in a 200 x 70 km2area developed some time after a westward relocation of the plate boundary at 2 Ma. In contrast, north and south of this broad pull-apart structure, major transform faults accommodate Pacific-North America plate motion. Here we propose that the mechanism for distributed brittle deformation results from the boundary conditions present in the Northern Gulf, where basal shear is distributed between the Cerro Prieto strike-slip fault (southernmost fault of the San Andreas fault system) and the Ballenas Transform fault. We hypothesize that in oblique-extensional settings whether deformation is partitioned in a few dip-slip and strike-slip faults, or in numerous oblique-slip faults may depend on (1) bottom-driven, distributed extension and shear deformation of the lower crust or upper mantle, and (2) the rift obliquity. To test this idea, we explore the effects of bottom-driven shear on the deformation of a brittle elastic-plastic layer with pseudo-three dimensional numerical models that include side forces. Strain localization results when the basal shear is a step-function while oblique-slip on numerous faults dominates when basal shear is distributed. We further investigate how the style of faulting varies with obliquity and demonstrate that the style of faulting observed in the Northern Gulf of California is reproduced in models with an obliquity of 0.7 and distributed basal shear boundary conditions, consistent with the interpreted obliquity and boundary conditions of the study area. Our findings motivate a suite of 3D models of the early plate boundary evolution in the Gulf, and highlight the importance of local stress field perturbations as a mechanism for broadening the deformation zone in other regions such as the Basin and Range, Rio Grande Rift and Malawi Rift.

From Subduction to a Compressional transform system: Diffuse Deformation Processes at the Southeastern Boundary of the Caribbean Plate

NASA Astrophysics Data System (ADS)

Deville, E.; Padron, C.; Huyghe, P.; Callec, Y.; Lallemant, S.; Lebrun, J.; Mascle, A.; Mascle, G.; Noble, M.

2006-12-01

Geophysical data acquired in the southeastern Caribbean marine area (CARAMBA survey of the French O/V Atalante) provide new information about the deformation processes occurring in this subduction-to-strike-slip transitions zone. The 65 000 km2 of multibeam data and 5600 km of seismic reflection and 3.5 kHz profiles which have been collected evidence that the connection between the Barbados accretionary prism and the south Caribbean transform system is partitioned between a wide variety of recently active tectonic superficial features (complex folding, diffuse faulting, and mud volcanism), which accommodate the relative displacement between the Caribbean and the South America plates. The active deformation within the sedimentary pile is mostly aseismic (creeping) and this deformation is relatively diffuse over a large diffuse plate boundary. There is no direct fault connection between the front of the Barbados prism and the strike-slip system of northern Venezuela. The toe thrust system at the southern edge of the Barbados prism, exhibits clear en-echelon geometry. The geometry of the syntectonic deposits evidence the diachronism of the deformation processes. Notably, it is well evidenced that early folds have been sealed by the recent turbidite deposits, whereas, some of the fold and thrust structures were active recently. Within this active compressional region, extension growth faults develop on the platform and on the slope of the Orinoco delta along a WNW-ESE trending en-echelon fault system that we called the Orinoco Delta Fault Zone (ODFZ). This fault system is clearly oblique with respect to the present-day Orinoco delta slope. These faults are not simply related to a passive gravitary collapse of the sediments accumulated on the Orinoco platform. Though there a decoupling between the shallow deformation processes in the sediments and the deep deformation characterized by earthquake activity, the ODFZ is inferred to be partly controlled by deep structures associated the shearing of the lithosphere at depth (probably at the Continent-Ocean Boundary).

Dynamic analysis of submerged microscale plates: the effects of acoustic radiation and viscous dissipation.

PubMed

Wu, Zhangming; Ma, Xianghong

2016-03-01

The aim of this paper is to study the dynamic characteristics of micromechanical rectangular plates used as sensing elements in a viscous compressible fluid. A novel modelling procedure for the plate-fluid interaction problem is developed on the basis of linearized Navier-Stokes equations and no-slip conditions. Analytical expression for the fluid-loading impedance is obtained using a double Fourier transform approach. This modelling work provides us an analytical means to study the effects of inertial loading, acoustic radiation and viscous dissipation of the fluid acting on the vibration of microplates. The numerical simulation is conducted on microplates with different boundary conditions and fluids with different viscosities. The simulation results reveal that the acoustic radiation dominates the damping mechanism of the submerged microplates. It is also proved that microplates offer better sensitivities (Q-factors) than the conventional beam type microcantilevers being mass sensing platforms in a viscous fluid environment. The frequency response features of microplates under highly viscous fluid loading are studied using the present model. The dynamics of the microplates with all edges clamped are less influenced by the highly viscous dissipation of the fluid than the microplates with other types of boundary conditions.

Seafloor Volcanic and Structural Features Adjacent to the 90deg 50'N Transform - Galapagos Spreading Center: Clues for Understanding Plate Boundary Kinematics and Lithospheric Melting Processes (Invited)

NASA Astrophysics Data System (ADS)

Fornari, D. J.; Soule, S.; Harpp, K. S.; Mittelstaedt, E. L.; Geist, D.; Kurz, M. D.; R/v Melville Mv1007 Cruise Scientific Party

2010-12-01

High-resolution EM122 multibeam and MR-1 sidescan sonar data collected over a wide area of seafloor west and east of the 90deg 50’N transform along the Galapagos Spreading Center (GSC) reveal seafloor morpho-structural fabric created along this intermediate spreading plate boundary. In concert with geochemical and geophysical data collected during the cruise, these data will be used to help unravel the kinematics of hotspot-ridge interactions in the northern Galapagos. West of the transform, the seafloor is dominated by three prominent NW-SE trending seamount lineaments, each ~20-30 km wide, including the prominent Wolf-Darwin Lineament (WDL) as well as two other smaller volcanic chains east of the WDL, which are oriented along intermediate trends that become more subparallel to the N-S trend of the transform from west to east. This suggests a possible strong controlling influence of the transform on the orientation of lithospheric fractures involved in supplying magmas to the volcanic centers. Interestingly, each seamount lineament west of the transform appears to have nascent volcanoes nucleating immediately south of the GSC axis at locations that mark along-axis discontinuities of the spreading center, suggesting ridge-related magmatic focusing is also influencing crustal generation on the Nazca plate in this region. The tectonized terrain associated with the transform is 60 km wide, whereas the transform valley is only 20 km wide. The northern 40 km of the transform has a well-defined linear shear zone and bounding faults. The southern 50 km of the transform are characterized by a wide zone of extensive oblique shear structures that trend NW-SE. Within this zone are numerous small volcanic cones and ridges that decorate the margins and axis of the transform domain. The structural evolution of the transform appears to be undergoing a transition along its length with intra-transform volcanism in the south and more normal shear in the north, however the tectonic imprint of the oblique structures is observed along nearly all of the length of the transform out to 15-20 km from the margins of the transform valley. Terrain east of the transform is markedly different in morphological character and structural elements. A series of five, generally E-W ridges, some of which display clear volcanic constructional terrain, extend from the eastern margin of the oblique fabric associated with the transform domain. Some of these E-W features are linked by N-S structures, creating a general patchwork pattern of seafloor that is unlike any we have observed at well-mapped ridge-transform intersections at fast and intermediate spreading mid-ocean ridges. The terrain bears some similarities to structures developed at microplates. We also note that this region lies at the southwestern extremity of the Cocos Ridge, an aseismic ridge that has undergone a complex history of volcanic and tectonic construction associated with hotspot magmatism and ridge jumps.

The evolution of shallow crustal structures in early rift-transform interaction: a case study in the northern Gulf of California.

NASA Astrophysics Data System (ADS)

Farangitakis, Georgios-Pavlos; van Hunen, Jeroen; Kalnins, Lara M.; Persaud, Patricia; McCaffrey, Kenneth J. W.

2017-04-01

The Gulf of California represents a young oblique rift/transtensional plate boundary in which all of the transform faults are actively shearing the crust, separated by active rift segments. Previous workers have shown that in the northern Gulf of California, the relative plate motion between the Pacific and North American plates is distributed between: a) the Cerro Prieto Fault (CPF) in the NE b) the Ballenas Transform Fault (BTF) in the SW and c) a pull-apart structure located between these two faults consisting of a number of extensional basins (the Wagner, Consag, and Upper and Lower Delfin basins). A plate boundary relocation at approximately 2 Ma, continued to separate Isla Angel de la Guarda from the Baja California peninsula and created the 200x70 km2 NE-SW pull-apart structure located northeast of the BTF. Here we use seismic stratigraphy analysis of the UL9905 high resolution reflection seismic dataset acquired by the Lamont-Doherty Earth Observatory, Caltech, and the Centro de Investigación Científica y de Educación Superior de Ensenada to build on previous structural interpretations and seek to further understand the processes that formed the structural and sedimentary architecture of the pull-apart basin in the northern Gulf of California. We examine the formation of depositional and deformation structures in relation to the regional tectonics to provide insight into the development of structural patterns and related seismic-stratigraphic features in young rift-transform interactions. Using bathymetric data, characteristic seismic-stratigraphic packages, and seismic evidence of faulting, we confirm the existence of three major structural domains in the northern Gulf of California and examine the interaction of the seismic stratigraphy and tectonic processes in each zone. The first and most distinctive is an abrupt NE-SW 28x5 km2 depression on the seabed of the Lower Delfin Basin. This is aligned orthogonally to the BTF, is situated at its northern end, and is an active rift. The second structural domain is a large, NE-SW-trending anticlinorium 60 km wide to the southeast of the rift zone, towards the Tiburon basin. One possibility is that it represents a positive flower structure and thus indicates a transpressional domain. However, individual structures within the broader zone are normal faults and negative flower structures, suggesting transtensional deformation, and the overall structure may be a roll-over antiform formed on a deep detachment structure. Finally, a strike-slip-dominated zone occurs along the northward continuation of the Ballenas Transform Fault. This is accompanied by the formation of submarine volcanic knolls. These patterns can be compared with seismic stratigraphy facies and structural patterns in mature transform margins and potentially give insight into their early history.

Pacific-North America plate boundary reorganization in response to a change in relative plate motion: Offshore Canada

NASA Astrophysics Data System (ADS)

Rohr, K. M. M.; Tryon, A. J.

2010-06-01

The transition from subduction in Cascadia to the transform Queen Charlotte fault along western Canada is often drawn as a subduction zone, yet recent studies of GPS and earthquake data from northern Vancouver Island are not consistent with that model. In this paper we synthesize seismic reflection and gravity interpretations with microseismicity data in order to test models of (1) microplate subduction and (2) reorganization of the preexisting strike-slip plate boundary. We focus on the critical region of outer Queen Charlotte Sound and the adjacent offshore. On much of the continental shelf, several million years of subsidence above thin crust are a counterindicator for subduction. An undated episode of compression uplifted the southernmost shelf, but subsidence patterns offshore show that recent subduction is unlikely to be responsible. Previously unremarked near-vertical faults and a mix of extensional and compressional faults offshore indicate that strike-slip faulting has been a significant mode of deformation. Seismicity in the last 18 years is dominantly strike-slip and shows large amounts of moment release on the Revere-Dellwood fault and its overlap with the Queen Charlotte fault. The relative plate motion between the Pacific and North American plates rotated clockwise ˜6 Ma and appears to have triggered formation of an evolving array of structures. We suggest that the paleo-Queen Charlotte fault which had defined this continental margin retreated northward as offshore distributed shear and the newly formed Revere Dellwood fault propagated to the northwest.

Detailed seismicity analysis revealing the dynamics of the southern Dead Sea area

NASA Astrophysics Data System (ADS)

Braeuer, B.; Asch, G.; Hofstetter, R.; Haberland, Ch.; Jaser, D.; El-Kelani, R.; Weber, M.

2014-10-01

Within the framework of the international DESIRE (DEad Sea Integrated REsearch) project, a dense temporary local seismological network was operated in the southern Dead Sea area. During 18 recording months, 648 events were detected. Based on an already published tomography study clustering, focal mechanisms, statistics and the distribution of the microseismicity in relation to the velocity models from the tomography are analysed. The determined b value of 0.74 leads to a relatively high risk of large earthquakes compared to the moderate microseismic activity. The distribution of the seismicity indicates an asymmetric basin with a vertical strike-slip fault forming the eastern boundary of the basin, and an inclined western boundary, made up of strike-slip and normal faults. Furthermore, significant differences between the area north and south of the Bokek fault were observed. South of the Bokek fault, the western boundary is inactive while the entire seismicity occurs on the eastern boundary and below the basin-fill sediments. The largest events occurred here, and their focal mechanisms represent the northwards transform motion of the Arabian plate along the Dead Sea Transform. The vertical extension of the spatial and temporal cluster from February 2007 is interpreted as being related to the locking of the region around the Bokek fault. North of the Bokek fault similar seismic activity occurs on both boundaries most notably within the basin-fill sediments, displaying mainly small events with strike-slip mechanism and normal faulting in EW direction. Therefore, we suggest that the Bokek fault forms the border between the single transform fault and the pull-apart basin with two active border faults.

A New Look at Spreading in Iceland: Propagating Rifts, Migrating Transform Faults, and Microplate Tectonics

NASA Astrophysics Data System (ADS)

Karson, J.; Horst, A. J.; Nanfito, A.

2011-12-01

Iceland has long been used as an analog for studies of seafloor spreading. Despite its thick (~25 km) oceanic crust and subaerial lavas, many features associated with accretion along mid-ocean ridge spreading centers, and the processes that generate them, are well represented in the actively spreading Neovolcanic Zone and deeply glaciated Tertiary crust that flanks it. Integrated results of structural and geodetic studies show that the plate boundary zone on Iceland is a complex array of linked structures bounding major crustal blocks or microplates, similar to oceanic microplates. Major rift zones propagate N and S from the hotspot centered beneath the Vatnajökull icecap in SE central Iceland. The southern propagator has extended southward beyond the South Iceland Seismic Zone transform fault to the Westman Islands, resulting in abandonment of the Eastern Rift Zone. Continued propagation may cause abandonment of the Reykjanes Ridge. The northern propagator is linked to the southern end of the receding Kolbeinsey Ridge to the north. The NNW-trending Kerlingar Pseudo-fault bounds the propagator system to the E. The Tjörnes Transform Fault links the propagator tip to the Kolbeinsey Ridge and appears to be migrating northward in incremental steps, leaving a swath of deformed crustal blocks in its wake. Block rotations, concentrated mainly to the west of the propagators, are clockwise to the N of the hotspot and counter-clockwise to the S, possibly resulting in a component of NS divergence across EW-oriented rift zones. These rotations may help accommodate adjustments of the plate boundary zone to the relative movements of the N American and Eurasian plates. The rotated crustal blocks are composed of highly anisotropic crust with rift-parallel internal fabric generated by spreading processes. Block rotations result in reactivation of spreading-related faults as major rift-parallel, strike-slip faults. Structural details found in Iceland can help provide information that is difficult or impossible to obtain in propagating systems of the deep seafloor.

Strike-slip tectonics during rift linkage

NASA Astrophysics Data System (ADS)

Pagli, C.; Yun, S. H.; Ebinger, C.; Keir, D.; Wang, H.

2017-12-01

The kinematics of triple junction linkage and the initiation of transforms in magmatic rifts remain debated. Strain patterns from the Afar triple junction provide tests of current models of how rifts grow to link in area of incipient oceanic spreading. Here we present a combined analysis of seismicity, InSAR and GPS derived strain rate maps to reveal that the plate boundary deformation in Afar is accommodated primarily by extensional tectonics in the Red Sea and Gulf of Aden rifts, and does not require large rotations about vertical axes (bookshelf faulting). Additionally, models of stress changes and seismicity induced by recent dykes in one sector of the Afar triple junction provide poor fit to the observed strike-slip earthquakes. Instead we explain these patterns as rift-perpendicular shearing at the tips of spreading rifts where extensional strains terminate against less stretched lithosphere. Our results demonstrate that rift-perpendicular strike-slip faulting between rift segments achieves plate boundary linkage during incipient seafloor spreading.

Resilience by Design: Bringing Science to Policy Makers

USGS Publications Warehouse

Jones, Lucile M.

2015-01-01

No one questions that Los Angeles has an earthquake problem. The “Big Bend” of the San Andreas fault in southern California complicates the plate boundary between the North American and Pacific plates, creating a convergent component to the primarily transform boundary. The Southern California Earthquake Center Community Fault Model has over 150 fault segments, each capable of generating a damaging earthquake, in an area with more than 23 million residents (Fig. 1). A Federal Emergency Management Agency (FEMA) analysis of the expected losses from all future earthquakes in the National Seismic Hazard Maps (Petersen et al., 2014) predicts an annual average of more than $3 billion per year in the eight counties of southern California, with half of those losses in Los Angeles County alone (Federal Emergency Management Agency [FEMA], 2008). According to Swiss Re, one of the world’s largest reinsurance companies, Los Angeles faces one of the greatest risks of catastrophic losses from earthquakes of any city in the world, eclipsed only by Tokyo, Jakarta, and Manila (Swiss Re, 2013).

Global tectonics and space geodesy.

PubMed

Gordon, R G; Stein, S

1992-04-17

Much of the success of plate tectonics can be attributed to the near rigidity of tectonic plates and the availability of data that describe the rates and directions of motion across narrow plate boundaries \\m=~\\1 to 60 kilometers wide. Nonetheless, many plate boundaries in both continental and oceanic lithosphere are not narrow but are hundreds to thousands of kilometers wide. Wide plate boundary zones cover \\m=~\\15 percent of Earth's surface area. Space geodesy, which includes very long baseline radio interferometry, satellite laser ranging, and the global positioning system, is providing the accurate long-distance measurements needed to estimate the present motion across and within wide plate boundary zones. Space geodetic data show that plate velocities averaged over years are remarkably similar to velocities averaged over millions of years.

Global tectonics and space geodesy

NASA Technical Reports Server (NTRS)

Gordon, Richard G.; Stein, Seth

1992-01-01

Much of the success of plate tectonics can be attributed to the near rigidity of tectonic plates and the availability of data that describe the rates and directions of motion across narrow plate boundaries of about 1 to 60 kilometers. Nonetheless, many plate boundaries in both continental and oceanic lithosphere are not narrow but are hundreds to thousands of kilometers wide. Wide plate boundary zones cover approximately 15 percent of earth's surface area. Space geodesy, which includes very long baseline radio interferometry, satellite laser ranging, and the global positioning system, provides the accurate long-distance measurements needed to estimate the present motion across and within wide plate boundary zones. Space geodetic data show that plate velocities averaged over years are remarkably similar to velocities avaraged over millions of years.

Analysis of edge impact stresses in composite plates

NASA Technical Reports Server (NTRS)

Moon, F. C.; Kang, C. K.

1974-01-01

The in-plane edge impact of composite plates, with or without a protection strip, is investigated. A computational analysis based on the Fast Fourier Transform technique is presented. The particular application of the present method is in the understanding of the foreign object damage problem of composite fan blades. The method is completely general and may be applied to the study of other stress wave propagation problems in a half space. Results indicate that for the protective strip to be effective in reducing impact stresses in the composite the thickness must be equal or greater than the impact contact dimension. Large interface shear stresses at the strip - composite boundary can be induced under impact.

Global tectonic studies: Hotspots and anomalous topography

NASA Technical Reports Server (NTRS)

Burke, K.; Kidd, W. S. F.; Delong, S.; Thiessen, R. L.; Carosella, R.; Mcgetchin, T. R.

1979-01-01

Volcanic activity on Earth and its secular variations are compared with that on other terrestrial planets. Activity at divergent, transform, and convergent plate margins is described with particular emphasis on hot spots and flood basalts. The timing and causing of uplifting above 500 meters, which in not associated with either plate boundaries or the normal nonplate margin edges of continents is considered with particular focus on the Guyana Highlands in southern Venezuela and western British Guiana, and the Brazilian Highlands in the central, eastern, and southern parts of the country. The mode and mechanism of plateau uplifting and the re-elevation of old mountain belts and subsidence of intra-continental basins are also discussed.

Magnetic character of a large continental transform: an aeromagnetic survey of the Dead Sea Fault

USGS Publications Warehouse

ten Brink, Uri S.; Rybakov, Michael; Al-Zoubi, Abdallah S.; Rotstein, Yair

2007-01-01

New high-resolution airborne magnetic (HRAM) data along a 120-km-long section of the Dead Sea Transform in southern Jordan and Israel shed light on the shallow structure of the fault zone and on the kinematics of the plate boundary. Despite infrequent seismic activity and only intermittent surface exposure, the fault is delineated clearly on a map of the first vertical derivative of the magnetic intensity, indicating that the source of the magnetic anomaly is shallow. The fault is manifested by a 10–20 nT negative anomaly in areas where the fault cuts through magnetic basement and by a

Deformation, Fluid Flow and Mantle Serpentinization at Oceanic Transform Faults

NASA Astrophysics Data System (ADS)

Rupke, L.; Hasenclever, J.

2017-12-01

Oceanic transform faults (OTF) and fracture zones have long been hypothesized to be sites of enhanced fluid flow and biogeochemical exchange. In this context, the serpentine forming interaction between seawater and cold lithospheric mantle rocks is particularly interesting. The transformation of peridotite to serpentinite not only leads to hydration of oceanic plates and is thereby an important agent of the geological water cycle, it is also a mechanism of abiotic hydrogen and methane formation, which can support archeal and bacterial communities at the seafloor. Inferring the likely amount of mantle undergoing serpentinization reactions therefore allows estimating the amount of biomass that may be autotrophically produced at and around oceanic transform faults and mid-ocean ridges Here we present results of 3-D geodynamic model simulations that explore the interrelations between deformation, fluid flow, and mantle serpentinization at oceanic transform faults. We investigate how slip rate and fault offset affect the predicted patterns of mantle serpentinization around oceanic transform faults. Global rates of mantle serpentinization and associated H2 production are calculated by integrating the modeling results with plate boundary data. The global additional OTF-related production of H2 is found to be between 6.1 and 10.7 x 1011 mol per year, which is comparable to the predicted background mid-ocean ridge rate of 4.1 - 15.0 x 1011 mol H2/yr. This points to oceanic transform faults as potential sites of intense fluid-rock interaction, where chemosynthetic life could be sustained by serpentinization reactions.

Satellite-Based Investigations of the Transition from an Oceanic to Continental Transform Margin

NASA Technical Reports Server (NTRS)

Miller, M. Meghan

1998-01-01

Detailed characterization of neotectonics evolution of the Valle de San Felipe and Arroyo Grande regions in northern Baja California. Reoccupied GEOMEX GPS sites, and occupied a regional GPS (Global Positioning System) network. The Baja California peninsula in Mexico offers a unique setting for studying the kinematic evolution of a complex, active strike-slip/rift plate boundary. We are currently conducting remote sensing, geologic, and geodetic studies of this boundary. The combined data sets will yield instantaneous and time integrated views of its evolution. This proposal solicits renewed funding from NASA to support remote sensing and geologic studies. During the late Cenozoic, Baja California has been the locus of changing fault geometry that has accommodated components of the relative motion between the North America and Pacific plates. Contemporary slip between the two plates occurs in a broad zone that encompasses much of southern California and the Baja California Peninsula. The transfer of slip across this zone in southern California is relatively well understood. South of the border, the geometry and role of specific faults and structural provinces in transferring plate margin deformation across the peninsula is enigmatic. Results We use Landsat Thematic Mapper imagery of the Baja California Peninsula to identify recent and active faults, and then conduct field studies that characterize the temporal and spatial structural evolution of the plate margin. These data address questions concerning the neotectonic development of the Gulf of California, the Baja California Peninsula, and their role in evolution of the post-Miocene Pacific - North American plate boundary. Moreover, these studies provide constraints on the geometry of active faults, allowing more exact understanding of the results of ongoing NASA-supported geodetic experiments. In addition, anticipated publication of the TM scenes will provide a widely available geological data base for relatively little-known peninsula California. Achievements include development of an ArcInfo data base of Landsat and SPOT imagery, detailed field studies of Neogene structures in northeastern Baja California, and new constraint on Pacific - North America plate motion at Baja California latitudes. These results are reported in maps, manuscripts and data products which are published or near completion.

Movies of Finite Deformation within Western North American Plate Boundary Zone

NASA Astrophysics Data System (ADS)

Holt, W. E.; Birkes, B.; Richard, G. A.

2004-12-01

Animations of finite strain within deforming continental zones can be an important tool for both education and research. We present finite strain models for western North America. We have found that these moving images, which portray plate motions, landform uplift, and subsidence, are highly useful for enabling students to conceptualize the dramatic changes that can occur within plate boundary zones over geologic time. These models use instantaneous rates of strain inferred from both space geodetic observations and Quaternary fault slip rates. Geodetic velocities and Quaternary strain rates are interpolated to define a continuous, instantaneous velocity field for western North America. This velocity field is then used to track topography points and fault locations through time (both backward and forward in time), using small time steps, to produce a 6 million year image. The strain rate solution is updated at each time step, accounting for changes in boundary conditions of plate motion, and changes in fault orientation. Assuming zero volume change, Airy isostasy, and a ratio of erosion rate to tectonic uplift rate, the topography is also calculated as a function of time. The animations provide interesting moving images of the transform boundary, highlighting ongoing extension and subsidence, convergence and uplift, and large translations taking place within the strike-slip regime. Moving images of the strain components, uplift volume through time, and inferred erosion volume through time, have also been produced. These animations are an excellent demonstration for education purposes and also hold potential as an important tool for research enabling the quantification of finite rotations of fault blocks, potential erosion volume, uplift volume, and the influence of climate on these parameters. The models, however, point to numerous shortcomings of taking constraints from instantaneous calculations to provide insight into time evolution and reconstruction models. More rigorous calculations are needed to account for changes in dynamics (body forces) through time and resultant changes in fault behavior and crustal rheology.

Re-Innovating Recycling for Turbulent Boundary Layer Simulations

NASA Astrophysics Data System (ADS)

Ruan, Joseph; Blanquart, Guillaume

2017-11-01

Historically, turbulent boundary layers along a flat plate have been expensive to simulate numerically, in part due to the difficulty of initializing the inflow with ``realistic'' turbulence, but also due to boundary layer growth. The former has been resolved in several ways, primarily dedicating a region of at least 10 boundary layer thicknesses in width to rescale and recycle flow or by extending the region far enough downstream to allow a laminar flow to develop into turbulence. Both of these methods are relatively costly. We propose a new method to remove the need for an inflow region, thus reducing computational costs significantly. Leveraging the scale similarity of the mean flow profiles, we introduce a coordinate transformation so that the boundary layer problem can be solved as a parallel flow problem with additional source terms. The solutions in the new coordinate system are statistically homogeneous in the downstream direction and so the problem can be solved with periodic boundary conditions. The present study shows the stability of this method, its implementation and its validation for a few laminar and turbulent boundary layer cases.

Regional seismic wave propagation (Lg and Sn) and Pn attenuation in the Arabian Plate and surrounding regions

NASA Astrophysics Data System (ADS)

Al-Damegh, Khaled; Sandvol, Eric; Al-Lazki, Ali; Barazangi, Muawia

2004-05-01

Continuous recordings of 17 broadband and short-period digital seismic stations from a newly established seismological network in Saudi Arabia, along with digital recordings from the broadband stations of the GSN, MEDNET, GEOFON, a temporary array in Saudi Arabia, and temporary short period stations in Oman, were analysed to study the lithospheric structure of the Arabian Plate and surrounding regions. The Arabian Plate is surrounded by a variety of types of plate boundaries: continental collision (Zagros Belt and Bitlis Suture), continental transform (Dead Sea fault system), young seafloor spreading (Red Sea and the Gulf of Aden) and oceanic transform (Owen fracture zone). Also, there are many intraplate Cenozoic processes such as volcanic eruptions, faulting and folding that are taking place. We used this massive waveform database of more than 6200 regional seismograms to map zones of blockage, inefficient and efficient propagation of the Lg and Sn phases in the Middle East and East Africa. We observed Lg blockage across the Bitlis Suture and the Zagros fold and thrust belt, corresponding to the boundary between the Arabian and Eurasian plates. This is probably due to a major lateral change in the Lg crustal waveguide. We also observed inefficient Lg propagation along the Oman mountains. Blockage and inefficient Sn propagation is observed along and for a considerable distance to the east of the Dead Sea fault system and in the northern portion of the Arabian Plate (south of the Bitlis Suture). These mapped zones of high Sn attenuation, moreover, closely coincide with extensive Neogene and Quaternary volcanic activity. We have also carefully mapped the boundaries of the Sn blockage within the Turkish and Iranian plateaus. Furthermore, we observed Sn blockage across the Owen fracture zone and across some segments of the Red Sea. These regions of high Sn attenuation most probably have anomalously hot and possibly thin lithospheric mantle (i.e. mantle lid). A surprising result is the efficient propagation of Sn across a segment of the Red Sea, an indication that active seafloor spreading is not continuous along the axis of the Red Sea. We also investigated the attenuation of Pn phase (QPn) for 1-2 Hz along the Red Sea, the Dead Sea fault system, within the Arabian Shield and in the Arabian Platform. Consistent with the Sn attenuation, we observed low QPn values of 22 and 15 along the western coast of the Arabian Plate and along the Dead Sea fault system, respectively, for a frequency of 1.5 Hz. Higher QPn values of the order of 400 were observed within the Arabian Shield and Platform for the same frequency. Our results based on Sn and Pn observations along the western and northern portions of the Arabian Plate imply the presence of a major anomalously hot and thinned lithosphere in these regions that may be caused by the extensive upper mantle anomaly that appears to span most of East Africa and western Arabia.

Present day geodynamics in Iceland monitored by a permanent network of continuous GPS stations

NASA Astrophysics Data System (ADS)

Völksen, Christof; Árnadóttir, Thóra; Geirsson, Halldór; Valsson, Guðmundur

2009-12-01

Iceland is located on the Mid-Atlantic Ridge and thereby offers a rare opportunity to study crustal movements at a divergent plate boundary. Iceland is not only characterized by the divergence of the Eurasian and North American Plates, as several active volcanoes are located on the island. Moderate size earthquakes occur in the transform zones, causing measurable crustal deformation. In 1999 the installation of a permanent network of continuous GPS stations (ISGPS) was initiated in order to observe deformation due to unrest in the Hengill volcanic system and at the Katla volcano. The ISGPS network has been enlarged over the years and consists today of more than 25 CGPS stations. Most of the stations are located along the plate boundary, where most of the active deformation takes place. Uplift due to post-glacial rebound due to the melting of the largest glacier in Europe, Vatnajökull, is also detected by the ISGPS network. This study presents results from analysis of 9 years of data from the ISGPS network, in the global reference frame PDR05, which has been evaluated by the Potsdam-Dresden-Reprocessing group with reprocessed GPS data only. We thus determine subsidence or land uplift in a global frame. The horizontal station velocities clearly show spreading across the plate boundary of about 20 mm/a. Stations in the vicinity of the glacier Vatnajökull indicate uplift in the range of 12 mm/a, while a station in the central part of Iceland shows uplift rates of about 25 mm/a. Tide gauge readings in Reykjavik and current subsidence rates observed with CGPS agree also quite well.

Anomalous Accretionary Margin Topography Formed By Repeated Earthquakes

NASA Astrophysics Data System (ADS)

Furlong, Kevin P.

2014-05-01

It has long been recognized that accretionary margins of major subduction zones undergo substantial deformation. However even with the large amounts of shortening accommodated within the margin, for most subduction zones, there is an extended submarine portion to the accretionary, highly-deformed upper-plate between the trench and the coast. This is a vexing situation since this submarine section typically overlies the actual locked or coupled patch of the plate interface. The result of this is added difficulty in directly observing processes related to the plate interface coupling - such processes as micro-seismicity and the actual patterns of plate coupling. There are a few locations globally in which there are sub-aerially exposed terranes that lie closer to the trench and overlie the inferred coupled or seismogenic portion of the plate interface. Such regions have taken on significance in subduction zone studies as they provide locations to observe the plate interface coupling effects in the near-field. In particular the Pacific coast of Costa Rica provides such a location, and there has been substantial geologic, geophysical, and geodetic research exploiting the positions of these near-trench peninsulas (Nicoya, Osa, and Burica). These sites provide near-field access to plate-interface processes, but whether they represent typical subduction zone behavior remains an open question as the deformational processes or inherited structures that have produced this anomalous topography are not well constrained. Simply put, if the existence of these sub-aerial, near-trench terranes is a result of anomalous behavior on the plate interface (as has been suggested), then their utility in providing high-fidelity near-field insight into the plate interface properties and processes is substantially reduced. Here we propose a new mechanism that could be responsible for the formation of both the Nicoya and Osa Peninsulas in the past, and is currently producing a third peninsula - the Burica Peninsula at the intersection of the Panama fracture zone and the margin. Specifically we propose that the anomalous topography along the Pacific coast of Costa Rica has been produced by repeated, great subduction earthquakes that have ruptured across the boundary separating the Cocos and Nazca plates - the subducted continuation of the Panama fracture zone. The pattern of upper-plate shortening generated by such a process (documented in the 2007 Mw 8.1 Solomon Islands earthquake, which produced co-seismic localized uplift above the subducted transform plate boundary) convolved with the migration history of the Panama triple junction (PTJ) is proposed as the mechanism to produce substantial along-margin, long-lived accretionary margin topography. Specifically we argue that repeated great subduction earthquakes that rupture across fundamental plate boundary structures can produce substantial, long-lived upper plate deformation above the inter-seismically coupled plate interface.

Various methods of determining the natural frequencies and damping of composite cantilever plates. 1. Exact solution for the binomial model of deformation

NASA Astrophysics Data System (ADS)

Skel'chik, V. S.; Ryabov, V. M.

1996-11-01

On the basis of the classical theory of thin anisotropic laminated plates the article analyzes the free vibrations of rectangular cantilever plates made of fibrous composites. The application of Kantorovich's method for the binomial representation of the shape of the elastic surface of a plate yielded for two unknown functions a system of two connected differential equations and the corresponding boundary conditions at the place of constraint and at the free edge. The exact solution for the frequencies and forms of the free vibrations was found with the use of Laplace transformation with respect to the space variable. The magnitudes of several first dimensionless frequencies of the bending and torsional vibrations of the plate were calculated for a wide range of change of two dimensionless complexes, with the dimensions of the plate and the anisotropy of the elastic properties of the material taken into account. The article shows that with torsional vibrations the warping constraint at the fixed end explains the apparent dependence of the shear modulus of the composite on the length of the specimen that had been discovered earlier on in experiments with a torsional pendulum. It examines the interaction and transformation of the second bending mode and of the first torsional mode of the vibrations. It analyzes the asymptotics of the dimensionless frequencies when the length of the plate is increased, and it shows that taking into account the bending-torsion interaction in strongly anisotropic materials type unidirectional carbon reinforced plastic can reduce substantially the frequencies of the bending vibrations but has no effect (within the framework of the binomial model) on the frequencies of the torsional vibrations.

Generic buckling curves for specially orthotropic rectangular plates

NASA Technical Reports Server (NTRS)

Brunnelle, E. J.; Oyibo, G. A.

1983-01-01

Using a double affine transformation, the classical buckling equation for specially orthotropic plates and the corresponding virtual work theorem are presented in a particularly simple fashion. These dual representations are characterized by a single material constant, called the generalized rigidity ratio, whose range is predicted to be the closed interval from 0 to 1 (if this prediction is correct then the numerical results using a ratio greater than 1 in the specially orthotropic plate literature are incorrect); when natural boundary conditions are considered a generalized Poisson's ratio is introduced. Thus the buckling results are valid for any specially orthotropic material; hence the curves presented in the text are generic rather than specific. The solution trends are twofold; the buckling coefficients decrease with decreasing generalized rigidity ratio and, when applicable, they decrease with increasing generalized Poisson's ratio. Since the isotropic plate is one limiting case of the above analysis, it is also true that isotropic buckling coefficients decrease with increasing Poission's ratio.

Aseismic Transform Fault Slip at the Mendocino Triple Junction From Characteristically Repeating Earthquakes

NASA Astrophysics Data System (ADS)

Materna, Kathryn; Taira, Taka'aki; Bürgmann, Roland

2018-01-01

The Mendocino Triple Junction (MTJ), at the northern terminus of the San Andreas Fault system, is an actively deforming plate boundary region with poorly constrained estimates of seismic coupling on most offshore fault surfaces. Characteristically repeating earthquakes provide spatial and temporal descriptions of aseismic creep at the MTJ, including on the oceanic transform Mendocino Fault Zone (MFZ) as it subducts beneath North America. Using a dataset of earthquakes from 2008 to 2017, we find that the easternmost segment of the MFZ displays creep during this period at about 65% of the long-term slip rate. We also find creep at slower rates on the shallower strike-slip interface between the Pacific plate and the North American accretionary wedge, as well as on a fault that accommodates Gorda subplate internal deformation. After a nearby M5.7 earthquake in 2015, we observe a possible decrease in aseismic slip on the near-shore MFZ that lasts from 2015 to at least early 2017.

On the relationship between tectonic plates and thermal mantle plume morphology

NASA Technical Reports Server (NTRS)

Lenardic, A.; Kaula, W. M.

1993-01-01

Models incorporating plate-like behavior, i.e., near uniform surface velocity and deformation concentrated at plate boundaries, into a convective system, heated by a mix of internal and basal heating and allowing for temperature dependent viscosity, were constructed and compared to similar models not possessing plate-like behavior. The simplified numerical models are used to explore how plate-like behavior in a convective system can effect the lower boundary layer from which thermal plumes form. A principal conclusion is that plate-like behavior can significantly increase the temperature drop across the lower thermal boundary layer. This temperature drop affects the morphology of plumes by determining the viscosity drop across the boundary layer. Model results suggest that plumes on planets possessing plate-like behavior, e.g., the Earth, may differ in morphologic type from plumes on planets not possessing plate-like behavior, e.g., Venus and Mars.

Kinematic reconstruction of the Caribbean region since the Early Jurassic

NASA Astrophysics Data System (ADS)

Bochman, Lydian; van Hinsbergen, Douwe; Torsvik, Trond; Spakman, Wim; Pindell, James

2014-05-01

The Caribbean region results from a complex tectonic history governed by the interplay of the North American, South American and (Paleo-)Pacific plates, between which the Caribbean plate evolved since the early Cretaceous. During its entire tectonic evolution, the Caribbean plate was largely surrounded by subduction and transform boundaries, which hampers a quantitative integration into the global circuit of plate motions. In addition, reconstructions of the region have so far not resulted in a first order kinematic description of the main tectonic units in terms of Euler poles and finite rotation angles. Here, we present an updated, quantitatively described kinematic reconstruction of the Caribbean region back to 200 Ma integrated into the global plate circuit, and implemented with GPlates free software. Our analysis of Caribbean tectonic evolution incorporates an extensive literature review. To constrain the Caribbean plate motion between the American continents, we use a novel approach that takes structural geological observations rather than marine magnetic anomalies as prime input, and uses regionally extensive metamorphic and magmatic phenomena such as the Great Arc of the Caribbean, the Caribbean Large Igneous Province (CLIP) and the Caribbean high-pressure belt as correlation markers. The resulting model restores the Caribbean plate back along the Cayman Trough and major strike-slip faults in Guatemala, offshore Nicaragua, offshore Belize and along the Northern Andes towards its position of origin, west of the North and South American continents in early Cretaceous time. We provide the paleomagnetic reference frame for the Caribbean region by rotating the Global Apparent Polar Wander Path into coordinates of the Caribbean plate interior, Cuba, and the Chortis Block. We conclude that a plate kinematic scenario for a Panthalassa/Pacific origin of Caribbean lithosphere leads to a much simpler explanation than a Proto-Caribbean/Atlantic origin. Placing our reconstruction in the most recent mantle reference frames shows that the CLIP erupted 2000-3000 km east of the modern Galápagos hotspot, and may not have been derived from the corresponding mantle plume. Finally, our reconstruction suggests that most if not all modern subduction zones surrounding the Caribbean plate initiated at transform faults, two of these (along the southern Mexican and NW South American margins) evolved diachronously as a result of migrating trench-trench-transform triple junctions.

High resolution reconstructions of Southwest Indian Ridge plate motions during the Neogene: Comparison to GPS estimates and implications for global plate motion estimates

NASA Astrophysics Data System (ADS)

DeMets, C.; Merkouriev, S.; Sauter, D.; Calais, E.

2013-12-01

Plate kinematic data from the slow-spreading Southwest Indian Ridge (SWIR) are the primary source of information about relative movements between Antarctica and Africa over geologic time and are critical for linking the movements of plates in the Atlantic and Indian Ocean basins. We describe the first high-resolution model of SWIR plate kinematics from the present to 20 Ma, consisting of rotations based on 21 magnetic reversals with ~1 million-year spacing. The new rotations, which are derived from 4822 identifications of magnetic reversals C1n to C6no and 6000 crossings of 21 fracture zones and transform faults, describe in detail the ultra-slow motions of the Nubia, Lwandle, and Somalia plates north of the SWIR relative to the Antarctic plate. A search for the Nubia-Lwandle-Antarctic triple junction with all data since C5n.2 (11.0 Ma) gives a best location at the Andrew Bain transform fault (~32E), in accord with previous work. Plate kinematic data from the SWIR east of the Andrew Bain fracture zone support the existence of the previously proposed Lwandle plate at high confidence level. The likely diffuse Lwandle-Somalia plate boundary north of the SWIR is however only loosely constrained to 45E-52E. After calibrating the new rotations for the biasing effects of finite-width magnetic polarity transition zones (i.e. outward displacement), the new rotations reveal that SWIR plate motion has remained steady from the present back to 7.5 Ma, but was modestly faster (~25%) from 19.6 Ma to 7.5 Ma. GPS estimates of present SWIR plate motions based on more than 100 continuous GPS sites on the Antarctic, Nubia, and Somalia plates are remarkably consistent with SWIR velocities determined with the new geological reconstructions. The superb agreement between the two independent plate motion estimates validates both sets of estimates and our calibration for outward displacement. Implications of the new estimates, including evidence for anomalously wide outward displacement across parts of the SWIR, will be discussed

Effect of thermal radiation on laminar boundary layer flow over a permeable flat plate with Newtonian heating

NASA Astrophysics Data System (ADS)

Khairul Anuar Mohamed, Muhammad; Zuki Salleh, Mohd; Noar, Nor Aida Zuraimi Md; Ishak, Anuar

2017-09-01

The laminar boundary layer flow over a permeable flat plat with the presence of thermal radiation and Newtonian heating is numerically studied. The non linear partial differential equations that governed the model are transformed to ordinary differential equations before being solved numerically by Runge-Kutta-Fehlberg (RKF) method using Maple software. The influenced and characteristic of pertinent parameters which are the Prandtl number, the suction/blowing parameter, the thermal radiation parameter and the conjugate parameter are analyzed and discussed. It is found that the presence of thermal radiation and blowing parameter has increased the value of wall temperature. Meanwhile, the trend is contrary with the suction effect.

Water Release from Cold Serpentinized Forearc Mantle During Subduction Associated with Changes in Incoming Oceanic Plate Thermal Structure and Plate Boundary Kinematics: New Insights into Serpentinite Belts and Plate-Boundary Rheology

NASA Astrophysics Data System (ADS)

Kirby, Stephen

2016-04-01

Kirby, Wang, and Brocher (Earth Planets and Space, 2014) recently showed how the change in kinematics of the California margin from subduction motion to continental transform motion with the birth and growth of the San Andreas Fault System (SAFS) beginning at about 33 Ma BP likely led to a warming of the former forearc mantle and the release of water from serpentinized mantle by dehydration and a likely increase in fluid pressures along the SAFS. Such a mantle source of pressurized water gives insights into both the low sliding resistance for the SAFS and the mobilization and ascent of some serpentinized mantle peridotites through the crust. Thermal modeling by others has also shown that changes in the incoming plate age and subduction rate can also lead to warming of the forearc mantle during subduction. This development gives insights into the Mesozoic and Paleogene ages of emplacement of some, but not all, California serpentinites. Recent mineralogical and geochemical observations of serpentinite blocks in serpentinize mélange bodies in the San Francisco Bay Area (Uno and Kirby, 2014 AGU Meeting and Lewis and Kirby, 2015 AGU Meeting) suggest that these rocks sustained multiple stages of serpentinization that are broadly consistent with the model of Kirby et al. (2014). A new development comes from interpretation of investigations in the literature of localized late-stage silica-carbonate-water alteration of serpentinite bodies in California that this alteration occurred largely in Neogene time when the highest rates of water release from the former forearc mantle probably occurred. This presentation also suggests that the occurrence of serpentinite belts emplaced in Cenozoic time during changing plate-boundary kinematics, such as the Cenozoic closing of the Tethys Ocean bordering Eurasia by subduction and collision and arc reversal and decreasing convergence rates under the Greater Antilles and Colombia and New Guinea, may give insights into the serpentinite belts in those regions. The weak rheological behavior of present collisional plate boundaries under high fluid pressures from the mantle also provides possible explanations of the mobility of "tectonic escape" strike-slip faulting in Turkey, Syria, and SE Asia following subduction.

Finite element simulation of piezoelectric transformers.

PubMed

Tsuchiya, T; Kagawa, Y; Wakatsuki, N; Okamura, H

2001-07-01

Piezoelectric transformers are nothing but ultrasonic resonators with two pairs of electrodes provided on the surface of a piezoelectric substrate in which electrical energy is carried in the mechanical form. The input and output electrodes are arranged to provide the impedance transformation, which results in the voltage transformation. As they are operated at a resonance, the electrical equivalent circuit approach has traditionally been developed in a rather empirical way and has been used for analysis and design. The present paper deals with the analysis of the piezoelectric transformers based on the three-dimensional finite element modelling. The PIEZO3D code that we have developed is modified to include the external loading conditions. The finite element approach is now available for a wide variety of the electrical boundary conditions. The equivalent circuit of lumped parameters can also be derived from the finite element method (FEM) solution if required. The simulation of the present transformers is made for the low intensity operation and compared with the experimental results. Demonstration is made for basic Rosen-type transformers in which the longitudinal mode of a plate plays an important role; in which the equivalent circuit of lumped constants has been used. However, there are many modes of vibration associated with the plate, the effect of which cannot always be ignored. In the experiment, the double resonances are sometimes observed in the vicinity of the operating frequency. The simulation demonstrates that this is due to the coupling of the longitudinal mode with the flexural mode. Thus, the simulation provides an invaluable guideline to the transformer design.

Boundary-Layer Bypass Transition Over Large-Scale Bodies

DTIC Science & Technology

2016-12-16

shape of the streamwise velocity profile compared to the flat- plate boundary layer. The research showed that the streamwise wavenumber plays a key role...many works on the suppression of the transitional boundary layer. Most of the results in the literature are for the flat- plate boundary layer but the...behaviour of the velocity and pressure changes with the curvature. This work aims to extend the results of the flat- plate boundary layer to a Rankine

Scalar Casimir densities and forces for parallel plates in cosmic string spacetime

NASA Astrophysics Data System (ADS)

Bezerra de Mello, E. R.; Saharian, A. A.; Abajyan, S. V.

2018-04-01

We analyze the Green function, the Casimir densities and forces associated with a massive scalar quantum field confined between two parallel plates in a higher dimensional cosmic string spacetime. The plates are placed orthogonal to the string, and the field obeys the Robin boundary conditions on them. The boundary-induced contributions are explicitly extracted in the vacuum expectation values (VEVs) of the field squared and of the energy-momentum tensor for both the single plate and two plates geometries. The VEV of the energy-momentum tensor, in additional to the diagonal components, contains an off diagonal component corresponding to the shear stress. The latter vanishes on the plates in special cases of Dirichlet and Neumann boundary conditions. For points outside the string core the topological contributions in the VEVs are finite on the plates. Near the string the VEVs are dominated by the boundary-free part, whereas at large distances the boundary-induced contributions dominate. Due to the nonzero off diagonal component of the vacuum energy-momentum tensor, in addition to the normal component, the Casimir forces have nonzero component parallel to the boundary (shear force). Unlike the problem on the Minkowski bulk, the normal forces acting on the separate plates, in general, do not coincide if the corresponding Robin coefficients are different. Another difference is that in the presence of the cosmic string the Casimir forces for Dirichlet and Neumann boundary conditions differ. For Dirichlet boundary condition the normal Casimir force does not depend on the curvature coupling parameter. This is not the case for other boundary conditions. A new qualitative feature induced by the cosmic string is the appearance of the shear stress acting on the plates. The corresponding force is directed along the radial coordinate and vanishes for Dirichlet and Neumann boundary conditions. Depending on the parameters of the problem, the radial component of the shear force can be either positive or negative.

Seismicity of the Earth 1900-2012 Philippine Sea plate and vicinity

USGS Publications Warehouse

Smoczyk, Gregory M.; Hayes, Gavin P.; Hamburger, Michael W.; Benz, Harley M.; Villaseñor, Antonio; Furlong, Kevin P.

2013-01-01

The complex tectonics surrounding the Philippine Islands are dominated by the interactions of the Pacific, Sunda, and Eurasia plates with the Philippine Sea plate (PSP). The latter is unique because it is almost exclusively surrounded by zones of plate convergence. At its eastern and southeastern edges, the Pacific plate is subducted beneath the PSP at the Izu-Bonin, Mariana, and Yap trenches. Here, the subduction zone exhibits high rates of seismic activity to depths of over 600 km, though no great earthquakes (M>8.0) have been observed, likely because of weak coupling along the plate interface. In the northeast, the PSP subducts beneath Japan and the eastern margin of the Eurasia plate at the Nankai and Ryukyu trenches, extending westward to Taiwan. The Nankai portion of this subduction zone has hosted some of the largest earthquakes along the margins of the PSP, including a pair of Mw8.1 megathrust events in 1944 and 1946. Along its western margin, the convergence of the PSP and the Sunda plate is responsible for a broad and active plate boundary system extending along both sides of the Philippine Islands chain. The region is characterized by opposite-facing subduction systems on the east and west sides of the islands, and the archipelago is cut by a major transform structure: the Philippine Fault. Subduction of the Philippine Sea plate occurs at the eastern margin of the islands along the Philippine Trench and its northern extension, the East Luzon Trough. On the west side of Luzon, the Sunda Plate subducts eastward along a series of trenches, including the Manila Trench in the north, the smaller Negros Trench in the central Philippines, and the Sulu and Cotabato trenches in the south. Twentieth and early twentyfirst century seismic activity along the boundaries of the Philippine Sea plate has produced seven great (M>8.0) earthquakes and 250 large (M>7) events. Among the most destructive events were the 1923 Kanto, the 1948 Fukui, and the 1995 Kobe, Japan, earthquakes; the 1935 and the 1999 Chi-Chi, Taiwan, earthquakes; and the 1976 M7.6 Moro Gulf and 1990 M7.6 Luzon, Philippines, earthquakes.

Mountain building, strike-slip faulting, and landscape evolution in the Marlborough Fault System, NZ: Insights from new low-temperature thermochronology and modeling

NASA Astrophysics Data System (ADS)

Duvall, A. R.; Collett, C.; Flowers, R. M.; Tucker, G. E.; Upton, P.

2016-12-01

The 150 km wide Marlborough Fault System (MFS) and adjacent dextral-reverse Alpine Fault accommodate oblique convergence of the Australian and Pacific plates in a broad transform boundary that extends for much of the South Island New Zealand. Understanding the deformation history of the Marlborough region offers the opportunity to study topographic evolution in a strike-slip setting and a fuller picture of the evolving New Zealand plate boundary as the MFS lies at the transition from oceanic Pacific plate subduction to oblique continental collision. Here we present low-temperature thermochronology from the MFS to place new limits on the timing and style of mountain building. We sampled a range of elevations spanning 2 km within and adjacent to the Kaikoura Mountains, which stand high as topographic anomalies above active strike-slip faults. Young apatite (U-Th)/He ages ( 2-5 Ma) on both sides of range-bounding faults are consistent with regional distributed deformation since the Pliocene initiation of strike-slip faulting. However, large differences in both zircon helium and apatite fission track ages, from Paleogene/Neogene ages within hanging walls to unreset >100 Ma ages in footwalls, indicate an early phase of fault-related vertical exhumation. Thermal modeling using the QTQt program reveals two phases of exhumation within the Kaikoura Ranges: rapid cooling at 15-12 Ma localized to hanging wall rocks and regional rapid cooling reflected in all samples starting at 4-5 Ma. These results and landscape evolution models suggest that, despite the presence of active mountain front faults, much of the topographic relief in this region may predate the onset of strike-slip faulting and that portions of the Marlborough Faults are re-activated thrusts that coincide with the early development of the transpressive plate boundary. Regional exhumation after 5 Ma likely reflects increased proximity to the migrating Pacific plate subduction zone and the buoyant Chatham Rise.

Iberian plate kinematics: A jumping plate boundary between Eurasia and Africa

USGS Publications Warehouse

Srivastava, S.P.; Schouten, Hans; Roest, W.R.; Klitgord, Kim D.; Kovacs, L.C.; Verhoef, J.; Macnab, R.

1990-01-01

THE rotation of Iberia and its relation to the formation of the Pyrenees has been difficult to decipher because of the lack of detailed sea-floor spreading data, although several models have been proposed1-7. Here we use detailed aeromagnetic measurements from the sea floor offshore of the Grand Banks of Newfoundland to show that Iberia moved as part of the African plate from late Cretaceous to mid-Eocene time, with a plate boundary extending westward from the Bay of Biscay. When motion along this boundary ceased, a boundary linking extension in the King's Trough to compression along the Pyrenees came into existence. Finally, since the late Oligocene, Iberia has been part of the Eurasian plate, with the boundary between Eurasia and Africa situated along the Azores-Gibraltar fracture zone.

Structural acoustic control of plates with variable boundary conditions: design methodology.

PubMed

Sprofera, Joseph D; Cabell, Randolph H; Gibbs, Gary P; Clark, Robert L

2007-07-01

A method for optimizing a structural acoustic control system subject to variations in plate boundary conditions is provided. The assumed modes method is used to build a plate model with varying levels of rotational boundary stiffness to simulate the dynamics of a plate with uncertain edge conditions. A transducer placement scoring process, involving Hankel singular values, is combined with a genetic optimization routine to find spatial locations robust to boundary condition variation. Predicted frequency response characteristics are examined, and theoretically optimized results are discussed in relation to the range of boundary conditions investigated. Modeled results indicate that it is possible to minimize the impact of uncertain boundary conditions in active structural acoustic control by optimizing the placement of transducers with respect to those uncertainties.

Unique Outcomes of Internal Heat Generation and Thermal Deposition on Viscous Dissipative Transport of Viscoplastic Fluid over a Riga-Plate

NASA Astrophysics Data System (ADS)

Iqbal, Z.; Azhar, Ehtsham; Mehmood, Zaffar; Maraj, E. N.

2018-01-01

Boundary layer stagnation point flow of Casson fluid over a Riga plate of variable thickness is investigated in present article. Riga plate is an electromagnetic actuator consists of enduring magnets and gyrated aligned array of alternating electrodes mounted on a plane surface. Physical problem is modeled and simplified under appropriate transformations. Effects of thermal radiation and viscous dissipation are incorporated. These differential equations are solved by Keller Box Scheme using MATLAB. Comparison is given with shooting techniques along with Range-Kutta Fehlberg method of order 5. Graphical and tabulated analysis is drawn. The results reveal that Eckert number, radiation and fluid parameters enhance temperature whereas they contribute in lowering rate of heat transfer. The numerical outcomes of present analysis depicts that Keller Box Method is capable and consistent to solve proposed nonlinear problem with high accuracy.

Kinematics and segmentation of the South Shetland Islands-Bransfield basin system, northern Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Taylor, Frederick W.; Bevis, Michael G.; Dalziel, Ian W. D.; Smalley, Robert; Frohlich, Cliff; Kendrick, Eric; Foster, James; Phillips, David; Gudipati, Krishnavikas

2008-04-01

New GPS measurements demonstrate tectonic segmentation of the South Shetland Islands platform, regarded as a microplate separating the Antarctic Peninsula from the oceanic portion of the Antarctic plate. King George, Greenwich, and Livingston islands on the central and largest segment are separating from the Antarctic Peninsula at 7-9 mm/a, moving NNW, roughly perpendicular to the continental margin. Smith and Low islands on the small southwestern segment are moving in the same direction, but at 2.2-3.0 mm/a. The Elephant Island subgroup in the northeast moves at ˜7 mm/a relative to the Peninsula, like the central group, but toward the WNW. This implies that it is presently coupled to the Scotia plate on the northern side of the South Scotia Ridge transform boundary; thus the uplift of these northeasternmost islands may be caused by Scotia-Antarctic plate convergence rather than by subduction of thickened oceanic crust.

An Integrated View of Tectonics in the North Pacific Derived from GPS

NASA Astrophysics Data System (ADS)

Elliott, J.; Freymueller, J.; Marechal, A.; Larsen, C.; Perea Barreto, M. A.

2015-12-01

Textbooks show a simple picture of the tectonics of the North Pacific, with discrete deformation along the boundary between the Pacific and North American plates along the Aleutian megathrust and Fairweather/Queen Charlotte fault system. Reality is much more complex, with a pattern of broadly distributed deformation. This is in part due to a number of studies and initiatives (such as PBO) in recent years that have greatly expanded the density of GPS data throughout the region. We present an overview of the GPS data acquired and various tectonic interpretations developed over the past decade and discuss a current effort to integrate the available data into a regional tectonic model for Alaska and northwestern Canada. Rather than discrete plate boundaries, we observe zones of concentrated deformation where the majority of the relative plate motion is accommodated. Within these zones, there are major fault systems, such as the Fairweather-Queen Charlotte transform and the Aleutian megathrust, where most of the deformation occurs along a main structure, but often motion is instead partitioned across multiple faults, such as the fold-and-thrust belt of the eastern St. Elias orogen. In zones of particular complexity, such as the eastern syntaxis of the St. Elias orogen, the deformation is better described by continuum deformation than localized strain along crustal structures. Strain is transferred far inboard, either by diffuse deformation or along fault system such as the Denali fault, and outboard of the main zones of deformation. The upper plate, if it can be called such, consists of a number of blocks and deforming zones while the lower plate is segmented between the Yakutat block and Pacific plate and is also likely undergoing internal deformation.

Simulating faults and plate boundaries with a transversely isotropic plasticity model

NASA Astrophysics Data System (ADS)

Sharples, W.; Moresi, L. N.; Velic, M.; Jadamec, M. A.; May, D. A.

2016-03-01

In mantle convection simulations, dynamically evolving plate boundaries have, for the most part, been represented using an visco-plastic flow law. These systems develop fine-scale, localized, weak shear band structures which are reminiscent of faults but it is a significant challenge to resolve the large- and the emergent, small-scale-behavior. We address this issue of resolution by taking into account the observation that a rock element with embedded, planar, failure surfaces responds as a non-linear, transversely isotropic material with a weak orientation defined by the plane of the failure surface. This approach partly accounts for the large-scale behavior of fine-scale systems of shear bands which we are not in a position to resolve explicitly. We evaluate the capacity of this continuum approach to model plate boundaries, specifically in the context of subduction models where the plate boundary interface has often been represented as a planar discontinuity. We show that the inclusion of the transversely isotropic plasticity model for the plate boundary promotes asymmetric subduction from initiation. A realistic evolution of the plate boundary interface and associated stresses is crucial to understanding inter-plate coupling, convergent margin driven topography, and earthquakes.

The Effect of MHD on Free Convection with Periodic Temperature and Concentration in the Presence of Thermal Radiation and Chemical Reaction

NASA Astrophysics Data System (ADS)

Zigta, B.; Koya, P. R.

2017-12-01

This paper studies the effect of magneto hydrodynamics on unsteady free convection between a pair of infinite vertical Couette plates. The temperature of the plates and concentration between the plates vary with time. Convection between the plates is considered in the presence of thermal radiation and chemical reaction. The solution is obtained using perturbation techniques. These techniques are used to transform nonlinear coupled partial differential equations to a system of ordinary differential equations. The resulting equations are solved analytically. The solution is expressed in terms of power series with some small parameter. The effect of various parameters, viz., velocity, temperature and concentration, has been discussed. Mat lab code simulation study is carried out to support the theoretical results. The result shows that as the thermal radiation parameter R increases, the temperature decreases near the moving porous plate while it approaches to a zero in the region close to the boundary layer of the stationary plate. Moreover, as the modified Grashof number, i.e., based on concentration difference, increases, the velocity of the fluid flow increases hence the concentration decreases. An increase in both the chemical reaction parameter and Schmidt number results in decreased concentration.

The Role of Rift Obliquity in Formation of the Gulf of California

NASA Astrophysics Data System (ADS)

Bennett, Scott Edmund Kelsey

The Gulf of California illustrates how highly oblique rift geometries, where transform faults are kinematically linked to large-offset normal faults in adjacent pull-apart basins, enhance the ability of continental lithosphere to rupture and, ultimately, hasten the formation of new oceanic basins. The Gulf of California rift has accommodated oblique divergence of the Pacific and North America tectonic plates in northwestern Mexico since Miocene time. Due to its infancy, the rifted margins of the Gulf of California preserve a rare onshore record of early continental break-up processes from which to investigate the role of rift obliquity in strain localization. Using new high-precision paleomagnetic vectors from tectonically stable sites in north-central Baja California, I compile a paleomagnetic transect of Miocene ignimbrites across northern Baja California and Sonora that reveals the timing and distribution of dextral shear associated with inception of this oblique rift. I integrate detailed geologic mapping, basin analysis, and geochronology of pre-rift and syn-rift volcanic units to determine the timing of fault activity on Isla Tiburon, a proximal onshore exposure of the rifted North America margin, adjacent to the axis of the Gulf of California. The onset of strike-slip faulting on Isla Tiburon, ca. 8 - 7 Ma, was synchronous with the onset of transform faulting along a significant length of the nascent plate boundary within the rift. This tectonic transition coincides with a clockwise azimuthal shift in Pacific-North America relative motion that increased rift obliquity. I constrain the earliest marine conditions on southwest Isla Tiburon to ca. 6.4 - 6.0 Ma, coincident with a regional latest Miocene marine incursion in the northern proto-Gulf of California. This event likely flooded a narrow, incipient topographic depression along a ˜650 km-long portion of the latest Miocene plate boundary and corresponds in time and space with formation of a newly-constrained ˜50-100 kilometer-wide transtensional belt of focused strike-slip faulting, basin formation, and rotating crustal blocks. This proto-Gulf of California shear zone, embedded within the wider Mexican Basin and Range extensional province and connected to the San Andreas fault in southern California, hosted subsequent localization of the plate boundary and rupture of the continental lithosphere.

Seismicity of the Earth 1900–2010 Middle East and vicinity

USGS Publications Warehouse

Jenkins, Jennifer; Turner, Bethan; Turner, Rebecca; Hayes, Gavin P.; Davies, Sian; Dart, Richard L.; Tarr, Arthur C.; Villaseñor, Antonio; Benz, Harley M.

2013-01-01

No fewer than four major tectonic plates (Arabia, Eurasia, India, and Africa) and one smaller tectonic block (Anatolia) are responsible for seismicity and tectonics in the Middle East and surrounding region. Geologic development of the region is a consequence of a number of first-order plate tectonic processes that include subduction, large-scale transform faulting, compressional mountain building, and crustal extension. In the east, tectonics are dominated by the collision of the India plate with Eurasia, driving the uplift of the Himalaya, Karakorum, Pamir and Hindu Kush mountain ranges. Beneath the Pamir‒Hindu Kush Mountains of northern Afghanistan, earthquakes occur to depths as great as 200 km as a result of remnant lithospheric subduction. Along the western margin of the India plate, relative motions between India and Eurasia are accommodated by strike-slip, reverse, and oblique-slip faulting, resulting in the complex Sulaiman Range fold and thrust belt, and the major translational Chaman Fault in Afghanistan. Off the south coasts of Pakistan and Iran, the Makran trench is the surface expression of active subduction of the Arabia plate beneath Eurasia. Northwest of this subduction zone, collision between the two plates forms the approximately 1,500-km-long fold and thrust belts of the Zagros Mountains, which cross the whole of western Iran and extend into northeastern Iraq. Tectonics in the eastern Mediterranean region are dominated by complex interactions between the Africa, Arabia, and Eurasia plates, and the Anatolia block. Dominant structures in this region include: the Red Sea Rift, the spreading center between the Africa and Arabia plates; the Dead Sea Transform, a major strike-slip fault, also accommodating Africa-Arabia relative motions; the North Anatolia Fault, a right-lateral strike-slip structure in northern Turkey accommodating much of the translational motion of the Anatolia block westwards with respect to Eurasia and Africa; and the Cyprian Arc, a convergent boundary between the Africa plate to the south, and Anatolia Block to the north.

The geology of the Oceanographer Transform: The ridge-transform intersection

NASA Astrophysics Data System (ADS)

Karson, J. A.; Fox, P. J.; Sloan, H.; Crane, K. T.; Kidd, W. S. F.; Bonatti, E.; Stroup, J. B.; Fornari, D. J.; Elthon, D.; Hamlyn, P.; Casey, J. F.; Gallo, D. G.; Needham, D.; Sartori, R.

1984-06-01

Seven dives in the submersible ALVIN and four deep-towed (ANGUS) camera lowerings have been made at the eastern ridge-transform intersection of the Oceanographer Transform with the axis of the Mid-Atlantic Ridge. These data constrain our understanding of the processes that create and shape the distinctive morphology that is characteristic of slowly-slipping ridge-transform-ridge plate boundaries. Although the geological relationships observed in the rift valley floor in the study area are similar to those reported for the FAMOUS area, we observe a distinct change in the character of the rift valley floor with increasing proximity to the transform. Over a distance of approximately ten kilometers the volcanic constructional terrain becomes increasingly more disrupted by faulting and degraded by mass wasting. Moreover, proximal to the transform boundary, faults with orientations oblique to the trend of the rift valley are recognized. The morphology of the eastern rift valley wall is characterized by inward-facing scarps that are ridge-axis parallel, but the western rift valley wall, adjacent to the active transform zone, is characterized by a complex fault pattern defined by faults exhibiting a wide range of orientations. However, even for transform parallel faults no evidence for strike-slip displacement is observed throughout the study area and evidence for normal (dip-slip) displacement is ubiquitous. Basalts, semi-consolidated sediments (chalks, debris slide deposits) and serpentinized ultramafic rocks are recovered from localities within or proximal to the rift valley. The axis of accretion-principal transform displacement zone intersection is not clearly established, but appears to be located along the E-W trending, southern flank of the deep nodal basin that defines the intersection of the transform valley with the rift floor.

Geological process of the slow earthquakes -A hypothesis from an ancient plate boundary fault rock

NASA Astrophysics Data System (ADS)

Kitamura, Y.; Kimura, G.; Kawabata, K.

2012-12-01

We present an integrated model of the deformation along the subduction plate boundary from the trench to the seismogenic zone. Over years of field based research in the Shimanto Belt accretionary complex, southwest Japan, yielded breaking-through discoveries on plate boundary processes, for example, the first finding of pseudotachylyte in the accretionary prism (Ikesawa et al., 2003). Our aim here is to unveil the geological aspects of slow earthquakes and the related plate boundary processes. Studied tectonic mélanges in the Shimanto Belt are regarded as fossils of plate boundary fault zone in subduction zone. We traced material from different depths along subduction channel using samples from on-land outcrops and ocean drilling cores. As a result, a series of progressive deformation down to the down-dip limit of the seismogenic zone was revealed. Detailed geological survey and structural analyses enabled us to separate superimposed deformation events during subduction. Material involved in the plate boundary deformation is mainly an alternation of sand and mud. As they have different competency and are suffered by simple shear stress field, sandstones break apart in flowing mudstones. We distinguished several stages of these deformations in sandstones and recognized progress in the intensity of deformation with increment of underthrusting. It is also known that the studied Mugi mélange bears pseudotachylyte in its upper bounding fault. Our conclusion illustrates that the subduction channel around the depth of the seismogenic zone forms a thick plate boundary fault zone, where there is a clear segregation in deformation style: a fast and episodic slip at the upper boundary fault and a slow and continuous deformation within the zone. The former fast deformation corresponds to the plate boundary earthquakes and the latter to the slow earthquakes. We further examined numerically whether this plate boundary fault rock is capable of releasing seismic moment enough to fit the observed slow earthquakes. The shallow very low frequent earthquakes (VLFs) are chosen to be modeled and our estimation satisfies the natural data. We emphasize that the plate boundary is not a plane but a zone. Geological setting is a clue for differentiating slow and normal earthquakes. We propose to focus on the three-dimensional fault zone comprising numbers of microfaults as the source of slow earthquakes instead of planar plate boundary. Our results also make an impact on the study of seismic energy balance because we show a possibility to give an absolute value of them from geological approach, which could not have been achieved with seismology.

Block modeling of crustal deformation in Tierra del Fuego from GNSS velocities

NASA Astrophysics Data System (ADS)

Mendoza, L.; Richter, A.; Fritsche, M.; Hormaechea, J. L.; Perdomo, R.; Dietrich, R.

2015-05-01

The Tierra del Fuego (TDF) main island is divided by a major transform boundary between the South America and Scotia tectonic plates. Using a block model, we infer slip rates, locking depths and inclinations of active faults in TDF from inversion of site velocities derived from Global Navigation Satellite System observations. We use interseismic velocities from 48 sites, obtained from field measurements spanning 20 years. Euler vectors consistent with a simple seismic cycle are estimated for each block. In addition, we introduce far-field information into the modeling by applying constraints on Euler vectors of major tectonic plates. The difference between model and observed surface deformation near the Magallanes Fagnano Fault System (MFS) is reduced by considering finite dip in the forward model. For this tectonic boundary global plate circuits models predict relative movements between 7 and 9 mm yr- 1, while our regional model indicates that a strike-slip rate of 5.9 ± 0.2 mm yr- 1 is accommodated across the MFS. Our results indicate faults dipping 66- 4+ 6° southward, locked to a depth of 11- 5+ 5 km, which are consistent with geological models for the MFS. However, normal slip also dominates the fault perpendicular motion throughout the eastern MFS, with a maximum rate along the Fagnano Lake.

Global plate motion frames: Toward a unified model

NASA Astrophysics Data System (ADS)

Torsvik, Trond H.; Müller, R. Dietmar; van der Voo, Rob; Steinberger, Bernhard; Gaina, Carmen

2008-09-01

Plate tectonics constitutes our primary framework for understanding how the Earth works over geological timescales. High-resolution mapping of relative plate motions based on marine geophysical data has followed the discovery of geomagnetic reversals, mid-ocean ridges, transform faults, and seafloor spreading, cementing the plate tectonic paradigm. However, so-called "absolute plate motions," describing how the fragments of the outer shell of the Earth have moved relative to a reference system such as the Earth's mantle, are still poorly understood. Accurate absolute plate motion models are essential surface boundary conditions for mantle convection models as well as for understanding past ocean circulation and climate as continent-ocean distributions change with time. A fundamental problem with deciphering absolute plate motions is that the Earth's rotation axis and the averaged magnetic dipole axis are not necessarily fixed to the mantle reference system. Absolute plate motion models based on volcanic hot spot tracks are largely confined to the last 130 Ma and ideally would require knowledge about the motions within the convecting mantle. In contrast, models based on paleomagnetic data reflect plate motion relative to the magnetic dipole axis for most of Earth's history but cannot provide paleolongitudes because of the axial symmetry of the Earth's magnetic dipole field. We analyze four different reference frames (paleomagnetic, African fixed hot spot, African moving hot spot, and global moving hot spot), discuss their uncertainties, and develop a unifying approach for connecting a hot spot track system and a paleomagnetic absolute plate reference system into a "hybrid" model for the time period from the assembly of Pangea (˜320 Ma) to the present. For the last 100 Ma we use a moving hot spot reference frame that takes mantle convection into account, and we connect this to a pre-100 Ma global paleomagnetic frame adjusted 5° in longitude to smooth the reference frame transition. Using plate driving force arguments and the mapping of reconstructed large igneous provinces to core-mantle boundary topography, we argue that continental paleolongitudes can be constrained with reasonable confidence.

Sequence stratigraphy, tectonics and hydrocarbon trap geometries of Middle Tertiary strata in the southern San Joaquin Basin, California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Phillips, S.; Hewlett, J.S.; Bazeley, W.J.M.

1996-01-01

Tectonic evolution of the southern San Joaquin basin exerted a fundamental control on Cenozoic sequence boundary development, reservoir, source and seal facies distribution, and hydrocarbon trap development. Spatial and temporal variations in Tertiary sequence architecture across the basin reflect differences in eastside versus westside basin-margin geometries and deformation histories. Deposition of Tertiary sequences initiated in a forearc basin setting, bounded on the east by a ramp-margin adjacent to the eroded Sierran arc complex and on the west by the imbricated accretionary wedge of the Coast Ranges thrust. The major stages of Cenozoic basin evolution are: (1) Episodic compressional folding andmore » thrusting associated with oblique convergence of the Farallon and North American plates (Late Cretaceous to Oligocene), (2) localized folding and onset of basin subsidence related to Pacific Plate reorganization, microplate formation and rotation (Oligocene to Early Miocene), (3) transtensional faulting, folding basin subsidence associated with initiation of the San Andreas transform and continued microplate rotation (Micocene to Pliocene), and (4) compressional folding, extensional and strike- slip faulting related to evolution of the Pacific-North American transform boundary (Plio- Pleistocene). Complex stratigraphic relationships within Eocene to Middle Miocene rocks provide examples of tectonic influences on sequence architecture. These include development of: (1) Tectonically enhanced sequence boundaries (Early Eocene base Domengine unconformity) and local mid-sequence angular unconformities, (2) westside-derived syntectonic [open quotes]lowstand[close quotes] systems (Yokut/Turitella Silt wedge and Leda Sand/Cymric/Salt Creek wedge), (3) regional seals associated with subsidence-related transgressions (Round Mountain Silt), and (4) combination traps formed by structural inversion of distal lowstand delta reservoirs (e.g. Coalinga East Extension field).« less

Sequence stratigraphy, tectonics and hydrocarbon trap geometries of Middle Tertiary strata in the southern San Joaquin Basin, California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Phillips, S.; Hewlett, J.S.; Bazeley, W.J.M.

1996-12-31

Tectonic evolution of the southern San Joaquin basin exerted a fundamental control on Cenozoic sequence boundary development, reservoir, source and seal facies distribution, and hydrocarbon trap development. Spatial and temporal variations in Tertiary sequence architecture across the basin reflect differences in eastside versus westside basin-margin geometries and deformation histories. Deposition of Tertiary sequences initiated in a forearc basin setting, bounded on the east by a ramp-margin adjacent to the eroded Sierran arc complex and on the west by the imbricated accretionary wedge of the Coast Ranges thrust. The major stages of Cenozoic basin evolution are: (1) Episodic compressional folding andmore » thrusting associated with oblique convergence of the Farallon and North American plates (Late Cretaceous to Oligocene), (2) localized folding and onset of basin subsidence related to Pacific Plate reorganization, microplate formation and rotation (Oligocene to Early Miocene), (3) transtensional faulting, folding basin subsidence associated with initiation of the San Andreas transform and continued microplate rotation (Micocene to Pliocene), and (4) compressional folding, extensional and strike- slip faulting related to evolution of the Pacific-North American transform boundary (Plio- Pleistocene). Complex stratigraphic relationships within Eocene to Middle Miocene rocks provide examples of tectonic influences on sequence architecture. These include development of: (1) Tectonically enhanced sequence boundaries (Early Eocene base Domengine unconformity) and local mid-sequence angular unconformities, (2) westside-derived syntectonic {open_quotes}lowstand{close_quotes} systems (Yokut/Turitella Silt wedge and Leda Sand/Cymric/Salt Creek wedge), (3) regional seals associated with subsidence-related transgressions (Round Mountain Silt), and (4) combination traps formed by structural inversion of distal lowstand delta reservoirs (e.g. Coalinga East Extension field).« less

Elastostatic stress analysis of orthotropic rectangular center-cracked plates

NASA Technical Reports Server (NTRS)

Gyekenyesi, G. S.; Mendelson, A.

1972-01-01

A mapping-collocation method was developed for the elastostatic stress analysis of finite, anisotropic plates with centrally located traction-free cracks. The method essentially consists of mapping the crack into the unit circle and satisfying the crack boundary conditions exactly with the help of Muskhelishvili's function extension concept. The conditions on the outer boundary are satisfied approximately by applying the method of least-squares boundary collocation. A parametric study of finite-plate stress intensity factors, employing this mapping-collocation method, is presented. It shows the effects of varying material properties, orientation angle, and crack-length-to-plate-width and plate-height-to-plate-width ratios for rectangular orthotropic plates under constant tensile and shear loads.

Global continental and ocean basin reconstructions since 200 Ma

NASA Astrophysics Data System (ADS)

Seton, M.; Müller, R. D.; Zahirovic, S.; Gaina, C.; Torsvik, T.; Shephard, G.; Talsma, A.; Gurnis, M.; Turner, M.; Maus, S.; Chandler, M.

2012-07-01

Global plate motion models provide a spatial and temporal framework for geological data and have been effective tools for exploring processes occurring at the earth's surface. However, published models either have insufficient temporal coverage or fail to treat tectonic plates in a self-consistent manner. They usually consider the motions of selected features attached to tectonic plates, such as continents, but generally do not explicitly account for the continuous evolution of plate boundaries through time. In order to explore the coupling between the surface and mantle, plate models are required that extend over at least a few hundred million years and treat plates as dynamic features with dynamically evolving plate boundaries. We have constructed a new type of global plate motion model consisting of a set of continuously-closing topological plate polygons with associated plate boundaries and plate velocities since the break-up of the supercontinent Pangea. Our model is underpinned by plate motions derived from reconstructing the seafloor-spreading history of the ocean basins and motions of the continents and utilizes a hybrid absolute reference frame, based on a moving hotspot model for the last 100 Ma, and a true-polar wander corrected paleomagnetic model for 200 to 100 Ma. Detailed regional geological and geophysical observations constrain plate boundary inception or cessation, and time-dependent geometry. Although our plate model is primarily designed as a reference model for a new generation of geodynamic studies by providing the surface boundary conditions for the deep earth, it is also useful for studies in disparate fields when a framework is needed for analyzing and interpreting spatio-temporal data.

Porous and Microporous Honeycomb Composites as Potential Boundary-Layer Bleed Materials

NASA Technical Reports Server (NTRS)

Davis, D. O.; Willis, B. P.; Schoenenberger, M.

1997-01-01

Results of an experimental investigation are presented in which the use of porous and microporous honeycomb composite materials is evaluated as an alternate to perforated solid plates for boundary-layer bleed in supersonic aircraft inlets. The terms "porous" and "microporous," respectively, refer to bleed orifice diameters roughly equal to and much less than the displacement thickness of the approach boundary-layer. A Baseline porous solid plate, two porous honeycomb, and three microporous honeycomb configurations are evaluated. The performance of the plates is characterized by the flow coefficient and relative change in boundary-layer profile parameters across the bleed region. The tests were conducted at Mach numbers of 1.27 and 1.98. The results show the porous honeycomb is not as efficient at removing mass compared to the baseline. The microporous plates were about equal to the baseline with one plate demonstrating a significantly higher efficiency. The microporous plates produced significantly fuller boundary-layer profiles downstream of the bleed region for a given mass flow removal rate than either the baseline or the porous honeycomb plates.

Oblique Collision of the Leeward Antilles, Offshore Venezuela: Linking Onshore and Offshore Data from BOLIVAR

NASA Astrophysics Data System (ADS)

Beardsley, A. G.; Avé Lallemant, H. G.; Levander, A.; Clark, S. A.

2006-12-01

The kinematic history of the Leeward Antilles (offshore Venezuela) can be characterized with the integration of onshore outcrop data and offshore seismic reflection data. Deformation structures and seismic interpretation show that oblique convergence and wrench tectonics have controlled the diachronous deformation identified along the Caribbean - South America plate boundary. Field studies of structural features in outcrop indicate one generation of ductile deformation (D1) structures and three generations of brittle deformation (F1 - F3) structures. The earliest deformation (D1/F1) began ~ 110 Ma with oblique convergence between the Caribbean plate and South American plate. The second generation of deformation (F2) structures initiated in the Eocene with the extensive development of strike-slip fault systems along the diffuse plate boundary and the onset of wrench tectonics within a large-scale releasing bend. The most recent deformation (F3) has been observed in the west since the Miocene where continued dextral strike-slip motion has led to the development of a major restraining bend between the Caribbean plate transform fault and the Oca - San Sebastian - El Pilar fault system. Deformation since the late Cretaceous has been accompanied by a total of 135° clockwise rotation. Interpretation of 2D marine reflection data indicates similar onshore and offshore deformation trends. Seismic lines that approximately parallel the coastline (NW-SE striking) show syndepositional normal faulting during F1/F2 and thrust faulting associated with F3. On seismic lines striking NNE-SSW, we interpret inversion of F2 normal faults with recent F3 deformation. We also observe both normal and thrust faults related to F3. The thick sequence of recent basin sedimentation (Miocene - Recent), interpreted from the seismic data, supports the ongoing uplift and erosion of the islands; as suggested by fluid inclusion analysis. Overall, there appears to be a strong correlation between onshore micro- and mesoscopic deformational structures and offshore macro-scale structural features seen in the reflection data. The agreement of features supports our regional deformation and rotation model along the Caribbean - South America obliquely convergent plate boundary.

Lectures on the Numerical Solution of Partial Differential Equations.

DTIC Science & Technology

1981-12-01

2 can be treated similarly. By a translation and a rotation, we can transform it to the do- main 2 : -45 ° ( 9 225 ° . It is a good exercise to ...of boundary conditions along the lateral surface does not naturally give rise to a two-dimensional plate model. I According to the Rivlin-Erzcksen...series (3.17). In the sequel, we shall be concerned with the computation of the first term (u,o) which, according to the above considerations, should

Analysis of turbulent free-convection boundary layer on flat plate

NASA Technical Reports Server (NTRS)

Eckert, E R G; Jackson, Thomas W

1950-01-01

A calculation was made for the flow and heat transfer in the turbulent free-convection boundary layer on a vertical flat plate. Formulas for the heat-transfer coefficient, boundary layer thickness, and the maximum velocity in the boundary layer were obtained.

An exact solution on unsteady MHD free convection chemically reacting silver nanofluid flow past an exponentially accelerated vertical plate through porous medium

NASA Astrophysics Data System (ADS)

Kumaresan, E.; Vijaya Kumar, A. G.; Rushi Kumar, B.

2017-11-01

This article studies, an exact solution of unsteady MHD free convection boundary-layer flow of a silver nanofluid past an exponentially accelerated moving vertical plate through aporous medium in the presence of thermal radiation, transverse applied amagnetic field, radiation absorption and Heat generation or absorption with chemical reaction are investigated theoretically. We consider nanofluids contain spherical shaped nanoparticle of silverwith a nanoparticle volume concentration range smaller than or equal to 0.04. This phenomenon is modeled in the form of partial differential equations with initial boundary conditions. Some suitable dimensional variables are introduced. The corresponding dimensionless equations with boundary conditions are solved by using Laplace transform technique. The exact solutions for velocity, energy, and species are obtained, also the corresponding numerical values of nanofluid velocity, temperature and concentration profiles are represented graphically. The expressions for skin friction coefficient, the rate of heat transfer and mass transfer are derived. The present study finds applications involving heat transfer, enhancement of thermal conductivity and other applications like transportation, industrial cooling applications, heating buildings and reducing pollution, energy applications and solar absorption. The effect of heat transfer is found to be more pronounced in a silver-water nanofluid than in the other nanofluids.

New evidence on the accurate displacement along the Arava/Araba segment of the Dead Sea Transform

NASA Astrophysics Data System (ADS)

Beyth, M.; Sagy, A.; Hajazi, H.; Alkhraisha, S.; Mushkin, A.; Ginat, H.

2018-06-01

The sinistral displacement along the Dead Sea Transform (DST), the plate boundary between the African and the Arabian plates, south of the Dead Sea basin, was previously attributed to two main fault zones: the Arava/Araba or Dead Sea fault and the Feinan or Al Quwayra fault zone. This was based on similarities of features on either side of the Araba Valley. In particular, the Timna and the Feinan copper mines, located north of the Themed and Dana faults, and the onlap of the Cambrian formations southward onto the Amram rhyolite and Ahyamir volcanics. To these we add a more accurate offset indicator in the form of an offset Early Cambrian (532 Ma) dolerite dyke previously mapped in Mount Amram (Israel) on the African plate and recently discovered across the Araba Valley in Jabal Sumr al Tayyiba (southwest Jordan) on the Arabian plate. This dolerite dyke is 20 m thick, strikes N50°E and is the only dyke intruding the Jabal Sumr al Tayyiba pink rhyolite flows of the Ahyamir Volcanics. Geochemical and geochronological correlations between the Jabal Sumr al Tayyiba dolerite dyke and the Mount Amram dolerite dyke demonstrate 85 km of sinistral offset across the Arava/Araba fault. Our results also suggest approximately 109 km of combined sinistral displacement across the Arava/Araba and Feinan faults based on petrological correlations between the Timna and Jabal Hanna igneous complexes on the African and Arabian plates, respectively. This constrains the total sinistral displacement of the Feinan fault and its accessory faults to be 24 km.

New evidence on the accurate displacement along the Arava/Araba segment of the Dead Sea Transform

NASA Astrophysics Data System (ADS)

Beyth, M.; Sagy, A.; Hajazi, H.; Alkhraisha, S.; Mushkin, A.; Ginat, H.

2017-11-01

The sinistral displacement along the Dead Sea Transform (DST), the plate boundary between the African and the Arabian plates, south of the Dead Sea basin, was previously attributed to two main fault zones: the Arava/Araba or Dead Sea fault and the Feinan or Al Quwayra fault zone. This was based on similarities of features on either side of the Araba Valley. In particular, the Timna and the Feinan copper mines, located north of the Themed and Dana faults, and the onlap of the Cambrian formations southward onto the Amram rhyolite and Ahyamir volcanics. To these we add a more accurate offset indicator in the form of an offset Early Cambrian (532 Ma) dolerite dyke previously mapped in Mount Amram (Israel) on the African plate and recently discovered across the Araba Valley in Jabal Sumr al Tayyiba (southwest Jordan) on the Arabian plate. This dolerite dyke is 20 m thick, strikes N50°E and is the only dyke intruding the Jabal Sumr al Tayyiba pink rhyolite flows of the Ahyamir Volcanics. Geochemical and geochronological correlations between the Jabal Sumr al Tayyiba dolerite dyke and the Mount Amram dolerite dyke demonstrate 85 km of sinistral offset across the Arava/Araba fault. Our results also suggest approximately 109 km of combined sinistral displacement across the Arava/Araba and Feinan faults based on petrological correlations between the Timna and Jabal Hanna igneous complexes on the African and Arabian plates, respectively. This constrains the total sinistral displacement of the Feinan fault and its accessory faults to be 24 km.

Searching for Hysteresis in Models of Mantle Convection with Grain-Damage

NASA Astrophysics Data System (ADS)

Lamichhane, R.; Foley, B. J.

2017-12-01

The mode of surface tectonics on terrestrial planets is determined by whether mantle convective forces are capable of forming weak zones of localized deformation in the lithosphere, which act as plate boundaries. If plate boundaries can form then a plate tectonic mode develops, and if not convection will be in the stagnant lid regime. Episodic subduction or sluggish lid convection are also possible in between the nominal plate tectonic and stagnant lid regimes. Plate boundary formation is largely a function of the state of the mantle, e.g. mantle temperature or surface temperature, and how these conditions influence both mantle convection and the mantle rheology's propensity for forming weak, localized plate boundaries. However, a planet's tectonic mode also influences whether plate boundaries can form, as the driving forces for plate boundary formation (e.g. stress and viscous dissipation) are different in a plate tectonic versus stagnant lid regime. As a result, tectonic mode can display hysteresis, where convection under otherwise identical conditions can reach different final states as a result of the initial regime of convection. Previous work has explored this effect in pseudoplastic models, finding that it is more difficult to initiate plate tectonics starting from a stagnant lid state than it is to sustain plate tectonics when already in a mobile lid regime, because convective stresses in the lithosphere are lower in a stagnant lid regime than in a plate tectonic regime. However, whether and to what extent such hysteresis is displayed when alternative rheological models for lithospheric shear localization are used is unknown. In particular, grainsize reduction is commonly hypothesized to be a primary cause of shear localization and plate boundary formation. We use new models of mantle convection with grain-size evolution to determine how the initial mode of surface tectonics influences the final convective regime reached when convection reaches statistical steady-state. Scaling analysis is performed to quantify how subduction initiation from a stagnant lid differs from sustaining subduction in a mobile lid. The implications of our results for the evolution of the mode of surface tectonics on terrestrial planets will also be discussed.

Effects of boundary layer refraction and fuselage scattering on fuselage surface noise from advanced turboprop propellers

NASA Technical Reports Server (NTRS)

Mcaninch, G. L.; Rawls, J. W., Jr.

1984-01-01

An acoustic disturbance's propagation through a boundary layer is discussed with a view to the analysis of the acoustic field generated by a propfan rotor incident to the fuselage of an aircraft. Applying the parallel flow assumption, the resulting partial differential equations are reduced to an ordinary acoustic pressure differential equation by means of the Fourier transform. The methods used for the solution of this equation include those of Frobenius and of analytic continuation; both yield exact solutions in series form. Two models of the aircraft fuselage-boundary layer system are considered, in the first of which the fuselage is replaced by a flat plate and the acoustic field is assumed to be two-dimensional, while in the second the fuselage is a cylinder in a fully three-dimensional acoustic field. It is shown that the boundary layer correction improves theory-data comparisons over simple application of a pressure-doubling rule at the fuselage.

Inverse methods-based estimation of plate coupling in a plate motion model governed by mantle flow

NASA Astrophysics Data System (ADS)

Ratnaswamy, V.; Stadler, G.; Gurnis, M.

2013-12-01

Plate motion is primarily controlled by buoyancy (slab pull) which occurs at convergent plate margins where oceanic plates undergo deformation near the seismogenic zone. Yielding within subducting plates, lateral variations in viscosity, and the strength of seismic coupling between plate margins likely have an important control on plate motion. Here, we wish to infer the inter-plate coupling for different subduction zones, and develop a method for inferring it as a PDE-constrained optimization problem, where the cost functional is the misfit in plate velocities and is constrained by the nonlinear Stokes equation. The inverse models have well resolved slabs, plates, and plate margins in addition to a power law rheology with yielding in the upper mantle. Additionally, a Newton method is used to solve the nonlinear Stokes equation with viscosity bounds. We infer plate boundary strength using an inexact Gauss-Newton method with line search for backtracking. Each inverse model is applied to two simple 2-D scenarios (each with three subduction zones), one with back-arc spreading and one without. For each case we examine the sensitivity of the inversion to the amount of surface velocity used: 1) full surface velocity data and 2) surface velocity data simplified using a single scalar average (2-D equivalent to an Euler pole) for each plate. We can recover plate boundary strength in each case, even in the presence of highly nonlinear flow with extreme variations in viscosity. Additionally, we ascribe an uncertainty in each plate's velocity and perform an uncertainty quantification (UQ) through the Hessian of the misfit in plate velocities. We find that as plate boundaries become strongly coupled, the uncertainty in the inferred plate boundary strength decreases. For very weak, uncoupled subduction zones, the uncertainty of inferred plate margin strength increases since there is little sensitivity between plate margin strength and plate velocity. This result is significant because it implies we can infer which plate boundaries are more coupled (seismically) for a realistic dynamic model of plates and mantle flow.

Plume-induced subduction initiation at the Cretaceous India-Arabia transform plate boundary: paleomagnetic constraints from the Semail ophiolite, Oman

NASA Astrophysics Data System (ADS)

Van Hinsbergen, D. J. J.; Maffione, M.; Koornneef, L.; Guilmette, C.

2016-12-01

The Neotethyan realm hosts a prominent belt of Cretaceous supra-subduction zone ophiolites from Turkey and Cyprus in the west, to Oman in the east. Associated crustal and metamorphic sole ages tightly cluster at 95-90 Ma, interpreted to shortly post-date subduction initiation in an intra-oceanic setting along transform faults or ridge segments (or ridge-parallel oceanic detachments). This subduction episode ended when the Arabian-African continental lithosphere arrived in the trench in the late Cretaceous and the leading edge of the overriding oceanic lithosphere obducted as ophiolites, including the famous Semail ophiolite of Oman. This catastrophic subduction initiation phase is assumed to be as response to some far-field trigger. Here, we analyzed whether the Semail ophiolite was generated at an E-W trending Neotethyan ridge or at a N-S trending transform. Therefore we paleomagnetically analyzed 10 localities in sheeted dyke sections of the Semail ophiolite that trend parallel to the obduction front of the ophiolite taken to reflect the paleo-trench. We demonstrate that the sheeted dyke sections, and thus also the trench, had an initial N-S strike, indicating that subduction below the Semail ophiolite probably initiated along a N-S striking transform plate boundary between the Indian and Arabian plate rather than at a Neotethyan mid-ocean ridge. Sometime before 83 Ma, India broke away from Madagascar, and underwent a counterclockwise rotation relative to Africa/Arabia around an Euler pole just north of Madagascar, likely triggered by the arrival of the Morondova mantle plume, the associated large igneous province formed since at least 91 Ma. Numerical models have shown that plume push was a likely driver for the inception of India-Madagascar spreading and associated Indian rotation. North of the associated Euler pole, E-W convergence India-Arabia must have occurred during India-Madagascar break-up. This has already been related to 96-90 Ma subduction initiation below the Waziristan ophiolite of Pakistan. Our new results suggest that subduction initiation below the Semail ophiolite is directly related to this plume-triggered break-up. We speculate that also the synchronous subduction initiation farther west in the Neotethys, towards Cyprus and Turkey, may have been triggered by this mechanism.

Finite-Difference Solutions for Compressible Laminar Boundary-Layer Flows of a Dusty Gas over a Semi-Infinite Flat Plate.

DTIC Science & Technology

1986-08-01

AD-A174 952 FINITE - DIFFERENCE SOLUTIONS FOR CONPRESSIBLE LANINAR 1/2 BOUNDARY-LAYER FLOUS (U) TORONTO UNIV DOWNSVIEW (ONTARIO) INST FOR AEROSPACE...dilute dusty gas over a semi-infinite flat plate. Details are given of the impliit finite , difference schemes as well as the boundary conditions... FINITE - DIFFERENCE SOLUTIONS FOR COMPRESSIBLE LAMINAR BOUNDARY-LAYER FLOWS OF A DUSTY GAS OVER A SEMI-INFINITE FLAT PLATE by B. Y. Wang and I. I

Investigation of 3D Shock-Boundary Layer Interaction: A Combined Approach using Experiments, Numerical Simulations and Stability Analysis

DTIC Science & Technology

2015-12-02

layer , the non-reflecting boundary condition suggested by Poinsot and Lele is adopted.38 On the flat – plate surface, the no-penetration (v = 0) and the no...generator plate is emulated to create an oblique shock that impinges on the boundary layer causing separation. This is similar to the experimental...without SBLI and with SBLI. To calculate the steady flat – plate solution with no shock, a characteristic boundary condition according to Harris is used.39

Earthquakes along the Azores-Iberia plate boundary revisited

NASA Astrophysics Data System (ADS)

Batlló, Josep; Matos, Catarina; Torres, Ricardo; Cruz, Jorge; Custódio, Susana

2017-04-01

The plate boundary that separates the Eurasian and African plates between the Azores triple junction and Gibraltar has unleashed some of the highest magnitude earthquakes in Europe in the historical and instrumental periods, including the 1755 great Lisbon earthquake with an estimated magnitude of M8.5-8.7, a M8.3 earthquake in 1941 in a transform oceanic fault, a M8.1 fault in 1975 in an oceanic intraplate domain, and a M7.9 earthquake in 1969 offshore SW Portugal. The plate boundary evolves from a divergent boundary in the east - the Azores domain - through a strike-slip domain at the center - the Gloria fault domain - to an oblique convergence domain in the west - west Iberia and its oceanic margin. A proper mapping of the seismicity along this plate boundary is key to better understanding it. Prior to the early eighties, many earthquakes with epicentre in the Atlantic and even in mainland Portugal were undetected or not located instrumentally. However knowledge of the occurrence and location of earthquakes prior to this period is critical to understanding the seismicity of the region and for the assessment of seismic hazard and risk. The relocation of events recorded instrumentally until 1960 is particularly difficult due to the poor sensitivity of the seismographs, few available stations, incompleteness of the reports and lack of accuracy of station chronometers. Thus, different catalogues often provide different locations for the same event, with no information about how they were obtained. On the other hand, there are also conspicuous gaps in the instrumental records of some Portuguese stations. For many earthquakes of the studied period records rely solely on felt effects. In general, a good control on the accuracy or quality of epicenters lacks. Here we present a review of the locations of instrumental earthquakes of the Azores-west Iberia region in the period 1900-1960. In total, we reviewed around 350 earthquakes. More than 160 additional events have been consigned in the resulting catalogue. Earthquakes were re-located using both a 1D velocity structure and a linear inversion procedure (Hypocenter) and using a 3D structure developed for the region and a non-linear inversion algorithm (NonLinLoc). The results are interpreted in light of the most recent knowledge of geological structures, precise earthquake locations obtained for the most recent decades, which identify belts of preferential clustering of earthquakes, focal mechanisms and gravity anomalies.

The major tectonic boundaries of the Northern Red Sea rift, Egypt derived from geophysical data analysis

NASA Astrophysics Data System (ADS)

Saleh, Salah; Pamukçu, Oya; Brimich, Ladislav

2017-09-01

In the present study, we have attempted to map the plate boundary between Arabia and Africa at the Northern Red Sea rift region including the Suez rift, Gulf of Aqaba-Dead Sea transform and southeastern Mediterranean region by using gravity data analysis. In the boundary analysis method which was used; low-pass filtered gravity anomalies of the Northern Red Sea rift region were computed. Different crustal types and thicknesses, sediment thicknesses and different heat flow anomalies were evaluated. According to the results, there are six subzones (crustal blocks) separated from each other by tectonic plate boundaries and/or lineaments. It seems that these tectonic boundaries reveal complex structural lineaments, which are mostly influenced by a predominant set of NNW-SSE to NW-SE trending lineaments bordering the Red Sea and Suez rift regions. On the other side, the E-W and N-S to NNE-SSW trended lineaments bordering the South-eastern Mediterranean, Northern Sinai and Aqaba-Dead Sea transform regions, respectively. The analysis of the low pass filtered Bouguer anomaly maps reveals that the positive regional anomaly over both the Red Sea rift and South-eastern Mediterranean basin subzones are considered to be caused by the high density of the oceanic crust and/or the anomalous upper mantle structures beneath these regions whereas, the broad medium anomalies along the western half of Central Sinai with the Suez rift and the Eastern Desert subzones are attributed to low-density sediments of the Suez rift and/or the thick upper continental crustal thickness below these zones. There are observable negative anomalies over the Northern Arabia subzone, particularly in the areas covered by Cenozoic volcanics. These negative anomalies may be attributed to both the low densities of the surface volcanics and/or to a very thick upper continental crust. On the contrary, the negative anomaly which belongs to the Gulf of Aqaba-Dead Sea transform zone is due to crustal thickening (with limited heat flow values) below this region. Additionally in this study, the crustal thinning was investigated with heat flow, magnetic and free air gravity anomalies in the Northern Red Sea rift region. In fact, the crustal thinning of the study area was also proportional to the regions of observable high heat flow values. Finally, our results were found to be well correlated with the topography, free air, aeromagnetic and heat flow dataset profiles crossing most of the study area.

Using natural laboratories and modeling to decipher lithospheric rheology

NASA Astrophysics Data System (ADS)

Sobolev, Stephan

2013-04-01

Rheology is obviously important for geodynamic modeling but at the same time rheological parameters appear to be least constrained. Laboratory experiments give rather large ranges of rheological parameters and their scaling to nature is not entirely clear. Therefore finding rheological proxies in nature is very important. One way to do that is finding appropriate values of rheological parameter by fitting models to the lithospheric structure in the highly deformed regions where lithospheric structure and geologic evolution is well constrained. Here I will present two examples of such studies at plate boundaries. One case is the Dead Sea Transform (DST) that comprises a boundary between African and Arabian plates. During the last 15- 20 Myr more than 100 km of left lateral transform displacement has been accumulated on the DST and about 10 km thick Dead Sea Basin (DSB) was formed in the central part of the DST. Lithospheric structure and geological evolution of DST and DSB is rather well constrained by a number of interdisciplinary projects including DESERT and DESIRE projects leaded by the GFZ Potsdam. Detailed observations reveal apparently contradictory picture. From one hand widespread igneous activity, especially in the last 5 Myr, thin (60-80 km) lithosphere constrained from seismic data and absence of seismicity below the Moho, seem to be quite natural for this tectonically active plate boundary. However, surface heat flow of less than 50-60mW/m2 and deep seismicity in the lower crust ( deeper than 20 km) reported for this region are apparently inconsistent with the tectonic settings specific for an active continental plate boundary and with the crustal structure of the DSB. To address these inconsistencies which comprise what I call the "DST heat-flow paradox", a 3D numerical thermo-mechanical model was developed operating with non-linear elasto-visco-plastic rheology of the lithosphere. Results of the numerical experiments show that the entire set of observations for the DSB can be explained within the classical pull-apart model assuming that (1) the lithosphere has been thermally eroded at about 20 Ma, just before the active faulting at the DST, and (2) the uppermost mantle in the region have relatively weak rheology consistent with the experimental data for wet olivine or pyroxenite. Another example is modeling of the collision of India and Eurasia in Tibet. Our recent thermo-mechanical model (see abstract by Tympel et al) reproduce well many important features of this orogeny, including observed convergence and distance of underthrusting of Indian lithosphere beneath Tibet, if long-term friction at India-Eurasia interface is about 0.04- 0.05, which is typical for oceanic subduction zones, but is unexpected low for continental setting.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cleveland, K. Michael; VanDeMark, Thomas F.; Ammon, Charles J.

We report that double-difference methods applied to cross-correlation measured Rayleigh wave time shifts are an effective tool to improve epicentroid locations and relative origin time shifts in remote regions. We apply these methods to seismicity offshore of southwestern Canada and the U.S. Pacific Northwest, occurring along the boundaries of the Pacific and Juan de Fuca (including the Explorer Plate and Gorda Block) Plates. The Blanco, Mendocino, Revere-Dellwood, Nootka, and Sovanco fracture zones host the majority of this seismicity, largely consisting of strike-slip earthquakes. The Explorer, Juan de Fuca, and Gorda spreading ridges join these fracture zones and host normal faultingmore » earthquakes. Our results show that at least the moderate-magnitude activity clusters along fault strike, supporting suggestions of large variations in seismic coupling along oceanic transform faults. Our improved relative locations corroborate earlier interpretations of the internal deformation in the Explorer and Gorda Plates. North of the Explorer Plate, improved locations support models that propose northern extension of the Revere-Dellwood fault. Relocations also support interpretations that favor multiple parallel active faults along the Blanco Transform Fault Zone. Seismicity of the western half of the Blanco appears more scattered and less collinear than the eastern half, possibly related to fault maturity. We use azimuthal variations in the Rayleigh wave cross-correlation amplitude to detect and model rupture directivity for a moderate size earthquake along the eastern Blanco Fault. Lastly, the observations constrain the seismogenic zone geometry and suggest a relatively narrow seismogenic zone width of 2 to 4 km.« less

Seismicity of the Indo-Australian/Solomon Sea Plate boundary in the Southeast Papua region

NASA Astrophysics Data System (ADS)

Ripper, I. D.

1982-08-01

Seismicity and earthquake focal mechanism plots of the Southeast Papua and Woodlark Basin region for the period January 1960 to May 1979 show that: (a) the West Woodlark Basin spreading centre extends from the deep West Woodlark Basin, through Dawson Strait into Goodenough Bay, Southeast Papua; (b) a southeast seismic trend in the West Woodlark Basin is associated with a left-lateral transform fault, but a gap exists between this zone and the seismic East Woodlark Basin spreading centre; (c) Southeast Papua Seismicity divides into a shallow earthquake zone in which the earthquakes occur mainly in the northeast side of the Owen Stanley Range, and an intermediate depth southwest dipping Benioff zone which extends almost from Mt. Lamington to Goroka. The Benioff zone indicates the presence of a southwest dipping slab of Solomon Sea Plate beneath the Indo-Australian Plate in the Southeast Papua and Ramu-Markham Valley region. This subduction zone has collided with the New Britain subduction zone of the Solomon Sea Plate along the Ramu-Markham Valley. The Solomon Sea Plate is now hanging suspended in the form of an arch beneath Ramu-Markham Valley, inhibiting further subduction beneath Southeast Papua.

Tectonic Evolution of the Terceira Rift (Azores)

NASA Astrophysics Data System (ADS)

Stratmann, Sjard; Huebscher, Christian; Terrinha, Pedro; Ornelas Marques, Fernando; Weiß, Benedik

2017-04-01

The Azores Plateau is located in the Central Atlantic at the Eurasian, Nubian and North-American plates (RRT) Azores Triple Junction. The Terceira Rift (TR) connects the Mid-Atlantic Ridge with the Gloria Fault, hence establishing a transtensional-transform present day plate boundary between the Eurasian and the Nubian plates. Three volcanic islands arose along the TR, Graciosa, Terceira and Sao Miguel. In the geological past, the plate boundary in the Azores area between the Eurasian and Nubian plates was located further south at the East Azores Fracture Zone. The timing of the plate boundary jump, which marks the onset of rifting along the TR, is heavily disputed. Published ages vary from 36 to 1 Ma. Based on bathymetric data and high-resolution marine 2D multi-channel seismic data acquired during M113 cruise of R/V Meteor in 2014/2015 we discuss the structural evolution of the TR and address the question whether the divergence between both plates is entirely accommodated by the TR. The central TR between São Miguel and Terceira, also known as Hirondelle Basin, is up to 70 km wide. Rifting created two asymmetric graben sections separated by a rift parallel horst. The north-eastern and south-western graben sections are ca. 4 km and 3 km deep, respectively, and the corresponding graben floors are tilted towards the central horst. Volcanic cones emerged on the central horst and rift shoulders. Bright spots in the basin fill deposits indicate fluid flow out of the volcanic basement. The seafloor is displaced by faults which suggest recent fault displacement. In the Eastern Graciosa Basin between Terceira and Graciosa Islands the rift narrows to ca. 40 km and shallows to ca. 3200 m water depth. The central horst is no longer detectable. Instead, a buried normal fault and a small escarpment are observed. Shallow faults and block rotation are less pronounced compared to the basins to the south-east and north-west. The Western Graciosa Basin is about 30 km wide and ca. 3050 m deep. The floor of the wider and deeper north-eastern rift valley dips to the northeast. The southwestern basin is represented by tilted fault blocks. The relatively undisturbed rift valley between Terceira and Graciosa (Eastern Graciosa Basin) is consistent with a rather low earthquake activity compared to the other TR segments. We therefore conclude that the TR west of Terceira does not accommodate the entire Nubia-Eurasia plate motion. In fact, we assume that tectonic stress is also dissipated in a seismically active area south of the TR where the lineaments of Pico and São Jorge Island are located. Consequently, the new seismic data support the assumption of a diffuse plate boundary in the western half of the TR. Estimating the age of the TR on the basis of fault geometry and present day extension rates supports all those previous studies which suggested a TR age of 1-3 Ma.

Geographic information system (GIS) compilation of geophysical, geologic, and tectonic data for the Circum-North Pacific

USGS Publications Warehouse

Greninger, Mark L.; Klemperer, Simon L.; Nokleberg, Warren J.

1999-01-01

The accompanying directory structure contains a Geographic Information Systems (GIS) compilation of geophysical, geological, and tectonic data for the Circum-North Pacific. This area includes the Russian Far East, Alaska, the Canadian Cordillera, linking continental shelves, and adjacent oceans. This GIS compilation extends from 120?E to 115?W, and from 40?N to 80?N. This area encompasses: (1) to the south, the modern Pacific plate boundary of the Japan-Kuril and Aleutian subduction zones, the Queen Charlotte transform fault, and the Cascadia subduction zone; (2) to the north, the continent-ocean transition from the Eurasian and North American continents to the Arctic Ocean; (3) to the west, the diffuse Eurasian-North American plate boundary, including the probable Okhotsk plate; and (4) to the east, the Alaskan-Canadian Cordilleran fold belt. This compilation should be useful for: (1) studying the Mesozoic and Cenozoic collisional and accretionary tectonics that assembled this continental crust of this region; (2) studying the neotectonics of active and passive plate margins in this region; and (3) constructing and interpreting geophysical, geologic, and tectonic models of the region. Geographic Information Systems (GIS) programs provide powerful tools for managing and analyzing spatial databases. Geological applications include regional tectonics, geophysics, mineral and petroleum exploration, resource management, and land-use planning. This CD-ROM contains thematic layers of spatial data-sets for geology, gravity field, magnetic field, oceanic plates, overlap assemblages, seismology (earthquakes), tectonostratigraphic terranes, topography, and volcanoes. The GIS compilation can be viewed, manipulated, and plotted with commercial software (ArcView and ArcInfo) or through a freeware program (ArcExplorer) that can be downloaded from http://www.esri.com for both Unix and Windows computers using the button below.

The Tectonic Boundary Between Eastern Subbaisin and South-West Subbasin of the South China Sea Revealed from the Normalized Magnetic Source Strength

NASA Astrophysics Data System (ADS)

Guo, L.; Meng, X.

2014-12-01

The South China Sea (SCS), surrounded by the Eurasia, Pacific and India-Australia plates, is one of the largest marginal seas in the Western Pacific. It was formed by the interaction of the three plates and the seafloor spreading during Late Oligocene time to Early Miocene time. The boundary between Eastern Subbaisin and South-west Subbasin of the SCS has long been debated in the literature. Refining the boundary is one of the crucial tasks for correctly understanding the seafloor spreading model of the SCS. Due to few drills on the deep ocean basin of the SCS, magnetic data become important information for refining the boundary. However, the interpretation of magnetic data in the SCS suffers from the remanent magnetization of ocean crust as well as igneous rock and seamounts. The conventional reduction-to-pole anomalies at low latitudes usually neglect the remanent magnetization, making the interpretation incorrect. Here, we assembled high-resolution total magnetic intensity (TMI) data around the ocean basin of the SCS, and then did a special transformation of the TMI anomalies with a varying magnetic inclinations algorithm to obtain the normalized source strength (NSS). The NSS has advantage of insensitivity to remanent magnetization, benefitting correct interpretation. The NSS presents discriminative features from east to west in the ocean basin. The boundary of the discriminative features is clear and just ranges from the northeastern edge of the Zhongsha Islands running in the southeast direction to the northeastern edge of the Reed Bank. These imply that magnetic structure and tectonic features in the crust are discriminative between both sides of this boundary. It can be deduced that this boundary is the tectonic boundary between Eastern Subbaisin and South-west Subbasin. We acknowledge the financial support of the National Natural Science Foundation of China (41374093) and the SinoProbe-01-05 project.

Crustal gravitational potential energy change at the convergent plate boundary near Taiwan

NASA Astrophysics Data System (ADS)

Lo, C.; Hsu, S.

2003-12-01

The Taiwan orogen has formed due to the convergence between the Philippine Sea plate and Eurasian plate. Numerous earthquakes are occurring along the active convergent plate boundary in eastern Taiwan. To the northeast, the Philippine Sea plates is subducting northwards beneath the Ryukyu Arc. To the south, the Eurasian plate is subducting eastwards beneath the Luzon Arc. The plate interaction has caused crustal deformation and produced earthquakes. The earthquakes have caused radial permanent displacement of the crust and have altered the crustal gravitational potential energy. Here we use the earthquake source mechanisms, determined by the Broadband Array in Taiwan for Seismology (BATs) from 1995 to 2003, to calculate the crustal gravitational potential energy (GPE) change and discuss their tectonic implication along the convergent plate boundary. In Ilan Plain, the westernmost Okinawa Trough, it shows a crustal GPE loss. It is related to the crustal subsidence because of the backarc extension of the Okinawa Trough. In contrast, due to the Philippine Sea plate subucting northwards beneath Eurasian Plate, the Ryukyu convergent boundary shows systematic crustal GPE gain. Near Taiwan, the crustal GPE change is gained, indicating the collisional convergence of the Luzon Arc. To the south of Taiwan, along the Luzon Arc the crustal GPE is also gain, representing the initial uplifting of the Taiwan mountain belt.

High-Fidelity Numerical Modeling of Compressible Flow

DTIC Science & Technology

2015-11-01

details on these aspects of the implementation were reported in an earlier paper by Poggie.42 C. Flowfield Two flat - plate turbulent boundary layer flows...work investigated flat plate turbulent boundary layer flows. The baseline case was a flow at Mach 2.3, under conditions similar to those employed in...analyzed. The solutions are compared to a spanwise- periodic flat - plate turbulent boundary layer developed at the same conditions and yield similar

Segmentation and disruption of the East Pacific Rise in the mouth of the Gulf of California

NASA Astrophysics Data System (ADS)

Lonsdale, Peter

1995-08-01

Analysis of new multibeam bathymetry and all available magnetic data shows that the 340 km-long crest of the East Pacific Rise between Rivera and Tamayo transforms contains segments of both the Pacific-Rivera and the Pacific-North America plate boundaries. Another Pacific-North America spreading segment (“Alarcon Rise”) extends 60 km further north to the Mexican continental margin. The Pacific-North America-Rivera triple junction is now of the RRR type, located on the risecrest 60 km south of Tamayo transform. Slow North America-Rivera rifting has ruptured the young lithosphere accreted to the east flank of the rise, and extends across the adjacent turbidite plain to the vicinity of the North America-Rivera Euler pole, which is located on the plate boundary. The present absolute motion of the Rivera microplate is an anticlockwise spin at 4° m.y.-1 around a pole located near its southeast corner; its motion has recently changed as the driving forces applied to its margins have changed, especially with the evolution of the southern margin from a broad shear zone between Rivera and Mathematician microplates to a long Pacific-Rivera transform. Pleistocene rotations in spreading direction, by as much as 15° on the Pacific-Rivera boundary, have segmented the East Pacific Rise into a staircase of en echelon spreading axes, which overlap at lengthening and migrating nontransform offsets. The spreading segments vary greatly in risecrest geomorphology, including the full range of structural types found on other rises with intermediate spreading rates: axial rift valleys, split shield volcanoes, and axial ridges. Most offsets between the segments have migrated southward, but within the past 1 m.y. the largest of them (with 14 27 km of lateral displacement) have shown “dueling” behavior, with short-lived reversals in migration direction. Migration involves propagation of a spreading axis into abyssal hill terrain, which is deformed and uplifted while it occupies the broad shear zones between overlapping spreading axes. Tectonic rotation of the deformed crust occurs by bookshelf faulting, which generates teleseismically recorded strike-slip earthquakes. When reversals of migration direction occur, plateaus of rotated crust are shed onto the rise flanks.

The roof plate boundary is a bi-directional organiser of dorsal neural tube and choroid plexus development

PubMed Central

Broom, Emma R.; Gilthorpe, Jonathan D.; Butts, Thomas; Campo-Paysaa, Florent; Wingate, Richard J. T.

2012-01-01

The roof plate is a signalling centre positioned at the dorsal midline of the central nervous system and generates dorsalising morphogenic signals along the length of the neuraxis. Within cranial ventricles, the roof plate gives rise to choroid plexus, which regulates the internal environment of the developing and adult brain and spinal cord via the secretion of cerebrospinal fluid. Using the fourth ventricle as our model, we show that the organiser properties of the roof plate are determined by its boundaries with the adjacent neuroepithelium. Through a combination of in ovo transplantation, co-culture and electroporation techniques in chick embryos between embryonic days 3 and 6, we demonstrate that organiser properties are maintained by interactions between the non-neural roof plate and the neural rhombic lip. At the molecular level, this interaction is mediated by Delta-Notch signalling and upregulation of the chick homologue of Hes1: chairy2. Gain- and loss-of-function approaches reveal that cdelta1 is both necessary and sufficient for organiser function. Our results also demonstrate that while chairy2 is specifically required for the maintenance of the organiser, its ectopic expression is not sufficient to recapitulate organiser properties. Expression of atonal1 in the rhombic lip adjacent at the roof plate boundary is acutely dependent on both boundary cell interactions and Delta-Notch signalling. Correspondingly, the roof plate boundary organiser also signals to the roof plate itself to specify the expression of early choroid plexus markers. Thus, the roof plate boundary organiser signals bi-directionally to acutely coordinate the development of adjacent neural and non-neural tissues. PMID:23052907

The roof plate boundary is a bi-directional organiser of dorsal neural tube and choroid plexus development.

PubMed

Broom, Emma R; Gilthorpe, Jonathan D; Butts, Thomas; Campo-Paysaa, Florent; Wingate, Richard J T

2012-11-01

The roof plate is a signalling centre positioned at the dorsal midline of the central nervous system and generates dorsalising morphogenic signals along the length of the neuraxis. Within cranial ventricles, the roof plate gives rise to choroid plexus, which regulates the internal environment of the developing and adult brain and spinal cord via the secretion of cerebrospinal fluid. Using the fourth ventricle as our model, we show that the organiser properties of the roof plate are determined by its boundaries with the adjacent neuroepithelium. Through a combination of in ovo transplantation, co-culture and electroporation techniques in chick embryos between embryonic days 3 and 6, we demonstrate that organiser properties are maintained by interactions between the non-neural roof plate and the neural rhombic lip. At the molecular level, this interaction is mediated by Delta-Notch signalling and upregulation of the chick homologue of Hes1: chairy2. Gain- and loss-of-function approaches reveal that cdelta1 is both necessary and sufficient for organiser function. Our results also demonstrate that while chairy2 is specifically required for the maintenance of the organiser, its ectopic expression is not sufficient to recapitulate organiser properties. Expression of atonal1 in the rhombic lip adjacent at the roof plate boundary is acutely dependent on both boundary cell interactions and Delta-Notch signalling. Correspondingly, the roof plate boundary organiser also signals to the roof plate itself to specify the expression of early choroid plexus markers. Thus, the roof plate boundary organiser signals bi-directionally to acutely coordinate the development of adjacent neural and non-neural tissues.

Two-dimensional thermal modeling associated with subduction of the Philippine Sea plate in southern Kyushu, Japan

NASA Astrophysics Data System (ADS)

Suenaga, Nobuaki; Yoshioka, Shoichi; Matsumoto, Takumi; Ji, Yingfeng

2018-01-01

In Hyuga-nada, southern Kyushu in southwest Japan, afterslip events were found in association with the two large interplate earthquakes, which occurred on October 19 and December 3, 1996. In Kyushu, low-frequency earthquakes (LFEs) and tectonic tremors are not common, but a considerable concentration of tectonic tremors is observed beneath the Pacific coast of the Miyazaki prefecture. To investigate the generation mechanisms of these seismic events, we performed 2-D box-type time-dependent thermal modeling in southern Kyushu. As a result, the temperature range of the upper surface of the subducting Philippine Sea (PHS) plate, where the afterslip occurred, reached approximately 300 to 350 °C. The temperatures where the tectonic tremors occurred ranged from 450 to 650 °C in the mantle wedge corner. We also estimated the spatial distribution of water content within the subducting PHS plate, using phase diagrams of hydrous mid-ocean ridge basalt (MORB) and ultramafic rock. Then, we found that no characteristic phase transformations accompany the dehydration of the subducting PHS plate in the afterslip region, but phase transformation from lawsonite blueschist to lawsonite eclogite is expected within the oceanic crust of the PHS plate just below the active region of the tectonic tremors. Our estimated water content distribution is consistent with the VP/VS ratio calculated from the seismic tomography. Therefore, we conclude that the occurrence of the afterslip is controlled by the temperature condition at the plate boundary, and occurs near the down-dip limit of the seismogenic zone. On the other hand, determining the major factors leading to the occurrence of the tectonic tremors is difficult, we estimated the temperature in the mantle wedge is ranging from 450 °C to 650 °C, and dehydration of 1.0 wt% would be expected from the subducting PHS plate near the active region of the tectonic tremors.

Geophysical Data (Gravity and Magnetic) from the Area Between Adana, Kahramanmaras and Hatay in the Eastern Mediterranean Region: Tectonic Implications

NASA Astrophysics Data System (ADS)

Over, Semir; Akin, Ugur; Sen, Rahime

2018-01-01

The gravity and magnetic maps of the area between Adana-Kahramanmaras-Hatay provinces were produced from a compilation of data gathered during the period between 1973 and 1989. Reduced to the pole (RTP) and pseudo-gravity transformation (PGT) methods were applied to the magnetic data, while derivative ratio (DR) processing was applied to both gravity and magnetic data, respectively. Bouguer, RTP and PGT maps show the image of a buried structure corresponding to ophiolites under undifferentiated Quaternary deposits in the Adana depression and Iskenderun Gulf. DR maps show two important faults which reflect the tectonic framework in the study area: (1) the Karatas-Osmaniye Fault extending from Osmaniye to Karatas in the south between Adana and Iskenderun depressions and (2) Amanos Fault (southern part of East Anatolian Fault) in the Hatay region running southward from Turkoglu to Amik Basin along Amanos Mountain forming the actual plate boundary between the Anatolian block (part of Eurasian plate) and Arabian plate.

Analog Modeling of the Interplay between Subduction and Lateral Extrusion in the European Alps

NASA Astrophysics Data System (ADS)

van Gelder, I. E.; Willingshofer, E.; Sokoutis, D.

2014-12-01

In the European Alps lateral extrusion is traditionally viewed as a lithospheric scale process that is related to northward indentation of a weak orogenic wedge (the eastern Alps) by a rigid indenter in upper plate position (the Adriatic plate). Critical for the efficiency of the extrusion process is the presence of a 'free boundary' at high angle to the indentation direction. The 'free boundary' in the eastern Alps is the result of the eastward extending Pannonian realm synchronous to indentation. However, indentation has become debatable as recent high-resolution tomography suggests that the Adriatic mantle lithosphere subducted under the extruding Alps. These findings raise first order questions related to: (a) the partitioning of deformation between lateral extrusion of the upper plate and coeval subduction of Adria, (b) the rheology of the lower and upper plates, and (c) the rheology of the plate contact controlling the amount of extrusion on the upper plate vs. accretion on the lower plate.In this analog modeling study, we couple for the first time lateral extrusion tectonics to subduction of the lower plate; thus, extrusion taking place in the upper plate. Within the lithospheric scale models, the lithospheres of the two plates are weakly coupled along an inclined boundary and have contrasting mantle lithosphere strength (stronger in the subducting plate). The interplay of extrusion vs subduction is inferred by varying the mechanical boundary conditions, e.g. the degree of resistance at the 'unconstrained' margin, the strength contrast between the upper and the lower plates and the width of the indented region.The experimental results emphasize that extrusion in the eastern Alps is compatible with coeval subduction of the Adriatic plate. The first experimental series suggests that the following mechanical conditions play a key role in the interplay between extrusion and subduction: (a) the extruding plate is weaker than the subducting plate, (b) the plate contact is weak in order to trigger the subduction of the lower plate, and (c) the eastern boundary is weak and thus allows for accommodating the extruding upper plate.

Thermoelastic martensitic transformations in ternary Ni50Mn50- z Ga z alloys

NASA Astrophysics Data System (ADS)

Belosludtseva, E. S.; Kuranova, N. N.; Marchenkova, E. B.; Popov, A. G.; Pushin, V. G.

2016-01-01

We have studied the effect of gallium alloying on the structure, phase composition, and physical properties of ternary alloys of the Ni50Mn50- z Ga z (0 ≤ z ≤ 25 at %) quasi-binary section in a broad temperature range. Dependences of the type of crystalline structure of the high-temperature austenite phase and martensite, as well as the critical temperatures of martensitic transformations on the alloy composition, are determined. A phase diagram of the structural and magnetic transformations is constructed. Concentration boundaries of the existence of tetragonal L10 (2 M) martensite and martensitic phases (10 M and 14 M) with complex multilayer crystalline lattices are found. It is established that the predominant martensite morphology is determined by the hierarchy of packets of thin coherent nano- and submicrocrystalline plates with habit planes close to {011} B2, pairwise twinned along one of 24 equivalent {011}<011> B2 twinning shear systems.

Mineralogical Evidence for the Bulk Transformation of Continental Crust to Ultrahigh-Pressure Conditions in Subduction Zones

NASA Astrophysics Data System (ADS)

Peterman, E. M.; Hacker, B. R.; Kylander-Clark, A. R.

2005-12-01

Evidence for (ultra)high-pressure --(U)HP-- metamorphism in modern orogenic belts and the preservation of exhumed (U)HP terranes around the world suggest that subduction and exhumation of continental crust plays an important role in Phanerozoic plate tectonics. The Western Gneiss region (WGR) of Norway, a major (U)HP province extending over 60,000 km2, provides an excellent opportunity to study how subduction to depths >100 km affects continental crust. By studying a ~60 km wide transect bounded to the north by Vartdalsfjorden and Rovdefjorden and the south by the Möre og Romsdal county boundary, we are able to examine mineralogical changes that occurred during subduction and exhumation within a rock composed predominantly of orthogneiss and variably transformed mafic bodies, which indicate the depths to which these rocks were subducted. Previous studies (e.g. Hacker et al., 2005) have suggested that Caledonian deformation in WGR host gneisses is primarily limited to brittle-ductile fabrics characterized by greenschist to lower-amphibolite facies metamorphism; the majority of the deformation in the rocks, including the pervasive foliation and foliation-parallel isoclinal folds, occurred between 1200 and 900 Ma. On the northern half of our study area, however, locally occurring neoblastic garnet crosscuts the foliation in the gneiss. The boundary of this garnet zone coincides with the local HP-UHP boundary, as determined by the presence of coesite in eclogite. Because garnet can retain information about changes in pressure and temperature, as well as the availability of water within the crust to catalyze chemical reactions, our findings suggest that 1) portions of the orthogneiss did transform at high pressures, 2) the presence of garnet within the orthogneiss may indicate conditions that approximate UHP and can therefore be useful in defining the boundaries between UHP and HP conditions, and 3) the growth of garnet during (U)HP metamorphism may be controlled by hydration of the crust, thus explaining the partial transformation to (U)HP mineral assemblages throughout the WGR.

Crustal seismic velocity structure from Eratosthenes Seamount to Hecataeus Rise across the Cyprus Arc, eastern Mediterranean

NASA Astrophysics Data System (ADS)

Welford, J. Kim; Hall, Jeremy; Hübscher, Christian; Reiche, Sönke; Louden, Keith

2015-02-01

Wide-angle reflection/refraction seismic profiles were recorded across the Cyprus Arc, the plate boundary between the African Plate and the Aegean-Anatolian microplate, from the Eratosthenes Seamount to the Hecataeus Rise immediately south of Cyprus. The resultant models were able to resolve detail of significant lateral velocity variations, though the deepest crust and Moho are not well resolved from the seismic data alone. Conclusions from the modelling suggest that (i) Eratosthenes Seamount consists of continental crust but exhibits a laterally variable velocity structure with a thicker middle crust and thinner lower crust to the northeast; (ii) the Hecataeus Rise has a thick sedimentary rock cover on an indeterminate crust (likely continental) and the crust is significantly thinner than Eratosthenes Seamount based on gravity modelling; (iii) high velocity basement blocks, coincident with highs in the magnetic field, occur in the deep water between Eratosthenes and Hecataeus, and are separated and bounded by deep low-velocity troughs and (iv) one of the high velocity blocks runs parallel to the Cyprus Arc, while the other two appear linked based on the magnetic data and run NW-SE, parallel to the margin of the Hecataeus Rise. The high velocity block beneath the edge of Eratosthenes Seamount is interpreted as an older magmatic intrusion while the linked high velocity blocks along Hecataeus Rise are interpreted as deformed remnant Tethyan oceanic crust or mafic intrusives from the NNW-SSE oriented transform margin marking the northern boundary of Eratosthenes Seamount. Eratosthenes Seamount, the northwestern limit of rifted continental crust from the Levant Margin, is part of a jagged rifted margin transected by transform faults on the northern edge of the lower African Plate that is being obliquely subducted under the Aegean-Anatolian upper plate. The thicker crust of Eratosthenes Seamount may be acting as an asperity on the subducting slab, locally locking up subduction of the Cyprus Arc on its northern margin, while deformed Tethyan oceanic crust remains trapped between its northeastern margin and the Hecataeus Rise.

Validation of High-Speed Turbulent Boundary Layer and Shock-Boundary Layer Interaction Computations with the OVERFLOW Code

NASA Technical Reports Server (NTRS)

Oliver, A. B.; Lillard, R. P.; Blaisdell, G. A.; Lyrintizis, A. S.

2006-01-01

The capability of the OVERFLOW code to accurately compute high-speed turbulent boundary layers and turbulent shock-boundary layer interactions is being evaluated. Configurations being investigated include a Mach 2.87 flat plate to compare experimental velocity profiles and boundary layer growth, a Mach 6 flat plate to compare experimental surface heat transfer,a direct numerical simulation (DNS) at Mach 2.25 for turbulent quantities, and several Mach 3 compression ramps to compare computations of shock-boundary layer interactions to experimental laser doppler velocimetry (LDV) data and hot-wire data. The present paper describes outlines the study and presents preliminary results for two of the flat plate cases and two small-angle compression corner test cases.

Geophysical surveys of the Queen Charlotte Fault plate boundary off SE Alaska: Preliminary results

NASA Astrophysics Data System (ADS)

Ten Brink, U. S.; Brothers, D. S.; Andrews, B. D.; Kluesner, J.; Haeussler, P. J.; Miller, N. C.; Watt, J. T.; Dartnell, P.; East, A. E.

2016-12-01

Recent multibeam sonar and high-resolution seismic surveys covering the northern 400-km-long segment of Queen Charlotte Fault off SE Alaska, indicate that the entire 50 mm/yr right-lateral Pacific-North America plate motion is currently accommodated by a single fault trace. The trace is remarkably straight rarely interrupted by step-overs, and is often <100 m wide. It runs along the shelf edge dropping into the slope only in the southern end of the mapped area. The straight and narrow surficial fault expression and its location with respect to the shelf may be due to high sedimentation rate during the collapse of the SE Alaska ice cap 17,000 yr ago, which obliterated the previous surficial deformation. Gravity data suggests that the fault may separate the 15-20 Ma oceanic crust of the Pacific plate from continental forearc and arc terrains of a former subduction zone. This unusual setting for a transform plate boundary might have resulted from the northward passage of the thick crust of the Yakutat Terrane during the Late Cenozoic. A step-over at the mouth of Chatham Strait has formed a 20-km-long 1.6-km-wide pull-apart basin composed of 3 sub-basins. Internal basin stratigraphy indicates possible southward migration of the step-over with time. Slight outward curving of the southern strand may suggest the presence of a deeper barrier there, which could have terminated the northward super-shear rupture of the 2013 M7.5 Craig Earthquake. Whether this possible barrier is related to the intersection of the Aja Fracture Zone with the plate boundary is unclear. No other surficial impediments to rupture were observed along the 315 km trace between this fault step-over and a 20° bend near Icy Point, where the fault extends onshore and becomes highly transpressional. An enigmatic oval depression, 1.5-2 km wide and 500 m deep, south of the step-over and a possible mud volcano north of the step-over, may attest to possible vigorous gas and fluid upwelling along the fault zone.

Crustal Deformation at the Arabian Plate-Boundary observed by InSAR

NASA Astrophysics Data System (ADS)

Jonsson, S.; Cavalié, O.; Akoglu, A. M.; Wang, T.; Xu, W.; Feng, G.; Dutta, R.; Abdullin, A. K.

2013-12-01

The Arabian plate is bounded by a variety of active plate boundaries, with extension in the Red Sea and Gulf of Aden to the south, compression in Turkey and Iran to the north, and transform faults to the west and to the east. Internally, however, the Arabian plate has been shown to be tectonically rather stable, despite evidence of recent volcanism and earthquake faulting. We use InSAR observations to study recent tectonic and volcanic activity at several locations at the Arabian plate boundary as well within the plate itself. The region near the triple junction between the Arabian, Eurasian, and Anatolian plates has often been the focus of studies on continental deformation behavior and interseismic deformation. Here we use large-scale InSAR data processing to map the deformation near the triple junction and find the deformation to be focused on major faults with little intra-plate deformation. The eastern part of the East Anatolian Fault appears to have a very shallow locking depth with limited fault-normal deformation. Several major earthquakes that have occurred in recent years on the Arabian plate boundary, including the 2011 magnitude 7.1 Van earthquake in eastern Turkey. It occurred as a result of convergence of the Arabian plate towards Eurasia and caused significant surface deformation that we have analyzed with multiple coseismic InSAR, GPS, and coastal uplift observations. We use high-resolution Cosmo-Skymed and TerraSAR-X data to derive 3D coseismic displacements from offsets alone, as some of the interferograms are almost completely incoherent. By identifying point-like targets within the images, we were able to derive accurate pixel offsets between SAR sub-images containing such targets, which we used to estimate the 3D coseismic displacements. The derived 3D displacement field helped in constraining the causative northward dipping thrust-fault. The Qadimah fault is a recently discovered fault located on the Red Sea coast north of Jeddah and under the King Abdullah Economic City, a planned $50 billion harbor city. The fault is a normal fault, parallel to the Red Sea, but it is unclear if the fault is still active and poses significant hazard to the new city. We use MERIS-corrected Envisat InSAR data to study the limited interseismic deformation across the fault and the results suggest that more investigations will be needed to assess the activity of the fault. Several volcanic events have taken place in the region during the past several years, including the 2007-8 Jebel at Tair island (Red Sea) eruption, the 2009 Harrat Lunayyir (western Saudi Arabia) magmatic intrusion, and the 2011-12 Zubair islands (Red Sea) eruption. All these three volcanic events were fed by dike intrusions whose geometry we constrain using the InSAR and optical data. The derived dike orientations provide information about extensional stress field in and around the Red Sea, although on Tair island the upper-most part of the feeder dike was controlled by local stresses within the volcanic edifice.

Mechanical decoupling along a subduction boundary fault: the case of the Tindari-Alfeo Fault System, Calabrian Arc (central Mediterranean Sea)

NASA Astrophysics Data System (ADS)

Maesano, F. E.; Tiberti, M. M.; Basili, R.

2017-12-01

In recent years an increasing number of studies have been focused in understanding the lateral terminations of subduction zones. In the Mediterranean region, this topic is of particular interest for the presence of a "land-locked" system of subduction zones interrupted by continental collision and back-arc opening. We present a 3D reconstruction of the area surrounding the Tindari-Alfeo Fault System (TAFS) based on a dense set of deep seismic reflection profiles. This fault system represents a major NNW-SSE trending subduction-transform edge propagator (STEP) that controls the deformation zone bounding the Calabrian subduction zone (central Mediterranean Sea) to the southwest. This 3D model allowed us to characterize the mechanical and kinematic evolution of the TAFS during the Plio-Quaternary. Our study highlights the presence of a mechanical decoupling between the deformation observed in the lower plate, constituted by the Ionian oceanic crust entering the subduction zone, and the upper plate, where a thick accretionary wedge has formed. The lower plate hosts the master faults of the TAFS, whereas the upper plate is affected by secondary deformation (bending-moment faulting, localized subsidence, stepovers, and restraining/releasing bends). The analysis of the syn-tectonic sedimentary basins related to the activity of the TAFS at depth allow us to constrain the propagation rate of the deformation and of the vertical component of the slip-rate. Our findings provide a comprehensive framework of the structural setting that can be expected along a STEP boundary where contractional and transtensional features coexist at close distance from one another.

The Influence of TIG Welding Thermal Cycles on HSLA-100 Steel Plate

DTIC Science & Technology

1993-11-01

8217 1.0’ 1,i 1.0’ 10’ TZ•ME. Secznas Figure 15. CCT diagram for a HSLA-100 steel with composition similar to that of the present work from Wilson...cooling rate through the transformation and ends up with a HAZ hardness of 345 HV which indicates a predominantly martensitic structure, on the CCT ... diagram . This is confirmed by the TEM micrograph of the HAZ taken close to fusion boundary, figure 14. On the other hand, the high heat input weld 1, with

Direct view on the phase evolution in individual LiFePO4 nanoparticles during Li-ion battery cycling.

PubMed

Zhang, Xiaoyu; van Hulzen, Martijn; Singh, Deepak P; Brownrigg, Alex; Wright, Jonathan P; van Dijk, Niels H; Wagemaker, Marnix

2015-09-23

Phase transitions in Li-ion electrode materials during (dis)charge are decisive for battery performance, limiting high-rate capabilities and playing a crucial role in the cycle life of Li-ion batteries. However, the difficulty to probe the phase nucleation and growth in individual grains is hindering fundamental understanding and progress. Here we use synchrotron microbeam diffraction to disclose the cycling rate-dependent phase transition mechanism within individual particles of LiFePO4, a key Li-ion electrode material. At low (dis)charge rates well-defined nanometer thin plate-shaped domains co-exist and transform much slower and concurrent as compared with the commonly assumed mosaic transformation mechanism. As the (dis)charge rate increases phase boundaries become diffuse speeding up the transformation rates of individual grains. Direct observation of the transformation of individual grains reveals that local current densities significantly differ from what has previously been assumed, giving new insights in the working of Li-ion battery electrodes and their potential improvements.

Direct view on the phase evolution in individual LiFePO4 nanoparticles during Li-ion battery cycling

PubMed Central

Zhang, Xiaoyu; van Hulzen, Martijn; Singh, Deepak P.; Brownrigg, Alex; Wright, Jonathan P.; van Dijk, Niels H.; Wagemaker, Marnix

2015-01-01

Phase transitions in Li-ion electrode materials during (dis)charge are decisive for battery performance, limiting high-rate capabilities and playing a crucial role in the cycle life of Li-ion batteries. However, the difficulty to probe the phase nucleation and growth in individual grains is hindering fundamental understanding and progress. Here we use synchrotron microbeam diffraction to disclose the cycling rate-dependent phase transition mechanism within individual particles of LiFePO4, a key Li-ion electrode material. At low (dis)charge rates well-defined nanometer thin plate-shaped domains co-exist and transform much slower and concurrent as compared with the commonly assumed mosaic transformation mechanism. As the (dis)charge rate increases phase boundaries become diffuse speeding up the transformation rates of individual grains. Direct observation of the transformation of individual grains reveals that local current densities significantly differ from what has previously been assumed, giving new insights in the working of Li-ion battery electrodes and their potential improvements. PMID:26395323

Weak incident shock interactions with Mach 8 laminar boundary layers. [of flat plate

NASA Technical Reports Server (NTRS)

Kaufman, L. G., II; Johnson, C. B.

1974-01-01

Weak shock-wave interactions with boundary layers on a flat plate were investigated experimentally in Mach 8 variable-density tunnel for plate-length Reynolds numbers. The undisturbed boundary layers were laminar over the entire plate length. Pressure and heat-transfer distributions were obtained for wedge-generated incident shock waves that resulted in pressure rises ranging from 1.36 to 4.46 (both nonseparated and separated boundary-layer flows). The resulting heat-transfer amplifications ranged from 1.45 to 14. The distributions followed established trends for nonseparated flows, for incipient separation, and for laminar free-interaction pressure rises. The experimental results corroborated established trends for the extent of the pressure rise and for certain peak heat-transfer correlations.

Block structure and geodynamics of the continental lithosphere on plate boundaries

NASA Astrophysics Data System (ADS)

Gatinsky, Yu. G.; Prokhorova, T. V.; Romanyuk, T. V.; Vladova, G. L.

2009-04-01

Division of the Earth lithosphere on large plates must be considered only as the first and most general approximation in its structure hierarchy. Some transit zones or difuuse boundaries after other authors take place in lithosphere plate boundaries. The tectonic tension of plate interaction is transferred and relaxed within these zones, which consist of blocks limited by seismoactive faults. Vectors of block horizontal displacements often don't coincide with vectors of main plates and change together with changing block rigidity. As a rule the intensity the seismic energy at plate and transit zone boundaries decreases linearly with distancing from these boundaries and correlates with decreasing of velocities of block horizontal displacements. But sometimes the maximum of the energy manifestation takes place in inner parts of transit zones. Some relatively tight interblock zones established in central and east Asia are the most seismically active. They limited such blocks as Pamir, Tien Shan, Bayanhar, Shan, Japanese-Korean, as well as the north boundary of the Indian Plate. A seismic energy intensity of these zones can be compared with the energy of Pacific subduction zones. It is worthy to note that the majority catastrophic earthquakes took place in Central Asia just within interblock zones. A level of block displacement is situated mainly in the bottom or inside the Earth crust, more rare in the lithosphere mantle. Blocks with the most thick lithosphere roots (SE China, Amurian) are the most rigid and weakly deformed.

Comments on the Parameters and Processes that Affect the Preservation Potential and Style of Oblique-Divergent Plate Boundaries

NASA Astrophysics Data System (ADS)

Umhoefer, P. J.

2014-12-01

Oblique-divergent or transtensional zones present particular challenges in ancient belts because of the poor preservation potential of the thinned continental crust and young oceanic crust. Many oblique belts will preferentially preserve their boundary zones that lie within continents rather than the main plate boundary zone, which will be at a much lower elevation and composed of denser crust. Zones of tectonic escape or strike-slip overprinting of arcs or plateaus deform continental crust and may be better preserved. Here I highlight parameters and processes that have major effects on oblique divergent belts. Strain partitioning is common, but not ubiquitous, along and across oblique boundaries; the causes of partitioning are not always clear and make this especially vexing for work in ancient belts. Partitioning causes complexity in the patterns of structures at all scales. Inherited structures commonly determine the orientation and style of structures along oblique boundaries and can control the pattern of faults across transtensional belts. Regionally, inherited trends of arcs or other 1000-km-scale features can control boundary structures. Experiments and natural examples suggest that oblique boundary zones contain less of a record of strike-slip faulting and more extensional structures. The obliquity of divergence produces predictable families of structures that typify (i) strike-slip dominated zones (obliquity <~20°), (ii) mixed zones (~20° - ~35°), and (iii) extension dominated zones (>~35°). The combination of partitioning and mixed structures in oblique zones means that the boundaries of belts with large-magnitude strike-slip faulting will commonly preserve little of no record of that faulting history. Plate boundaries localize strain onto the main plate boundary structures from the broader plate boundary and therefore the boundary zones commonly preserve the earlier structures more than later structures, a major problem in interpreting ancient belts. Sediment input is critical in some oblique plate boundaries because these belts become more pronounced sediment sinks over time. The evolving topography of oblique boundaries means that they have great variability of sediment flux into differing parts of the system; large rivers enter these belts only in special circumstances.

Counter-Rotating Magellan and Trinidad Microplates at the Mesozoic Pacific-Phoenix-Farallon Triple Junction

NASA Astrophysics Data System (ADS)

Schouten, H.; Smith, D. K.

2005-12-01

Magellan and Trinidad microplates developed at the Mesozoic triple junction between the Pacific, Phoenix and Farallon plates; the microplates were instrumental in the transition from a transform-ridge-transform to a ridge-ridge-ridge triple junction, which took several tens of millions of years. Contrasting qualitative models for the evolution of these microplates [e.g., Tamaki and Larson, 1988; Nakanishi et al., 1992] provide meager insight in the mechanics of microplate evolution and triple junction transformation. We propose a quantitative model for the evolution of Magellan and Trinidad microplates based on the edge-driven microplate kinematic principles [Schouten et al., 1993] that have provided successful quantitative solutions for the motions of Easter, Juan Fernandez, and Galapagos microplates. In these edge-driven solutions, two angular velocity vectors (describing motion between microplate and driving plates) are located on the microplate boundaries at the tip of rifts that propagate between microplate and driving plates. The rift propagation leaves pseudofaults on microplate and driving plates; the pseudofaults, which can be recognized in the seafloor topography, then become proxies for the trajectories of the angular velocity vectors from which a quantitative solution of microplate motion is derived. Using the estimated seafloor topography of the region and published marine magnetic anomaly lineations we propose the following scenario. The Magellan microplate rotated counterclockwise as evidenced by the fanning of magnetic lineations about the Magellan Trough and the rotation of the older Mid-Pac Mountains lineation set. The Trinidad microplate rotated clockwise relative to the Pacific plate to judge from the wedge-shaped region about the Trinidad trough that has its narrow tip on the Victoria fracture zone (recognized in the estimated seafloor topograpy). The clockwise motion of the Trinidad microplate was driven by Pacific-Phoenix motion; the counterclockwise motion of the Magellan microplate by Pacific-Farallon motion. Thus the Magellan trough opened between the counter-rotating Trinidad and Magellan microplates, similar to the opening of Hess Deep between two counter-rotating Galapagos microplates at the present Galapagos triple junction [Klein et al., 2005]. When the northeastward propagating rift between the Trindad microplate and the Phoenix plate and the southward propagating rift between the Magellan microplate and the Farallon plate broke through to the Phoenix-Farallon spreading center, a new ridge-ridge-ridge triple junction was established between the Pacific, Phoenix and Farallon plates and the Trinidad and Magellan microplates ceased rotating and were abandoned on the Pacific plate.

Impacts and Ophiolites: A Way to Recognize Large Terrestrial Impact Basins?

NASA Astrophysics Data System (ADS)

Olds, E. P.

2015-12-01

That Chicxulub Crater is located on ~35 km thick continental crust is apparently inconsistent with oceanic crustal/upper mantle geochemical signatures detected globally in the KT boundary impact layer [1-5 and unpublished Cr isotope data from the Yin lab at UC Davis] since introduction of the Alvarez hypothesis [6]. Apparent excavation and ejection of mafic/ultramafic target rock by the KT boundary impact might imply an additional KT impact site involving oceanic lithosphere. We speculate: 1) The Greater Antilles island chain ophiolite belt marks the rim of a ~700 km diameter impact basin, deformed and dismembered from an originally circular form by at least 50 million years of left lateral shear on the North American-Caribbean transform plate boundary; 2) Other ophiolite segments may similarly mark rims of large impact basins deformed to greater or lesser extent by, and serving as strain markers for, relative plate motions over geologic time; 3) The Greater Antilles/Chicxulub and Sulu Sea Basin/Spratly Island cases may constitute doublet craters of similar size ratio and separation distance; 4) Plate boundaries may be formed or modified by such impacts. Problems include: 1) The KT fireball layer should be tens of cm thick rather than a few mm thick [8-9]; 2) Impact basins of this size/scale are not expected in the Phanerozoic/Proterozoic [10]; References: [1] DePaolo D. J. et al. 1983. EPSL 64:356-373. [2] Hildebrand A. R. and Boynton W. V. 1988, LPI Contributions 673:78-79. [3] Hildebrand A. R. and Boynton W. V.. 1990. Science 248:843-847. [4] Montanari A. et al. 1983. Geology 11:668. [5] Bohor B. F. et al. 1989. Meteoritics 24:253. [6] Alvarez L. W. et al. 1980 Science 208:1095-1108. [7][8] Grieve R.A.F. and Cintala M.J. 1992 Meteoritics 27: 526-538. [9] Pierazzo E. et al. 1997 Icarus 127/2:408-423. [10] Ivanov B.A. et al. 2002 Asteroids III 89-101

Deformation during terrane accretion in the Saint Elias orogen, Alaska

USGS Publications Warehouse

Bruhn, R.L.; Pavlis, T.L.; Plafker, G.; Serpa, L.

2004-01-01

The Saint Elias orogen of southern Alaska and adjacent Canada is a complex belt of mountains formed by collision and accretion of the Yakutat terrane into the transition zone from transform faulting to subduction in the northeast Pacific. The orogen is an active analog for tectonic processes that formed much of the North American Cordillera, and is also an important site to study (1) the relationships between climate and tectonics, and (2) structures that generate large- to great-magnitude earthquakes. The Yakutat terrane is a fragment of the North American plate margin that is partly subducted beneath and partly accreted to the continental margin of southern Alaska. Interaction between the Yakutat terrane and the North American and Pacific plates causes significant differences in the style of deformation within the terrane. Deformation in the eastern part of the terrane is caused by strike-slip faulting along the Fairweather transform fault and by reverse faulting beneath the coastal mountains, but there is little deformation immediately offshore. The central part of the orogen is marked by thrusting of the Yakutat terrane beneath the North American plate along the Chugach-Saint Elias fault and development of a wide, thin-skinned fold-and-thrust belt. Strike-slip faulting in this segment may he localized in the hanging wall of the Chugach-Saint Elias fault, or dissipated by thrust faulting beneath a north-northeast-trending belt of active deformation that cuts obliquely across the eastern end of the fold-and-thrust belt. Superimposed folds with complex shapes and plunging hinge lines accommodate horizontal shortening and extension in the western part of the orogen, where the sedimentary cover of the Yakutat terrane is accreted into the upper plate of the Aleutian subduction zone. These three structural segments are separated by transverse tectonic boundaries that cut across the Yakutat terrane and also coincide with the courses of piedmont glaciers that flow from the topographic backbone of the Saint Elias Mountains onto the coastal plain. The Malaspina fault-Pamplona structural zone separates the eastern and central parts of the orogen and is marked by reverse faulting and folding. Onshore, most of this boundary is buried beneath the western or "Agassiz" lobe of the Malaspina piedmont glacier. The boundary between the central fold-and-thrust belt and western zone of superimposed folding lies beneath the middle and lower course of the Bering piedmont glacier. ?? 2004 Geological Society of America.

Repulsive Casimir effect from extra dimensions and Robin boundary conditions: From branes to pistons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elizalde, E.; Odintsov, S. D.; Institucio Catalana de Recerca i Estudis Avanccats

2009-03-15

We evaluate the Casimir energy and force for a massive scalar field with general curvature coupling parameter, subject to Robin boundary conditions on two codimension-one parallel plates, located on a (D+1)-dimensional background spacetime with an arbitrary internal space. The most general case of different Robin coefficients on the two separate plates is considered. With independence of the geometry of the internal space, the Casimir forces are seen to be attractive for special cases of Dirichlet or Neumann boundary conditions on both plates and repulsive for Dirichlet boundary conditions on one plate and Neumann boundary conditions on the other. For Robinmore » boundary conditions, the Casimir forces can be either attractive or repulsive, depending on the Robin coefficients and the separation between the plates, what is actually remarkable and useful. Indeed, we demonstrate the existence of an equilibrium point for the interplate distance, which is stabilized due to the Casimir force, and show that stability is enhanced by the presence of the extra dimensions. Applications of these properties in braneworld models are discussed. Finally, the corresponding results are generalized to the geometry of a piston of arbitrary cross section.« less

Continuous Spectrum of Crustal Structures and Spreading Processes from Volcanic Rifted Margins to Mid-Ocean Ridges

NASA Astrophysics Data System (ADS)

Karson, J. A.

2016-12-01

Structures generated by seafloor spreading in oceanic crust (and ophiolites) and thick oceanic crust of Iceland show a continuous spectrum of features that formed by similar mechanisms but at different scales. A high magma budget near the Iceland hotspot generates thick (40-25 km) mafic crust in a plate boundary zone about 50 km wide. The upper crust ( 10 km thick) is constructed by the subaxial subsidence and thickening of lavas fed by dense dike swarms over a hot, weak lower crust to produce structures analogous to seaward-dipping reflectors of volcanic rifted margins. Segmented rift zones propagate away from the hotspot creating migrating transform fault zones, microplate-like crustal blocks and rift-parallel strike-slip faults. These structures are decoupled from the underlying lower crustal gabbroic rocks that thin by along-axis flow that reduces the overall crustal thickness and smooths-out local crustal thickness variations. Spreading on mid-ocean ridges with high magma budgets have much thinner crust (10-5 km) generated at a much narrower (few km) plate boundary zone. Subaxial subsidence accommodates the thickening of the upper crust of inward-dipping lavas and outward-dipping dikes about 1-2 km thick over a hot weak lower crust. Along-axis (high-temperature ductile and magmatic) flow of lower crustal material may help account for the relatively uniform seismic thickness of oceanic crust worldwide. Spreading along even slow-spreading mid-ocean ridges near hotspots (e.g., the Reykjanes Ridge) probably have similar features that are transitional between these extremes. In all of these settings, upper crustal and lower crustal structures are decoupled near the plate boundary but eventually welded together as the crust ages and cools. Similar processes are likely to occur along volcanic rifted margins as spreading begins.

How the gas hydrate system gives insight into subduction wedge dewatering processes in a zone of highly-oblique convergence on the southern Hikurangi margin of New Zealand

NASA Astrophysics Data System (ADS)

Crutchley, Gareth; Klaeschen, Dirk; Pecher, Ingo; Henrys, Stuart

2017-04-01

The southern end of New Zealand's Hikurangi subduction margin is characterised by highly-oblique convergence as it makes a southward transition into a right-lateral transform plate boundary at the Alpine Fault. Long-offset seismic data that cross part of the offshore portion of this transition zone give new insight into the nature of the plate boundary. We have carried out 2D pre-stack depth migrations, with an iterative reflection tomography to update the velocity field, on two seismic lines in this area to investigate fluid flow processes that have implications for the mechanical stability of the subduction interface. The results show distinct and focused fluid expulsion pathways from the subduction interface to the shallow sub-surface. For example, on one of the seismic lines there is a clear disruption of the gas hydrate system at its intersection with a splay fault - a clear indication of focused fluid release from the subduction interface. The seismic velocities derived from tomography also highlight a broad, pronounced low velocity zone beneath the deforming wedge that we interpret as a thick zone of gas-charged fluids that may have important implications for the long-term frictional stability of the plate boundary in this area. The focused flow upward toward the seafloor has the potential to result in the formation of concentrated gas hydrate deposits. Our on-going work on these data will include amplitude versus offset analysis in an attempt to better characterise the nature of the subduction interface, the fluids in that region, and also the shallower gas hydrate system.

Theoretical analysis of a ceramic plate thickness-shear mode piezoelectric transformer.

PubMed

Xu, Limei; Zhang, Ying; Fan, Hui; Hu, Junhui; Yang, Jiashi

2009-03-01

We perform a theoretical analysis on a ceramic plate piezoelectric transformer operating with thickness-shear modes. Mindlin's first-order theory of piezoelectric plates is employed, and a forced vibration solution is obtained. Transforming ratio, resonant frequencies, and vibration mode shapes are calculated, and the effects of plate thickness and electrode dimension are examined.

The Influence of the Induced Ferrite and Precipitates of Ti-bearing Steel on the Ductility of Continuous Casting Slab

NASA Astrophysics Data System (ADS)

Qian, Guoyu; Cheng, Guoguang; Hou, Zibing

2015-11-01

In order to investigate the loss of the ductility of Ti-bearing ship plate steel under 1000 °C, where the ductility begins to reduce rapidly, so the hot ductility of Ti-bearing ship plate steel has been obtained using the Gleeble 1500 thermal-mechanical simulator and also the studies about the effect of grain boundary ferrite films and precipitates containing Ti on the ductility has been carried out. The result showed that the TiN particles precipitating at 950 °C with a larger size and smaller volume fraction cannot effectively suppress the occurrence of recrystallization and the ductility still retains at a high level, although R.A. value presents a certain degree of decline compared with 1000 °C. A large number of smaller Ti(C,N) particles precipitate at 900 °C and can induce the formation of a very small amount of fine grain boundary ferrite, which deteriorates the adhesion strength of the grain boundary, so the R.A. value rapidly reduces to less than 50%. When the temperature falls to close Ae3 (827 °C), the amount of the grain boundary ferrite films increase due to the ferrite phase transformation, but the ferrite film thickness becomes more uneven at the same time, which results in the increase of strain concentration and plays a leading role in causing the decrease of ductility, so the R.A. value has been kept less than 40% as the temperature cooling to 800 °C from 850 °C. When the temperature further decreases, the ductility starts to recover due to the increase of average ferrite film thickness to a greater degree which greatly reduces the strain concentration of the grain boundary.

Deformation Response of Unsymmetrically Laminated Plates Subjected to Inplane Loading

NASA Technical Reports Server (NTRS)

Ochinero, Tomoya T.; Hyer, Michael W.

2002-01-01

This paper discusses the out-of-plane deformation behavior of unsymmetric cross-ply composite plates compressed inplane by displacing one edge of the plate a known amount. The plates are assumed to be initially flat and several boundary conditions are considered. Geometrically nonlinear behavior is assumed. The primary objectives are to study the out-of-plane behavior as a function of increasing inplane compression and to determine if bifurcation behavior and secondary buckling can occur. It is shown that, depending on the boundary conditions, both can occur, though the characteristics are different than the pre and post-buckling behavior of a companion symmetric cross-ply plate. Furthermore, while a symmetric cross-ply plate can postbuckle with either a positive or negative out-of-plane displacement, the unsymmetric cross-ply plates studied deflect out-of-plane only in one direction throughout the range of inplane compression, the direction again depending on the boundary conditions

Cenozoic forearc tectonics in northeastern Japan: Relationships between outer forearc subsidence and plate boundary kinematics

NASA Astrophysics Data System (ADS)

Regalla, Christine

Here we investigate the relationships between outer forearc subsidence, the timing and kinematics of upper plate deformation and plate convergence rate in Northeast Japan to evaluate the role of plate boundary dynamics in driving forearc subsidence. The Northeastern Japan margin is one of the first non-accretionary subduction zones where regional forearc subsidence was argued to reflect tectonic erosion of large volumes of upper crustal rocks. However, we propose that a significant component of forearc subsidence could be the result of dynamic changes in plate boundary geometry. We provide new constraints on the timing and kinematics of deformation along inner forearc faults, new analyses of the evolution of outer forearc tectonic subsidence, and updated calculations of plate convergence rate. These data collectively reveal a temporal correlation between the onset of regional forearc subsidence, the initiation of upper plate extension, and an acceleration in local plate convergence rate. A similar analysis of the kinematic evolution of the Tonga, Izu-Bonin, and Mariana subduction zones indicates that the temporal correlations observed in Japan are also characteristic of these three non-accretionary margins. Comparison of these data with published geodynamic models suggests that forearc subsidence is the result of temporal variability in slab geometry due to changes in slab buoyancy and plate convergence rate. These observations suggest that a significant component of forearc subsidence at these four margins is not the product of tectonic erosion, but instead reflects changes in plate boundary dynamics driven by variable plate kinematics.

Turbulent Combustion Study of Scramjet Problem

DTIC Science & Technology

2015-08-01

boundary layer model for 2D simulations of a supersonic flat plate boundary layer . The inflow O2 has an average density of...flow above the flat plate has a transition from a laminar boundary layer to a turbulent boundary layer at a position downstream from the inlet. The...δ. Chapman [13] estimated the number of cells need to resolve the outer layer is proportional to Re0.4 for flat plat boundary layer and

Convection in three dimensions with surface plates - Generation of toroidal flow

NASA Technical Reports Server (NTRS)

Gable, Carl W.; O'Connell, Richard J.; Travis, Bryan J.

1991-01-01

This work presents numerical calculations of mantle convection that incorporate some of the basic observational constraints imposed by plate tectonics. The model is three-dimensional and includes surface plates; it allows plate velocity to change dynamically according to the forces which result from convection. It is shown that plates are an effective means of introducing a toroidal component into the flow field. After initial transients the plate motion is nearly parallel to transform faults and in the direction that tends to minimize the toroidal flow field. The toroidal field decays with depth from its value at the surface; the poloidal field is relatively constant throughout the layer but falls off slightly at the top and bottom boundaries. Layered viscosity increasing with depth causes the toroidal field to decay more rapidly, effectively confining it to the upper, low-viscosity layer. The effect of viscosity layering on the poloidal field is relatively small, which is attributed to its generation by temperature variations distributed throughout the system. The generation of toroidal flow by surface plates would seem to account for the observed nearly equal energy of toroidal and poloidal fields of plate motions on the earth. A low-viscosity region in the upper mantle will cause the toroidal flow to decay significantly before reaching the lower mantle. The resulting concentration of toroidal flow in the upper mantle may result in more thorough mixing there and account for some of the geochemical and isotopic differences proposed to exist between the upper and lower mantles.

Active faults and minor plates in NE Asia

NASA Astrophysics Data System (ADS)

Kozhurin, Andrey I.; Zelenin, Egor A.

2014-05-01

Stated nearly 40 yr ago the uncertainty with plate boundaries location in NE Asia (Chapman, Solomon, 1976) still remains unresolved. Based on the prepositions that a plate boundary must, first, reveal itself in linear sets of active structures, and, second, be continuous and closed, we have undertaken interpretation of medium-resolution KH-9 Hexagon satellite imageries, mostly in stereoscopic regime, for nearly the entire region of NE Asia. Main findings are as follows. There are two major active fault zones in the region north of the Bering Sea. One of them, the Khatyrka-Vyvenka zone, stretches NE to ENE skirting the Bering Sea from the Kamchatka isthmus to the Navarin Cape. Judging by the kinematics of the Olyutorsky 2006 earthquake fault, the fault zones move both right-laterally and reversely. The second active fault zone, the Lankovaya-Omolon zone, starts close to the NE margin of the Okhotsk Sea and extends NE up to nearly the margin of the Chukcha Sea. The fault zone is mostly right-lateral, with topographically expressed cumulative horizontal offsets amounting to 2.5-2.6 km. There may be a third NE-SW zone between the major two coinciding with the Penzhina Range as several active faults found in the southern termination of the Range indicate. The two active fault zones divide the NE Asia area into two large domains, which both could be parts of the Bering Sea plate internally broken and with uncertain western limit. Another variant implies the Khatyrka-Vyvenka zone as the Bering Sea plate northern limit, and the Lankovaya-Omolon zone as separating an additional minor plate from the North-American plate. The choice is actually not crucial, and more important is that both variants leave the question of where the Bering Sea plate boundary is in Alaska. The Lankovaya-Omolon zone stretches just across the proposed northern boundary of the Okhorsk Sea plate. NW of the zone, there is a prominent left-lateral Ulakhan fault, which is commonly interpreted to be a portion of the plate northern boundary. With this, we have discovered no active faults or fault zones of the Ulakhan fault strike, which could be the portion of the boundary between the Lankovaya-Omolon zone and either the western margin of the Komandor basin or the westernmost Aleutians. We conclude that there is a certain disagreement between active faulting pattern and plate models for NE Asia, relating to the extent of the plates and missing portions of the plate boundaries. The research was supported by grant # 110500136-a from the Russian Foundation for Basic Research.

Dynamic analysis of submerged microscale plates: the effects of acoustic radiation and viscous dissipation

PubMed Central

Ma, Xianghong

2016-01-01

The aim of this paper is to study the dynamic characteristics of micromechanical rectangular plates used as sensing elements in a viscous compressible fluid. A novel modelling procedure for the plate–fluid interaction problem is developed on the basis of linearized Navier–Stokes equations and no-slip conditions. Analytical expression for the fluid-loading impedance is obtained using a double Fourier transform approach. This modelling work provides us an analytical means to study the effects of inertial loading, acoustic radiation and viscous dissipation of the fluid acting on the vibration of microplates. The numerical simulation is conducted on microplates with different boundary conditions and fluids with different viscosities. The simulation results reveal that the acoustic radiation dominates the damping mechanism of the submerged microplates. It is also proved that microplates offer better sensitivities (Q-factors) than the conventional beam type microcantilevers being mass sensing platforms in a viscous fluid environment. The frequency response features of microplates under highly viscous fluid loading are studied using the present model. The dynamics of the microplates with all edges clamped are less influenced by the highly viscous dissipation of the fluid than the microplates with other types of boundary conditions. PMID:27118914

Crystallographic features of the martensitic transformation and their impact on variant organization in the intermetallic compound Ni50Mn38Sb12 studied by SEM/EBSD.

PubMed

Zhang, Chunyang; Zhang, Yudong; Esling, Claude; Zhao, Xiang; Zuo, Liang

2017-09-01

The mechanical and magnetic properties of Ni-Mn-Sb intermetallic compounds are closely related to the martensitic transformation and martensite variant organization. However, studies of these issues are very limited. Thus, a thorough crystallographic investigation of the martensitic transformation orientation relationship (OR), the transformation deformation and their impact on the variant organization of an Ni 50 Mn 38 Sb 12 alloy using scanning electron microscopy/electron backscatter diffraction (SEM/EBSD) was conducted in this work. It is shown that the martensite variants are hierarchically organized into plates, each possessing four distinct twin-related variants, and the plates into plate colonies, each containing four distinct plates delimited by compatible and incompatible plate interfaces. Such a characteristic organization is produced by the martensitic transformation. It is revealed that the transformation obeys the Pitsch relation ({0[Formula: see text]} A // {2[Formula: see text]} M and 〈0[Formula: see text]1〉 A // 〈[Formula: see text]2〉 M ; the subscripts A and M refer to austenite and martensite, respectively). The type I twinning plane K 1 of the intra-plate variants and the compatible plate interface plane correspond to the respective orientation relationship planes {0[Formula: see text]} A and {0[Formula: see text]} A of austenite. The three {0[Formula: see text]} A planes possessed by each pair of compatible plates, one corresponding to the compatible plate interface and the other two to the variants in the two plates, are interrelated by 60° and belong to a single 〈11[Formula: see text]〉 A axis zone. The {0[Formula: see text]} A planes representing the two pairs of compatible plates in each plate colony belong to two 〈11[Formula: see text]〉 A axis zones having one {0[Formula: see text]} A plane in common. This common plane defines the compatible plate interfaces of the two pairs of plates. The transformation strains to form the variants in the compatible plates are compatible and demonstrate an edge-to-edge character. Thus, such plates should nucleate and grow simultaneously. On the other hand, the strains to form the variants in the incompatible plates are incompatible, so they nucleate and grow separately until they meet during the transformation. The results of the present work provide comprehensive information on the martensitic transformation of Ni-Mn-Sb intermetallic compounds and its impact on martensite variant organization.

Prediction and measurement of heat transfer rates for the shock-induced unsteady laminar boundary layer on a flat plate

NASA Technical Reports Server (NTRS)

Cook, W. J.

1972-01-01

The unsteady laminar boundary layer induced by the flow-initiating shock wave passing over a flat plate mounted in a shock tube was theoretically and experimentally studied in terms of heat transfer rates to the plate for shock speeds ranging from 1.695 to 7.34 km/sec. The theory presented by Cook and Chapman for the shock-induced unsteady boundary layer on a plate is reviewed with emphasis on unsteady heat transfer. A method of measuring time-dependent heat-transfer rates using thin-film heat-flux gages and an associated data reduction technique are outlined in detail. Particular consideration is given to heat-flux measurement in short-duration ionized shocktube flows. Experimental unsteady plate heat transfer rates obtained in both air and nitrogen using thin-film heat-flux gages generally agree well with theoretical predictions. The experimental results indicate that the theory continues to predict the unsteady boundary layer behavior after the shock wave leaves the trailing edge of the plate even though the theory is strictly applicable only for the time interval in which the shock remains on the plate.

Precise relative locations for earthquakes in the northeast Pacific region

DOE PAGES

Cleveland, K. Michael; VanDeMark, Thomas F.; Ammon, Charles J.

2015-10-09

We report that double-difference methods applied to cross-correlation measured Rayleigh wave time shifts are an effective tool to improve epicentroid locations and relative origin time shifts in remote regions. We apply these methods to seismicity offshore of southwestern Canada and the U.S. Pacific Northwest, occurring along the boundaries of the Pacific and Juan de Fuca (including the Explorer Plate and Gorda Block) Plates. The Blanco, Mendocino, Revere-Dellwood, Nootka, and Sovanco fracture zones host the majority of this seismicity, largely consisting of strike-slip earthquakes. The Explorer, Juan de Fuca, and Gorda spreading ridges join these fracture zones and host normal faultingmore » earthquakes. Our results show that at least the moderate-magnitude activity clusters along fault strike, supporting suggestions of large variations in seismic coupling along oceanic transform faults. Our improved relative locations corroborate earlier interpretations of the internal deformation in the Explorer and Gorda Plates. North of the Explorer Plate, improved locations support models that propose northern extension of the Revere-Dellwood fault. Relocations also support interpretations that favor multiple parallel active faults along the Blanco Transform Fault Zone. Seismicity of the western half of the Blanco appears more scattered and less collinear than the eastern half, possibly related to fault maturity. We use azimuthal variations in the Rayleigh wave cross-correlation amplitude to detect and model rupture directivity for a moderate size earthquake along the eastern Blanco Fault. Lastly, the observations constrain the seismogenic zone geometry and suggest a relatively narrow seismogenic zone width of 2 to 4 km.« less

Air flow in the boundary layer near a plate

NASA Technical Reports Server (NTRS)

Dryden, Hugh L

1937-01-01

The published data on the distribution of speed near a thin flat plate with sharp leading edge placed parallel to the flow (skin friction plate) are reviewed and the results of some additional measurements are described. The purpose of the experiments was to study the basic phenomena of boundary-layer flow under simple conditions.

Extending Alaska's plate boundary: tectonic tremor generated by Yakutat subduction

USGS Publications Warehouse

Wech, Aaron G.

2016-01-01

The tectonics of the eastern end of the Alaska-Aleutian subduction zone are complicated by the inclusion of the Yakutat microplate, which is colliding into and subducting beneath continental North America at near-Pacific-plate rates. The interaction among these plates at depth is not well understood, and further east, even less is known about the plate boundary or the source of Wrangell volcanism. The drop-off in Wadati-Benioff zone (WBZ) seismicity could signal the end of the plate boundary, the start of aseismic subduction, or a tear in the downgoing plate. Further compounding the issue is the possible presence of the Wrangell slab, which is faintly outlined by an anemic, eastward-dipping WBZ beneath the Wrangell volcanoes. In this study, I performed a search for tectonic tremor to map slow, plate-boundary slip in south-central Alaska. I identified ∼11,000 tremor epicenters, which continue 85 km east of the inferred Pacific plate edge marked by WBZ seismicity. The tremor zone coincides with the edges of the downgoing Yakutat terrane, and tremors transition from periodic to continuous behavior as they near the aseismic Wrangell slab. I interpret tremor to mark slow, semicontinuous slip occurring at the interface between the Yakutat and North America plates. The slow slip region lengthens the megathrust interface beyond the WBZ and may provide evidence for a connection between the Yakutat slab and the aseismic Wrangell slab.

Kinematic signature of India/Australia plates break-up

NASA Astrophysics Data System (ADS)

Iaffaldano, G.; Bunge, H.

2008-12-01

The paradigm of Plate Tectonics states that the uppermost layer of the Earth is made of a number of quasi- rigid blocks moving at different rates in different directions, while most of the deformation is focused along their boundaries. Perhaps one of the most interesting and intriguing processes in Plate Tectonics is the generation of new plate boundaries. The principle of inertia implies that any such event would invariably trigger changes in plate motions, because the budget of mantle basal-drag and plate-boundary forces would be repartitioned. A recent episode is thought to have occurred in the Indian Ocean, where a variety of evidences - including localized seismicity along the Nienty East Ridge, compression-generated unconformities of ocean-floor sediments, and identified paleomagnetic isochrones - suggest the genesis of a boundary separating the India and Australia plates. Here we use global numerical models of the coupled mantle/lithosphere system to show for the first time that an event of separation between India and Australia, having occurred sometime between 11 and 8 Myrs ago, has left a distinct signature in the observed record of plate motions. Specifically, while motions of India and Australia relative to fixed Eurasia are almost indistinguishable prior to 11 Myrs ago, their convergence to Eurasia since then differs significantly, by as much as 2 cm/yr. Finally, we speculate about possible causes for the separation between India and Australia plates.

Kinematic signature of India/Australia plates break-up

NASA Astrophysics Data System (ADS)

Iaffaldano, G.; Bunge, H.-P.

2009-04-01

The paradigm of Plate Tectonics states that the uppermost layer of the Earth is made of a number of quasi-rigid blocks moving at different rates in different directions, while most of the deformation is focused along their boundaries. Perhaps one of the most interesting and intriguing processes in Plate Tectonics is the generation of new plate boundaries. The principle of inertia implies that any such event would invariably trigger changes in plate motions, because the budget of mantle basal-drag and plate-boundary forces would be repartitioned. A recent episode is thought to have occurred in the Indian Ocean, where a variety of evidences - including localized seismicity along the Nienty East Ridge, compression-generated unconformities of ocean-floor sediments, and identified paleomagnetic isochrones - suggest the genesis of a boundary separating the India and Australia plates. Here we use global numerical models of the coupled mantle/lithosphere system to show for the first time that an event of separation between India and Australia, having occurred sometime between 11 and 8 Myrs ago, has left a distinct signature in the observed record of plate motions. Specifically, while motions of India and Australia relative to fixed Eurasia are almost indistinguishable prior to 11 Myrs ago, their convergence to Eurasia since then differs significantly, by as much as 2 cm/yr. Finally, we speculate about possible causes for the separation between India and Australia plates.

Shock induced phase transitions and current generation in ferroelectric ceramics

NASA Astrophysics Data System (ADS)

Agrawal, Vinamra; Bhattacharya, Kaushik

2017-06-01

Ferroelectric materials are used as ferroelectric generators to obtain pulsed power by subjecting them to a shock loading. The impact induces a phase transition and at high impact speeds, dielectric breakdown. Depending on the loading conditions and the electromechanical boundary conditions, the current or voltage profiles obtained vary. We explore the phenomenon of large deformation dynamic behavior and the associated electro-thermo-mechanical coupling of ferroelectric materials in adiabatic environments. Using conservation laws, Maxwell's equations and second law of thermodynamics, we obtain a set of governing equations for the material and the driving force acting on the propagating phase boundary. We also account for the possibility of surface charges on the phase boundary in case of dielectric breakdown which introduces contribution of curvature of the phase boundary in the equations. Next, the governing equations are used to solve a plate impact problem. The Helmholtz energy of the material is chosen be a combination of piecewise quadratic potential in polarization and thermo-elastic material capable of undergoing phase transformation. We obtain current profiles for short circuit boundary conditions along with strain, particle velocity and temperature maps. US AFOSR through Center of Excellence in High Rate Deformation of Heterogeneous Materials FA 9550-12-1-0091.

Multi-type Tectonic Responses to Plate Motion Changes of Mega-Offset Transform Faults at the Pacific-Antarctic Ridge

NASA Astrophysics Data System (ADS)

Zhang, F.; Lin, J.; Yang, H.; Zhou, Z.

2017-12-01

Magmatic and tectonic responses of a mid-ocean ridge system to plate motion changes can provide important constraints on the mechanisms of ridge-transform interaction and lithospheric properties. Here we present new analysis of multi-type responses of the mega-offset transform faults at the Pacific-Antarctic Ridge (PAR) system to plate motion changes in the last 12 Ma. Detailed analysis of the Heezen, Tharp, and Udintsev transform faults showed that the extensional stresses induced by plate motion changes could have been released through a combination of magmatic and tectonic processes: (1) For a number of ridge segments with abundant magma supply, plate motion changes might have caused the lateral transport of magma along the ridge axis and into the abutting transform valley, forming curved "hook" ridges at the ridge-transform intersection. (2) Plate motion changes might also have caused vertical deformation on steeply-dipping transtensional faults that were developed along the Heezen, Tharp, and Udintsev transform faults. (3) Distinct zones of intensive tectonic deformation, resembling belts of "rift zones", were found to be sub-parallel to the investigated transform faults. These rift-like deformation zones were hypothesized to have developed when the stresses required to drive the vertical deformation on the steeply-dipping transtensional faults along the transform faults becomes excessive, and thus deformation on off-transform "rift zones" became favored. (4) However, to explain the observed large offsets on the steeply-dipping transtensional faults, the transform faults must be relatively weak with low apparent friction coefficient comparing to the adjacent lithospheric plates.

Large-scale fault interactions at the termination of a subduction margin

NASA Astrophysics Data System (ADS)

Mouslopoulou, V.; Nicol, A., , Prof; Moreno, M.; Oncken, O.; Begg, J.; Kufner, S. K.

2017-12-01

Active subduction margins terminate against, and transfer their slip onto, plate-boundary transform faults. The manner in which plate motion is accommodated and partitioned across such kinematic transitions from thrust to strike-slip faulting over earthquake timescales, is poorly documented. The 2016 November 14th, Mw 7.8 Kaikoura Earthquake provides a rare snapshot of how seismic-slip may be accommodated at the tip of an active subduction margin. Analysis of uplift data collected using a range of techniques (field measurements, GPS, LiDAR) and published mapping coupled with 3D dislocation modelling indicates that earthquake-slip ruptured multiple faults with various orientations and slip mechanisms. Modelled and measured uplift patterns indicate that slip on the plate-interface was minor. Instead, a large offshore thrust fault, modelled to splay-off the plate-interface and to extend to the seafloor up to 15 km east of the South Island, appears to have released subduction-related strain and to have facilitated slip on numerous, strike-slip and oblique-slip faults on its hanging-wall. The Kaikoura earthquake suggests that these large splay-thrust faults provide a key mechanism in the transfer of plate motion at the termination of a subduction margin and represent an important seismic hazard.

Swath sonar mapping of Earth's submarine plate boundaries

NASA Astrophysics Data System (ADS)

Carbotte, S. M.; Ferrini, V. L.; Celnick, M.; Nitsche, F. O.; Ryan, W. B. F.

2014-12-01

The recent loss of Malaysia Airlines flight MH370 in an area of the Indian Ocean where less than 5% of the seafloor is mapped with depth sounding data (Smith and Marks, EOS 2014) highlights the striking lack of detailed knowledge of the topography of the seabed for much of the worlds' oceans. Advances in swath sonar mapping technology over the past 30 years have led to dramatic improvements in our capability to map the seabed. However, the oceans are vast and only an estimated 10% of the seafloor has been mapped with these systems. Furthermore, the available coverage is highly heterogeneous and focused within areas of national strategic priority and community scientific interest. The major plate boundaries that encircle the globe, most of which are located in the submarine environment, have been a significant focus of marine geoscience research since the advent of swath sonar mapping. While the location of these plate boundaries are well defined from satellite-derived bathymetry, significant regions remain unmapped at the high-resolutions provided by swath sonars and that are needed to study active volcanic and tectonic plate boundary processes. Within the plate interiors, some fossil plate boundary zones, major hotspot volcanoes, and other volcanic provinces have been the focus of dedicated research programs. Away from these major tectonic structures, swath mapping coverage is limited to sparse ocean transit lines which often reveal previously unknown deep-sea channels and other little studied sedimentary structures not resolvable in existing low-resolution global compilations, highlighting the value of these data even in the tectonically quiet plate interiors. Here, we give an overview of multibeam swath sonar mapping of the major plate boundaries of the globe as extracted from public archives. Significant quantities of swath sonar data acquired from deep-sea regions are in restricted-access international archives. Open access to more of these data sets would enable global comparisons of plate boundary structures and processes and could facilitate a more coordinated approach to optimizing the future acquisition of these high-value data by the global research community.

High-resolution estimates of Southwest Indian Ridge plate motions, 20 Ma to present

NASA Astrophysics Data System (ADS)

DeMets, C.; Merkouriev, S.; Sauter, D.

2015-12-01

We present the first estimates of Southwest Indian Ridge (SWIR) plate motions at high temporal resolution during the Quaternary and Neogene based on nearly 5000 crossings of 21 magnetic reversals out to C6no (19.72 Ma) and the digitized traces of 17 fracture zones and transform faults. Our reconstructions of this slow-spreading mid-ocean ridge reveal several unexpected results with notable implications for regional and global plate reconstructions since 20 Ma. Extrapolations of seafloor opening distances to zero-age seafloor based on reconstructions of reversals C1n (0.78 Ma) through C3n.4 (5.2 Ma) reveal evidence for surprisingly large outward displacement of 5 ± 1 km west of 32°E, where motion between the Nubia and Antarctic plates occurs, but 2 ± 1 km east of 32°E, more typical of most mid-ocean ridges. Newly estimated SWIR seafloor spreading rates are up to 15 per cent slower everywhere along the ridge than previous estimates. Reconstructions of the numerous observations for times back to 11 Ma confirm the existence of the hypothesized Lwandle plate at high confidence level and indicate that the Lwandle plate's western and eastern boundaries respectively intersect the ridge near the Andrew Bain transform fault complex at 32°E and between ˜45°E and 52°E, in accord with previous results. The Nubia-Antarctic, Lwandle-Antarctic and Somalia-Antarctic rotation sequences that best fit many magnetic reversal, fracture zone and transform fault crossings define previously unknown changes in the Neogene motions of all three plate pairs, consisting of ˜20 per cent slowdowns in their spreading rates at 7.2^{+0.9 }_{ -1.4} Ma if we enforce a simultaneous change in motion everywhere along the SWIR and gradual 3°-7° anticlockwise rotations of the relative slip directions. We apply trans-dimensional Bayesian analysis to our noisy, best-fitting rotation sequences in order to estimate less-noisy rotation sequences suitable for use in future global plate reconstructions and geodynamic studies. Notably, our new Nubia-Antarctic reconstruction of C5n.2 (11.0 Ma) predicts 20 per cent less opening than do two previous estimates, with important implications for motion that is estimated between the Nubia and Somalia plates. A Nubia-Somalia rotation determined from our Nubia-Antarctic and Somalia-Antarctic plate rotations for C5n.2 (11.0 Ma) predicts cumulative opening of 45 ± 4 km (95 per cent uncertainty) across the northernmost East Africa rift since 11.0 Ma, 70 per cent less than a recent 129 ± 62 km opening estimate based on a now-superseded interpretation of Anomaly 5 along the western portion of the SWIR.

Validation of a High-Order Prefactored Compact Scheme on Nonlinear Flows with Complex Geometries

NASA Technical Reports Server (NTRS)

Hixon, Ray; Mankbadi, Reda R.; Povinelli, L. A. (Technical Monitor)

2000-01-01

Three benchmark problems are solved using a sixth-order prefactored compact scheme employing an explicit 10th-order filter with optimized fourth-order Runge-Kutta time stepping. The problems solved are the following: (1) propagation of sound waves through a transonic nozzle; (2) shock-sound interaction; and (3) single airfoil gust response. In the first two problems, the spatial accuracy of the scheme is tested on a stretched grid, and the effectiveness of boundary conditions is shown. The solution stability and accuracy near a shock discontinuity is shown as well. Also, 1-D nonlinear characteristic boundary conditions will be evaluated. In the third problem, a nonlinear Euler solver will be used that solves the equations in generalized curvilinear coordinates using the chain rule transformation. This work, continuing earlier work on flat-plate cascades and Joukowski airfoils, will focus mainly on the effect of the grid and boundary conditions on the accuracy of the solution. The grids were generated using a commercially available grid generator, GridPro/az3000.

Experimental and numerical investigation of the effect of distributed suction on oblique shock wave/turbulent boundary layer interaction. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Benhachmi, Driss; Greber, Isaac; Hingst, Warren R.

1988-01-01

A combined experimental and numerical study of the interaction of an incident oblique shock wave with a turbulent boundary layer on a rough plate and on a porous plate with suction is presented. The experimental phase involved the acquisition of mean data upstream of, within, and downstream of the interaction region at Mach numbers 2.5 and 3.0. Data were taken at unit Reynolds numbers of 1.66 E7 and 1.85 E7 m respectively, and for flow deflection angles of 0, 4, 6 and 8 degs. Measured data include wall static pressure, pitot pressure profiles, and local bleed distributions on the porous plate. On the rough plate, with no suction, the boundary layer profiles were modified near the wall, but not separated for the 4 deg flow deflection angle. For the higher deflection angles of 6 and 8 degs, the boundary layer was separated. Suction increases the strength of the incident shock required to separate the turbulent boundary layer; for all shock strengths tested, separation is completely eliminated. The pitot pressure profiles are affected throughout the whole boundary layer; they are fuller than the ones obtained on the rough plate. It is also found that the combination of suction and roughness introduces spatial perturbations.

Robustness of a multimodal piezoelectric damping involving the electrical analogue of a plate

NASA Astrophysics Data System (ADS)

Lossouarn, Boris; Cunefare, Kenneth A.; Aucejo, Mathieu; Deü, Jean-François

2016-04-01

Multimodal passive damping of a mechanical structure can be implemented by a coupling to a secondary structure exhibiting similar modal properties. When considering a piezoelectric coupling, the secondary structure is an electrical network. A suitable topology for such a network can be obtained by a finite difference formulation of the mechanical equations, followed by a direct electromechanical analogy. This procedure is applied to the Kirchhoff-Love theory in order to find the electrical analogue of a clamped plate. The passive electrical network is implemented with inductors, transformers and the inherent capacitance of the piezoelectric patches. The electrical resonances are tuned to approach those of several mechanical modes simultaneously. This yields a broadband reduction of the plate vibrations through the array of interconnected piezoelectric patches. The robustness of the control strategy is evaluated by introducing perturbations in the mechanical or electrical designs. A non-optimal tuning is considered by way of a uniform variation of the network inductance. Then, the effect of local or boundary modifications of the electromechanical system is observed experimentally. In the end, the use of an analogous electrical network appears as an efficient and robust solution for the multimodal control of a plate.

Linking plate reconstructions with deforming lithosphere to geodynamic models

NASA Astrophysics Data System (ADS)

Müller, R. D.; Gurnis, M.; Flament, N.; Seton, M.; Spasojevic, S.; Williams, S.; Zahirovic, S.

2011-12-01

While global computational models are rapidly advancing in terms of their capabilities, there is an increasing need for assimilating observations into these models and/or ground-truthing model outputs. The open-source and platform independent GPlates software fills this gap. It was originally conceived as a tool to interactively visualize and manipulate classical rigid plate reconstructions and represent them as time-dependent topological networks of editable plate boundaries. The user can export time-dependent plate velocity meshes that can be used either to define initial surface boundary conditions for geodynamic models or alternatively impose plate motions throughout a geodynamic model run. However, tectonic plates are not rigid, and neglecting plate deformation, especially that of the edges of overriding plates, can result in significant misplacing of plate boundaries through time. A new, substantially re-engineered version of GPlates is now being developed that allows an embedding of deforming plates into topological plate boundary networks. We use geophysical and geological data to define the limit between rigid and deforming areas, and the deformation history of non-rigid blocks. The velocity field predicted by these reconstructions can then be used as a time-dependent surface boundary condition in regional or global 3-D geodynamic models, or alternatively as an initial boundary condition for a particular plate configuration at a given time. For time-dependent models with imposed plate motions (e.g. using CitcomS) we incorporate the continental lithosphere by embedding compositionally distinct crust and continental lithosphere within the thermal lithosphere. We define three isostatic columns of different thickness and buoyancy based on the tectonothermal age of the continents: Archean, Proterozoic and Phanerozoic. In the fourth isostatic column, the oceans, the thickness of the thermal lithosphere is assimilated using a half-space cooling model. We also define the thickness of the thermal lithosphere for different continental types, with the exception of the deforming areas that are fully dynamic. Finally, we introduce a "slab assimilation" method in which the thermal structure of the slab, derived analytically, is progressively assimilated into the upper mantle through time. This method not only improves the continuity of slabs in forward models with imposed plate motions, but it also allows us to model flat slab segments that are particularly relevant for understanding dynamic surface topography. When it comes to post-processing and visualisation, GPlates allows the user to import time-dependent model output image stacks to visualise mantle properties (e.g. temperature) at a given depth through time, with plate boundaries and other data attached to plates overlain. This approach provides an avenue to simultaneously investigate the contributions of lithospheric deformation and mantle flow to surface topography. Currently GPlates is being used in conjunction with the codes CitcomS, Terra, BEMEarth and the adaptive mesh refinement code Rhea. A GPlates python plugin infrastructure makes it easy to extend interoperability with other geodynamic modelling codes.

Simulating wave-turbulence on thin elastic plates with arbitrary boundary conditions

NASA Astrophysics Data System (ADS)

van Rees, Wim M.; Mahadevan, L.

2016-11-01

The statistical characteristics of interacting waves are described by the theory of wave turbulence, with the study of deep water gravity wave turbulence serving as a paradigmatic physical example. Here we consider the elastic analog of this problem in the context of flexural waves arising from vibrations of a thin elastic plate. Such flexural waves generate the unique sounds of so-called thunder machines used in orchestras - thin metal plates that make a thunder-like sound when forcefully shaken. Wave turbulence in elastic plates is typically investigated numerically using spectral simulations with periodic boundary conditions, which are not very realistic. We will present the results of numerical simulations of the dynamics of thin elastic plates in physical space, with arbitrary shapes, boundary conditions, anisotropy and inhomogeneity, and show first results on wave turbulence beyond the conventionally studied rectangular plates. Finally, motivated by a possible method to measure ice-sheet thicknesses in the open ocean, we will further discuss the behavior of a vibrating plate when floating on an inviscid fluid.

The proximity of hotspots to convergent and divergent plate boundaries

NASA Technical Reports Server (NTRS)

Weinstein, Stuart A.; Olson, Peter L.

1989-01-01

An analysis of four different hotspot distributions, ranging from Morgan's (1972) original list of 19 to Vogt's (1981) list of 117 reveals that the hotspots are preferentially located near divergent plate boundaries. The probability of this proximity occurring by chance alone is quite remote, less than 0.01 for all four hotspot distributions. The same analysis also reveals that the hotspots are preferentially excluded from regions near convergent plate boundaries. The probability of this exclusion occurring by chance alone is 0.1 or less for three out of the four distributions examined. We interpret this behavior as being a consequence of the effects of large scale convective circulation on ascending mantle plumes. Mantle thermal plumes, the most probable source of hotspots, arise from instabilities in a basal thermal boundary layer. Plumes are suppressed from regions beneath convergent boundaries by descending flow and are entrained into the upwelling flow beneath spreading centers. Plate-scale convective circulation driven by subduction may also advect mantle thermal plumes toward spreading centers.

3-D Simulation of Tectonic Evolution in Mariana with a Coupled Model of Plate Subduction and Back-Arc Spreading

NASA Astrophysics Data System (ADS)

Hashima, A.; Matsu'Ura, M.

2006-12-01

We obtained the expressions for internal deformation fields due to a moment tensor in an elastic-viscoelastic layered holf-space. This unified formulation of internal deformation fields for shear faulting and crack opening enabled us to deal with the problem of tectonic deformation at a composite type of plate boundary zones. The tectonic deformation can be ascribed to mechanical interaction at plate boundaries, which make a closed circuit with the mode of relative plate motion changing from divergence to convergence through transcurrent motion. One of the rational ways to represent mechanical interaction at plate boundaries is specifying the increase rates of normal or tangential displacement discontinuity across plate interfaces. On the basis of such a basic idea we developed a 3-D simulation model for the nonlinear, coupled system of plate subduction and back-arc spreading in Mariana. Through numerical simulations we revealed the evolution process of back-arc spreading. At the first stage, steady plate subduction (shear faulting at a plate interface) gradually forms tensile stress fields in the back-arc region of the overriding plate. When the accumulated tensile stress reaches a critical level, back-arc spreading (crack opening) starts at a structurally weak portion of the overriding plate. The horizontal motion of the frontal part of the overriding plate due to back-arc spreading pushes out the plate boundary toward the oceanic plate. In steady-state plate subduction the shear stress acting on a plate interface must balance with the maximum frictional resistance (shear strength) of the plate interface. Therefore, the increase of shear stress at the plate interface leads to the increase of slip rate at the plate interface. The local increase of slip rate at the plate interface produces the additional tensile stress in the back-arc region. The increased tensile stress must be canceled out by the additional crack opening. Such a feedback mechanism between plate subduction and back-arc spreading is crucial to understand the development of back-ark spreading.

Does intraplate brittle deformation indicate far-field stress signals? A case study of Central Europe

NASA Astrophysics Data System (ADS)

Navabpour, Payman; Kley, Jonas; Le Breton, Eline; van Hinsbergen, Douwe J. J.; Ustaszewski, Kamil

2017-04-01

Even though Central Europe has been located within a plate interior since the end of the Variscan orogeny, its intracontinental basins and highs recorded a succession of different tectonic regimes throughout the Mesozoic and Cenozoic, which were coeval with events at distant plate margins. A long Triassic-Cretaceous period of weak subsidence with intermittent extension was followed by NNE-SSW contraction in the Late Cretaceous-Paleocene. Renewed extension led to the formation of the Cenozoic Rift System and eventually evolved to the present-day variable stress regimes with a consistent NW-SE-oriented maximum horizontal shortening, SHmax. The detailed knowledge of this evolution relies on exhaustive lithostratigraphy and geochronological datasets, as well as on reconstruction of successive states of paleostress that controlled the formation and/or inversion of intracontinental basins. In combination, these data provide an excellent opportunity of linking the intracontinental deformation to the lithospheric plate boundary kinematics. Regional-scale analysis of fault kinematics in Central Europe unveiled a succession of consistent stress states for the crystalline basement and sedimentary cover of the brittle crust. These states of stress include a post-Triassic normal faulting regime with NE-SW-trending σ3 axis, strike-slip and thrust faulting regimes with NNE-SSW-trending σ1 axis, supposedly of Late Cretaceous age, and two younger events of normal and strike-slip faulting regimes with NW-SE-trending σ3 and σ1 axes, respectively. In this study, we report on the first attempts of linking the central European intraplate kinematics to changes in relative motion between the plates. The integration of stress fields with plate boundary kinematics suggests that the Late Cretaceous contraction may be explained by a change in African plate motion with respect to Eurasia from SE-directed sinistral transform to NNE-directed convergence. The reorientation of contraction to the present-day SHmax likely results from a change in direction of Africa-Eurasia plate convergence from N-S to NW-SE combined with plume-enhanced ridge push of the North Atlantic Ocean.

Spatial distribution of non volcanic tremors offshore eastern Taiwan

NASA Astrophysics Data System (ADS)

Xie, X. S.; Lin, J. Y.; Hsu, S. K.; Lee, C. H.; Liang, C. W.

2012-04-01

Non-volcanic tremor (NVT), originally identified in the subduction zone of the southwest Japan, have been well studied in the circum-Pacific subduction zones and the transform plate boundary in California. Most studies related NVT to the release of fluids, while some others associated them with slow-slip events, and can be triggered instantaneously by the surface waves of teleseismic events. Taiwan is located at a complex intersection of the Philippines Sea Plate and the Eurasian Plate. East of Taiwan, the Philippine Sea plate subducts northward beneath the Ryukyu arc. The major part of the island results from the strong convergence between the two plates and the convergent boundary is along the Longitudinal Valley. Moreover, an active strike-slip fault along the Taitung Canyon was reported in the offshore eastern Taiwan. In such complicate tectonic environments, NVT behavior could probably bring us more information about the interaction of all the geological components in the area. In this study, we analyze the seismic signals recorded by the Ocean bottom Seismometer (OBS) deployed offshore eastern Taiwan in September 2009. TAMS (Tremor Active Monitor System) software was used to detect the presence of NVT. 200 tremor-like signals were obtained from the 3 weeks recording period. We use the SSA (Source-Scanning Algorithm) to map the possible distribution of the tremor. In total, 180 tremors were located around the eastern offshore Taiwan. The tremors are mainly distributed in two source areas: one is along the Taitung Canyon, and the other is sub-parallel to the Ryukyu Trench, probably along the plate interface. Many tremors are located at depth shallower than 5 km, which suggests a possible existence of a weak basal detachment along the sea bottom. Other tremors with larger depth may be related to the dehydration of the subducting sea plate as suggested by the former studies. Limited by the short recording period of the OBS experiment, we could not obtain any possible repeating interval and the spatial migration about the tremor occurrence. However, the presence of NVT offshore eastern Taiwan shown in our study still brings us valuable understanding about the undergoing tectonic processes in the marine area.

Application of coordinate transform on ball plate calibration

NASA Astrophysics Data System (ADS)

Wei, Hengzheng; Wang, Weinong; Ren, Guoying; Pei, Limei

2015-02-01

For the ball plate calibration method with coordinate measurement machine (CMM) equipped with laser interferometer, it is essential to adjust the ball plate parallel to the direction of laser beam. It is very time-consuming. To solve this problem, a method based on coordinate transformation between machine system and object system is presented. With the fixed points' coordinates of the ball plate measured in the object system and machine system, the transformation matrix between the coordinate systems is calculated. The laser interferometer measurement data error due to the placement of ball plate can be corrected with this transformation matrix. Experimental results indicate that this method is consistent with the handy adjustment method. It avoids the complexity of ball plate adjustment. It also can be applied to the ball beam calibration.

Non-Orthogonality of Seafloor Spreading: A New Look at Fast Spreading Centers

NASA Astrophysics Data System (ADS)

Zhang, T.; Gordon, R. G.

2015-12-01

Most of Earth's surface is created by seafloor spreading. While most seafloor spreading is orthogonal, that is, the strike of mid-ocean ridge segments is perpendicular to nearby transform faults, examples of significant non-orthogonality have been noted since the 1970s, in particular in regions of slow seafloor spreading such as the western Gulf of Aden with non-orthogonality up to 45°. In contrast, here we focus on fast and ultra-fast seafloor spreading along the East Pacific Rise. To estimate non-orthogonality, we compare ridge-segment strikes with the direction of plate motion determined from the angular velocity that best fits all the data along the boundary of a single plate pair [DeMets et al., 2010]. The advantages of this approach include greater accuracy and the ability to estimate non-orthogonality where there are no nearby transform faults. Estimating the strikes of fast-spreading mid-ocean ridge segments present several challenges as non-transform offsets on various scales affect the estimate of the strike. While spreading is orthogonal or nearly orthogonal along much of the East Pacific Rise, some ridge segments along the Pacific-Nazca boundary near 30°S and near 16°S-22°S deviate from orthogonality by as much as 6°-12° even when we exclude the portions of mid-ocean ridge segments involved in overlapping spreading centers. Thus modest but significant non-orthogonality occurs where seafloor spreading is the fastest on the planet. If a plume lies near the ridge segment, we assume it contributes to magma overpressure along the ridge segment [Abelson & Agnon, 1997]. We further assume that the contribution to magma overpressure is proportional to the buoyancy flux of the plume [Sleep, 1990] and inversely proportional to the distance between the mid-ocean ridge segment and a given plume. We find that the non-orthogonal angle tends to decrease with increasing spreading rate and with increasing distance between ridge segment and plume.

A scientific report on heat transfer analysis in mixed convection flow of Maxwell fluid over an oscillating vertical plate.

PubMed

Khan, Ilyas; Shah, Nehad Ali; Dennis, L C C

2017-03-15

This scientific report investigates the heat transfer analysis in mixed convection flow of Maxwell fluid over an oscillating vertical plate with constant wall temperature. The problem is modelled in terms of coupled partial differential equations with initial and boundary conditions. Some suitable non-dimensional variables are introduced in order to transform the governing problem into dimensionless form. The resulting problem is solved via Laplace transform method and exact solutions for velocity, shear stress and temperature are obtained. These solutions are greatly influenced with the variation of embedded parameters which include the Prandtl number and Grashof number for various times. In the absence of free convection, the corresponding solutions representing the mechanical part of velocity reduced to the well known solutions in the literature. The total velocity is presented as a sum of both cosine and sine velocities. The unsteady velocity in each case is arranged in the form of transient and post transient parts. It is found that the post transient parts are independent of time. The solutions corresponding to Newtonian fluids are recovered as a special case and comparison between Newtonian fluid and Maxwell fluid is shown graphically.

A scientific report on heat transfer analysis in mixed convection flow of Maxwell fluid over an oscillating vertical plate

NASA Astrophysics Data System (ADS)

Khan, Ilyas; Shah, Nehad Ali; Dennis, L. C. C.

2017-03-01

This scientific report investigates the heat transfer analysis in mixed convection flow of Maxwell fluid over an oscillating vertical plate with constant wall temperature. The problem is modelled in terms of coupled partial differential equations with initial and boundary conditions. Some suitable non-dimensional variables are introduced in order to transform the governing problem into dimensionless form. The resulting problem is solved via Laplace transform method and exact solutions for velocity, shear stress and temperature are obtained. These solutions are greatly influenced with the variation of embedded parameters which include the Prandtl number and Grashof number for various times. In the absence of free convection, the corresponding solutions representing the mechanical part of velocity reduced to the well known solutions in the literature. The total velocity is presented as a sum of both cosine and sine velocities. The unsteady velocity in each case is arranged in the form of transient and post transient parts. It is found that the post transient parts are independent of time. The solutions corresponding to Newtonian fluids are recovered as a special case and comparison between Newtonian fluid and Maxwell fluid is shown graphically.

A scientific report on heat transfer analysis in mixed convection flow of Maxwell fluid over an oscillating vertical plate

PubMed Central

Khan, Ilyas; Shah, Nehad Ali; Dennis, L. C. C.

2017-01-01

This scientific report investigates the heat transfer analysis in mixed convection flow of Maxwell fluid over an oscillating vertical plate with constant wall temperature. The problem is modelled in terms of coupled partial differential equations with initial and boundary conditions. Some suitable non-dimensional variables are introduced in order to transform the governing problem into dimensionless form. The resulting problem is solved via Laplace transform method and exact solutions for velocity, shear stress and temperature are obtained. These solutions are greatly influenced with the variation of embedded parameters which include the Prandtl number and Grashof number for various times. In the absence of free convection, the corresponding solutions representing the mechanical part of velocity reduced to the well known solutions in the literature. The total velocity is presented as a sum of both cosine and sine velocities. The unsteady velocity in each case is arranged in the form of transient and post transient parts. It is found that the post transient parts are independent of time. The solutions corresponding to Newtonian fluids are recovered as a special case and comparison between Newtonian fluid and Maxwell fluid is shown graphically. PMID:28294186

Drag reduction using wrinkled surfaces in high Reynolds number laminar boundary layer flows

NASA Astrophysics Data System (ADS)

Raayai-Ardakani, Shabnam; McKinley, Gareth H.

2017-09-01

Inspired by the design of the ribbed structure of shark skin, passive drag reduction methods using stream-wise riblet surfaces have previously been developed and tested over a wide range of flow conditions. Such textures aligned in the flow direction have been shown to be able to reduce skin friction drag by 4%-8%. Here, we explore the effects of periodic sinusoidal riblet surfaces aligned in the flow direction (also known as a "wrinkled" texture) on the evolution of a laminar boundary layer flow. Using numerical analysis with the open source Computational Fluid Dynamics solver OpenFOAM, boundary layer flow over sinusoidal wrinkled plates with a range of wavelength to plate length ratios ( λ / L ), aspect ratios ( 2 A / λ ), and inlet velocities are examined. It is shown that in the laminar boundary layer regime, the riblets are able to retard the viscous flow inside the grooves creating a cushion of stagnant fluid that the high-speed fluid above can partially slide over, thus reducing the shear stress inside the grooves and the total integrated viscous drag force on the plate. Additionally, we explore how the boundary layer thickness, local average shear stress distribution, and total drag force on the wrinkled plate vary with the aspect ratio of the riblets as well as the length of the plate. We show that riblets with an aspect ratio of close to unity lead to the highest reduction in the total drag, and that because of the interplay between the local stress distribution on the plate and stream-wise evolution of the boundary layer the plate has to exceed a critical length to give a net decrease in the total drag force.

Lagrangian analysis of the laminar flat plate boundary layer

NASA Astrophysics Data System (ADS)

Gabr, Mohammad

2016-10-01

The flow properties at the leading edge of a flat plate represent a singularity to the Blasius laminar boundary layer equations; by applying the Lagrangian approach, the leading edge velocity profiles of the laminar boundary layer over a flat plate are studied. Experimental observations as well as the theoretical analysis show an exact Gaussian distribution curve as the original starting profile of the laminar flow. Comparisons between the Blasius solution and the Gaussian curve solution are carried out providing a new insight into the physics of the laminar flow.

A diffuse plate boundary model for Indian Ocean tectonics

NASA Technical Reports Server (NTRS)

Wiens, D. A.; Demets, C.; Gordon, R. G.; Stein, S.; Argus, D.

1985-01-01

It is suggested that motion along the virtually aseismic Owen fracture zone is negligible, so that Arabia and India are contained within a single Indo-Arabian plate divided from the Australian plate by a diffuse boundary. The boundary is a zone of concentrated seismicity and deformation commonly characterized as 'intraplate'. The rotation vector of Australia relative to Indo-Arabia is consistent with the seismologically observed 2 cm/yr of left-lateral strike-slip along the Ninetyeast Ridge, north-south compression in the Central Indian Ocean, and the north-south extension near Chagos.

Acoustic monitoring of earthquakes along the Blanco Transform Fault zone and Gorda Plate and their tectonic implications

NASA Astrophysics Data System (ADS)

Dziak, Robert Paul

Hydroacoustic tertiary (T-) waves are seismically generated acoustic waves that propagate over great distances in the ocean sound channel with little loss in signal strength. Hydrophone recorded T-waves can provide a lower earthquake detection threshold and an improved epicenter location accuracy for oceanic earthquakes than land-based seismic networks. Thus detection and location of NE Pacific ocean earthquakes along the Blanco Transform Fault (BTFZ) and Gorda plate using the U.S. Navy's SOSUS (SOund SUrveillance System) hydrophone arrays afford greater insight into the current state of stress and crustal deformation mechanics than previously available. Acoustic earthquake information combined with bathymetry, submersible observations, earthquake source- parameter estimates, petrologic samples, and water-column chemistry renders a new tectonic view of the southern Juan de Fuca plate boundaries. Chapter 2 discusses development of seismo-acoustic analysis techniques using the well-documented April 1992 Cape Mendocino earthquake sequence. Findings include a hydrophone detection threshold estimate (M ~ 2.4), and T-wave propagation path modeling to approximate earthquake acoustic source energy. Empirical analyses indicate that acoustic energy provides a reasonable magnitude and seismic moment estimate of oceanic earthquakes not detected by seismic networks. Chapters 3 documents a probable volcanogenic T-wave event swarm along a pull-apart basin within the western BTFZ during January 1994. Response efforts yielded evidence of anomalous water-column 3He concentrations, pillow- lava volcanism, and the first discovery of active hydrothermal vents along an oceanic fracture zone. Chapter 4 discusses the detection of a NE-SW trending microearthquake band along the mid-Gorda plate which was active from initiation of SOSUS recording in August 1991 through July 1992, then abruptly ceased. It is proposed that eventual termination of the Gorda plate seismicity band is due to strain reduction associated with the Cape Mendocino earthquake sequence. Chapter 5 combines bathymetric, hydro-acoustic, seismic, submersible, and gravity data to investigate the active tectonics of the transform parallel Blanco Ridge (BR), along the eastern BTFZ. The BR formation mechanism preferred here is uplift through strike-slip motion (with a normal component) followed by formation and intrusion of mantle-derived serpentinized-peridotite into the shallow ocean crust. The conclusion considers a potential link between the deformation patterns observed along the BTFZ and Gorda plate regions.

Transpressional Tectonics across the N. American-Caribbean Plate Boundary: Preliminary Results of a Multichannel Seismic Survey of Lake Azuei, Haiti.

NASA Astrophysics Data System (ADS)

Hearn, C. K.; Cormier, M. H.; Sloan, H.; Wattrus, N. J.; Boisson, D.; Brown, B.; Guerrier, K.; King, J. W.; Knotts, P.; Momplaisir, R.; Sorlien, C. C.; Stempel, R.; Symithe, S. J.; Ulysse, S. M. J.

2017-12-01

On January 12, 2010, a Mw 7.0 earthquake struck Haiti, killing over 200,000 people and devastating the Capital city of Port-au-Prince and the surrounding regions. It ruptured a previously unknown blind-thrust fault that abuts the Enriquillo Plantain Garden Fault (EPGF), one of two transform faults that define the North American-Caribbean plate boundary. That earthquake highlighted how transpression across this complex boundary is accommodated by slip partitioning into strike-slip and compressional structures. Because the seismic hazard is higher for a rupture on a reverse or oblique-slip fault than on a vertical strike-slip fault, the need to characterize the geometry of that fault system is clear. Lake Azuei overlies this plate boundary 60 km east of the 2010 epicenter. The lake's 23 km long axis trends NW-SE, parallel to the Haitian fold-and-thrust belt and oblique to the EPGF. This tectonic context makes it an ideal target for investigating the partitioning of plate motion between strike-slip and compressional structures. In January 2017, we acquired 222 km of multichannel seismic (MCS) profiles in the lake, largely concurrent with subbottom seismic (CHIRP) profiles. The MCS data were acquired using a high-frequency BubbleGun source and a 75 m-long, 24-channel streamer, achieving a 24 seismic fold with a penetration of 200 m below lakebed. With the goal of resolving tectonic structures in 3-D, survey lines were laid out in a grid with profiles spaced 1.2 km apart. Additional profiles were acquired at the SE end of the lake where most of the tectonic activity is presumably occurring. The co-located CHIRP and MCS profiles document the continuity of tectonic deformation between the surficial sediments and the deeper strata. Preliminary processing suggests that a SW-dipping blind thrust fault, expressed updip as a large monocline fold, may control the western edge of the lake. Gentle, young folds that protrude from the flat lakebed are also imaged with the CHIRP data. No obvious strike-slip faults are revealed in the MCS or CHIRP imagery. This result is consistent with a published analysis of GPS measurements that suggests oblique convergence on a south-dipping reverse fault along the southern shore of the lake.

Earthquakes and submarine volcanism in the Northeast Pacific: Exploration in the time domain based on 21-years of hydroacoustic monitoring

NASA Astrophysics Data System (ADS)

Hammond, S. R.; Dziak, R. P.; Fox, C. G.

2012-12-01

Monitoring of regional seismic activity in the Northeast Pacific has been accomplished for the past 21 years using US Navy's Sound Surveillance System (SOSUS) hydrophone arrays. Seafloor seismic activity in this region occurs along the spreading center and transform boundaries between the Juan de Fuca, Pacific and North American plates. During the time span, from 1991 through 2011, nearly 50,000 earthquakes were detected and located. The majority of these events were associated with these tectonic boundaries but sections of several plate boundaries were largely aseismic during the this time span. While most of the earthquakes were associated with geological structures revealed in bathymetric maps of the region, there were also less easily explained intraplate events including a swarm of events within the interior of the southern portion of the Juan de Fuca plate. The location and sequential timing of events on portions of the plate boundaries also suggests ordered patterns of stress release. Among the most scientifically significant outcomes of acoustic monitoring was the discovery that deep seafloor magmatic activity can be accompanied by intense (> 1000 events/day) earthquake swarms. The first swarm detected by SOSUS, in 1993, was confirmed to have been associated with an extrusive volcanic eruption which occurred along a segment of the Juan de Fuca spreading center. Notably, this was the first deep spreading center eruption detected, located, and studied while it was active. Subsequently, two more swarms were confirmed to have been associated with volcanic eruptions, one on the Gorda spreading center in 1996 and the other at Axial volcano in 1998. One characteristic of these swarm events is migration of their earthquake locations 10s of km along the ridge axis tracking the movement of magma down-rift. The most rapid magma propagation events have been shown to be associated with seafloor eruptions and dramatic, transient changes in hydrothermal circulation as well as discharges of large volumes of hot water, i.e., megaplumes. Hydroacoustic monitoring using SOSUS, and now augmented with hydrophones deployed on stationary moorings as well as mobile platforms (e.g. gliders), provides a unique means for gaining knowledge concerning a broad diversity of present-day topics of scientific importance including, sources and fate of carbon in the deep ocean, deep ocean micro- and macro-ecosystems, and changes in ocean ambient noise levels.

Intrastab Earthquakes: Dehydration of the Cascadia Slab

USGS Publications Warehouse

Preston, L.A.; Creager, K.C.; Crosson, R.S.; Brocher, T.M.; Trehu, A.M.

2003-01-01

We simultaneously invert travel times of refracted and wide-angle reflected waves for three-dimensional compressional-wave velocity structure, earthquake locations, and reflector geometry in northwest Washington state. The reflector, interpreted to be the crust-mantle boundary (Moho) of the subducting Juan de Fuca plate, separates intrastab earthquakes into two groups, permitting a new understanding of the origins of intrastab earthquakes in Cascadia. Earthquakes up-dip of the Moho's 45-kilometer depth contour occur below the reflector, in the subducted oceanic mantle, consistent with serpentinite dehydration; earthquakes located down-dip occur primarily within the subducted crust, consistent with the basalt-to-eclogite transformation.

Plate coupling across the northern Manila subduction zone deduced from mantle lithosphere buoyancy

NASA Astrophysics Data System (ADS)

Lo, Chung-Liang; Doo, Wen-Bin; Kuo-Chen, Hao; Hsu, Shu-Kun

2017-12-01

The Manila subduction zone is located at the plate boundary where the Philippine Sea plate (PSP) moves northwestward toward the Eurasian plate (EU) with a high convergence rate. However, historically, no large earthquakes greater than Mw7 have been observed across the northern Manila subduction zone. The poorly understood plate interaction between these two plates in this region creates significant issues for evaluating the seismic hazard. Therefore, the variation of mantle lithospheric buoyancy is calculated to evaluate the plate coupling status across the northern Manila subduction zone, based on recently published forward gravity modeling constrained by the results of the P-wave seismic crustal structure of the TAIGER (Taiwan Integrated Geodynamic Research) project. The results indicate weak plate coupling between the PSP and EU, which could be related to the release of the overriding PSP from the descending EU's dragging force, which was deduced from the higher elevation of the Luzon arc and the fore-arc basin northward toward the Taiwan orogen. Moreover, serpentinized peridotite is present above the plate boundary and is distributed more widely and thickly closer to offshore southern Taiwan orogen. We suggest that low plate coupling may facilitate the uplifting of serpentinized mantle material up to the plate boundary.

Spatio-temporal mapping of plate boundary faults in California using geodetic imaging

USGS Publications Warehouse

Donnellan, Andrea; Arrowsmith, Ramon; DeLong, Stephen B.

2017-01-01

The Pacific–North American plate boundary in California is composed of a 400-km-wide network of faults and zones of distributed deformation. Earthquakes, even large ones, can occur along individual or combinations of faults within the larger plate boundary system. While research often focuses on the primary and secondary faults, holistic study of the plate boundary is required to answer several fundamental questions. How do plate boundary motions partition across California faults? How do faults within the plate boundary interact during earthquakes? What fraction of strain accumulation is relieved aseismically and does this provide limits on fault rupture propagation? Geodetic imaging, broadly defined as measurement of crustal deformation and topography of the Earth’s surface, enables assessment of topographic characteristics and the spatio-temporal behavior of the Earth’s crust. We focus here on crustal deformation observed with continuous Global Positioning System (GPS) data and Interferometric Synthetic Aperture Radar (InSAR) from NASA’s airborne UAVSAR platform, and on high-resolution topography acquired from lidar and Structure from Motion (SfM) methods. Combined, these measurements are used to identify active structures, past ruptures, transient motions, and distribution of deformation. The observations inform estimates of the mechanical and geometric properties of faults. We discuss five areas in California as examples of different fault behavior, fault maturity and times within the earthquake cycle: the M6.0 2014 South Napa earthquake rupture, the San Jacinto fault, the creeping and locked Carrizo sections of the San Andreas fault, the Landers rupture in the Eastern California Shear Zone, and the convergence of the Eastern California Shear Zone and San Andreas fault in southern California. These examples indicate that distribution of crustal deformation can be measured using interferometric synthetic aperture radar (InSAR), Global Navigation Satellite System (GNSS), and high-resolution topography and can improve our understanding of tectonic deformation and rupture characteristics within the broad plate boundary zone.

A study of the effect of a boundary layer profile on the dynamic response and acoustic radiation of flat panels. Ph.D. Thesis - Virginia Univ.

NASA Technical Reports Server (NTRS)

Mixson, J. S.

1973-01-01

The response of a thin, elastic plate to a harmonic force which drives the plate from below and a compressible air stream with a viscous boundary layer flowing parallel to the upper surface along the length was investigated. Equations governing the forced response of the coupled plate-aerodynamic system are derived along with appropriate boundary conditions. Calculations of basic solution parameters for a linear velocity profile and for a Blasius profile showed that the same system response could be obtained from each profile if appropriate values of boundary layer thickness were chosen for each profile.

Oceanic ridges and transform faults: Their intersection angles and resistance to plate motion

USGS Publications Warehouse

Lachenbruch, A.H.; Thompson, G.A.

1972-01-01

The persistent near-orthogonal pattern formed by oceanic ridges and transform faults defies explanation in terms of rigid plates because it probably depends on the energy associated with deformation. For passive spreading, it is likely that the ridges and transforms adjust to a configuration offering minimum resistance to plate separation. This leads to a simple geometric model which yields conditions for the occurrence of transform faults and an aid to interpretation of structural patterns in the sea floor. Under reasonable assumptions, it is much more difficult for diverging plates to spread a kilometer of ridge than to slip a kilometer of transform fault, and the patterns observed at spreading centers might extend to lithospheric depths. Under these conditions, the resisting force at spreading centers could play a significant role in the dynamics of plate-tectonic systems. ?? 1972.

Effects of boundary-layer separation controllers on a desktop fume hood.

PubMed

Huang, Rong Fung; Chen, Jia-Kun; Hsu, Ching Min; Hung, Shuo-Fu

2016-10-02

A desktop fume hood installed with an innovative design of flow boundary-layer separation controllers on the leading edges of the side plates, work surface, and corners was developed and characterized for its flow and containment leakage characteristics. The geometric features of the developed desktop fume hood included a rearward offset suction slot, two side plates, two side-plate boundary-layer separation controllers on the leading edges of the side plates, a slanted surface on the leading edge of the work surface, and two small triangular plates on the upper left and right corners of the hood face. The flow characteristics were examined using the laser-assisted smoke flow visualization technique. The containment leakages were measured by the tracer gas (sulphur hexafluoride) detection method on the hood face plane with a mannequin installed in front of the hood. The results of flow visualization showed that the smoke dispersions induced by the boundary-layer separations on the leading edges of the side plates and work surface, as well as the three-dimensional complex flows on the upper-left and -right corners of the hood face, were effectively alleviated by the boundary-layer separation controllers. The results of the tracer gas detection method with a mannequin standing in front of the hood showed that the leakage levels were negligibly small (≤0.003 ppm) at low face velocities (≥0.19 m/s).

Boundary layer control device for duct silencers

NASA Technical Reports Server (NTRS)

Schmitz, Fredric H. (Inventor); Soderman, Paul T. (Inventor)

1993-01-01

A boundary layer control device includes a porous cover plate, an acoustic absorber disposed under the porous cover plate, and a porous flow resistive membrane interposed between the porous cover plate and the acoustic absorber. The porous flow resistive membrane has a flow resistance low enough to permit sound to enter the acoustic absorber and high enough to damp unsteady flow oscillations.

Tectonic lineaments in the cenozoic volcanics of southern Guatemala: Evidence for a broad continental plate boundary zone

NASA Technical Reports Server (NTRS)

Baltuck, M.; Dixon, T. H.

1984-01-01

The northern Caribbean plate boundary has been undergoing left lateral strike slip motion since middle Tertiary time. The western part of the boundary occurs in a complex tectonic zone in the continental crust of Guatemala and southernmost Mexico, along the Chixoy-Polochic, Motogua and possibly Jocotan-Chamelecon faults. Prominent lineaments visible in radar imagery in the Neogene volcanic belt of southern Guatemala and western El Salvador were mapped and interpreted to suggest southwest extensions of this already broad plate boundary zone. Because these extensions can be traced beneath Quaternary volcanic cover, it is thought that this newly mapped fault zone is active and is accommodating some of the strain related to motion between the North American and Caribbean plates. Onshore exposures of the Motoqua-Polochic fault systems are characterized by abundant, tectonically emplaced ultramafic rocks. A similar mode of emplacement for these off shore ultramafics, is suggested.

Effect of leading-edge geometry on boundary-layer receptivity to freestream sound

NASA Technical Reports Server (NTRS)

Lin, Nay; Reed, Helen L.; Saric, W. S.

1991-01-01

The receptivity to freestream sound of the laminar boundary layer over a semi-infinite flat plate with an elliptic leading edge is simulated numerically. The incompressible flow past the flat plate is computed by solving the full Navier-Stokes equations in general curvilinear coordinates. A finite-difference method which is second-order accurate in space and time is used. Spatial and temporal developments of the Tollmien-Schlichting wave in the boundary layer, due to small-amplitude time-harmonic oscillations of the freestream velocity that closely simulate a sound wave travelling parallel to the plate, are observed. The effect of leading-edge curvature is studied by varying the aspect ratio of the ellipse. The boundary layer over the flat plate with a sharper leading edge is found to be less receptive. The relative contribution of the discontinuity in curvature at the ellipse-flat-plate juncture to receptivity is investigated by smoothing the juncture with a polynomial. Continuous curvature leads to less receptivity. A new geometry of the leading edge, a modified super ellipse, which provides continuous curvature at the juncture with the flat plate, is used to study the effect of continuous curvature and inherent pressure gradient on receptivity.

Morphology of Proeutectoid Ferrite

NASA Astrophysics Data System (ADS)

Yin, Jiaqing; Hillert, Mats; Borgenstam, Annika

2017-03-01

The morphology of grain boundary nucleated ferrite particles in iron alloys with 0.3 mass pct carbon has been classified according to the presence of facets. Several kinds of particles extend into both grains of austenite and have facets to both. It is proposed that they all belong to a continuous series of shapes. Ferrite plates can nucleate directly on the grain boundary but can also develop from edges on many kinds of particles. Feathery structures of parallel plates on both sides of a grain boundary can thus form. In sections, parallel to their main growth direction, plates have been seen to extend the whole way from the nucleation site at the grain boundary and to the growth front. This happens in the whole temperature range studied from 973 K to 673 K (700 °C to 400 °C). The plates thus grow continuously and not by subunits stopping at limited length and continuing the growth by new ones nucleating. Sometimes, the plates have ridges and in oblique sections they could be mistaken for the start of new plates. No morphological signs were observed indicating a transition between Widmanstätten ferrite and bainitic ferrite. It is proposed that there is only one kind of acicular ferrite.

Characterization of microstructure and texture across dissimilar super duplex/austenitic stainless steel weldment joint by super duplex filler metal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eghlimi, Abbas, E-mail: a.eghlimi@ma.iut.ac.ir; Shamanian, Morteza; Eskandarian, Masoomeh

In the present paper, microstructural changes across an as-welded dissimilar austenitic/duplex stainless steel couple welded by a super duplex stainless steel filler metal using gas tungsten arc welding process is characterized with optical microscopy and electron back-scattered diffraction techniques. Accordingly, variations of microstructure, texture, and grain boundary character distribution of base metals, heat affected zones, and weld metal were investigated. The results showed that the weld metal, which was composed of Widmanstätten austenite side-plates and allotriomorphic grain boundary austenite morphologies, had the weakest texture and was dominated by low angle boundaries. The welding process increased the ferrite content but decreasedmore » the texture intensity at the heat affected zone of the super duplex stainless steel base metal. In addition, through partial ferritization, it changed the morphology of elongated grains of the rolled microstructure to twinned partially transformed austenite plateaus scattered between ferrite textured colonies. However, the texture of the austenitic stainless steel heat affected zone was strengthened via encouraging recrystallization and formation of annealing twins. At both interfaces, an increase in the special character coincident site lattice boundaries of the primary phase as well as a strong texture with <100> orientation, mainly of Goss component, was observed. - Graphical abstract: Display Omitted - Highlights: • Weld metal showed local orientation at microscale but random texture at macroscale. • Intensification of <100> orientated grains was observed adjacent to the fusion lines. • The austenite texture was weaker than that of the ferrite in all duplex regions. • Welding caused twinned partially transformed austenites to form at SDSS HAZ. • At both interfaces, the ratio of special CSL boundaries of the primary phase increased.« less

Inter-plate aseismic slip on the subducting plate boundaries estimated from repeating earthquakes

NASA Astrophysics Data System (ADS)

Igarashi, T.

2015-12-01

Sequences of repeating earthquakes are caused by repeating slips of small patches surrounded by aseismic slip areas at plate boundary zones. Recently, they have been detected in many regions. In this study, I detected repeating earthquakes which occurred in Japan and the world by using seismograms observed in the Japanese seismic network, and investigated the space-time characteristics of inter-plate aseismic slip on the subducting plate boundaries. To extract repeating earthquakes, I calculate cross-correlation coefficients of band-pass filtering seismograms at each station following Igarashi [2010]. I used two data-set based on USGS catalog for about 25 years from May 1990 and JMA catalog for about 13 years from January 2002. As a result, I found many sequences of repeating earthquakes in the subducting plate boundaries of the Andaman-Sumatra-Java and Japan-Kuril-Kamchatka-Aleutian subduction zones. By applying the scaling relations among a seismic moment, recurrence interval and slip proposed by Nadeau and Johnson [1998], they indicate the space-time changes of inter-plate aseismic slips. Pairs of repeating earthquakes with the longest time interval occurred in the Solomon Islands area and the recurrence interval was about 18.5 years. The estimated slip-rate is about 46 mm/year, which correspond to about half of the relative plate motion in this area. Several sequences with fast slip-rates correspond to the post-seismic slips after the 2004 Sumatra-Andaman earthquake (M9.0), the 2006 Kuril earthquake (M8.3), the 2007 southern Sumatra earthquake (M8.5), and the 2011 Tohoku-oki earthquake (M9.0). The database of global repeating earthquakes enables the comparison of the inter-plate aseismic slips of various plate boundary zones of the world. I believe that I am likely to detect more sequences by extending analysis periods in the area where they were not found in this analysis.

Consequences of Rift Propagation for Spreading in Thick Oceanic Crust in Iceland

NASA Astrophysics Data System (ADS)

Karson, J. A.

2015-12-01

Iceland has long been considered a natural laboratory for processes related to seafloor spreading, including propagating rifts, migrating transforms and rotating microplates. The thick, hot, weak crust and subaerial processes of Iceland result in variations on the themes developed along more typical parts of the global MOR system. Compared to most other parts of the MOR, Icelandic rift zones and transform faults are wider and more complex. Rift zones are defined by overlapping arrays of volcanic/tectonic spreading segments as much as 50 km wide. The most active rift zones propagate N and S away from the Iceland hot spot causing migration of transform faults. A trail of crust deformed by bookshelf faulting forms in their wakes. Dead or dying transform strands are truncated along pseudofaults that define propagation rates close to the full spreading rate of ~20 mm/yr. Pseudofaults are blurred by spreading across wide rift zones and laterally extensive subaerial lava flows. Propagation, with decreasing spreading toward the propagator tips causes rotation of crustal blocks on both sides of the active rift zones. The blocks deform internally by the widespread reactivation of spreading-related faults and zones of weakness along dike margins. The sense of slip on these rift-parallel strike-slip faults is inconsistent with transform-fault deformation. These various deformation features as well as subaxial subsidence that accommodate the thickening of the volcanic upper crustal units are probably confined to the brittle, seismogenic, upper 10 km of the crust. At least beneath the active rift zones, the upper crust is probably decoupled from hot, mechanically weak middle and lower gabbroic crust resulting in a broad plate boundary zone between the diverging lithosphere plates. Similar processes may occur at other types of propagating spreading centers and magmatic rifts.

Relaxation of the accelerating-gas boundary layer to the test-gas boundary layer on a flat plate in an expansion tube

NASA Technical Reports Server (NTRS)

Gupta, R. N.; Trimpi, R. L.

1973-01-01

An analytic investigation of the relaxation of the accelerating-gas boundary layer to the test-gas boundary layer over a flat plate mounted in an expansion tube has been conducted. In this treatment, nitrogen has been considered as the test gas and helium as the accelerating gas. The problem is analyzed in two conically similar limits: (1) when the time lag between the arrival of the shock and the interface at the leading edge of the plate is very large, and (2) when this time lag is negligible. The transient laminar boundary-layer equations of a perfect binary-gas mixture are taken as the flow governing equations. These coupled equations have been solved numerically by Gauss-Seidel line-relaxation method. The results predict the transient behavior as well as the time required for an all-helium accelerating-gas boundary layer to relax to an all-nitrogen boundary layer.

Seismicity of the Earth 1900-2010 Aleutian arc and vicinity

USGS Publications Warehouse

Benz, Harley M.; Herman, Matthew; Tarr, Arthur C.; Hayes, Gavin P.; Furlong, Kevin P.; Villaseñor, Antonio; Dart, Richard L.; Rhea, Susan

2011-01-01

This map shows details of the Aleutian arc not visible in an earlier publication. The Aleutian arc extends about 3,000 km from the Gulf of Alaska to the Kamchatka Peninsula. It marks the region where the Pacific plate subducts into the mantle beneath the North America plate. This subduction is responsible for the generation of the Aleutian Islands and the deep offshore Aleutian Trench. Relative to a fixed North America plate, the Pacific plate is moving northwest at a rate that increases from about 55 mm per year at the arc's eastern edge to 75 mm per year near its western terminus. In the east, the convergence of the plates is nearly perpendicular to the plate boundary. However, because of the boundary's curvature, as one travels westward along the arc, the subduction becomes more and more oblique to the boundary until the relative plate motion becomes parallel to the arc at the Near Islands near its western edge. Subduction zones such as the Aleutian arc are geologically complex and produce numerous earthquakes from multiple sources. Deformation of the overriding North America plate generates shallow crustal earthquakes, whereas slip at the interface of the plates generates interplate earthquakes that extend from near the base of the trench to depths of 40 to 60 km. At greater depths, Aleutian arc earthquakes occur within the subducting Pacific plate and can reach depths of 300 km. Since 1900, six great earthquakes have occurred along the Aleutian Trench, Alaska Peninsula, and Gulf of Alaska: M8.4 1906 Rat Islands; M8.6 1938 Shumagin Islands; M8.6 1946 Unimak Island; M8.6 1957 Andreanof Islands; M9.2 1964 Prince William Sound; and M8.7 1965 Rat Islands. Several relevant tectonic elements (plate boundaries and active volcanoes) provide a context for the seismicity presented on the main map panel. The plate boundaries are most accurate along the axis of the Aleutian Trench and more diffuse or speculative in extreme northeastern Russia. The active volcanoes parallel the Aleutian Trench from the Gulf of Alaska to the Rat Islands.

Thermally stratified squeezed flow between two vertical Riga plates with no slip conditions

NASA Astrophysics Data System (ADS)

Farooq, M.; Mansoor, Zahira; Ijaz Khan, M.; Hayat, T.; Anjum, A.; Mir, N. A.

2018-04-01

This paper demonstrates the mixed convective squeezing nanomaterials flow between two vertical plates, one of which is a Riga plate embedded in a thermally stratified medium subject to convective boundary conditions. Heat transfer features are elaborated with viscous dissipation. Single-wall and multi-wall carbon nanotubes are taken as nanoparticles to form a homogeneous solution in the water. A non-linear system of differential equations is obtained for the considered flow by using suitable transformations. Convergence analysis for velocity and temperature is computed and discussed explicitly through BVPh 2.0. Residual errors are also computed by BVPh 2.0 for the dimensionless governing equations. We introduce two undetermined convergence control parameters, i.e. \\hslash_{θ} and \\hslashf , to compute the lowest entire error. The average residual error for the k -th-order approximation is given in a table. The effects of different flow variables on temperature and velocity distributions are sketched graphically and discussed comprehensively. Furthermore the coefficient of skin friction and the Nusselt number are also analyzed through graphical data.

Using Global Plate Velocity Boundary Conditions for Embedded Regional Geodynamic Models

NASA Astrophysics Data System (ADS)

Taramon Gomez, Jorge; Morgan, Jason; Perez-Gussinye, Marta

2015-04-01

The treatment of far-field boundary conditions is one of the most poorly resolved issues for regional modeling of geodynamic processes. In viscous flow, the choice of far-field boundary conditions often strongly shapes the large-scale structure of a geosimulation. The mantle velocity field along the sidewalls and base of a modeling region is typically much more poorly known than the geometry of past global motions of the surface plates as constrained by global plate motion reconstructions. For regional rifting models it has become routine to apply highly simplified 'plate spreading' or 'uniform rifting' boundary conditions to a 3-D model that limits its ability to simulate the geodynamic evolution of a specific rifted margin. One way researchers are exploring the sensitivity of regional models to uncertain boundary conditions is to use a nested modeling approach in which a global model is used to determine a large-scale flow pattern that is imposed as a constraint along the boundaries of the region to be modeled. Here we explore the utility of a different approach that takes advantage of the ability of finite element models to use unstructured meshes than can embed much higher resolution sub-regions within a spherical global mesh. In our initial project to validate this approach, we create a global spherical mesh in which a higher resolution sub-region is created around the nascent South Atlantic Rifting Margin. Global Plate motion BCs and plate boundaries are applied for the time of the onset of rifting, continuing through several 10s of Ma of rifting. Thermal, compositional, and melt-related buoyancy forces are only non-zero within the high-resolution subregion, elsewhere, motions are constrained by surface plate-motion constraints. The total number of unknowns needed to solve an embedded regional model with this approach is less than 1/3 larger than that needed for a structured-mesh solution on a Cartesian or spherical cap sub-regional mesh. Here we illustrate the initial steps within this workflow for creating time-varying surface boundary conditions (using GPlates), and a time-variable unstructured 3-D spherical mesh.

Effects of Periodic Unsteady Wake Flow and Pressure Gradient on Boundary Layer Transition Along the Concave Surface of a Curved Plate. Part 3

NASA Technical Reports Server (NTRS)

Schobeiri, M. T.; Radke, R. E.

1996-01-01

Boundary layer transition and development on a turbomachinery blade is subjected to highly periodic unsteady turbulent flow, pressure gradient in longitudinal as well as lateral direction, and surface curvature. To study the effects of periodic unsteady wakes on the concave surface of a turbine blade, a curved plate was utilized. On the concave surface of this plate, detailed experimental investigations were carried out under zero and negative pressure gradient. The measurements were performed in an unsteady flow research facility using a rotating cascade of rods positioned upstream of the curved plate. Boundary layer measurements using a hot-wire probe were analyzed by the ensemble-averaging technique. The results presented in the temporal-spatial domain display the transition and further development of the boundary layer, specifically the ensemble-averaged velocity and turbulence intensity. As the results show, the turbulent patches generated by the wakes have different leading and trailing edge velocities and merge with the boundary layer resulting in a strong deformation and generation of a high turbulence intensity core. After the turbulent patch has totally penetrated into the boundary layer, pronounced becalmed regions were formed behind the turbulent patch and were extended far beyond the point they would occur in the corresponding undisturbed steady boundary layer.

Numerical modeling of the transitional boundary layer over a flat plate

NASA Astrophysics Data System (ADS)

Ivanov, Dimitry; Chorny, Andrei

2015-11-01

Our example is connected with fundamental research on understanding how an initially laminar boundary layer becomes turbulent. We have chosen the flow over a flat plate as a prototype for boundary-layer flows around bodies. Special attention was paid to the near-wall region in order to capture all levels of the boundary layer. In this study, the numerical software package OpenFOAM has been used in order to solve the flow field. The results were used in a comparative study with data obtained from Large Eddy Simulation (LES). The composite SGS-wall model is presently incorporated into a computer code suitable for the LES of developing flat-plate boundary layers. Presently this model is extended to the LES of the zero-pressure gradient, flat-plate turbulent boundary layer. In current study the time discretization is based on a second order Crank-Nicolson/Adams-Bashforth method. LES solver using Smagorinsky and the one-equation LES turbulence models. The transition models significantly improve the prediction of the onset location compared to the fully turbulent models.LES methods appear to be the most promising new tool for the design and analysis of flow devices including transition regions of the turbulent flow.

Exact solution for heat transfer free convection flow of Maxwell nanofluids with graphene nanoparticles

NASA Astrophysics Data System (ADS)

Aman, Sidra; Zuki Salleh, Mohd; Ismail, Zulkhibri; Khan, Ilyas

2017-09-01

This article focuses on the flow of Maxwell nanofluids with graphene nanoparticles over a vertical plate (static) with constant wall temperature. Possessing high thermal conductivity, engine oil is useful to be chosen as base fluid with free convection. The problem is modelled in terms of PDE’s with boundary conditions. Some suitable non-dimensional variables are interposed to transform the governing equations into dimensionless form. The generated equations are solved via Laplace transform technique. Exact solutions are evaluated for velocity and temperature. These solutions are significantly controlled by some parameters involved. Temperature rises with elevation in volume fraction while Velocity decreases with increment in volume fraction. A comparison with previous published results are established and discussed. Moreover, a detailed discussion is made for influence of volume fraction on the flow and heat profile.

Inverse Thermal Analysis of Titanium GTA Welds Using Multiple Constraints

NASA Astrophysics Data System (ADS)

Lambrakos, S. G.; Shabaev, A.; Huang, L.

2015-06-01

Inverse thermal analysis of titanium gas-tungsten-arc welds using multiple constraint conditions is presented. This analysis employs a methodology that is in terms of numerical-analytical basis functions for inverse thermal analysis of steady-state energy deposition in plate structures. The results of this type of analysis provide parametric representations of weld temperature histories that can be adopted as input data to various types of computational procedures, such as those for prediction of solid-state phase transformations. In addition, these temperature histories can be used to construct parametric function representations for inverse thermal analysis of welds corresponding to other process parameters or welding processes whose process conditions are within similar regimes. The present study applies an inverse thermal analysis procedure that provides for the inclusion of constraint conditions associated with both solidification and phase transformation boundaries.

The buckling response of symmetrically laminated composite plates having a trapezoidal planform area. M.S. Thesis Interim Report No. 98, Aug. 1990 - May 1994

NASA Technical Reports Server (NTRS)

Radloff, H. D., II; Hyer, M. W.; Nemeth, M. P.

1994-01-01

The focus of this work is the buckling response of symmetrically laminated composite plates having a planform area in the shape of an isosceles trapezoid. The loading is assumed to be inplane and applied perpendicular to the parallel ends of the plate. The tapered edges of the plate are assumed to have simply supported boundary conditions, while the parallel ends are assumed to have either simply supported or clamped boundary conditions. A semi-analytic closed-form solution based on energy principles and the Trefftz stability criterion is derived and solutions are obtained using the Rayleigh-Ritz method. Intrinsic in this solution is a simplified prebuckling analysis which approximates the inplane force resultant distributions by the forms Nx=P/W(x) and Ny=Nxy=0, where P is the applied load and W(x) is the plate width which, for the trapezoidal planform, varies linearly with the lengthwise coordinate x. The out-of-plane displacement is approximated by a double trigonometric series. This analysis is posed in terms of four nondimensional parameters representing orthotropic and anisotropic material properties, and two nondimensional parameters representing geometric properties. For comparison purposes, a number of specific plate geometry, ply orientation, and stacking sequence combinations are investigated using the general purpose finite element code ABAQUS. Comparison of buckling coefficients calculated using the semi-analytical model and the finite element model show agreement within 5 percent, in general, and within 15 percent for the worst cases. In order to verify both the finite element and semi-analytical analyses, buckling loads are measured for graphite/epoxy plates having a wide range of plate geometries and stacking sequences. Test fixtures, instrumentation system, and experimental technique are described. Experimental results for the buckling load, the buckled mode shape, and the prebuckling plate stiffness are presented and show good agreement with the analytical results regarding the buckling load and the prebuckling plate stiffness. However, the experimental results show that for some cases the analysis underpredicts the number of halfwaves in the buckled mode shape. In the context of the definitions of taper ratio and aspect ratio used in this study, it is concluded that the buckling load always increases as taper ratio increases for a given aspect ratio for plates having simply supported boundary conditions on the parallel ends. There are combinations of plate geometry and ply stackling sequences, however, that reverse this trend for plates having clamped boundary conditions on the parallel ends such that an increase in the taper ratio causes a decrease in the buckling load. The clamped boundary conditions on the parallel ends of the plate are shown to increase the buckling load compared to simply supported boundary conditions. Also, anisotropy (the D16 and D26 terms) is shown to decrease the buckling load and skew the buckled mode shape for both the simply supported and clamped boundary conditions.

Complex Plate Tectonic Features on Planetary Bodies: Analogs from Earth

NASA Astrophysics Data System (ADS)

Stock, J. M.; Smrekar, S. E.

2016-12-01

We review the types and scales of observations needed on other rocky planetary bodies (e.g., Mars, Venus, exoplanets) to evaluate evidence of present or past plate motions. Earth's plate boundaries were initially simplified into three basic types (ridges, trenches, and transform faults). Previous studies examined the Moon, Mars, Venus, Mercury and icy moons such as Europa, for evidence of features, including linear rifts, arcuate convergent zones, strike-slip faults, and distributed deformation (rifting or folding). Yet, several aspects merit further consideration. 1) Is the feature active or fossil? Earth's active mid ocean ridges are bathymetric highs, and seafloor depth increases on either side; whereas, fossil mid ocean ridges may be as deep as the surrounding abyssal plain with no major rift valley, although with a minor gravity low (e.g., Osbourn Trough, W. Pacific Ocean). Fossil trenches have less topographic relief than active trenches (e.g., the fossil trench along the Patton Escarpment, west of California). 2) On Earth, fault patterns of spreading centers depend on volcanism. Excess volcanism reduced faulting. Fault visibility increases as spreading rates slow, or as magmatism decreases, producing high-angle normal faults parallel to the spreading center. At magma-poor spreading centers, high resolution bathymetry shows low angle detachment faults with large scale mullions and striations parallel to plate motion (e.g., Mid Atlantic Ridge, Southwest Indian Ridge). 3) Sedimentation on Earth masks features that might be visible on a non-erosional planet. Subduction zones on Earth in areas of low sedimentation have clear trench -parallel faults causing flexural deformation of the downgoing plate; in highly sedimented subduction zones, no such faults can be seen, and there may be no bathymetric trench at all. 4) Areas of Earth with broad upwelling, such as the North Fiji Basin, have complex plate tectonic patterns with many individual but poorly linked ridge segments and transform faults. These details and scales of features should be considered in planning future surveys of altimetry, reflectance, magnetics, compositional, and gravity data from other planetary bodies aimed at understanding the link between a planet's surface and interior, whether via plate tectonics or other processes.

High Resolution Quaternary and Neogene Reconstructions of the Southwest Indian Ridge and Rifting in Eastern Africa

NASA Astrophysics Data System (ADS)

DeMets, C.; Merkuryev, S. A.; Calais, E.; Sauter, D.

2014-12-01

The Southwest Indian Ridge (SWIR) south of Africa is a critical link in plate circuits between the Atlantic and Indian Ocean basins and between the Nubia and Somalia plates. Detailed reconstructions of its seafloor spreading history are challenging due to the low fidelity of its magnetic anomalies, which were mostly created at slow to ultraslow spreading rates, and gaps in data coverage for some areas of the ridge. Here, we describe the first high-resolution analysis of Quaternary/Neogene SWIR plate kinematics based on nearly 5000 identifications that we made of magnetic reversals C1n (0.78 Ma) to C6no (19.7 Ma) and ~6000 crossings of 21 fracture zones and transform faults that offset the ridge. We also outline the implications for estimates of motion between the Nubia and Somalia plates since 20 Ma across rifts in eastern Africa. Searches for the Nubia-Lwandle and Lwandle-Somalia plate boundaries north of the SWIR with our new data corroborate previous evidence for respective locations near the Andrew Bain transform fault at ~30°E and at ~50°E. Inversions of the abundant new data to find best-fitting rotations at ~1 Myr intervals since 20 Ma reveal a previously unknown, ~20% deceleration of seafloor spreading rates at 7.2±1 Ma everywhere along the SWIR. Motion since 7 Ma has remained remarkably steady and agrees within uncertainties with GPS estimates that are based on more than 100 continuous GPS sites on the Nubia, Somalia, and Antarctic plates. The consistency of the geodetic and geologic estimates validates both and also supports evidence we will describe for anomalously wide outward displacement west of ~30E. Nubia-Somalia rotations determined from our new model indicate that the two plates have undergone steady relative motion since at least 19 Ma. Our new rotation for C5n.2 predicts ~70% less opening across the East Africa rift since 11 Ma than the most recently published kinematic estimate, in better accord with at least one geologically-derived estimate for the total extension.

Crustal stress across the northern Arabian plate and the relationship with the plate boundary forces

NASA Astrophysics Data System (ADS)

Yassminh, Rayan

The region encompassing the collision of northern Arabia with Eurasia is a tectonically heterogeneous region of distributed deformation. The northern Arabia plate is bounded to the west by the subducting Sinai plate and the left-lateral Dead Sea transform. This complexity suggests that there are multiple competing processes that may influence regional tectonics in northern Arabia and adjacent areas. Earthquake mechanisms provide insight into crustal kinematics and stress; however, reliable determination of earthquake source parameters can be challenging in a complex geological region, such as the continental collision zone between the Arabian and Eurasian plates. The goal of this study is to investigate spatial patterns of the crustal stress in the northern Arabian plate and surrounding area. The focal mechanisms used in this study are based on (1) first-motion polarities for earthquakes recorded by Syrian earthquake center during 2000-2011, and (2) regional moment tensors from broadband seismic data, from Turkey and Iraq. First motion focal mechanisms were assigned quality classifications based on the variation of both nodal planes. Regional moment tensor analysis can be significantly influenced by seismic velocity structure; thus, we have divided the study area into regions based on tectonic units. For each region, the velocity model is described using a waveform-modeling technique prior to the regional moment tensor inversion. The resulting focal mechanisms, combined with other previously published focal mechanisms for the study area, provide a basis for stress inversion analysis. The resulting deviatoric stress tensors show the spatial distribution of the maximum horizontal stress varies from NW-SE along the Dead Sea Fault to the N-S toward the east. We interpret this to reflect the eastward change from the transform to collision processes in northern Arabia. Along the Dead Sea Fault, transposition of the sigma-1 and sigma-2 to vertical and horizontal, respectively, may relate to influences from the subducted part of the Sinai plate. This change in regional stress is also consistent with extensional strains observed from GPS velocities.

Numerical solution of acoustic scattering by finite perforated elastic plates

PubMed Central

2016-01-01

We present a numerical method to compute the acoustic field scattered by finite perforated elastic plates. A boundary element method is developed to solve the Helmholtz equation subjected to boundary conditions related to the plate vibration. These boundary conditions are recast in terms of the vibration modes of the plate and its porosity, which enables a direct solution procedure. A parametric study is performed for a two-dimensional problem whereby a cantilevered perforated elastic plate scatters sound from a point quadrupole near the free edge. Both elasticity and porosity tend to diminish the scattered sound, in agreement with previous work considering semi-infinite plates. Finite elastic plates are shown to reduce acoustic scattering when excited at high Helmholtz numbers k0 based on the plate length. However, at low k0, finite elastic plates produce only modest reductions or, in cases related to structural resonance, an increase to the scattered sound level relative to the rigid case. Porosity, on the other hand, is shown to be more effective in reducing the radiated sound for low k0. The combined beneficial effects of elasticity and porosity are shown to be effective in reducing the scattered sound for a broader range of k0 for perforated elastic plates. PMID:27274685

Numerical solution of acoustic scattering by finite perforated elastic plates.

PubMed

Cavalieri, A V G; Wolf, W R; Jaworski, J W

2016-04-01

We present a numerical method to compute the acoustic field scattered by finite perforated elastic plates. A boundary element method is developed to solve the Helmholtz equation subjected to boundary conditions related to the plate vibration. These boundary conditions are recast in terms of the vibration modes of the plate and its porosity, which enables a direct solution procedure. A parametric study is performed for a two-dimensional problem whereby a cantilevered perforated elastic plate scatters sound from a point quadrupole near the free edge. Both elasticity and porosity tend to diminish the scattered sound, in agreement with previous work considering semi-infinite plates. Finite elastic plates are shown to reduce acoustic scattering when excited at high Helmholtz numbers k 0 based on the plate length. However, at low k 0 , finite elastic plates produce only modest reductions or, in cases related to structural resonance, an increase to the scattered sound level relative to the rigid case. Porosity, on the other hand, is shown to be more effective in reducing the radiated sound for low k 0 . The combined beneficial effects of elasticity and porosity are shown to be effective in reducing the scattered sound for a broader range of k 0 for perforated elastic plates.

Solving the Problem of Linear Viscoelasticity for Piecewise-Homogeneous Anisotropic Plates

NASA Astrophysics Data System (ADS)

Kaloerov, S. A.; Koshkin, A. A.

2017-11-01

An approximate method for solving the problem of linear viscoelasticity for thin anisotropic plates subject to transverse bending is proposed. The method of small parameter is used to reduce the problem to a sequence of boundary problems of applied theory of bending of plates solved using complex potentials. The general form of complex potentials in approximations and the boundary conditions for determining them are obtained. Problems for a plate with elliptic elastic inclusions are solved as an example. The numerical results for a plate with one, two elliptical (circular), and linear inclusions are analyzed.

Microstructure and mechanical properties of bulk and plasma-sprayed y2O3-partially stabilized zirconia

NASA Technical Reports Server (NTRS)

Valentine, P. G.; Maier, R. D.

1980-01-01

Bulk 8.0 weight percent yttria partially stabilied zirconia (PSZ) was studied by light microscopy, transmission electron microscopy, X-ray analysis, microhardness testing, and fracture toughness testing. The as received PSZ contained spheroidal and grain boundary precipitates up to 4 micrometers in size. Spheroids up to 1.26 micrometers were metastable tetragonal; large spheroids were monoclinic. Grinding the PSZ into powder did not cause a significant amount of tetragonal to transform to monoclinic. This indicates that transformation toughness is not a significant mechanism in PSZ. Aging the PSZ at 1500 C caused the fine tetragonal precipitates to grow from 0.06 to 0.12 micrometers, in 250 minutes. A peak hardness of 1400 kg/sq mm was attained after 50 minutes. Solution annealing and quenching the as received PSZ eliminated the large precipitates, but fine tetragonal precipitates reformed on quenching. Aging at 1500 C caused the fine 0.02 micrometers tetragonal precipitates to grow into plates about 0.10 by 0.50 micrometers. A peak hardness of 1517 kg/sq mm was obtained after 250 minutes. On further aging, monoclinic percipitates formed along grain boundaries. The fracture toughness of the aged and unaged solution annealed and quenched PSZ was found to be between 2 and 3 MN /square root of m cubed. This range of fracture toughness is consistent with PSZ's that do not undergo transformation toughening.

Scaling of mean inertia and theoretical basis for a log law in turbulent boundary layers

NASA Astrophysics Data System (ADS)

Philip, Jimmy; Morrill-Winter, Caleb; Klewicki, Joseph

2017-11-01

Log law in the mean streamwise velocity (U) for pipes/channels is well accepted based on the derivation from the mean momentum balance (MMB) equation and support from experimental data. For flat plate turbulent boundary layers (TBLs), however, there is only empirical evidence and a theoretical underpinning of the kind available for pipes/channels in lacking. The main difficultly is the mean inertia (MI) term in the MMB equation, which, unlike in pipes/channels, is not a constant in TBLs. We present results from our paper (JFM `` 2017, Vol 813, pp 594-617), where the MI term for TBL is transformed so as to render it invariant in the outer region, corroborated with high Re (δ+) data from Melbourne Wind Tunnel and New Hampshire Flow Physics Facility. The transformation is possible because the MI term in the TBL has a `shape' which becomes invariant with increasing δ+ and a `magnitude' which is proportional to 1 /δ+ . The transformed equation is then employed to derive a log law for U with κ an order one (von-Karman) constant. We also show that the log law begins at y+ =C1√{δ+} , and the peak location of the Reynolds shear stress, ym+ =C2√{δ+} , where, C1 3.6 and C2 2.17 are from high Re data. Australian Research Council and the US National Science Foundation.

Habitat characterization of the Vema Fracture Zone and Puerto Rico Trench

NASA Astrophysics Data System (ADS)

Devey, C. W.; Augustin, N.; Brandt, A.; Brenke, N.; Köhler, J.; Lins, L.; Schmidt, C.; Yeo, I. A.

2018-02-01

Although many of the regions on and close to the mid-ocean ridges have been extensively mapped and sampled, the abyssal intraplate regions remain essentially unsampled and unmapped, leaving huge gaps in our understanding of their geologic history and present activity. Prominent bathymetric features in these intraplate regions are fracture zones. Here we present bathymetric and sampling information from a transatlantic transect along the Vema Fracture Zone (ca. 11°N), covering crustal ages from 109 - 0 Ma on the African plate and 0-62 Ma on the South American plate. The Vema Fracture Zone is the intraplate trace of the active Vema Transform plate boundary, which offsets the present-day Mid-Atlantic Ridge by ca. 300 km left-laterally, juxtaposing zero-age crust with crust of 20 million years age. Our results show clear evidence of tectonic activity along most of the Fracture Zone, in most places likely associated with active fluid flow. Within the active Vema Transform at crustal ages of ca. 10 Ma we found clear indications of fluid flow both in the sediments and the overlying water column. This region is > 120 km from the nearest spreading axis and increases by almost an order of magnitude the maximum off-axis distance that active hydrothermal discharge has been found on the oceanic crust. Sampling of the igneous seafloor was possible at all crustal ages and the accretionary fabric imprinted on the plate during its production was prominent everywhere. Seafloor sediments show signs of extensive bioturbation. In one area, high concentrations of spherical Mn-nodules were also found and sampled. At the end of the transect we also mapped and sampled the Puerto Rico Trough, a > 8000 m-deep basin north of the Caribbean arc. Here the seafloor morphology is more complicated and strongly influenced by transpressive tectonics.

Rigid and non-rigid micro-plates: Philippines and Myanmar-Andaman case studies

NASA Astrophysics Data System (ADS)

Rangin, Claude

2016-01-01

Generally, tectonic plates are considered as rigid. Oblique plate convergence favors the development of micro-plates along the converging boundaries. The north-south-trending Philippines archipelago (here named Philippine Mobile Belt, PMB), a few hundreds kilometers wide, is one of such complex tectonic zones. We show here that it is composed of rigid rotating crustal blocks (here called platelets). In Myanmar, the northernmost tip of the Sumatra-Andaman subduction system is another complex zone made of various crustal blocks in-between convergent plates. Yet, contrary to PMB, it sustains internal deformation with platelet buckling, altogether indicative of a non-rigid behavior. Therefore, the two case studies, Philippine Mobile Belt and Myanmar-Andaman micro-plate (MAS), illustrate the complexity of micro-plate tectonics and kinematics at convergent plate boundaries.

Flat Plate Boundary Layer Stimulation Using Trip Wires and Hama Strips

NASA Astrophysics Data System (ADS)

Peguero, Charles; Henoch, Charles; Hrubes, James; Fredette, Albert; Roberts, Raymond; Huyer, Stephen

2017-11-01

Water tunnel experiments on a flat plate at zero angle of attack were performed to investigate the effect of single roughness elements, i.e., trip wires and Hama strips, on the transition to turbulence. Boundary layer trips are traditionally used in scale model testing to force a boundary layer to transition from laminar to turbulent flow at a single location to aid in scaling of flow characteristics. Several investigations of trip wire effects exist in the literature, but there is a dearth of information regarding the influence of Hama strips on the flat plate boundary layer. The intent of this investigation is to better understand the effects of boundary layer trips, particularly Hama strips, and to investigate the pressure-induced drag of both styles of boundary layer trips. Untripped and tripped boundary layers along a flat plate at a range of flow speeds were characterized with multiple diagnostic measurements in the NUWC/Newport 12-inch water tunnel. A wide range of Hama strip and wire trip thicknesses were used. Measurements included dye flow visualization, direct skin friction and parasitic drag force, boundary layer profiles using LDV, wall shear stress fluctuations using hot film anemometry, and streamwise pressure gradients. Test results will be compared to the CFD and boundary layer model results as well as the existing body of work. Conclusions, resulting in guidance for application of Hama strips in model scale experiments and non-dimensional predictions of pressure drag will be presented.

Strain transfer between disconnected, propagating rifts in Afar

NASA Astrophysics Data System (ADS)

Manighetti, I.; Tapponnier, P.; Courtillot, V.; Gallet, Y.; Jacques, E.; Gillot, P.-Y.

2001-01-01

We showed before that both the Aden and Red Sea plate boundaries are currently rifting and propagating along two distinct paths into Afar through the opening of a series of disconnected, propagating rifts. Here we use new geochronological, tectonic, and paleomagnetic data that we acquired mostly in the southeastern part of Afar to examine the geometry, kinematics, and time-space evolution of faulting related to strain transfer processes. It appears that transfer of strain is accommodated by a bookshelf faulting mechanism wherever rifts or plate boundaries happen to overlap without being connected. This mechanism implies the rotation about a vertical axis of small rigid blocks along rift-parallel faults that are shown to slip with a left-lateral component, which is as important as their normal component of slip (rates of ˜2-3 mm/yr). By contrast, where rifts do not overlap, either a classic transform fault (Maskali) or an oblique transfer zone (Mak'arrasou) kinematically connects them. The length of the Aden-Red Sea overlap has increased in the last ˜0.9 Myr, as the Aden plate boundary propagated northward into Afar. As a consequence, the first-order blocks that we identify within the overlap did not all rotate during the same time-span nor by the same amounts. Similarly, the major faults that bound them did not necessarily initiate and grow as their neighboring faults did. Despite these variations in strain distribution and kinematics, the overlap kept accommodating a constant amount of strain (7 to 15% of the extension amount imposed by plate driving forces), which remained distributed on a limited number (seven or eight) of major faults, each one having slipped at constant rates (˜3 and 2 mm/yr for vertical and lateral rates, respectively). The fault propagation rates and the block rotation rates that we either measure or deduce are so fast (30-130 mm/yr and 15-38°/Myr, respectively) that they imply that strain transfer processes are transient, as has been shown to be the case for the processes of tearing, rift propagation, and strain jumps in Afar.

Active Tectonics of the Far North Pacific Observed with GPS

NASA Astrophysics Data System (ADS)

Elliott, J.; Freymueller, J. T.; Jiang, Y.; Leonard, L. J.; Hyndman, R. D.; Mazzotti, S.

2017-12-01

The idea that the tectonics of the northeastern Pacific is defined by relatively discrete deformation along the boundary between the Pacific and North American plates has given way to a more complex picture of broad plate boundary zones and distributed deformation. This is due in large part to the Plate Boundary Observatory and several focused GPS studies, which have greatly increased the density of high-quality GPS data throughout the region. We will present an updated GPS velocity field in a consistent reference frame as well as a new, integrated block model that sheds light on regional tectonics and provides improved estimates of motion along faults and their potential seismic hazard. Crustal motions in southern Alaska are strongly influenced by the collision and flat-slab subduction of the Yakutat block along the central Gulf of Alaska margin. In the area nearest to the collisional front, small blocks showing evidence of internal deformation are required. East of the front, block motions show clockwise rotation into the Canadian Cordillera while west of the front there are counterclockwise rotations that extend along the Alaska forearc, suggesting crustal extrusion. Farther from the convergent margin, the crust appears to move as rigid blocks, with uniform motion over large areas. In western Alaska, block motions show a southwesterly rotation into the Bering Sea. Arctic Alaska displays southeasterly motions that gradually transition into easterly motion in Canada. Much of the southeastern Alaska panhandle and coastal British Columbia exhibit northwesterly motions. Although the relative plate motions are mainly accommodated along major faults systems, including the Fairweather-Queen Charlotte transform system, the St. Elias fold-and-thrust belt, the Denali-Totschunda system, and the Alaska-Aleutian subduction zone, a number of other faults accommodate lesser but still significant amounts of motion in the model. These faults include the eastern Denali/Duke River system, the Castle Mountain fault, the western Denali fault, the Kaltag fault, and the Kobuk fault. Based on the expanded GPS data set, locked or partially locked sections of the Alaska subduction zone may extend as far north and east as the eastern Alaska Range.

The effect of plate-scale rheology and plate interactions on intraplate seismicity

NASA Astrophysics Data System (ADS)

So, Byung-Dal; Capitanio, Fabio A.

2017-11-01

We use finite element modeling to investigate on the stress loading-unloading cycles and earthquakes occurrence in the plate interiors, resulting from the interactions of tectonic plates along their boundary. We model a visco-elasto-plastic plate embedding a single or multiple faults, while the tectonic stress is applied along the plate boundary by an external loading visco-elastic plate, reproducing the tectonic setting of two interacting lithospheres. Because the two plates deform viscously, the timescale of stress accumulation and release on the faults is self-consistently determined, from the boundary to the interiors, and seismic recurrence is an emerging feature. This approach overcomes the constraints on recurrence period imposed by stress (stress-drop) and velocity boundary conditions, while here it is unconstrained. We illustrate emerging macroscopic characteristics of this system, showing that the seismic recurrence period τ becomes shorter as Γ and Θ decreases, where Γ =ηI /ηL, the viscosity ratio of the viscosities of the internal fault-embedded to external loading plates, respectively, and Θ =σY /σL the stress ratio of the elastic limit of the fault to far-field loading stress. When the system embeds multiple, randomly distributed faults, stress transfer results in recurrence period deviations, however the time-averaged recurrence period of each fault show the same dependence on Γ and Θ, illustrating a characteristic collective behavior. The control of these parameters prevails even when initial pre-stress was randomly assigned in terms of the spatial arrangement and orientation on the internal plate, mimicking local fluctuations. Our study shows the relevance of macroscopic rheological properties of tectonic plates on the earthquake occurrence in plate interiors, as opposed to local factors, proposing a viable model for the seismic behavior of continent interiors in the context of large-scale, long-term deformation of interacting tectonic plates.

On approximating guided waves in plates with thin anisotropic coatings by means of effective boundary conditions

PubMed

Niklasson; Datta; Dunn

2000-09-01

In this paper, effective boundary conditions for elastic wave propagation in plates with thin coatings are derived. These effective boundary conditions are used to obtain an approximate dispersion relation for guided waves in an isotropic plate with thin anisotropic coating layers. The accuracy of the effective boundary conditions is investigated numerically by comparison with exact solutions for two different material systems. The systems considered consist of a metallic core with thin superconducting coatings. It is shown that for wavelengths long compared to the coating thickness there is excellent agreement between the approximate and exact solutions for both systems. Furthermore, numerical results presented might be used to characterize coating properties by ultrasonic techniques.

Structural and geophysical interpretation of Roatan Island, Honduras, Western Caribbean

NASA Astrophysics Data System (ADS)

Sutton, Daniel Scott

Roatan Island is the largest of the Bay Islands of Honduras. These islands form an emergent crest off the Caribbean coast of Honduras called the Bonacca Ridge. The Bartlett Trough to the north and subsequent Bonacca Ridge were likely formed due to the transform fault system of the Motagua-Swan Islands Fault System. This fault system forms the tectonic plate boundary between the North American and Caribbean plates. Although the timing and kinematics are poorly constrained, the Bay Islands and the Bonacca Ridge were likely uplifted due to transpression along this left-lateral strike-slip system. With limited regional exposures along the adjacent tectonic boundary, this study aimed to present a structural interpretation for Roatan. This new interpretation is further explained through regional considerations for a suggested geologic history of the northwestern Caribbean. In order to better constrain the kinematics of uplift and exhumation of Roatan Island, structural, gravity, and magnetic surveys were conducted. Principal attention was directed to the structural relationship between the geologic units and their relationship to one another through deformation. Resulting geologic cross-sections from this study present the metamorphic basement exposed throughout the island to be in a normal structural order consisting of biotite schist and gneiss, with overlying units of chlorite schist, carbonate, and conglomerate. These units have relatively concordant strike and dip measurements, consistent with resultant magnetic survey readings. Additionally, large and irregular bodies of amphibolite and serpentinite throughout the island are interpreted to have been emplaced as mafic and ultra-mafic intrusions in weakness zones along Early Paleogene transform system fault planes. The interpretation and suggested geologic history from this study demonstrate the importance of transpressive tectonics both local to Roatan and regionally throughout geologic history. Consideration of this interpretation will help to further constrain regional studies over the northwestern Caribbean.

The May 29 2008 earthquake aftershock sequence within the South Iceland Seismic Zone: Fault locations and source parameters of aftershocks

NASA Astrophysics Data System (ADS)

Brandsdottir, B.; Parsons, M.; White, R. S.; Gudmundsson, O.; Drew, J.

2010-12-01

The mid-Atlantic plate boundary breaks up into a series of segments across Iceland. The South Iceland Seismic Zone (SISZ) is a complex transform zone where left-lateral E-W shear between the Reykjanes Peninsula Rift Zone and the Eastern Volcanic Zone is accommodated by bookshelf faulting along N-S lateral strike-slip faults. The SISZ is also a transient feature, migrating sideways in response to the southward propagation of the Eastern Volcanic Zone. Sequences of large earthquakes (M > 6) lasting from days to years and affecting most of the seismic zone have occurred repeatedly in historical time (last 1100 years), separated by intervals of relative quiescence lasting decades to more than a century. On May 29 2008, a Mw 6.1 earthquake struck the western part of the South Iceland Seismic Zone, followed within seconds by a slightly smaller event on a second fault ~5 km further west. Aftershocks, detected by a temporal array of 11 seismometers and three permanent Icelandic Meteorological Office stations were located using an automated Coalescence Microseismic Mapping technique. The epicenters delineate two major and several smaller N-S faults as well as an E-W zone of activity stretching further west into the Reykjanes Peninsula Rift Zone. Fault plane solutions show both right lateral and oblique strike slip mechanisms along the two major N-S faults. The aftershocks deepen from 3-5 km in the north to 8-9 km in the south, suggesting that the main faults dip southwards. The faulting is interpreted to be driven by the local stress due to transform motion between two parallel segments of the divergent plate boundary crossing Iceland.

Geosphere - Cryosphere Interactions in the Saint Elias orogen, Alaska and Yukon (Invited)

NASA Astrophysics Data System (ADS)

Bruhn, R. L.; Sauber, J. M.; Forster, R. R.; Cotton, M. M.

2009-12-01

North America's largest alpine and piedmont glaciers occur in the Saint Elias orogen, where microplate collision together with the transition from transform faulting to subduction along the North American plate boundary, create extreme topographic relief, unusually high annual precipitation by orographic lift, and crustal displacements induced by both tectonic and glacio-isostatic deformation. Lithosphere-scale structure dominates the spatial pattern of glaciation; the piedmont Bering and Agassiz-Malaspina glaciers lay along deeply eroded troughs where reverse faults rise from the underlying Aleutian megathrust. The alpine Seward and Bagley Ice Valley glaciers flow along an early Tertiary plate boundary that has been reactivated by reverse faulting, and also by dextral shearing at the NW end of the Fairweather transform fault. Folding above a crustal-scale fault ramp near Icy Bay localizes orographic uplift of air masses, creating alpine glaciers that spill off the highlands into large ice falls, and rapidly dissect evolving structure by erosion. The rate and orientation of ice surface velocities, and the location of crevassing and folding partly reflect changes in basal topography of the glaciers caused by differential erosion of strata, and juxtaposition of variably oriented structures across faults. The effects of basal topography on ice flow are investigated using remote sensing measurements and analog models of glacier flow over uneven topography. Deformation of the ice in turn affects englacial hydrology and sub-ice fluvial systems, potentially impacting ice mass balance, on-set of surging, and loci of glacier quakes. The glaciers impact tectonics by localizing uplift and exhumation within the orogen, and modulating tectonic stress fields as ice masses wax and wane. This is particularly evident in crustal seismicity rates at annual to decadal time scales, while stratigraphy of coastal terraces record both earthquake deformation and glacial isostasy over millennia.

CRUSTAL TECTONICS AND SEISMICITY OF THE MIDDLE EAST

NASA Astrophysics Data System (ADS)

Ghalib, H. A.; Gritto, R.; Sibol, M. S.; Herrmann, R. B.; Aleqabi, G. I.; Caron, P. F.; Wagner, R. A.; Ali, B. S.; Ali, A. A.

2009-12-01

The Arabian plate describes a geological entity and a dynamic system that has been in continuous interaction with the African plate to the west and south and the Eurasian plate to the north and east. The western and southern boundaries are distinguished by see floor spreading along the Gulf of Aden and Red Sea and transform faulting along the Dead Sea, whereas the northern and eastern boundaries are portrayed by compressional suture zones under thrusting the Turkish and Iranian plateaus. Despite this favorable juxtaposition of continental land masses and the plethora of national seismic networks in every country of the Middle East, the majority of published research on the Arabian plate and surrounding tectonic blocks still depends primarily on global seismographic stations and occasional local networks. Since 2005, we deployed a number of seismic stations, and more recently a five elements array, in close proximity to the northeastern boundary of the Arabian plate. The primary objective of the effort is to better understand the regional seismicity and seismotectonics of the Arabian plate and surrounding regions. To date over a terabyte of high quality 100 sps continuous three-component broadband data have been collected and being analyzed to derive models representative of the greater Middle East tectonic setting. This goal is, in part, achieved by estimating local and regional seismic velocity models using receiver function and surface wave dispersion analyses, and by using these models to obtain accurate hypocenter locations and event focal mechanisms. The resulting events distribution reveals a distinct picture of the interaction between the seismicity and tectonics of the region. The highest seismicity rate seems to be confined to the active northern section of the Zagros thrust zone, while it decreases towards the southern end, before the intensity increases again in the Bandar Abbas region. Spatial distribution of the events and stations provide thorough coverage of all the tectonic provinces in the region. Phases including Pn, Pg, Sn, Lg, as well as LR are clearly observed on recorded seismograms. Blockage or attenuation of some of the crustal body waves is observed along propagation paths crossing the Zagros-Bitlis zone. These findings are also in support of earlier tectonic models that suggest the existence of multiple parallel listric faults splitting off the main Zagros fault zone in east-west direction. Surface- and body wave results in support of these findings will be presented. Our initial structural models of the crust beneath north-eastern Iraq depict a thickness of 40-50 km in the foothills, which increases to 45-55 km beneath the Zagros-Bitlis zone.

Plate-tectonic boundary formation by grain-damage and pinning

NASA Astrophysics Data System (ADS)

Bercovici, David

2015-04-01

Shear weakening in the lithosphere is an essential ingredient for understanding how and why plate tectonics is generated from mantle convection on terrestrial planets. I present continued work on a theoretical model for lithospheric shear-localization and plate generation through damage, grain evolution and Zener pinning in two-phase (polycrystalline) lithospheric rocks. Grain size evolves through the competition between coarsening, which drives grain-growth, with damage, which drives grain reduction. The interface between phases controls Zener pinning, which impedes grain growth. Damage to the interface enhances the Zener pinning effect, which then reduces grain-size, forcing the rheology into the grain-size-dependent diffusion creep regime. This process thus allows damage and rheological weakening to co-exist, providing a necessary shear-localizing feedback. Moreover, because pinning inhibits grain-growth it promotes shear-zone longevity and plate-boundary inheritance. This theory has been applied recently to the emergence of plate tectonics in the Archean by transient subduction and accumulation of plate boundaries over 1Gyr, as well as to rapid slab detachment and abrupt tectonic changes. New work explores the saturation of interface damage at low interface curvature (e.g., because it is associated with larger grains that take up more of the damage, and/or because interface area is reduced). This effect allows three possible equilibrium grain-sizes for a given stress; a small-grain-size high-shear state in diffusion creep, a large grain-size low shear state in dislocation creep, and an intermediate state (often near the deformation map phase-boundary). The low and high grain-size states are stable, while the intermediate one is unstable. This implies that a material deformed at a given stress can acquire two stable deformation regimes, a low- and high- shear state; these are indicative of plate-like flows, i.e, the coexistence of both slowly deforming plates and rapidly deforming plate boundaries.

EBSD Analysis of Relationship Between Microstructural Features and Toughness of a Medium-Carbon Quenching and Partitioning Bainitic Steel

NASA Astrophysics Data System (ADS)

Li, Qiangguo; Huang, Xuefei; Huang, Weigang

2017-12-01

A multiphase microstructure of bainite, martensite and retained austenite in a 0.3C bainitic steel was obtained by a novel bainite isothermal transformation plus quenching and partitioning (B-QP) process. The correlations between microstructural features and toughness were investigated by electron backscatter diffraction (EBSD), and the results showed that the multiphase microstructure containing approximately 50% bainite exhibits higher strength (1617 MPa), greater elongation (18.6%) and greater impact toughness (103 J) than the full martensite. The EBSD analysis indicated that the multiphase microstructure with a smaller average local misorientation (1.22°) has a lower inner stress concentration possibility and that the first formed bainitic ferrite plates in the multiphase microstructure can refine subsequently generated packets and blocks. The corresponding packet and block average size decrease from 11.9 and 2.3 to 8.4 and 1.6 μm, respectively. A boundary misorientation analysis indicated that the multiphase microstructure has a higher percentage of high-angle boundaries (67.1%) than the full martensite (57.9%) because of the larger numbers and smaller sizes of packets and blocks. The packet boundary obstructs crack propagation more effectively than the block boundary.

The Angular Velocity of Nubia Relative to Somalia and the Location of the Nubia-Somalia-Antarctica Triple Junction

NASA Astrophysics Data System (ADS)

Horner-Johnson, B. C.; Gordon, R. G.; Cowles, S. M.; Argus, D. F.

2003-12-01

A new analysis of geologically current plate motion across the Southwest Indian Ridge and of the current location of the Nubia-Antarctica-Somalia triple junction is presented. We estimate spreading rates averaged over the past 3.2 Myr from 103 well-distributed, nearly ridge-perpendicular profiles crossing the Southwest Indian Ridge. We evaluate all available bathymetric data to estimate the azimuths and uncertainties of transform faults; six are estimated from multi-beam data and twelve from precision depth recorder data. If the Nubia-Somalia boundary is narrow where it intersects the Southwest Indian Ridge, that intersection lies between about 26° E and 32° E. This places it either along the spreading ridge segment just west of the Andrew Bain transform fault complex or along the transform fault complex itself. These limits are narrower than, and contained within, limits of about 24° E to 33° E previously found by Lemaux et al. (2002) from an analysis of the locations of magnetic anomaly 5. The data are consistent with a narrow boundary, but also consistent with a diffuse boundary as wide as about 700 km. The new Nubia-Somalia pole of rotation lies southwest of southern Africa and differs significantly from previously estimated poles, including that from data in the Red Sea and Gulf of Aden. The new pole indicates displacement rates of Somalia relative to Nubia of 3.4 +/- 1.3\\ mm yr-1 (95% confidence limits) towards 176.8° between Somalia and Nubia near the Southwest Indian Ridge, and of 8.4 +/- 1.3\\ mm yr-1 (95% confidence limits) towards 118.5° near Afar.

Actively dewatering fluid-rich zones along the Costa Rica plate boundary fault

NASA Astrophysics Data System (ADS)

Bangs, N. L.; McIntosh, K. D.; Silver, E. A.; Kluesner, J. W.; Ranero, C. R.; von Huene, R.

2012-12-01

New 3D seismic reflection data reveal distinct evidence for active dewatering above a 12 km wide segment of the plate boundary fault within the Costa Rica subduction zone NW of the Osa Peninsula. In the spring of 2011 we acquired a 11 x 55 km 3D seismic reflection data set on the R/V Langseth using four 6,000 m streamers and two 3,300 in3 airgun arrays to examine the structure of the Costa Rica margin from the trench into the seismogenic zone. We can trace the plate-boundary interface from the trench across our entire survey to where the plate-boundary thrust lies > 10 km beneath the margin shelf. Approximately 20 km landward of the trench beneath the mid slope and at the updip edge of the seismogenic zone, a 12 km wide zone of the plate-boundary interface has a distinctly higher-amplitude seismic reflection than deeper or shallower segments of the fault. Directly above and potentially directly connected with this zone are high-amplitude, reversed-polarity fault-plane reflections that extend through the margin wedge and into overlying slope sediment cover. Within the slope cover, high-amplitude reversed-polarity reflections are common within the network of closely-spaced nearly vertical normal faults and several broadly spaced, more gently dipping thrust faults. These faults appear to be directing fluids vertically toward the seafloor, where numerous seafloor fluid flow indicators, such as pockmarks, mounds and ridges, and slope failure features, are distinct in multibeam and backscatter images. There are distinctly fewer seafloor and subsurface fluid flow indicators both updip and downdip of this zone. We believe these fluids come from a 12 km wide fluid-rich segment of the plate-boundary interface that is likely overpressured and has relatively low shear stress.

Tectonic plates, D (double prime) thermal structure, and the nature of mantle plumes

NASA Technical Reports Server (NTRS)

Lenardic, A.; Kaula, W. M.

1994-01-01

It is proposed that subducting tectonic plates can affect the nature of thermal mantle plumes by determining the temperature drop across a plume source layer. The temperature drop affects source layer stability and the morphology of plumes emitted from it. Numerical models are presented to demonstrate how introduction of platelike behavior in a convecting temperature dependent medium, driven by a combination of internal and basal heating, can increase the temperature drop across the lower boundary layer. The temperature drop increases dramatically following introduction of platelike behavior due to formation of a cold temperature inversion above the lower boundary layer. This thermal inversion, induced by deposition of upper boundary layer material to the system base, decays in time, but the temperature drop across the lower boundary layer always remains considerably higher than in models lacking platelike behavior. On the basis of model-inferred boundary layer temperature drops and previous studies of plume dynamics, we argue that generally accepted notions as to the nature of mantle plumes on Earth may hinge on the presence of plates. The implication for Mars and Venus, planets apparently lacking plate tectonics, is that mantle plumes of these planets may differ morphologically from those of Earth. A corollary model-based argument is that as a result of slab-induced thermal inversions above the core mantle boundary the lower most mantle may be subadiabatic, on average (in space and time), if major plate reorganization timescales are less than those acquired to diffuse newly deposited slab material.

Numerical modeling of intraplate seismicity with a deformable loading plate

NASA Astrophysics Data System (ADS)

So, B. D.; Capitanio, F. A.

2017-12-01

We use finite element modeling to investigate on the stress loading-unloading cycles and earthquakes occurrence in the plate interiors, resulting from the interactions of tectonic plates along their boundary. We model a visco-elasto-plastic plate embedding a single or multiple faults, while the tectonic stress is applied along the plate boundary by an external loading visco-elastic plate, reproducing the tectonic setting of two interacting lithospheres. Because the two plates deform viscously, the timescale of stress accumulation and release on the faults is self-consistently determined, from the boundary to the interiors, and seismic recurrence is an emerging feature. This approach overcomes the constraints on recurrence period imposed by stress (stress-drop) and velocity boundary conditions, while here it is unconstrained. We illustrate emerging macroscopic characteristics of this system, showing that the seismic recurrence period τ becomes shorter as Γ and Θ decreases, where Γ = ηI/ηL the viscosity ratio of the viscosities of the internal fault-embedded to external loading plates, respectively, and Θ = σY/σL the stress ratio of the elastic limit of the fault to far-field loading stress. When the system embeds multiple, randomly distributed faults, stress transfer results in recurrence period deviations, however the time-averaged recurrence period of each fault show the same dependence on Γ and Θ, illustrating a characteristic collective behavior. The control of these parameters prevails even when initial pre-stress was randomly assigned in terms of the spatial arrangement and orientation on the internal plate, mimicking local fluctuations. Our study shows the relevance of macroscopic rheological properties of tectonic plates on the earthquake occurrence in plate interiors, as opposed to local factors, proposing a viable model for the seismic behavior of continent interiors in the context of large-scale, long-term deformation of interacting tectonic plates.

Plate Motions, Regional Deformation, and Time-Variation of Plate Motions

NASA Technical Reports Server (NTRS)

Gordon, R. G.

1998-01-01

The significant results obtained with support of this grant include the following: (1) Using VLBI data in combination with other geodetical, geophysical, and geological data to bound the present rotation of the Colorado Plateau, and to evaluate to its implications for the kinematics and seismogenic potential of the western half of the conterminous U.S. (2) Determining realistic estimates of uncertainties for VLBI data and then applying the data and uncertainties to obtain an upper bound on the integral of deformation within the "stable interior" of the North American and other plates and thus to place an upper bound on the seismogenic potential within these regions. (3) Combining VLBI data with other geodetic, geophysical, and geologic data to estimate the motion of coastal California in a frame of reference attached to the Sierra Nevada-Great Valley microplate. This analysis has provided new insights into the kinematic boundary conditions that may control or at least strongly influence the locations of asperities that rupture in great earthquakes along the San Andreas transform system. (4) Determining a global tectonic model from VLBI geodetic data that combines the estimation of plate angular velocities with individual site linear velocities where tectonically appropriate. and (5) Investigation of the some of the outstanding problems defined by the work leading to global plate motion model NUVEL-1. These problems, such as the motion between the Pacific and North American plates and between west Africa and east Africa, are focused on regions where the seismogenic potential may be greater than implied by published plate tectonic models.

Tectonics of the Scotia-Antarctica plate boundary constrained from seismic and seismological data

NASA Astrophysics Data System (ADS)

Civile, D.; Lodolo, E.; Vuan, A.; Loreto, M. F.

2012-07-01

The plate boundary between the Scotia and Antarctic plates runs along the broadly E-W trending South Scotia Ridge. It is a mainly transcurrent margin that juxtaposes thinned continental and transitional crust elements with restricted oceanic basins and deep troughs. Seismic profiles and regional-scale seismological constraints are used to define the peculiarities of the crustal structures in and around the southern Scotia Sea, and focal solutions from recent earthquakes help to understand the present-day geodynamic setting. The northern edge of the western South Scotia Ridge is marked by a sub-vertical, left-lateral master fault. Locally, a narrow wedge of accreted sediments is present at the base of the slope. This segment represents the boundary between the Scotia plate and the independent South Shetland continental block. Along the northern margin of the South Orkney microcontinent, the largest fragment of the South Scotia Ridge, an accretionary prism is present at the base of the slope, which was possibly created by the eastward drift of the South Orkney microcontinent and the consequent subduction of the transitional crust present to the north. East of the South Orkney microcontinent, the physiography and structure of the plate boundary are less constrained. Here the tectonic regime exhibits mainly strike-slip behavior with some grade of extensional component, and the plate boundary is segmented by a series of NNW-SSE trending release zones which favored the fragmentation and dispersion of the crustal blocks. Seismic data have also identified, along the north-western edge of the South Scotia Ridge, an elevated region - the Ona Platform - which can be considered, along with the Terror Rise, as the conjugate margin of the Tierra del Fuego, before the Drake Passage opening. We propose here an evolutionary sketch for the plate boundary (from the Late Oligocene to the present) encompassing the segment from the Elephant Island platform to the Herdman Bank.

Motion of the Rivera plate since 10 Ma relative to the Pacific and North American plates and the mantle

NASA Astrophysics Data System (ADS)

DeMets, Charles; Traylen, Stephen

2000-03-01

To better understand the influence of Rivera plate kinematics on the geodynamic evolution of western Mexico, we use more than 1400 crossings of seafloor spreading magnetic lineations along the Pacific-Rivera rise and northern Mathematician ridge to solve for rotations of the Rivera plate relative to the underlying mantle and the Pacific and North American plates at 14 times since 9.9 Ma. Our comparison of magnetic anomaly crossings from the undeformed Pacific plate to their counterparts on the Rivera plate indicates that significant areas of the Rivera plate have deformed since 9.9 Ma. Dextral shear along the southern edge of the plate from 3.3-2.2 Ma during a regional plate boundary reorganization deformed the Rivera plate farther into its interior than previously recognized. In addition, seafloor located north of two rupture zones within the Rivera plate sutured to North America after 1.5 Ma. Anomaly crossings from these two deformed regions thus cannot be used to reconstruct motion of the Rivera plate. Finite rotations that best reconstruct Pacific plate anomaly crossings onto their undeformed counterparts on the Rivera plate yield stage spreading rates that decrease gradually by 10% between 10 and 3.6 Ma, decrease rapidly by 20% after ˜3.6 Ma, and recover after 1 Ma. The slowdown in Pacific-Rivera seafloor spreading at 3.6 Ma coincided with the onset of dextral shear across the then-incipient southern boundary of the Rivera plate with the Pacific plate. The available evidence indicates that the Rivera plate has been an independent microplate since at least 10 Ma, contrary to published assertions that it fragmented from the Cocos plate at ˜5 Ma. Motion of the Rivera plate relative to North America has changed significantly since 10 Ma, in concert with significant changes in Pacific-Rivera motion. A significant and robust feature of Rivera-North America motion not previously recognized is the cessation of margin-normal convergence and thus subduction from 2.6 to 1.0 Ma along the entire plate boundary, followed by a resumption of trench-normal subduction along the southern half of the Rivera-North America plate boundary after 1.0 Ma. Motion of the Rivera plate relative to the underlying mantle since 10 Ma has oscillated between periods of landward motion and seaward motion. The evidence suggests that the torque exerted by slab pull on this young and hot oceanic plate is either minimal or is effectively counterbalanced by forces that resist its motion.

Effect of velocity boundary conditions on the heat transfer and flow topology in two-dimensional Rayleigh-Bénard convection.

PubMed

van der Poel, Erwin P; Ostilla-Mónico, Rodolfo; Verzicco, Roberto; Lohse, Detlef

2014-07-01

The effect of various velocity boundary condition is studied in two-dimensional Rayleigh-Bénard convection. Combinations of no-slip, stress-free, and periodic boundary conditions are used on both the sidewalls and the horizontal plates. For the studied Rayleigh numbers Ra between 10(8) and 10(11) the heat transport is lower for Γ=0.33 than for Γ=1 in case of no-slip sidewalls. This is, surprisingly, the opposite for stress-free sidewalls, where the heat transport increases for a lower aspect ratio. In wider cells the aspect-ratio dependence is observed to disappear for Ra ≥ 10(10). Two distinct flow types with very different dynamics can be seen, mostly dependent on the plate velocity boundary condition, namely roll-like flow and zonal flow, which have a substantial effect on the dynamics and heat transport in the system. The predominantly horizontal zonal flow suppresses heat flux and is observed for stress-free and asymmetric plates. Low aspect-ratio periodic sidewall simulations with a no-slip boundary condition on the plates also exhibit zonal flow. In all the other cases, the flow is roll like. In two-dimensional Rayleigh-Bénard convection, the velocity boundary conditions thus have large implications on both roll-like and zonal flow that have to be taken into consideration before the boundary conditions are imposed.

Circum-Pacific diatomite deposits

DOE Office of Scientific and Technical Information (OSTI.GOV)

North, F.K.

1986-07-01

Deformed diatomites of assured identification are all Oligocene or younger. They are not to be interpreted with oceanic diatom oozes as analogs, nor with California's Monterey Formation as prototype. All examples, apart from the unique Monterey, are deposits of relatively shallow waters at convergent plate or microplate boundaries: in arc-trench gaps or (less importantly) in immediate back-arc belts. Tethyan examples, along a collision boundary, are now slivers in the late stages of external flysch along the fronts of Alpine thrust belts. Circum-Pacific examples, at ocean-continent subduction boundaries, are preserved only on mountainous islands or peninsulas, the uplift (not folding) ofmore » which has protected the diatomites and their overlying evaporites from subduction. The control is tectonic and volcanic, not by water temperature or eustatism. Preserved deposits appear to be restricted to particular segments of the Pacific boundary delineated by Benioff zones having some significant minimum dip. The unique Monterey Formation owes its spectacular development and preservation to the conversion of an arc-trench boundary to a transform boundary, at a triple junction, before the diatomite was deposited. The Monterey's importance as an oil source sediment does not stem from its true diatomite component. Other Circum-Pacific diatomites are of negligible significance to the petroleum geologist, but are potentially minable for other uses in Japan, the Philippines, and Peru, and possibly in Chile.« less

Boundary-layer transition on a plate subjected to simultaneous spanwise and chordwise pressure gradients

NASA Technical Reports Server (NTRS)

Boldman, D. R.; Brinich, P. F.

1974-01-01

The boundary-layer transition on a short plate was studied by means of the china-clay visual technique. The plate model was mounted in a wind tunnel so that it was subjected to small simultaneous spanwise and chordwise pressure gradients. Results of the experimental study, which was performed at three subsonic velocities, indicated that the transition pattern was appreciably curved in the spanwise direction but quite smooth and well behaved. Reasonable comparisons between predictions of transition and experiment were obtained from two finite-difference two-dimensional boundary-layer calculation methods which incorporated transition models based on the concept of a transition intermittency factor.

Investigation of Low-Pressure Turbine Endwall Flows: Simulations and Experiments (Postprint)

DTIC Science & Technology

2015-01-01

direction) minor semiaxis of 0.0417Cx (0.25in). Measured in the axial direction, the flat plate leading edge was located at x=-3.958Cx (23.75in) where...for public release; distribution unlimited. plate boundary layer is δ∗ = 1.721s/Re0.5s . For s = 4.833Cx, Reδ∗ = 1.721 √ s/CxRe = 1, 200. At this...boundary which was located at x=-1.4Cx. The following approximations hold for a turbulent flat plate boundary layer: δ99 = 0.37s Re0.2s , δ∗ = 0.046s

Sediment Accretion During Horst and Graben Subduction associated with the Tohoku Oki M9 Earthquake, Northern Japan

NASA Astrophysics Data System (ADS)

Moore, J. C.; Chester, F. M.

2015-12-01

The stratigraphic sequence within the frontal accretionary prism of the Japan Trench, the site of large slip during the Tohoku earthquake, is unique due to horst and graben subduction. Boreholes at IODP Site C0019, penetrating the toe of the Tohoku accretionary prism, document a younger over older intraprism thrust contact with a 9 Ma age gap across the basal plate boundary fault. The anomalously young (Quaternary to Pliocene), fault-bounded sediment package is 130 m thick, of a total of 820 m of sediment above the plate boundary fault. In contrast, typical accretionary prism structure consists of stacked sediment packages on imbricate faults above the basal decollement resulting in an overall increase in age downward. Site C0019 penetrates the prism directly above a horst of the subducting Pacific oceanic crust. Here the plate-boundary fault consists of a thin, weak smectitic pelagic clay that is probably the principal slip surface of ~50 m offset in the 2011 Tohoku earthquake. The fault continues seaward deepening off the seaward edge of the horst and beneath the sediment fill of the adjacent graben, dying out at the landward base of the next incoming horst. The plate boundary fault and its splays in the graben form a narrow-taper protoprism and a small sedimentary basin of trench fill marking the seaward edge of the upper plate. The modern fault and sediment distributions within the graben are used to motivate a viable model for the presence of anomalously young sediments directly above the plate boundary fault. In this model sediments in the trench are thrust over the incoming horst by propagation of the plate boundary thrust up the landward-dipping fault of the incoming horst and along the smectitic clay layer to emplace Quaternary and Pliocene trench deposits directly on top of the incoming horst. These young deposits are in turn overlain by sediments 9 Ma or older that have been transported out of the graben along imbricate faults associated with the necessary increase in the taper of the prism above the graben. The Quaternary to Pliocene units thicken due to internal deformation accounting for the 130 m thickness now observed over the plate boundary fault at Site C0019. Conversely emplacement of very young sediment directly above a basal detachment would be unexpected in accretionary prisms subducting smoother oceanic crust.

Style of Plate Spreading Derived from the 2008-2014 Velocity Field Across the Northern Volcanic Zone of Iceland

NASA Astrophysics Data System (ADS)

Drouin, V.; Sigmundsson, F.; Hreinsdottir, S.; Ofeigsson, B.; Sturkell, E.; Einarsson, P.

2015-12-01

The Northern Volcanic Zone (NVZ) of Iceland is a subaerial part of the divergent boundary between the North-American and Eurasian Plates. At this latitude, the full spreading between the plates is accommodated by the NVZ. We derived the plate boundary velocity field from GPS campaign and continuous measurements between 2008 and 2014, a time period free of any magma intrusion. Average velocities were estimated in the ITRF08 reference frame. The overall extension is consistent with 18 mm/yr in the 104°N direction spreading, in accordance with the MORVEL2010 plate motion model. We find that a 40km-wide band along the plate boundary accommodates about 75% of the full plate velocities. Within this zone, the average strain rate is approximately 0.35 μstrain/yr. The deformation field and the strain rate are, however, much affected by other sources of deformations in the NVZ. These include magmatic sources at the most active volcanic centers, glacial rebound near the ice-caps and geothermal power-plant water extraction. Magmatic sources include a shallow magma chamber deflation under Askja caldera, as well as under Þeistareykir and eventual deep magma inflation north of Krafla volcano. Vatnajökull ice cap melting causes large uplift and outward displacements in the southern part of the NVZ. The two geothermal power-plants near Krafla are inducing local deflations. Our GPS velocities show a 35° change in the direction of the plate boundary axis north of Askja volcano that we infer to be linked to the geometric arrangement of volcanic systems within the NVZ.We use a simple arctangent model to describe the plate spreading to provide constraints on the location and the locking depth of the spreading axis. For that purpose we divided the area in short overlapping segments having the same amount of GPS points along the plate spreading direction and inverted for the location of the center of the spreading axis and locking depth. With this simple model we can account for most of the plate spreading related deformation in the NVZ. It appears that the locking depth is not uniform all along the length of the plate boundary, with a deeper locking depth in the low activity volcanic systems and a shallower locking depth in the more active volcanic systems of Krafla and Askja.

Shed vortex structure and phase-averaged velocity statistics in symmetric/asymmetric turbulent flat plate wakes

NASA Astrophysics Data System (ADS)

Rai, Man Mohan

2018-05-01

The near wake of a flat plate is investigated via direct numerical simulations. Many earlier experimental investigations have used thin plates with sharp trailing edges and turbulent boundary layers to create the wake. This results in large θ/DTE values (θ is the boundary layer momentum thickness toward the end of the plate and DTE is the trailing edge thickness). In the present study, the emphasis is on relatively thick plates with circular trailing edges (CTEs) resulting in θ/D values less than one (D is the plate thickness and the diameter of the CTE) and vigorous vortex shedding. The Reynolds numbers based on the plate length and D are 1.255 × 106 and 10 000, respectively. Two cases are computed: one with turbulent boundary layers on both the upper and lower surfaces of the plate (statistically the same, symmetric wake, Case TT) and the other with turbulent and laminar boundary layers on the upper and lower surfaces, respectively (asymmetric case, Case TL). The data and understanding obtained are of considerable engineering interest, particularly in turbomachinery where the pressure side of an airfoil can remain laminar or transitional because of a favorable pressure gradient and the suction side is turbulent. Shed-vortex structure and phase-averaged velocity statistics obtained in the two cases are compared here. The upper negative shed vortices in Case TL (turbulent separating boundary layer) are weaker than the lower positive ones (laminar separating boundary layer) at inception (a factor of 1.27 weaker in terms of peak phase-averaged spanwise vorticity at the first appearance of a peak). The upper vortices weaken rapidly as they travel downstream. A second feature of interest in Case TL is a considerable increase in the peak phase-averaged, streamwise normal intensity (random component) with increasing streamwise distance (x/D) that occurs near the positive vortex cores. This behavior is observed for a few diameters in the near wake. This is counter to Case TT where the peak value essentially decreases with increasing x/D. Both these effects are examined in detail, and the important contributors are identified.

Strength and Deformation Rate of Plate Boundaries: The Rheological Effects of Grain Size Reduction, Structure, and Serpentinization.

NASA Astrophysics Data System (ADS)

Montesi, L.; Gueydan, F.

2016-12-01

Global strain rate maps reveal 1000-fold contrasts between plate interiors, oceanic or continental diffuse plate boundaries and narrow plate boundaries. Here, we show that rheological models based on the concepts of shear zone localization and the evolution of rock structure upon strain can explain these strain rate contrasts. Ductile shear zones constitute a mechanical paradox in the lithosphere. As every plastic deformation mechanism is strain-rate-hardening, ductile rocks are expected to deform at low strain rate and low stress (broad zone of deformation). Localized ductile shear zones require either a localized forcing (locally high stress) or a thermal or structural anomaly in the shear zone; either can be inherited or develop progressively as rocks deform. We previously identified the most effective process at each depth level of the lithosphere. In the upper crust and middle crust, rocks fabric controls localization. Grain size reduction is the most efficient mechanism in the uppermost mantle. This analysis can be generalized to consider a complete lithospheric section. We assume strain rate does not vary with depth and that the depth-integrated strength of the lithospheric does not change over time, as the total force is controlled by external process such as mantle convection and plate and slab buoyancy. Reducing grain size from a coarse value typical of undeformed peridotite to a value in agreement with the stress level (piezometer) while letting that stress vary from depth to depth (the integrated stress remains the same) increases the lithospheric strain rate by about a factor of 1000. This can explain the development of diffuse plate boundaries. The slightly higher strain rate of continental plate boundary may reflect development of a layered rock fabric in the middle crust. Narrow plate boundaries require additional weakening process. The high heat flux near mid-ocean ridge implies a thin lithosphere, which enhances stress (for constant integrated stress). While this can increase strain rate by another factor of 1000, another process must generate the lithospheric thickness variation in the first place. One possibility is serpentinization, which reduces the strength of the brittle crust, especially when coupled with the development of a fabric in brittle faults.

Casimir effect for parallel plates in a Friedmann-Robertson-Walker universe

NASA Astrophysics Data System (ADS)

Bezerra de Mello, E. R.; Saharian, A. A.; Setare, M. R.

2017-03-01

We evaluate the Hadamard function, the vacuum expectation values (VEVs) of the field squared and the energy-momentum tensor for a massive scalar field with a general curvature coupling parameter in the geometry of two parallel plates on a spatially flat Friedmann-Robertson-Walker background with a general scale factor. On the plates, the field operator obeys the Robin boundary conditions with the coefficients depending on the scale factor. In all the spatial regions, the VEVs are decomposed into the boundary-free and boundary-induced contributions. Unlike the problem with the Minkowski bulk, in the region between the plates, the normal stress is not homogeneous and does not vanish in the geometry of a single plate. Near the plates, it has different signs for accelerated and decelerated expansions of the Universe. The VEV of the energy-momentum tensor, in addition to the diagonal components, has a nonzero off-diagonal component describing an energy flux along the direction normal to the boundaries. Expressions are derived for the Casimir forces acting on the plates. Depending on the Robin coefficients and on the vacuum state, these forces can be either attractive or repulsive. An important difference from the corresponding result in the Minkowski bulk is that the forces on the separate plates, in general, are different if the corresponding Robin coefficients differ. We give the applications of general results for the class of α vacua in the de Sitter bulk. It is shown that, compared with the Bunch-Davies vacuum state, the Casimir forces for a given α vacuum may change the sign.

Multigrid methods for a semilinear PDE in the theory of pseudoplastic fluids

NASA Technical Reports Server (NTRS)

Henson, Van Emden; Shaker, A. W.

1993-01-01

We show that by certain transformations the boundary layer equations for the class of non-Newtonian fluids named pseudoplastic can be generalized in the form the vector differential operator(u) + p(x)u(exp -lambda) = 0, where x is a member of the set Omega and Omega is a subset of R(exp n), n is greater than or equal to 1 under the classical conditions for steady flow over a semi-infinite flat plate. We provide a survey of the existence, uniqueness, and analyticity of the solutions for this problem. We also establish numerical solutions in one- and two-dimensional regions using multigrid methods.

Clustering and interpretation of local earthquake tomography models in the southern Dead Sea basin

NASA Astrophysics Data System (ADS)

Bauer, Klaus; Braeuer, Benjamin

2016-04-01

The Dead Sea transform (DST) marks the boundary between the Arabian and the African plates. Ongoing left-lateral relative plate motion and strike-slip deformation started in the Early Miocene (20 MA) and produced a total shift of 107 km until presence. The Dead Sea basin (DSB) located in the central part of the DST is one of the largest pull-apart basins in the world. It was formed from step-over of different fault strands at a major segment boundary of the transform fault system. The basin development was accompanied by deposition of clastics and evaporites and subsequent salt diapirism. Ongoing deformation within the basin and activity of the boundary faults are indicated by increased seismicity. The internal architecture of the DSB and the crustal structure around the DST were subject of several large scientific projects carried out since 2000. Here we report on a local earthquake tomography study from the southern DSB. In 2006-2008, a dense seismic network consisting of 65 stations was operated for 18 months in the southern part of the DSB and surrounding regions. Altogether 530 well-constrained seismic events with 13,970 P- and 12,760 S-wave arrival times were used for a travel time inversion for Vp, Vp/Vs velocity structure and seismicity distribution. The work flow included 1D inversion, 2.5D and 3D tomography, and resolution analysis. We demonstrate a possible strategy how several tomographic models such as Vp, Vs and Vp/Vs can be integrated for a combined lithological interpretation. We analyzed the tomographic models derived by 2.5D inversion using neural network clustering techniques. The method allows us to identify major lithologies by their petrophysical signatures. Remapping the clusters into the subsurface reveals the distribution of basin sediments, prebasin sedimentary rocks, and crystalline basement. The DSB shows an asymmetric structure with thickness variation from 5 km in the west to 13 km in the east. Most importantly, a well-defined body under the eastern part of the basin down to 18 km depth was identified by the algorithm. Considering its geometry and petrophysical signature, this unit is interpreted as prebasin sediments and not as crystalline basement. The seismicity distribution supports our results, where events are concentrated along boundaries of the basin and the deep prebasin sedimentary body.

a Lattice Boltzmann Study of the 2d Boundary Layer Created by AN Oscillating Plate

NASA Astrophysics Data System (ADS)

Cappietti, L.; Chopard, B.

We study the applicability of the Lattice Boltzmann Method (LBM) to simulate the 2D laminar boundary layer induced by an oscillating flat plate. We also investigate the transition to the disturbed laminar regime that occurs with a rough oscillating plate. The simulations were performed in two cases: first with a fluid otherwise at rest and second in presence of superimposed current. The generation of coherent vortex structures and their evolution are commented. The accuracy of the method was checked by comparisons with the exact analytical solution of the Navier-Stokes equations for the so-called Stokes' Second Problem. The comparisons show that LBM reproduces this time varying flow with first order accuracy. In the case of the wavy-plate, the results show that a mechanism of vortex-jet formations, low speed-streak and shear instability sustain a systems of stationary vortices outside the boundary layer. The vortex-jet takes place at the end of the decelerating phase whereas the boundary layer turns out to be laminar when the plate accelerates. In the presence of the superimposed current, the vortex-jet mechanism is still effective but the vortices outside the boundary layer are only present during part of the oscillating period. During the remaining part, the flow turns out to be laminar although a wave perturbation in the velocity field is present.

Seismo-thermo-mechanical modeling of mature and immature transform faults

NASA Astrophysics Data System (ADS)

Preuss, Simon; Gerya, Taras; van Dinther, Ylona

2016-04-01

Transform faults (TF) are subdivided into continental and oceanic ones due to their markedly different tectonic position, structure, surface expression, dynamics and seismicity. Both continental and oceanic TFs are zones of rheological weakness, which is a pre-requisite for their existence and long-term stability. Compared to subduction zones, TFs are typically characterized by smaller earthquake magnitudes as both their potential seismogenic width and length are reduced. However, a few very large magnitude (Mw>8) strike-slip events were documented, which are presumably related to the generation of new transform boundaries and/or sudden reactivation of pre-existing fossil structures. In particular, the 11 April 2012 Sumatra Mw 8.6 earthquake is challenging the general concept that such high magnitude events only occur at megathrusts. Hence, the processes of TF nucleation, propagation and their direct relation to the seismic cycle and long-term deformation at both oceanic and continental transforms needs to be investigated jointly to overcome the restricted direct observations in time and space. To gain fundamental understanding of involved physical processes the numerical seismo-thermo-mechanical (STM) modeling approach, validated in a subduction zone setting (Van Dinther et al. 2013), will be adapted for TFs. A simple 2D plane view model geometry using visco-elasto-plastic material behavior will be adopted. We will study and compare seismicity patterns and evolution in two end member TF setups, each with strain-dependent and rate-dependent brittle-plastic weakening processes: (1) A single weak and mature transform fault separating two strong plates (e.g., in between oceanic ridges) and (2) A nucleating or evolving (continental) TF system with disconnected predefined faults within a plate subjected to simple shear deformation (e.g., San Andreas Fault system). The modeling of TFs provides a first tool to establish the STM model approach for transform faults in a more general case.

The ribbon continent of northwestern South America

NASA Astrophysics Data System (ADS)

Altamira-Areyan, Armando

The tectonic structure of the Plate Boundary Zone (PBZ) between the Caribbean Plate (CARIB) and the South American Plate (SOAM) is interpreted using models that require CARIB motion from the Pacific into the Atlantic. Those models can be subdivided into: (1) those in which the island arc rocks that are now in the CARIB-SOAM PBZ have collided with the northern South America margin, either obliquely or directly during the Cretaceous or during the Cenozoic, and (2) those in which the island arc rocks now in the CARIB-SOAM PBZ collided with the west coast of South America during the Cretaceous and were transferred to the northern margin by transform motion during the Cenozoic. Magnetic anomalies were first rotated in the Central and South Atlantic, holding Africa fixed to establish how much NOAM had converged on SOAM during the Cenozoic. WSW convergence was discovered to have been accommodated in the northern boundary of the CARIB. There is no evidence of convergence in the form of Cenozoic island arc igneous rocks on the north coast of South America. Those results are consistent only with models of Class (2) that call for transform movement of material that had collided with the west coast of South America along the CARIB-SOAM PBZ on the northern margin of South America. 40Ar/39Ar ages of island arc rocks from northern Venezuela were found to be older than ca 70 Ma, which is consistent with a requirement of models of Class (2) that those rocks are from an island arc which collided with the west coast of South America during Cretaceous times. Testing that conclusion using data from Ecuador, Colombia, Venezuela, the Netherlands Antilles, Trinidad and Tobago has led to the construction of a new ribbon continent model of the northwestern Cordillera of South America. Because the part of the ribbon continent on the north coast of South America has been experiencing substantial deformation in the Maracaibo block during the past 10 m.y., structures in that body have had to be retro-deformed to establish the form and history of the ribbon continent on the north coast of South America.

Link between SSZ ophiolite formation, emplacement and arc inception, Northland, New Zealand: U Pb SHRIMP constraints; Cenozoic SW Pacific tectonic implications

NASA Astrophysics Data System (ADS)

Whattam, Scott A.; Malpas, John; Smith, Ian E. M.; Ali, Jason R.

2006-10-01

New U-Pb age-data from zircons separated from a Northland ophiolite gabbro yield a mean 206Pb/ 238U age of 31.6 ± 0.2 Ma, providing support for a recently determined 28.3 ± 0.2 Ma SHRIMP age of an associated plagiogranite and ˜ 29-26 Ma 40Ar/ 39Ar ages ( n = 9) of basalts of the ophiolite. Elsewhere, Miocene arc-related calc-alkaline andesite dikes which intrude the ophiolitic rocks contain zircons which yield mean 206Pb/ 238U ages of 20.1 ± 0.2 and 19.8 ± 0.2 Ma. The ophiolite gabbro and the andesites both contain rare inherited zircons ranging from 122-104 Ma. The Early Cretaceous zircons in the arc andesites are interpreted as xenocrysts from the Mt. Camel basement terrane through which magmas of the Northland Miocene arc lavas erupted. The inherited zircons in the ophiolite gabbros suggest that a small fraction of this basement was introduced into the suboceanic mantle by subduction and mixed with mantle melts during ophiolite formation. We postulate that the tholeiitic suite of the ophiolite represents the crustal segment of SSZ lithosphere (SSZL) generated in the southern South Fiji Basin (SFB) at a northeast-dipping subduction zone that was initiated at about 35 Ma. The subduction zone nucleated along a pre-existing transform boundary separating circa 45-20 Ma oceanic lithosphere to the north and west of the Northland Peninsula from nascent back arc basin lithosphere of the SFB. Construction of the SSZL propagated southward along the transform boundary as the SFB continued to unzip to the southeast. After subduction of a large portion of oceanic lithosphere by about 26 Ma and collision of the SSZL with New Zealand, compression between the Australian Plate and the Pacific Plate was taken up along a new southwest-dipping subduction zone behind the SSZL. Renewed volcanism began in the oceanic forearc at 25 Ma producing boninitic-like, SSZ and within-plate alkalic and calc-alkaline rocks. Rocks of these types temporally overlap ophiolite emplacement and subsequent Miocene continental arc construction.

Surface capillary currents: Rediscovery of fluid-structure interaction by forced evolving boundary theory

NASA Astrophysics Data System (ADS)

Wang, Chunbai; Mitra, Ambar K.

2016-01-01

Any boundary surface evolving in viscous fluid is driven with surface capillary currents. By step function defined for the fluid-structure interface, surface currents are found near a flat wall in a logarithmic form. The general flat-plate boundary layer is demonstrated through the interface kinematics. The dynamics analysis elucidates the relationship of the surface currents with the adhering region as well as the no-slip boundary condition. The wall skin friction coefficient, displacement thickness, and the logarithmic velocity-defect law of the smooth flat-plate boundary-layer flow are derived with the advent of the forced evolving boundary method. This fundamental theory has wide applications in applied science and engineering.

Viscoelastic deformation near active plate boundaries

NASA Technical Reports Server (NTRS)

Ward, S. N.

1986-01-01

Model deformations near the active plate boundaries of Western North America using space-based geodetic measurements as constraints are discussed. The first six months of this project were spent gaining familarity with space-based measurements, accessing the Crustal Dynamics Data Information Computer, and building time independent deformation models. The initial goal was to see how well the simplest elastic models can reproduce very long base interferometry (VLBI) baseline data. From the Crustal Dynamics Data Information Service, a total of 18 VLBI baselines are available which have been surveyed on four or more occasions. These data were fed into weighted and unweighted inversions to obtain baseline closure rates. Four of the better quality lines are illustrated. The deformation model assumes that the observed baseline rates result from a combination of rigid plate tectonic motions plus a component resulting from elastic strain build up due to a failure of the plate boundary to slip at the full plate tectonic rate. The elastic deformation resulting from the locked plate boundary is meant to portray interseismic strain accumulation. During and shortly after a large interplate earthquake, these strains are largely released, and points near the fault which were previously retarded suddenly catch up to the positions predicted by rigid plate models. Researchers judge the quality of fit by the sum squares of weighted residuals, termed total variance. The observed baseline closures have a total variance of 99 (cm/y)squared. When the RM2 velocities are assumed to model the data, the total variance increases to 154 (cm/y)squared.

An analysis of the relaxation of laminar boundary layer on a flat plate after passage of an interface with application to expansion-tube flows

NASA Technical Reports Server (NTRS)

Gupta, R. N.

1972-01-01

The relaxation of the accelerating-gas boundary layer to the test-gas boundary layer over a flat plate in an expansion tube is analyzed. Several combinations of test gas and acceleration gas are considered. The problem is treated in two conically similar limits: (1) when the time lag between the arrival of the shock and the interface at the leading edge of the plate is very large, and (2) when this lag is negligible. The time-dependent laminar-boundary-layer equations of a binary mixture of perfect gases are taken as the flow-governing equations. This coupled set of differential equations, written in terms of the Lam-Crocco variables, has been solved by a line-relaxation finite-difference techniques. The results presented include the Stanton number and the local skin-friction coefficient as functions of shock Mach number and the nondimensional distance-time variable. The results indicate that more than 95 percent of the test-gas boundary layer exists over a length, measured from the leading edge of the plate, equal to about three-tenths of the distance traversed by the interface in the free stream.

Computational analysis of non-Newtonian boundary layer flow of nanofluid past a semi-infinite vertical plate with partial slip

NASA Astrophysics Data System (ADS)

Amanulla, C. H.; Nagendra, N.; Suryanarayana Reddy, M.

2018-03-01

An analysis of this paper is examined, two-dimensional, laminar with heat and mass transfer of natural convective nanofluid flow past a semi-infinite vertical plate surface with velocity and thermal slip effects are studied theoretically. The coupled governing partial differential equations are transformed to ordinary differential equations by using non-similarity transformations. The obtained ordinary differential equations are solved numerically by a well-known method named as Keller Box Method (KBM). The influences of the emerging parameters i.e. Casson fluid parameter (β), Brownian motion parameter (Nb), thermophoresis parameter (Nt), Buoyancy ratio parameter (N), Lewis number (Le), Prandtl number (Pr), Velocity slip factor (Sf) and Thermal slip factor (ST) on velocity, temperature and nano-particle concentration distributions is illustrated graphically and interpreted at length. The major sources of nanoparticle migration in Nanofluids are Thermophoresis and Brownian motion. A suitable agreement with existing published literature is made and an excellent agreement is observed for the limiting case and also validation of solutions with a Nakamura tridiagonal method has been included. It is observed that nanoparticle concentrations on surface decreases with an increase in slip parameter. The study is relevant to enrobing processes for electric-conductive nano-materials, of potential use in aerospace and other industries.

Fem Simulation of Triple Diffusive Natural Convection Along Inclined Plate in Porous Medium: Prescribed Surface Heat, Solute and Nanoparticles Flux

NASA Astrophysics Data System (ADS)

Goyal, M.; Goyal, R.; Bhargava, R.

2017-12-01

In this paper, triple diffusive natural convection under Darcy flow over an inclined plate embedded in a porous medium saturated with a binary base fluid containing nanoparticles and two salts is studied. The model used for the nanofluid is the one which incorporates the effects of Brownian motion and thermophoresis. In addition, the thermal energy equations include regular diffusion and cross-diffusion terms. The vertical surface has the heat, mass and nanoparticle fluxes each prescribed as a power law function of the distance along the wall. The boundary layer equations are transformed into a set of ordinary differential equations with the help of group theory transformations. A wide range of parameter values are chosen to bring out the effect of buoyancy ratio, regular Lewis number and modified Dufour parameters of both salts and nanofluid parameters with varying angle of inclinations. The effects of parameters on the velocity, temperature, solutal and nanoparticles volume fraction profiles, as well as on the important parameters of heat and mass transfer, i.e., the reduced Nusselt, regular and nanofluid Sherwood numbers, are discussed. Such problems find application in extrusion of metals, polymers and ceramics, production of plastic films, insulation of wires and liquid packaging.

Structure and lithology of the Japan Trench subduction plate boundary fault

NASA Astrophysics Data System (ADS)

Kirkpatrick, James D.; Rowe, Christie D.; Ujiie, Kohtaro; Moore, J. Casey; Regalla, Christine; Remitti, Francesca; Toy, Virginia; Wolfson-Schwehr, Monica; Kameda, Jun; Bose, Santanu; Chester, Frederick M.

2015-01-01

The 2011 Mw9.0 Tohoku-oki earthquake ruptured to the trench with maximum coseismic slip located on the shallow portion of the plate boundary fault. To investigate the conditions and physical processes that promoted slip to the trench, Integrated Ocean Drilling Program Expedition 343/343T sailed 1 year after the earthquake and drilled into the plate boundary ˜7 km landward of the trench, in the region of maximum slip. Core analyses show that the plate boundary décollement is localized onto an interval of smectite-rich, pelagic clay. Subsidiary structures are present in both the upper and lower plates, which define a fault zone ˜5-15m thick. Fault rocks recovered from within the clay-rich interval contain a pervasive scaly fabric defined by anastomosing, polished, and lineated surfaces with two predominant orientations. The scaly fabric is crosscut in several places by discrete contacts across which the scaly fabric is truncated and rotated, or different rocks are juxtaposed. These contacts are inferred to be faults. The plate boundary décollement therefore contains structures resulting from both distributed and localized deformation. We infer that the formation of both of these types of structures is controlled by the frictional properties of the clay: the distributed scaly fabric formed at low strain rates associated with velocity-strengthening frictional behavior, and the localized faults formed at high strain rates characterized by velocity-weakening behavior. The presence of multiple discrete faults resulting from seismic slip within the décollement suggests that rupture to the trench may be characteristic of this margin.

Subcontinental-scale crustal velocity changes along the Pacific-North America plate boundary.

PubMed

Davis, J L; Wernicke, B P; Bisnath, S; Niemi, N A; Elósegui, P

2006-06-29

Transient tectonic deformation has long been noted within approximately 100 km of plate boundary fault zones and within active volcanic regions, but it is unknown whether transient motions also occur at larger scales within plates. Relatively localized transients are known to occur as both seismic and episodic aseismic events, and are generally ascribed to motions of magma bodies, aseismic creep on faults, or elastic or viscoelastic effects associated with earthquakes. However, triggering phenomena and systematic patterns of seismic strain release at subcontinental (approximately 1,000 km) scale along diffuse plate boundaries have long suggested that energy transfer occurs at larger scale. Such transfer appears to occur by the interaction of stresses induced by surface wave propagation and magma or groundwater in the crust, or from large-scale stress diffusion within the oceanic mantle in the decades following clusters of great earthquakes. Here we report geodetic evidence for a coherent, subcontinental-scale change in tectonic velocity along a diffuse approximately 1,000-km-wide deformation zone. Our observations are derived from continuous GPS (Global Positioning System) data collected over the past decade across the Basin and Range province, which absorbs approximately 25 per cent of Pacific-North America relative plate motion. The observed changes in site velocity define a sharp boundary near the centre of the province oriented roughly parallel to the north-northwest relative plate motion vector. We show that sites to the west of this boundary slowed relative to sites east of it by approximately 1 mm yr(-1) starting in late 1999.

A New Estimate for Total Offset on the Southern San Andreas Fault: Implications for Cumulative Plate Boundary Shear in the Northern Gulf of California

NASA Astrophysics Data System (ADS)

Darin, M. H.; Dorsey, R. J.

2012-12-01

Development of a consistent and balanced tectonic reconstruction for the late Cenozoic San Andreas fault (SAF) in southern California has been hindered for decades by incompatible estimates of total dextral offset based on different geologic cross-fault markers. The older estimate of 240-270 km is based on offset fluvial conglomerates of the middle Miocene Mint Canyon and Caliente Formations west of the SAF from their presumed source area in the northern Chocolate Mountains NE of the SAF (Ehlig et al., 1975; Ehlert, 2003). The second widely cited offset marker is a distinctive Triassic megaporphyritic monzogranite that has been offset 160 ± 10 km between Liebre Mountain west of the SAF and the San Bernadino Mountains (Matti and Morton, 1993). In this analysis we use existing paleocurrent data and late Miocene clockwise rotation in the eastern Transverse Ranges (ETR) to re-assess the orientation of the piercing line used in the 240 km-correlation, and present a palinspastic reconstruction that satisfies all existing geologic constraints. Our reconstruction of the Mint Canyon piercing line reduces the original estimate of 240-270 km to 195 ± 15 km of cumulative right-lateral slip on the southern SAF (sensu stricto), which is consistent with other published estimates of 185 ± 20 km based on correlative basement terranes in the Salton Trough region. Our estimate of ~195 km is consistent with the lower estimate of ~160 km on the Mojave segment because transform-parallel extension along the southwestern boundary of the ETR during transrotation produces ~25-40 km of displacement that does not affect offset markers of the Liebre/San Bernadino correlation located northwest of the ETR rotating domain. Reconciliation of these disparate estimates places an important new constraint on the total plate boundary shear that is likely accommodated in the adjacent northern Gulf of California. Global plate circuit models require ~650 km of cumulative Pacific-North America (PAC-NAM) relative plate motion since ~12 Ma (Atwater and Stock, 1998). We propose that the continental component of PAC-NAM shear is accommodated by: (1) 195 ± 15 km on the southern SAF (this study); (2) 12 ± 2 km on the Whittier-Elsinore fault; (3) 75 ± 20 km of cumulative shear across the central Mojave in the eastern California shear zone; (4) 30 ± 4 km of post-13 Ma slip on the Stateline fault; and (5) 47 ± 18 km of NW-directed translation produced by north-south shortening. Together, these components sum to 359 ± 31 km of net dextral displacement on the SAF system (sensu lato) in southern California since ca. 12 Ma, or ~300 km less than what is required by the global plate circuit. This suggests that the continental component of post-12 Ma PAC-NAM transform motion can be no more than ~390 km in the adjacent northern Gulf of California, substantially less than the 450 km of shear proposed in some models. We suggest that the remaining ~270-300 km of NW-directed relative plate motion is accommodated by a small component of late Miocene extension and roughly 225 km of slip on the offshore borderland fault system west of Baja California.

Unsteady laminar boundary-layer calculations on oscillating configurations including backflow. Part 1: Flat plate, oscillating in its own plane

NASA Technical Reports Server (NTRS)

Geissler, W.

1983-01-01

A finite difference method has been developed to calculate the unsteady boundary layer over an oscillating flat plate. Low- and high frequency approximations were used for comparison with numerical results. Special emphasis was placed on the behavior of the flow and on the numerical calculation procedure as soon as reversed flow has occurred over part of the oscillation cycle. The numerical method displayed neither problems nor singular behavior at the beginning of or within the reversed flow region. Calculations, however, came to a limit where the back-flow region reached the plate's leading edge in the case of high oscillation amplitudes. It is assumed that this limit is caused by the special behavior of the flow at the plate's leading edge where the boundary layer equations are not valid.

Contact stresses in pin-loaded orthotropic plates

NASA Technical Reports Server (NTRS)

Hyer, M. W.; Klang, E. C.

1984-01-01

The effects of pin elasticity, friction, and clearance on the stresses near the hole in a pin-loaded orthotropic plate are described. The problem is modeled as a contact elasticity problem using complex variable theory, the pin and the plate being two elastic bodies interacting through contact. This modeling is in contrast to previous works which assumed that the pin is rigid or that it exerts a known cosinusoidal radial traction on the hole boundary. Neither of these approaches explicitly involves a pin. A collocation procedure and iteration were used to obtain numerical results for a variety of plate and pin elastic properties and various levels of friction and clearance. Collocation was used to enforce the boundary and iteration was used to find the contact and no-slip regions on the boundary. Details of the numerical scheme are discussed.

Airborne Aero-Optics Laboratory - Transonic (AAOL-T)

DTIC Science & Technology

2016-10-03

122–151. [30] DeGraaff, D. B. and Eaton, J. K., “Reynolds-Number Scaling of the Flat - Plate Turbulent Boundary Layer ,” Journal of Fluid Mechanics, Vol...elevation angle of the turret is fixed at 120 o . The inflow turbulence data are generated by a separate flat - plate boundary layers simulation. The...aero-optical distortion magnitude for turbulent boundary layers . Subsonic Flow over a Cylindrical Turret with a Flat Window. The flow over a

Global isostatic geoid anomalies for plate and boundary layer models of the lithosphere

NASA Technical Reports Server (NTRS)

Hager, B. H.

1981-01-01

Commonly used one dimensional geoid models predict that the isostatic geoid anomaly over old ocean basins for the boundary layer thermal model of the lithosphere is a factor of two greater than that for the plate model. Calculations presented, using the spherical analogues of the plate and boundary layer thermal models, show that for the actual global distribution of plate ages, one dimensional models are not accurate and a spherical, fully three dimensional treatment is necessary. The maximum difference in geoid heights predicted for the two models is only about two meters. The thermal structure of old lithosphere is unlikely to be resolvable using global geoid anomalies. Stripping the effects of plate aging and a hypothetical uniform, 35 km, isostatically-compensated continental crust from the observed geoid emphasizes that the largest-amplitude geoid anomaly is the geoid low of almost 120 m over West Antarctica, a factor of two greater than the low of 60 m over Ceylon.

Numerical study of large-eddy breakup and its effect on the drag characteristics of boundary layers

NASA Technical Reports Server (NTRS)

Kinney, R. B.; Taslim, M. E.; Hung, S. C.

1985-01-01

The break-up of a field of eddies by a flat-plate obstacle embedded in a boundary layer is studied using numerical solutions to the two-dimensional Navier-Stokes equations. The flow is taken to be incompressible and unsteady. The flow field is initiated from rest. A train of eddies of predetermined size and strength are swept into the computational domain upstream of the plate. The undisturbed velocity profile is given by the Blasius solution. The disturbance vorticity generated at the plate and wall, plus that introduced with the eddies, mix with the background vorticity and is transported throughout the entire flow. All quantities are scaled by the plate length, the unidsturbed free-stream velocity, and the fluid kinematic viscosity. The Reynolds number is 1000, the Blasius boundary layer thickness is 2.0, and the plate is positioned a distance of 1.0 above the wall. The computational domain is four units high and sixteen units long.

Sonograph mosaic of northern California and southern Oregon Exclusive Economic Zone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cacchione, D.A.; Drake, D.E.; Clarke, S.H.

1985-02-01

During June 15 to July 9, 1984, the third leg of the cooperative US Geological Survey-Institute of Oceanographic Sciences GLORIA survey of the conterminous US Exclusive Economic Zone (EEZ) collected digital acoustic data off northern California and southern Oregon. The region covered during leg 3 extends from the 200-m isobath westward to the 375-km (200-nmi) EEZ boundary and from about 39/sup 0/ to 43/sup 0/N. The survey used the IOS GLORIA long-range side-scan sonar, a 2-channel airgun seismic reflection system, and 3.5 kHz and 10 kHz high-resolution seismic systems. The GLORIA data were collected in a pattern that permitted overlappingmore » coverage so that a mosaic of the sonographs could be constructed. These sonographs were slant-range and anamorphically corrected aboard ship, and a mosaic was constructed at a scale of 1:375,000. Among the most striking geomorphic features revealed in this segment of the EEZ is the Mendocino transform fault, which extends for more than 120 nmi along the northern base of the Mendocino fracture zone and delineates the southern boundary of the Gorda plate. Other features clearly revealed are the complex geometry of the Gorda rift valley, and the subparallel flanking ridges and dramatically deformed base of the continental slope at the eastern boundary of the Gorda plate. The data are presently being processed by image analytical techniques to enhance the fine-scale features such as sediment waves, slumps, and areas of differing sedimentary facies.« less

Large deflection random response of cross-ply laminated plates with elastically restrained edges and initial imperfections

NASA Technical Reports Server (NTRS)

Prasad, C. B.; Mei, Chuh

1988-01-01

The large deflection random response of symmetrically laminated cross-ply rectangular thin plates subjected to random excitation is studied. The out-of-plane boundary conditions are such that all the edges are rigidly supported against translation, but elastically restrained against rotation. The plate is also assumed to have a small initial imperfection. The assumed membrane boundary conditions are such that all the edges are free from normal and tangential forces in the plane of the plate. Mean-square deflections and mean-square strains are determined for a three-layered cross-ply laminate.

Jet-boundary and Plan-form Corrections for Partial-Span Models with Reflection-Plane, End-Plate, or No End-Plate in a Closed Circular Wind Tunnel

NASA Technical Reports Server (NTRS)

Sivells, James C; Deters, Owen J

1946-01-01

A method is presented for determining the jet-boundary and plan-form corrections necessary for application to test data for a partial-span model with a reflection plane, an end plate, or no end plate in a closed circular wind tunnel. Examples are worked out for a partial-span model with each of the three end conditions in the Langley 19-foot pressure tunnel and the corrections are applied to measured values of lift, drag, pitching-moment, rolling-moment, and yawing-moment coefficients.

Tsujal Marine Survey: Crustal Characterization of the Rivera Plate-Jalisco Block Boundary and its Implications for Seismic and Tsunami Hazard Assessment

NASA Astrophysics Data System (ADS)

Bartolome, R.; Danobeitia, J.; Barba, D. C., Sr.; Nunez-Cornu, F. J.; Cameselle, A. L.; Estrada, F.; Prada, M.; Bandy, W. L.

2014-12-01

During the spring of 2014, a team of Spanish and Mexican scientists explored the western margin of Mexico in the frame of the TSUJAL project. The two main objectives were to characterize the nature and structure of the lithosphere and to identify potential sources triggering earthquakes and tsunamis at the contact between Rivera plate-Jalisco block with the North American Plate. With these purposes a set of marine geophysical data were acquired aboard the RRS James Cook. This work is focus in the southern part of the TSUJAL survey, where we obtain seismic images from the oceanic domain up to the continental shelf. Thus, more than 800 km of MCS data, divided in 7 profiles, have been acquired with a 6km long streamer and using an air-gun sources ranging from 5800 c.i. to 3540 c.i. Furthermore, a wide-angle seismic profile of 190 km length was recorded in 16 OBS deployed perpendicular to the coast of Manzanillo. Gravity and magnetic, multibeam bathymetry and sub-bottom profiler data were recorded simultaneously with seismic data in the offshore area. Preliminary stacked MCS seismic sections reveal the crustal structure in the different domains of the Mexican margin. The contact between the Rivera and NA Plates is observed as a strong reflection at 6 s two way travel time (TWTT), in a parallel offshore profile (TS01), south of Manzanillo. This contact is also identified in a perpendicular profile, TS02, along a section of more than 100 km in length crossing the Rivera transform zone, and the plate boundary between Cocos and Rivera Plates. Northwards, offshore Pto. Vallarta, the MCS data reveals high amplitude reflections at around 7-8.5 s TWTT, roughly 2.5-3.5 s TWTT below the seafloor, that conspicuously define the subduction plane (TS06b). These strong reflections which we interpret as the Moho discontinuity define the starting bending of subduction of Rivera Plate. Another clear pattern observed within the first second of the MCS data shows evidences of a bottom simulating reflector (BSR) along the continental margin, particularly strong offshore Pto. Vallarta. The integration of all these acquired geophysical information will allow obtaining a comprehensive image of the lithosphere that will be valuable for the seismic and tsunamigenic hazard assessment.

Impact of Vishnu Fracture Zone on Tectono-Stratigraphy of Kerala Deepwater Basin, India

NASA Astrophysics Data System (ADS)

Bastia, R.; Krishna, K. S.; Nathaniel, D. M.; Tenepalli, S.

2008-12-01

Integration of regional seismic data extending from coast to deep water with the gravity-magnetics reveals the expression and evolution of ridge systems and fracture zones in Indian Ocean. Kerala deepwater basin, situated in the south-western tip of India, is bounded by two prominent north-south oriented ocean fracture zones viz., Vishnu (west) and Indrani (east) of the Indian Ocean. Vishnu Fracture Zone (VFZ), which extends from the Kerala shelf southward to the Carlsberg-Ridge, over a length of more than 2500 km, has a strong bearing on the sedimentation as well as structural fabric of the basin. VFZ is identified as the transform plate margin formed during Late-Cretaceous-Tertiary separation of Seychelles from India. Represented by a highly deformed structural fabric, VFZ forms an abrupt boundary between ocean floors of about 65 MY in the west and 140 MY in the east, implying a great scope for sedimentary pile on this very older ocean floor. Armed with this premise of an older sedimentary pile towards east of VFZ, congenial for petroleum hunt, the implemented modern long offset seismic program with an objective to enhance sub-basalt (Deccan) imagery, gravity-magnetic modelling and plate-tectonic reconstructions unraveled huge Mesozoic Basin, unheard earlier. Multi-episodic rifting in western continental margin of India starting during Mid Jurassic Karoo rift along the western Madagascar, Kerala deepwater basin, and western Antarctica and conjugate margins of Africa forms the main corridor for sedimentation. Subsequent Late Cretaceous dextral oblique extension of Madagascar rift reactivated pre-existing structural framework creating major accommodation zones along the southern tip of India. Followed by separation of Seychelles during KT boundary led to the formation of VFZ (an oceanic fracture zone) forming a transform boundary between newly formed Tertiary oceanic crust to the west and older basin to the east. The pulses of right-lateral movement were associated with various degrees of transpression, transtension, uplift and erosion. This activity continued in stages until Mid.Miocene, subsequent to phase of India- Seychelles separation. As a result, Mesozoic stratigraphy was inverted along VFZ's eastern border, folded in the basin centers and finally shifted the Tertiary depo-center towards east of VFZ. Plate tectonic reconstruction of Late Jurassic to Early Cretaceous demonstrates that the basin as situated in the north-east part of Proto-Mozambique Ocean, with Antarctica as the major provenance of sediment supply under favorable conditions for organic enrichment of sediments.

Genetic transformation system in the archaebacterium Methanobacterium thermoautotrophicum Marburg.

PubMed Central

Worrell, V E; Nagle, D P; McCarthy, D; Eisenbraun, A

1988-01-01

A wild-type strain of Methanobacterium thermoautotrophicum Marburg was transformed by DNA from strains resistant to 5-fluorouracil. Recipient cells were grown without selection on gellan gum (GELRITE) plates with DNA. Drug-resistant cells were recovered by replica plating the resulting colonies onto drug plates. Transformation required high-molecular-weight DNA with appropriate markers and was not observed on agar or in liquid media under a variety of conditions. PMID:3422229

Comments on ``seismic properties of the Eltanin transform system, south Pacific'' by Emile A. Okal and Amy R. Langenhorst

NASA Astrophysics Data System (ADS)

Wessel, Paul; Kroenke, Loren W.

2001-03-01

Seismicity in the Eltanin transform system region reflects the current relative motion between the Pacific and Antarctica plates. As such, the seismicity provides little or no constraints on models for late Neogene Pacific absolute plate motion changes that in turn forced a synchronous change in relative plate motions resulting in the current relative plate motion.

Prediction of interior noise due to random acoustic or turbulent boundary layer excitation using statistical energy analysis

NASA Technical Reports Server (NTRS)

Grosveld, Ferdinand W.

1990-01-01

The feasibility of predicting interior noise due to random acoustic or turbulent boundary layer excitation was investigated in experiments in which a statistical energy analysis model (VAPEPS) was used to analyze measurements of the acceleration response and sound transmission of flat aluminum, lucite, and graphite/epoxy plates exposed to random acoustic or turbulent boundary layer excitation. The noise reduction of the plate, when backed by a shallow cavity and excited by a turbulent boundary layer, was predicted using a simplified theory based on the assumption of adiabatic compression of the fluid in the cavity. The predicted plate acceleration response was used as input in the noise reduction prediction. Reasonable agreement was found between the predictions and the measured noise reduction in the frequency range 315-1000 Hz.

Lacustrine Paleoseismology Reveals Earthquake Segmentation of the Alpine Fault, New Zealand

NASA Astrophysics Data System (ADS)

Howarth, J. D.; Fitzsimons, S.; Norris, R.; Langridge, R. M.

2013-12-01

Transform plate boundary faults accommodate high rates of strain and are capable of producing large (Mw>7.0) to great (Mw>8.0) earthquakes that pose significant seismic hazard. The Alpine Fault in New Zealand is one of the longest, straightest and fastest slipping plate boundary transform faults on Earth and produces earthquakes at quasi-periodic intervals. Theoretically, the fault's linearity, isolation from other faults and quasi-periodicity should promote the generation of earthquakes that have similar magnitudes over multiple seismic cycles. We test the hypothesis that the Alpine Fault produces quasi-regular earthquakes that contiguously rupture the southern and central fault segments, using a novel lacustrine paleoseismic proxy to reconstruct spatial and temporal patterns of fault rupture over the last 2000 years. In three lakes located close to the Alpine Fault the last nine earthquakes are recorded as megaturbidites formed by co-seismic subaqueous slope failures, which occur when shaking exceeds Modified Mercalli (MM) VII. When the fault ruptures adjacent to a lake the co-seismic megaturbidites are overlain by stacks of turbidites produced by enhanced fluvial sediment fluxes from earthquake-induced landslides. The turbidite stacks record shaking intensities of MM>IX in the lake catchments and can be used to map the spatial location of fault rupture. The lake records can be dated precisely, facilitating meaningful along strike correlations, and the continuous records allow earthquakes closely spaced in time on adjacent fault segments to be distinguished. The results show that while multi-segment ruptures of the Alpine Fault occurred during most seismic cycles, sequential earthquakes on adjacent segments and single segment ruptures have also occurred. The complexity of the fault rupture pattern suggests that the subtle variations in fault geometry, sense of motion and slip rate that have been used to distinguish the central and southern segments of the Alpine Fault can inhibit rupture propagation, producing a soft earthquake segment boundary. The study demonstrates the utility of lakes as paleoseismometers that can be used to reconstruct the spatial and temporal patterns of earthquakes on a fault.

Interaction of a mantle plume and a segmented mid-ocean ridge: Results from numerical modeling

NASA Astrophysics Data System (ADS)

Georgen, Jennifer E.

2014-04-01

Previous investigations have proposed that changes in lithospheric thickness across a transform fault, due to the juxtaposition of seafloor of different ages, can impede lateral dispersion of an on-ridge mantle plume. The application of this “transform damming” mechanism has been considered for several plume-ridge systems, including the Reunion hotspot and the Central Indian Ridge, the Amsterdam-St. Paul hotspot and the Southeast Indian Ridge, the Cobb hotspot and the Juan de Fuca Ridge, the Iceland hotspot and the Kolbeinsey Ridge, the Afar plume and the ridges of the Gulf of Aden, and the Marion/Crozet hotspot and the Southwest Indian Ridge. This study explores the geodynamics of the transform damming mechanism using a three-dimensional finite element numerical model. The model solves the coupled steady-state equations for conservation of mass, momentum, and energy, including thermal buoyancy and viscosity that is dependent on pressure and temperature. The plume is introduced as a circular thermal anomaly on the bottom boundary of the numerical domain. The center of the plume conduit is located directly beneath a spreading segment, at a distance of 200 km (measured in the along-axis direction) from a transform offset with length 100 km. Half-spreading rate is 0.5 cm/yr. In a series of numerical experiments, the buoyancy flux of the modeled plume is progressively increased to investigate the effects on the temperature and velocity structure of the upper mantle in the vicinity of the transform. Unlike earlier studies, which suggest that a transform always acts to decrease the along-axis extent of plume signature, these models imply that the effect of a transform on plume dispersion may be complex. Under certain ranges of plume flux modeled in this study, the region of the upper mantle undergoing along-axis flow directed away from the plume could be enhanced by the three-dimensional velocity and temperature structure associated with ridge-transform-ridge geometry. It is suggested that, for a setting where a plume-ridge system has one or more transforms, a location-specific model with appropriate plate boundary geometry be used to assess the importance of ridge offsets on upper mantle geodynamics

Generation and development of small-amplitude disturbances in a laminar boundary layer in the presence of an acoustic field

NASA Technical Reports Server (NTRS)

Kachanov, Y. S.; Kozlov, V. V.; Levchenko, V. Y.

1985-01-01

A low-turbulence subsonic wind tunnel was used to study the influence of acoustic disturbances on the development of small sinusoidal oscillations (Tollmien-Schlichting waves) which constitute the initial phase of turbulent transition. It is found that acoustic waves propagating opposite to the flow generate vibrations of the model (plate) in the flow. Neither the plate vibrations nor the acoustic field itself have any appreciable influence on the stability of the laminar boundary layer. The influence of an acoustic field on laminar boundary layer disturbances is limited to the generation of Tollmien-Schlichting waves at the leading-edge of the plate.

Nonvolcanic Deep Tremors in the Transform Plate Bounding San Andreas Fault Zone

NASA Astrophysics Data System (ADS)

Nadeau, R. M.; Dolenc, D.

2004-12-01

Recently, deep ( ˜ 20 to 40 km) nonvolcanic tremor activity has been observed on convergent plate boundaries in Japan and in the Cascadia region of North America (Obara, 2002; Rodgers and Dragert, 2003; Szeliga et al., 2004). Because of the abundance of available fluids from subduction processes in these convergent zones, fluids are believed to play an important role in the generation of the tremor activity. The transient rates of tremor activity in these regions are also observed to correlate either with the occurrence of larger earthquakes (Obara, 2002) or with geodetically determined transient creep events that release large amounts of strain energy deep beneath the locked Cascadia megathrust (M.M. Miller et al., 2002; Rodgers and Dragert, 2003; Szeliga et al., 2004). These associations suggest that nonvolcanic tremor activity may participate in a fundamental mode of deep moment release and in the triggering of large subduction zone events (Rodgers and Dragert, 2003). We report the discovery of deep ( ˜ 20 to 45 km) nonvolcanic tremor activity on the transform plate bounding San Andreas Fault (SAF) in central California where, in contrast to subduction zones, long-term deformation directions are horizontal and fluid availability from subduction zone processes is absent. The source region of the SAF tremors lies beneath the epicentral region of the great 1857 magnitude (M) ˜ 8, Fort Tejon earthquake whose rupture zone is currently locked (Sieh, 1978). Activity rate transients of the tremors occurring since early 2001 also correlate with seismicity rate variations above the tremor source region.

Bouguer gravity and crustal structure of the Dead Sea transform fault and adjacent mountain belts in Lebanon

NASA Astrophysics Data System (ADS)

Kamal; Khawlie, Mohamad; Haddad, Fuad; Barazangi, Muawia; Seber, Dogan; Chaimov, Thomas

1993-08-01

The northern extension of the Dead Sea transform fault in southern Lebanon bifurcates into several faults that cross Lebanon from south to north. The main strand, the Yammouneh fault, marks the boundary between the Levantine (eastern Mediterranean) and Arabian plates and separates the western mountain range (Mount Lebanon) from the eastern mountain range (Anti-Lebanon). Bouguer gravity contours in Lebanon approximately follow topographic contours; i.e., positive Bouguer anomalies are associated with the Mount Lebanon and Anti-Lebanon ranges. This suggests that the region is not in simple isostatic compensation. Gravity observations based on 2.5-dimensional modeling and other available geological and geophysical information have produced the following interpretations. (1) The crust of Lebanon thins from ˜35 km beneath the Anti-Lebanon range, near the Syrian border, to ˜27 km beneath the Lebanese coast. No crustal roots exist beneath the Lebanese ranges. (2) The depth to basement is ˜3.5-6 km below sea level under the ranges and is ˜8-10 km beneath the Bekaa depression. (3) The Yammouneh fault bifurcates northward into two branches; one passes beneath the Yammouneh Lake through the eastern part of Mount Lebanon and another bisects the northern part of the Bekaa Valley (i.e., Mid-Bekaa fault). The Lebanese mountain ranges and the Bekaa depression were formed as a result of transtension and later transpression associated with the relative motion of a few crustal blocks in response to the northward movement of the Arabian plate relative to the Levantine plate.

The rigid-plate and shrinking-plate hypotheses: Implications for the azimuths of transform faults

NASA Astrophysics Data System (ADS)

Mishra, Jay Kumar; Gordon, Richard G.

2016-08-01

The rigid-plate hypothesis implies that oceanic lithosphere does not contract horizontally as it cools (hereinafter "rigid plate"). An alternative hypothesis, that vertically averaged tensional thermal stress in the competent lithosphere is fully relieved by horizontal thermal contraction (hereinafter "shrinking plate"), predicts subtly different azimuths for transform faults. The size of the predicted difference is as large as 2.44° with a mean and median of 0.46° and 0.31°, respectively, and changes sign between right-lateral (RL)-slipping and left-lateral (LL)-slipping faults. For the MORVEL transform-fault data set, all six plate pairs with both RL- and LL-slipping faults differ in the predicted sense, with the observed difference averaging 1.4° ± 0.9° (95% confidence limits), which is consistent with the predicted difference of 0.9°. The sum-squared normalized misfit, r, to global transform-fault azimuths is minimized for γ = 0.8 ± 0.4 (95% confidence limits), where γ is the fractional multiple of the predicted difference in azimuth between the shrinking-plate (γ = 1) and rigid-plate (γ = 0) hypotheses. Thus, observed transform azimuths differ significantly between RL-slipping and LL-slipping faults, which is inconsistent with the rigid-plate hypothesis but consistent with the shrinking-plate hypothesis, which indicates horizontal shrinking rates of 2% Ma-1 for newly created lithosphere, 1% Ma-1 for 0.1 Ma old lithosphere, 0.2% Ma-1 for 1 Ma old lithosphere, and 0.02% Ma-1 for 10 Ma old lithosphere, which are orders of magnitude higher than the mean intraplate seismic strain rate of 10-6 Ma-1 (5 × 10-19 s-1).

Tectonic predictions with mantle convection models

NASA Astrophysics Data System (ADS)

Coltice, Nicolas; Shephard, Grace E.

2018-04-01

Over the past 15 yr, numerical models of convection in Earth's mantle have made a leap forward: they can now produce self-consistent plate-like behaviour at the surface together with deep mantle circulation. These digital tools provide a new window into the intimate connections between plate tectonics and mantle dynamics, and can therefore be used for tectonic predictions, in principle. This contribution explores this assumption. First, initial conditions at 30, 20, 10 and 0 Ma are generated by driving a convective flow with imposed plate velocities at the surface. We then compute instantaneous mantle flows in response to the guessed temperature fields without imposing any boundary conditions. Plate boundaries self-consistently emerge at correct locations with respect to reconstructions, except for small plates close to subduction zones. As already observed for other types of instantaneous flow calculations, the structure of the top boundary layer and upper-mantle slab is the dominant character that leads to accurate predictions of surface velocities. Perturbations of the rheological parameters have little impact on the resulting surface velocities. We then compute fully dynamic model evolution from 30 and 10 to 0 Ma, without imposing plate boundaries or plate velocities. Contrary to instantaneous calculations, errors in kinematic predictions are substantial, although the plate layout and kinematics in several areas remain consistent with the expectations for the Earth. For these calculations, varying the rheological parameters makes a difference for plate boundary evolution. Also, identified errors in initial conditions contribute to first-order kinematic errors. This experiment shows that the tectonic predictions of dynamic models over 10 My are highly sensitive to uncertainties of rheological parameters and initial temperature field in comparison to instantaneous flow calculations. Indeed, the initial conditions and the rheological parameters can be good enough for an accurate prediction of instantaneous flow, but not for a prediction after 10 My of evolution. Therefore, inverse methods (sequential or data assimilation methods) using short-term fully dynamic evolution that predict surface kinematics are promising tools for a better understanding of the state of the Earth's mantle.

Kinematics of the New Zealand plate boundary: Relative motion by GPS across networks of 1000 km and 50 km spacing

NASA Technical Reports Server (NTRS)

Meertens, Charles M.; Rocken, Christian; Perin, Barbara; Walcott, Richard

1993-01-01

The NASA/DOSE 'Kinematics of the New Zealand Plate Boundary' experiment is a four-year cooperative Global Positioning System (GPS) experiment involving 6 universities and institutions in New Zealand and the United States. The investigation covers two scales, the first on the scale of plates (approximately 1000 km) and the second is on the scale of the plate boundary zone (approximately 50 km). In the first portion of the experiment, phase A, the objective is to make direct measurements of tectonic plate motion between the Australian and Pacific plates using GPS in order to determine the Euler vector of this plate pair. The phase A portion of this experiment was initiated in December 1992 with the first-epoch baseline measurements on the large scale network. The network will be resurveyed two years later to obtain velocities. The stations which were observed for phase A are shown and listed. Additional regional stations which will be used for this study are listed and are part of either CIGNET or other global tracking networks. The phase A portion of the experiment is primarily the responsibility of the UNAVCO investigators. Therefore, this report concentrates on phase A. The first year of NASA funding for phase A included only support for the field work. Processing and analysis will take place with the second year of funding. The second part of the experiemnt measured relative motion between the Australian and Pacific plates across the pate boundary zone between Hokitika and Christchurch on the South Island of New Zealand. The extent and rate of deformation will be determined by comparisons with historical, conventional surveys and by repeated GPS measurements to be made in two years. This activity was the emphasis of the LDGO portion of the study. An ancillary experiment, phase C, concentrated on plate boundary deformation in the vicinity of Wellington and was done as part of training during the early portion of the field campaign. Details of the objectives of the field investigations are given in the appendix. An overview of the 1992 GPS field program is also given in the appendix.

Plate tectonics of the Mediterranean region.

PubMed

McKenzie, D P

1970-04-18

The seismicity and fault plane solutions in the Mediterranean area show that two small rapidly moving plates exist in the Eastern Mediterranean, and such plates may be a common feature of contracting ocean basins. The results show that the concepts of plate tectonics apply to instantaneous motions across continental plate boundaries.

Studies of acoustic effects on a flow boundary layer in air

NASA Technical Reports Server (NTRS)

Mechel, F.; Schilz, W.

1986-01-01

Effects of sound fields on the flow boundary layer on a flat plate subjected to a parallel flow are studied. The boundary layer is influenced by controlling the stagnation point flow at the front edge of the plate. Depending on the Reynolds number and sound frequency, excitation or suppression of turbulent is observed. Measurements were taken at wind velocities between 10 and 30 m/sec and sound frequencies between 0.2 and 3.0 kHz.

Attractors for non-dissipative irrotational von Karman plates with boundary damping

NASA Astrophysics Data System (ADS)

Bociu, Lorena; Toundykov, Daniel

Long-time behavior of solutions to a von Karman plate equation is considered. The system has an unrestricted first-order perturbation and a nonlinear damping acting through free boundary conditions only. This model differs from those previously considered (e.g. in the extensive treatise (Chueshov and Lasiecka, 2010 [11])) because the semi-flow may be of a non-gradient type: the unique continuation property is not known to hold, and there is no strict Lyapunov function on the natural finite-energy space. Consequently, global bounds on the energy, let alone the existence of an absorbing ball, cannot be a priori inferred. Moreover, the free boundary conditions are not recognized by weak solutions and some helpful estimates available for clamped, hinged or simply-supported plates cannot be invoked. It is shown that this non-monotone flow can converge to a global compact attractor with the help of viscous boundary damping and appropriately structured restoring forces acting only on the boundary or its collar.

Motion of the Scotia sea plates

USGS Publications Warehouse

Thomas, C.; Livermore, R.; Pollitz, F.

2003-01-01

Earthquake data from the Scotia Arc to early 2002 are reviewed in the light of satellite gravity and other data in order to derive a model for the motion of plates in the Scotia Sea region. Events with magnitude ???5, which occurred on or near the boundaries of the Scotia and Sandwich plates, and for which Centroid Moment Tensor (CMT) solutions are available, are examined. The newer data fill some of the previous sampling gaps along the boundaries of the Scotia and Sandwich plates, and provide tighter constraints on relative motions. Variations in the width of the Brunhes anomaly on evenly spaced marine magnetic profiles over the East Scotia Ridge provide new estimates of Scotia-Sandwich plate spreading rates. Since there are no stable fracture zones in the east Scotia Sea, the mean azimuth of sea floor fabric mapped by sidescan is used to constrain the direction of spreading. 18 new rate estimates and four azimuths from the East Scotia Ridge are combined with 68 selected earthquake slip vectors from the boundaries of the Scotia Sea in a least-squares inversion for the best-fitting set of Euler poles and angular rotation rates describing the 'present-day' motions of the Scotia and Sandwich plates relative to South America and Antarctica. Our preferred model (TLP2003) gives poles that are similar to previous estimates, except for Scotia Plate motion with respect to South America, which is significantly different from earlier estimates; predicted rates of motion also differ slightly. Our results are much more robust than earlier work. We examine the implications of the model for motion and deformation along the various plate boundaries, with particular reference to the North and South Scotia Ridges, where rates are obtained by closure.

Completed Beltrami-Michell Formulation for Analyzing Radially Symmetrical Bodies

NASA Technical Reports Server (NTRS)

Kaljevic, Igor; Saigal, Sunil; Hopkins, Dale A.; Patnaik, Surya N.

1994-01-01

A force method formulation, the completed Beltrami-Michell formulation (CBMF), has been developed for analyzing boundary value problems in elastic continua. The CBMF is obtained by augmenting the classical Beltrami-Michell formulation with novel boundary compatibility conditions. It can analyze general elastic continua with stress, displacement, or mixed boundary conditions. The CBMF alleviates the limitations of the classical formulation, which can solve stress boundary value problems only. In this report, the CBMF is specialized for plates and shells. All equations of the CBMF, including the boundary compatibility conditions, are derived from the variational formulation of the integrated force method (IFM). These equations are defined only in terms of stresses. Their solution for kinematically stable elastic continua provides stress fields without any reference to displacements. In addition, a stress function formulation for plates and shells is developed by augmenting the classical Airy's formulation with boundary compatibility conditions expressed in terms of the stress function. The versatility of the CBMF and the augmented stress function formulation is demonstrated through analytical solutions of several mixed boundary value problems. The example problems include a composite circular plate and a composite circular cylindrical shell under the simultaneous actions of mechanical and thermal loads.

Vortex detection through pressure measurements

NASA Astrophysics Data System (ADS)

Bhide, Aditi

Vortex Generators (VGs) are known to hinder boundary layer separation, a frequently unwanted phenomenon when it comes to external flows over aircraft wings, on-ground vehicles or internal flows within pipes, diffusers and turbomachinery. Boundary layer separation leads to loss of lift, higher drag and subsequently, energy losses. The vortices generated inhibit boundary layer separation. This thesis is an effort to discern the strength and location of these generated vortices using an array of VGs over a flat plate. Such information may be useful in the future in active control systems for streamwise vortices, which have been proposed to relaminarize turbulent boundary layers. Flow over flat plates, simulated using wind tunnel experiments, is studied for pressure variation using an array of pressure ports mounted over the plate and connected to suitable pressure sensors. Pressure coefficient and Velocity maps are generated using the data obtained from the Kirsten Wind Tunnel data acquisition system. These represent the nature of the flow field over the plate and are used to locate the vortices and determine their strength. It was found that the vortices can be detected using this method and their strength and location can be estimated.

Effects of variables upon pyrotechnically induced shock response spectra, part 2

NASA Technical Reports Server (NTRS)

Smith, James Lee

1988-01-01

Throughout the aerospace industry, large variations of 50 percent (6 dB) or more in shock response spectra (SRS) derived from pyrotechnic separation events continue to be reported from actual spaceflight data and from laboratory tests. As a result of these variations, NASA funded a research program for 1984 through 1986. The purpose of the 1984 through 1986 project was to analyze variations in pyrotechnically induced SRS and to determine if and to what degree manufacturing and assembly variables and tolerances, distance from the shock source, data acquisition instrumentation, and shock energy propagation affect the SRS. Sixty-four free-free boundary plate tests were performed. NASA funded an additional study for 1987 through 1988. This paper is a summary of the additional study. The purpose was to evaluate shock dissipation through various spacecraft structural joint types, to evaluate shock variation for various manufacturing and assembly variables on clamped boundary test plates, and to verify data correction techniques. Five clamped boundary plate tests investigated manufacturing and assembly variables and mass loading effects. Six free-free boundary plate tests investigated shock dissipation across spacecraft joint structures.

Analysis of a rectangular ceramic plate in electrically forced thickness-twist vibration as a piezoelectric transformer.

PubMed

Yang, Jiashi; Liu, Jinjin; Li, Jiangyu

2007-04-01

A rectangular ceramic plate with appropriate electrical load and operating mode is analyzed for piezoelectric transformer application. An exact solution from the three-dimensional equations of linear piezoelectricity is obtained. The solution simulates the real operating situation of a transformer as a vibrating piezoelectric body connected to a circuit. Transforming ratio, input admittance, and efficiency of the transformer are obtained.

Super-deep low-velocity layer beneath the Arabian plate

NASA Astrophysics Data System (ADS)

Vinnik, L.; Ravi Kumar, M.; Kind, R.; Farra, V.

2003-04-01

S and P receiver functions reveal indications of a low S velocity layer at 350-410 km depths beneath the Arabian plate. A similar layer was previously found beneath the Kaapvaal craton in southern Africa and Tunguska basin of the Siberian platform. We hypothesize, that the boundary at 350 km depth may separate dry mantle root of the Arabian plate from the underlying wet mantle layer. This boundary is not found beneath the Gulf of Aden, where the root is destroyed by sea-floor spreading.

Using the Mesozoic History of the Canadian Cordillera as a Case Study in Teaching Plate Tectonics.

ERIC Educational Resources Information Center

Chamberlain, Valerie Elaine

1989-01-01

Reviews a model used in the teaching of plate tectonics which includes processes and concepts related to: terranes and the amalgamation of terranes, relative plate motion and oblique subduction, the effects of continent-continent collision, changes in plate motion, plate configuration, and the type of plate boundary. Diagrams are included.…

Identifying Fault Connections of the Southern Pacific-North American Plate Boundary Using Triggered Slip and Crustal Velocities

NASA Astrophysics Data System (ADS)

Donnellan, A.; Grant Ludwig, L.; Rundle, J. B.; Parker, J. W.; Granat, R.; Heflin, M. B.; Pierce, M. E.; Wang, J.; Gunson, M.; Lyzenga, G. A.

2017-12-01

The 2010 M7.2 El Mayor - Cucapah earthquake caused extensive triggering of slip on faults proximal to the Salton Trough in southern California. Triggered slip and postseismic motions that have continued for over five years following the earthquake highlight connections between the El Mayor - Cucapah rupture and the network of faults that branch out along the southern Pacific - North American Plate Boundary. Coseismic triggering follows a network of conjugate faults from the northern end of the rupture to the Coachella segment of the southernmost San Andreas fault. Larger aftershocks and postseismic motions favor connections to the San Jacinto and Elsinore faults further west. The 2012 Brawley Swarm can be considered part of the branching on the Imperial Valley or east side of the plate boundary. Cluster analysis of long-term GPS velocities using Lloyds Algorithm, identifies bifurcation of the Pacific - North American plate boundary; The San Jacinto fault joins with the southern San Andreas fault, and the Salton Trough and Coachella segment of the San Andreas fault join with the Eastern California Shear Zone. The clustering analysis does not identify throughgoing deformation connecting the Coachella segment of the San Andreas fault with the rest of the San Andreas fault system through the San Gorgonio Pass. This observation is consistent with triggered slip from both the 1992 Landers and 2010 El Mayor - Cucapah earthquakes that follows the plate boundary bifurcation and with paleoseismic evidence of smaller earthquakes in the San Gorgonio Pass.

Qualitative and semiquantitative Fourier transformation using a noncoherent system.

PubMed

Rogers, G L

1979-09-15

A number of authors have pointed out that a system of zone plates combined with a diffuse source, transparent input, lens, and focusing screen will display on the output screen the Fourier transform of the input. Strictly speaking, the transform normally displayed is the cosine transform, and the bipolar output is superimposed on a dc gray level to give a positive-only intensity variation. By phase-shifting one zone plate the sine transform is obtained. Temporal modulation is possible. It is also possible to redesign the system to accept a diffusely reflecting input at the cost of introducing a phase gradient in the output. Results are given of the sine and cosine transforms of a small circular aperture. As expected, the sine transform is a uniform gray. Both transforms show unwanted artifacts beyond 0.1 rad off-axis. An analysis shows this is due to unwanted circularly symmetrical moire patterns between the zone plates.

Early Permian Pangea `B' to Late Permian Pangea `A'

NASA Astrophysics Data System (ADS)

Muttoni, Giovanni; Kent, Dennis V.; Garzanti, Eduardo; Brack, Peter; Abrahamsen, Niels; Gaetani, Maurizio

2003-10-01

The pre-drift Wegenerian model of Pangea is almost universally accepted, but debate exists on its pre-Jurassic configuration since Ted Irving introduced Pangea 'B' by placing Gondwana farther to the east by ˜3000 km with respect to Laurasia on the basis of paleomagnetic data. New paleomagnetic data from radiometrically dated Early Permian volcanic rocks from parts of Adria that are tectonically coherent with Africa (Gondwana), integrated with published coeval data from Gondwana and Laurasia, again only from igneous rocks, fully support a Pangea 'B' configuration in the Early Permian. The use of paleomagnetic data strictly from igneous rocks excludes artifacts from sedimentary inclination error as a contributing explanation for Pangea 'B'. The ultimate option to reject Pangea 'B' is to abandon the geocentric axial dipole hypothesis by introducing a significant non-dipole (zonal octupole) component in the Late Paleozoic time-averaged geomagnetic field. We demonstrate, however, by using a dataset consisting entirely of paleomagnetic directions with low inclinations from sampling sites confined to one hemisphere from Gondwana as well as Laurasia that the effects of a zonal octupole field contribution would not explain away the paleomagnetic evidence for Pangea 'B' in the Early Permian. We therefore regard the paleomagnetic evidence for an Early Permian Pangea 'B' as robust. The transformation from Pangea 'B' to Pangea 'A' took place during the Permian because Late Permian paleomagnetic data allow a Pangea 'A' configuration. We therefore review geological evidence from the literature in support of an intra-Pangea dextral megashear system. The transformation occurred after the cooling of the Variscan mega-suture and lasted ˜20 Myr. In this interval, the Neotethys Ocean opened between India/Arabia and the Cimmerian microcontinents in the east, while widespread lithospheric wrenching and magmatism took place in the west around the Adriatic promontory. The general distribution of plate boundaries and resulting driving forces are qualitatively consistent with a right-lateral shear couple between Gondwana and Laurasia during the Permian. Transcurrent plate boundaries associated with the Pangea transformation reactivated Variscan shear zones and were subsequently exploited by the opening of western Neotethyan seaways in the Jurassic.

Shock-induced thermal wave propagation and response analysis of a viscoelastic thin plate under transient heating loads

NASA Astrophysics Data System (ADS)

Li, Chenlin; Guo, Huili; Tian, Xiaogeng

2018-04-01

This paper is devoted to the thermal shock analysis for viscoelastic materials under transient heating loads. The governing coupled equations with time-delay parameter and nonlocal scale parameter are derived based on the generalized thermo-viscoelasticity theory. The problem of a thin plate composed of viscoelastic material, subjected to a sudden temperature rise at the boundary plane, is solved by employing Laplace transformation techniques. The transient responses, i.e. temperature, displacement, stresses, heat flux as well as strain, are obtained and discussed. The effects of time-delay and nonlocal scale parameter on the transient responses are analyzed and discussed. It can be observed that: the propagation of thermal wave is dynamically smoothed and changed with the variation of time-delay; while the displacement, strain, and stress can be rapidly reduced by nonlocal scale parameter, which can be viewed as an important indicator for predicting the stiffness softening behavior for viscoelastic materials.

Thermophoresis on boundary layer heat and mass transfer flow of Walters-B fluid past a radiate plate with heat sink/source

NASA Astrophysics Data System (ADS)

Vasu, B.; Gorla, Rama Subba Reddy; Murthy, P. V. S. N.

2017-05-01

The Walters-B liquid model is employed to simulate medical creams and other rheological liquids encountered in biotechnology and chemical engineering. This rheological model introduces supplementary terms into the momentum conservation equation. The combined effects of thermal radiation and heat sink/source on transient free convective, laminar flow and mass transfer in a viscoelastic fluid past a vertical plate are presented by taking thermophoresis effect into account. The transformed conservation equations are solved using a stable, robust finite difference method. A parametric study illustrating the influence of viscoelasticity parameter ( Γ), thermophoretic parameter ( τ), thermal radiation parameter ( F), heat sink/source ( ϕ), Prandtl number ( Pr), Schmidt number ( Sc), thermal Grashof number ( Gr), solutal Grashof number ( Gm), temperature and concentration profiles as well as local skin-friction, Nusselt and Sherwood number is conducted. The results of this parametric study are shown graphically and inform of table. The study has applications in polymer materials processing.

Using Remote Sensing Data to Constrain Models of Fault Interactions and Plate Boundary Deformation

NASA Astrophysics Data System (ADS)

Glasscoe, M. T.; Donnellan, A.; Lyzenga, G. A.; Parker, J. W.; Milliner, C. W. D.

2016-12-01

Determining the distribution of slip and behavior of fault interactions at plate boundaries is a complex problem. Field and remotely sensed data often lack the necessary coverage to fully resolve fault behavior. However, realistic physical models may be used to more accurately characterize the complex behavior of faults constrained with observed data, such as GPS, InSAR, and SfM. These results will improve the utility of using combined models and data to estimate earthquake potential and characterize plate boundary behavior. Plate boundary faults exhibit complex behavior, with partitioned slip and distributed deformation. To investigate what fraction of slip becomes distributed deformation off major faults, we examine a model fault embedded within a damage zone of reduced elastic rigidity that narrows with depth and forward model the slip and resulting surface deformation. The fault segments and slip distributions are modeled using the JPL GeoFEST software. GeoFEST (Geophysical Finite Element Simulation Tool) is a two- and three-dimensional finite element software package for modeling solid stress and strain in geophysical and other continuum domain applications [Lyzenga, et al., 2000; Glasscoe, et al., 2004; Parker, et al., 2008, 2010]. New methods to advance geohazards research using computer simulations and remotely sensed observations for model validation are required to understand fault slip, the complex nature of fault interaction and plate boundary deformation. These models help enhance our understanding of the underlying processes, such as transient deformation and fault creep, and can aid in developing observation strategies for sUAV, airborne, and upcoming satellite missions seeking to determine how faults behave and interact and assess their associated hazard. Models will also help to characterize this behavior, which will enable improvements in hazard estimation. Validating the model results against remotely sensed observations will allow us to better constrain fault zone rheology and physical properties, having implications for the overall understanding of earthquake physics, fault interactions, plate boundary deformation and earthquake hazard, preparedness and risk reduction.

Extending Resolution of Fault Slip With Geodetic Networks Through Optimal Network Design

NASA Astrophysics Data System (ADS)

Sathiakumar, Sharadha; Barbot, Sylvain Denis; Agram, Piyush

2017-12-01

Geodetic networks consisting of high precision and high rate Global Navigation Satellite Systems (GNSS) stations continuously monitor seismically active regions of the world. These networks measure surface displacements and the amount of geodetic strain accumulated in the region and give insight into the seismic potential. SuGar (Sumatra GPS Array) in Sumatra, GEONET (GNSS Earth Observation Network System) in Japan, and PBO (Plate Boundary Observatory) in California are some examples of established networks around the world that are constantly expanding with the addition of new stations to improve the quality of measurements. However, installing new stations to existing networks is tedious and expensive. Therefore, it is important to choose suitable locations for new stations to increase the precision obtained in measuring the geophysical parameters of interest. Here we describe a methodology to design optimal geodetic networks that augment the existing system and use it to investigate seismo-tectonics at convergent and transform boundaries considering land-based and seafloor geodesy. The proposed network design optimization would be pivotal to better understand seismic and tsunami hazards around the world. Land-based and seafloor networks can monitor fault slip around subduction zones with significant resolution, but transform faults are more challenging to monitor due to their near-vertical geometry.

Strengthening and Toughening of a Heavy Plate Steel for Shipbuilding with Yield Strength of Approximately 690 MPa

NASA Astrophysics Data System (ADS)

Liu, Dongsheng; Cheng, Binggui; Chen, Yuanyuan

2013-01-01

HSLA-100 steel with high content of alloying elements (nominally in wt pct, 3.5 Ni, 1.6 Cu, and 0.6Mo) is now used to produce heavy plates for constructing a hull and drilling platform. We proposed here a substantially leaner steel composition (containing 1.7 Ni, 1.1 Cu, and 0.5Mo) to produce a heavy plate to 80 mm thickness with mechanical properties comparable with those of the HSLA-100 grade. A continuous cooling transformation (CCT) diagram of the steel was constructed. Key parameters of thermal treatment and revealing mechanisms of strengthening and toughening were derived based on industrial production trials. The microstructures of the 80-mm-thick plate were lath-like bainite (LB) at near surface of the quarter thickness ( t/4), and granular bainite (GB)+LB at center thickness ( t/2) after solutionizing and water quenching (Q). The effect of tempering (T) on the microstructures and properties of the plate was investigated. Excellent combination of room temperature strength and low-temperature Charpy V-notch (CVN) toughness approximately equivalent to that of the HSLA 100 grade (YS > 690 MPa, CVN energy >100 J even at 193 K [-80 °C]) was achieved in the plate treated by the QT process with tempering temperature of 898 K (625 °C). The combination of strength and toughness at t/4 is superior to that at t/2 of the plate under both as-quenched and QT conditions. This result is attributed to that the fraction of high-angle grain boundaries (HAGBs) at t/4 is higher than that at t/2.

Stress rotation across the Cascadia megathrust requires a weak subduction plate boundary at seismogenic depths

NASA Astrophysics Data System (ADS)

Li, Duo; McGuire, Jeffrey J.; Liu, Yajing; Hardebeck, Jeanne L.

2018-03-01

The Mendocino Triple Junction region is the most seismically active part of the Cascadia Subduction Zone. The northward moving Pacific plate collides with the subducting Gorda plate causing intense internal deformation within it. Here we show that the stress field rotates rapidly with depth across the thrust interface from a strike-slip regime within the subducting plate, reflecting the Pacific plate collision, to a thrust regime in the overriding plate. We utilize a dense focal mechanism dataset, including observations from the Cascadia Initiative ocean bottom seismograph experiment, to constrain the stress orientations. To quantify the implications of this rotation for the strength of the plate boundary, we designed an inversion that solves for the absolute stress tensors in a three-layer model subject to assumptions about the strength of the subducting mantle. Our results indicate that the shear stress on the plate boundary fault is likely no more than about ∼50 MPa at ∼20 km depth. Regardless of the assumed mantle strength, we infer a relatively weak megathrust fault with an effective friction coefficient of ∼0 to 0.2 at seismogenic depths. Such a low value for the effective friction coefficient requires a combination of high fluid pressures and/or fault-zone minerals with low inherent friction in the region where a great earthquake is expected in Cascadia.

Stress rotation across the Cascadia megathrust requires a weak subduction plate boundary at seismogenic depths

USGS Publications Warehouse

Li, Duo; McGuire, Jeffrey J.; Liu, Yajing; Hardebeck, Jeanne L.

2018-01-01

The Mendocino Triple Junction region is the most seismically active part of the Cascadia Subduction Zone. The northward moving Pacific plate collides with the subducting Gorda plate causing intense internal deformation within it. Here we show that the stress field rotates rapidly with depth across the thrust interface from a strike-slip regime within the subducting plate, reflecting the Pacific plate collision, to a thrust regime in the overriding plate. We utilize a dense focal mechanism dataset, including observations from the Cascadia Initiative ocean bottom seismograph experiment, to constrain the stress orientations. To quantify the implications of this rotation for the strength of the plate boundary, we designed an inversion that solves for the absolute stress tensors in a three-layer model subject to assumptions about the strength of the subducting mantle. Our results indicate that the shear stress on the plate boundary fault is likely no more than about ∼50 MPa at ∼20 km depth. Regardless of the assumed mantle strength, we infer a relatively weak megathrust fault with an effective friction coefficient of ∼0 to 0.2 at seismogenic depths. Such a low value for the effective friction coefficient requires a combination of high fluid pressures and/or fault-zone minerals with low inherent friction in the region where a great earthquake is expected in Cascadia.

Dislocation models of interseismic deformation in the western United States

USGS Publications Warehouse

Pollitz, F.F.; McCrory, P.; Svarc, J.; Murray, J.

2008-01-01

The GPS-derived crustal velocity field of the western United States is used to construct dislocation models in a viscoelastic medium of interseismic crustal deformation. The interseismic velocity field is constrained by 1052 GPS velocity vectors spanning the ???2500-km-long plate boundary zone adjacent to the San Andreas fault and Cascadia subduction zone and extending ???1000 km into the plate interior. The GPS data set is compiled from U.S. Geological Survey campaign data, Plate Boundary Observatory data, and the Western U.S. Cordillera velocity field of Bennett et al. (1999). In the context of viscoelastic cycle models of postearthquake deformation, the interseismic velocity field is modeled with a combination of earthquake sources on ???100 known faults plus broadly distributed sources. Models that best explain the observed interseismic velocity field include the contributions of viscoelastic relaxation from faulting near the major plate margins, viscoelastic relaxation from distributed faulting in the plate interior, as well as lateral variations in depth-averaged rigidity in the elastic lithosphere. Resulting rigidity variations are consistent with reduced effective elastic plate thickness in a zone a few tens of kilometers wide surrounding the San Andreas fault (SAF) system. Primary deformation characteristics are captured along the entire SAF system, Eastern California Shear Zone, Walker Lane, the Mendocino triple junction, the Cascadia margin, and the plate interior up to ???1000 km from the major plate boundaries.

Study of the Effect of Free-Stream Turbulence upon Disturbances in the Pre-Transitional Laminar Boundary Layer. Part I. Laminar Boundary Layer Distortion by Surface Roughness; Effect upon Stability. Part II.

DTIC Science & Technology

1982-04-01

Boundary Layer Near a Plate." NACA Rept. 562, 1936. 5) A. A. Hall and G. S. Hislop , "Experiments on the Transition of the Laminar Boundary Layer on a...Cylinder." Proc. 5th Inter. Congr. Appl. Math, 1938. 7) G. S. Hislop , "The Transition of a Laminar Boundary Layer in a Wind Tunnel." Ph.D. Thesis...Small Vertical Cylinder Attached to a Flat Plate", h Fa- Elul"s, Vol. 23, Part 1, pp. 221-223, Jan. 1980 . 9. A. Von Doenhoff and E. A. Horton, "A Low

Plate tectonics, damage and inheritance.

PubMed

Bercovici, David; Ricard, Yanick

2014-04-24

The initiation of plate tectonics on Earth is a critical event in our planet's history. The time lag between the first proto-subduction (about 4 billion years ago) and global tectonics (approximately 3 billion years ago) suggests that plates and plate boundaries became widespread over a period of 1 billion years. The reason for this time lag is unknown but fundamental to understanding the origin of plate tectonics. Here we suggest that when sufficient lithospheric damage (which promotes shear localization and long-lived weak zones) combines with transient mantle flow and migrating proto-subduction, it leads to the accumulation of weak plate boundaries and eventually to fully formed tectonic plates driven by subduction alone. We simulate this process using a grain evolution and damage mechanism with a composite rheology (which is compatible with field and laboratory observations of polycrystalline rocks), coupled to an idealized model of pressure-driven lithospheric flow in which a low-pressure zone is equivalent to the suction of convective downwellings. In the simplest case, for Earth-like conditions, a few successive rotations of the driving pressure field yield relic damaged weak zones that are inherited by the lithospheric flow to form a nearly perfect plate, with passive spreading and strike-slip margins that persist and localize further, even though flow is driven only by subduction. But for hotter surface conditions, such as those on Venus, accumulation and inheritance of damage is negligible; hence only subduction zones survive and plate tectonics does not spread, which corresponds to observations. After plates have developed, continued changes in driving forces, combined with inherited damage and weak zones, promote increased tectonic complexity, such as oblique subduction, strike-slip boundaries that are subparallel to plate motion, and spalling of minor plates.

SeaMARC II mapping of transform faults in the Cayman Trough, Caribbean Sea

USGS Publications Warehouse

Rosencrantz, Eric; Mann, Paul

1992-01-01

SeaMARC II maps of the southern wall of the Cayman Trough between Honduras and Jamaica show zones of continuous, well-defined fault lineaments adjacent and parallel to the wall, both to the east and west of the Cayman spreading axis. These lineaments mark the present, active traces of transform faults which intersect the southern end of the spreading axis at a triple junction. The Swan Islands transform fault to the west is dominated by two major lineaments that overlap with right-stepping sense across a large push-up ridge beneath the Swan Islands. The fault zone to the east of the axis, named the Walton fault, is more complex, containing multiple fault strands and a large pull-apart structure. The Walton fault links the spreading axis to Jamaican and Hispaniolan strike-slip faults, and it defines the southern boundary of a microplate composed of the eastern Cayman Trough and western Hispaniola. The presence of this microplate raises questions about the veracity of Caribbean plate velocities based primarily on Cayman Trough opening rates.

Strain release along ocean transform faults

NASA Astrophysics Data System (ADS)

Stewart, L. M.

A global study of the nature of seismic rupture along oceanic transform faults (TFs) is presented, and many aspects of fault behavior and Mid-Ocean Ridge processes are discussed. A classification of TF earthquakes is developed based on their relative excitation of short period body waves to long period surface waves. Since the ways in which transform faults release their accumulated strain varies, for more than 50 earthquakes occurring on 30 TFs since 1963 form the database for a comparison of rupture processes. The variation of TF rupture processes is not related to spreading rate or TF offset. A study of seismicity of the Eltanin Fracture Zone system shows that unlike many TFs, the Eltanin FZ realizes more than 90% of its slip aseismically. This identifies a major portion of plate boundary whose motion persists undetected by seismic instruments. The global variations in rupture patterns are discussed in terms of current models of fault behavior. The versatility of the asperity model accommodates the entire range of observed patterns. Variations in physical properties within TF contact zones (asperities) are documented in the petrology and geochemistry of rocks from ophiolite sections and TFs.

Tsunamis and splay fault dynamics

USGS Publications Warehouse

Wendt, J.; Oglesby, D.D.; Geist, E.L.

2009-01-01

The geometry of a fault system can have significant effects on tsunami generation, but most tsunami models to date have not investigated the dynamic processes that determine which path rupture will take in a complex fault system. To gain insight into this problem, we use the 3D finite element method to model the dynamics of a plate boundary/splay fault system. We use the resulting ground deformation as a time-dependent boundary condition for a 2D shallow-water hydrodynamic tsunami calculation. We find that if me stress distribution is homogeneous, rupture remains on the plate boundary thrust. When a barrier is introduced along the strike of the plate boundary thrust, rupture propagates to the splay faults, and produces a significantly larger tsunami man in the homogeneous case. The results have implications for the dynamics of megathrust earthquakes, and also suggest mat dynamic earthquake modeling may be a useful tool in tsunami researcn. Copyright 2009 by the American Geophysical Union.

An integral wall model for Large Eddy Simulation (iWMLES) and applications to developing boundary layers over smooth and rough plates

NASA Astrophysics Data System (ADS)

Yang, Xiang; Sadique, Jasim; Mittal, Rajat; Meneveau, Charles

2014-11-01

A new wall model for Large-Eddy-Simulations is proposed. It is based on an integral boundary layer method that assumes a functional form for the local mean velocity profile. The method, iWMLES, evaluates required unsteady and advective terms in the vertically integrated boundary layer equations analytically. The assumed profile contains a viscous or roughness sublayer, and a logarithmic layer with an additional linear term accounting for inertial and pressure gradient effects. The iWMLES method is tested in the context of a finite difference LES code. Test cases include developing turbulent boundary layers on a smooth flat plate at various Reynolds numbers, over flat plates with unresolved roughness, and a sample application to boundary layer flow over a plate that includes resolved roughness elements. The elements are truncated cones acting as idealized barnacle-like roughness elements that often occur in biofouling of marine surfaces. Comparisons with data show that iWMLES provides accurate predictions of near-wall velocity profiles in LES while, similarly to equilibrium wall models, its cost remains independent of Reynolds number and is thus significantly lower compared to standard zonal or hybrid wall models. This work is funded by ONR Grant N00014-12-1-0582 (Dr. R. Joslin, program manager).

In-Flight Boundary-Layer Transition of a Large Flat Plate at Supersonic Speeds

NASA Technical Reports Server (NTRS)

Banks, D. W.; Frederick, M. A.; Tracy, R. R.; Matisheck, J. R.; Vanecek, N. D.

2012-01-01

A flight experiment was conducted to investigate the pressure distribution, local-flow conditions, and boundary-layer transition characteristics on a large flat plate in flight at supersonic speeds up to Mach 2.00. The tests used a NASA testbed aircraft with a bottom centerline mounted test fixture. The primary objective of the test was to characterize the local flow field in preparation for future tests of a high Reynolds number natural laminar flow test article. A second objective was to determine the boundary-layer transition characteristics on the flat plate and the effectiveness of using a simplified surface coating. Boundary-layer transition was captured in both analog and digital formats using an onboard infrared imaging system. Surface pressures were measured on the surface of the flat plate. Flow field measurements near the leading edge of the test fixture revealed the local flow characteristics including downwash, sidewash, and local Mach number. Results also indicated that the simplified surface coating did not provide sufficient insulation from the metallic structure, which likely had a substantial effect on boundary-layer transition compared with that of an adiabatic surface. Cold wall conditions were predominant during the acceleration to maximum Mach number, and warm wall conditions were evident during the subsequent deceleration.

Receptivity of Flat-Plate Boundary Layer in a Non-Uniform Free Stream (Vorticity Normal to the Plate)

NASA Technical Reports Server (NTRS)

Kogan, M. N.; Ustinov, M. V.

1997-01-01

Work is devoted to study of free-stream vorticity normal to leading edge interaction with boundary layer over plate and resulting flow distortion influence on laminar-turbulent transition. In experiments made the wake behind the vertically stretched wire was used as a source of vortical disturbances and its effect on the boundary layer over the horizontally mounted plate with various leading edge shapes was investigated. The purpose of experiments was to check the predictions of theoretical works of M.E. Goldstein, et. al. This theory shows that small free-stream inhomogeneity interacting with leading edge produces considerable distortion of boundary layer flow. In general, results obtained confirms predictions of Goldstein's theory, i.e., the amplification of steady vortical disturbances in boundary layer caused by vortex lines stretching was observed. Experimental results fully coincide with predictions of theory for large Reynolds number, relatively sharp leading edge and small disturbances. For large enough disturbances the flow distortion caused by symmetric wake unexpectedly becomes antisymmetric in spanwise direction. If the leading edge is too blunt the maximal distortion takes place immediately at the nose and no further amplification was observed. All these conditions and results are beyond the scope of Goldstein's theory.

Analogies between Kirchhoff plates and functionally graded Saint-Venant beams under torsion

NASA Astrophysics Data System (ADS)

Barretta, Raffaele; Luciano, Raimondo

2015-05-01

Exact solutions of elastic Kirchhoff plates are available only for special geometries, loadings and kinematic boundary constraints. An effective solution procedure, based on an analogy between functionally graded orthotropic Saint-Venant beams under torsion and inhomogeneous isotropic Kirchhoff plates, with no kinematic boundary constraints, is proposed. The result extends the one contributed in Barretta (Acta Mech 224(12):2955-2964, 2013) for the special case of homogeneous Saint-Venant beams under torsion. Closed-form solutions for displacement, bending-twisting moment and curvature fields of an elliptic plate, corresponding to a functionally graded orthotropic beam, are evaluated. A new benchmark for computational mechanics is thus provided.

Elastic stability of laminated, flat and curved, long rectangular plates subjected to combined inplane loads

NASA Technical Reports Server (NTRS)

Viswanathan, A. V.; Tamekuni, M.; Baker, L. L.

1974-01-01

A method is presented to predict theoretical buckling loads of long, rectangular flat and curved laminated plates with arbitrary orientation of orthotropic axes each lamina. The plate is subjected to combined inplane normal and shear loads. Arbitrary boundary conditions may be stipulated along the longitudinal sides of the plate. In the absence of inplane shear loads and extensional-shear coupling, the analysis is also applicable to finite length plates. Numerical results are presented for curved laminated composite plates with boundary conditions and subjected to various loadings. These results indicate some of the complexities involved in the numerical solution of the analysis for general laminates. The results also show that the reduced bending stiffness approximation when applied to buckling problems could lead to considerable error in some cases and therefore must be used with caution.

Shed Vortex Structure and Phase-Averaged Velocity Statistics in Symmetric/Asymmetric Turbulent Flat Plate Wakes

NASA Technical Reports Server (NTRS)

Rai, Man Mohan

2017-01-01

The near wake of a flat plate is investigated via direct numerical simulations (DNS). Many earlier experimental investigations have used thin plates with sharp trailing edges and turbulent boundary layers to create the wake. This results in large theta divided by D (sub TE) values (theta is the boundary layer momentum thickness towards the end of the plate and D (sub TE) is the trailing edge thickness). In the present study the emphasis is on relatively thick plates with circular trailing edges (CTE) resulting in theta divided by D values less than one (D is the plate thickness and the diameter of the CTE), and vigorous vortex shedding. The Reynolds numbers based on the plate length and D are 1.255 x 10 (sup 6) and 10,000, respectively. Two cases are computed; one with turbulent boundary layers on both the upper and lower surfaces of the plate (statistically the same, symmetric wake, Case TT) and, a second with turbulent and laminar boundary layers on the upper and lower surfaces, respectively (asymmetric case, Case TL). The data and understanding obtained is of considerable engineering interest, particularly in turbomachinery where the pressure side of an airfoil can remain laminar or transitional because of a favorable pressure gradient and the suction side is turbulent. Shed-vortex structure and phase-averaged velocity statistics obtained in the two cases are compared here. The upper negative shed vortices in Case TL (turbulent separating boundary layer) are weaker than the lower positive ones (laminar separating boundary layer) at inception (a factor 1.27 weaker in terms of peak phase-averaged spanwise vorticity at first appearance of a peak). The upper vortices weaken rapidly as they travel downstream. A second feature of interest in Case TL is a considerable increase in the peak phase-averaged, streamwise normal intensity (random component) with increasing streamwise distance (x divided by D) that occurs nears the positive vortex cores. This behavior is observed for a few diameters in the near wake. This is counter to Case TT where the peak value essentially decreases with increasing x divided by D. Both these effects are examined in detail and the important contributors are identified.

Vortex Shedding Characteristics of the Wake of a Thin Flat Plate with a Circular Trailing Edge

NASA Technical Reports Server (NTRS)

Rai, Man Mohan

2018-01-01

The near and very near wake of a thin flat plate with a circular trailing edge are investigated with direct numerical simulations (DNS). Data obtained for two different Reynolds numbers (based on plate thickness, D) are the main focus of this study. The separating boundary layers are turbulent in both cases. An earlier investigation of one of the cases (Case F) showed shed vortices in the wake that were about 1.0 D to 4.0 D in spanwise length. Considerable variation in both the strength and frequency of these shed vortices was observed. One objective of the present investigation is to determine the important contributors to this variability in strength and frequency of shed vortices and their finite spanwise extent. Analysis of the data shows that streamwise vortices in the separating boundary layer play an important role in strengthening/weakening of the shed vortices and that high/low-speed streaks in the boundary layer are important contributors to variability in shedding frequency. Both these features of the boundary layer contribute to the finite extent of the vortices in the spanwise direction. The second plate DNS (Case G, with 40 percent of the plate thickness of Case F) shows that while shedding intensity is weaker than obtained in Case F, many of the wake features are similar to that of Case F. This is important in understanding the path to the wake of the thin plate with a sharp trailing edge where shedding is absent. Here we also test the efficacy of a functional relationship between the shedding frequency and the Reynolds numbers based on the boundary layer momentum thickness (Re (sub theta) and D (Re (sub D)); data for developing this behavioral model is from Cases F & G and five earlier DNSs of the flat plate wake.

Repeating Earthquakes on the Queen Charlotte Plate Boundary

NASA Astrophysics Data System (ADS)

Hayward, T. W.; Bostock, M. G.

2015-12-01

The Queen Charlotte Fault (QCF) is a major plate boundary located off the northwest coast of North America that has produced large earthquakes in 1949 (M8.1) and more recently in October, 2012 (M7.8). The 2012 event was dominated by thrusting despite the fact that plate motions at the boundary are nearly transcurrent. It is now widely believed that the plate boundary comprises the QCF (i.e., a dextral strike-slip fault) as well as an element of subduction of the Pacific Plate beneath the North American Plate. Repeating earthquakes and seismic tremor have been observed in the vicinity of the QCF; providing insight into the spatial and temporal characteristics of repeating earthquakes is the goal of this research. Due to poor station coverage and data quality, traditional methods of locating earthquakes are not applicable to these events. Instead, we have implemented an algorithm to locate local (i.e., < 100 km distance to epicenter) earthquakes using a single, three-component seismogram. This algorithm relies on the P-wave polarization and, through comparison with larger local events in the Geological Survey of Canada catalogue, is shown to yield epicentral locations accurate to within 5-10 km. A total of 24 unique families of repeating earthquakes has been identified, and 4 of these families have been located with high confidence. Their epicenters locate directly on the trace of the QCF and their depths are shallow (i.e., 5-15 km), consistent with the proposed depth of the QCF. Analysis of temporal recurrence leading up to the 2012 M7.8 event reveals a non-random pattern, with an approximately 15 day periodicity. Further analysis is planned to study whether this behaviour persists after the 2012 event and to gain insight into the effects of the 2012 event on the stress field and frictional properties of the plate boundary.

Shear wave velocity structure in the lithosphere and asthenosphere across the Southern California continent and Pacific plate margin using inversion of Rayleigh wave data from the ALBACORE project.

NASA Astrophysics Data System (ADS)

Price, A. C.; Weeraratne, D. S.; Kohler, M. D.; Rathnayaka, S.; Escobar, L., Sr.

2015-12-01

The North American and Pacific plate boundary is a unique example of past subduction of an oceanic spreading center which has involved oceanic plate capture and inception of a continental transform boundary that juxtaposes continental and oceanic lithosphere on a single plate. The amphibious ALBACORE seismic project (Asthenospheric and Lithospheric Broadband Architecture from the California Offshore Region Experiment) deployed 34 ocean bottom seismometers (OBS) on 15-35 Ma seafloor and offers a unique opportunity to compare the LAB in continental and oceanic lithosphere in one seismic study. Rayleigh waves were recorded simultaneously by our offshore array and 82 CISN network land stations from 2010-2011. Here we predict phase velocities for a starting shear wave velocity model for each of 5 regions in our study area and compare to observed phase velocities from our array in a least-squares sense that produces the best fit 1-D shear wave velocity structure for each region. Preliminary results for the deep ocean (seafloor 25-32 Ma) indicates high velocities reaching 4.5 km/s at depths of 50 km associated with the lithosphere for seafloor 25-32 Ma. A negative velocity gradient is observed below this which reaches a minimum of 4.0 km/s at 160 km depth. The mid-ocean region (age 13-25 Ma) indicates a slightly lower magnitude and shallower LVZ. The Inner Borderland displays the highest lithospheric velocities offshore reaching 4.8 km/s at 40 km depth indicating underplating. The base of the LVZ in the Borderland increases sharply from 4.0 km/s to 4.5 km/s at 80-150 km depth indicating partial melt and compositional changes. The LVZ displays a very gradual positive velocity gradient in all other regions such as the deep seafloor and continent reaching 4.5 km/s at 300 km depth. The deep ocean, Borderlands, and continental region each have unique lithospheric velocities, LAB depths, and LVZ character that indicate stark differences in mantle structure that occur on a single plate as well as across the continental margin.

Modeling of Structural-Acoustic Interaction Using Coupled FE/BE Method and Control of Interior Acoustic Pressure Using Piezoelectric Actuators

NASA Technical Reports Server (NTRS)

Mei, Chuh; Shi, Yacheng

1997-01-01

A coupled finite element (FE) and boundary element (BE) approach is presented to model full coupled structural/acoustic/piezoelectric systems. The dual reciprocity boundary element method is used so that the natural frequencies and mode shapes of the coupled system can be obtained, and to extend this approach to time dependent problems. The boundary element method is applied to interior acoustic domains, and the results are very accurate when compared with limited exact solutions. Structural-acoustic problems are then analyzed with the coupled finite element/boundary element method, where the finite element method models the structural domain and the boundary element method models the acoustic domain. Results for a system consisting of an isotropic panel and a cubic cavity are in good agreement with exact solutions and experiment data. The response of a composite panel backed cavity is then obtained. The results show that the mass and stiffness of piezoelectric layers have to be considered. The coupled finite element and boundary element equations are transformed into modal coordinates, which is more convenient for transient excitation. Several transient problems are solved based on this formulation. Two control designs, a linear quadratic regulator (LQR) and a feedforward controller, are applied to reduce the acoustic pressure inside the cavity based on the equations in modal coordinates. The results indicate that both controllers can reduce the interior acoustic pressure and the plate deflection.

Numerical Study of Effects of Fluid-Structure Interaction on Dynamic Responses of Composite Plates

DTIC Science & Technology

2009-09-01

FORCE LOAD AND CLAMPED BOUNDARY.................73 APPENDIX F: ADDITIONAL FIGURES FOR COMPOSITE DE NSITY EFFECTS WITH CONCE NTRATED FORCE LOAD AND...Structure Strain and Kine tic Energy Comparison for Elastic Modulus Variations with Concentrated Force and Clamped Boundary .........................31...48 Figure 49. Experiment Strain Gage La yout on Underside of Composite Plate

The seismotectonics of plate boundaries

NASA Technical Reports Server (NTRS)

Berger, J.; Brune, J. N.; Goodkind, J.; Wyatt, F.; Agnew, D. C.; Beaumont, C.

1981-01-01

Research on the seismotectonics of plate boundaries is summarized. Instrumental development and an observational program designed to study various aspects of the seismotectonics of southern California and the northern Gulf of California are described. A unique superconducting gravimeter was further developed and supported under this program for deployment and operation at several sites. Work on Earth tides is also discussed.

Near Continuum Velocity and Temperature Coupled Compressible Boundary Layer Flow over a Flat Plate

NASA Astrophysics Data System (ADS)

He, Xin; Cai, Chunpei

2017-04-01

The problem of a compressible gas flows over a flat plate with the velocity-slip and temperature-jump boundary conditions are being studied. The standard single- shooting method is applied to obtain the exact solutions for velocity and temperature profiles when the momentum and energy equations are weakly coupled. A double-shooting method is applied if these two equations are closely coupled. If the temperature affects the velocity directly, more significant velocity slip happens at locations closer to the plate's leading edge, and inflections on the velocity profiles appear, indicating flows may become unstable. As a consequence, the temperature-jump and velocity-slip boundary conditions may trigger earlier flow transitions from a laminar to a turbulent flow state.

Experimental Results from a Flat Plate, Turbulent Boundary Layer Modified for the Purpose of Drag Reduction

NASA Astrophysics Data System (ADS)

Elbing, Brian R.

2006-11-01

Recent experiments on a flat plate, turbulent boundary layer at high Reynolds numbers (>10^7) were performed to investigate various methods of reducing skin friction drag. The methods used involved injecting either air or a polymer solution into the boundary layer through a slot injector. Two slot injectors were mounted on the model with one located 1.4 meters downstream of the nose and the second located 3.75 meters downstream. This allowed for some synergetic experiments to be performed by varying the injections from each slot and comparing the skin friction along the plate. Skin friction measurements were made with 6 shear stress sensors flush mounted along the stream-wise direction of the model.

A seismic gap along an accreting plate boundary : Example of the Djibouti Ridge, Afar, East Africa

NASA Astrophysics Data System (ADS)

Ruegg, Jean-Claude; Lépine, Jean-Claude

1983-05-01

A segment of the Gulf of Tadjoura (Djibouti, East-Africa) accreting plate boundary, shows a period of quiescence in the seismic activity since 1974. This segment corresponds to the extension area of the aftershock activity that has occured after a cluster of magnitude 5.5 earthquakes in April 1973. From this example we propose that the seismic gap concept can be extended to moderate earthquakes occuring at extensional plate boundaries. The magnitude of the largest earthquakes at the spreading axis is limited by the size of the rupture length and by the strength of the brittle lithosphere. In the case of the Djibouti ridge recurrence time of 10-20 years are found for earthquakes of about M =6.

Stress wave calculations in composite plates using the fast Fourier transform.

NASA Technical Reports Server (NTRS)

Moon, F. C.

1973-01-01

The protection of composite turbine fan blades against impact forces has prompted the study of dynamic stresses in composites due to transient loads. The mathematical model treats the laminated plate as an equivalent anisotropic material. The use of Mindlin's approximate theory of crystal plates results in five two-dimensional stress waves. Three of the waves are flexural and two involve in-plane extensional strains. The initial value problem due to a transient distributed transverse force on the plate is solved using Laplace and Fourier transforms. A fast computer program for inverting the two-dimensional Fourier transform is used. Stress contours for various stresses and times after application of load are obtained for a graphite fiber-epoxy matrix composite plate. Results indicate that the points of maximum stress travel along the fiber directions.

Tertiary plate tectonics and high-pressure metamorphism in New Caledonia

USGS Publications Warehouse

Brothers, R.N.; Blake, M.C.

1973-01-01

The sialic basement of New Caledonia is a Permian-Jurassic greywacke sequence which was folded and metamorphosed to prehnite-pumpellyite or low-grade greenschist facies by the Late Jurassic. Succeeding Cretaceous-Eocene sediments unconformably overlie this basement and extend outwards onto oceanic crust. Tertiary tectonism occurred in three distinct phases. 1. (1) During the Late Eocene a nappe of peridotite was obducted onto southern New Caledonia from northeast to southwest, but without causing significant metamorphism in the underlying sialic rocks. 2. (2) Oligocene compressive thrust tectonics in the northern part of the island accompanied a major east-west subduction zone, at least 30 km wide, which is identified by an imbricate system of tectonically intruded melanges and by development of lawsonite-bearing assemblages in adjacent country rocks; this high-pressure mineralogy constituted a primary metamorphism for the Cretaceous-Eocene sedimentary pile, but was overprinted on the Mesozoic prehnite-pumpellyite metagreywackes. 3. (3) Post-Oligocene transcurrent faulting along a northwest-southeast line (the sillon) parallel to the west coast caused at least 150 km of dextral offset of the southwest frontal margin of the Eocene ultramafic nappe. At the present time, the tectonics of the southwest Pacific are related to a series of opposite facing subduction (Benioff) zones connected by transform faults extending from New Britain-Solomon Islands south through the New Hebrides to New Zealand and marking the boundary between the Australian and Pacific plates. Available geologic data from this region suggest that a similar geometry existed during the Tertiary and that the microcontinents of New Guinea, New Caledonia and New Zealand all lay along the former plate boundary which has since migrated north and east by a complex process of sea-floor spreading behind the active island arcs. ?? 1973.

On the determination of stress fields and displacements in a thin elastoplastic plate containing elastic inclusion - a shim

NASA Astrophysics Data System (ADS)

Kovalev, A. V.; Rusina, E. Y.; Yakovlev, A. Y.

2018-03-01

The paper is devoted to the determination of the stress-strain state of a mechanical structure, which consists of a thin infinite elastoplastic plate with a hole and a continuous fine elastic inclusion. The complexity of this problem lies in the fact that the shape of the boundary between the elastic and plastic zones in the plate is not known in advance. The small parameter method is used as the solution method, while the small parameter characterizes the deviation of the shape of the contour from the circle and the perturbation of external static boundary conditions. As the zero solution, the axisymmetric elastoplastic state of the plate with inclusion is chosen. Two variants of inclusion fixation in a plate are considered: inclusion is enclosed with tension or soldered. As a result of solving the problem within the framework of ideal plasticity, the distribution of the stress and displacement fields and the shape of the elastoplastic boundary are obtained. To illustrate the case of a plane-stressed state, the results of a numerical experiment on the mathematical model obtained are presented.

GPS and seismological constraints on active tectonics and arc-continent collision in Papua New Guinea: Implications for mechanics of microplate rotations in a plate boundary zone

NASA Astrophysics Data System (ADS)

Wallace, Laura M.; Stevens, Colleen; Silver, Eli; McCaffrey, Rob; Loratung, Wesley; Hasiata, Suvenia; Stanaway, Richard; Curley, Robert; Rosa, Robert; Taugaloidi, Jones

2004-05-01

The island of New Guinea is located within the deforming zone between the Pacific and Australian plates that converge obliquely at ˜110 mm/yr. New Guinea has been fragmented into a complex array of microplates, some of which rotate rapidly about nearby vertical axes. We present velocities from a network of 38 Global Positioning System (GPS) sites spanning much of the nation of Papua New Guinea (PNG). The GPS-derived velocities are used to explain the kinematics of major tectonic blocks in the region and the nature of strain accumulation on major faults in PNG. We simultaneously invert GPS velocities, earthquake slip vectors on faults, and transform orientations in the Woodlark Basin for the poles of rotation of the tectonic blocks and the degree of elastic strain accumulation on faults in the region. The data are best explained by six distinct tectonic blocks: the Australian, Pacific, South Bismarck, North Bismarck, and Woodlark plates and a previously unrecognized New Guinea Highlands Block. Significant portions of the Ramu-Markham Fault appear to be locked, which has implications for seismic hazard determination in the Markham Valley region. We also propose that rapid clockwise rotation of the South Bismarck plate is controlled by edge forces initiated by the collision between the Finisterre arc and the New Guinea Highlands.

High-Resolution P'P' Precursor Imaging of Nazca-South America Plate Boundary Zones and Inferences for Transition Zone Temperature and Composition

NASA Astrophysics Data System (ADS)

Gu, Y. J.; Schultz, R.

2013-12-01

Knowledge of upper mantle transition zone stratification and composition is highly dependent on our ability to efficiently extract and properly interpret small seismic arrivals. A promising high-frequency seismic phase group particularly suitable for a global analysis is P'P' precursors, which are capable of resolving mantle structures at vertical and lateral resolution of approximately 5 and 200 km, respectively, owing to their shallow incidence angle and small, quasi-symmetric Fresnel zones. This study presents a simultaneous analysis of SS and P'P' precursors based on deconvolution, Radon transform and depth migration. Our multi-resolution survey of the mantle near Nazca-South America subduction zone reveals both olivine and garnet related transitions at depth below 400 km. We attribute a depressed 660 to thermal variations, whereas compositional variations atop the upper-mantle transition zone are needed to explain the diminished or highly complex reflected/scattered signals from the 410 km discontinuity. We also observe prominent P'P' reflections within the transition zone, especially near the plate boundary zone where anomalously high reflection amplitudes result from a sharp (~10 km thick) mineral phase change resonant with the dominant frequency of the P'P' precursors. Near the base of the upper mantle, the migration of SS precursors shows no evidence of split reflections near the 660-km discontinuity, but potential majorite-ilmenite (590-640 km) and ilmenite-perovskite transitions (740-750 km) are identified based on similarly processed high-frequency P'P' precursors. At nominal mantle temperatures these two phase changes may be seismically indistinguishable, but colder mantle conditions from the descending Nazca plate, the presence of water and variable Fe contents may cause sufficient separation for a reliable analysis. In addition, our preliminary results provide compelling evidence for multiple shallow lower-mantle reflections (at ~800 km) along the elongated plate boundary zones of South America. Slab stagnation at the base of the transition zone could play a key role, though a proper interpretation of this finding would likely entail compositional (rather than strictly thermal) variations in the vicinity of the descending oceanic crust and lithosphere. Overall, the resolution and sensitivity differences between low/intermediate- S and high-frequency P wave reflections are key considerations toward reconciling seismic and mineralogical models of transition zone structure, both at the study location and worldwide.

The Intersection between the Gloria Transform Fault and the Tore-Madeira Rise in the NE Atlantic: New Tectonic Insights from Analog Modeling Results

NASA Astrophysics Data System (ADS)

Rosas, F. M.; Tomas, R.; Duarte, J. C.; Schellart, W. P.; Terrinha, P.

2014-12-01

The intersection between the Gloria Fault (GF) and the Tore-Madeira rise (TMR) in NE Atlantic marks a transition from a discrete to a diffuse nature along a critical segment of the Eurasia/Africa plate boundary. To the West of such intersection, approximately since the Azores triple junction, this plate boundary is mostly characterized by a set of closely aligned and continuous strike-slip faults that make up the narrow active dextral transcurrent system of the GF (with high magnitude M>7 historical earthquakes). While intersecting the TMR the closely E-W trending trace of the GF system is slightly deflected (changing to WNW-ESE), and splays into several fault branches that often coincide with aligned (TMR related?) active volcanic plugs. The segment of the plate boundary between the TMR and the Gorringe Bank (further to the East) corresponds to a more complex (less discrete) tectonic configuration, within which the tectonic connection between the Gloria Fault and another major dextral transcurrent system (the so called SWIM system) occurs. This SWIM fault system has been described to extend even further to the East (almost until the Straits of Gibraltar) across the Gulf of Cadiz domain. In this domain the relative movement between the Eurasian and the African plates is thought to be accommodated through a diffuse manner, involving large scale strain partition between a dextral transcurrent fault-system (the SWIM system), and a set of active west-directed én-échelon major thrusts extending to the North along the SW Iberian margin. We present new analog modeling results, in which we employed different experimental settings to address (namely) the following main questions (as a first step to gain new insight on the tectonic evolution of the TRM-GF critical intersection area): Could the observed morphotectonic configuration of such intersection be simply caused by a bathymetric anomaly determined by a postulated thickened oceanic crust, or is it more compatible with a crustal rheological (viscous) anomaly, possibly related with the active volcanism in the intersection zone? What could cause the observed deflection and splaying of the GF in the intersection with the TMR? Is the GF cutting across the TMR, or is it ending against a morpho-rheological anomaly through waning lateral propagation?

Application of the algebraic RNG model for transition simulation. [renormalization group theory

NASA Technical Reports Server (NTRS)

Lund, Thomas S.

1990-01-01

The algebraic form of the RNG model of Yakhot and Orszag (1986) is investigated as a transition model for the Reynolds averaged boundary layer equations. It is found that the cubic equation for the eddy viscosity contains both a jump discontinuity and one spurious root. A yet unpublished transformation to a quartic equation is shown to remove the numerical difficulties associated with the discontinuity, but only at the expense of merging both the physical and spurious root of the cubic. Jumps between the branches of the resulting multiple-valued solution are found to lead to oscillations in flat plate transition calculations. Aside from the oscillations, the transition behavior is qualitatively correct.

Structural patterns and tectonic history of the Bauer microplate, Eastern Tropical Pacific

USGS Publications Warehouse

Eakins, B.W.; Lonsdale, P.F.

2003-01-01

The Bauer microplate was an independent slab of oceanic lithosphere that from 17 Ma to 6 Ma grew from 1.4 ?? 105 km2 to 1.2 ?? 106 km2 between the rapidly diverging Pacific and Nazca plates. Growth was by accretion at the lengthening and overlapping axes of the (Bauer-Nazca) Galapagos Rise (GR) and the (Pacific-Bauer) East Pacific Rise (EPR). EPR and GR axial propagation to create and rapidly grow the counter-clockwise spinning microplate occurred in two phases: (1) 17-15Ma, when the EPR axis propagated north and the GR axis propagated south around a narrow (100- to 200-km-wide) core of older lithosphere; and (2) 8-6 Ma, when rapid northward propagation of the EPR axis resumed, overlapping ???400 km of the fast-spreading Pacific-Nazca rise-crest and appending a large (200- to 400-km-wide) area of the west flank of that rise as a 'northern annex' to the microplate. Between 15 and 8 Ma the microplate grew principally by crustal accretion at the crest of its rises. The microplate was captured by the Nazca plate and the Galapagos Rise axis became extinct soon after 6 Ma, when the south end of the Pacific-Bauer EPR axis became aligned with the southern Pacific-Nazca EPR axis and its north end was linked by the Quebrada Transform to the northern Pacific-Nazca EPR axis. Incomplete multibeam bathymetry of the microplate margins, and of both flanks of the Pacific-Bauer and Bauer-Nazca Rises, together with archival magnetic and satellite altimetry data, clarifies the growth and (counter-clockwise) rotation of the microplate, and tests tectonic models derived from studies of the still active, much smaller, Easter and Juan Fernandez microplates. Our interpretations differ from model predictions in that Euler poles were not located on the microplate boundary, propagation in the 15-8 Ma phase of growth was not toward these poles, and microplate rotation rates were small (5??/m.y.) for much of its history, when long, bounding transform faults reduced coupling to Nazca plate motion. Some structures of the Bauer microplate boundary, such as deep rift valleys and a broad zone of thrust-faulted lithosphere, are, however, similar to those observed around the smaller, active microplates. Analysis of how the Bauer microplate was captured when coupling to the Pacific plate was reduced invites speculation on why risecrest microplates eventually lose their independence. ?? Springer 2005.

Fundamental structure model of island arcs and subducted plates in and around Japan

NASA Astrophysics Data System (ADS)

Iwasaki, T.; Sato, H.; Ishiyama, T.; Shinohara, M.; Hashima, A.

2015-12-01

The eastern margin of the Asian continent is a well-known subduction zone, where the Pacific (PAC) and Philippine Sea (PHS) plates are being subducted. In this region, several island arcs (Kuril, Northeast Japan, Southwest Japan, Izu-Bonin and Ryukyu arcs) meet one another to form a very complicated tectonic environment. At 2014, we started to construct fundamental structure models for island arcs and subducted plates in and around Japan. Our research is composed of 6 items of (1) topography, (2) plate geometry, (3) fault models, (4) the Moho and brittle-ductile transition zone, (5) the lithosphere-asthenosphere boundary, and (6) petrological/rheological models. Such information is basic but inevitably important in qualitative understanding not only for short-term crustal activities in the subduction zone (particularly caused by megathrust earthquakes) but also for long-term cumulative deformation of the arcs as a result of strong plate-arc/arc-arc interactions. This paper is the first presentation of our research, mainly presenting the results of items (1) and (2). The area of our modelling is 12o-54o N and 118o-164o E to cover almost the entire part of Japanese Islands together with Kuril, Ryukyu and Izu-Bonin trenches. The topography model was constructed from the 500-m mesh data provided from GSJ, JODC, GINA and Alaska University. Plate geometry models are being constructed through the two steps. In the first step, we modelled very smooth plate boundaries of the Pacific and Philippine Sea plates in our whole model area using 42,000 earthquake data from JMA, USGS and ISC. For 7,800 cross sections taken with several directions to the trench axes, 2D plate boundaries were defined by fitting to the earthquake distribution (the Wadati-Benioff zone), from which we obtained equi-depth points of the plate boundary. These equi-depth points were then approximated by spline interpolation technique to eliminate shorter wave length undulation (<50-100 km). The obtained models represent the plate geometry with longer wave lengths (>75-150 km), but provide a rather clear undulation of the PHS plate under the SW Japan arc. In the second step, finer scale plate configuration is being constrained especially in the vicinity of Japan by recent results from seismic tomography, RF analysis and active source experiment.

How broad and deep is the region of chemical alteration of oceanic plates at trenches?

NASA Astrophysics Data System (ADS)

Ranero, C. R.; Grevemeyer, I.; Barckhausen, U.

2017-12-01

Different lines of evidence indicate that oceanic plates are affected by pervasive bending-related deformation approaching ocean trenches. Results from active-seismic work support that deformation provides paths for exchange between hydrosphere and lithosphere, possibly causing chemical alteration of the incoming lithosphere. Much work focused on the potential transformation of peridotite to serpentine in the uppermost mantle of incoming plates, but there is no consensus on the region where it may occur or the intensity of alteration, let alone on limiting factors for the process. Teleseismic (large-great) earthquakes with normal-fault mechanism in the outer rise region have been often called to speculate on the depth of penetration of plate hydration. However, large-great outer-rise earthquakes may be related to stress changes due to slab pull after decoupling along the inter-plate boundary, and not necessarily controlled by bending stresses only. If so, the majority of the time the depth of water percolation may be related to local bending stresses expressed by micro-earthquakes rather than large events. Seismic images and multibeam bathymetry from lithosphere of similar thermal thickness from different trenches display a remarkable variability of the intensity of bending-related deformation along the subduction zones where plate age does not change significantly indicating that the intensity of deformation (not the depth) and perhaps hydration is very variable in space and not controlled by plate age. Seismic images showing hundreds of kilometers perpendicular to the trench into the incoming plate show that the bending-related deformation reaches mantle under the outer rise, well before the lithosphere plunges into the trench and develops the marked bend-faulting fabric observable in bathymetric maps. Thus, alteration occurs in a hundreds-of-km wide area, with deformation intensity related to local characteristics, and deformation depth to plate age.

Correlation of heat transfer for the zero pressure gradient hypersonic laminar boundary layer for several gases

NASA Technical Reports Server (NTRS)

Cook, W. J.

1973-01-01

A theoretical study of heat transfer for zero pressure gradient hypersonic laminar boundary layers for various gases with particular application to the flows produced in an expansion tube facility was conducted. A correlation based on results obtained from solutions to the governing equations for five gases was formulated. Particular attention was directed toward the laminar boundary layer shock tube splitter plates in carbon dioxide flows generated by high speed shock waves. Computer analysis of the splitter plate boundary layer flow provided information that is useful in interpreting experimental data obtained in shock tube gas radiation studies.

High precision refractometry based on Fresnel diffraction from phase plates.

PubMed

Tavassoly, M Taghi; Naraghi, Roxana Rezvani; Nahal, Arashmid; Hassani, Khosrow

2012-05-01

When a transparent plane-parallel plate is illuminated at a boundary region by a monochromatic parallel beam of light, Fresnel diffraction occurs because of the abrupt change in phase imposed by the finite change in refractive index at the plate boundary. The visibility of the diffraction fringes varies periodically with changes in incident angle. The visibility period depends on the plate thickness and the refractive indices of the plate and the surrounding medium. Plotting the phase change versus incident angle or counting the visibility repetition in an incident-angle interval provides, for a given plate thickness, the refractive index of the plate very accurately. It is shown here that the refractive index of a plate can be determined without knowing the plate thickness. Therefore, the technique can be utilized for measuring plate thickness with high precision. In addition, by installing a plate with known refractive index in a rectangular cell filled with a liquid and following the described procedures, the refractive index of the liquid is obtained. The technique is applied to measure the refractive indices of a glass slide, distilled water, and ethanol. The potential and merits of the technique are also discussed.

Intermittent Granular Dynamics at a Seismogenic Plate Boundary.

PubMed

Meroz, Yasmine; Meade, Brendan J

2017-09-29

Earthquakes at seismogenic plate boundaries are a response to the differential motions of tectonic blocks embedded within a geometrically complex network of branching and coalescing faults. Elastic strain is accumulated at a slow strain rate on the order of 10^{-15}  s^{-1}, and released intermittently at intervals >100  yr, in the form of rapid (seconds to minutes) coseismic ruptures. The development of macroscopic models of quasistatic planar tectonic dynamics at these plate boundaries has remained challenging due to uncertainty with regard to the spatial and kinematic complexity of fault system behaviors. The characteristic length scale of kinematically distinct tectonic structures is particularly poorly constrained. Here, we analyze fluctuations in Global Positioning System observations of interseismic motion from the southern California plate boundary, identifying heavy-tailed scaling behavior. Namely, we show that, consistent with findings for slowly sheared granular media, the distribution of velocity fluctuations deviates from a Gaussian, exhibiting broad tails, and the correlation function decays as a stretched exponential. This suggests that the plate boundary can be understood as a densely packed granular medium, predicting a characteristic tectonic length scale of 91±20  km, here representing the characteristic size of tectonic blocks in the southern California fault network, and relating the characteristic duration and recurrence interval of earthquakes, with the observed sheared strain rate, and the nanosecond value for the crack tip evolution time scale. Within a granular description, fault and blocks systems may rapidly rearrange the distribution of forces within them, driving a mixture of transient and intermittent fault slip behaviors over tectonic time scales.

Intermittent Granular Dynamics at a Seismogenic Plate Boundary

NASA Astrophysics Data System (ADS)

Meroz, Yasmine; Meade, Brendan J.

2017-09-01

Earthquakes at seismogenic plate boundaries are a response to the differential motions of tectonic blocks embedded within a geometrically complex network of branching and coalescing faults. Elastic strain is accumulated at a slow strain rate on the order of 10-15 s-1 , and released intermittently at intervals >100 yr , in the form of rapid (seconds to minutes) coseismic ruptures. The development of macroscopic models of quasistatic planar tectonic dynamics at these plate boundaries has remained challenging due to uncertainty with regard to the spatial and kinematic complexity of fault system behaviors. The characteristic length scale of kinematically distinct tectonic structures is particularly poorly constrained. Here, we analyze fluctuations in Global Positioning System observations of interseismic motion from the southern California plate boundary, identifying heavy-tailed scaling behavior. Namely, we show that, consistent with findings for slowly sheared granular media, the distribution of velocity fluctuations deviates from a Gaussian, exhibiting broad tails, and the correlation function decays as a stretched exponential. This suggests that the plate boundary can be understood as a densely packed granular medium, predicting a characteristic tectonic length scale of 91 ±20 km , here representing the characteristic size of tectonic blocks in the southern California fault network, and relating the characteristic duration and recurrence interval of earthquakes, with the observed sheared strain rate, and the nanosecond value for the crack tip evolution time scale. Within a granular description, fault and blocks systems may rapidly rearrange the distribution of forces within them, driving a mixture of transient and intermittent fault slip behaviors over tectonic time scales.

Geometric invariance of compressible turbulent boundary layers

NASA Astrophysics Data System (ADS)

Bi, Wei-Tao; Wu, Bin; She, Zhen-Su; Hussain, Fazle

2015-11-01

A symmetry based approach is applied to analyze the mean velocity and temperature fields of compressible, flat plate turbulent boundary layers (CTBL). A Reynolds stress length scale and a turbulent heat flux length scale are identified to possess the same defect scaling law in the CTBL bulk, which is solely owing to the constraint of the wall to the geometry of the wall-attached eddies, but invariant to compressibility and wall heat transfer. This invariance is called the geometric invariance of CTBL eddies and is likely the origin of the Mach number invariance of Morkovin's hypothesis, as well as the similarity of energy and momentum transports. A closure for the turbulent transport by using the invariant lengths is attainted to predict the mean velocity and temperature profiles in the CTBL bulk- superior to the van Driest transformation and the Reynolds analogy based relations for its sound physics and higher accuracy. Additionally, our approach offers a new understanding of turbulent Prandtl number.

Linkages Between the Megathrust and Upper-plate Deformation: Lessons From the Deformational Dichotomy of the 2016 Kaikoura New Zealand Earthquake

NASA Astrophysics Data System (ADS)

Furlong, K. P.; Herman, M. W.

2017-12-01

Following the 2016 Mw 7.8 Kaikoura earthquake, the nature of the coseismic rupture was unclear. Seismological and tsunami evidence pointed to significant involvement of the subduction megathrust, while geodetic and field observations pointed to a shallow set of intra-crustal faults as the main participants during the earthquake. It now appears that the Kaikoura earthquake produced synchronous faulting on the plate boundary subduction interface - the megathrust - and on a suite of crustal faults above the rupture zone in the overlying plate. This Kaikoura-style earthquake, involving synchronous ruptures on multiple components of the plate boundary, may be an important mode of plate boundary deformation affecting seismic hazard along subduction zones. Here we propose a model to explain how these upper-plate faults are loaded during the periods between megathrust earthquakes and subsequently can rupture synchronously with the megathrust. Between megathrust earthquakes, horizontal compression, driven by plate convergence, locks the upper-plate faults, particularly those at higher angles to the convergence direction and the oblique plate motion of the subducting Pacific plate deforms the upper-plate in bulk shear. During the time interval of megathrust rupture, two things happen which directly affect the stress conditions acting on these upper-plate faults: (1) slip on the megathrust and the associated `rebound' of the upper plate reduces the compressive or normal stress acting on the upper plate faults, and (2) the base of the upper plate faults (and the upper plate itself) is decoupled from the slab in the region above rupture area. The reduction in normal stress acting on these faults increases their Coulomb Stress state to strongly favor strike-slip fault slip, and the basal decoupling of the upper plate allows it to undergo nearly complete stress recovery in that region; enabling the occurrence of very large offsets on these faults - offsets that exceed the slip on the plate interface. With these results it is clear that the 2016 Kaikoura NZ earthquake represents a mode of subduction zone rupture that must be considered in other regions.

The tectonic evolution of the southeastern Terceira Rift/São Miguel region (Azores)

NASA Astrophysics Data System (ADS)

Weiß, B. J.; Hübscher, C.; Lüdmann, T.

2015-07-01

The eastern Azores Archipelago with São Miguel being the dominant subaerial structure is located at the intersection of an oceanic rift (Terceira Rift) with a major transform fault (Gloria Fault) representing the westernmost part of the Nubian-Eurasian plate boundary. The evolution of islands, bathymetric highs and basin margins involves strong volcanism, but the controlling geodynamic and tectonic processes are currently under debate. In order to study this evolution, multibeam bathymetry and marine seismic reflection data were collected to image faults and stratigraphy. The basins of the southeastern Terceira Rift are rift valleys whose southwestern and northeastern margins are defined by few major normal faults and several minor normal faults, respectively. Since São Miguel in between the rift valleys shows an unusual W-E orientation, it is supposed to be located on a leaky transform. South of the island and separated by a N120° trending graben system, the Monacco Bank represents a N160° oriented flat topped volcanic ridge dominated by tilted fault blocks. Up to six seismic units are interpreted for each basin. Although volcanic ridges hamper a direct linking of depositional strata between the rift and adjacent basins, the individual seismic stratigraphic units have distinct characteristics. Using these units to provide a consistent relative chrono-stratigraphic scheme for the entire study area, we suggest that the evolution of the southeastern Terceira Rift occurred in two stages. Considering age constrains from previous studies, we conclude that N140° structures developed orthogonal to the SW-NE direction of plate-tectonic extension before ~ 10 Ma. The N160° trending volcanic ridges and faults developed later as the plate tectonic spreading direction changed to WSW-ENE. Hence, the evolution of the southeastern Terceira Rift domain is predominantly controlled by plate kinematics and lithospheric stress forming a kind of a re-organized rift system.

Driving forces: Slab subduction and mantle convection

NASA Technical Reports Server (NTRS)

Hager, Bradford H.

1988-01-01

Mantle convection is the mechanism ultimately responsible for most geological activity at Earth's surface. To zeroth order, the lithosphere is the cold outer thermal boundary layer of the convecting mantle. Subduction of cold dense lithosphere provides tha major source of negative buoyancy driving mantle convection and, hence, surface tectonics. There are, however, importnat differences between plate tectonics and the more familiar convecting systems observed in the laboratory. Most important, the temperature dependence of the effective viscosity of mantle rocks makes the thermal boundary layer mechanically strong, leading to nearly rigid plates. This strength stabilizes the cold boundary layer against small amplitude perturbations and allows it to store substantial gravitational potential energy. Paradoxically, through going faults at subduction zones make the lithosphere there locally weak, allowing rapid convergence, unlike what is observed in laboratory experiments using fluids with temperature dependent viscosities. This bimodal strength distribution of the lithosphere distinguishes plate tectonics from simple convection experiments. In addition, Earth has a buoyant, relatively weak layer (the crust) occupying the upper part of the thermal boundary layer. Phase changes lead to extra sources of heat and bouyancy. These phenomena lead to observed richness of behavior of the plate tectonic style of mantle convection.

Long-range Receiver Function Profile of Crustal and Mantle Discontinuities From the Aleutian Arc to Tierra del Fuego

NASA Astrophysics Data System (ADS)

Spieker, Kathrin; Rondenay, Stéphane; Sawade, Lucas

2016-04-01

The Circum-Pacific belt, also called the Pacific Ring of Fire, is the most seismically active region on Earth. Multiple plate boundaries form a zone characterized by frequent volcanic eruptions and seismicity. While convergent plate boundaries such as the Peru-Chile trench dominate the Circum-Pacific belt, divergent and transform boundaries are present as well. The eastern section of the Circum-Pacific belt extends from the Aleutian arc, through the Cascadia subduction zone, San Andreas Fault, middle America trench and the Andean margin down to Tierra del Fuego. Due to the significant hazards posed by this tectonic activity, the region has been densely instrumented by thousands of seismic stations deployed across fifteen countries, over a distance of more than 15000 km. Various seismological studies, including receiver function analyses, have been carried out to investigate the crustal and mantle structure beneath local segments of the eastern Circum-Pacific belt (i.e., at ~100-500 km scale). However, to the best of our knowledge, no study to date has ever attempted to combine all available seismic data from the eastern Circum-Pacific belt to generate a continuous profile of seismic discontinuities extending from the Aleutians to Tierra del Fuego. Here, we use results from the "Global Imaging using Earthquake Records" (GLImER) P-wave receiver function database to create a long-range profile of crustal and upper mantle discontinuities across the entire eastern portion of the Circum-Pacific belt. We image intermittent crustal and mantle discontinuities along the profile, and examine them with regard to their behaviour and properties across transitions between different tectonic regimes.

Passive seismic monitoring of natural and induced earthquakes: case studies, future directions and socio-economic relevance

USGS Publications Warehouse

Bohnhoff, Marco; Dresen, Georg; Ellsworth, William L.; Ito, Hisao; Cloetingh, Sierd; Negendank, Jörg

2010-01-01

An important discovery in crustal mechanics has been that the Earth’s crust is commonly stressed close to failure, even in tectonically quiet areas. As a result, small natural or man-made perturbations to the local stress field may trigger earthquakes. To understand these processes, Passive Seismic Monitoring (PSM) with seismometer arrays is a widely used technique that has been successfully applied to study seismicity at different magnitude levels ranging from acoustic emissions generated in the laboratory under controlled conditions, to seismicity induced by hydraulic stimulations in geological reservoirs, and up to great earthquakes occurring along plate boundaries. In all these environments the appropriate deployment of seismic sensors, i.e., directly on the rock sample, at the earth’s surface or in boreholes close to the seismic sources allows for the detection and location of brittle failure processes at sufficiently low magnitude-detection threshold and with adequate spatial resolution for further analysis. One principal aim is to develop an improved understanding of the physical processes occurring at the seismic source and their relationship to the host geologic environment. In this paper we review selected case studies and future directions of PSM efforts across a wide range of scales and environments. These include induced failure within small rock samples, hydrocarbon reservoirs, and natural seismicity at convergent and transform plate boundaries. Each example represents a milestone with regard to bridging the gap between laboratory-scale experiments under controlled boundary conditions and large-scale field studies. The common motivation for all studies is to refine the understanding of how earthquakes nucleate, how they proceed and how they interact in space and time. This is of special relevance at the larger end of the magnitude scale, i.e., for large devastating earthquakes due to their severe socio-economic impact.

Life and death of the resurrection plate: Evidence for its existence and subduction in the northeastern Pacific in Paleocene-Eocene time

USGS Publications Warehouse

Haeussler, P.J.; Bradley, D.C.; Wells, R.E.; Miller, M.L.

2003-01-01

Onshore evidence suggests that a plate is missing from published reconstructions of the northeastern Pacific Ooean in Paleocene- Eocene time. The Resurrection plate, named for the Resurrection Peninsula ophiolite near Seward, Alaska, was located east of the Kula plate and north of the Farallon plate. We interpret coeval near-trench magmatism in southern Alaska and the Cascadia margin as evidence for two slab windows associated with trench-ridge-trench (TRT) triple junctions, which formed the western and southern boundaries of the Resurrection plate. In Alaska, the Sanak-Baranof belt of near-trench intrusions records a west-to-east migration, from 61 to 50 Ma, of the northern TRT triple junction along a 2100-km-long section of coastline. In Oregon, Washington, and southern Vancouver Island, voluminous basaltic volcanism of the Siletz River Volcanics, Crescent Formation, and Metchosin Volcanics occurred between ca. 66 and 48 Ma. Lack of a clear age progression of magmatism along the Cascadia margin suggests that this southern triple junction did not migrate significantly. Synchronous near-trench magmatism from southeastern Alaska to Puget Sound at ca. 50 Ma documents the middle Eocene subduction of a spreading center, the crest of which was subparallel to the margin. We interpret this ca. 50 Ma event as recording the subduction-zone consumption of the last of the Resurrection plate. The existence and subsequent subduction of the Resurrection plate explains (1) northward terrane transport along the southeastern Alaska-British Columbia margin between 70 and 50 Ma, synchronous with an eastward-migrating triple junction in southern Alaska; (2) rapid uplift and voluminous magmatism in the Coast Mountains of British Columbia prior to 50 Ma related to subduction of buoyant, young oceanic crust of the Resurrection plate; (3) cessation of Coast Mountains magmatism at ca. 50 Ma due to cessation of subduction, (4) primitive mafic magmatism in the Coast Mountains and Cascade Range just after 50 Ma, related to slab-window magmatism, (5) birth of the Queen Charlotte transform margin at ca. 50 Ma, (6) extensional exhumation of high-grade metamorphic terranes and development of core complexes in British Columbia, Idaho, and Washington, and extensional collapse of the Cordilleran foreland fold-and-thrust belt in Alberta, Montana, and Idaho after 50 Ma related to initiation of the transform margin, (7) enigmatic 53-45 Ma magmatism associated with extension from Montana to the Yukon Territory as related to slab breakup and the formation of a slab window, (8) right-lateral margin-parallel strike-slip faulting in southern and western Alaska during Late Cretaceous and Paleocene time, which cannot be explained by Farallon convergence vectors, and (9) simultaneous changes in Pacific-Farallon and Pacific-Kula plate motions concurrent with demise of the Kula-Resurrection Ridge.

Quantifying Arabia-Eurasia convergence accommodated in the Greater Caucasus by paleomagnetic reconstruction

NASA Astrophysics Data System (ADS)

van der Boon, A.; van Hinsbergen, D. J. J.; Rezaeian, M.; Gürer, D.; Honarmand, M.; Pastor-Galán, D.; Krijgsman, W.; Langereis, C. G.

2018-01-01

Since the late Eocene, convergence and subsequent collision between Arabia and Eurasia was accommodated both in the overriding Eurasian plate forming the Greater Caucasus orogen and the Iranian plateau, and by subduction and accretion of the Neotethys and Arabian margin forming the East Anatolian plateau and the Zagros. To quantify how much Arabia-Eurasia convergence was accommodated in the Greater Caucasus region, we here provide new paleomagnetic results from 97 volcanic sites (∼500 samples) in the Talysh Mountains of NW Iran, that show ∼15° net clockwise rotation relative to Eurasia since the Eocene. We apply a first-order kinematic restoration of the northward convex orocline that formed to the south of the Greater Caucasus, integrating our new data with previously published constraints on rotations of the Eastern Pontides and Lesser Caucasus. This suggests that north of the Talysh ∼120 km of convergence must have been accommodated. North of the Eastern Pontides and Lesser Caucasus this is significantly more: 200-280 km. Our reconstruction independently confirms previous Caucasus convergence estimates. Moreover, we show for the first time a sharp contrast of convergence between the Lesser Caucasus and the Talysh. This implies that the ancient Paleozoic-Mesozoic transform plate boundary, preserved between the Iranian and East-Anatolian plateaus, was likely reactivated as a right-lateral transform fault since late Eocene time.

The Rovuma Transform Margin: the enigmatic continent-ocean boundary of East Africa

NASA Astrophysics Data System (ADS)

Phethean, Jordan; Kalnins, Lara; van Hunen, Jeroen; McCaffrey, Ken; Davies, Richard

2017-04-01

The N-S trending Davie Fracture Zone (DFZ) is often assumed to form the continent-ocean transform margin (COTM) of the Western Somali Basin. However, multiple plate tectonic reconstructions favour a pre-breakup location for Madagascar that crosses the DFZ, incompatible with its interpretation as the COTM (e.g., Lottes & Rowley, 1990; Reeves, 2014; Phethean et al., 2016). For the first time, we have identified classic COTM features in seismic reflection data from the Southern Rovuma Basin, to the west and inboard of the DFZ. These suggest a NNW trend to the margin, consistent with the tectonic reconstructions. 2D gravity models, with the seabed and top basement constrained by seismic data, are used to investigate the Moho structure across the Rovuma margin and are best fit using steep 'transform style' geometries, confirming the nature of the margin. We thus model generic COTM geometries elsewhere along the East African and Madagascan transform margins to locate best-fitting positions for these conjugate COTMs. This analysis confirms that the COTMs follow a NNW trend along the Rovuma Basin and Southern Madagascar, respectively, and allows a restoration of the conjugate COTMs. This restoration is used alongside geological maps and satellite imagery from Madagascar and East Africa to refine early plate motions and further constrain the precise origin of Madagascar within Gondwana. Our refined plate tectonic model independently predicts major observations made from seismic reflection and gravity data across the basin, including: regions of major transpression/transtension along the DFZ, merging of fracture zones to form the DFZ, oceanic crust on either side of the DFZ and within the Tanzania coastal basin, and the location of an abandoned MOR within the Tanzania coastal basin. We believe that this study finally provides conclusive evidence that Madagascar originated from within the Tanzania Coastal Basin, inboard of the DFZ, after some 30 years of debate regarding this matter. Lottes, A.L., Rowley, D.B., 1990. Reconstruction of the Laurasian and Gondwanan segments of Permian Pangea. Geol. Soc. London Mem., 12, 383-395. Reeves, C., 2014. The position of Madagascar within Gondwana and its movements during Gondwana dispersal. J. Afr. Earth Sci., 94, 45-57. Phethean, J.J.J., Kalnins, L.M., van Hunen, J.,Biffi, P.G., Davies, R.J., McCaffrey, K.J.W., 2016. Madagascar's escape from Africa: A high-resolution plate reconstruction for the Western Somali Basin and implications for supercontinent dispersal. Geochem. Geophys. Geosyst., 17, doi:10.1002/2016GC006624.

Wall Turbulence with Designer Properties: Identification, Characterization and Manipulation of Energy Pathways

DTIC Science & Technology

2016-02-26

zero-pressure- gradient boundary layer to develop over a flat plate . As shown in figure 6.1, the flat plate contains an insert to allow for a thin...B. J. ‘Triadic scale interactions in a turbulent boundary layer ’ J. Fluid Mech., 767, R4 (2015). 6. Luhar, M., Sharma, A. S. & McKeon, B. J. ‘A... boundary layer ’, Paper H22.00003, 68th Meeting of the American Physical Society Division of Fluid Dynamics, Boston, MA, Nov., 2015.  Duvvuri

Hydroelastic behaviour of a structure exposed to an underwater explosion

PubMed Central

Colicchio, G.; Greco, M.; Brocchini, M.; Faltinsen, O. M.

2015-01-01

The hydroelastic interaction between an underwater explosion and an elastic plate is investigated num- erically through a domain-decomposition strategy. The three-dimensional features of the problem require a large computational effort, which is reduced through a weak coupling between a one-dimensional radial blast solver, which resolves the blast evolution far from the boundaries, and a three-dimensional compressible flow solver used where the interactions between the compression wave and the boundaries take place and the flow becomes three-dimensional. The three-dimensional flow solver at the boundaries is directly coupled with a modal structural solver that models the response of the solid boundaries like elastic plates. This enables one to simulate the fluid–structure interaction as a strong coupling, in order to capture hydroelastic effects. The method has been applied to the experimental case of Hung et al. (2005 Int. J. Impact Eng. 31, 151–168 (doi:10.1016/j.ijimpeng.2003.10.039)) with explosion and structure sufficiently far from other boundaries and successfully validated in terms of the evolution of the acceleration induced on the plate. It was also used to investigate the interaction of an underwater explosion with the bottom of a close-by ship modelled as an orthotropic plate. In the application, the acoustic phase of the fluid–structure interaction is examined, highlighting the need of the fluid–structure coupling to capture correctly the possible inception of cavitation. PMID:25512585

Ancient Continental Lithosphere Dislocated Beneath Ocean Basins Along the Mid-Lithosphere Discontinuity: A Hypothesis

NASA Astrophysics Data System (ADS)

Wang, Zhensheng; Kusky, Timothy M.; Capitanio, Fabio A.

2017-09-01

The documented occurrence of ancient continental cratonic roots beneath several oceanic basins remains poorly explained by the plate tectonic paradigm. These roots are found beneath some ocean-continent boundaries, on the trailing sides of some continents, extending for hundreds of kilometers or farther into oceanic basins. We postulate that these cratonic roots were left behind during plate motion, by differential shearing along the seismically imaged mid-lithosphere discontinuity (MLD), and then emplaced beneath the ocean-continent boundary. Here we use numerical models of cratons with realistic crustal rheologies drifting at observed plate velocities to support the idea that the mid-lithosphere weak layer fostered the decoupling and offset of the African continent's buoyant cratonic root, which was left behind during Meso-Cenozoic continental drift and emplaced beneath the Atlantic Ocean. We show that in some cratonic areas, the MLD plays a similar role as the lithosphere-asthenosphere boundary for accommodating lateral plate tectonic displacements.

High risk of tsunami in the northern Caribbean

NASA Astrophysics Data System (ADS)

Grindlay, Nancy R.; Hearne, Meghan; Mann, Paul

The magnitude Mw = 9.3 Sumatra earthquake of 26 December 2004 claimed the lives of an estimated 300,000 people living in coastal areas of seven different countries around the Indian Ocean. This event raised the question of whether similar far-traveled tsunamis generated by plate boundary faulting could affect the estimated 150 million people living in coastal areas of the United States, including Alaska, Hawaii, Puerto Rico, and the U.S. Virgin Islands.Aside from the Pacific plate margin of North America, the North America-Caribbean plate boundary is the closest (˜2000 km) active plate boundary to coastal areas in the Gulf of Mexico and the U.S. Atlantic seaboard. Researchers also have proposed that other possible tsunami-generating sources that could affect coastal areas of the United States include slumping of the shelf margin along the Virginia-North Carolina margin [Driscoll et al., 2000] and slumping of volcanic edifices in the Canary Islands [Ward and Day, 2001].

Discovering the plates boundaries in the Mediterranean sea

NASA Astrophysics Data System (ADS)

Marinelli, Maurizio

2017-04-01

During the 8th class the students learn geology. We analyze the earth's layers, the earthquakes, the volcanoes and other natural phenomena like subduction and orogeny. We start with a global study but our goal is to focus on the crust to discover the plates boundaries, particularly the boundary between Eurasian and African Plate in the Mediterranean sea. It's very simple for the students to discover all the information using the Internet or the science book, but I want to make with them an exploration of earth science with the help of the natural phenomena we studied during the year. We connect with Istituto Nazionale di Geofisica e Vulcanologia ( http://www.ingv.it/en/ ) where we can find a map with the earthquakes happened in the last years in Italy and in the Mediterranean sea and the list of the main volcanoes. In this way we can draw a map of the mediterranean plates and we can talk about the past and the future of the Mediterranean sea, Europe and Africa based on our maps and on the Alps orogeny. Using youtube we can have a confirm of our hypothesis about the future of the Mediterranean sea (https://www.youtube.com/watch?v=uGcDed4xVD4 ). A good observation for the students is given by the fact that we live in Europe but actually we stay on the African plate. The boundary is 5 km north of our school and we can go and visit the place where it is possible to see the different height of the two plates.

Plate boundary deformation at the latitude of the Salton Trough - northern Gulf of California (Invited)

NASA Astrophysics Data System (ADS)

Stock, J. M.

2013-12-01

Along the Pacific-North America plate boundary zone, the segment including the southern San Andreas fault to Salton Trough and northern Gulf of California basins has been transtensional throughout its evolution, based on Pacific-North America displacement vectors calculated from the global plate circuit (900 × 20 km at N54°W since 20 Ma; 460 × 20 km at N48°W since 11 Ma). Nevertheless, active seismicity and focal mechanisms show a broad zone of plate boundary deformation within which the inferred stress regime varies locally (Yang & Hauksson 2013 GJI), and fault patterns in some regions suggest ongoing tectonic rotation. Similar behavior is inferred to have occurred in this zone over most of its history. Crustal structure in this region is constrained by surface geology, geophysical experiments (e.g., the 2011 Salton Seismic Imaging Project (SSIP), USGS Imperial Valley 1979, PACE), and interdisciplinary marine and onland studies in Mexico (e.g., NARS-Baja, Cortes, and surveys by PEMEX). Magnetic data (e.g., EMAG-2) aids in the recognition of large-scale crustal provinces and fault boundaries in regions lacking detailed geophysical surveys. Consideration of existing constraints on crustal thickness and architecture, and fault and basin evolution suggests that to reconcile geological deformation with plate motion history, the following additional factors need to be taken into account. 1) Plate boundary displacement via interacting systems of rotating blocks, coeval with slip on steep strike slip faults, and possibly related to slip on low angle extensional faults (e.g, Axen & Fletcher 1998 IGR) may be typical prior to the onset of seafloor spreading. This fault style may have accommodated up to 150 km of plate motion in the Mexican Continental Borderland and north of the Vizcaino Peninsula, likely between 12 and 15 Ma, as well as explaining younger rotations adjacent to the Gulf of California and current deformation southwest of the Salton Sea. 2) Geophysical characteristics suggest that the zone of strike-slip faults related to past plate boundary deformation extends eastward into SW Arizona and beneath the Sonoran coastal plain. 3) 'New' crust and mantle lithosphere at the plate boundary, in the Salton Trough and the non-oceanic part of the northern Gulf of California, varies in seismic velocity structure and dimensions, both within and across extensional segments. Details of within-segment variations imaged by SSIP (e.g., Ma et al., and Han et al., this meeting) are attributed to active fault patterns and small scale variations in hydrothermal activity and magmatism superposed on a more uniform sedimentation. Differences between the Imperial Valley rift segment and the north Gulf of California segments may be due to more involvement of low angle normal faults in the marine basins in the south (Martin et al., 2013, Tectonics), as well as differences in lower crustal or mantle lithospheric flow from the adjacent continental regions.

Acoustic Reverse Time Migration of the Cascadia Subduction Zone Dataset

NASA Astrophysics Data System (ADS)

Jia, L.; Mallick, S.

2017-12-01

Reverse time migration (RTM) is a wave-equation based migration method, which provides more accurate images than ray-based migration methods, especially for the structures in deep areas, making it an effective tool for imaging the subduction plate boundary. In this work, we extend the work of Fortin (2015) and applied acoustic finite-element RTM on the Cascadia Subduction Zone (CSZ) dataset. The dataset was acquired by Cascadia Open-Access Seismic Transects (COAST) program, targeting the megathrust in the central Cascadia subduction zone (Figure 1). The data on a 2D seismic reflection line that crosses the Juan de Fuca/North American subduction boundary off Washington (Line 5) were pre-processed and worked through Kirchhoff prestack depth migration (PSDM). Figure 2 compares the depth image of Line 5 of the CSZ data using Kirchhoff PSDM (top) and RTM (bottom). In both images, the subducting plate is indicated with yellow arrows. Notice that the RTM image is much superior to the PSDM image by several aspects. First, the plate boundary appears to be much more continuous in the RTM image than the PSDM image. Second, the RTM image indicates the subducting plate is relatively smooth on the seaward (west) side between 0-50 km. Within the deformation front of the accretionary prism (50-80 km), the RTM image shows substantial roughness in the subducting plate. These features are not clear in the PSDM image. Third, the RTM image shows a lot of fine structures below the subducting plate which are almost absent in the PSDM image. Finally, the RTM image indicates that the plate is gently dipping within the undeformed sediment (0-50 km) and becomes steeply dipping beyond 50 km as it enters the deformation front of the accretionary prism. Although the same conclusion could be drawn from the discontinuous plate boundary imaged by PSDM, RTM results are far more convincing than the PSDM.

Possible microplate generation at RRR triple junctions due to the non-circular finite motion of plates relative to each other

NASA Astrophysics Data System (ADS)

Cronin, V. S.

2012-12-01

First generation ideas of the kinematic stability of triple junctions lead to the common belief that the geometry of ridge-ridge-ridge (RRR) triple junctions remains constant over time under conditions of symmetric spreading. Given constant relative motion between each plate pair -- that is, the pole of plate relative motion is fixed to both plates in each pair during finite motion, as assumed in many accounts of plate kinematics -- there would be no boundary mismatch at the triple junction and no apparent kinematic reason why a microplate might develop there. But if, in a given RRR triple junction, the finite motion of one plate as observed from the other plate is not circular (as is generally the case, given the three-plate problem of plate kinematics), the geometry of the ridges and the triple junction will vary with time (Cronin, 1992, Tectonophys 207, 287-301). To explore the possible consequences of non-circular finite motion between plates at an RRR triple junction, a simple model was coded based on the cycloid finite-motion model (e.g., Cronin, 1987, Geology 15, 1006-1009) using NNR-MORVEL56 velocities for individual plates (Argus et al., 2011, G3 12, doi: 10.1029/2011GC003751). Initial assumptions include a spherical Earth, symmetric spreading, and constant angular velocities during the modeled finite time interval. The assumed-constant angular velocity vectors constitute a reference frame for observing finite plate motion. Typical results are [1] that the triple junction migrates relative to a coordinate system fixed to the angular-velocity vectors, [2] ridge axes rotates relative to each other, and [3] a boundary mismatch develops at the synthetic triple junction that might result in microplate nucleation. In a model simulating the Galapagos triple junction between the Cocos, Nazca and Pacific plates whose initial state did not include the Galapagos microplate, the mismatch gap was as much as ~3.4 km during 3 Myr of model displacement (see figure). The centroid of the synthetic triple junction translates ~81 km toward azimuth ~352° in 3 Myr. Of course, the details will vary as different angular velocity vectors are used; however, modeling indicates that non-circular finite relative motion between adjacent plates generally results in boundary mismatches and rotation of ridge segments relative to each other at RRR triple junctions. Left: synthetic Galapagos triple junction at initial model time, without a microplate. Right: synthetic triple junction after 3 Myr displacement, illustrating the resulting boundary mismatch (gap) and rotated ridge axes.

Virtual Research Expeditions along Plate Margins: Examples from an Online Oceanography Course

NASA Astrophysics Data System (ADS)

Reed, D. L.; Moore, G. F.; Bangs, N. L.; Tobin, H. J.

2010-12-01

An undergraduate online course in oceanography is based on the participation of each student in a series of virtual, at-sea, research expeditions, two of which are used to examine the tectonic processes at plate boundaries. The objective is to leverage the results of major federal research initiatives in the ocean sciences into effective learning tools with a long lifespan for use in undergraduate geoscience courses. These web-based expeditions examine: (1) hydrothermal vents along the divergent plate boundary at the Explorer Ridge and (2) the convergent plate boundary fault along the Nankai Trough, which is the objective of the multi-year NanTroSEIZE drilling program. Here we focus on the convergent plate boundary in NanTroSEIZE 3-D, which is based on a seismic survey supported through NSF-MARGINS, IODP and CDEX in Japan to study the properties of the plate boundary fault system in the upper limit of the seismogenic zone off Japan. The virtual voyage can be used in undergraduate classes at anytime, since it is not directly tied to the finite duration of a specific seagoing project, and comes in two versions, one that is being used in geoscience major courses and the other in non-major courses, such as the oceanography course mentioned above and a lower-division global studies course with a science emphasis. NanTroSEIZE in 3-D places undergraduate learning in an experiential framework as students participate on the expedition and carry out research on the structure of the plate boundary fault. Students learn the scientific background of the program, especially the critical role of international collaboration, and meet the chief scientists before joining the 3-D seismic imaging expedition to identify the active faults that were the likely sources of devastating earthquakes and tsunamis in Japan in 1944 and 1948. The initial results of phase I ODP drilling that began in 2007 are also reviewed. Students document their research on a worksheet that accompanies the expedition, interpret a slice through the 3-D seismic volume, and compose an “AGU-style” abstract summarizing their work, which is submitted to the instructor for review. NanTroSEIZE in 3-D is openly available and can be accessed through the MARGINS Mini-lesson section of the Science Education Resource Center (SERC).

Crust-mantle boundaries in the Taiwan - Luzon arc-continent collision system determined from local earthquake tomography and layered Vp models

NASA Astrophysics Data System (ADS)

Ustaszewski, K. M.; Wu, Y.; Suppe, J.; Huang, H.; Carena, S.; Chang, C.

2011-12-01

We performed 3D mapping of crust-mantle boundaries in the Taiwan-Luzon arc-continent collision zone using a local earthquake tomographic model, providing better insight into the mode of subduction polarity reversal. The mapped crust-mantle discontinuities include three tectonically distinct Mohos. Furthermore, a crust-mantle boundary marks the eastern limit of the Eurasian lower crust against the mantle of the Philippine Sea plate. It dips steeply to the east underneath eastern and southern Taiwan and steepens progressively towards north until it becomes vertical at 23.7°N. From there it continues northward in a slightly overturned orientation, where the limit of the tomographic model at the northern tip of the island prevents further mapping. In order to map several Moho discontinuities, we contoured a surface of constant Vp = 7.5 km s-1 constrained from local earthquake tomography and confined to regions with a minimum of 500 rays per tomography cell. Additional constraints for the Moho were derived from layered (1D) Vp models using P-wave arrivals of local earthquakes recorded at 52 seismic stations, employing a genetic algorithm. The Moho of the Eurasian and the Philippine Sea plates are topologically disconnected across the plate boundary. Beneath southern Taiwan, the Eurasian Moho dips to the E at 50-60°, following the orientation of the plate boundary and continuous with the Benioff zone. Towards north, the Eurasian Moho twists to become subvertical, again together with the plate boundary. At the same time, it steps westward into a more external position underneath the thrust belt, giving way to the north-dipping Philippine Sea plate. The Philippine Sea plate Moho shallows towards the surface along the Longitudinal Valley suture. It forms a synform-like crustal root with an axis parallel to the trend of geological units at surface and it is interpreted as the base of the magmatic Luzon arc. Towards the north, the crustal root deepens from 30 km to about 70 km underneath the Ryukyu trench. In northeasternmost Taiwan, a subhorizontal Moho lies at about 30-35 km depth and is topologically disconnected from the main eastward subducting Eurasian Moho. It lies above the north-dipping Philippine Sea slab and is interpreted to be a newly formed Moho established by delamination of the Eurasian mantle lithosphere and lowermost crust.

Fundamental studies in geodynamics

NASA Technical Reports Server (NTRS)

Anderson, D. L.

1980-01-01

Progress in modeling instantaneous plate kinematics is reviewed, with emphasis on recently developed models of present day plate motions derived by the systematic inversion of globally distributed data sets. Rivera plate motions, the Caribbean South American boundary, Indian plate deformation, Pacific-North America, seismicity and subduction processes, and the study of slow earthquakes and free oscillations are discussed.

Stability and natural vibration analysis of laminated plates by using a mixed element based on a refined plate theory

NASA Technical Reports Server (NTRS)

Putcha, N. S.; Reddy, J. N.

1986-01-01

A mixed shear flexible finite element, with relaxed continuity, is developed for the geometrically linear and nonlinear analysis of layered anisotropic plates. The element formulation is based on a refined higher order theory which satisfies the zero transverse shear stress boundary conditions on the top and bottom faces of the plate and requires no shear correction coefficients. The mixed finite element developed herein consists of eleven degrees of freedom per node which include three displacements, two rotations and six moment resultants. The element is evaluated for its accuracy in the analysis of the stability and vibration of anisotropic rectangular plates with different lamination schemes and boundary conditions. The mixed finite element described here for the higher order theory gives very accurate results for buckling loads and natural frequencies.

High-Resolution Geophysical Constraints on Late Pleistocene-Present Deformation History, Seabed Morphology, and Slip-Rate along the Queen Charlotte-Fairweather Fault, Offshore Southeastern Alaska

NASA Astrophysics Data System (ADS)

Brothers, D. S.; Haeussler, P. J.; Dartnell, P.; Conrad, J. E.; Kluesner, J. W.; Hart, P. E.; Witter, R. C.; Balster-Gee, A. F.; Maier, K. L.; Watt, J. T.; East, A. E.

2015-12-01

The Queen Charlotte-Fairweather Fault (QCFF) of southeastern Alaska and British Columbia is the dominant fault along the 1200 km-long transform boundary between the Pacific and North American plates. More than 900 km of the QCFF lies offshore where the style and rates of deformation are poorly constrained due to a lack of high-resolution marine geophysical data. In May 2015, the USGS acquired ~900 km2 of high-resolution multibeam bathymetry data and >2000 line-km of high-resolution multichannel seismic reflection profiles between Cross Sound, Yakobi Sea Valley, and Icy Point (the northernmost offshore section of the QCFF) using a 24-ch streamer and 500 Joule minisparker source. During a second cruise in August 2015 we conducted targeted multichannel seismic and subbottom CHIRP profiling in the same region. The new data reveal a single trace of the QCFF expressed as a clear and remarkably straight seafloor lineation for >60 km. Subtle jogs in the fault (<3 degrees) are associated with pop-up structures and en echelon pull-apart basins. The near surface deformation along the fault never exceeds a width of 1.2 km. Northward, as the fault approaches Icy Point and a restraining bend, it splays into multiple strands and displays evidence for uplift and transpression. The fault appears to transition from almost purely strike-slip in the south to oblique-convergence as it steps onshore to the north. The QCFF cuts through the Yakobi Sea Valley and Cross Sound, two elongate bathymetric troughs that were filled with glaciers as recently as 17-19 ka. The southern wall of the Yakobi Sea Valley is offset 890±30 m by the QCFF, providing a late Pleistocene-present slip-rate estimate of 45-54 mm/yr. This suggests that nearly the entire plate boundary slip budget is confined to a single, narrow, strike-slip fault zone, which may have implications for models of plate boundary strain localization.

Structure of the Lithosphere-Asthenosphere Boundary Onshore and Offshore the California Continental Margin from Three-Dimensional Seismic Anisotropy

NASA Astrophysics Data System (ADS)

Gomez, C. D.; Escobar, L., Sr.; Rathnayaka, S.; Weeraratne, D. S.; Kohler, M. D.

2016-12-01

The California continental margin, a major transform plate boundary in continental North America, is the locus of complex tectonic stress fields that are important in interpreting both remnant and ongoing deformational strain. Ancient subduction of the East Pacific Rise spreading center, the rotation and translation of tectonic blocks and inception of the San Andreas fault all contribute to the dynamic stress fields located both onshore and offshore southern California. Data obtained by the ALBACORE (Asthenospheric and Lithospheric Broadband Architecture from the California Offshore Region Experiment) and the CISN (California Integrated Seismic Network) seismic array are analyzed for azimuthal anisotropy of Rayleigh waves from 80 teleseismic events at periods 16 - 78 s. Here we invert Rayleigh wave data for shear wave velocity structure and three-dimensional seismic anisotropy in the thee regions designated within the continental margin including the continent, seafloor and California Borderlands. Preliminary results show that seismic anisotropy is resolved in multiple layers and can be used to determine the lithosphere-asthenosphere boundary (LAB) in offshore and continental regions. The oldest seafloor in our study at age 25-35 Ma indicates that the anisotropic transition across the LAB occurs at 73 km +/- 25 km with the lithospheric fast direction oriented WNW-ESE, consistent with current Pacific plate motion direction. The continent region west of the San Andreas indicates similar WNW-ESE anisotropy and LAB depth. Regions east of the San Andreas fault indicate NW-SE anisotropy transitioning to a N-S alignment at 80 km depth north of the Garlock fault. The youngest seafloor (15 - 25 Ma) and outer Borderlands indicate a more complex three layer fabric where shallow lithospheric NE-SW fast directions are perpendicular with ancient Farallon subduction arc, a mid-layer with E-W fast directions are perpendicular to remnant fossil fabric, and the deepest layer indicates NW-SE fast directions below the LAB likely controlled by current Pacific plate motion. The inner Borderland indicates two layer anisotropic structure with a shallow NW-SE lithospheric fast direction that changes to NE-SW fast directions below the LAB, possibly consistent with the ancient subduction direction.

Plates and Mantle Convection: A Far-From Equilibrium Self-Organized System

NASA Astrophysics Data System (ADS)

King, S. D.; Lowman, J. P.; Gable, C. W.

2001-12-01

A common observation of plate tectonics is that plate velocities change over short time scales. Some have speculated that these reorganization events are triggered by evolving plate boundaries. This work presents an alternative mechanism, due to the interaction of mobil plates and internally heated convection. We present numerical models of 3D Cartesian convection in an internally-heated fluid with mobile plates that exhibit rapid changes in plate motion. A persistent feature of these calculations is that plate motion is relatively uniform punctuated by rapid reorganization events where plate speed and direction change over a short time period. The rapid changes in plate motion result solely from the interaction of internally-heated convection and the mobile plates. Without plates, the convective planform of an internally-heated fluid evolves into a pattern with a larger number of small cells. When plates are included, the fluid is dominated by plate-scale structures; however, isolated regions develop where heat builds up. These isolated regions are near the location of mature slabs where the plates are older and thicker. As the system evolves, the temperature (and buoyancy) in these isolated regions increases, they become unstable and, as they rise, the net force on the plate is no longer dominated by `slab pull' from the mature slab. The plate reorganization allows the system to transfer heat from the short-wavelength, internal-heating scale, to the longer-wavelength, plate-cooling scale. As we will demonstrate, the interaction between plate motions and the mantle is sufficiently dynamic that evolving plate boundaries are not necessary to achieve rapid changes in plate motion.

Frequency-domain prediction of broadband trailing edge noise from a blunt flat plate

NASA Astrophysics Data System (ADS)

Lee, Gwang-Se; Cheong, Cheolung

2013-10-01

The aim of this study is to develop an efficient methodology for frequency-domain prediction of broadband trailing edge noise from a blunt flat plate where non-zero pressure gradient may exist in its boundary layer. This is achieved in two ways: (i) by developing new models for point pressure spectra within the boundary layer over a flat plate, and (ii) by deriving a simple formula to approximate the effect of convective velocity on the radiated noise spectrum. Firstly, two types of point pressure spectra-required as input data to predict the trailing edge noise in the frequency domain-are used. One is determined using the semi-analytic (S-A) models based on the boundary-layer theory combined with existing empirical models. It is shown that the prediction using these models show good agreements with the measurements where zero-pressure gradient assumption is valid. However, the prediction show poor agreement with that obtained from large eddy simulation results where negative (favorable) pressure gradient is observed with the boundary layer. Based on boundary layer characteristics predicted using the large eddy simulations, new model for point wall pressure spectra is proposed to account for the effect of favorable pressure gradient over the blunt flat plate on the wall pressure spectra. Sound spectra that were predicted using these models are compared with measurements to validate the proposed prediction scheme. The advantage of the semi-analytic model is that it can be applied to problems at Reynolds numbers for which the empirical model is not available. In addition, it is expected that the current models can be applied to the cases where favorable pressure gradient exists in the boundary layer over a blunt flat plate. Secondly, in order to quantitatively analyze contributions of the pressure field within the turbulent boundary layer on the flat plate to trailing edge noise, total pressure over the surface of airfoil is decomposed into its two constituents: incident pressure generated in the boundary layer without a trailing edge and the pressure formed by the scattering of the incident pressure at the trailing edge. The predictions made using each of the incident and scattered pressures reveal that the convective velocity of turbulence in the boundary layer dominantly affects the radiated sound pressure spectrum, both in terms of the gross behavior of the overall acoustic pressure spectrum through the scattered pressure and in terms of the narrow band small fluctuations of the spectrum through the incident pressure. The interaction term between the incident and the scattered is defined and the incident is shown to contribute to the radiated acoustic pressure through the interaction term. Based on this finding, a simple model to effectively compute the effects of convection velocities of the turbulence on the radiated sound pressure spectrum is proposed. It is shown that the proposed method can effectively and accurately predict the broadband trailing edge noise from the plate with considering both the incident and the scattered contributions.

Generalized wall function and its application to compressible turbulent boundary layer over a flat plate

NASA Astrophysics Data System (ADS)

Liu, J.; Wu, S. P.

2017-04-01

Wall function boundary conditions including the effects of compressibility and heat transfer are improved for compressible turbulent boundary flows. Generalized wall function formulation at zero-pressure gradient is proposed based on coupled velocity and temperature profiles in the entire near-wall region. The parameters in the generalized wall function are well revised. The proposed boundary conditions are integrated into Navier-Stokes computational fluid dynamics code that includes the shear stress transport turbulence model. Numerical results are presented for a compressible boundary layer over a flat plate at zero-pressure gradient. Compared with experimental data, the computational results show that the generalized wall function reduces the first grid spacing in the directed normal to the wall and proves the feasibility and effectivity of the generalized wall function method.

Initiation of the Pyrenean plate boundary fault and its effect on the near- and far-field deformation of the European plate

NASA Astrophysics Data System (ADS)

Dielforder, Armin; Frasca, Gianluca; Ford, Mary

2017-04-01

The European plate was affected by contractional deformation events in Late Cretaceous time. This is recorded by inception of thrusting and foreland basin subsidence in the Pyrenean realm, and inversion of Mesozoic rift systems in the interior of the European plate. It is widely accepted that the plate-wide deformation resulted from the onset of NE-directed convergence of Africa-Iberia relative to Europe, and a strong mechanical coupling of the plates, which allowed the transfer of stresses far into Europe. Geological data from both the Pyrenean orogen and the interior of the European plate indicate, however, that these conditions persisted only for 15-20 Myr and that Europe experienced a plate-wide stress relaxation during Paleocene time. Although a slow down in plate convergence between Africa and Europe and North Atlantic continental rifting were proposed as potential causes for the stress relaxation, the subject has remained controversial. In particular, none of the mechanisms seem to be suitable to explain the required changes in the mechanical coupling of Iberian and European plates and the associated stress transfer. Here we propose a new model for the Upper Cretaceous to Paleocene tectonic evolution of the European plate, which takes the temporal evolution of the Pyrenean plate boundary fault into account. Based on plate reconstructions, geological field-data, and restored cross-sections we argue that the plate boundary fault initiated during the Upper Cretaceous within the exhumed mantle domain situated between the rifted margins of the Iberian and European plates. At the transition from the Late Cretaceous to Paleocene, the mantle domain was closed and the rifted margins collided. This evolution was associated with a substantial change in the fault rheology leading to an overall decrease in the plate coupling force. During Paleocene time, the plate coupling force was efficiently balanced by the gravitational push of the European plate, leading to a near neutral stress state in the upper plate and the observed plate-wide stress relaxation in Europe. This study is part of the Orogen research program and conducted in close collaboration with the BRGM (Bureau de Recherches Géologiques et Minières), the CNRS (Centre National de la Recherche Scientifique), and Total.

Present-day Kinematics of Papua New Guinea from GPS campaign measurements

NASA Astrophysics Data System (ADS)

Koulali Idrissi, A.; McClusky, S.; Tregoning, P.

2013-12-01

Papua New Guinea (PNG) is a complex tectonic region located in the convergence zone between the Australian and Pacific Plate. It occupies arguably one of the most tectonically complicated regions of the world, and its geodynamic evolution involves micro-plate rotation, lithospheric rupture forming ocean basins, arc-continent collision, subduction polarity reversal, collisional orogenesis, ophiolite obduction, and exhumation of high-pressure metamorphic (ultramafic) rocks. In this study we present a GPS derived velocity field based on 1993-2008 survey mode observations at 30 GPS sites. We combine our results with previously published GPS velocities to investigate the deformation in northern and northwestern Papua New Guinea. We use an elastic block model to invert the regional GPS velocities as well as earthquake slip vectors for poles of rotation of several micro-plates. The micro-plate block boundary fault geometry is based on geological mapping and regional seismicity. The results show that fault system north of the Highlands fold and thrust belt is the major boundary between the rigid Australian Plate and the north Highlands block, with convergence occurring at rates of between ~ 6 and 11.5 mm/yr. The relative motion across the northern Highlands block increases to the north to ~ 21-24 mm/yr, meaning that the New Guinea trench is likely accumulating elastic strain and confirming that the new Guinea Trench is an active inter-plate boundary. Our results also show, that the north New Guinea Highlands and the Papuan peninsula are best modelled as two blocks separated by a boundary through the Aure Fold belt Belt complex. This block boundary today is accommodating an estimated 4-5 mm/yr dextral motion. Our model also confirms previous results showing that the Ramu-Markham fault accommodates the deformation associated with the Finisterre arc-continent collision. This new GPS velocity field provides fresh insights into the details of the kinematics of the PNG present-day deformation.

A refined mixed shear flexible finite element for the nonlinear analysis of laminated plates

NASA Technical Reports Server (NTRS)

Putcha, N. S.; Reddy, J. N.

1986-01-01

The present study is concerned with the development of a mixed shear flexible finite element with relaxed continuity for the geometrically linear and nonlinear analysis of laminated anisotropic plates. The formulation of the element is based on a refined higher-order theory. This theory satisfies the zero transverse shear stress boundary conditions on the top and bottom faces of the plate. Shear correction coefficients are not needed. The developed element consists of 11 degrees-of-freedom per node, taking into account three displacements, two rotations, and six moment resultants. An evaluation of the element is conducted with respect to the accuracy obtained in the bending of laminated anistropic rectangular plates with different lamination schemes, loadings, and boundary conditions.

Stress intensities for cracks emanating from pin-loaded holes

NASA Technical Reports Server (NTRS)

Smith, C. W.; Jolles, M.; Peters, W. H.

1977-01-01

A series of stress freezing photoelastic experiments were conducted on large plates containing central holes with cracks emanating from the edge formed by the intersection of the hole with the plate surface. Loads were applied through rigid pins with neat fits in the holes. Stress-intensity factors (SIF) were estimated by a computer assisted least squares analysis of the photoelastic data taken from slices near the points of intersection of the flaw border with the hole boundary and the plate surface. Results indicate that the local mode of loading changes from Mode 1 near the hole boundary to mixed mode near the plate surface. The analysis is extended to include mixed mode loading, and results are compared with an existing approximate theory.

Microstructural evolution associated with martensitic transformation in Ni-Mn-Ga alloy

NASA Astrophysics Data System (ADS)

Li, Z.; Zhang, Y.; Esling, C.; Zhao, X.; Zuo, L.

2015-04-01

Based on the spatially resolved electron backscatter diffraction technique, the microstructural evolution accompanying the martensitic transformation (austenite to 7M martensite) and the intermartensitic transformation (7M martensite to NM martensite) was studied on a polycrystalline Ni53Mn22Ga25 alloy. Results show that the 7M martensite plate groups transformed from initial austenite have a diamond-shape with four twin-related variants. The 7M to NM intermartensitic transformation was accompanied by the thickening of martensite plates. With the experimental results, the characteristics of microstructural evolution during the phase transformations were further analyzed.

Deep-sea mud volcanoes - a window to alteration processes in old oceanic crust?

NASA Astrophysics Data System (ADS)

Hensen, Christian; Scholz, Florian; Nuzzo, Marianne; Valadares, Vasco; Terrinha, Pedro; Liebetrau, Volker; Kaul, Norbert; Manzoni, Sonia; Schmidt, Mark; Gràcia, Eulàlia

2013-04-01

A number of deep sea mud volcanoes (>4700 m water depth) were discovered during a recent expedition with the German research vessel Meteor along a prominent WSW-ENE trending strike-slip fault (SWIM 1; Zitellini et al., 2009) in the western extension of the Gulf of Cadiz (NE Atlantic). Mud volcanism was unambiguously related to tectonic activity along the fault and fluids expelled at these sites show a very distinct geochemical composition that has not been reported from any other mud volcano to date. In previous studies on deep-water mud volcanoes in the Western Gulf of Cadiz accretionary wedge it was hypothesized that the discharge fluids were affected by alteration processes occurring in the old (>140 Ma) and deeply buried (>4 km) oceanic crust (Scholz et al., 2009; Sallarès et al, 2011). This hypothesis is supported by recent findings at the mud volcanoes located to the west of the realm of tectonic deformation driven by the accretionary wedge of the Gulf of Cadiz. Pore water geochemical analyses revealed fluid sources from oceanic crust and oldest sedimentary strata. Regardless of the ultimate source, these findings suggest that large strike-slip faults may play a significant, yet unrecognized role in terms of fluid circulation and element redistribution. To date, hot vents and cold seeps occurring at active spreading centers and forearcs of subduction zones have been pinpointed as hotspots of fluid activity. However, bearing in mind that transform-type plate boundaries are equal in length compared to other types of plate boundaries, fluid exchange at this type of plate boundary may provide a similarly important pathway for water and element exchange between the lithosphere and ocean. Sallarès V., Gailler A., Gutscher M.-A., Graindorge D., Bartolomé R., Gràcia E., Díaz J., Dañobeitia J.J. and Zitellini N. (2011) Seismic evidence for the presence of Jurassic oceanic crust in the central Gulf of Cadiz (SW Iberian margin), Earth and Planetary Science Letters 311(1-2), 112-123. Scholz F., Hensen C., Reitz A., Romer R.L., Liebetrau V., Meixner A., Weise S.M., and Haeckel M. (2009) Isotopic evidence (87Sr/86Sr, δ7Li) for alteration of the oceanic crust at deep-rooted mud volcanoes in the Gulf of Cadiz, NE Atlantic Ocean. Geochimica et Cosmochimica Acta 73, 5444-5459. Zitellini N., Gràcia E., Matias L., Terrinha P., Abreu M.A., Dealteriis G., Henriet J.P., Dañobeitia J.J., Masson D.G., Mulder T., Ramella R., Somoza L., and Diez S. (2009) The quest for the Africa-Eurasia plate boundary west of the Strait of Gibraltar. Earth and Planetary Science Letters 280, 13-50.

Overview of Compact Toroidal Hybrid research program progress and plans

NASA Astrophysics Data System (ADS)

Maurer, David; Ennis, David; Hanson, James; Hartwell, Gregory; Herfindal, Jeffrey; Knowlton, Stephen; Ma, Xingxing; Pandya, Mihir; Roberds, Nicholas; Ross, Kevin; Traverso, Peter

2016-10-01

disruptive behavior on the level of applied 3D magnetic shaping; (2) test and advance the V3FIT reconstruction code and NIMROD modeling of CTH; and (3) study the implementation of an island divertor. Progress towards these goals and other developments are summarized. The disruptive density limit exceeds the Greenwald limit as the vacuum transform is increased, but a threshold for avoidance is not observed. Low- q disruptions, with 1.1 < q (a) <2.0, cease to occur if the vacuum transform is raised above 0.07. Application of vacuum transform can reduce and eliminate the vertical drift of elongated discharges that would otherwise be vertically unstable. Reconstructions using external magnetics give accurate estimates for quantities near the plasma boundary, and internal diagnostics have been implemented to extend the range of accuracy into the plasma core. Sawtooth behavior has been reproducibly modified with external transform and NIMROD is used to model these observations and reproduces experimental trends. An island divertor design has begun with connection length studies to model energy deposition on divertor plates located in an edge 1/3 island as well as the study of a non-resonant divertor configuration. This work is supported by U.S. Department of Energy Grant No. DE-FG02-00ER54610.

Global Dynamic Numerical Simulations of Plate Tectonic Reorganizations

NASA Astrophysics Data System (ADS)

Morra, G.; Quevedo, L.; Butterworth, N.; Matthews, K. J.; Müller, D.

2010-12-01

We use a new numerical approach for global geodynamics to investigate the origin of present global plate motion and to identify the causes of the last two global tectonic reorganizations occurred about 50 and 100 million years ago (Ma) [1]. While the 50 Ma event is the most well-known global plate-mantle event, expressed by the bend in the Hawaiian-Emperor volcanic chain, a prominent plate reorganization at about 100 Ma, although presently little studied, is clearly indicated by a major bend in the fracture zones in the Indian Ocean and by a change in Pacific plate motion [2]. Our workflow involves turning plate reconstructions into surface meshes that are subsequently employed as initial conditions for global Boundary Element numerical models. The tectonic setting that anticipates the reorganizations is processed with the software GPlates, combining the 3D mesh of the paleo-plate morphology and the reconstruction of paleo-subducted slabs, elaborated from tectonic history [3]. All our models involve the entire planetary system, are fully dynamic, have free surface, are characterized by a spectacular computational speed due to the simultaneous use of the multi-pole algorithm and the Boundary Element formulation and are limited only by the use of sharp material property variations [4]. We employ this new tool to unravel the causes of plate tectonic reorganizations, producing and comparing global plate motion with the reconstructed ones. References: [1] Torsvik, T., Müller, R.D., Van der Voo, R., Steinberger, B., and Gaina, C., 2008, Global Plate Motion Frames: Toward a unified model: Reviews in Geophysics, VOL. 46, RG3004, 44 PP., 2008 [2] Wessel, P. and Kroenke, L.W. Pacific absolute plate motion since 145 Ma: An assessment of the fixed hot spot hypothesis. Journal of Geophysical Research, Vol 113, B06101, 2008 [3] L. Quevedo, G. Morra, R. D. Mueller. Parallel Fast Multipole Boundary Element Method for Crustal Dynamics, Proceeding 9th World Congress and 4th Asian Pacific Congress on Computational Mechanics, July 2010, iopscience.iop.org/1757-899X/10/1/012012. [4] G. Morra, P. Chatelain, P. Tackley and P. Koumoutzakos, 2007, Large scale three-dimensional boundary element simulation of subduction, in Proceeding International Conference on Computational Science - Part III, LNCS 4489, pp. 1122-1129. Interaction between two subducting slabs.

The brittle-ductile transition in porous sedimentary rocks: geological implications for accretionary wedge aseismicity

NASA Astrophysics Data System (ADS)

Zhang, Jiaxiang; Davis, Dan M.; Wong, Teng-Fong

1993-07-01

Thrusting earthquakes in subduction zones generally occur along only part of the plate boundary, with motion along the shallowest part of the plate boundary occurring ascismically. The maximum size of subduction boundary thrust earthquakes depends strongly upon the down-dip width of the seismogenic zone. The single most uncertain factor in determining that width is the location of the up-dip limit of the zone (the seismic front), which depends upon the mechanical state of the sedimentary rocks in the plate boundary zone. In order to come to a better understanding of the seismic potential of sediments in a subduction zone, we carried out a series of triaxial experiments on Berea and Kayenta sandstones. Based on our experimental data, a brittle-ductile transition map was constructed showing that both porosity and effective pressure are important factors controlling the transition from brittle to macroscopically ductile behavior in porous rocks. In the brittle field, a sample fails by shear localization on one slip plane accompanied by strain softening and dilatancy, whereas in the ductile field, a sample deforms homogeneously with a constant yield stress or slight hardening. By comparing such a map with the estimated porosity profile of an accretionary wedge, the likely nature and rough location of the boundary between brittle and ductile behavior can be inferred. If the sediments along a plate boundary are too young and undercompacted to be capable of brittle shear localization, then their deformation is likely to be aseismic. In this way, it may be possible for even a very broad fore-arcs to produce no great earthquakes. However, great earthquakes are to be expected at margins that have large zones of plate contact along which many sediments are compacted and well lithified. Such rocks are expected to be capable of shear localization and brittle failure with the potential for stick-slip behavior.

A review of turbulent-boundary-layer heat transfer research at Stanford, 1958-1983

NASA Technical Reports Server (NTRS)

Moffat, R. J.; Kays, W. M.

1984-01-01

For the past 25 years, there has existed in the Thermosciences Laboratory of the Mechanical Engineering Department of Stanford University a research program, primarily experimental, concerned with heat transfer through turbulent boundary layers. In the early phases of the program, the topics considered were the simple zero-pressure-gradient turbulent boundary layer with constant and with varying surface temperature, and the accelerated boundary layer. Later equilibrium boundary layers were considered along with factors affecting the boundary layer, taking into account transpired flows, flows with axial pressure gradients, transpiration, acceleration, deceleration, roughness, full-coverage film cooling, surface curvature, free convection, and mixed convection. A description is provided of the apparatus and techniques used, giving attention to the smooth plate rig, the rough plate rig, the full-coverage film cooling rig, the curvature rig, the concave wall rig, the mixed convection tunnel, and aspects of data reduction and uncertainty analysis.

Bootstrap current control studies in the Wendelstein 7-X stellarator using the free-plasma-boundary version of the SIESTA MHD equilibrium code

NASA Astrophysics Data System (ADS)

Peraza-Rodriguez, H.; Reynolds-Barredo, J. M.; Sanchez, R.; Tribaldos, V.; Geiger, J.

2018-02-01

The recently developed free-plasma-boundary version of the SIESTA MHD equilibrium code (Hirshman et al 2011 Phys. Plasmas 18 062504; Peraza-Rodriguez et al 2017 Phys. Plasmas 24 082516) is used for the first time to study scenarios with considerable bootstrap currents for the Wendelstein 7-X (W7-X) stellarator. Bootstrap currents in the range of tens of kAs can lead to the formation of unwanted magnetic island chains or stochastic regions within the plasma and alter the boundary rotational transform due to the small shear in W7-X. The latter issue is of relevance since the island divertor operation of W7-X relies on a proper positioning of magnetic island chains at the plasma edge to control the particle and energy exhaust towards the divertor plates. Two scenarios are examined with the new free-plasma-boundary capabilities of SIESTA: a freely evolving bootstrap current one that illustrates the difficulties arising from the dislocation of the boundary islands, and a second one in which off-axis electron cyclotron current drive (ECCD) is applied to compensate the effects of the bootstrap current and keep the island divertor configuration intact. SIESTA finds that off-axis ECCD is indeed able to keep the location and phase of the edge magnetic island chain unchanged, but it may also lead to an undesired stochastization of parts of the confined plasma if the EC deposition radial profile becomes too narrow.

Structure and composition of the plate-boundary slip zone for the 2011 Tohoku-Oki earthquake.

PubMed

Chester, Frederick M; Rowe, Christie; Ujiie, Kohtaro; Kirkpatrick, James; Regalla, Christine; Remitti, Francesca; Moore, J Casey; Toy, Virginia; Wolfson-Schwehr, Monica; Bose, Santanu; Kameda, Jun; Mori, James J; Brodsky, Emily E; Eguchi, Nobuhisa; Toczko, Sean

2013-12-06

The mechanics of great subduction earthquakes are influenced by the frictional properties, structure, and composition of the plate-boundary fault. We present observations of the structure and composition of the shallow source fault of the 2011 Tohoku-Oki earthquake and tsunami from boreholes drilled by the Integrated Ocean Drilling Program Expedition 343 and 343T. Logging-while-drilling and core-sample observations show a single major plate-boundary fault accommodated the large slip of the Tohoku-Oki earthquake rupture, as well as nearly all the cumulative interplate motion at the drill site. The localization of deformation onto a limited thickness (less than 5 meters) of pelagic clay is the defining characteristic of the shallow earthquake fault, suggesting that the pelagic clay may be a regionally important control on tsunamigenic earthquakes.

Survey explores active tectonics in northeastern Caribbean

USGS Publications Warehouse

Carbó, A.; Córdoba, D.; Muñoz-Martín, A.; Granja, J.L.; Martín-Dávila, J.; Pazos, A.; Catalán, M.; Gómez, M.; ten Brink, Uri S.; von Hillebrandt, Christa; Payero, J.

2005-01-01

There is renewed interest in studying the active and complex northeastern Caribbean plate boundary to better understand subduction zone processes and for earthquake and tsunami hazard assessments [e.g., ten Brink and Lin, 2004; ten Brink et al., 2004; Grindlay et al., 2005]. To study the active tectonics of this plate boundary, the GEOPRICO-DO (Geological, Puerto Rico-Dominican) marine geophysical cruise, carried out between 28 March and 17 April 2005 (Figure 1), studied the active tectonics of this plate boundary.Initial findings from the cruise have revealed a large underwater landslide, and active faults on the seafloor (Figures 2a and 2c). These findings indicate that the islands within this region face a high risk from tsunami hazards, and that local governments should be alerted in order to develop and coordinate possible mitigation strategies.

Earthquakes in the Orozco transform zone: seismicity, source mechanisms, and tectonics

USGS Publications Warehouse

Tréhu, Anne M.; Solomon, Sean C.

1983-01-01

As part of the Rivera Ocean Seismic Experiment, a network of ocean bottom seismometers and hydrophones was deployed in order to determine the seismic characteristics of the Orozco transform fault in the central eastern Pacific. We present hypocentral locations and source mechanisms for 70 earthquakes recorded by this network. All epicenters are within the transform region of the Orozco Fracture Zone and clearly delineate the active plate boundary. About half of the epicenters define a narrow line of activity parallel to the spreading direction and situated along a deep topographic trough that forms the northern boundary of the transform zone (region 1). Most focal depths for these events are very shallow, within 4 km of the seafloor; several well-determined focal depths, however, are as great as 7 km. No shallowing of seismic activity is observed as the rise-transform intersection is approached; to the contrary, the deepest events are within 10 km of the intersection. First motion polarities for most of the earthquakes in region 1 are compatible with right-lateral strike slip faulting along a nearly vertical plane, striking parallel to the spreading direction. Another zone of activity is observed in the central part of the transform (region 2). The apparent horizontal and vertical distribution of activity in this region is more scattered than in the first, and the first motion radiation patterns of these events do not appear to be compatible with any known fault mechanism. Pronounced lateral variations in crustal velocity structure are indicated for the transform region from refraction data and measurements of wave propagation directions. The effect of this lateral heterogeneity on hypocenters and fault plane solutions is evaluated by tracing rays through a three-dimensional velocity grid. While findings for events in region 1 are not significantly affected, in region 2, epicentral mislocations of up to 10 km and azimuthal deflections of up to 45° may result from assuming a laterally homogeneous velocity structure. When corrected for the effects of lateral heterogeneity, the epicenters and fault plane solutions for earthquakes in region 2 are compatible with predominantly normal faulting along a topographic trough trending NW–SE; the focal depths, however, are poorly constrained. These results suggest an en echelon spreading center or leaky transform regime in the central transform region.

Mechanical deformation model of the western United States instantaneous strain-rate field

USGS Publications Warehouse

Pollitz, F.F.; Vergnolle, M.

2006-01-01

We present a relationship between the long-term fault slip rates and instantaneous velocities as measured by Global Positioning System (GPS) or other geodetic measurements over a short time span. The main elements are the secularly increasing forces imposed by the bounding Pacific and Juan de Fuca (JdF) plates on the North American plate, viscoelastic relaxation following selected large earthquakes occurring on faults that are locked during their respective interseismic periods, and steady slip along creeping portions of faults in the context of a thin-plate system. In detail, the physical model allows separate treatments of faults with known geometry and slip history, faults with incomplete characterization (i.e. fault geometry but not necessarily slip history is available), creeping faults, and dislocation sources distributed between the faults. We model the western United States strain-rate field, derived from 746 GPS velocity vectors, in order to test the importance of the relaxation from historic events and characterize the tectonic forces imposed by the bounding Pacific and JdF plates. Relaxation following major earthquakes (M ??? 8.0) strongly shapes the present strain-rate field over most of the plate boundary zone. Equally important are lateral shear transmitted across the Pacific-North America plate boundary along ???1000 km of the continental shelf, downdip forces distributed along the Cascadia subduction interface, and distributed slip in the lower lithosphere. Post-earthquake relaxation and tectonic forcing, combined with distributed deep slip, constructively interfere near the western margin of the plate boundary zone, producing locally large strain accumulation along the San Andreas fault (SAF) system. However, they destructively interfere further into the plate interior, resulting in smaller and more variable strain accumulation patterns in the eastern part of the plate boundary zone. Much of the right-lateral strain accumulation along the SAF system is systematically underpredicted by models which account only for relaxation from known large earthquakes. This strongly suggests that in addition to viscoelastic-cycle effects, steady deep slip in the lower lithosphere is needed to explain the observed strain-rate field. ?? 2006 The Authors Journal compilation ?? 2006 RAS.

SubductionGenerator: A program to build three-dimensional plate configurations

NASA Astrophysics Data System (ADS)

Jadamec, M. A.; Kreylos, O.; Billen, M. I.; Turcotte, D. L.; Knepley, M.

2016-12-01

Geologic, geochemical, and geophysical data from subduction zones indicate that a two-dimensional paradigm for plate tectonic boundaries is no longer adequate to explain the observations. Many open source software packages exist to simulate the viscous flow of the Earth, such as the dynamics of subduction. However, there are few open source programs that generate the three-dimensional model input. We present an open source software program, SubductionGenerator, that constructs the three-dimensional initial thermal structure and plate boundary structure. A 3D model mesh and tectonic configuration are constructed based on a user specified model domain, slab surface, seafloor age grid file, and shear zone surface. The initial 3D thermal structure for the plates and mantle within the model domain is then constructed using a series of libraries within the code that use a half-space cooling model, plate cooling model, and smoothing functions. The code maps the initial 3D thermal structure and the 3D plate interface onto the mesh nodes using a series of libraries including a k-d tree to increase efficiency. In this way, complicated geometries and multiple plates with variable thickness can be built onto a multi-resolution finite element mesh with a 3D thermal structure and 3D isotropic shear zones oriented at any angle with respect to the grid. SubductionGenerator is aimed at model set-ups more representative of the earth, which can be particularly challenging to construct. Examples include subduction zones where the physical attributes vary in space, such as slab dip and temperature, and overriding plate temperature and thickness. Thus, the program can been used to construct initial tectonic configurations for triple junctions and plate boundary corners.

Peculiarities of the tectonic and magma evolution of the southwestern Indian middle-ocean crust within the range of 51°-67° eastern longitude

NASA Astrophysics Data System (ADS)

Shreider, A. A.; Kashintsev, G. L.

2010-02-01

The comparative estimation of the parameters of the lithosphere of the Mid-Ocean Southwestern Indian range in the areas westwards and eastwards of the Atlantis II transform fault zone shows that, within this zone, an alteration in the basalt composition occurred. Eastwards of this zone, a decrease of the anomaly of the magnetic field occurred and increased average depths of the axial part (4.7 km) and thinning (up to 4-5 km) of the ocean crust with increased rates of seismic waves in the upper mantle were observed. This, first of all, indicates an anomalously cold mantle below the oceanic crust. The changes that occurred in the location of the Euler pole within the last millions of years resulted in slanting spreading in the area of the investigation with rates of opening lower than 1.8 cm/year probably accompanied by the phenomena of transtension in the active parts of the transform faults. The interaction between the Landly and Somali lithosphere plates occurred along the diffusion boundary and was accompanied by problems with tracing the chrones between the neighboring profiles of geomagnetic observations. Consequently, the more detailed investigation of the configuration of the diffusion boundary will contribute to the more accurate reconstruction of the paleogeodynamics of the central part of the Indian Ocean.

The Presence of Dense Material in the Deep Mantle: Implications for Plate Motion

NASA Astrophysics Data System (ADS)

Stein, C.; Hansen, U.

2017-12-01

The dense material in the deep mantle strongly interacts with the convective flow in the mantle. On the one hand, it has a restoring effect on rising plumes. On the other hand, the dense material is swept about by the flow forming dense piles. Consequently this affects the plate motion and, in particular, the onset time and the style of plate tectonics varies considerably for different model scenarios. In this study we apply a thermochemical mantle convection model combined with a rheological model (temperature- and stress-dependent viscosity) that allows for plate formation according to the convective flow. The model's starting condition is the post-magma ocean period. We analyse a large number of model scenarios ranging from variations in thickness, density and depth of a layer of dense material to different initial temperatures.Furthermore, we present a mechanism in which the dense layer at the core-mantle boundary forms without prescribing the thickness or the density contrast. Due to advection-assisted diffusion, long-lived piles can be established that act on the style of convection and therefore on plate motion. We distinguish between the subduction-triggered regime with early plate tectonics and the plume-triggered regime with a late onset of plate tectonics. The formation of piles by advection-assisted diffusion is a typical phenomenon that appears not only at the lower boundary, but also at internal boundaries that form in the layering phase during the evolution of the system.

Sensor for Boundary Shear Stress in Fluid Flow

NASA Technical Reports Server (NTRS)

Bao, Xiaoqi; Badescu, Mircea; Sherrit, Stewart; Bar-Cohen, Yoseph; Lih, Shyh-Shiuh; Chang, Zensheu; Trease, Brian P.; Kerenyi, Kornel; Widholm, Scott E.; Ostlund, Patrick N.

2012-01-01

The formation of scour patterns at bridge piers is driven by the forces at the boundary of the water flow. In most experimental scour studies, indirect processes have been applied to estimate the shear stress using measured velocity profiles. The estimations are based on theoretical models and associated assumptions. However, the turbulence flow fields and boundary layer in the pier-scour region are very complex and lead to low-fidelity results. In addition, available turbulence models cannot account accurately for the bed roughness effect. Direct measurement of the boundary shear stress, normal stress, and their fluctuations are attractive alternatives. However, most direct-measurement shear sensors are bulky in size or not compatible to fluid flow. A sensor has been developed that consists of a floating plate with folded beam support and an optical grid on the back, combined with a high-resolution optical position probe. The folded beam support makes the floating plate more flexible in the sensing direction within a small footprint, while maintaining high stiffness in the other directions. The floating plate converts the shear force to displacement, and the optical probe detects the plate s position with nanometer resolution by sensing the pattern of the diffraction field of the grid through a glass window. This configuration makes the sensor compatible with liquid flow applications.

Transitional and turbulent flat-plate boundary layers with heat transfer

NASA Astrophysics Data System (ADS)

Wu, Xiaohua; Moin, Parviz

2010-11-01

We report on our direct numerical simulation of two incompressible, nominally zero-pressure-gradient flat-plate boundary layers from momentum thickness Reynolds number 80 to 1950. Heat transfer between the constant-temperature solid surface and the free-stream is also simulated with molecular Prandtl number=1. Throughout the entire flat-plate, the ratio of Stanton number and skin-friction St/Cfdeviates from the exact Reynolds analogy value of 0.5 by less than 1.5%. Turbulent Prandtl number t peaks at the wall. Preponderance of hairpin vortices is observed in both the transitional and turbulent regions of the boundary layers. In particular, the internal structure of merged turbulent spots is hairpin forest; the internal structure of infant turbulent spots is hairpin packet. Numerous hairpin vortices are readily detected in both the near-wall and outer regions of the boundary layers up to momentum thickness Reynolds number 1950. This suggests that the hairpin vortices in the turbulent region are not simply the aged hairpin forests convected from the upstream transitional region. Temperature iso-surfaces in the companion thermal boundary layers are found to be a useful tracer in identifying hairpin vortex structures.

Zoogeography of the San Andreas Fault system: Great Pacific Fracture Zones correspond with spatially concordant phylogeographic boundaries in western North America.

PubMed

Gottscho, Andrew D

2016-02-01

The purpose of this article is to provide an ultimate tectonic explanation for several well-studied zoogeographic boundaries along the west coast of North America, specifically, along the boundary of the North American and Pacific plates (the San Andreas Fault system). By reviewing 177 references from the plate tectonics and zoogeography literature, I demonstrate that four Great Pacific Fracture Zones (GPFZs) in the Pacific plate correspond with distributional limits and spatially concordant phylogeographic breaks for a wide variety of marine and terrestrial animals, including invertebrates, fish, amphibians, reptiles, birds, and mammals. These boundaries are: (1) Cape Mendocino and the North Coast Divide, (2) Point Conception and the Transverse Ranges, (3) Punta Eugenia and the Vizcaíno Desert, and (4) Cabo Corrientes and the Sierra Transvolcanica. However, discussion of the GPFZs is mostly absent from the zoogeography and phylogeography literature likely due to a disconnect between biologists and geologists. I argue that the four zoogeographic boundaries reviewed here ultimately originated via the same geological process (triple junction evolution). Finally, I suggest how a comparative phylogeographic approach can be used to test the hypothesis presented here. © 2014 Cambridge Philosophical Society.

Motion of Caribbean Plate during last 7 million years and implications for earlier Cenozoic movements

NASA Astrophysics Data System (ADS)

Sykes, Lynn R.; McCann, William R.; Kafka, Alan L.

1982-12-01

The direction and rate of movement of the Caribbean plate with respect to North America are determined from the slip vectors of shallow earthquakes and from the configuration of downgoing seismic zones in the Greater and Lesser Antilles. A calibration of the relative plate motion for the northeastern Caribbean using data from other subduction zones indicates an average rate of 3.7±0.5 cm/yr for the past 7 million years (Ma). The direction of plate motion inferred from focal mechanisms (ENE) is nearly the same as that deduced from the configuration of downgoing seismic zones going around the major bend in the arc. With respect to North America, the Caribbean plate is moving at an angular velocity of 0.36°/Ma about a center of rotation near 66°N, 132°W. Vector addition using those data and that for the relative motion of North and South America indicates that the Caribbean is moving at an angular velocity of 0.47°/Ma about a center of rotation near 60°N, 88°W with respect to South America. The presence of intermediate-depth earthquakes beneath Puerto Rico and the Virgin Islands is ascribed to the curvature of the plate boundary and a component of underthrusting that has been going on for at least the past 7 Ma and is likely occurring today. The alternative hypothesis that earthquakes beneath those areas are occurring in materials that were subducted during the Eocene, the last major episode of magmatism, is not tenable from thermal considerations. The lack of recent magmatism in the eastern Greater Antilles is ascribed to the relatively small component of underthrusting. The 2 cm/yr rate of seafloor creation along the mid-Cayman spreading center for the past 2.4 Ma does not appear to reflect the total Caribbean-North American plate motion while the 4 cm/yr spreading rate from 6.0 to 2.4 Ma does. Between the mid-Cayman spreading center and eastern Guatemala, the northern boundary of the Caribbean plate is narrow and follows the southern margin of the Cayman trough. Seismic activity between the spreading center and eastern Hispaniola, however, occurs over a zone about 250 km wide that extends from Cuba to Jamaica and across the entire width of Hispaniola. Individual faults within this broad plate boundary appear to have accommodated differing amounts of motion as a function of geological time while the cumulative plate motion across the zone remained nearly constant. The percentage of total plate motion accommodated near southern Hispaniola and Jamaica is inferred to have increased about 2.4 Ma ago. That change may have been caused by the collision of parts of the Bahama bank and northern Hispaniola. This explanation for the sudden decrease in seafloor creation along the mid-Cayman spreading center is less catastrophist than the hypothesis that the entire Caribbean plate suddenly changed its velocity with respect to surrounding plates. The Caribbean plate may be regarded as a small buffer plate whose motion is now governed by the movement of the larger North and South American plates which bound it on three sides. The Caribbean plate is either at rest or moving eastward at a rate of no more than 1 cm/yr in the hot spot reference frame. Since the relative motion of the larger plates surrounding the Caribbean has been nearly constant for the last 38 Ma (anomaly 13 time) and since the forces on the Caribbean plate do not appear to have changed greatly during that interval, we extrapolate the motion of the last 7 Ma back to 38 Ma. A reconstruction for the late Eocene places the Caribbean plate about 1400 km west of its present position. The faster rate of plate motion we calculate makes it more likely that the lithosphere beneath the basins of the Caribbean originated in the Pacific. It also has implications for the seismic potential of the region, paleocirculation in the Atlantic Ocean and origin of sediments in the area. Our late Eocene reconstruction aligns the eastern continental margin of Yucatan with that along the southeast side of the Nicaragua rise. This 2500-km-long feature may have acted as an arc-arc transform fault from the late Mesozoic to the late Eocene. Arc-related rocks of those ages in the Greater Antilles and northern Lesser Antilles define a northwesterly trending subduction zone along the northeastern edge of the former East Pacific-Caribbean plate. At least three fragments of anomalous seafloor have been sutured onto Hispaniola in the past 50 Ma.

Gradual unlocking of plate boundary controlled initiation of the 2014 Iquique earthquake.

PubMed

Schurr, Bernd; Asch, Günter; Hainzl, Sebastian; Bedford, Jonathan; Hoechner, Andreas; Palo, Mauro; Wang, Rongjiang; Moreno, Marcos; Bartsch, Mitja; Zhang, Yong; Oncken, Onno; Tilmann, Frederik; Dahm, Torsten; Victor, Pia; Barrientos, Sergio; Vilotte, Jean-Pierre

2014-08-21

On 1 April 2014, Northern Chile was struck by a magnitude 8.1 earthquake following a protracted series of foreshocks. The Integrated Plate Boundary Observatory Chile monitored the entire sequence of events, providing unprecedented resolution of the build-up to the main event and its rupture evolution. Here we show that the Iquique earthquake broke a central fraction of the so-called northern Chile seismic gap, the last major segment of the South American plate boundary that had not ruptured in the past century. Since July 2013 three seismic clusters, each lasting a few weeks, hit this part of the plate boundary with earthquakes of increasing peak magnitudes. Starting with the second cluster, geodetic observations show surface displacements that can be associated with slip on the plate interface. These seismic clusters and their slip transients occupied a part of the plate interface that was transitional between a fully locked and a creeping portion. Leading up to this earthquake, the b value of the foreshocks gradually decreased during the years before the earthquake, reversing its trend a few days before the Iquique earthquake. The mainshock finally nucleated at the northern end of the foreshock area, which skirted a locked patch, and ruptured mainly downdip towards higher locking. Peak slip was attained immediately downdip of the foreshock region and at the margin of the locked patch. We conclude that gradual weakening of the central part of the seismic gap accentuated by the foreshock activity in a zone of intermediate seismic coupling was instrumental in causing final failure, distinguishing the Iquique earthquake from most great earthquakes. Finally, only one-third of the gap was broken and the remaining locked segments now pose a significant, increased seismic hazard with the potential to host an earthquake with a magnitude of >8.5.

The lithosphere-asthenosphere boundary beneath the South Island of New Zealand

NASA Astrophysics Data System (ADS)

Hua, Junlin; Fischer, Karen M.; Savage, Martha K.

2018-02-01

Lithosphere-asthenosphere boundary (LAB) properties beneath the South Island of New Zealand have been imaged by Sp receiver function common-conversion point stacking. In this transpressional boundary between the Australian and Pacific plates, dextral offset on the Alpine fault and convergence have occurred for the past 20 My, with the Alpine fault now bounded by Australian plate subduction to the south and Pacific plate subduction to the north. Using data from onland seismometers, especially the 29 broadband stations of the New Zealand permanent seismic network (GeoNet), we obtained 24,971 individual receiver functions by extended-time multi-taper deconvolution, and mapped them to three-dimensional space using a Fresnel zone approximation. Pervasive strong positive Sp phases are observed in the LAB depth range indicated by surface wave tomography. These phases are interpreted as conversions from a velocity decrease across the LAB. In the central South Island, the LAB is observed to be deeper and broader to the northwest of the Alpine fault. The deeper LAB to the northwest of the Alpine fault is consistent with models in which oceanic lithosphere attached to the Australian plate was partially subducted, or models in which the Pacific lithosphere has been underthrust northwest past the Alpine fault. Further north, a zone of thin lithosphere with a strong and vertically localized LAB velocity gradient occurs to the northwest of the fault, juxtaposed against a region of anomalously weak LAB conversions to the southeast of the fault. This structure could be explained by lithospheric blocks with contrasting LAB properties that meet beneath the Alpine fault, or by the effects of Pacific plate subduction. The observed variations in LAB properties indicate strong modification of the LAB by the interplay of convergence and strike-slip deformation along and across this transpressional plate boundary.

Buckling transition and boundary layer in non-Euclidean plates.

PubMed

Efrati, Efi; Sharon, Eran; Kupferman, Raz

2009-07-01

Non-Euclidean plates are thin elastic bodies having no stress-free configuration, hence exhibiting residual stresses in the absence of external constraints. These bodies are endowed with a three-dimensional reference metric, which may not necessarily be immersible in physical space. Here, based on a recently developed theory for such bodies, we characterize the transition from flat to buckled equilibrium configurations at a critical value of the plate thickness. Depending on the reference metric, the buckling transition may be either continuous or discontinuous. In the infinitely thin plate limit, under the assumption that a limiting configuration exists, we show that the limit is a configuration that minimizes the bending content, among all configurations with zero stretching content (isometric immersions of the midsurface). For small but finite plate thickness, we show the formation of a boundary layer, whose size scales with the square root of the plate thickness and whose shape is determined by a balance between stretching and bending energies.

Dynamic behaviour of thin composite plates for different boundary conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sprintu, Iuliana, E-mail: sprintui@yahoo.com, E-mail: rotaruconstantin@yahoo.com; Rotaru, Constantin, E-mail: sprintui@yahoo.com, E-mail: rotaruconstantin@yahoo.com

2014-12-10

In the context of composite materials technology, which is increasingly present in industry, this article covers a topic of great interest and theoretical and practical importance. Given the complex design of fiber-reinforced materials and their heterogeneous nature, mathematical modeling of the mechanical response under different external stresses is very difficult to address in the absence of simplifying assumptions. In most structural applications, composite structures can be idealized as beams, plates, or shells. The analysis is reduced from a three-dimensional elasticity problem to a oneor two-dimensional problem, based on certain simplifying assumptions that can be made because the structure is thin.more » This paper aims to validate a mathematical model illustrating how thin rectangular orthotropic plates respond to the actual load. Thus, from the theory of thin plates, new analytical solutions are proposed corresponding to orthotropic rectangular plates having different boundary conditions. The proposed analytical solutions are considered both for solving equation orthotropic rectangular plates and for modal analysis.« less

MHD Flow of Sodium Alginate-Based Casson Type Nanofluid Passing Through A Porous Medium With Newtonian Heating.

PubMed

Khan, Arshad; Khan, Dolat; Khan, Ilyas; Ali, Farhad; Karim, Faizan Ul; Imran, Muhammad

2018-06-05

Casson nanofluid, unsteady flow over an isothermal vertical plate with Newtonian heating (NH) is investigated. Sodium alginate (base fluid)is taken as counter example of Casson fluid. MHD and porosity effects are considered. Effects of thermal radiation along with heat generation are examined. Sodium alginate with Silver, Titanium oxide, Copper and Aluminum oxide are added as nano particles. Initial value problem with physical boundary condition is solved by using Laplace transform method. Exact results are obtained for temperature and velocity fields. Skin-friction and Nusselt number are calculated. The obtained results are analyzed graphically for emerging flow parameters and discussed. It is bring into being that temperature and velocity profile are decreasing with increasing nano particles volume fraction.

Development of a three-dimensional Navier-Stokes code on CDC star-100 computer

NASA Technical Reports Server (NTRS)

Vatsa, V. N.; Goglia, G. L.

1978-01-01

A three-dimensional code in body-fitted coordinates was developed using MacCormack's algorithm. The code is structured to be compatible with any general configuration, provided that the metric coefficients for the transformation are available. The governing equations are developed in primitive variables in order to facilitate the incorporation of physical boundary conditions and turbulence-closure models. MacCormack's two-step, unsplit, time-marching algorithm is used to solve the unsteady Navier-Stokes equations until steady-state solution is achieved. Cases discussed include (1) flat plate in supersonic free stream; (2) supersonic flow along an axial corner; (3) subsonic flow in an axial corner at M infinity = 0.95; and (4) supersonic flow in an axial corner at M infinity 1.5.

Hydroelastic behaviour of a structure exposed to an underwater explosion.

PubMed

Colicchio, G; Greco, M; Brocchini, M; Faltinsen, O M

2015-01-28

The hydroelastic interaction between an underwater explosion and an elastic plate is investigated num- erically through a domain-decomposition strategy. The three-dimensional features of the problem require a large computational effort, which is reduced through a weak coupling between a one-dimensional radial blast solver, which resolves the blast evolution far from the boundaries, and a three-dimensional compressible flow solver used where the interactions between the compression wave and the boundaries take place and the flow becomes three-dimensional. The three-dimensional flow solver at the boundaries is directly coupled with a modal structural solver that models the response of the solid boundaries like elastic plates. This enables one to simulate the fluid-structure interaction as a strong coupling, in order to capture hydroelastic effects. The method has been applied to the experimental case of Hung et al. (2005 Int. J. Impact Eng. 31, 151-168 (doi:10.1016/j.ijimpeng.2003.10.039)) with explosion and structure sufficiently far from other boundaries and successfully validated in terms of the evolution of the acceleration induced on the plate. It was also used to investigate the interaction of an underwater explosion with the bottom of a close-by ship modelled as an orthotropic plate. In the application, the acoustic phase of the fluid-structure interaction is examined, highlighting the need of the fluid-structure coupling to capture correctly the possible inception of cavitation. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Two-axis direct fluid shear stress sensor

NASA Technical Reports Server (NTRS)

Bajikar, Sateesh (Inventor); Scott, Michael A. (Inventor); Adcock, Edward E. (Inventor)

2011-01-01

A micro sized multi-axis semiconductor skin friction/wall shear stress induced by fluid flow. The sensor design includes a shear/strain transduction gimble connected to a force collecting plate located at the flow boundary surface. The shear force collecting plate is interconnected by an arm to offset the tortional hinges from the fluid flow. The arm is connected to the shear force collecting plate through dual axis torsional hinges with piezoresistive torsional strain gauges. These gauges are disposed on the tortional hinges and provide a voltage output indicative of applied shear stress acting on the force collection plate proximate the flow boundary surface. Offsetting the torsional hinges creates a force concentration and resolution structure that enables the generation of a large stress on the strain gauge from small shear stress, or small displacement of the collecting plate. The design also isolates the torsional sensors from exposure to the fluid flow.

Phase Transitions of MgO Along the Hugoniot (Invited)

NASA Astrophysics Data System (ADS)

Root, S.; Shulenburger, L.; Lemke, R. W.; Cochrane, K. R.; Mattsson, T. R.

2013-12-01

The formation of terrestrial planets and planetary structure has become of great interest because of recent exoplanet discoveries of super earths. MgO is a major constituent of Earth's mantle, the rocky cores of gas giants such as Jupiter, and likely constitutes the interiors of many exoplanets. The high pressure - high temperature behavior of MgO directly affects equation of state models for planetary structure and formation. In this work, we examine single crystal MgO under shock compression utilizing experimental and density functional theory (DFT) methods to determine phase transformations along the Hugoniot. We perform plate impact experiments using Sandia's Z - facility on MgO up to 11.6 Mbar. The plate impact experiments generate highly accurate Hugoniot state data. The experimental results show the B1 - B2 solid - solid phase transition occurs near 4 Mbar on the Hugoniot. The solid - liquid transition is determined to be near 7 Mbar with a large region of B2-liquid coexistence. Using DFT methods, we also determine melt along the B1 and B2 solid phase boundaries as well as along the Hugoniot. The combined experimental and DFT results have determined the phase boundaries along the Hugoniot, which can be implemented into new planetary and EOS models. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Securities Administration under Contract No. DE-AC04-94AL85000.

Subsurface signature of North Anatolian Fault Zone and its relation with old sutures: New insight from receiver function analysis.

NASA Astrophysics Data System (ADS)

Özacar, Arda A.; Abgarmi, Bizhan

2017-04-01

The North Anatolian Fault Zone (NAFZ) is an active continental transform plate boundary that accommodates the westward extrusion of the Anatolian plate. The central segment of NAFZ displays northward convex surface trace which coincides partly with the Paleo-Tethyan suture formed during the early Cenozoic. The depth extent and detailed structure of the actively deforming crust along the NAF is still under much debate and processes responsible from rapid uplift are enigmatic. In this study, over five thousand high quality P receiver functions are computed using teleseismic earthquakes recorded by permanent stations of national agencies and temporary North Anatolian Fault Passive Seismic experiment (2005-2008). In order to map the crustal thickness and Vp/Vs variations accurately, the study area is divided into grids with 20 km spacing and along each grid line Moho phase and its multiples are picked through constructed common conversion point (CCP) profiles. According to our results, nature of discontinuities and crustal thickness display sharp changes across the main strand of NAFZ supporting a lithospheric scale faulting that offsets Moho discontinuity. In the southern block, crust is relatively thin in the west ( 35 km) and becomes thicker gradually towards east ( 40 km). In contrast, the northern block displays a strong lateral change in crustal thickness reaching up to 10 km across a narrow roughly N-S oriented zone which is interpreted as the subsurface signature of the ambiguous boundary between Istanbul Block and Pontides located further west at the surface.

The Queen Charlotte-Fairweather Fault Zone - The Knife-Edged Pacific-North American Plate Boundary

NASA Astrophysics Data System (ADS)

Greene, H. G.; Barrie, J. V. J.; Brothers, D. S.; Nishenko, S. P.; Conway, K.; Enkin, R.; Conrad, J. E.; Maier, K. L.; Stacy, C.

2016-12-01

Recent investigations of the Queen Charlotte-Fairweather (QC-FW) Fault zone using multibeam echosounder bathymetric and 3.5-kHz sub-bottom profile data show that the fault zone is primarily represented by a single linear structure with small, localized pull-apart basins suggestive of transtension. Water column acoustical data imaged gas plumes concentrated along the fault zone with plume columns extending as much as 700 m above the crest of mud volcanoes. Piston cores indicate that the fault zone cuts hard-packed dense sands that have been dated as Pleistocene in age. The newly discovered fluids associated with the southern half of the fault zone and volcanic edifices with oceanic and continental plate petrologic affinities suggest that the QC-FW is a leaky transform system. Two independent investigations, one in the north part and one in the central part of the fault zone, using two different types of piercing points, found that the slip rate along at least a 200 km length was consistent at between 40-55 mm/yr. since about 14 ka, equivalent to the relative plate motion between the Pacific and North American plates in the NE Pacific region. We surmise that the QC-FW is accommodating most, if not all, of relative motion along a single primary strand without any detectable partitioning of motion onto other faults. This right-lateral strike-slip fault zone is expressed on the seafloor as a very straight feature that probably represents nearly pure strike-slip motion.

A New Southern North Atlantic Isochron Map: Insights Into the Drift of the Iberian Plate Since the Late Cretaceous

NASA Astrophysics Data System (ADS)

Macchiavelli, Chiara; Vergés, Jaume; Schettino, Antonio; Fernández, Manel; Turco, Eugenio; Casciello, Emilio; Torne, Montserrat; Pierantoni, Pietro Paolo; Tunini, Lavinia

2017-12-01

This paper presents a new southern North Atlantic plate model from Late Cretaceous to present, with the aim of constraining the kinematics of the Iberian plate during the last 83.5 Myr. This model is presented along with a detailed isochron map generated through the analysis of 3 aeromagnetic tracks and 400 ship tracks from the National Centers for Environmental Information database. We present a new technique to obtain well-constrained estimates of the Iberia-North America plate motions from magnetic anomalies, overcoming the scarcity of large-offset fracture zones and transform faults. We build an integrated kinematic model for NW Africa, Morocco, Iberia, Europe, and North America, which shows that the deformation is partitioned between Pyrenees and Betic-Rif orogenic domain during the Late Cretaceous-Oligocene time interval. In the Eastern Betics domain, the calculated amount of NW Africa-Iberia convergence is 80 km between 83.5 and 34 Ma, followed by 150 km since the Oligocene. The motion of Iberia relative to Europe in the Central Pyrenees is characterized by overall NE directed transpressional motion during the Campanian and the Paleocene, followed by NW directed transpressional movement until the Lutetian and overall NNW directed convergence from Bartonian to Chattian. This motion occurs along the axis of the Bay of Biscay from the Santonian-Campanian boundary to the middle Priabonian, subsequently jumping to King's Trough at Anomaly 17 (36.62 Ma).

Tectonic setting for ophiolite obduction in Oman.

USGS Publications Warehouse

Coleman, R.G.

1981-01-01

The Samail ophiolite is part of an elongate belt in the Middle East that forms an integral part of the Alpine mountain chains that make up the N boundary of the Arabian-African plate. The Samail ophiolite represents a portion of the Tethyan ocean crust formed at a spreading center of Middle Cretaceous age (Cenomanian). During the Cretaceous spreading of the Tethyan Sea, Gondwana Land continued its dispersal, and the Arabian-African plate drifted northward about 10o. These events, combined with the opposite rotation of Eurasia and Africa, initiated the closing of the Tethyan during the Late Cretaceous. At the early stages of closure, downwarping of the Arabian continental margin, combined with the compressional forces of closure from the Eurasian plate, initiated obduction of the Tethyan oceanic crust along preexisting transform faults and still-hot oceanic crust was detached along oblique NE dipping thrust faults. Plate configurations combined with palinspastic reconstructions show that subduction and attendant large-scale island arc volcanism did not commence until after the Tethyan sea began to close and the Samail ophiolite was emplaced southward across the Arabian continental margin. The Samail ophiolite nappe now rests upon a melange consisting mainly of pelagic sediments, volcanics and detached fragments of the basal amphibolites, which in turn rest on autochthonous shelf carbonates of the Arabian platform. Following emplacement (Eocene) of the Samail ophiolite, the Tethyan oceanic crust began northward subduction, and active arc volcanism started just N of the present Jaz Murian depression in Iran.-Author

Analysis of laminated plates under thermal environment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Iyenger, N.G.R.; Shankara, C.A.

1995-12-31

Use of composites in advanced aircrafts and spacecraft structures calls for a thorough understanding of their behaviour under various types of loads. In the present paper, an attempt has been made to study the effect of thermal loads on the flexural response of composite laminated plates. Most of the studies in this area are either based on Classical Lamination Theory or First Order Shear Deformation Theory. In the present investigation, analysis has been carried out using a Higher Order Shear Deformation Theory, that allows for a parabolic variation of transverse shear stress through the thickness. The displacement model presented bymore » Reddy has been transformed so that only C{degrees} continuous element is required. This, however, increases the Degree of freedom per node from 5 to 7. Nine-noded isoparametric Legrangian elements are used for computing the results. The results were found to be very stable and comparable with those of exact elasticity solutions. The temperature is assumed to remain constant or vary linearly through the thickness. However, it varies sinusoidally in the plane of the plate. Effect of various parameters like material, fiber orientation, number of layers and boundary conditions on the response of the laminate has been investigated. The present study indicates that the flexural behaviour of laminates under thermal loads is very much different from that when subjected only to mechanical loads. Further, the variation of plate deflection with increase in temperature is not linear.« less

Structure and Tectonics of the Saint Elias Orogen

NASA Astrophysics Data System (ADS)

Bruhn, R. L.; Pavlis, T. L.; Plafker, G.; Serpa, L.; Picornell, C.

2001-12-01

The Saint Elias orogen of western Canada and southern Alaska is a complex mountain belt formed by transform faulting and subduction between the Pacific and North American plates, and collision of the Yakutat terrane. The orogen is segmented into three regions of different structural style caused by lateral variations in transpression and processes of terrane accretion. Deformation is strain and displacement partitioned throughout the orogen; transcurrent motion is focused along discrete strike-slip faults, and shortening is distributed among reverse faults and folds with sub-horizontal axes. Plunging folds accommodate horizontal shortening and extension in the western part of the orogen. Segment boundaries extend across the Yakutat terrane where they coincide with the courses of huge piedmont glaciers that flow from the topographic backbone of the range onto the coastal plain. The eastern segment is marked by strike-slip faulting along the Fairweather transform fault and by a narrow belt of reverse faulting where the transpression ratio is 0.4:1 shortening to dextral shear. The transpression ratio is 1.7:1 in the central part of the orogen where a broad thin-skinned fold and thrust belt deforms the Yakutat terrane south of the Chugach-Saint Elias (CSE) suture. Dextral shearing is accommodated by strike-slip faulting beneath the Seward and Bagley glaciers in the hanging wall of the CSE suture, and partly by reverse faulting along a structural belt that cuts across the Yakutat terrane along the western edge of the Malaspina Glacier and links to the Pamplona fold and thrust belt offshore. Deformation along this segment boundary is probably also driven by vertical axis bending of the Yakutat microplate during collision. Subduction & accretion in the western segment of the orogen causes re-folding of previously formed structures when they are emplaced into the upper plate of the Alaska-Aleutian mega-thrust. Second phase folds plunge at moderate to steep angles and accretion is marked by only modest amounts of uplift. The structural boundary between the central and western segments of the orogen localizes the course of the Bering piedmont glacier. The structural segments coincide with subdivisions in historical seismicity, particularly ruptures of great to large magnitude earthquakes. The results of this structural study provide the requisite geological framework to design new-generation geophysical monitoring systems to study active deformation within the orogen.

Accelerated plate tectonics.

PubMed

Anderson, D L

1975-03-21

The concept of a stressed elastic lithospheric plate riding on a viscous asthenosphere is used to calculate the recurrence interval of great earthquakes at convergent plate boundaries, the separation of decoupling and lithospheric earthquakes, and the migration pattern of large earthquakes along an arc. It is proposed that plate motions accelerate after great decoupling earthquakes and that most of the observed plate motions occur during short periods of time, separated by periods of relative quiescence.

India plate angular velocity and contemporary deformation rates from continuous GPS measurements from 1996 to 2015.

PubMed

Jade, Sridevi; Shrungeshwara, T S; Kumar, Kireet; Choudhury, Pallabee; Dumka, Rakesh K; Bhu, Harsh

2017-09-12

We estimate a new angular velocity for the India plate and contemporary deformation rates in the plate interior and along its seismically active margins from Global Positioning System (GPS) measurements from 1996 to 2015 at 70 continuous and 3 episodic stations. A new India-ITRF2008 angular velocity is estimated from 30 GPS sites, which include stations from western and eastern regions of the plate interior that were unrepresented or only sparsely sampled in previous studies. Our newly estimated India-ITRF2008 Euler pole is located significantly closer to the plate with ~3% higher angular velocity than all previous estimates and thus predicts more rapid variations in rates and directions along the plate boundaries. The 30 India plate GPS site velocities are well fit by the new angular velocity, with north and east RMS misfits of only 0.8 and 0.9 mm/yr, respectively. India fixed velocities suggest an approximate of 1-2 mm/yr intra-plate deformation that might be concentrated along regional dislocations, faults in Peninsular India, Kachchh and Indo-Gangetic plain. Relative to our newly-defined India plate frame of reference, the newly estimated velocities for 43 other GPS sites along the plate margins give insights into active deformation along India's seismically active northern and eastern boundaries.

The stress distribution in pin-loaded orthotropic plates

NASA Technical Reports Server (NTRS)

Klang, E. C.; Hyer, M. W.

1985-01-01

The performance of mechanically fastened composite joints was studied. Specially, a single-bolt connector was modeled as a pin-loaded, infinite plate. The model that was developed used two dimensional, complex variable, elasticity techniques combined with a boundary collocation procedure to produce solutions for the problem. Through iteration, the boundary conditions were satisfied and the stresses in the plate were calculated. Several graphite epoxy laminates were studied. In addition, parameters such as the pin modulus, coefficient of friction, and pin-plate clearance were varied. Conclusions drawn from this study indicate: (1) the material properties (i.e., laminate configuration) of the plate alter the stress state and, for highly orthotropic materials, the contact stress deviates greatly from the cosinusoidal distribution often assumed; (2) friction plays a major role in the distribution of stresses in the plate; (3) reversing the load direction also greatly effects the stress distribution in the plate; (4) clearance (or interference) fits change the contact angle and thus the location of the peak hoop stress; and (5) a rigid pin appears to be a good assumption for typical material systems.

Boundary particle method for Laplace transformed time fractional diffusion equations

NASA Astrophysics Data System (ADS)

Fu, Zhuo-Jia; Chen, Wen; Yang, Hai-Tian

2013-02-01

This paper develops a novel boundary meshless approach, Laplace transformed boundary particle method (LTBPM), for numerical modeling of time fractional diffusion equations. It implements Laplace transform technique to obtain the corresponding time-independent inhomogeneous equation in Laplace space and then employs a truly boundary-only meshless boundary particle method (BPM) to solve this Laplace-transformed problem. Unlike the other boundary discretization methods, the BPM does not require any inner nodes, since the recursive composite multiple reciprocity technique (RC-MRM) is used to convert the inhomogeneous problem into the higher-order homogeneous problem. Finally, the Stehfest numerical inverse Laplace transform (NILT) is implemented to retrieve the numerical solutions of time fractional diffusion equations from the corresponding BPM solutions. In comparison with finite difference discretization, the LTBPM introduces Laplace transform and Stehfest NILT algorithm to deal with time fractional derivative term, which evades costly convolution integral calculation in time fractional derivation approximation and avoids the effect of time step on numerical accuracy and stability. Consequently, it can effectively simulate long time-history fractional diffusion systems. Error analysis and numerical experiments demonstrate that the present LTBPM is highly accurate and computationally efficient for 2D and 3D time fractional diffusion equations.

Microstructural and Textural Differences Induced by Water and Furnace Cooling in Commercially Pure Zr Annealed in the α + β Region

NASA Astrophysics Data System (ADS)

Chai, Linjiang; Wang, Tingting; Ren, Yi; Song, Bo; Guo, Ning; Chen, Liangyu

2018-07-01

In this work, a commercially pure Zr sheet with a typical bimodal basal texture was annealed in an α + β region and then subjected to different coolings (in water and furnace). Microstructures and textures of both the as-received and the heat-treated specimens were investigated by electron channeling contrast imaging and electron backscatter diffraction techniques. Results show that a duplex microstructure consisting of untransformed bulk α grains and twinned martensitic plates is produced in the water-cooled specimen, which possesses a weakened texture compared to the initial one. For the specimen cooled in furnace, however, a uniform microstructure fully comprised of coarser equiaxed grains with a strengthened texture is obtained. Analyses reveal that the rapid cooling in water could suppress variant selection behaviors during β → α transformation and allow α plates with scattered orientations to be nucleated inside β phases, contributing to the weakened texture. In contrast, during slow cooling in furnace, β boundaries would act as preferred nucleation sites of α embryos, resulting in a strong variant selection that accounts for the intensified texture.

Microstructural and Textural Differences Induced by Water and Furnace Cooling in Commercially Pure Zr Annealed in the α + β Region

NASA Astrophysics Data System (ADS)

Chai, Linjiang; Wang, Tingting; Ren, Yi; Song, Bo; Guo, Ning; Chen, Liangyu

2018-03-01

In this work, a commercially pure Zr sheet with a typical bimodal basal texture was annealed in an α + β region and then subjected to different coolings (in water and furnace). Microstructures and textures of both the as-received and the heat-treated specimens were investigated by electron channeling contrast imaging and electron backscatter diffraction techniques. Results show that a duplex microstructure consisting of untransformed bulk α grains and twinned martensitic plates is produced in the water-cooled specimen, which possesses a weakened texture compared to the initial one. For the specimen cooled in furnace, however, a uniform microstructure fully comprised of coarser equiaxed grains with a strengthened texture is obtained. Analyses reveal that the rapid cooling in water could suppress variant selection behaviors during β → α transformation and allow α plates with scattered orientations to be nucleated inside β phases, contributing to the weakened texture. In contrast, during slow cooling in furnace, β boundaries would act as preferred nucleation sites of α embryos, resulting in a strong variant selection that accounts for the intensified texture.

On the aeroacoustic and flow structures developed on a flat plate with a serrated sawtooth trailing edge

NASA Astrophysics Data System (ADS)

Chong, Tze Pei; Vathylakis, Alexandros

2015-10-01

Results of an experimental study on turbulent flow over a flat plate with a serrated sawtooth trailing edge are presented in this paper. After tripping the boundary layer to become turbulent, the broadband noise sources at the sawtooth serrated trailing edge is studied by several experimental techniques. Broadband noise reduction by the serrated sawtooth trailing edge can be realistically achieved in the flat plate configuration. The variations of wall pressure power spectral density and the spanwise coherence (which relates to the spanwise correlation length) in a sawtooth trailing edge play a minor role in the mechanisms underpinning the reduction of self noise radiation. Conditional-averaging technique was applied in the boundary layer data where a pair of pressure-driven oblique vortical structures near the sawtooth side edges is identified. In the current flat plate configuration, the interaction between the vortical structures and the local turbulent boundary layer results in a redistribution of the momentum transport and turbulent shear stress near the sawtooth side edges as well as the sawtooth tip, thus affecting the efficiency of self noise radiation.

North America-Pacific plate boundary, an elastic-plastic megashear - Evidence from very long baseline interferometry

NASA Technical Reports Server (NTRS)

Ward, Steven N.

1988-01-01

Data obtained by Mark III VLBI measurements of radio signals from permanent and mobile VLBI sites for 5.5 years of observations, starting in October 1982, were used to derive a picture of the earth crust deformation near the North America-Pacific plate boundary. The data, which included the vector positions of the VLBI sites and their rate of change, were used for comparison with a number of lithospheric deformation models based upon the concept that the motions of points near the North America-Pacific plate boundary are a linear combination of North America and Pacific velocities. The best of these models were found to fit 95 percent of the variance in 139 VLBI length and transverse velocity observations. Instantaneous shear deformation associated with plate tectonics is apparently developing in a zone 450 km wide paralleling the San Andreas Fault; some of this deformation will be recovered through elastic rebound, while the rest will be permanently set through plastic processes. Because the VLBI data have not been collected for a significant fraction of the earthquake cycle, they cannot discriminate between elastic and plastic behaviors.

Collisional zones in Puerto Rico and the northern Caribbean

NASA Astrophysics Data System (ADS)

Laó-Dávila, Daniel A.

2014-10-01

Puerto Rico is an amalgamation of island arc terranes that has recorded the deformational and tectonic history of the North American-Caribbean Plate boundary. Four collisional zones indicate the contractional events that have occurred at the plate boundary. Metamorphism and deformation of Middle Jurassic to Early Cretaceous oceanic lithosphere during the Early Cretaceous indicate the earliest collisional event. Then, an ophiolitic mélange, mostly comprised of blocks of the metamorphosed oceanic lithosphere, was formed and emplaced in the backarc region during the Turonian-Coniacian deformational event. A possible collision with a buoyant block in the North American Plate caused late Maastrichtian-early Paleocene contraction that created fold-and-thrust belts and the remobilization and uplift of serpentinite bodies in the Southwest Block. Late Eocene-early Oligocene transpression was localized along the Southern and Northern Puerto Rico fault zones, which occur north and south of large granodiorite intrusions in the strong Central Block. The deformation was accommodated in pure shear domains of fold-and-thrust belts and conjugate strike-slip faults, and simple shear domains of large mostly left-lateral faults. In addition, it reactivated faults in the weak Southwest Block. This island-wide transpression is the result of a Greater Antilles arc and continental North American collision. The kinematic model of the structures described in Puerto Rico correlate with some structures in Hispaniola and Cuba, and shows how the northern boundary of the Caribbean Plate was shortened by collisions with continental lithosphere of the North American Plate throughout its history. The tectonic evolution of the Greater Antilles shows a history of collisions, in which the latest collision accretes Cuba to the North American Plate, reorganizes the plate boundary, and deforms with transpression Hispaniola and Puerto Rico. The latest collision in Puerto Rico shows the case in which an arc collides obliquely with buoyant crust producing left-lateral transpression and converges obliquely with dense oceanic lithosphere.

Convective diffusion in protein crystal growth

NASA Technical Reports Server (NTRS)

Baird, J. K.; Meehan, E. J., Jr.; Xidis, A. L.; Howard, S. B.

1986-01-01

A protein crystal modeled as a flat plate suspended in the parent solution, with the normal to the largest face perpendicular to gravity and the protein concentration in the solution adjacent to the plate taken to be the equilibrium solubility, is studied. The Navier-Stokes equation and the equation for convective diffusion in the boundary layer next to the plate are solved to calculate the flow velocity and the protein mass flux. The local rate of growth of the plate is shown to vary significantly with depth due to the convection. For an aqueous solution of lysozyme at a concentration of 40 mg/ml, the boundary layer at the top of a 1-mm-high crystal has a thickness of 80 microns at 1 g, and 2570 microns at 10 to the -6th g.

Transformation elastodynamics and cloaking for flexural waves

NASA Astrophysics Data System (ADS)

Colquitt, D. J.; Brun, M.; Gei, M.; Movchan, A. B.; Movchan, N. V.; Jones, I. S.

2014-12-01

The paper addresses an important issue of cloaking transformations for fourth-order partial differential equations representing flexural waves in thin elastic plates. It is shown that, in contrast with the Helmholtz equation, the general form of the partial differential equation is not invariant with respect to the cloaking transformation. The significant result of this paper is the analysis of the transformed equation and its interpretation in the framework of the linear theory of pre-stressed plates. The paper provides a formal framework for transformation elastodynamics as applied to elastic plates. Furthermore, an algorithm is proposed for designing a broadband square cloak for flexural waves, which employs a regularised push-out transformation. Illustrative numerical examples show high accuracy and efficiency of the proposed cloaking algorithm. In particular, a physical configuration involving a perturbation of an interference pattern generated by two coherent sources is presented. It is demonstrated that the perturbation produced by a cloaked defect is negligibly small even for such a delicate interference pattern.

In-Flight Boundary-Layer Transition on a Large Flat Plate at Supersonic Speeds

NASA Technical Reports Server (NTRS)

Banks, Daniel W.; Fredericks, Michael Alan; Tracy, Richard R.; Matisheck, Jason R.; Vanecek, Neal D.

2012-01-01

A flight experiment was conducted to investigate the pressure distribution, local flow conditions, and boundary-layer transition characteristics on a large flat plate in flight at supersonic speeds up to Mach 2.0. The primary objective of the test was to characterize the local flow field in preparation for future tests of a high Reynolds number natural laminar flow test article. The tests used a F-15B testbed aircraft with a bottom centerline mounted test fixture. A second objective was to determine the boundary-layer transition characteristics on the flat plate and the effectiveness of using a simplified surface coating for future laminar flow flight tests employing infrared thermography. Boundary-layer transition was captured using an onboard infrared imaging system. The infrared imagery was captured in both analog and digital formats. Surface pressures were measured with electronically scanned pressure modules connected to 60 surface-mounted pressure orifices. The local flow field was measured with five 5-hole conical probes mounted near the leading edge of the test fixture. Flow field measurements revealed the local flow characteristics including downwash, sidewash, and local Mach number. Results also indicated that the simplified surface coating did not provide sufficient insulation from the metallic structure, which likely had a substantial effect on boundary-layer transition compared with that of an adiabatic surface. Cold wall conditions were predominant during the acceleration to maximum Mach number, and warm wall conditions were evident during the subsequent deceleration. The infrared imaging system was able to capture shock wave impingement on the surface of the flat plate in addition to indicating laminar-to-turbulent boundary-layer transition.

Long aftershock sequences within continents and implications for earthquake hazard assessment.

PubMed

Stein, Seth; Liu, Mian

2009-11-05

One of the most powerful features of plate tectonics is that the known plate motions give insight into both the locations and average recurrence interval of future large earthquakes on plate boundaries. Plate tectonics gives no insight, however, into where and when earthquakes will occur within plates, because the interiors of ideal plates should not deform. As a result, within plate interiors, assessments of earthquake hazards rely heavily on the assumption that the locations of small earthquakes shown by the short historical record reflect continuing deformation that will cause future large earthquakes. Here, however, we show that many of these recent earthquakes are probably aftershocks of large earthquakes that occurred hundreds of years ago. We present a simple model predicting that the length of aftershock sequences varies inversely with the rate at which faults are loaded. Aftershock sequences within the slowly deforming continents are predicted to be significantly longer than the decade typically observed at rapidly loaded plate boundaries. These predictions are in accord with observations. So the common practice of treating continental earthquakes as steady-state seismicity overestimates the hazard in presently active areas and underestimates it elsewhere.

The Tasmanides: Phanerozoic Tectonic Evolution of Eastern Australia

NASA Astrophysics Data System (ADS)

Rosenbaum, Gideon

2018-05-01

The Tasmanides occupy the eastern third of Australia and provide an extensive record of the evolution of the eastern Gondwanan convergent plate boundary from the Cambrian to the Triassic. This article presents a summary of the primary building blocks (igneous provinces and sedimentary basins) within the Tasmanides, followed by a discussion of the timing and extent of deformation events. Relatively short episodes of contractional deformation alternated with longer periods of crustal extension accompanied by voluminous magmatism. This behavior was likely controlled by plate boundary migration (trench retreat and advance) that was also responsible for bending and segmentation of the convergent plate margin. As a result, the Tasmanides were subjected to at least three major phases of oroclinal bending, in the Silurian, Devonian, and Permian. The most significant segmentation likely occurred at ˜420–400 Ma along a lithospheric-scale boundary that separated the northern and southern parts of the Tasmanides.

Plane elasto-plastic analysis of v-notched plate under bending by boundary integral equation method. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Rzasnicki, W.

1973-01-01

A method of solution is presented, which, when applied to the elasto-plastic analysis of plates having a v-notch on one edge and subjected to pure bending, will produce stress and strain fields in much greater detail than presently available. Application of the boundary integral equation method results in two coupled Fredholm-type integral equations, subject to prescribed boundary conditions. These equations are replaced by a system of simultaneous algebraic equations and solved by a successive approximation method employing Prandtl-Reuss incremental plasticity relations. The method is first applied to number of elasto-static problems and the results compared with available solutions. Good agreement is obtained in all cases. The elasto-plastic analysis provides detailed stress and strain distributions for several cases of plates with various notch angles and notch depths. A strain hardening material is assumed and both plane strain and plane stress conditions are considered.

Using Global Plate Velocity Boundary Conditions for Embedded Regional Geodynamic Models: Application to 3-D Modeling of the Early Rifting of the South Atlantic

NASA Astrophysics Data System (ADS)

Taramón, Jorge M.; Morgan, Jason P.; Pérez-Gussinyé, Marta

2016-04-01

The treatment of far-field boundary conditions is one of the most poorly resolved issues for regional modeling of geodynamic processes. In viscous flow, the choice of far-field boundary conditions often strongly shapes the large-scale structure of a geosimulation. The mantle velocity field along the sidewalls and base of a modeling region is typically much more poorly known than the geometry of past global motions of the surface plates as constrained by global plate motion reconstructions. For regional rifting models it has become routine to apply highly simplified 'plate spreading' or 'uniform rifting' boundary conditions to a 3-D model that limits its ability to simulate the geodynamic evolution of a specific rifted margin. One way researchers are exploring the sensitivity of regional models to uncertain boundary conditions is to use a nested modeling approach in which a global model is used to determine a large-scale flow pattern that is imposed as a constraint along the boundaries of the region to be modeled. Here we explore the utility of a different approach that takes advantage of the ability of finite element models to use unstructured meshes than can embed much higher resolution sub-regions. Here we demonstrate the workflow and code tools that we created to generate this unstructured mesh: solver based on springs, guide-mesh and routines to improve the quality, e.g., closeness to a regular tetrahedron, of the tetrahedral elements of the mesh. Note that the same routines are used to generate a new mesh in the remeshing of a distorted Lagrangian mesh. In our initial project to validate this approach, we create a global spherical shell mesh in which a higher resolution sub-region is created around the nascent South Atlantic Rifting Margin. Global Plate motion BCs and plate boundaries are applied for the time of the onset of rifting, continuing through several 10s of Ma of rifting. Thermal, compositional, and melt-related buoyancy forces are only non-zero within the high-resolution sub-region, elsewhere, motions are constrained by surface plate-motion constraints. The total number of unknowns needed to solve an embedded regional model with this approach is less than 1/3 larger than that needed for a structured-mesh solution on a Cartesian or spherical cap sub-regional mesh. Here we illustrate the steps within this workflow for modeling the potential mantle flow associated with the early rifting evolution of the South Atlantic, in particular studying the potential effects of a 'Parana Plume' during the transition from rift to drift.

Closure of the Africa-Eurasia-North America plate motion circuit and tectonics of the Gloria fault

NASA Technical Reports Server (NTRS)

Argus, Donald F.; Gordon, Richard G.; Demets, Charles; Stein, Seth

1989-01-01

The current motions of the African, Eurasian, and North American plates are examined. The problems addressed include whether there is resolvable motion of a Spitsbergen microplate, the direction of motion between the African and North American plates, whether the Gloria fault is an active transform fault, and the implications of plate circuit closures for rates of intraplate deformation. Marine geophysical data and magnetic profiles are used to construct a model which predicts about 4 mm/yr slip across the Azores-Gibraltar Ridge, and west-northwest convergence near Gibraltar. The analyzed data are consistent with a rigid plate model with the Gloria fault being a transform fault.

Three-dimensional transformation optics for arbitrary coordinate systems: transforming conductive materials and boundaries.

PubMed

Kazemzadeh, Mohammad-Rahim; Alighanbari, Abbas

2018-04-16

A three-dimensional transformation optics method, leading to homogeneous materials, applicable to any non-Cartesian coordinate systems or waveguides/objects of arbitrary cross-sections is presented. Both the conductive boundary and internal material of the desired device is determined by the proposed formulation. The method is applicable to a wide range of waveguide, radiation, and cloaking problems, and is demonstrated for circular waveguide couplers and an external cloak. An advantage of the present method is that the material properties are simplified by appropriately selecting the conductive boundaries. For instance, a right-angle circular waveguide bend is presented which uses only one homogenous material. Also, transformation of conductive materials and boundaries are studied. The conditions in which the transformed boundaries remain conductive are discussed. In addition, it is demonstrated that negative infinite conductivity can be replaced with positive conductivity, without affecting the field outside the conductive boundary. It is also observed that a negative finite conductivity can be replaced with a positive one, by accepting some small errors. The general mathematical procedure and formulation for calculating the parametric surface equations of the conductive peripheries are presented.

Basement and regional structure along strike of the Queen Charlotte Fault in the context of modern and historical earthquake ruptures

USGS Publications Warehouse

Walton, Maureen A. L.; Gulick, Sean P. S.; Haeussler, Peter J.; Roland, Emily C.; Tréhu, Anne M.

2015-01-01

The Queen Charlotte fault (QCF) is a dextral transform system located offshore of southeastern Alaska and western Canada, accommodating ∼4.4  cm/yr of relative motion between the Pacific and North American plates. Oblique convergence along the fault increases southward, and how this convergence is accommodated is still debated. Using seismic reflection data, we interpret offshore basement structure, faulting, and stratigraphy to provide a geological context for two recent earthquakes, an Mw 7.5 strike‐slip event near Craig, Alaska, and an Mw 7.8 thrust event near Haida Gwaii, Canada. We map downwarped Pacific oceanic crust near 54° N, between the two rupture zones. Observed downwarping decreases north and south of 54° N, parallel to the strike of the QCF. Bending of the Pacific plate here may have initiated with increased convergence rates due to a plate motion change at ∼6  Ma. Tectonic reconstruction implies convergence‐driven Pacific plate flexure, beginning at 6 Ma south of a 10° bend the QCF (which is currently at 53.2° N) and lasting until the plate translated past the bend by ∼2  Ma. Normal‐faulted approximately late Miocene sediment above the deep flexural depression at 54° N, topped by relatively undeformed Pleistocene and younger sediment, supports this model. Aftershocks of the Haida Gwaii event indicate a normal‐faulting stress regime, suggesting present‐day plate flexure and underthrusting, which is also consistent with reconstruction of past conditions. We thus favor a Pacific plate underthrusting model to initiate flexure and accommodation space for sediment loading. In addition, mapped structures indicate two possible fault segment boundaries along the QCF at 53.2° N and at 56° N.

Vibration characteristics of functionally graded carbon nanotube reinforced composite rectangular plates on Pasternak foundation with arbitrary boundary conditions and internal line supports

NASA Astrophysics Data System (ADS)

Zhong, Rui; Wang, Qingshan; Tang, Jinyuan; Shuai, Cijun; Liang, Qian

2018-02-01

This paper presents the first known vibration characteristics of moderately thick functionally graded carbon nanotube reinforced composite rectangular plates on Pasternak foundation with arbitrary boundary conditions and internal line supports on the basis of the firstorder shear deformation theory. Different distributions of single walled carbon nanotubes (SWCNTs) along the thickness are considered. Uniform and other three kinds of functionally graded distributions of carbon nanotubes along the thickness direction of plates are studied. The solutions carried out using an enhanced Ritz method mainly include the following three points: Firstly, create the Lagrange energy function by the energy principle; Secondly, as the main innovation point, the modified Fourier series are chosen as the basic functions of the admissible functions of the plates to eliminate all the relevant discontinuities of the displacements and their derivatives at the edges; Lastly, solve the natural frequencies as well as the associated mode shapes by means of the Ritz-variational energy method. In this study, the influences of the volume fraction of CNTs, distribution type of CNTs, boundary restrain parameters, location of the internal line supports, foundation coefficients on the natural frequencies and mode shapes of the FG-CNT reinforced composite rectangular plates are presented.

Fractures, not Plumes, Have Controlled Major Seamount Volcanism in the Pacific over 170 Million Years

NASA Astrophysics Data System (ADS)

Natland, J. H.; Winterer, E. L.

2003-12-01

The distribution of guyots and atolls and large volcanic islands on the Pacific plate can be used to outline the likely connection between stresses acting on the plate and the gradual development of large, linear volcanic chains over the past 170 Ma. We construe three general periods with different stress regimes in the history of the Pacific plate. 1) During the Jurassic and Early Cretaceous, the Pacific plate was surrounded by ridge segments and there were no major stress alignments within it. Within-plate volcanism thus assumed the scattered arrangement for the condition of no tectonic stress (1), and the large Magellan and Wake seamount clusters formed. Near the eastern boundaries of the plate, complex and shifting patterns of ridge reorganization dictated formation of very long, splayed, near-axis ridges such as Horizon Guyot and Necker Ridge. 2) At about 90 Ma, the growing middle-aged Pacific plate achieved its first persistent stress regime with the formation of subduction boundaries along its western or northwestern margin. The plate was no longer static but began to move over the asthenosphere and into the mantle. Subduction boundaries and the overall direction of subduction are uncertain, but this imparted a general yet not fully stable component of tension across the plate, producing the NNW Gilbert-Marshall, Line and Emperor Seamount ridges, generally orthogonal to the overall direction of least principal stress. The Line Island seamount chain, being near ridge axes, sustained a variable stress regime. It thus has no age progression of rocks dated between 70-90 Ma (2), great width, and a dual orientations of ridges. 3) By 47 Ma, nearly half of the boundaries of the Pacific plate now were trenches spanning from the Aleutians to New Zealand. In addition, northward migration of the Indian plate and Australia caught a major portion of the westerly moving Pacific plate between the northeast corner of the Tonga Trench and the Aleutians. The plate could not shift laterally in response to whatever was occurring along its eastern spreading boundaries. A very consistent and strong stress regime therefore developed across the Pacific plate with a NNE direction of least principal stress. The change in stress orientation may have taken up to 10 million years, during an interval marked by little or no volcanic productivity at the western end of the Hawaiian chain. Since that time, the predominant alignment of both linear island chains and Puka Puka-type ridges, from the Kodiak-Bowie chain in the Gulf of Alaska to the Louisville Ridge south of the Antarctic convergence, has been orthogonal to this direction. Development of large-volume persistent chains and shorter small-volume chains indicates patterns of differential stress in the plate, variable fertility and geochemistry of the asthenosphere and/or shallow convective overturn of the asthenosphere rather than the action of mantle plumes of different sizes and depths of origin. Tapping of enriched mantle by widespread volcano clusters during the Mesozoic suggests the presence of a shallow asthenospheric source layer rather than multiple narrow conduits. (1) Hieronymus, C.F., and Bercovici, D. 2000. Earth Planet. Sci. Lett. 181, 539-554. (2) Davis, A.S., Gray, L.B., Clague, D.A., and Hein, J.R., 2002 Geochem. Geophys. Geosyst. 3: 10.1029/2001GC0000190, 1-28.

Preliminary results on the current tectonic setting of South Georgia Island from GPS geodetic data.

NASA Astrophysics Data System (ADS)

Matheny, P.; Smalley, R., Jr.; Dalziel, I. W. D.; Lawver, L. A.; Gomez, D.; Teferle, F. N.; Hunegnaw, A.; Abraha, K. E.

2017-12-01

The South Georgia microcontinent is an allochthonous block from the south eastern part of Tierra del Fuego of South America that has been transported over the past 80-100 My as part of the development of the Scotia Plate. While the trajectory to its current position is poorly constrained, the microcontinent is now part of the eastern end of the North Scotia Ridge between the South America and the Scotia Plates almost 1600 km east of its original position. Based on bathymetric morphology and geological history of the Scotia Arc the microcontinent has been considered to be part of the Scotia Plate, with the plate boundary continuing along the North Scotia Ridge on the north side of the microcontinent, to the east where it transitions into the South Sandwich subduction boundary. Seismic activity in the region, while very low, is concentrated along the southern border of the microcontinent. This seismicity has been interpreted, based on a few small events with thrust mechanisms, to represent underthrusting and uplift of the island on a restraining bend in the North Scotia Ridge geometry to the north-east of the microcontinent. More recently, based on the seismicity distribution, the plate boundary has been placed along the south side of the microcontinent, suggesting that it has, or is being, transferred to the South America plate. In order to address the current tectonic affinity of South Georgia a four station continuous GPS network was installed on South Georgia Island to determine the block's relative motion with respect to the South America and Scotia Plates. The question is whether it is now attached to either plate or is an independent platelet, and whether it is suffering internal deformation. We will present the preliminary geodetic results based on 3 years of continuous GPS data.

Using Google Earth to Explore Multiple Data Sets and Plate Tectonic Concepts

NASA Astrophysics Data System (ADS)

Goodell, L. P.

2015-12-01

Google Earth (GE) offers an engaging and dynamic environment for exploration of earth science data. While GIS software offers higher-level analytical capability, it comes with a steep learning curve and complex interface that is not easy for the novice, and in many cases the instructor, to negotiate. In contrast, the intuitive interface of GE makes it easy for students to quickly become proficient in manipulating the globe and independently exploring relationships between multiple data sets at a wide range of scales. Inquiry-based, data-rich exercises have been developed for both introductory and upper-level activities including: exploration of plate boundary characteristics and relative motion across plate boundaries; determination and comparison of short-term and long-term average plate velocities; crustal strain analysis (modeled after the UNAVCO activity); and determining earthquake epicenters, body-wave magnitudes, and focal plane solutions. Used successfully in undergraduate course settings, for TA training and for professional development programs for middle and high school teachers, the exercises use the following GE data sets (with sources) that have been collected/compiled by the author and are freely available for non-commercial use: 1) tectonic plate boundaries and plate names (Bird, 2003 model); 2) real-time earthquakes (USGS); 3) 30 years of M>=5.0 earthquakes, plotted by depth (USGS); 4) seafloor age (Mueller et al., 1997, 2008); 5) location and age data for hot spot tracks (published literature); 6) Holocene volcanoes (Smithsonian Global Volcanism Program); 7) GPS station locations with links to times series (JPL, NASA, UNAVCO); 8) short-term motion vectors derived from GPS times series; 9) long-term average motion vectors derived from plate motion models (UNAVCO plate motion calculator); 10) earthquake data sets consisting of seismic station locations and links to relevant seismograms (Rapid Earthquake Viewer, USC/IRIS/DELESE).

Active Deformation of the Northern Cordillera Observed with GPS

NASA Astrophysics Data System (ADS)

Elliott, J.; Jiang, Y.; Leonard, L. J.; Hyndman, R. D.; Freymueller, J.; Mazzotti, S.

2017-12-01

The Northern Cordillera, which encompasses western Canada and eastern Alaska, is a complex tectonic puzzle. Past terrane accretions, the present collision of the Yakutat block, large-scale plate motions, and past and present glacier change have created a tectonic landscape that includes a major transform system, most of the highest peaks in North America, and far-flung ongoing distributed deformation. We present an updated GPS velocity field as well as a new integrated tectonic block model for the region. The style of deformation varies through the region. Surrounding the Yakutat collision, the model includes a number of small blocks that indicate rotations to the east, north, and west as material moves away from the collisional front. These small blocks also show evidence of internal deformation. Farther from the collisional front, blocks are larger and appear to behave more rigidly. In the south, northwestward motion resulting in a prominent band of coastal shear extends from Vancouver Island to Glacier Bay. In the Arctic, small southeastward motions in Alaska transition to easterly motion in Canada that extends to the Mackenize Mountains near the Cordillera-craton boundary. A number of faults and fault systems accommodate relative Pacific-North America plate motion in the region, although the significant majority is along the Fairweather-Queen Charlotte transform system and the St. Elias fold-and-thrust belt. Along the Fairweather-Queen Charlotte system, the motion is dominantly dextral with increasing oblique transpression to the south corresponding to a change in margin trend. At the northern end of the transform system, motion is distributed onto multiple faults. Roughly 75% of the Fairweather motion is transferred west into the St. Elias fold-and-thrust belt, which accommodates 30 mm/yr of convergence. The remaining 25% is transferred north towards the dextral Denali-Totschunda system. The eastern Denali fault presently plays a minor role in accommodating relative plate motion, with 2-3 mm/yr of transpression. Based on a sequence of earthquakes in May 2017, this motion may be distributed along multiple fault strands.