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1

Partitioning of Oblique Plate Convergence at the Sumatran Plate Boundary  

NASA Astrophysics Data System (ADS)

At the Sumatran plate boundary, the Indo-Australian plate subducts beneath the Sunda block at a rate of ~5-6 cm/yr, in a direction of ~10° oblique to the trench-normal. Such oblique plate convergence is partitioned into subduction along the Sumatran subduction interface and strike-slip motion along the Sumatran fault. The Sumatran GPS Array (SuGAr), first established in 2002 with 6 stations, now has 50 stations. Using the decade-long time series, we have estimated long-term background rates for the SuGAr stations, with simultaneous estimation of a large number of earthquake parameters. By projecting the long-term rates into trench-normal and trench-parallel directions, we are able to separate deformation related to subduction and transform motion, respectively, to first order. For subduction-related trench-normal velocities, we find stations on the Mentawai islands -- where a great earthquake has been forecast for the coming decades -- have almost double the velocity of stations on the Batu islands where low coupling has been proposed. This observation strongly supports the idea that an earthquake on the Mentawai seismic gap is overdue, and the Batu section is likely a weakly coupled barrier between strongly coupled regions to the north and south. For transform-related trench-parallel velocities, we find rates progressively decrease from ~25 mm/yr on islands offshore Sumatra to ~15 mm/yr at the Sumatran west coast, and close to zero in the backarc. We will explore plausible models for the heterogeneous coupling on the Mentawai subduction interface and forearc sliver translation.

Feng, L.; Hill, E. M.; Qiu, Q.; Banerjee, P.; Lubis, A.; Sieh, K. E.

2012-12-01

2

Plate Boundaries  

NSDL National Science Digital Library

This site provides information on plate boundaries, which are found at the edge of the lithospheric plates and are of three types: convergent, divergent and conservative. Wide zones of deformation are usually characteristic of plate boundaries because of the interaction between two plates. The three boundaries are characterized by their distinct motions which are described in the text and depicted with block diagram illustrations, all of which are animated. There are also two maps that show the direction of motion of the plates. Active links lead to more information on plate tectonics.

3

Tectonic Plates and Plate Boundaries  

NSDL National Science Digital Library

This interactive activity adapted from NASA features world maps that identify different sections of the Earth's crust called tectonic plates. The locations of different types of plate boundaries are also identified, including convergent, divergent, and transform boundaries.

2005-12-17

4

Kinematic evolution of the Northeast Japan convergent margin and implications for plate boundary dynamics  

NASA Astrophysics Data System (ADS)

Tectonic erosion along convergent plate boundaries, whereby removal of upper plate material along the subduction zone interface drives mass loss and subsidence of the outer forearc, has been invoked to explain the geologically recent evolution of nearly half the world's subduction margins. However, the mechanisms that initiate and sustain forearc subsidence are not well understood. We provide new analyses of the kinematic evolution of the northeast Japan margin, considered a type example of erosive margins, that demonstrate that vertical motions of the outer forearc are coincident with changes in upper plate kinematics and lower plate convergence rate. New constraints on the timing and kinematics of deformation along inner forearc faults indicate Plio-Quaternary inversion of Miocene extensional structures. The initiation of reverse slip along the inner forearc Futaba (5.6 to 3.9 Ma), Oritusme (5.9 to 4.8 Ma), and Noehij (Pliocene) faults are constrained by new U-Pb ages from tephras in growth strata. The initiation of an earlier phase of extension along the Oritusme and Futaba faults is identified from thick sequences of Miocene rift-related sediments in the hanging walls that are absent in the footwalls. Existing biostratigraphic and geochronolgic ages near the base of the syn-extensional sequences constrain the initiation of extension to 23.9-21.0 and ~20.8 Ma for the Futaba and Oritsume faults, and cross sections across these structures require nearly complete thrust inversion of Miocene extensional displacement. A regional synthesis of deformation demonstrates that the timing and kinematics of forearc deformation are contemporaneous with previously documented Miocene extension and Plio-Quaternary inversion in the backarc. Moreover, reconstructions of Pacific-Honshu convergence rates indicate that 1) the initiation of forearc subsidence and upper plate extension is coincident with a two to three fold increase in margin-perpendicular convergence, and 2) the onset of arc-normal shortening and increased frontal accretion occurred during a period of relatively constant convergence rate. The temporal correlation between deformation along upper plate faults, forearc subsidence, and lower plate convergence rates at the Northeast Japan margin suggests that the vertical motions of the forearc are likely governed by changes in lower plate kinematics. We hypothesize that an acceleration in plate convergence drives changes in slab geometry at shallow depths that allows for subsidence of the forearc, and suggest that a portion of the subsidence record previously interpreted as tectonic erosion instead reflects an upper plate response to plate boundary dynamics.

Regalla, C.; Fisher, D. M.; Furlong, K. P.; Kirby, E.

2012-12-01

5

Subduction at Convergent Boundary  

NSDL National Science Digital Library

The representation depicts subduction. The narrated animated movie (simulation) shows subduction of the Indian Plate as the Indian Plate and the Eurasian Plate converge at the plate boundary. The segment begins showing a world view of the Earth's plates and zooms in on the highlighted Indian and Eurasian plate activity. The animation transitions to a cross-sectional view, giving an inside-the-Earth look at what happens as these plates converge. The movie can be viewed in two ways- in continuous play or step by step.

6

Seismicity at the convergent plate boundary offshore Crete, Greece, observed by an amphibian network  

NASA Astrophysics Data System (ADS)

We investigate microseismic activity at the convergent plate boundary of the Hellenic subduction zone on- and offshore south-eastern Crete with unprecedented precision using recordings from an amphibian seismic network. The network configuration consisted of up to eight ocean bottom seismometers as well as five temporary short-period and six permanent broadband stations on Crete and surrounding islands. More than 2,500 local and regional events with magnitudes up to M L = 4.5 were recorded during the time period July 2003-June 2004. The magnitude of completeness varies between 1.5 on Crete and adjacent areas and increases to 2.5 in the vicinity of the Strabo trench 100 km south of Crete. Tests with different localization schemes and velocity models showed that the best results were obtained from a probabilistic earthquake localization using a 1-D velocity model and corresponding station corrections obtained by simultaneous inversion. Most of the seismic activity is located offshore of central and eastern Crete and interpreted to be associated with the intracrustal graben system (Ptolemy and Pliny trenches). Furthermore, a significant portion of events represents interplate seismicity along the NNE-ward dipping plate interface. The concentration of seismicity along the Ptolemy and Pliny trenches extends from shallow depths down to the plate interface and indicates active movement. We propose that both trenches form transtensional structures within the Aegean plate. The Aegean continental crust between these two trenches is interpreted as a forearc sliver as it exhibits only low microseismic activity during the observation period and little or no internal deformation. Interplate seismicity between the Aegean and African plates forms a 100-km wide zone along dip from the Strabo trench in the south to the southern shore-line of Crete in the north. The seismicity at the plate contact is randomly distributed and no indications for locked zones were observed. The plate contact below and north of Crete shows no microseismic activity and seems to be decoupled. The crustal seismicity of the Aegean plate in this area is generally confined to the upper 20 km in agreement with the idea of a ductile deformation of the lower crust caused by a rapid return flow of metamorphic rocks that spread out below the forearc. In the region of the Messara half-graben at the south coast of central Crete, a southward dipping seismogenic structure is found that coalesces with the seismicity of the Ptolemy trench at a depth of about 20 km. The accretionary prism south of Crete indicated by the Mediterranean Ridge showed no seismic activity during the observation period and seems to be deforming aseismically.

Becker, D.; Meier, T.; Bohnhoff, M.; Harjes, H.-P.

2010-04-01

7

Plate Tectonics II: Plates, plate boundaries, and driving forces  

NSDL National Science Digital Library

The distribution of earthquakes and volcanoes around the world confirmed the theory of plate tectonics first proposed by Wegener. These phenomena also help categorize plate boundaries into three different types: convergent, divergent, and transform.

Egger, Anne

2003-03-18

8

Continental Margin Tectonics Along the Convergent Plate Boundary of Central Chile  

NASA Astrophysics Data System (ADS)

Multibeam bathymetry along central Chile provides a detailed map of recent tectonic deformation of the margin and incoming oceanic plate from about 28? S to 36? S. The data were collected during R/V SONNE cruises 101, 102, 104 and 161 and a cruise with R/V Vidal Gormaz. Individual pings were edited and cleaned and the different surveys have been merged after depth calculations using a different measured velocity function for each of them. The oceanic Nazca plate is covered by about 100 m of pelagic sediment and the morphology of the igneous basement is displayed well in the bathymetric maps. The oceanic plate topography changes markedly along the subduction zone and exerts a first order control in the distribution of trench sediment infill and in the tectonic style of deformation of the margin. A major boundary occurs at latitude 32?-33? S where the hotspot volcanic chain of Juan Fernadez is currently subducting. The chain subducts oblique to the margin strike and thus the tectonic boundary has been migrating along the subduction zone through time. South of the area of ridge subduction the trench is filled with turbidites and a 20-40 km wide accretionary prism occurs at the front of the continental slope. The upper slope has a smooth morphology indicative of a quiet tectonic domain. At the current area of ridge subduction and north of it (28?-33?S) the trench has a reduced turbiditic infill. The trench infill seems to be at minimum at 31-32S and slightly larger to the north as the trench axis becomes deeper. Here, a small ridge at the slope toe may indicate that reduced accretion is active. The continental slope is deeper and more rugged that to the south displaying a series of small midslope basins. Here, the continental slope morphotectonic structure is the product of tectonic erosion due to the passage of the volcanic ridge.

Weinrebe, W.; Ranero, C. R.; Diaz, J.; Reichert, C.; Vera, E. E.

2003-12-01

9

Plate boundary readjustment in oblique convergence: Example of the Neogene of Hispaniola, Greater Antilles  

NASA Astrophysics Data System (ADS)

The Haitian fold-and-thrust belt is the major mountain belt of Haiti (western part of Hispaniola, Greater Antilles) and resembles a compressive restraining bend between the two major faults which have driven the opening of the Cayman Basin since the Eocene. During the rifting stage, from the middle to the late Eocene, this area underwent an extensional evolution with fissural volcanic activity along NE-SW tilted blocks. The Haitian fold-and-thrust belt was constructed from the Early Miocene until the Present by stacking sedimentary units into a collisional wedge perpendicular to the tilted blocks, which was propagating to the southwest. During the construction of the wedge, piggyback basins were formed and progressively uplifted. During the late Neogene, convergence is localized in the Cul-de-Sac-Enriquillo trough where the active front proceeds southward onto the Beata ridge. In this area, Miocene to Quaternary wrench structures of the lower plate, like the Southern Peninsula and the Enriquillo-Plantain Garden faults, are reactivated as normal faults, owing to the loading of the fold-and-thrust belt.

Pubellier, Manuel; Mauffret, Alain; Leroy, Sylvie; Vila, Jean Marie; Amilcar, Helliot

2000-08-01

10

Deformation kinematics along oblique convergent plate boundary zones in the western United States, Japanese Islands, and Pakistan  

NASA Astrophysics Data System (ADS)

Horizontal velocity gradient tensor field in the western U.S is estimated using moment tensors of earthquakes between 1850 to 1995. The velocity vectors obtained from the integration of the seismic strain rates across the entire plate boundary lie within 5° of the NUVEL-1A Pacific-North American plate motion direction. The magnitude of the earthquake-related velocity is 62% of the NUVEL-1A total Pacific-North American plate motion. The total velocity obtained from the Quaternary fault slip rate data across the entire plate boundary is within 2 mm/yr of the NUVEL-1A predicted Pacific (PA)-North American (NA) plate motion velocity, but directions are 6° anticlockwise of directions given by NUVEL-1A. The total velocity obtained from inversion of recent geodetic data is 2°--3° anticlockwise from the NUVEL-1A NA-PA velocity, but the difference between the two is not significant at the 95% confidence level. Relative motions within the deforming Japanese Islands with respect to the Sea of Japan are determined using earthquake records over the last 414 years, slip rates on Quaternary faults, and angular change rates obtained from triangulation in the last century. The directions of the principal strain axes obtained from seismic, geological, and geodetic data are in general agreement with each other, with the maximum shortening axis oriented in a WNW direction. Intraplate deformation in southwestern Japan determined from the seismic data accommodates a velocity of 5.5 +/- 2 (1sigma) mm/yr in a direction parallel to the Nankai trough, which is about 25% of the plate motion velocity component parallel to the Nankai trough between the Philippine Sea and Eurasian plates. A comparison of shear strain rates, principal strain rates, and velocity fields determined from geodetic data with those calculated from the elastic dislocation models involving interplate motion at the Japan trench indicates that the geodetic strain field in northern Honshu is primarily elastic strain transmitted from the Japan trench. Horizontal strain rate and velocity field that accommodate India-Eurasia plate motion in Pakistan are determined based on constraints from geological and geodetic information in the region. The optimal model that yields a strain rate field consistent with observed geologic, seismologic, and geodetic data gives 17--28 mm/yr of left-lateral strike-slip motion along the Chaman fault zone, 3--6 mm/yr of east-west convergence and 5--14 mm/yr of north-south left-lateral shear across the roughly NS trending Sulaiman Range. (Abstract shortened by UMI.)

Shen-Tu, Bingming

11

Dynamics of convergent plate boundaries: Insights from subduction-related serpentinite melanges from the northern edge of the Caribbean plate  

NASA Astrophysics Data System (ADS)

Subduction-related rock complexes, many of them tectonic melanges, occur in the Central America-Caribbean-Andean belt. I review the lithology and P-T-t paths of HP rocks and offer interpretations and generalizations on the thermal estate of the subducting plate(s), the melange forming events, and the exhumation history of rock complexes formed in the northern branch of the Caribbean subduction zone (Cuba and nearby Guatemala and Dominican Republic; ca. 3000 km apart). These complexes contain high pressure rocks formed and exhumed at the convergent (Pacific-Atlantic) leading edge of the Caribbean plate during ca. 100 Ma (early Cretaceous-Oligocene), attesting for long lasting oceanic -followed by continental- subduction/accretion in the region. Lithologic data indicate a complex melange-forming process. In most cases, the HP rocks represent subducted MOR-related lithologies occurring as tectonic blocks within serpentinite-matrix melanges interpreted as exhumed fragments of the subduction channel(s). Most of these melanges, however, contain fragments of arc/forearc-related non metamorphic and metamorphic (low-P and high-P) sedimentary and igneous rocks. While the HP blocks of arc/forearc material indicate subduction erosion at depth, the interpretation of the LP and non-metamorphic blocks is not straight forward. Indeed, tectonic blocks of HP metamafic rocks are surrounded by antigorite-serpentinite which, in turn, is surrounded by a low-P, low-T (chrysotile-lizardite) serpentinite that makes much of the mélange. These relations indicate that the melanges represent, in fact, tectonic stacks of shallow low-T forearc serpentinite that incorporate tectonic blocks/slices of the subduction-channel (high-P, high-T serpentinite and HP metamafic blocks) and of the arc/forearc crust (low-P and non-metamorphic blocks). This picture is similar to that of HP continental margin-derived tectonic stacks containing exotic slices of antigoritite-serpentine melanges (with blocks of MORB-derived eclogite) incorporated late in the convergent history when oceanic subduction was completed. Hence, incorporation of tectonic slices of the subduction channel into the shallow (low-P, low-T) melanges and subducted/accreted continental margins occur when collision-related dynamics imposed by subduction of buoyant continental or oceanic lithosphere affected the plate margin. Aqueous fluid, sourced from both subducted sediment and metamafic/ultramafic material, was available in large quantity in the subduction environment, as indicated by massive antigoritite, rinds of metasomatic rocks around included HP metamafic rocks, retrogressed eclogite, jadeitite and hydrothermal veins within antigoritite. Such a vigorous hydrology (fluid-flow) deep in the subduction environment point to the development of wide subduction channels and explain the abundance of accreted blocks. It can also explain the scarcity of large scale (>km) slices of the subducted oceanic lithosphere in the belt, for these are likely the result of focalized distribution of deformation occurring when forearc peridotite is barely hydrated (Agard et al., Long-term coupling along the subduction plate interface: Insights from exhumed rocks and models. This session, EGU 2012). Alternatively, these large tectonic slices may have been formed by the collision dynamics caused by late-stage subduction/accretion of the continental margin (or buoyant -thick- oceanic crust). Except maturation (cooling) of the subduction zone with time at orogenic belt-scale, no other simple generalization can be reached on the thermal state of the subducting plate and the exhumation process of the subduction channel. P-T-t paths of HP rocks indicate that slab fragments ranging from cold to hot coexisted during relatively short time intervals (ca. 10 Myr), and some fragments of the subduction channel were exhumed shortly after formation while others lasted several tens of Myr to arrive to the near-surface forearc/accretionary environment. A rather variable thermal state and dynamic history of the subduction environme

García-Casco, A.

2012-04-01

12

Pore fluid pressure detection within the plate boundary fault interface of the Costa Rica convergent margin using AVO attributes  

NASA Astrophysics Data System (ADS)

We conducted an amplitude vs. offset (AVO) analysis on newly acquired 3D seismic reflection data to detect elevated pore fluid content and pore fluid pressure along the Costa Rica convergent margin to address dewatering processes of subduction zone sediments. These data provide the highest quality 3D seismic data acquired to date along a convergent margin for detailed analysis of geophysical properties along the plate boundary fault interface. In 2011, a 55 km by 11 km 3D seismic reflection survey was completed using the R/V Marcus G. Langseth offshore western Costa Rica at the convergent margin of the Cocos and Caribbean plates. We applied pre-stack Kirchhoff time migration to a subset of these data across the frontal prism where amplitude versus offset (AVO) attributes were extracted along the decollement. When pore fluid pressure, ?*, exceeds ?*?0.7, the pressure at which Poisson's ratio begins to approach that of water, the AVO response of a fluid-filled, clay-rich decollement requires a high Poisson's ratio and an excessively low seismic P-wave and S-wave velocity. Acute wedge taper, undercompacted subducted hemipelagic and pelagic sediments, and a smooth decollement in the northwest half of the survey correspond with decollement AVO response of relatively high values of Poisson's ratio. These findings suggest increased pore fluid content and vertical containment of near-lithostatic pore fluid pressures within the decollement. In contrast, increased wedge taper angles, thin hemipelagic and pelagic sediments, and a rugose decollement beneath the southeastern frontal prism, produce an AVO response interpreted as due to lower pore fluid contents and pressures. We propose that large-offset subducting basement normal faults in this area, as close as 20 m from the decollement, induce vertical fractures within the decollement that allow for fluid expulsion into the frontal prism and lower fluid pressure. Lateral variability of overpressure within the decollement shear zone of subduction margins is important in understanding the evolution of frontal prism strain accumulation and seismogenic rupture.

Graf, S.; Bangs, N. L.; McIntosh, K. D.

2012-12-01

13

ConcepTest: EQ and Convergent Boundary Sketch  

NSDL National Science Digital Library

The figure below was drawn by a student to show the relationship between earthquake epicenters (filled circles) and a convergent plate boundary (red line). The figure represents a boundary between an oceanic plate ...

14

ConcepTest: EQ and Convergent Boundary Sketch2  

NSDL National Science Digital Library

The figure below was drawn by a student to show the relationship between earthquake epicenters (filled circles) and a convergent plate boundary (red line). The figure represents a boundary between an oceanic plate ...

15

India Plate Motion, Intraplate deformation and Plate Boundary Processes (Invited)  

NASA Astrophysics Data System (ADS)

We use GPS-measured velocities to geodetically constrain India plate motion, intraplate strain, and examine plate boundary deformation and plate interactions around the India plate. Our solution includes 15 GPS velocities from continuously recording stations from within the stable India plate interior that are used to estimate angular velocity of the India plate with respect to its neighbors. We test a two-plate India system divided along the topographically prominent Narmada Son Lineament and find this scenario to be significant only to 89%. Dense station coverage along the Himalayan range front allows us to rigorously test boundary parameterizations and develop a preferred plate boundary model. In our preferred model the Himalayan Range Front accumulates ~50% of the India-Eurasia convergence with as much as 18 mm/yr of slip accumulation along some segments. We compare earthquake slip vector orientations with predicted divergence directions from our preferred model along the India-Somalia plate boundary. We see good agreement between predicted plate directions from our preferred model and the seismological data. Deviations between our model and the slip vectors highlight areas of diffuse oceanic deformation along the plate boundary. We estimate convergence vectors for the relative plate pairs along the Sumatra subduction zone. We test for the transition between Australian plate convergence and India plate convergence along the Sumatra subduction zone and refine the estimated motion of the Burman sliver plate.

Apel, E. V.; Burgmann, R.; Banerjee, P.

2010-12-01

16

Mapping Plate Tectonic Boundaries  

NSDL National Science Digital Library

To prepare for this activity, students do background reading on Plate Tectonics from the course textbook. Students also participate in a lecture on the discovery and formulation of the unifying theory of plate tectonics, and the relationship between plate boundaries and geologic features such as volcanoes. Lastly, in lecture, students are introduced to a series of geologic hazards caused by certain plate tectonic interactions. The activity gives students practices at identifying plate boundaries and allows them to explore lesser known tectonically active regions.

Kerwin, Michael

17

Revised tectonic boundaries in the Cocos Plate off Costa Rica: Implications for the segmentation of the convergent margin and for plate tectonic models  

Microsoft Academic Search

The oceanic Cocos Plate subducting beneath Costa Rica has a complex plate tectonic history resulting in segmentation. New lines of magnetic data clearly define tectonic boundaries which separate lithosphere formed at the East Pacific Rise from lithosphere formed at the Cocos-Nazca spreading center. They also define two early phase Cocos-Nazca spreading regimes and a major propagator. In addition to these

Udo Barckhausen; Cesar R. Ranero; R. von Huene; Steven C. Cande; Hans A. Roeser

2001-01-01

18

Visualizing Earthquakes at Convergent Plate Margins  

NSDL National Science Digital Library

This screenshot shows the Fiji subduction zone, one of the featured convergent margins in this visualization. The visualization shows how earthquakes at this margin occur at depth, and define the slope of the subducting plate. This visualization also includes other examples of subduction zones and continental convergent margins (Himalayas). Click the image to enlarge or view the MP4 movie (MP4 Video 30.3MB Dec20 11). The purpose of this activity is to introduce students to the distribution and characteristics of earthquakes associated with convergent plate boundaries. Students will learn about how the magnitude and distribution of earthquakes at convergent boundaries are related to processes that occur at these boundaries and to the geometry and position of the two converging plates. Because the depth of earthquakes can be difficult for students to visualize in 2D representations, this activity allows students to visualize the 3D distribution of earthquakes within Earth's surface, which is essential for understanding how different types of earthquakes occur in different tectonic settings. Locations featured in the visualization include the Chile-Peru Subduction Zone, the Aleutian Islands, the Fiji Subeuction Zone, and the Himalayas. Talking points and questions are included to use this visualization as part of an interactive lecture. In addition to playing back the visualization, instructors can also download the visualization software and data set and explore it themselves.

Cara Harwood

19

Mountain Maker- Earth Shaker (Convergent Boundary: oceanic-continental)  

NSDL National Science Digital Library

The representation depicts plate boundary interactions. The convergent boundary is one part of a larger interactive diagram (the 2nd slider/ arrow from the left), that focuses on an ocean plate pressing against a continental plate. This review specifically addresses the part of the resource dealing with what happens when plates pull apart. The "show intro" link provides instruction for diagram manipulation.

20

Tectonic Plates and Plate Boundaries  

NSDL National Science Digital Library

Continents were once thought to be static, locked tight in their positions in Earth's crust. Similarities between distant coastlines, such as those on opposite sides of the Atlantic, were thought to be the work of a scientist's overactive imagination, or, if real, the result of erosion on a massive scale. This interactive feature shows 11 tectonic plates and their names, the continents that occupy them, and the types of boundaries between them.

21

Investigating the strain accumulation of upper plate faults at the N-Chilean convergent plate boundary at different spatial and temporal scales  

NASA Astrophysics Data System (ADS)

According to recent paleoseismological investigations (Cortés et al., 2012), upper plate faults located at the N-Chilean convergent plate boundary well above the coupling zone of the subduction interface are capable of generating large earthquakes of up to Mw=7. We have chosen four active upper plate faults characterized by surface ruptures to investigate their activity and the processes responsible for strain accumulation. In this study, we use a combination of creepmeter time series and high-resolution topography data to assess fault deformation on spatial scales ranging from microns to meters and on temporal scales ranging from seconds to the geomorphological timescale (102-104 yrs). To investigate the short-term deformation signals, we monitor the target faults with an array of creepmeters at a sampling rate of 30 seconds and a resolution of 1 ?m. Despite the fact that long-term displacement rates range between 0.2-0.3 mm/yr for the 103-105 year timescale, displacement rates measured since 2008 are of the order of only a few ?m/yr to approx. 80 ?m/yr. There is no pronounced steady-state creep on the monitored faults. Time series analysis shows a few creep events, and numerous Sudden Displacement Events (SDEs) ranging from 1-59 ?m. The sum of SDEs accounts for a significant part of the cumulative displacement (e.g. Salar del Carmen Fault: 50-60 %, Cerro Fortuna Fault: >90 %), but is an order of magnitude less than the long-term displacement rates. To assess the long-term behavior of the monitored fault segments, high-resolution topography data has been acquired with Differential-GPS by measuring profiles perpendicular to the fault scarps and along incised gullies. The data show clear differences between individual segments of the target faults concerning the total fault scarp height, which is used as a proxy for cumulative displacement. The profiles enable us to distinguish single, composite and multiple scarps; allowing us to capture the number of seismic events that contributed to the creation of the fault scarp. Profiles measured inside gullies allow us to detect knickpoints used as proxy for seismic faulting and thus to quantify the number of events as well as the individual displacement per event. Fault scarp heights and styles/shapes as well as the amount and the height of knickpoints vary predominantly near step-overs, bends and between fault segments. This suggests individual deformation histories of the studied fault segments, possibly depending on their orientations and the local stress conditions both influencing the time dependent strain accumulation pattern. Displacements measured at knickpoints account for approx. 5-40 % of the cumulative displacement. This leaves a significant fraction of displacement probably accumulated by alternative processes, e.g. creep. Comparing the instrumental record with the long-term deformation of the studied fault segments, we note that, according to the instrumental observation, no pronounced steady-state creep could be observed in the recent past of the target faults. In contrast, the topographic data suggest that a significant part of strain was accumulated by aseismic processes. We propose that strain accumulation of the studied faults is highly variable in time, possibly driven or influenced by the stage of the megathrust seismic cycle.

Ewiak, O.; Victor, P.; Ziegenhagen, T.; Oncken, O.

2012-12-01

22

Mapping Plate Boundaries  

NSDL National Science Digital Library

This in-class exercise, profiled on the Starting Point website, is intended to have the students discover plate boundaries based on the uneven geographic occurrence of geologic hazards. The website details the learning goals, teaching notes and materials, and context for this activity. It offers an extensive list of links to additional resources and materials for lecture on geologic hazards and plate tectonics.

Johnson, Rurik

2009-11-12

23

Discovering Plate Boundaries  

NSDL National Science Digital Library

???d?ersity's Earth Science Department offers the Discovering Plate Boundaries educational activity. The exercise is described as a data rich exercise to help students discover the processes that occur at plate tectonic boundaries and has been used successfully with 5th graders to undergraduates. The site provides the necessary downloads of maps; earthquake, volcanic, seafloor, topographic, and bathymetric data; and teacher guides and complete instructions. Because the activity can be geared towards such a large range of students, is well designed, and is easily accessible, educators will definitely appreciate the site.

2007-12-12

24

The Arctic plate boundary  

Microsoft Academic Search

Earthquakes provide information on the regional segmentation and seismotectonics of the poorly known boundary between the Eurasian and the North American plates from the Knipovich Ridge to the Laptev Sea continental margin. To this end, we have sorted earthquake epicenter locations and focal mechanism solutions from global and regional catalogs, assessed location errors and network detectabilities, and compiled a well-constrained

Øyvind Engen; Olav Eldholm; Hilmar Bungum

2003-01-01

25

Discovering Plate Boundaries  

NSDL National Science Digital Library

Discovering Plate Boundaries is based on 5 world maps containing earthquake, volcano, topography, satellite gravity, and seafloor age data. The novel aspect of the exercise is the "jigsaw" manner in which student groups access the maps and use them to discover, classify, and describe plate boundary types. The exercise is based only on observation and description, which makes it useful at a wide variety of levels; it has been used successfully in 5th grade classes, as well as in non-major earth science classes. The exercise is based on a set of wall maps that are not consumed during the exercise. Other inexpensive materials required include two 11x17 black and white copies per student and colored pencils. Because the exercise is not based on student access to the web, it is not dependent on classroom technology equipment. The exercise takes three 50-minute class periods to complete, and involves the students in making presentations to one another in small groups as well as to the whole class. The students come away from the exercise with knowledge of the key features of each type of plate boundary and a sense of why each looks and acts the way it does.

Dale Sawyer

1997-09-15

26

Seismic gaps and plate tectonics: Seismic potential for major boundaries  

Microsoft Academic Search

The theory of plate tectonics provides a basic framework for evaluating the potential for future great earthquakes to occur along major plate boundaries. Along most of the transform and convergent plate boundaries considered in this paper, the majority of seismic slip occurs during large earthquakes, i.e., those of magnitude 7 or greater. The concepts that rupture zones, as delineated by

W. R. McCann; S. P. Nishenko; L. R. Sykes; J. Krause

1979-01-01

27

Isotopic composition of helium, and CO[sub 2] and CH[sub 4] contents in gases produced along the New Zealand part of a convergent plate boundary  

SciTech Connect

New Zealand straddles an active tectonic boundary between the Indo-Australian and Pacific plates. To the NE and SW oblique convergence of oceanic and continental crusts leads to the establishment of subduction zones; in the center continental crusts collide along a transform boundary. With regard to mantle degassing, and on the basis of chemical and He isotopic analyses of 140 samples from all over New Zealand, four major environments can be distinguished: (1) R/R[sub A] values approaching MORB values are observed in areas of andesitic and rhyolitic volcanisms and high-temperature geothermal activity over the center of the North Island. C/[sup 3]He ratios there vary from <10 [times] 10[sup 9], typical of volatiles released from the mantle, in the W, to >40 [times] 10[sup 9], suggesting considerable addition of CO[sub 2] from other than mantle sources, in the E. (2) In areas of recent igneous activity, residual mantle He is extracted from rocks through hydrothermal alteration by percolating groundwater. The gases are low in CO[sub 2] due to conversion to carbonate; any CH[sub 4] present is generated within the crust. C/[sup 3]He ratios are generally well below those of any magmatic vapor. (3) In the absence of recent igneous activity, but in areas of increased seismicity, mantle He may reach the surface along fractures provided by the movement of the subducting slab in forearc regions or by dilatancy pumping or fault-valving in highly compressional, but seismically active parts of an orogenic plate boundary. (4) Mantle degassing is greatly impeded in areas of crustal thickening as indicated by negative gravity anomalies, low seismicity and rapid uplift. There [sup 3]He/[sup 4]He ratios approach typical crustal values of <0.1 R[sub A]. Except in areas of present-day volcanic and geothermal activity, production, transport, storage, and release processes of [sup 3]He, CO[sub 2], and CH[sub 4] appear to be effectively decoupled.

Giggenbach, W.F. (Institute of Geological and Nuclear Sciences, Lower Hutt (New Zealand)); Sano, Y. (Hiroshima Univ. (Japan)); Wakita, H. (Univ. of Tokyo (Japan))

1993-07-01

28

The Role of Serpentinites at Convergent Plate Boundaries: Using New Discoveries to Facilitate the Learning of Major Earth Processes  

NASA Astrophysics Data System (ADS)

A benefit of integrating a vital educational enterprise into a cutting-edge funded research initiative is the ability to bring new scientific discoveries quickly into the classroom without being bound to the textbook publication cycle. A key objective the MARGINS Data in the Classroom project was to facilitate the discovery-to-the-classroom transition of knowledge through the development of Web-deliverable, modular MARGINS “Mini-Lessons”. Some 34 Mini-Lessons are available for classroom use at http://serc.carleton.edu/margins/collection.html, and the development of new Mini-Lessons is a listed Education/Outreach priority of the successor GeoPRISMS Program. An important discovery that arose from the MARGINS Subduction Factory Initiative was the recognition that serpentinites - metamorphically hydrated products of ultramafic rocks rich in serpentine group minerals - are significant constituents of both the mantle wedge and downgoing plate. Serpentines are interesting mineralogically because of their distinctive physical properties, habits and appearance; and for their close affinities with olivine and Mg-rich pyroxenes. Given that serpentines primarily form through the hydration of olivine or Mg-rich pyroxenes, serpentinites constitute a reservoir of subduction-related H2O and entrained trace species in modified mantle rocks of the wedge or slab. As well, serpentine group minerals are interesting rheologically because, as sheet silicates, they can behave in a plastic fashion in rocks that are undergoing deformation, and can thus flow along faults in response to deforming stresses, or be easily entrained in fault rock assemblages along a subduction thrust. Two different MARGINS Mini-Lessons address the issue of serpentinite in subduction zone settings, focusing primarily on the observed occurrences of serpentinite seamounts in the forearc regions of the Mariana subduction system, a MARGINS Subduction Factory Focus Site, and their geochemical and geodynamic implications (e.g., Savov et al 2007); and also on the geophysical inferences of DeShon and Schwartz (2004) and Syracuse et al (2006) as to the presence of abundant serpentinite in different parts of the MARGINS Central American subduction system Focus Site. The Mini-Lesson seeks to lead students through the arguments made in these very recent papers, both through an analysis of the presented data, and through GeoMapApp examinations of bathymetric and geochemical datasets that students can access independently. The instructional approach is one of guided inquiry, with learning goals focused on a deeper understanding of the subduction process through examining its geochemical and geodynamic implications, as well as providing students with experience in the critical reading of the scientific literature and the extraction of useful information from technical papers.

Ryan, J. G.

2010-12-01

29

Uplift of Zagros Mountains slows plate convergence  

NASA Astrophysics Data System (ADS)

Research has indicated that mountain ranges can slow down the convergence between two tectonic plates on timescales as short as a few million years, as the growing mountains provide enough tectonic force to impact plate motions. Focusing on the convergence of the Arabian and Eurasian plates at the Zagros mountain range, which runs across Iran and Iraq, Austermann and Iaffaldano reconstructed the relative motion of the plates using published paleomagnetic data covering the past 13 million years, as well as current geodetic measurements. They show that the convergence of the two plates has decreased by about 30% over the past 5 million years. Looking at the geological record to infer past topography and using a computer model of the mantle-lithosphere system, the authors examined whether the recent uplift across the Zagros Mountains could have caused the observed slowdown. They also considered several other geological events that might have influenced the convergence rate, but the authors were able to rule those out as dominant controls. The authors conclude that the uplift across the Zagros Mountains in the past 5 million years did indeed play a key role in slowing down the convergence between the Eurasian and Arabian plates. (Tectonics, doi:10.1002/tect.20027, 2013)

Balcerak, Ernie

2013-05-01

30

An updated digital model of plate boundaries  

NASA Astrophysics Data System (ADS)

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.

Bird, Peter

2003-03-01

31

Investigating the deformation of upper crustal faults at the N-Chilean convergent plate boundary at different scales using high-resolution topography datasets and creepmeter measurements  

NASA Astrophysics Data System (ADS)

The Chilean convergent plate boundary is one of the tectonically most active regions on earth and prone to large megathrust earthquakes as e. g. the 2010 Mw 8.8 Maule earthquake which ruptured a mature seismic gap in south-central Chile. In northern Chile historical data suggests the existence of a seismic gap between Arica and Mejillones Peninsula (MP), which has not ruptured since 1877. Further south, the 1995 Mw 8.0 Antofagasta earthquake ruptured the subduction interface between MP and Taltal. In this study we investigate the deformation at four active upper plate faults (dip-slip and strike-slip) located above the coupling zone of the subduction interface. The target faults (Mejillones Fault - MF, Salar del Carmen Fault - SCF, Cerro Fortuna Fault - CFF, Chomache Fault - CF) are situated in forearc segments, which are in different stages of the megathrust seismic cycle. The main question of this study is how strain is accumulated in the overriding plate, what is the response of the target faults to the megathrust seismic cycle and what are the mechanisms / processes involved. The hyper arid conditions of the Atacama desert and the extremely low erosion rates enable us to investigate geomorphic markers, e .g. fault scarps and knickpoints, which serve as a record for upper crustal deformation and fault activity about ten thousands years into the past. Fault scarp data has been acquired with Differential-GPS by measuring high-resolution topographic profiles perpendicular to the fault scarps and along incised gullies. The topographic data show clear variations between the target faults which possibly result from their position within the forearc. The surveyed faults, e. g. the SCF, exhibit clear along strike variations in the morphology of surface ruptures attributed to seismic events and can be subdivided into individual segments. The data allows us to distinguish single, composite and multiple fault scarps and thus to detect differences in fault growth initiated either by seismic rupture or fault creep. Additional information on the number of seismic events responsible for the cumulative displacement can be derived from the mapping of knickpoints. By reconstructing the stress field responsible for the formation of identified seismic surface ruptures we can determine stress conditions for failure of upper crustal faults. Comparing these paleo stress conditions with the recent forearc stresses (interseismic / coseismic) we can derive information about a possible activation of upper crustal faults during the megathrust seismic cycle. In addition to the morphotectonic surveys we explore the recent deformation of the target faults by analyzing time series of displacements recorded with micron precision by an array of creepmeters at the target faults for over three years. Total displacement is composed of steady state creep, creep events and sudden displacement events (SDEs) related to seismic rupture. The percentage of SDEs accounts for >50 % (SCF) to 90 % (CFF) of the cumulative displacement. This result very well reflects the field observation that a considerable amount of the total displacement has been accumulated during multiple seismic events.

Ewiak, O.; Victor, P.; Ziegenhagen, T.; Oncken, O.

2012-04-01

32

The seismotectonics of plate boundaries  

NASA Technical Reports Server (NTRS)

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.

Berger, J.; Brune, J. N.; Goodkind, J.; Wyatt, F.; Agnew, D. C.; Beaumont, C.

1981-01-01

33

HMK 1_Plate Boundaries: Present, future, & past  

NSDL National Science Digital Library

Prior to this homework assignment, students will have been exposed (for ~2-3 in class activities and lectures) to general concepts in plate tectonics, plate boundaries, hot spot volcanoes, use of earthquake/volcano trends at plate boundaries, as well as GPS as a modern use to document plate motion. Students receive this activity as a homework assignment to be completed outside of class. Their task is to use provided topographic/bathymetric data, earthquake and volcano distribution, GPS data, as well as ocean floor and hot spot age trends to characterize plate motion in modern, future, and ancient plate boundaries. This is a three-part exercise that involves a modern plate boundary study form the eastern margin of the Pacific plate, a potential future plate boundary in eastern Africa, and a identification of possible ancient plate boundaries in the Eurasian plate.

Hampton, Brian

34

Effective strength of incoming sediments and its implications for plate boundary propagation: Nankai and Costa Rica as type examples of accreting vs. erosive convergent margins  

NASA Astrophysics Data System (ADS)

The location of the seaward tip of a subduction thrust controls material transfer at convergent plate margins, and hence global mass balances. At approximately half of those margins, the material of the subducting plate is completely underthrust so that no accretion or even subduction erosion takes place. Along the remaining margins, material is scraped off the subducting plate and added to the upper plate by frontal accretion. We here examine the physical properties of subducting sediments off Costa Rica and Nankai, type examples for an erosional and an accretionary margin, to investigate which parameters control the level where the frontal thrust cuts into the incoming sediment pile. A series of rotary-shear experiments to measure the frictional strength of the various lithologies entering the two subduction zones were carried out. Results include the following findings: (1) At Costa Rica, clay-rich strata at the top of the incoming succession have the lowest strength (?res = 0.19) while underlying calcareous ooze, chalk and diatomite are strong (up to ?res = 0.43; ?peak = 0.56). Hence the entire sediment package is underthrust. (2) Off Japan, clay-rich deposits within the lower Shikoku Basin inventory are weakest (?res = 0.13-0.19) and favour the frontal proto-thrust to migrate into one particular horizon between sandy, competent turbidites below and ash-bearing mud above. (3) Taking in situ data and earlier geotechnical testing into account, it is suggested that mineralogical composition rather than pore-pressure defines the position of the frontal thrust, which locates in the weakest, clay mineral-rich (up to 85 wt.%) materials. (4) Smectite, the dominant clay mineral phase at either margin, shows rate strengthening and stable sliding in the frontal 50 km of the subduction thrust (0.0001-0.1 mm/s, 0.5-25 MPa effective normal stress). (5) Progressive illitization of smectite cannot explain seismogenesis, because illite-rich samples also show velocity strengthening at the conditions tested.

Kopf, Achim

2013-11-01

35

Flat plate puncture test convergence study.  

SciTech Connect

The ASME Task Group on Computational Mechanics for Explicit Dynamics is investigating the types of finite element models needed to accurately solve various problems that occur frequently in cask design. One type of problem is the 1-meter impact onto a puncture spike. The work described in this paper considers this impact for a relatively thin-walled shell, represented as a flat plate. The effects of mesh refinement, friction coefficient, material models, and finite element code will be discussed. The actual punch, as defined in the transport regulations, is 15 cm in diameter with a corner radius of no more than 6 mm. The punch used in the initial part of this study has the same diameter, but has a corner radius of 25 mm. This more rounded punch was used to allow convergence of the solution with a coarser mesh. A future task will be to investigate the effect of having a punch with a smaller corner radius. The 25-cm thick type 304 stainless steel plate that represents the cask wall is 1 meter in diameter and has added mass on the edge to represent the remainder of the cask. The amount of added mass to use was calculated using Nelm's equation, an empirically derived relationship between weight, wall thickness, and ultimate strength that prevents punch through. The outer edge of the plate is restrained so that it can only move in the direction parallel to the axis of the punch. Results that are compared include the deflection at the edge of the plate, the deflection at the center of the plate, the plastic strains at radius r=50 cm and r=100 cm , and qualitatively, the distribution of plastic strains. The strains of interest are those on the surface of the plate, not the integration point strains. Because cask designers are using analyses of this type to determine if shell will puncture, a failure theory, including the effect of the tri-axial nature of the stress state, is also discussed. The results of this study will help to determine what constitutes an adequate finite element model for analyzing the puncture hypothetical accident.

Snow, Spencer (Idaho National Laboratories); Ammerman, Douglas James; Molitoris, David (Westinghouse); Tso, Chi-Fung (ARUP); Yaksh, Mike (NAC International)

2010-10-01

36

Constraints on the Character of Plate Tectonics From the Study of Diffuse Plate Boundaries  

NASA Astrophysics Data System (ADS)

While the main global expression of tectonics at Earth's surface is that of plate tectonics, i.e., narrow boundaries between rigid plates, a significant fraction of the lithosphere (perhaps 15% of both ocean basins and continents) is undergoing diffuse deformation. The existence of these zones of deformation (often termed ``diffuse plate boundaries'') raises the question of why the majority of deformation occurs at narrow boundaries, and how narrow boundaries may form. Study of the best characterized diffuse zone of oceanic deformation, which occurs in the equatorial Indian Ocean and may also be the best candidate for an incipient convergent plate margin, may help to elucidate these questions. The Indo-Australian composite plate comprises 3 component plates (i.e., the nondeforming portions of the composite plate) and multiple diffuse plate boundaries. We determine the general relation between the relative angular velocity between two component plates and the torque that the two component plates exert on one another across their mutual diffuse boundary. We show that the torque between the Indian and Capricorn component plates (respectively north and south of the equatorial diffuse plate boundary) is oriented far from the relative angular velocity vector between the two plates, and is subparallel to the torque exerted on India by the Tibetan plateau. With earlier work showing that onset of the current episode of deformation in the Indian Ocean coincided with the attainment of maximum elevation of the Tibetan plateau, this indicates that the lithospheric deformation in the equatorial Indian Ocean is being driven by the outward push of the Tibetan plateau. To achieve a torque balance, we find that the force per unit length exerted by the Tibetan plateau on the Indian component plate must be nearly identical to the strength of the oceanic lithosphere, which we infer to be 9 (+/- 2) x 1012 N m-1. Given that the effect of plateau formation by horizontal shortening of continental crust strongly influences the compressive stress available to deform oceanic lithosphere, this coincidence may be necessary for plate tectonics to continue and evolve on geologically long time scales while restricting these zones of diffuse deformation to relatively minor proportions of the oceanic plate, if narrow plate boundaries such as subduction zones evolve from diffuse plate boundaries.

Gordon, R. G.; Zatman, S.

2001-12-01

37

BOLIVAR & GEODINOS: Investigations of the Southern Caribbean Plate Boundary  

NASA Astrophysics Data System (ADS)

The southern Caribbean-South American plate boundary has many similarities to California's San Andreas system: 1) The CAR-SA system consists of a series of strands of active right lateral strike-slip faults extending >1000 km from the Antilles subduction zone. This system has several names and includes the El Pilar, Coche, San Sebastian, Moron, and Oca faults. 2) The CAR-SA relative velocity has been about 20 mm/yr of mostly right lateral motion since about 55 Ma, giving a total displacement on the CAR-SA plate boundary similar to that of the San Andreas system. 3) The plate boundary has about 10% convergence in western SA, with less as one moves eastward due to relative convergence between North and South America. 4) The CAR-SA system has fold and thrust belts best developed continentward of the strike-slip faults, similar to the San Andreas. 5) There is a big bend in the CAR plate boundary at approximately the same distance from the Antilles trench as the big bend in Southern California is from the Cascadia subduction zone. The tectonic origins of the CAR-SA plate boundary and the San Andreas are very different, however, despite the similarities between the systems. Rather than impingement of a ridge on a trench, the CAR-SA system is thought to have resulted from a continuous oblique collision of the southern end of a Cretaceous island arc system with the northern edge of South America. During this process the CAR island arc and the modern CAR plate overrode a proto-Caribbean plate and destroyed a Mesozoic passive margin on the northern edge of SA. BOLIVAR and GEODINOS are multi-disciplinary investigations of the lithosphere and deeper structures associated with the diffuse CAR-SA plate boundary zone. We review a number of observations regarding the plate boundary obtained or confirmed from these studies: 1) The Caribbean Large Igneous Province, being overridden by the Maracaibo block in western Venezuela, can be identified beneath Aruba and coastal Venezuela, and is associated with broad uplift of the coastal regions. This is likely a site of continental growth. 2) The accretionary wedge terranes of the Southern Caribbean Deformed Belt formed in the Neogene, and extend as far east as the Aves Ridge. They result from SA overriding the CAR LIP, which for a number of reasons, we do not regard as normal subduction. 3) Igneous rocks on the islands of the Leeward Antilles arc, Aruba to Los Testigos, show a steady decrease in age from west to east (94.7-37.4 Ma), suggesting that the islands have been progressively captured from the Antilles arc by the plate boundary during the prolonged island arc-continent collision. Terrane capture models thus far cannot completely explain the data. 4) High (> 6.5 km/s) P-velocity bodies are found in the shallow crust along the main strike-slip faults along much of the plate boundary. We interpret these as elements of the HP/LT metamorphic terranes found in the adjacent thrust belts of central Venezuela. This suggests to us that displacement partitioning in the trench and subsequent strike-slip both play important roles in exhumation of the HP/LT terranes. 5) Crustal thickness variations in the plate boundary region are large (> 10 km), of short spatial wavelength (< 100 km), and indicate that the highest elevations of the coastal mountain belts are not supported isostatically.

Levander, A.; Schmitz, M.; Working Groups, B.

2006-12-01

38

The Rivera-Cocos Plate Boundary Revisited  

NASA Astrophysics Data System (ADS)

The nature of the boundary between the Rivera and Cocos plates has long been controversial. Early studies (predominantly earthquake studies) suggested that it was a NE oriented left lateral transform boundary. With the collection of multi-beam bathymetric data during the SEAMAT cruise of the N/O Jean Charcot in 1987 it became clear that this early proposal was not entirely correct as no clear transform morphology was observed. Shortly after the SEAMAT campaign, three main proposals emerged to explain this lack of transform morphology. The first two proposals favored the results of earthquake studies over the new multibeam data. The first proposed that the boundary is indeed a left-lateral transform boundary, you just cannot see it. In other words, it was a diffuse boundary and the resolution of the multi-beam data was not sufficient to reveal the associated deformation. The second proposal was that it was an east-west oriented, dextral transform, the proposal being based on the results of an earthquake directivity analysis. The third proposal favored the morphologic data over the earthquake data and proposed that the plate boundary was not a transform boundary, but was instead a divergent boundary, at least near the Middle America Trench in what is now called the EL Gordo Graben. Implicit in this proposal was that the earthquake activity did not reflect plate motions but rather were the result of local stresses. Since 2002, several marine geophysical campaigns have been conducted in the area of the Rivera-Cocos plate boundary with the aim of resolving this debate. During the 2002 BART and FAMEX campaigns of the N/O L'ATALANTE, multibeam bathymetric and seafloor backscatter data were collected along the boundary. During the MARTIC04 and MARTIC05 campaigns of the B/O EL PUMA dense total field magnetic surveys were conducted covering the entire plate boundary. Lastly, the multibeam coverage obtained during the BART/FAMEX campaigns was extended northward during the MORTIC07 campaign of the B/O EL PUMA. In this talk we will present these new data (some of which have already been published) and discuss the constraints that these data impose on the nature of the Rivera-Cocos plate boundary.

Bandy, W. L.; Mortera-Gutierrez, C. A.; Michaud, F.; Ortega Ramírez, J.

2013-05-01

39

Plate TectonicsPlate Tectonics Plate TectonicsPlate Tectonics  

E-print Network

Plate TectonicsPlate Tectonics #12;Plate TectonicsPlate Tectonics · Lithosphere ­ strong, rigid, transform boundaries ­ travel 1 to 11 cm/yr relative to one another #12;14 tectonic plates today #12;Mid asthenosphere that flows · 8 large lithospheric plates and 6 smaller ones ­ separated by divergent, convergent

Siebel, Wolfgang

40

Crustal deformation and volcanism at active plate boundaries  

NASA Astrophysics Data System (ADS)

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

Geirsson, Halldor

41

The simulation of Lamb waves in a cracked plate using the scaled boundary finite element method.  

PubMed

The scaled boundary finite element method is applied to the simulation of Lamb waves for ultrasonic testing applications. With this method, the general elastodynamic problem is solved, while only the boundary of the domain under consideration has to be discretized. The reflection of the fundamental Lamb wave modes from cracks of different geometry in a steel plate is modeled. A test problem is compared with commercial finite element software, showing the efficiency and convergence of the scaled boundary finite element method. A special formulation of this method is utilized to calculate dispersion relations for plate structures. For the discretization of the boundary, higher-order elements are employed to improve the efficiency of the simulations. The simplicity of mesh generation of a cracked plate for a scaled boundary finite element analysis is illustrated. PMID:22978864

Gravenkamp, Hauke; Prager, Jens; Saputra, Albert A; Song, Chongmin

2012-09-01

42

Convergent plate margin east of North Island, New Zealand  

SciTech Connect

The Indian-Pacific plate boundary passes along the eastern margin of North Island, New Zealand, with the Pacific plate being thrust under the Indian plate to the west. The continental slope forming the Indian plate margin is broad with a well-formed series of trench slope basins and intervening ridges along the continental slope and shelf, subparallel to the margin, and continuing onto land. Multichannel seismic reflection data recorded across this margin show a thick (2.5-km) sedimentary section overlying oceanic basement in the deep-water part of the profile, and part of this sedimentary section is apparently being subducted under the accretionary prism. At the toe of the continental slope, nascent thrusts, often showing little apparent offset but a change in reflection amplitude, occur over a broad region. Well-defined trench slope basins show several episodes of basin formation and thrusting and are similar to structural interpretations for adjacent onshore basins. A bottom simulating reflector, which may delineate a gas-hydrate layer, can be traced over the midslope part of the profile. A major reflector, interpreted as the base of the accretionary prism, can be traced discontinuously to the coast where it coincides with the top of a zone of high seismicity, considered to mark the top of the subducted Pacific plate.

Davey, F.J; Hampton, M.; Lewis, K.

1986-07-01

43

A plate tectonic model for the Paleozoic and Mesozoic constrained by dynamic plate boundaries and restored  

E-print Network

A plate tectonic model for the Paleozoic and Mesozoic constrained by dynamic plate boundaries November 2001; accepted 15 November 2001 Abstract We developed a plate tectonic model for the Paleozoic rates and major tectonic and magmatic events. Plates were constructed through time by adding

Cerveny, Vlastislav

44

Prototypical Concepts and Misconceptions of Plate Tectonic Boundaries  

NASA Astrophysics Data System (ADS)

Students of geology encounter many prototypical/exemplar concepts* that include representative, but not necessarily defining, features and characteristics. This study of students' prototypical representations of plate tectonic boundaries indicates that their representations are rich sources of information about their misconceptions about plate tectonics. After lectures in plate tectonics and mountain building, 353 students in a general education geology class were asked to draw a continent-continent convergent boundary. For this study, a correct answer is defined as having the major features in correct proportions as depicted in the plate boundary diagrams on the USGS web. Fifty-two percent of the drawings were either incorrect or incomplete such that they could not be interpreted. Only 48% were readily interpretable, and of these 22% drew the boundary correctly, showing a thickening of crust where two continents collide. Thirty-three percent drew the boundary showing concave slabs of continental crust as one might imagine two pieces of firm rubber pushed together on a rigid surface and 45% depicted mountains as one might imagine inverted ice cream cones on a rigid plank. Twenty-one senior class geology majors and graduate students were given the same assignment. Forty-eight percent rendered a correct drawing, whereas 38% drew the same ice cream cone on a plank type picture that 45% of the general education students drew. In a second class of 12 geology majors, only 1 student drew a cross section of a continent-ocean boundary similar to standard representation. Four of 12 drew mountains on the top of continental crust over a subduction zone but did not draw a compensating mass within the crust or lithosphere. Prototypical drawings provide more information about students' concepts than do most multiple-choice questions. For example, sixty-two percent of theses students who drew mountains similar to foam rubber pads pushed together on a desk or ice cream cones on a plank correctly answered a multiple-choice question that would appear to indicate a better understanding than the drawings reveal. Furthermore, 12 interviewed students made statements that could be interpreted to indicate that they understood the concept of mountain building at plate tectonic boundaries better than their drawings suggest. Incoherence of multiple-choice responses, verbal statements and drawings may be common in novice learners. If cognitive scientists are correct in their model of multiple types of mental representations for the same term, then the fact that novices may hold inconsistent representations is not surprising. The fact that students at various academic levels draw very similar prototypes that are incorrect is evidence that students have distinct and persistent prototype misconceptions. * Cognitive scientists define a prototypical/exemplar concept as a mental representation of the best examples or central tendencies of a term.

Sibley, D. F.; Patino, L. C.

2003-12-01

45

Earthquakes, Plate Boundaries, and Depth Indiana Standard Indicators  

E-print Network

, volcanoes, trenches, and mountains. ES.1.24 ­ Understand and discuss continental drift, sea-floor spreading of the ocean and continental crust and the depth of earthquakes, and types of plate boundaries where or continental crust? · What is the explanation behind the earthquakes that do not occur at plate boundaries? #12

Polly, David

46

Study on plate silencer with general boundary conditions  

NASA Astrophysics Data System (ADS)

A plate silencer consists of an expansion chamber with two side-branch rigid cavities covered by plates. Previous studies showed that, in a duct, the introduction of simply supported or clamped plates into an air conveying system could achieve broadband quieting from low to medium frequencies. In this study, analytical formulation is extended to the plate silencer with general boundary conditions. A set of static beam functions, which are a combination of sine series and third-order polynomial, is employed as the trial functions of the plate vibration velocity. Greens function and Kirchhoff-Helmholtz integral are used to solve the sound radiation in the duct and the cavity, and then the vibration velocity of the plate is obtained. Having obtained the vibration velocity, the pressure perturbations induced by the plate oscillation and the transmission loss are found. Optimization is carried out in order to obtain the widest stopband. The transmission loss calculated by the analytical method agrees closely with the result of the finite element method simulation. Further studies with regard to the plate under several different classical boundary conditions based on the validated model show that a clamped-free plate silencer has the worst stopband. Attempts to release the boundary restriction of the plate are also made to study its effect on sound reflection. Results show that a softer end for a clamped-clamped plate silencer helps increase the optimal bandwidth, while the same treatment for simply supported plate silencer will result in performance degradation.

Liu, Gongmin; Zhao, Xiaochen; Zhang, Wenping; Li, Shuaijun

2014-09-01

47

Dynamics of diffuse oceanic plate boundaries: insensitivity to rheology  

NASA Astrophysics Data System (ADS)

Diffuse plate boundaries, which are zones of deformation hundreds to thousands of kilometres wide, occur in both continental and oceanic lithosphere. Here, we build on our prior work in which we described analytic approximations to simple dynamical models that assume that the vertically averaged viscous force resisting deformation in diffuse oceanic plate boundaries (DOPBs) is described by either a linear Newtonian viscous rheology or a yield-stress (high-exponent power-law) rheology. An important observation is that the poles of relative rotation of adjacent component plates tend to lie in the diffuse plate boundary that separates them. A key cause of this tendency is that a faster spin is needed to balance a component of torque through the middle of a diffuse plate boundary than to balance an equal component of torque lying 90° from the middle of the diffuse boundary. The strength of that tendency depends on rheology, however, with the tendency being stronger for a yield-stress rheology than for a Newtonian viscous rheology. For the special case of the pole of rotation lying outside of and along the strike of the boundary, these large differences can be simply explained in terms of the distribution of boundary-perpendicular normal forces acting across the boundary. In the Newtonian case, the distribution of forces has an along-strike gradient that can balance a component of torque about the middle of the boundary, while in the yield-stress case, the distribution of forces has zero along-strike gradient and cannot balance a component of torque about the middle of the diffuse plate boundary. To expand our analysis to intermediate power laws of geophysical interest (i.e. power-law exponents of 3 to 30), as well as to investigate more thoroughly the behaviour for a high-exponent power law, we numerically integrate the force distribution to obtain the torques. Results for intermediate power laws resemble the yield-stress rheology much more than they resemble the Newtonian rheology and depend only weakly on the width of the deforming zone. To quantify the probability that a pole of rotation lies in a diffuse plate boundary, we numerically integrate the expectation assuming that all orientations of torque are equally probable. For a power-law exponent of n= 10: 49 per cent of possible torque orientations produce angular velocities outside the diffuse plate boundary if the boundary is 55° long (similar in length to the boundary between the Nubian and Somalian component plates); 21 per cent of possible torque orientations produce angular velocities outside the diffuse plate boundary if the boundary is 30° long (similar in length to the boundary between the Indian and Capricorn component plates and to that between the Capricorn and Australian component plates); and 6 per cent of possible torque orientations produce angular velocities outside the diffuse plate boundary if the boundary is 15° long (similar in length to the boundary between the North American and South American component plates and to that between the Macquarie and Australian component plates). These results reinforce the prior conclusion that the pole is more strongly locked into the boundary if a DOPB is short than if it is long. For all boundary lengths, but even more so for short boundaries, the relationship between angular velocity and torque depends only weakly on the power-law exponent of the rheology as long as n>= 3. From this, we conclude that orientation of the relative torque across a DOPB can be inferred from the location of the pole of rotation without precise knowledge of the appropriate power-law exponent.

Zatman, Stephen; Gordon, Richard G.; Mutnuri, Kartik

2005-07-01

48

Structure of the incoming ocean plate and the erosional convergent margin off Antofagasta, northern Chile  

NASA Astrophysics Data System (ADS)

The northern Chile convergent margin is a classical example of active tectonic erosion during subduction. Tectonic erosion probably started in late Jurassic times as indicated by the continuous eastward migration of the volcanic arc, and it is still active. The upper continental plate is mainly made of arc basement and shows widespread evidence of large scale mass wasting. The margin is fronted by a < 10 km wide sediment prism. The trench is largely sediment starved, but grabens are filled by ~ 1 km of slope debrie right before subduction indicating that a large volume of fluids is input into the subduction channel. The ocean plate displays a high relief horst-graben topography. In 1995, a number of multichannel seismic reflection (MCS) lines and several coincident wide-angle refraction profiles, complemented with multibeam bathymetry, were acquired by the BGR (Bundesanstalt fuer Geowissenschaften und Rohstoffe, Hannover, Germany) and GEOMAR in the area (CINCA experiment, SONNE cruise 104). In this work, we investigate the seismic structure of the margin off the Mejillones Peninsula just north of Antofagasta (23° S) along one of the CINCA seismic refraction transects (SO104 - 401). A 2D velocity field with the interplate geometry is obtained using joint refraction and reflection traveltime tomography. The velocity model is then compared with a coincident MCS line (SO104 - 13) and with the interplate seismogenic zone outlined from the 1995 Antofagasta earthquake (Mw=8) aftershock sequence. Results indicate that the upper plate is constituted by two bodies separated by a subhorizontal layer (7-8 km depth) defined by a velocity inversion. The low velocity layer is interpreted as a tectonic boundary between an upper body composed of a set of faulted and tilted blocks resulting from the collapse of the lower and middle slope due to basal erosion along the plate boundary, and a lower body made of crystalline basement. Seismic velocities within both bodies show significant lateral and vertical velocity gradients, indicating that the frontal part of the upper plate is highly fractured and invaded by fluids injected from the subduction channel. This interplate channel is well imaged by reflected seismic phases. The geometry of the plate boundary is coincident with that derived from the MCS line in the frontal part of the prism and with the seismogenic zone defined from the aftershock sequence beneath the coast line. Seismic velocity of the upper mantle of the incoming oceanic crust is < 7.8 km/s, indicating that the mantle peridotites may be largely serpentinized by fluids percolating along the faults formed by the bending of the ocean plate as it approaches the trench.

Sallarès, V.; Ranero, C. R.

2003-04-01

49

The Plate Boundary Observatory Borehole Seismic Network  

NASA Astrophysics Data System (ADS)

As part of the NSF-funded EarthScope Plate Boundary Observatory, UNAVCO will install and operate 103 borehole seismic stations throughout the western United States. These stations continuously record three- component seismic data at 100 samples per second, using Geo-Space HS-1-LT 2-HZ geophones in a sonde developed by SONDI and Consultants (Duke University). Each seismic package is connected to an uphole Quanterra Q330 data logger and Marmot external buffer, from which UNAVCO retrieves data in real time. UNAVCO uses the Antelope software suite from Boulder Real-Time Technologies (BRTT) for all data collection and transfer, metadata generation and distribution, and monitoring of the network. The first stations were installed in summer 2005, with 19 stations installed by September 2006, and a total of 28 stations expected by December 2006. In a prime example of cooperation between the PBO and USArray components of EarthScope, the USArray Array Network Facility (ANF), operated by UC San Diego, handled data flow and network monitoring for the PBO seismic stations in the initial stages of network operations. We thank the ANF staff for their gracious assistance over the last several months. Data flow in real time from the remote stations to the UNAVCO Boulder Network Operations Center, from which UNAVCO provides station command and control; verification and distribution of metadata; and basic quality control for all data. From Boulder, data flow in real time to the IRIS DMC for final quality checks, archiving, and distribution. Historic data are available from June 2005 to the present, and are updated in real time with typical latencies of less than ten seconds. As of 1 September 2006, the PBO seismic network had returned 60 GB of raw data. Please visit http://pboweb.unavco.org for additional information on the PBO seismic network.

Hasting, M.; Eakins, J.; Anderson, G.; Hodgkinson, K.; Johnson, W.; Mencin, D.; Smith, S.; Jackson, M.; Prescott, W.

2006-12-01

50

Dynamic implications of Baja California microplate kinematics on the North America - Pacific plate boundary region.  

E-print Network

??Many plate boundaries appear to be broad deformation zones, composed of several smaller microplates (e.g. California, Alaska, Mediterranean sea). To accurately address plate boundary deformation,… (more)

Plattner, Christina

2009-01-01

51

Bending of rectangular plates with discontinuous boundary conditions  

NASA Astrophysics Data System (ADS)

A method is presented for the numerical solution of the bending problem for a rectangular Kirchhoff plate loaded by transverse pressure, with boundary conditions including alternating clamped and free support sections. A solution is obtained by using second-, fourth-, and infinite-order straight line methods. Results of deflection and bending moment calculations are presented for the central point of a square plate.

Kolesnikov, I. Yu.

52

Convergence of adaptive BEM for some mixed boundary value problem  

PubMed Central

For a boundary integral formulation of the 2D Laplace equation with mixed boundary conditions, we consider an adaptive Galerkin BEM based on an (h?h/2)-type error estimator. We include the resolution of the Dirichlet, Neumann, and volume data into the adaptive algorithm. In particular, an implementation of the developed algorithm has only to deal with discrete integral operators. We prove that the proposed adaptive scheme leads to a sequence of discrete solutions, for which the corresponding error estimators tend to zero. Under a saturation assumption for the non-perturbed problem which is observed empirically, the sequence of discrete solutions thus converges to the exact solution in the energy norm. PMID:23482570

Aurada, M.; Ferraz-Leite, S.; Goldenits, P.; Karkulik, M.; Mayr, M.; Praetorius, D.

2012-01-01

53

Constraining Late Cretaceous to mid Eocene plate boundaries in the southwest Pacific  

NASA Astrophysics Data System (ADS)

The southwest Pacific has undergone a complex tectonic history since the Late Cretaceous, involving multiple episodes of subduction, back-arc spreading and continental deformation. Starkly contrasting reconstructions have been proposed for this period, ranging from tectonic quiescence with no plate boundary between the Lord Howe Rise (LHR) and Pacific, to widespread subduction and back-arc spreading, and this disparity reflects sparse and ambiguous data. Placing further constraints on these reconstructions is crucial for a variety of applications, from global-scale geodynamic studies using plate circuits to basin-scale studies of paleogeographic evolution and vertical motions. Geologic and kinematic data from the southwest Pacific are reviewed to better constrain the tectonic history of the region from the Late Cretaceous to mid Eocene, including the timing and location of plate boundary activity. This facilitates better constraints on the time-dependent evolution of the southwest Pacific plate circuit so that motion between plate pairs is consistent with geologic data and known tectonic regimes. The southwest Pacific comprised three spreading ridges during this time: in the Southeast Indian Ocean, Tasman Sea and Amundsen Sea. However, at least one, and possibly two other plate boundaries also accommodated relative motions: in the West Antarctic Rift System (WARS) and between the LHR and Pacific. Uncertainties in the timing and nature of plate boundaries prevent the construction of a robust reconstruction model and the implementation of a southwest Pacific plate circuit. Some previous plate models include continuous subduction east of the LHR throughout the Late Cretaceous-Cenozoic, while an alternative scenario involves the absence of plate boundaries between the LHR and Pacific until 45 Ma. Geologic observations suggests that subduction initiated to the east of New Caledonia at c. 55 Ma, including dyke emplacement and metamorphism in New Caledonia, and arc-type rocks dredged from the Tonga forearc. These geologic and kinematic data do not require a plate boundary between the LHR and Pacific from c. 84-55 Ma, in agreement with previous studies. A plate boundary may have existed before 55 Ma, however net convergence/divergence at this boundary would have been minor, with a possible strike-slip component. By combining geologic observations with a kinematic analysis, we propose that from 0-55 Ma an Antarctic plate circuit must be used in reconstructions, in which LHR-Pacific motion is unconstrained. From 55-74 Ma Antarctic or Australian circuits can be reconciled with regional geology when revised relative motion histories at the Australian-Antarctic ridge and in the WARS are adopted. A well-constrained Antarctic circuit predicts <50 km of strike-slip motion at a LHR-Pacific boundary. Alternatively, an Australian circuit assuming the LHR was part of the Pacific plate, predicts 100-150 km of extension in the WARS, that is orthogonal in the Ross Sea and oblique further east. Prior to 74 Ma neither plate circuit is preferable, as more data are needed to better constrain regional spreading histories.

Matthews, K. J.; Williams, S.; Whittaker, J. M.; Müller, D.; Clarke, G. L.; Seton, M.; Flament, N. E.

2013-12-01

54

A diffuse plate boundary model for Indian Ocean tectonics  

NASA Technical Reports Server (NTRS)

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.

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

1985-01-01

55

Dynamic behaviour of thin composite plates for different boundary conditions  

NASA Astrophysics Data System (ADS)

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. 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.

Sprintu, Iuliana; Rotaru, Constantin

2014-12-01

56

Melt generation in the Earth's mantle at Convergent Plate Margins  

E-print Network

The five geologic studies presented in this thesis document how the recycling of tectonic plates at subduction zones has a profound effect on the melting behavior of the Earth's mantle. Two experimental studies (Chapters ...

Till, Christy B

2011-01-01

57

Plate convergence west of Patagonia and the Antarctic Peninsula since 61 Ma  

NASA Astrophysics Data System (ADS)

A new plate kinematic model portrays plate motions immediately west and south of Drake Passage in the southeast Pacific Ocean. Overall intermediate-to-slow rate spreading generated oceanic lithosphere as the Phoenix plate diverged from the Antarctic plate. The model shows a history of Phoenix plate motion that is interpretable as having been affected by a northeast-increasing gradient in the slab pull force since chron 18 (39 Ma), during which time newer, less dense lithosphere was subducting in the southwest than in the northeast. The model allows first calculations of Phoenix-Farallon (Nazca) plate motion parameters in the south Pacific plate circuit. Using these parameters, it is possible to show that the simplest assumptions about the ridge's segmentation, length and migration are consistent with existing suggestions of its location from consideration of slab window-related volcanism at sites in South America around 50 and 20 Ma. The parameters thus define ridge locations that can be used to define which plates were subducting beneath South America and the Magallanes and Antarctic plates, and when. We consider the relationships between the plate convergence rate, obliquity and the history of magmatism on the Antarctic Peninsula and at the North Patagonian batholith, showing that magmatic pulses can be related to accelerations in the plate convergence rate. Between these settings, Phoenix-South American plate motion was almost parallel to the Fuegian trench. Here, magmatism in Paleocene to early Miocene times must be related to the presence of a slab subducted beneath the region by the less oblique collision further north. Later magmatism can be related to migration of the Phoenix-Farallon ridge and Phoenix-Farallon-Antarctic triple junction into the area south of the Fuegian margin, which brought it into slow low-obliquity convergence with first Farallon and then Antarctic plate lithosphere.

Eagles, Graeme; Scott, Benjamin G. C.

2014-12-01

58

Plate convergence, transcurrent faults and internal deformation adjacent to Southeast Asia and the western Pacific  

NASA Technical Reports Server (NTRS)

A model for oblique convergence between plates of lithosphere is proposed in which at least a fraction of slip parallel to the plate margin results in transcurrent movements on a nearly vertical fault which is located on the continental side of a zone of plate consumption. In an extreme case of complete decoupling only the component of slip normal to the plate margin can be inferred from underthrusting. Recent movements in the western Sunda region provide the most convincing evidence for decoupling of slip, which in this region is thought to be oblique to the plate margin. A speculative model for convergence along the margins of the Philippine Sea is constructed from an inferred direction of oblique slip in the Philippine region. This model requires that the triple point formed by the junction of the Japanese and Izu-Bonin trenches and the Nankai trough migrate along the Sagami trough.

Fitch, T. J.

1971-01-01

59

Natural frequencies of thick, symmetrically-laminated, skew, trapezoidal plates with various boundary supports  

SciTech Connect

Increasing use of composite materials in structures requires an accurate method of predicting response. Transverse shear effects can play an important role in laminated structures, even those that are considered thin, and as a result, should not be neglected. The free vibration response of generally laminated, thick, skewed, trapezoidal plates is investigated due of the lack of information in this area. In the method developed, Chebychev polynomials are used as displacement functions in the Rayleigh-Ritz method. To account for various edge supports, free, simply supported, and clamped, appropriate linear and rotational springs are introduced to satisfy the essential boundary conditions. First-order shear theory is used to account for transverse shear effects, and rotary inertia is also included in the model. Convergence of the solution resulting from changes in spring values and number of terms in the series is investigated. To demonstrate the accuracy of the method, results for thin isotropic and laminated plates are compared to past results for various planforms and boundary conditions. Next, thick isotropic plate results are compared to available published results. Thick laminated plate results for various planforms and boundary conditions are then presented. Variations in natural frequencies due to geometric parameter changes, such as taper ratio and sweep angle, are also studied.

Kapania, R.K.; Lovejoy, A.E.

1994-12-31

60

In-Plane Vibration Analysis of Annular Plates with Arbitrary Boundary Conditions  

PubMed Central

In comparison with the out-of-plane vibrations of annular plates, far less attention has been paid to the in-plane vibrations which may also play a vital important role in affecting the sound radiation from and power flows in a built-up structure. In this investigation, a generalized Fourier series method is proposed for the in-plane vibration analysis of annular plates with arbitrary boundary conditions along each of its edges. Regardless of the boundary conditions, the in-plane displacement fields are invariantly expressed as a new form of trigonometric series expansions with a drastically improved convergence as compared with the conventional Fourier series. All the unknown expansion coefficients are treated as the generalized coordinates and determined using the Rayleigh-Ritz technique. Unlike most of the existing studies, the presented method can be readily and universally applied to a wide spectrum of in-plane vibration problems involving different boundary conditions, varying material, and geometric properties with no need of modifying the basic functions or adapting solution procedures. Several numerical examples are presented to demonstrate the effectiveness and reliability of the current solution for predicting the in-plane vibration characteristics of annular plates subjected to different boundary conditions. PMID:24688416

Qin, Zhengrong; Wang, Qingshan

2014-01-01

61

Fluid budgets at convergent plate margins: Implications for the extent and duration of fault-zone dilation  

USGS Publications Warehouse

Faults at convergent plate boundaries are important conduits for fluid escape, and recent evidence suggests that fluid expulsion along them is both transient and heterogeneous. For the Nankai and Barbados convergent margins, we have used numerical models to investigate the long-term partitioning of expelled fluids between diffuse flow and flow along connected high-permeability fault conduits. For a simple case of spatial heterogeneity, we estimated the extent of high-permeability conduits necessary to maintain a balance between incoming and expelled fluids. For the case of transient expulsion, we constrained the duration of elevated permeability required to balance the fluid budgets. Comparison of modeled and observed geochemical profiles suggests that the initiation of connected flow conduits is delayed with respect to the time of accretion into each accretionary complex and may be related to burial below a critical depth, either where the overlying wedge is sufficiently thick to prevent fluid escape to the sea floor or where sediments behave brittlely.

Saffer, D.M.; Bekins, B.A.

1999-01-01

62

Integrating Seismological and Tectonic Studies to Constrain Lithospheric Evolution at Complex Plate Boundaries.  

E-print Network

??The relative motion of tectonic plates across their boundaries generates deformation in the surrounding lithosphere. How this deformation is expressed reflects both present-day plate configurations… (more)

Hayes, Gavin

2007-01-01

63

Preliminary estimates of plate convergence in the Caucasus collision zone from global positioning system measurements  

Microsoft Academic Search

Global Positioning System (GPS) measurements (1991-1994) traversing the Greater and Lesser Caucasus mountains indicate a minimum N-S shortening of 10+\\/-2mm\\/yr. This represents approximately 30-50% of the NUVEL-1A convergence rate between the Arabian and Eurasian plates. The remainder of the convergence appears to be accommodated in the areas south of the Lesser Caucasus, by a combination of right-lateral strike-slip faulting on

R. E. Reilinger; S. C. McClusky; B. J. Souter; M. W. Hamburger; M. T. Prilepin; A. Mishin; T. Guseva; S. Balassanian

1997-01-01

64

Modeling the Philippine Mobile Belt: Tectonic blocks in a deforming plate boundary zone  

NASA Astrophysics Data System (ADS)

The Philippine Mobile Belt, a seismically active, rapidly deforming plate boundary zone situated along the convergent Philippine Sea/Eurasian plate boundary, is examined using geodetic and seismological data. Oblique convergence between the Philippine Sea Plate and the Eurasian plate is accommodated by nearly orthogonal subduction along the Philippine Trench and the Manila Trench, as well as by strike-slip faulting along the Philippine Fault system. We develop a model of active plate boundary deformation in this region, using elastic block models constrained by known fault geometries, published GPS observations and focal mechanism solutions. We then present an estimate of block rotations, fault coupling, and intra-block deformation, based on the best-fit model that minimizes the misfit between observed and predicted geodetic vectors and earthquake slip vectors. Slip rates along the Philippine fault vary from ~22 - 36 mm/yr in the Central Visayas and about 10 to 40 mm/yr in Luzon, trending almost parallel to the fault trace. In northern Luzon, Philippine Fault splays accommodate transpressional strain. The Central Visayas block experiences convergence with the Sundaland block along the Negros Trench and the Mindoro-Palawan collision zone. On the eastern side of Central Visayas, sinistral strike-slip faulting occurs along the NNW-SSE-trending Philippine Fault. Mindanao Island in southern Philippines is dominated by east-verging subduction along the Cotabato Trench, and strain partitioning (strike- slip faulting with west-verging subduction) in eastern Mindanao along the southern Philippine Fault and Philippine Trench, respectively. Oblique active sinistral strike slip faults in Central and Eastern Mindanao that were hypothesized to be responsible for basin formation are obvious boundaries for tectonic blocks. Located south of Mindanao Island we define an adjoining oceanic block defined by the N-S trending complex dual subduction zone of Sangihe and Halmahera, primarily delineated by seismicity, bathymetric profiles and E-W thrust mechanisms. In our preferred model, the Philippine Mobile Belt can be represented by at least 12 independently moving rigid tectonic blocks, separated by active faults and subduction zones.

Galgana, G. A.; Hamburger, M. W.; McCaffrey, R.; Bacolcol, T. C.; Aurelio, M. A.

2007-12-01

65

Numerical Study of Flat-Plate Boundary Layer Bypass Transition.  

NASA Astrophysics Data System (ADS)

Previous numerical simulations of boundary-layer bypass transition due to free-stream-turbulence (FST) have focused primarily on the transition region itself, using an ad hoc inflow condition downstream of the plate leading edge. This approach involves significant assumptions regarding the spatial evolution of FST and its penetration into the boundary layer. Additionally, the effects of FST length-scale have largely been ignored, which can lead to incorrect decay rates over the boundary layer, making a quantitative comparison with experiments difficult. We present DNS of boundary-layer bypass transition, which addresses some of the above limitations by including the super-elliptic leading edge of the flat-plate model inside the computational domain. The FST is generated upstream of the plate, enabling the leading-edge/FST interaction region to be fully captured in the simulations. The FST also has the same decay rate as in the experiments of Roach and Brierlay (1992), facilitating a direct comparison with the experimental data.

Ovchinnikov, Victor; Piomelli, Ugo; Choudhari, Meelan M.

2004-11-01

66

A plate tectonic model for the Paleozoic and Mesozoic constrained by dynamic plate boundaries and restored synthetic oceanic isochrons  

Microsoft Academic Search

We developed a plate tectonic model for the Paleozoic and Mesozoic (Ordovician to Cretaceous) integrating dynamic plate boundaries, plate buoyancy, ocean spreading rates and major tectonic and magmatic events. Plates were constructed through time by adding\\/removing oceanic material, symbolized by synthetic isochrons, to major continents and terranes. Driving forces like slab pull and slab buoyancy were used to constrain the

G. M Stampfli; G. D. Borel

2002-01-01

67

Your Mission: To become familiar with the major plate boundaries through exploration of plate tectonic features using Google Earth.  

E-print Network

boundaries through exploration of plate tectonic features using Google Earth. Your Supplies: (1) A computer with internet access and the Google Earth program of Earth's tectonic plates using Google Earth. To do this, login

Smith-Konter, Bridget

68

Motion and rigidity of the Pacific Plate and implications for plate boundary deformation  

NASA Astrophysics Data System (ADS)

Using up to 11 years of data from a global network of Global Positioning System (GPS) stations, including 12 stations well distributed across the Pacific Plate, we derive present-day Euler vectors for the Pacific Plate more precisely than has previously been possible from space geodetic data. After rejecting on statistical grounds the velocity of one station on each of the Pacific and North American plates, we find that the quality of fit of the horizontal velocities of 11 Pacific Plate (PA) stations to the best fitting PA Euler vector is similar to the fit of 11 Australian Plate (AU) velocities to the AU Euler vector and ˜20% better than the fit of nine North American Plate (NA) velocities to the NA Euler vector. The velocities of stations on the Pacific and Australian Plates each fit a rigid plate model with an RMS residual of 0.4 mm/yr, while the North American velocities fit a rigid plate model with an RMS velocity of 0.6 mm/yr. Our best fitting PA/AU relative Euler vector is located ˜170 km southeast of the NUVEL-1A pole but is not significantly different at the 95% confidence level. It is also close (<70 km in position and <3% in rate) to a pole derived from transform faults identified from satellite altimetry, suggesting that the vector has not changed significantly over the past 3 Myr. Our relative Euler vector is also consistent with all known geological and geodetic evidence concerning the AU/PA plate boundary through New Zealand. The GPS sites offshore of southern California are presently moving 4-5 ± 1 mm/yr relative to predicted Pacific velocity, with their residual velocities in approximately the opposite direction to PA/NA relative motion. Likewise, the easternmost sites in South Island, New Zealand, are moving ˜3 ± 1 mm/yr relative to predicted Pacific velocity, with the residuals in approximately the opposite direction to PA/AU relative motion. These velocity residuals are in the same sense as predicted by elastic strain accumulation on known plate boundary faults but are of a significantly higher magnitude in both southern California and New Zealand, implying that the plate boundary zones in both regions are wider than previously believed.

Beavan, J.; Tregoning, P.; Bevis, M.; Kato, T.; Meertens, C.

2002-10-01

69

Finite element modeling of stress in the Nazca plate - Driving forces and plate boundary earthquakes  

NASA Technical Reports Server (NTRS)

The state of stress within the Nazca plate due to plate driving forces and large plate boundary earthquakes has been analyzed by applying a finite element method using the wave front solution technique to models of the intraplate stress field in a single plate using a refined grid. Although only static elastic models have been explicitly calculated, certain limiting cases of an elastic plate over a viscous asthenosphere were also treated. A state of nearly east-west compression inferred from the source mechanism of thrust earthquakes in the interior of the plate requires ridge pushing forces. The net pulling force on the oceanic plate by the subducted slab has a maximum value comparable to pushing forces. The estimated horizontal deviatoric stress in intraplate regions, based on potential forces associated with the ridge, is on the order of a few hundred bars. The intraplate stress field in the region of the 1960 earthquake may change by a few tens of bars at most once the asthenosphere has relaxed, with changes on the order of one bar occurring at greater distances into the plate. The changes in the intraplate stress field are probably not noticeable unless the lithosphere is near failure.

Richardson, R. M.

1978-01-01

70

Global positioning system measurements of Indian plate motion and convergence across the Lesser Himalaya  

Microsoft Academic Search

We use Global Positioning System (GPS) measurements acquired from 1991 to 1995 to constrain the motion of sites in Bangalore, in southern India, and Kathmandu, Nepal, relative to a global GPS network. These measurements permit estimates of the northward motion of the Indian plate and convergence between the southern Himalaya and the Indian subcontinent. The velocities of Bangalore and Kathmandu

J. Freymueller; R. Bilham; R. Bürgmann; K. M. Larson; J. Paul; S. Jade; V. Gaur

1996-01-01

71

Mountain belt growth inferred from histories of past plate convergence: A new tectonic inverse problem  

Microsoft Academic Search

Past plate motions display a range of variability, including speedups and slowdowns that cannot easily be attributed to changes in mantle related driving forces. One key controlling factor for these variations is the surface topography at convergent margins, as previous modeling shows that the topographic load of large mountain belts consumes a significant amount of the driving forces available for

Giampiero Iaffaldano; Hans-Peter Bunge; Martin Bücker

2007-01-01

72

Tectonics of the Nazca-Antarctic plate boundary  

NASA Technical Reports Server (NTRS)

A new bathymetric chart of part of the Chile transform system is constructed, based mainly on an R/V Endeavor survey from 100 deg W to its intersection with the East Ridge of the Juan Fernandez microplate. A generally continuous lineated trend can be followed through the entire region, with the transform valley being relatively narrow and well-defined from 109 deg W to approximately 104 deg 30 min W. The fracture zone then widens to the east, with at least two probable en echelon offsets to the south at 104 deg and 102 deg W. Six new strike-slip mechanisms along the Chile Transform and one normal fault mechanism near the northern end of the Chile Rise, inverted together with other plate-motion data from the eastern portion of the boundary, produce a new best-fit Euler pole for the Nazca-Antarctic plate pair, providing tighter constraints on the relative plate motions.

Anderson-Fontana, Sandra; Larson, Roger L.; Engeln, Joseph F.; Lundgren, Paul; Stein, Seth

1987-01-01

73

Sharp Lithosphere-asthenosphere Boundaries of Oceanic Plates  

NASA Astrophysics Data System (ADS)

P- and S-receiver function (RF) analysis of borehole broadband ocean bottom seismic data (Kumar et al., 2008, this meeting) and the high-resolution RF image of the subducting Pacific plate beneath the northeast Japan (Kawakatsu, 2008, this meeting) both show the presence of sharp lithosphere-asthenosphere boundaries (LABs) of oceanic plates which appear to show dependence on the plate age. The apparent plate-age dependence of the thickness of the oceanic plate is consistent with a thermally controlled origin for the oceanic LAB, but the fact it is observed in short period (~3s) indicates a sharp boundary (the transition thickness of less than 10-15km), thus a chemical or fabric origin. The observed amplitude of the LAB signals, on the other hand, requires a rather large S-wave speed reduction of ~7%, similar to the observation beneath the eastern North America (Rychert et al., 2007, JGR). One possibility to explain these features is the presence of partial melting in the asthenosphere. The depth of partial melting of the model of Mierdel et al. (2007, Science) estimated using a thermal model incorporating pressure and thermal effect on the thermal diffusivity (Honda&Yuen, 2001, GRL) reproduces the basic trend in the data. For a texturally equilibrated partially molten region, however, a 7% S-wave speed reduction translates into ~3.5% of melting (Takei, 2002, JGR) which may be unrealistically large. The presence of the rather strong LAB signal of oceanic plates reported here may be partly attributed to other mechanisms such as the presence of shear zone of partially-molten region in the asthenosphere (e.g., Holtzman et al., 2003, Science).

Kawakatsu, H.; Kumar, P.; Shinohara, M.; Kanazawa, T.; Araki, E.; Suyehiro, K.

2008-12-01

74

An Introduction to Plate Tectonics  

NSDL National Science Digital Library

This page is a brief introduction to plate tectonics. It starts with a discussion of the evolution of the theory of plate tectonics and the arguments supporting it. It then discusses the processes associated with tectonics and the types of plate boundaries: divergent, convergent and transform boundaries. It concludes with a discussion of the current hypotheses of what causes plates to move.

75

On the Relationship between SST Gradients, Boundary Layer Winds, and Convergence over the Tropical Oceans  

E-print Network

A linear mixed layer model that skillfully reproduces observed surface winds and convergence over the tropical oceans is used to examine the relative influence of boundary layer and free-tropospheric processes on the ...

Bretherton, Christopher S.

76

Free vibration of two elastically coupled rectangular plates with uniform elastic boundary restraints  

NASA Astrophysics Data System (ADS)

An analytical method is derived for determining the vibrations of two plates which are generally supported along the boundary edges, and elastically coupled together at an arbitrary angle. The interactions of all four wave groups (bending waves, out-of-plane shearing waves, in-plane longitudinal waves, and in-plane shearing waves) have been taken into account at the junction via four types of coupling springs of arbitrary stiffnesses. Each of the transverse and in-plane displacement functions is expressed as the superposition of a two-dimensional (2-D) Fourier cosine series and several supplementary functions which are introduced to ensure and improve the convergence of the series representation by removing the discontinuities that the original displacement and its derivatives will potentially exhibit at the edges when they are periodically expanded onto the entire x- y plane as mathematically implied by a 2-D Fourier series. The unknown expansions coefficients are calculated using the Rayleigh-Ritz procedure which is actually equivalent to solving the governing equation and the boundary and coupling conditions directly when the assumed solutions are sufficiently smooth over the solution domains. Numerical examples are presented for several different coupling configurations. A good comparison is observed between the current results and the FEA models. Although this study is specifically focused on the coupling of two plates, the proposed method can be directly extended to structures consisting of any number of plates.

Du, Jingtao; Li, Wen L.; Liu, Zhigang; Yang, Tiejun; Jin, Guoyong

2011-02-01

77

Vibrations of plates with clamped and free edges excited by low-speed turbulent boundary layer flow  

Microsoft Academic Search

Plate vibrations due to turbulent boundary layer (TBL) excitation can depend strongly on the plate boundary conditions, especially when the flow convects over the plate at speeds much slower than those of the bending waves in the plate. The vibration response of a TBL excited baffled flat rectangular plate is analyzed with two sets of boundary conditions: (a) all four

S. A. Hambric; Y. F. Hwang; W. K. Bonness

2004-01-01

78

Stress accumulation and release at complex transform plate boundaries  

SciTech Connect

Finite element methods are used to model the dynamics of deformation along complex transform plate boundaries, specifically the San Andreas fault system, California. Effects of mantle rheology and fault geometry on the stress buildup and release are investigated. No prior knowledge of the earthquake cycle time or amount of fault slip is assumed that the results suggest that the San Andreas fault slips at low shear stress (about 15 MPa). Although the maximum stress on the fault is 15 MPa, models with an upper mantle shear zone deforming entirely by dislocation creep accumulate stresses that exceed 100 MPa, a stress level high enough to drive localized dynamic recrystallization and a shift in dominant deformation mechanism to diffusion creep. Models in which the mantle shear zone deform locally by diffusion creep reach a dynamic steady state where lithospheric shear stresses never exceed the specified fault stress anywhere in the model and indicate that the strength of the upper mantle is an important parameter in the dynamics of plate boundary deformation. 17 refs.

Verdonck, D.; Furlong, K.P. (Pennsylvania State Univ., University Park (United States))

1992-10-01

79

Features on Venus generated by plate boundary processes  

NASA Technical Reports Server (NTRS)

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.

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

1992-01-01

80

Initiation of deep convection along boundary layer convergence lines in a semitropical environment  

SciTech Connect

The initiation of deep convection through forcing along boundary layer convergence lines is examined using observations from the Convection and Precipitation/Electrification (CaPE) Experiment conducted in east-central Florida during the summer of 1991. The study is concerned with the evolution and interaction of two converging air masses that were initially separated by an intervening boundary layer characterized by neutral stability and horizontal convective rolls. As anticipated, major thunderstorms erupt when the east coast breeze eventually collides with thunderstorm outflows from the west, but unexpected convection takes place prior to their merger along a well-defined confluence zone associated with a persistent quasi-stationary roll vortex signature. In this study, complementary interactions between roll vortex convergence lines and the sea-breeze front are not sufficient to trigger deep convection. However, organized convergence along the eastward-spreading thunderstorm outflows did interact periodically with roll vortex convergence maxima to initiate a new series of new storms. Results from two-dimensional numerical model simulations replicate many of the observed boundary layer features. Surface heating produces circulations similar to sea-breeze frontal zones that appear near the coastlines and progress steadily toward each other as the interior boundary layer deepens. Vertical velocity maxima develop over the associated convergence zones, but weaker periodic maxima also occur within the interior air mass at intervals similar to the spacing of observed horizontal roll vortices.

Fankhauser, J.C.; Crook, N.A.; Tuttle, J.; Miller, L.J.; Wade, C.G. [NCAR, Boulder, CO (United States)] [NCAR, Boulder, CO (United States)

1995-02-01

81

Diffuse Oceanic Plate Boundaries, Thin Viscous Sheets of Oceanic Lithosphere, and Late Miocene Changes in Plate Motion and Tectonic Regime  

NASA Astrophysics Data System (ADS)

Diffuse plate boundaries are often viewed as a characteristic only of continental lithosphere and as a consequence of its rheology, while narrow boundaries and plate rigidity are viewed as characteristic of oceanic lithosphere. Here we review some of the evidence that shows that deformation in the ocean basins is in many places just as diffuse as deformation in the continents. Moreover, we argue that the best description of these oceanic deforming zones is the un-plate tectonic-like representation as a fluid. Diffuse oceanic plate boundaries are deforming zones that are typically thousands of kilometers long (along strike) and hundreds to thousands of kilometers wide (across strike). These plate boundaries also appear to have deformation that is broadly distributed with no single fault or system of faults taking up most of the relative plate motion. Consequently the spatially averaged strain rates across diffuse oceanic plate boundaries are orders of magnitude lower than in narrow plate boundaries. One of Earth's best examples of a diffuse oceanic plate boundary is located in the equatorial Indian Ocean. A fluid-like representation of deformation in this diffuse boundary explains many observations, including the steadiness of the deformation process, the characteristic across-strike width of deformation relative to the along-strike length of the deforming zone, and the change of style in deformation across the 86°E fracture zone. In addition, poles of relative rotation between adjacent component plates tend to lie within the diffuse plate boundary that separates them; this is also predicted by models of diffuse plate boundaries that assume a power-law fluid approximation, irrespective of rheology (for power-law rheologies between Newtonian and plastic end-members). A change in behavior of the lithosphere from elastic or visco-elastic to that of a fluid may be interpreted as a phase change, not in microscopic but in megascopic properties, above a certain threshold of force per unit length applied to the lithosphere. There remain many outstanding fundamental kinematic, dynamical, and rheological questions, the answers to which would enhance our understanding of diffuse oceanic plate boundaries. These questions include the timing of initiation and acceleration of motion across various diffuse oceanic plate boundaries, the relative and absolute strengths of the upper and lower oceanic lithosphere, changes in torques across diffuse oceanic plate boundaries and their role in causing rapid changes in plate motion. Of particular interest is the role of diffuse oceanic plate boundaries in the widespread re-organization of plate motion and tectonic regime that occurred at ~8 Ma in the Tibetan Plateau, Indian Ocean, Pacific Ocean, and western North America. Diffuse plate boundaries, especially in the oceans, are excellent natural laboratories, not only as windows on the mechanical and rheological properties of the lithosphere, but also--at least in the oceans--for investigating a variety of styles of widely distributed deformation that is ignored by traditional plate tectonics.

Gordon, R. G.; Royer, J.

2005-12-01

82

The Scotia-Antarctica plate boundary from 35°W to 45°W  

NASA Astrophysics Data System (ADS)

A compilation of available multichannel seismic profiles acquired along the southern margin of the Scotia Sea east of the South Orkney microcontinent has allowed identifying and mapping the main morphological and structural features of the central segment of the Scotia-Antarctica plate boundary. This margin is composed by several bathymetric highs of variable size and uncertain crustal nature, separated by deep troughs and restricted oceanic basins. Some of these troughs represent pull-apart basins. Three main segments oriented WNW-ESE (the western sector), ENE-WSW (the central sector, here named Bruce Deep), and NE-SW (the eastern sector), have been described. These segments are separated by NNW-SSE-trending release zones, disposed in an en-echelon geometry, which represent mostly strike-slip faults. The western segment corresponds to the northern margin of the South Orkney microcontinent, where a subduction zone seems to be present, even if its present-day activity is unclear. The segment further to the east corresponds to an ENE-oriented basin (Bruce Deep), which separates the Bruce Bank from the eastern promontory of the South Orkney continental platform. To the south of the Bruce Deep, a wide deformation zone with N-verging folds and thrusts (here named Jane Thrust Belt), has been identified from seismic data. The eastern segment of the plate boundary is structurally the less constrained, and may be composed by a series of tectonic lineaments of different lengths. From the Bruce Bank to the east, focal mechanisms maintain a prevalent left-lateral strike-slip motion combined with an extensional component. In this sector, earthquakes are located in a 150 km wide area and on a local scale are difficult to follow unambiguously at the plate boundary. Lithologic analyses on dredged material recovered along a flank of one of the morphological relieves present south of the Discovery Bank to 35°W (here collectively named Irizar Highs), yielded a dominant granitic composition. A similar composition characterizes the rocks collected in the southern flank of the south-easternmost Jane Bank. This suggests a continental crust nature for these bathymetric highs, now dispersed along this sector of the Scotia-Antarctica plate boundary. We propose here a tectonic evolution for this margin, dominated since the Early Miocene by the northward subduction of the Weddell Sea oceanic crust. The development of a dextral, en-echelon transform fault system facilitated the process of fragmentation and dispersion of the crustal blocks, dismembered the subduction zone, and possibly inverted the direction of convergence: Therefore, the Scotia plate would subduct beneath the Antarctic plate, in the western sector, and Weddell Sea would subduct beneath Scotia plate, in the eastern sector. Finally, the activation of left-lateral transtensional strike-slip lineaments generated narrow pull-apart basins in the fore-arc sectors of the convergent zones.

Lodolo, E.; Civile, D.; Vuan, A.; Tassone, A.; Geletti, R.

2010-04-01

83

Mechanical Models of Coontinental Plate BoundariesL Fault Slip Rates and Interseismic Stress Rotation Rates.  

E-print Network

??We first describe the methodology for a two-dimensional, elastic deformable microplate modeling approach for continental plate boundaries. Deformable microplate models combine discrete slip on microplate… (more)

Langstaff, Meredith Avery

2014-01-01

84

Gelled propellant flow: Boundary layer theory for power-law fluids in a converging planar channel  

SciTech Connect

A boundary layer theory for the flow of power-law fluids in a converging planar channel has been developed. This theory suggests a Reynolds number for such flows, and following numerical integration, a boundary layer thickness. This boundary layer thickness has been used in the generation of a finite element mesh for the finite element code FIDAP. FIDAP was then used to simulate the flow of power-law fluids through a converging channel. Comparison of the analytic and finite element results shows the two to be in very good agreement in regions where entrance and exit effects (not considered in the boundary layer theory) can be neglected. 6 refs., 8 figs., 1 tab.

Kraynik, A.M.; Geller, A.S.; Glick, J.H.

1989-10-01

85

Patterns of seismogenesis for giant plate-boundary earthquakes in island-arc-type subduction systems  

NASA Astrophysics Data System (ADS)

The global record of giant earthquake occurrence in subduction zones during the instrumental and historical eras is woefully short; only about 16 events with magnitudes above 8.4 are reasonably well documented since 1700. We find no examples of giant (M > 8.4) interplate thrust events and/or wide-ranging tsunamis sourced in the classic island arcs with fast backarc spreading (Bonin, Marianas, Tonga-Kermadec, Vanuatu, and South Scotia). The Sumatra-Andaman Earthquake of 2004 (SAE) ruptured a sector of the INDIA-BURMA subduction boundary and evidently had no known historical antecedents, suggesting that the return time may be many centuries to millennia and consistent with low convergence rates. Moreover, the persistence of rupture to the north in the weakly volcanic Nicobar/Andaman sector gives one pause to reflect on the assumption that island arcs, especially those with active back-arc spreading such as the Marianas, do not produce great interplate- thrust earthquakes. The Andaman/Nicobar subduction segment is an unusual island arc. Only two arc volcanoes occur between the convergent plate boundary west of the Andamans and the backarc ridge/transform system to the east. Backarc spreading in the Andaman/ Nicobar segment is unusual because the NNW spreading directions are nearly parallel to the trench/deformation-front as do the INDIA-BURMA plate motions across it. This geometry suggests that arc-normal extension, trench migration and associated slab normal motions may not mechanically decouple this subduction system. The Nicobar sector of the rupture for the 2004 event is roughly 200 km wide judging from the aftershock distribution; a distribution that persists to the east under the Nicobar Islands, suggesting that the plate-boundary dip is very shallow in that latitude range. If this is correct, then the down-dip limitation on seismogenic slip set by serpentinized forearc mantle (Hyndman et al., 2003) may not control rupture width as it apparently does for many island arcs with steeper slab dips. Finally, this subduction system receives a large sediment influx from the giant Irrawadi and Ganges River delta systems to the north that drain the active collisional mountain belts further north. High sediment influx and trench sediment acumulation are factors that are present in 12 of the 14 subduction zones that have hosted the giant interplate thrust earthquakes mentioned earlier. This influx appears to be important in the development of a subduction channel of granular material in the plate boundary that may enable ruptures to run to great lengths by smoothing out barriers to earthquake slip. Several island-arc subduction systems (the Manus, SW Ryukyu, W Aleutians, and possibly the South Shetlands systems) have attributes similar to the Nicobar/Andaman segment of the SAE rupture. Moreover, arc volcanic activity is weak or absent and convergence also tends to be slow in all of these island-arc systems. Research done in collaboration with the USGS Tsunami Source Working Group (Steve Kirby and Eric Geist (Co-Chairs) David Scholl, Roland von Huene, Rick Blakely, Ray Wells, and Willie Lee (Secretary))

Kirby, S. H.

2006-12-01

86

Convergence  

Microsoft Academic Search

Call for Papers: Convergence The Journal of Optical Networking (JON) invites submissions to a special issue on Convergence. Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers,

Thomas E. Darcie; Robert Doverspike; Martin Zirngibl; Steven K. Korotky

2005-01-01

87

Discovering Plate Boundaries Update: Builds Content Knowledge and Models Inquiry-based Learning  

Microsoft Academic Search

Discovering Plate Boundaries (DPB) is a jigsaw-structured classroom exercise in which students explore the fundamental datasets from which plate boundary processes were discovered. The exercise has been widely used in the past ten years as a classroom activity for students in fifth grade through high school, and for Earth Science major and general education courses in college. Perhaps more importantly,

D. S. Sawyer; M. S. Pringle; A. T. Henning

2009-01-01

88

Sediment subduction - A probable key for seismicity and tectonics at active plate boundaries  

Microsoft Academic Search

A model involving extensive occurrence of sediment subduction and viscous interaction of lithospheric plates at convergent zones is applied to derive simple relations between extremal values of seismic and global tectonic parameters. The strength of mechanical coupling at the interface zone is defined as the maximum shear stress at the base of the over-thrusting plate. A test of these relations

Vladimir Kostoglodov

1988-01-01

89

Free vibrations of thermally stressed orthotropic plates with various boundary conditions  

NASA Technical Reports Server (NTRS)

An analytical investigation of the vibrations of thermally stressed orthotropic plates in the prebuckled region is presented. The investigation covers the broad class of trapezoidal plates with two opposite sides parallel. Each edge of the plate may be subjected to different uniform boundary conditions. variable thickness and arbitrary temperature distributions (analytical or experimental) for any desired combination of boundary conditions may be prescribed. Results obtained using this analysis are compared to experimental results obtained for isotropic plates with thermal stress, and to results contained in the literature for orthotropic plates without thermal stress. Good agreement exists for both sets of comparisons.

Bailey, C. D.; Greetham, J. C.

1973-01-01

90

Obduction at plate boundaries : thermo-mechanical modelling  

NASA Astrophysics Data System (ADS)

Obduction involves the emplacement of fragments of oceanic lithosphere (ophiolites) over a continental one. Ophiolitic sequences, composed of mafic to ultramafic lithologies, are characterized by a much higher density than continental material. For this reason the processes that control obduction are not straightforward and remain enigmatic in the framework of plate tectonics. The occurrence of large ophiolitic complexes in Oman (the Semail ophiolite) or New Caledonia nevertheless suggests that obduction can take place over large, regional-scale areas. Such obducted ophiolites are generally underlain by a thin, high temperature metamorphic sole and thrust onto high-pressure continental metamorphic units, both of which formed as a result of short-lived, almost coeval processes (~10 Ma offset between these main metamorphic events). In this study we present two-dimensional thermo-mechanical models of obduction. These models involve several different geodynamic settings (based on margin geometry, presence of a ridge, boundary conditions,...) that may lead or not to obduction. Major, first-order geological features (petrological, geochronological, structural data) are critically used to discriminate between these different models. An important result is that few situations actually enable to reproduce obduction in our numerical simulations, which indicates that only a narrow range of parameters can lead to realistic obduction. After assessing the respective influence of the key parameters, we finally propose a geodynamic model for the formation of the Semail ophiolite which is consistent with available data.

Duretz, Thibault; Agard, Philippe; Yamato, Philippe; Burov, Evgueni

2013-04-01

91

Obliquely convergent plate motion and its relation with forearc sliver movement, El Salvador volcanic arc  

NASA Astrophysics Data System (ADS)

The magmatic arc in El Salvador is interpreted to result from the subduction of the Cocos plate underneath the Caribbean plate along the Middle America trench. In addition, El Salvador contains a fore-arc sliver that moves 11 mm/yr westward relative to the back-arc. Well-defined strike-slip faults along the magmatic arc accommodate forearc sliver motion, but are offset at several locations by en echelon pull-apart step-overs with abundant normal faults. All basaltic-andesitic magmatic centers (San Miguel, San Vincente, San Salvador, Santa Ana) are located within these step-overs, while the two major rhyolitic calderas (Ilopango, Coatepeque) occur directly along the strike-slip faults. There are two puzzling aspects about the strike-slip tectonism. First, a silicic, shallow magma body that intrudes the San Miguel fault zone (part of the El Salvador fault system) was emplaced syn-tectonically (sigmoidal field and magnetic foliations, subhorizontally plunging magnetic lineations and dextral shear at the microscale). Within the dextrally sheared portion of the intrusion, an obsidian band with a 40Ar/39Ar age of 7.46 Ma indicates that dextral strike-slip tectonism in the Salvadoran arc has been an ongoing process for ~7.5 Ma. This casts significant doubt on whether Cocos ridge subduction (that started ~1 Ma ago) is the cause of the ongoing forearc movement. The potentially more significant problem is that the fore-arc sliver in El Salvador moves 11 mm/yr westward relative to the back-arc despite a nearly orthogonal angle of convergence (with a convergence rate of ~77 mm/yr) near El Salvador and absence of significant frictional coupling along the subduction interface. Further, GPS indicates that the Nicaraguan and Salvadoran forearcs define a semi-rigid sliver moving at nearly the same trench-parallel rates despite along-trench changes in the subduction angle. Consequently, it is tempting to attribute the movement of both forearc slivers to Cocos ridge subduction. However, as mentioned above, initiation of strike-slip movement during collision of the Cocos ridge appears incompatible with Miocene strike-slip deformation that occurs. These examples serve to highlight the difficulties in understanding forearc movement in obliquely convergent systems, even in relatively modern belts where the plate motions are well constrained.

Tikoff, B.; DeMets, C.; Garibaldi, N.; Hernandez, W.; Hernandez, D.

2012-12-01

92

Understanding Plate Motions  

NSDL National Science Digital Library

This interactive site uses illustrations and photographs along with text to explain the movement of tectonic plates and the result of this movement on the surface of the Earth. There is a detailed discussion of the movement at each of the four types of plate boundaries: divergent, convergent, transform, and plate boundary zones. Both lateral and vertical movements are depicted by maps and diagrams and resulting Earth structures are shown in photographs.

2007-12-12

93

Overview on the Plate Boundaries Along the Western Mexican Pacific Margin  

NASA Astrophysics Data System (ADS)

The cinematic of the Pacific, Rivera and Cocos oceanic plates have a significant impact on the subduction process and seismic cycles occurring along the western Mexican Pacific margin of the North American and Caribbean plates. Sections of Pacific (PAC), Rivera (RIV), Cocos (COC), North American (NAM) and Caribbean (CAB) plate boundaries along the western margin of Mexico are not well constrained. From north to south: the transform-rift system at Gulf of California has been generally considered as part of PAC-NAM plate boundary. However results of the FAMEX cruise at 2002 evidenced that Tosco-Abreojos Fault System along the western margin of Baja California Peninsula is active. Should this tectonic structure be considered as a plate boundary? At the RIV plate northern corner (including Mazatlan Basin), the scatter seismicity recorded between Tamayo FZ and the Marias Islands restricts the characterization of the plate boundary between the RIV and NAM plates. Some authors have proposed that Tamayo FZ and Marias I. Escarpment are the RIV-NAM plate boundary. Recently other authors have called that RIV-NAM boundary is a geomorphology lineament that runs from a Rivera Rise transform at 23N to the northern end of Marias I. Escarpment. Even so this concept is not sustained with seismic activity. Further this thought would imply that the oceanic lithosphere of Mazatlan Basin would form part of NAM plate. Other thoughts are either that there is a diffuse RIV-NAM plate boundary to the north of the Maria Archipelago, or Middle America Subduction Zone is gradually extending northward of the Maria Is. While the plate boundary at SE corner of the RIV plate is neither well defined morphologically nor seismically constraint, offshore Colima Coast. Some authors have proposed that this zone is a diffuse plate boundary between RIV and COC plates, result of a NE-SW shear plate motion. Other authors have proposed that the RIV-COC boundary extends E-W from the El Gordo Graben (EGG) at the Middle American Trench (MAT) to northern tip of the East Pacific Rise (EPR). Results of recently multibeam and magnetic surveys indicate that this boundary is possible segmented as an echelon E-W structure, north of EGG. Clearly these hypotheses on the RIV-COC plate boundary show that its configuration is neither well seismic nor morphology constrained. To the south, the triple junction point of COC, NAM, and CAB plate boundaries is also another case where the boundaries are poorly constrained seismically and morphologically. Traditionally, the COC-NAM-CAB triple junction point has been positioned where the MAT trend bends by the Tehuantepec Ridge (TR) collision, but no offshore geophysical data sustain that NAM-CAB plate boundary extends to MAT-TR point. In the last decade, the Servicio Sismológico Nacional (SSN) has extended its seismic station network at the southern Mexican territory. From this data, the distribution of offshore earthquakes covers a broad marine zone in front the Chiapas and Guatemala coastline and does not show a defined earthquake concentration associated to the proposed offshore extension of the Polochic-Motogua Fault through Guatemala and Mapastepec Fault through Chiapas, Mexico.

Mortera-Gutierrez, C. A.; Bandy, W. L.; Michaud, F.; Ortega Ramírez, J.

2013-05-01

94

BOLIVAR: the Caribbean-South America plate boundary between 60W and 71W as imaged by seismic reflection data  

NASA Astrophysics Data System (ADS)

We present the results of ~6000km of marine multi-channel seismic (MCS) reflection data collected offshore Venezuela as part of the Broadband Ocean Land Investigation of Venezuela and the Antilles arc Region project (BOLIVAR). The imaged area spans almost 12 degrees of longitude and 5 degrees of latitude and encompasses the diffuse plate boundary between South America (SA) and the SE Caribbean plate (CAR). This plate boundary has been evolving for at least the past 55My when the volcanic island arc that borders the CAR plate started colliding obliquely with the SA continent: the collision front has migrated from west to east. BOLIVAR MCS data show that the crustal architecture of the present plate boundary is dominated by the eastward motion of the Caribbean plate with respect to SA and is characterized by a complex combination of convergent and strike-slip tectonics. To the north, the reflection data image the South Caribbean Deformed Belt (SCDB) and the structures related to the thrusting of the CAR plate under the Leeward Antilles volcanic arc region. The data show that the CAR underthrusting continues as far east as the southern edge of the Aves ridge and detailed stratigraphic dating of the Venezuela basin and trench deposits suggests that the collision began in the Paleogene. The amount of shortening along the SCDB decreases toward the east, in part due to the geometry of plate motion vectors and in part as a result of the NNE escape of the Maracaibo block in western Venezuela. South of the SCDB the MCS profiles cross the Leeward Antilles island arc and Cenozoic sedimentary basins, revealing a complex history of Paleogene-Neogene multiphase extension, compression, and tectonic inversion, as well as the influence of the tectonic activity along the right-lateral El Pilar - San Sebastian fault system. East of the Bonaire basin the MCS data image the southern end of the Aves Ridge abandoned volcanic island arc and the southwestern termination of the Grenada basin, characterized here by middle Miocene inverted structures, likely related to the WNW-ESE transpression between CAR and SA. The easternmost MCS profile crosses the ongoing arc-continent collision of the Lesser Antilles arc with SA and the backarc (Grenada Basin) and forearc (Tobago Basin) basins as well as the suture between the Caribbean arc and the passive margin of the continental SA plate near eastern Trinidad.

Magnani, M.; Mann, P.; Clark, S. A.; Escalona, A.; Zelt, C. A.; Christeson, G. L.; Levander, A.

2007-12-01

95

Sequential Kinematic Restoration as a Tool for Deciphering Evolving Plate Boundaries: the Western North America-Pacific Plate Boundary System  

NASA Astrophysics Data System (ADS)

Orogens are often characterized by their most well known segment or most well described section. This tendency may inadvertently suggest that changes along strike may be anomalous, unique or wrong. Combining both cross section and plane view sequential reconstructions across several portions of an orogen allows us to track the evolution of a larger region in time and space. This four-dimensional reconstruction links together along strike changes and connects, in kinematically feasible ways, diverse portions of an orogen that may initially appear incompatible. This approach was tested on the Basin and Range province of western North America. The Basin and Range has been proposed to be the diffuse eastern edge of the Pacific-North American plate boundary with up to 20% of Pacific North America motion being accommodated east of the Sierra Nevada Mountains. However, how this percentage of plate motion is transferred from the Gulf of California through the southern Basin and Range/Mojave region to the eastern California shear zone is still not well understood. We obtained a permissible, kinematic history of the Basin and Range by compiling kinematic data (amount, timing and direction of displacement) along three transects through the northern (40\\deg N) central (37\\deg N) and southern (34\\deg N) portions of the province. Extension and strike-slip deformation in all areas was sequentially restored using the kinematic data in an ArcGIS program over 2 m.y. to 6 m.y. time intervals. The process of sequential restoration highlighted misalignments, overlaps or large gaps in each incremental step, particularly in the areas between data transects. In areas where no information is available we use regions where the kinematics are known to constrain adjacent areas where the kinematics are not defined. The new sequential reconstructions show that compatible slip along the entire N-S extent of the inland shear zone from Baja to the northern Walker Lane is possible and supported by available data and that this inland shear zone had migrated westward with time. The reconstructions also highlight new problems particularly with regard to strain compatible extension east and west of the Sierra Nevada/Great Valley block.

McQuarrie, N.

2004-12-01

96

Cenozoic plate tectonic reconstructions and plate boundary processes in the Southwest Pacific  

Microsoft Academic Search

The Australia-Pacific-Antarctic plate circuit has long been a weak link in global plate reconstruction models for Cenozoic time. The time period spanning chron 20 to chron 7 (43-25 Ma) is particularly problematic for global plate models because seafloor spreading was occurring in two poorly constrained regions in the Southwest Pacific - the Macquarie Basin southwest of New Zealand, and the

William R. Keller

2005-01-01

97

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)

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.

Beardsley, Amanda Gail

2007-12-01

98

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

PubMed

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. PMID:17614487

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

2007-07-01

99

Convergence  

NASA Astrophysics Data System (ADS)

Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers, and consumers. Spectacular advances in all layers of optical networking-leading to abundant, dynamic, cost-effective, and reliable wide-area and local-area connections-have been essential drivers of this evolution. As services and networks continue to evolve towards some notion of convergence, the continued role of optical networks must be explored. One vision of convergence renders all information in a common packet (especially IP) format. This vision is driven by the proliferation of data services. For example, time-division multiplexed (TDM) voice becomes VoIP. Analog cable-television signals become MPEG bits streamed to digital set-top boxes. T1 or OC-N private lines migrate to Ethernet virtual private networks (VPNs). All these packets coexist peacefully within a single packet-routing methodology built on an optical transport layer that combines the flexibility and cost of data networks with telecom-grade reliability. While this vision is appealing in its simplicity and shared widely, specifics of implementation raise many challenges and differences of opinion. For example, many seek to expand the role of Ethernet in these transport networks, while massive efforts are underway to make traditional TDM networks more data friendly within an evolved but backward-compatible SDH/SONET (synchronous digital hierarchy and synchronous optical network) multiplexing hierarchy. From this common underlying theme follow many specific instantiations. Examples include the convergence at the physical, logical, and operational levels of voice and data, video and data, private-line and virtual private-line, fixed and mobile, and local and long-haul services. These trends have many consequences for consumers, vendors, and carriers. Faced with large volumes of low-margin data traffic mixed with traditional voice services, the need for capital conservation and operational efficiency drives carriers away from today's separate overlay networks for each service and towards "converged" platforms. For example, cable operators require transport of multiple services over both hybrid fiber coax (HFC) and DWDM transport technologies. Local carriers seek an economical architecture to deliver integrated services on optically enabled broadband-access networks. Services over wireless-access networks must coexist with those from wired networks. In each case, convergence of networks and services inspires an important set of questions and challenges, driven by the need for low cost, operational efficiency, service performance requirements, and optical transport technology options. This Feature Issue explores the various interpretations and implications of network convergence pertinent to optical networking. How does convergence affect the evolution of optical transport-layer and control approaches? Are the implied directions consistent with research vision for optical networks? Substantial challenges remain. Papers are solicited across the broad spectrum of interests. These include, but are not limited to:

  • Architecture, design and performance of optical wide-area-network (WAN), metro, and access networks
  • Integration strategies for multiservice transport platforms
  • Access methods that bridge traditional and emerging services
  • Network signaling and control methodologies
  • All-optical packet routing and switching techniques

Manuscript Submission

To submit to this special issue, follow the normal procedure for submission to JON, indicating "Convergence feature" in the "Comments" field of the online submission form. For all other questions relat

Darcie, Thomas E.; Doverspike, Robert; Zirngibl, Martin; Korotky, Steven K.

2004-12-01

100

Convergence  

NASA Astrophysics Data System (ADS)

Call for Papers: Convergence Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers, and consumers. Spectacular advances in all layers of optical networking-leading to abundant, dynamic, cost-effective, and reliable wide-area and local-area connections-have been essential drivers of this evolution. As services and networks continue to evolve towards some notion of convergence, the continued role of optical networks must be explored. One vision of convergence renders all information in a common packet (especially IP) format. This vision is driven by the proliferation of data services. For example, time-division multiplexed (TDM) voice becomes VoIP. Analog cable-television signals become MPEG bits streamed to digital set-top boxes. T1 or OC-N private lines migrate to Ethernet virtual private networks (VPNs). All these packets coexist peacefully within a single packet-routing methodology built on an optical transport layer that combines the flexibility and cost of data networks with telecom-grade reliability. While this vision is appealing in its simplicity and shared widely, specifics of implementation raise many challenges and differences of opinion. For example, many seek to expand the role of Ethernet in these transport networks, while massive efforts are underway to make traditional TDM networks more data friendly within an evolved but backward-compatible SDH/SONET (synchronous digital hierarchy and synchronous optical network) multiplexing hierarchy. From this common underlying theme follow many specific instantiations. Examples include the convergence at the physical, logical, and operational levels of voice and data, video and data, private-line and virtual private-line, fixed and mobile, and local and long-haul services. These trends have many consequences for consumers, vendors, and carriers. Faced with large volumes of low-margin data traffic mixed with traditional voice services, the need for capital conservation and operational efficiency drives carriers away from today's separate overlay networks for each service and towards "converged" platforms. For example, cable operators require transport of multiple services over both hybrid fiber coax (HFC) and DWDM transport technologies. Local carriers seek an economical architecture to deliver integrated services on optically enabled broadband-access networks. Services over wireless-access networks must coexist with those from wired networks. In each case, convergence of networks and services inspires an important set of questions and challenges, driven by the need for low cost, operational efficiency, service performance requirements, and optical transport technology options. This Feature Issue explores the various interpretations and implications of network convergence pertinent to optical networking. How does convergence affect the evolution of optical transport-layer and control approaches? Are the implied directions consistent with research vision for optical networks? Substantial challenges remain. Papers are solicited across the broad spectrum of interests. These include, but are not limited to:

Darcie, Thomas E.; Doverspike, Robert; Zirngibl, Martin; Korotky, Steven K.

2005-03-01

101

Convergence  

NASA Astrophysics Data System (ADS)

Call for Papers: Convergence Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers, and consumers. Spectacular advances in all layers of optical networking-leading to abundant, dynamic, cost-effective, and reliable wide-area and local-area connections-have been essential drivers of this evolution. As services and networks continue to evolve towards some notion of convergence, the continued role of optical networks must be explored. One vision of convergence renders all information in a common packet (especially IP) format. This vision is driven by the proliferation of data services. For example, time-division multiplexed (TDM) voice becomes VoIP. Analog cable-television signals become MPEG bits streamed to digital set-top boxes. T1 or OC-N private lines migrate to Ethernet virtual private networks (VPNs). All these packets coexist peacefully within a single packet-routing methodology built on an optical transport layer that combines the flexibility and cost of data networks with telecom-grade reliability. While this vision is appealing in its simplicity and shared widely, specifics of implementation raise many challenges and differences of opinion. For example, many seek to expand the role of Ethernet in these transport networks, while massive efforts are underway to make traditional TDM networks more data friendly within an evolved but backward-compatible SDH/SONET (synchronous digital hierarchy and synchronous optical network) multiplexing hierarchy. From this common underlying theme follow many specific instantiations. Examples include the convergence at the physical, logical, and operational levels of voice and data, video and data, private-line and virtual private-line, fixed and mobile, and local and long-haul services. These trends have many consequences for consumers, vendors, and carriers. Faced with large volumes of low-margin data traffic mixed with traditional voice services, the need for capital conservation and operational efficiency drives carriers away from today's separate overlay networks for each service and towards "converged" platforms. For example, cable operators require transport of multiple services over both hybrid fiber coax (HFC) and DWDM transport technologies. Local carriers seek an economical architecture to deliver integrated services on optically enabled broadband-access networks. Services over wireless-access networks must coexist with those from wired networks. In each case, convergence of networks and services inspires an important set of questions and challenges, driven by the need for low cost, operational efficiency, service performance requirements, and optical transport technology options. This Feature Issue explores the various interpretations and implications of network convergence pertinent to optical networking. How does convergence affect the evolution of optical transport-layer and control approaches? Are the implied directions consistent with research vision for optical networks? Substantial challenges remain. Papers are solicited across the broad spectrum of interests. These include, but are not limited to:

Darcie, Thomas E.; Doverspike, Robert; Zirngibl, Martin; Korotky, Steven K.

2005-02-01

102

Boundary element analysis of Kirchhoff plates with direct evaluation of hypersingular integrals  

Microsoft Academic Search

SUMMARY The typical Boundary Element Method (BEM) for fourth-order problems, like bending of thin elastic plates, is based on two coupled boundary integral equations, one strongly singular and the other hypersingular. In this paper all singular integrals are evaluated directly, extending a general method formerly proposed for second-order problems. Actually, the direct method for the evaluation of singular integrals is

A. Frangi; M. Guiggiani

1999-01-01

103

Convergence  

Microsoft Academic Search

Convergence has become a popular theme in telecommunications, one that has broad implications across all segments of the industry. Continual evolution of technology and applications continues to erase lines between traditionally separate lines of business, with dramatic consequences for vendors, service providers, and consumers. Spectacular advances in all layers of optical networking-leading to abundant, dynamic, cost-effective, and reliable wide-area and

Thomas E. Darcie; Robert Doverspike; Martin Zirngibl; Steven K. Korotky

2004-01-01

104

An active vibration absorber for a flexible plate boundary-controlled by a linear motor  

NASA Astrophysics Data System (ADS)

A long, narrow flexible plate subjected to cyclic disturbances at the midsection is regulated by a linear motor at the boundary. Oscillations at the midsection will be eliminated while the rest of the plate is allowed to swing in a way as to counteract the external force. The control design is based on a virtual passive approach without referring to the detailed mathematical model. A vibration absorber integrating the flexible plate with a combination of passive elements attached to the boundary is first devised. Rather than built with hard physical devices, these passive elements including mechanical springs, dampers, and masses are emulated by the linear motor with a suitable feedback law. The feedback signal is the boundary displacement from an LVDT sensor. Numerical simulations illustrate how a node is developed in the middle of the plate while the rest of the structure tends to a harmonic motion. Experimental results confirm the effectiveness of the control scheme.

Wu, Shang-Teh; Chen, Jiann-Yeu; Yeh, Yuan-Chih; Chiu, Yea-Ying

2007-02-01

105

Boundary conditions for convergent radial tracer tests and effect of well bore mixing volume  

NASA Astrophysics Data System (ADS)

Convergent radial flow tracer tests have a complex spatial nonaxial transport structure caused by the flow in the vicinity of the injection well and its finite mixing volume. The formulation of the boundary value problem, and especially the treatment of the boundary conditions at the injection well, is nontrivial. Hodgkinson and Lever [1983], Moench [1989, 1991], and Welty and Gelhar [1994] have developed different models and methods for the analysis of breakthrough curves in the extraction well. To extend interpretation techniques to breakthrough curves in the zone between injection and extraction wells, an analysis of conventional transport models is given, and improved boundary conditions are formulated for a convergent radial tracer test problem. The formulation of the boundary conditions is based upon a more detailed analysis of the kinematic flow structure and tracer mass balance in the neighborhood of the injection well. Two practical applications of revised boundary conditions for field data analysis are given. First, the note explains anomalous high well bore mixing volumes of injection wells found by Cady et al. [1993] and allows one to establish the role of mixing versus other processes (retardation, matrix diffusion, etc.). Second, it is shown that the improper use of Moench's [1989] model can produce bias in the characteristics of breakthrough curves in the extraction well under conditions that involve a significant mixing factor in the injection well. A numerical example indicates an error in peak concentrations on a breakthrough curve by as much as 70% and in peak arrival time by 10% for Peclet numbers Pe=102. The effect becomes slightly less significant for Pe=1.

Zlotnik, Vitaly A.; David Logan, J.

106

Interaction between the Dauki and the Indo-Burman convergence boundaries from teleseismic and locally recorded earthquake data  

NASA Astrophysics Data System (ADS)

The Himalayan and the Burma Arcs converge onto the Indian plate from opposite sides near their syntaxial juncture and have reduced it to a sliver. Both geology and seismicity point to recent internal deformation and high seismogenic potential within this sliver. Large historical earthquakes, including the Great Indian earthquake of 1897 (Mw ~8.1), along with the recent seismicity, suggest that the cratonic blocks in the region are bounded by active faults. The most prominent is the E-W trending Dauki Fault, a deeply-rooted, north-dipping thrust fault, situated between the Shillong massif to the north and the Sylhet Basin to the south. Along the Burma Arc, the subducted seismogenic slab of the Indian plate is continuous north to the syntaxis. Yet the Naga and Tripura segments of the accretionary fold belt, respectively north and south of the easterly extrapolation of the Dauki fault, are distinct. Accretion has advanced far westward into the foredeep of the Dauki structure along the front of the Tripura segment, while it has remained stunted facing the uplifted Shillong massif along the Naga segment. Moreover, the Dauki topographic front can be traced eastwards across the Burma Arc separating the two segments. Recent earthquakes support the hypothesis that the Dauki convergence structure continues below the Burma accretionary belt. Using teleseismic and regional data from the deployment of a local network, we explore the interaction of the Dauki thrust fault with the Burma Arc subduction zone. Preliminary observations include: While seismicity is concentrated in the slab at the eastward extrapolation of the Dauki fault, shallow seismicity is diffuse and does not illuminate the Dauki fault itself. P-axes in moment-tensor solutions of earthquakes within the Indian plate tend to be directed N-S and are locally parallel to the India-Burma boundary, particularly in the slab. T-axes tend to be oriented E-W with a strong tendency to follow the slab down dip. This pattern is remarkably consistent, despite the scattered seismicity, and suggests that the stress in the Indian plate, including the subducted oceanic portion of the plate, is still primarily controlled by the Himalayan collision to the north and down-dip pull by the Burma slab. Moment tensor solutions for some of the shallow earthquakes along the fold belt are consistent with geodetic results, showing partitioning of the oblique India-Burma convergence between belt-parallel dextral faults and belt-normal shortening by thrust faults. Relocations of the events using the double-difference algorithm may provide additional constraints on the geometry of the slab. In addition to the analysis of teleseismic data, a network of six seismic stations was also installed in Bangladesh in the region surrounding Sylhet, south of the Shillong Plateau during 2007-2008. Over 200 regional and local events are detected and located by the Sylhet array. About a dozen events are large enough allowing us to determine focal depths and mechanisms that will augment the catalog of the teleseismic events, providing additional insights into the tectonics in the region.

Howe, M.; Moulik, P.; Seeber, L.; Kim, W.; Steckler, M. S.

2012-12-01

107

Prandtl boundary layer expansions of steady Navier-Stokes flows over a moving plate  

E-print Network

This paper concerns the validity of the Prandtl boundary layer theory in the inviscid limit for steady incompressible Navier-Stokes flows. The stationary flows, with small viscosity, are considered on $[0,L]\\times \\mathbb{R}_{+}$, assuming a no-slip boundary condition over a moving plate at $y=0$. We establish the validity of the Prandtl boundary layer expansion and its error estimates.

Yan Guo; Toan T. Nguyen

2014-11-25

108

Kinematics to dynamics in the New Zealand plate-boundary zone  

NASA Astrophysics Data System (ADS)

New Zealand straddles the boundary between the Australian and Pacific plate, with a transition from subduction of Pacific oceanic lithosphere beneath North Island, to oblique continental collision in South Island. Cenozoic relative plate motion has resulted in a complex pattern of faulting and block rotation in a zone up to 250 km wide, with displacements on individual faults up to 100s of kilometres. Active deformation must be driven by a combination of plate-boundary forces and internal buoyancy forces. I use a compilation of seismic reflection/refraction studies and high quality receiver function analyses, together with simple Airy isostasy, to determine regional crustal and mantle structure. Integration of the vertical normal stress to the base of the deforming layer yields the buoyancy stress. Horizontal gradients of this can be compared with horizontal gradients of strain rate, using the method of England & Molnar (1997), in the context of a simple thin sheet model of deformation. Thus, if deformation is that of a Newtonian fluid, then appropriate combinations of the horizontal gradients of vorticity and dilatation are related to gradients of buoyancy stress by the fluid viscosity. However, the short term geodetic deformation is strongly biased by elastic strain accumulation related to locking on the plate interface, and cannot be used to determine the plate-boundary velocity field averaged over many seismic cycles (see Lamb & Smith 2013). Therefore, I derive here a velocity field for the plate-boundary zone, which is representative of deformation over tens of thousands of years. This is based on an inversion of fault slip, strain rate azimuth and paleomagnetic data, in the context of the short term relative plate motions, solved in a network of triangles spanning the plate-boundary, using the method of Lamb (2000). A comparison of gradients of buoyancy stress with the appropriate combinations of gradients of vorticity and dilatation shows that deformation in the plate-boundary zone does have features that are fluid-like, characterized by a variable viscosity in the range 1 - 10 x 10^21 Pa s. Given the strain rates in the plate-boundary zone, viscosities imply plate-boundary deviatoric stresses < 20 MPa, and are consistent with previous low estimates of shear stresses in subduction zones based on a simple force balance (Lamb 2006). References: England, P.C., and P. Molnar, (1997), Science, 278, 647-649. Lamb, S. (2000), J. Geophys. Res., 105, 25,627-25,653. Lamb, S., (2006), J. Geophys. Res., 111, B07401, doi:10.1029/2005JB003916. Lamb, S., and E. Smith (2013), J. Geophys. Res. Solid Earth, 118, doi:10.1002/jgrb.50221.

Lamb, S. H.

2013-12-01

109

Lithospheric Evolution of the Pacific-North American Plate Boundary Considered in Three Dimensions  

NASA Astrophysics Data System (ADS)

Tomographic imaging indicates that the heterogeneity observed in the crust of westernmost North America is underlain by mantle structures of a similar scale and heterogeneity. When likely scaling relationships are used to interpret mantle velocity images, it becomes clear that much of the boundary is explained by mantle lithospheric processes and the crustal evolution is just the surficial expression of strength beneath the surface. The Sierra Nevada block provides something of a Rosetta stone for this interpretation. We note first that Sierra Nevada terrain is not distinguished at the surface from faulted and even shattered batholithic rocks in southern California. It does differ in the upper mantle, because the Sierra Nevada is underlain by a high- velocity root along almost its entire strike. Where that root is missing, roughly south of the White Wolf fault, and east of the Kern Canyon fault, the surface rocks are deforming. The origin of the strong upper mantle component is self-evident near 39.5N latitude, where the contact between the subducting Gorda Slab and the Sierran mantle root can be imaged directly. The upper plate structure dates to latest Mesozoic through Laramide times, with the pattern apparently reinforced on the west to some extent during post-Laramide subduction. Since the genesis of batholithic rocks and the subsequent Laramide history are similar south of the Sierran block, we extrapolate that a similar mantle root would have been present also. This assumption is confirmed with two lines of evidence. First, the mechanical evolution of southern and central California blocks seems to require it. Second, the volumes of the "drips" beneath the Transverse Ranges and southern Sierras exceed reasonable bounds for material scavenged from the mantle lithosphere unless it had distinct initial conditions. The local sources of mantle lithospheric material that could have delaminated around the southern Sierran drip are volumetrically insufficient by a factor of 4 to 7 to account for the drip itself. These problems are resolved if the primary source for southern California drips is Sierran-like mantle roots scavenged from beneath batholithic terrains farther south by dominantly convergence-related plate-boundary processes.

Biasi, G. P.

2006-12-01

110

Highly Accurate Solutions of the Blasius and Falkner-Skan Boundary Layer Equations via Convergence Acceleration  

E-print Network

A new highly accurate algorithm for the solution of the Falkner-Skan equation of boundary layer theory is presented. The algorithm, based on a Maclaurin series representation, finds its coefficients from recurrence. In addition, Wynn-epsilon convergence acceleration and continuous analytical continuation enable an accurate evaluation. The most accurate skin friction coefficients (shooting angle) to date are presented along with comparisons to past and present values found in the literature. The algorithm, coded in FORTRAN, uses neither enhanced precision arithmetic beyond quadruple precision nor computer algebra to achieve results in a timely fashion. Key Words: Falkner-Skan flow; Blasius flow; Wynn-epsilon acceleration; Romberg acceleration; Continuous analytical continuation

B. D. Ganapol

2010-06-19

111

The International Plate Boundary Observatory Chile (IPOC) in the northern Chile seismic gap  

NASA Astrophysics Data System (ADS)

Fast convergence between the oceanic Nazca and the continental South American plate is accommodated by recurrent rupture of large segments of the two plates' interface. The resulting earthquakes are among the largest and, for their sizes, most frequent on Earth. Along the Chilean and southern Peruvian margin, all segments have ruptured at least once in the past 150 years for which there exist historic and/or instrumental records. The one segment that is most mature for re-rupture stretches for more than 500 km along the northernmost Chilean coast between roughly -23° and -18° latitude. It last broke in 1877 in a magnitude ~8.8 earthquake, triggering a major Tsunami. From the historical record, it has been known to have a recurrence cycle of approximately 110 years. The adjoining segments to the north and south broke rather recently in 1995 and 2001 in M>8 earthquakes and an M 7.7 earthquake encroached the southern part of the gap in 2007. The IPOC project intends to investigate this segment of the Nazca-South American plate boundary, on which a strong to devastating earthquake is expected to occur within the next years, by monitoring at a variety of time-scales deformation, seismicity, and magnetotelluric fields in the subduction zone at the closing stages of the interseismic cycle before and possibly during occurrence of a big earthquake. For that purpose, installation of long-term observatories in Northern Chile started in 2006 in a close cooperation of the Universidad de Chile (Santiago, Chile), the Universidad Catolica del Norte (Antofagasta, Chile), the Institut de Physique du Globe de Paris (Paris, France), and the German Research Centre for Geosciences (GFZ, Potsdam, Germany). Currently we are operating 14 modern seismological stations equipped with STS-2 broadband seismometers and accelerometers (EPI sensor). At least two more stations will be installed in the near future. To cope with the high resolution and dynamic of the sensors and data acquisition, site installation was accomplished with special care. At each station a cavern was blasted into the bedrock up to 5 meters deep to ensure stable conditions for measurements. Currently five stations are additionally recording continuously GPS signals, another five are also recording meteorological data, and another seven are equipped with Magneto-Telluric (MT) probes (fluxgate magnetometers and electrode lines). It is planned to extend the multi-parameter observation to as many stations as possible. So far ten of the stations are sending continuous data via satellite links (VSAT) to the GEOFON data host at the GFZ. We will be reporting first results on seismicity, transient deformation and MT from the first two years of recording.

Schurr, B.; Asch, A.; Sodoudi, F.; Manzanares, A.; Ritter, O.; Klotz, J.; Chong-Diaz, G.; Barrientos, S.; Villotte, J.-P.; Oncken, O.

2009-04-01

112

Distributed Roughness Receptivity in a Flat Plate Boundary Layer  

E-print Network

(Re_(k) = 220), the discrete element created a turbulent wedge 15 boundary layer thicknesses downstream. When the distributed roughness was added around the discrete roughness, the wake amplitude decreased at the sub-critical Reynolds number...

Kuester, Matthew Scott

2014-04-18

113

Nonpolynomial sextic spline method for the solution along with convergence of linear special case fifth-order two-point boundary value problems  

Microsoft Academic Search

Nonpolynomial sextic spline functions are used to approximate the solution of linear special case fifth-order boundary value problems. Since, presently, the convergence of spline solution of fifth-order boundary value problem is not found in the literature, therefore the convergence of the method is determined which is found to be of fifth order. The convergence of the method is the extension

Shahid S. Siddiqi; Ghazala Akram; Salman A. Malik

2007-01-01

114

Ocean crust deformation at the North America-South America plate boundary: Results of the 2007 ANTIPLAC marine survey  

NASA Astrophysics Data System (ADS)

East of the Lesser Antilles active margin, the area of the Barracuda and Tiburon ridges is resulting from of a multidirectional and polyphase tectonic history at the diffuse plate boundary between the North and South American plates. These WNW-ESE trending ridges control the sediment distribution and they are bounded by sedimentary trenches, both ridges and trenches trending parallel to the Mid-Atlantic oceanic fracture zones. A marine survey (called ANTIPLAC) conducted in the beginning of the year (January 2007) has provide new evidences (multibeam and seismic acquisition) of the deformation processes which occurred at this plate boundary. On the seismic lines, a major angular unconformity can be recognized in the whole area of the survey. Interpreting the acquired seismic grid, the lower part of the stratigraphic series can be easily tied to the DSDP/ODP holes of legs 78A, 110, 156, 171A, especially with wells 543 and 672. Thus a Maastrichtian-Pliocene age can be attributed to the geological formations located below the regional unconformity. The very recent geological formations located above the unconformity (attributed to the Late Pliocene-Pleistocene) tend to fill the main depressions of the area and show very heterogeneous thickness. These recent deposits can be more than 3 s(TWT) thick in the Barracuda trough (north of Barracuda ridge). Globally they show clear onlapping characters above the older levels, but in some places these levels show spectacularly evidences of syntectonic deposition. This is notably the case of a narrow WNW-ESE trending fold and fault system trending along the axis of the Barracuda trough. South of Barracuda ridge the recent deposits show also locally spectacular fan geometries characterizing deposition during significant tilting. Also, between Barracuda and Tiburon ridges several fracture zones show evidences of very recent (and probably active) reactivation. This recent deformation is also characterized by recent basin inversion structures. Finally and more generally, the data acquired during the ANTIPLAC survey demonstrate that high deformation occurred at the boundary between the North and South American plates during much more recent times than previously thought, and that notably spectacular compressional structures resulting from the convergence between the two american plates developed recently during Late Pliocene-Quaternary times. The subduction of this structural pattern and its partial incorporation within the Barbados tectonic wedge has widely influenced the deformation processes within the accretionary prism and has also induced segmentation within the overriding Caribbean plate.

Patriat, M.; Benard, F.; Deville, E.; Le Drezen, E.; Loubrieu, B.; Maltese, L.; Roest, W.; Thereau, E.; Umber, M.; Vially, R.

2007-12-01

115

The Arctic Plate Boundary: Seismotectonics at Ultra-slow Spreading  

Microsoft Academic Search

Earthquakes reveal the dynamics of the Arctic midocean ridge (MOR) system between the Knipovich Ridge and the Laptev Sea continental margin, where the Eurasian and North American plates separate by 1.5-0.5 cm\\/a. By assessing location errors and network detectabilities we have evaluated and quality sorted earthquake reports north of 72°N from 1955-99. Sorting the earthquakes by number of recording stations

O. Eldholm; H. Bungum

2002-01-01

116

Kinematics to dynamics in the New Zealand plate-boundary zone  

NASA Astrophysics Data System (ADS)

New Zealand straddles the boundary between the Australian and Pacific plate, with a transition from subduction of Pacific plate oceanic lithosphere in the North, beneath North Island to oblique continental collision in South Island. Cenozoic relative plate motion has resulted in a complex pattern of faulting and block rotation in a zone up to 250 km wide, with displacements on individual faults up to 100s of kilometres. Here, I use a compilation of seismic reflection/refraction studies and high quality receiver function analyses, together with simple Airy isostasy, to determine the regional crustal and mantle structure. The buoyancy stress in the deforming layer is calculated by integrating the vertical normal stress with depth. This, in combination with plate-boundary stresses, must drive deformation. Horizontal gradients of buoyancy stress can be compared with horizontal gradients of strain rate, using the method of England & Molnar (1997), in the context of a simple thin sheet model of lithospheric deformation. I derive a velocity field for the New Zealand plate-boundary zone, using the method of Lamb (2000). This is representative of deformation over tens of thousands of years, based on fault slip, strain rate azimuth and paleomagnetic data, in the context of the short term relative plate motions. Comparison of appropriate combinations of horizontal gradients of vorticity and dilatation with horizontal gradients of buoyancy stress shows that deformation has some of the features of a Newtonian fluid. In detail, the minima in buoyancy stress, calculated from the vertical density structure, are offset horizontally from that calculated from gradients of strain rate, suggesting strong lateral contrasts in viscosity if deformation is strongly coupled at all levels in the lithosphere, with viscosities in the range 1 - 10 x 10**21 Pa s. However, subduction of Pacific plate lithosphere along the Hikurangi margin, and evidence for underthrusting beneath the Southern Alps, implies decoupling of deformation at depths > 50 km in these regions. In this case, best-fit viscosities for the top 50 km are in the range 1 - 5 x 10**21 Pa s. Given the characteristic strain rates in the plate-boundary zone, all these viscosities imply plate-boundary deviatoric stresses generally < 20 MPa, and are consistent with previous low estimates of shear stresses on the subduction plate interface based on a simple force balance (Lamb 2006). Fluid-like behaviour of the New Zealand plate-boundary zone is consistent with both geodetic data and the observed pattern of shear wave splitting. References: England, P.C., and P. Molnar, Science, 278, 647-649, 1997. Lamb, S., JGR, 105, 25,627-25,653, 2000. Lamb, S., JGR, 111, B07401, doi:10.1029/2005JB003916, 2006.

Lamb, Simon

2014-05-01

117

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

NASA Astrophysics Data System (ADS)

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.

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

2001-12-01

118

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

NASA Technical Reports Server (NTRS)

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.

Hager, B. H.

1981-01-01

119

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

NASA Technical Reports Server (NTRS)

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.

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

1974-01-01

120

Converging shear rheometer  

NASA Astrophysics Data System (ADS)

For highly viscous fluids that slip in parallel sliding plate rheometers, we want to use a slightly converging flow to suppress this wall slip. In this work, we first attack the steady shear flow of a highly viscous Newtonian fluid between two gently converging plates with no slip boundaries using the equation of motion in cylindrical coordinates, which yields no analytical solution. Then we treat the same problem using the lubrication approximation in Cartesian coordinates to yield exact, explicit solutions for dimensionless velocity, pressure and shear stress. This work deepens our understanding of a drag flow through a gently converging slit of arbitrary convergence angle. We also employ the corotational Maxwell model to explore the role of viscoelasticity in this converging shear flow. We then compare these analytical solutions to finite element calculations for both Newtonian and corotational Maxwell cases. A worked example for determining the Newtonian viscosity using a converging shear rheometer is also included. With this work, we provide the framework for exploring other constitutive equations or other boundary conditions in future work. Our results can also be used to design the linear bearings used for the parallel sliding plate rheometer (SPR). This work can also be used to evaluate the error in the shear stress that is caused by bearing misalignment and specify the parallelism tolerance for the linear bearings incorporated into a SPR.

Baek, Hyung M.; Mix, Adam W.; Giacomin, A. Jeffrey

2014-05-01

121

Continent-continent collision at the Pacific/Australian plate boundary: Lithospheric deformation, mountain building, and subsequent scientific endeavors  

NASA Astrophysics Data System (ADS)

Continental collision occurs at strike-slip plate boundaries where transform motion and oblique convergence create processes of surficial mountain building and deformation within the deeper crust and lithospheric mantle. The Pacific/Australian transform plate boundary in South Island, New Zealand, is characterized by active oblique continent-continent collision with an associated Southern Alps orogen that exhibits both high exhumation rates and rapid strike-slip movement. Beginning in the 1990s, this system was the focus of a decade-long collaborative USA-New Zealand multi-disciplinary study to understand lithospheric structure and processes involved in this transpression. Funded primarily by the NSF Continental Dynamics program and the New Zealand Science Foundation, this project known as SIGHT (South Island Geophysical Transect) with its companion SAPSE (Southern Alps Passive Seismic Experiment) included the following disciplines that involved substantial field observation experiments: seismic reflection, explosion refraction, onshore-offshore wide-angle reflection/refraction, regional and teleseismic passive seismology, magnetotellurics, laboratory petrophysics, gravity, regional geological investigations, and rheological analyses. More than fifty scientists and students from both nations participated in the combined set of studies that have led to over forty-five journal publications, an AGU Monograph, and a dozen graduate theses. Primary results of the project indicate the Pacific-Australian strike-slip plate boundary (Alpine fault) is not vertical but is eastward dipping and rheologically weak based on diverse geophysical data. Most deformation is within the Pacific plate that hosts the Southern Alps orogen. High mantle seismic velocities vertically disposed beneath the orogen suggest Pacific and perhaps Australian mantle lithosphere contribute to a zone of plate-boundary-parallel distributed mantle shortening. The crustal root of the overlying Southern Alps is larger than needed to support surface topography, and is offset from its topographic high, consistent with dynamic thickening of the Pacific crust by the mantle thickening. Teleseismic shear wave splitting is evidence of a wide zone of distributed strain for the mantle portion of the plate boundary. The collective set of results from the South Island projects have led to a number of subsequent studies by various teams, based on follow-up questions, expanded observational expertise, and international collaborative alliances with in particular the New Zealand science community. These studies include a search for the full width of Pacific/Australian distributed mantle strain using marine OBS studies, the transition from strike-slip to plate boundary subduction to the north, the search and discovery of seismic tremor on the Alpine fault, and high resolution geophysical characterization of Alpine fault seismogenesis. The success of geophysically imaging a narrow island using both marine sides led different SIGHT scientists to carry out expanded efforts to study North Island subduction and separately Taiwan mountain building. These efforts benefited and were largely motivated from multi-disciplinary, multi-national collaborations as typically supported by the NSF Continental Dynamics program.

Okaya, D. A.; Stern, T. A.; Davey, F. J.

2012-12-01

122

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

NASA Technical Reports Server (NTRS)

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.

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

1974-01-01

123

Seismic Imaging of the Cascadia Plate Boundary with Four Source Array Configurations  

NASA Astrophysics Data System (ADS)

Imaging the plate boundary in the Cascadia region has great importance for understanding seismic hazards in the coastal margin of the Pacific Northwest. The Cascadia margin is a potential earthquake and tsunami threat to the many millions who live in the area, yet the location and shape of the subducting oceanic plate boundary remains poorly understood. This is due in large part to the plate boundary being relatively aseismic and difficult to constrain through passive-source seismic methods. In July 2012, the COAST project acquired 15 seismic transects of the Cascadia margin intended to image the plate boundary. Four of the seismic transects were acquired over the same location with different source arrays: 36 air guns towed at 9m depth, 18 air guns towed at 9m depth, 36 air guns towed at 15m depth, and 18 air guns towed at 15m depth. These changes were chosen to represent possible configurations for 2D and 3D seismic data acquisitions with emphasis on identifying deep Earth features lying below complicated folding sediments of the accretionary wedge. Thirty-six air guns represents the full volume of the R/V Marcus G. Langseth source used when collecting 2D seismic data, while eighteen represents the half volume that would typically be fired for a 3D survey. Nine meters and fifteen meters are common source depths but have very different outputs in the frequency domain due to the "ghost notch" created by acoustic reflection off the sea surface. Here we present four identically processed, pre-stack depth migrated images of the Cascadia plate boundary and an analysis of the benefits and drawbacks of each seismic acquisition parameter set. While expressions of the plate boundary exist in all data acquired, preliminary results indicate that a deeper tow depth, and its lower frequency source output, captures more continuous representations of the plate boundary. However, a more shallow tow depth increases the resolution of the overlying sediments and the plate boundary itself helping to better define its precise location and shape.

Fortin, W. F.; Holbrook, W.; Kent, G.; Keranen, K. M.; Trehu, A. M.; Johnson, H. P.; Everson, E. D.

2012-12-01

124

Plate boundary evolution in the western-central Mediterranean: From the past to the present.  

NASA Astrophysics Data System (ADS)

The evolution of the Calabrian and Gibraltar arcs and that of the margins of northern Africa and Sicily are part of the final phase of opening of the western Mediterranean basins. Jointly, they are the central topic of the TopoMed project concerning the plate boundary reorganization of the western-central Mediterranean, one of the projects of the TOPO-EUROPE programme (EUROCORES/ESF). The structure and evolution of the Gibraltar arc region are discussed in a separate presentation. This final stage of opening shows intriguing lateral variations from the Calabrian Arc, via the northern margin of Sicily to the North-African (Algerian) margin. In concert, they provide an excellent opportunity to study the evolution of an expanding oceanic realm that may be at the verge of entering a new phase of closure. Our studies encompass detailed analyses of deep penetration seismic data, multibeam bathymetry and field observations, and numerical model experiments addressing lithospheric scale process-oriented aspects. Special attention is given to the aspect that the region is embedded in a context of ongoing Africa-Eurasia plate convergence and to the role of structures, inherited from earlier stages of basin opening, in controlling the recent and ongoing evolution. For the Calabrian accretionary wedge the focus is on assessing the present state of deformation, including seismic activity, and other accompanying processes. We show that the Calabrian wedge is segmented (in direction along the arc) in two different lobes, the western and eastern lobe corresponding with detached and still continuous parts of the subducting slab, respectively. For the Northern Sicily margin we propose that its earlier history involving STEP faulting has preconditioned the lithosphere structure to the extent that it promotes initiation of a new southward-dipping subduction zone. The northern African margin is in a very special transitional situation in which the retreating northward subduction has come to an end, and new southward-dipping subduction may possibly be initiated. The study area is a regional scale natural laboratory in which the principal features of a Wilson cycle and their effect on surface tectonics, can be identified and investigated.

Wortel, Rinus; Faccenna, Claudio; Govers, Rob; Polonia, Alina; Baes, Marzieh

2013-04-01

125

Large deformation of shear-deformable plates by the boundary-element method  

Microsoft Academic Search

Boundary-integral equations for large deformation of shear-deformable plates are presented. Two different methods are used to calculate the derivatives of the nonlinear terms in the domain integral. The first approach requires the evaluation of a hypersingular domain integral. The second approach avoids the calculation of a hypersingular integral by utilizing radial basis functions to approximate the integrand. Quadratic isoparametric boundary-elements

J. Purbolaksono; M. H. Aliabadi

2005-01-01

126

A study in transitional flat plate boundary layers: measurement and visualization  

Microsoft Academic Search

This study is concerned with transition in flat plate boundary layer flow. Sets of results are obtained as follows: (1) Very\\u000a clear pictures of the formation and the development of the butterfly-like structures rather than ?-structures in the K-regime of boundary layer transition are obtained. (2) A chain of ring like vortices, which generate the high-frequency spikes\\u000a on the time

C. B. Lee; Z. X. Hong; Y. S. Kachanov; V. I. Borodulin; V. V. Gaponenko

2000-01-01

127

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

NASA Astrophysics Data System (ADS)

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.

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

2012-07-01

128

Do fluids control locking and seismic slip on the subduction fault? - evidence from the Chilean plate boundary  

NASA Astrophysics Data System (ADS)

A number of recent studies have suggested that the interseismic locking degree inverted from geodetic data at convergent plate boundaries may be closely related to slip distribution of subsequent megathrust earthquakes as found recently for the Maule 2010 and Tohoku 2011 earthquakes. The physical nature of locking, however, remains a matter of debate. We explore seismic, seismological and geodetic data collected from the southern part of the Maule 2010 earthquake rupture zone - overlapping with the northern termination of the Valdivia 1960 earthquake - in the decade before the event to identify the spatial variability of pore fluid pressure and effective stress along the plate interface zone. The reflection seismic and the seismological data exhibit well defined changes of reflectivity and Vp/Vs ratio along the plate interface that can be correlated with different parts of the coupling zone as well as with changes during the seismic cycle. High Vp/Vs domains, interpreted as zones of elevated pore fluid pressure, spatially correlate with lower locking degree, and exhibit higher background seismicity as expected for partly creeping domains. In turn, unstable slip associated to a higher degree of locking is promoted in lower pore fluid pressure domains. This relationship is particularly well expressed in the upper two thirds of the seismic coupling zone down to a depth of some 25 km at an estimated 250°C. In the gradient zone towards deeper domains locking gradually decreases to very low values, and the elevated Vp/Vs-ratio returns to standard values. At the same time seismic reflectivity remains high to some 35 km and then disappears with only minor S-wave reflectivity persisting down to the zone of intermediate depth seismicity at some 60 km depth that is again highlighted by bright reflections. This transition zone, at temperatures > 250°C is also largely coincident with aftershock clusters and a concentration of geodetically recorded afterslip following the Maule earthquake. From their spatial interrelationship, we suggest similar, but less strongly expressed activity of an overpressured fluid. We demonstrate that variations of pore pressure at the plate interface control locking degree variations and therefore coseismic slip distribution of large earthquakes. Lateral variations of pore fluid pressure may be related to the subduction of a transform zone (Maule fracture zone) responsible for part of the fluid input. Finally, we speculate that pore pressure increase during the terminal stage of a seismic cycle to close to lithostatic pressure with an equivalent reduction of effective strength may be as relevant for earthquake triggering as stress loading from long-term plate convergence.

Oncken, Onno; Moreno, Marcos; Haberland, Christian; Rietbrock, Andreas; Angiboust, Samuel; Bedford, Jon

2014-05-01

129

Tectonic activity and plate boundaries along the northern flank of the Fiji Platform  

Microsoft Academic Search

Recent volcanic activity along the northern flank of the Fiji Platform, revealed for the first time from new GLORIA imagery, suggests that the loci of interplate motion in this region have migrated rapidly since the switch from Vitiaz to New Hebridean subduction at 5–8 Ma. At present the plate boundaries along the northern flank of the Fiji Platform consist of

J. E. Hughes Clarke; P. Jarvis; D. Tiffin; R. Price; L. Kroenke

1993-01-01

130

Mantle transition zone beneath the Caribbean-South American plate boundary and its tectonic implications  

E-print Network

seismic network of Venezuela to study the mantle transition zone structure beneath the Caribbean-South American plate boundary and Venezuela. Significant topography on both the 410-km and the 660-km a thick transition zone beneath the Falcon region in northwestern Venezuela, possibly associated

Niu, Fenglin

131

Investigating plate boundary zone deformation with geodetic GPS and modeling studies: A story of two ridges  

Microsoft Academic Search

The surface velocity field around plate boundaries and active faults contains information on a wide variety of processes and conditions, including the long-term fault slip rate, rheological properties of the crust and upper mantle and earthquake processes. Extracting this information requires not only high precision geodetic data, but also accurate models reflecting the critical properties of the crust and upper

Peter Christopher Lefemina

2006-01-01

132

Upper mantle deformation beneath the North American–Pacific plate boundary in California from SKS splitting  

Microsoft Academic Search

In order to constrain the vertical and lateral extent of deformation and the interactions between lithosphere and asthenosphere in a context of a transpressional plate boundary, we performed teleseismic shear wave splitting measurements for 65 permanent and temporary broadband stations in central California. We present evidence for the presence of two anisotropic domains: (1) one with clear E–W trending fast

Mickael Bonnin; Guilhem Barruol; Götz H. R. Bokelmann

2010-01-01

133

Evolution of vertical faults at an extensional plate boundary, southwest Iceland  

E-print Network

Evolution of vertical faults at an extensional plate boundary, southwest Iceland James V. Grant1 Abstract Vertical faults having both opening and vertical displacements are common in southwest Iceland of both oblique and normal spreading in southwest Iceland. Individual fracture segments are commonly

Kattenhorn, Simon

134

Rifting of the plate boundary in North Iceland 1975-1978  

Microsoft Academic Search

A rifting episode started in 1975 on the accreting plate boundary in North Iceland after 100 years of quiescence. Horizontal extension of some 3 m has been observed in the Krafla caldera and the associated 80 km long fissure swarm. The rifting occurs periodically in short active pulses at a few months intervals. Between these active pulses, continuous inflation of

Axel Björnsson; Gunnar Johnsen; Sven Sigurdsson; Gunnar Thorbergsson; Eysteinn Tryggvason

1979-01-01

135

An investigation of the turbulence scale tensor in a flat-plate boundary layer  

NASA Technical Reports Server (NTRS)

A differential equation for the scale tensor in turbulent flow is developed from basic considerations and applied to the flow of a constant-density fluid in the boundary layer on a flat plate. Results from preliminary runs of a computer implementation are discussed.

Sullivan, R. D.; Donaldson, C. D.; Sandri, G.

1979-01-01

136

Seismotectonics of plate boundaries. Final report, 1 November 1973-30 June 1981  

SciTech Connect

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.

Berger, J.; Brune, J.N.; Goodkind, J.; Wyatt, F.; Agnew, D.C.; Beaumont, C.

1981-06-01

137

Diffuse plate boundary and microplate motion: is the Sierra Nevada an independent block?  

NASA Astrophysics Data System (ADS)

The North America/ Pacific Plate boundary is an example of diffuse plate boundary where the motion is accommodated along localized shear zone dividing more rigid blocks. The Sierra Nevada Great Valley microplate (SNGV) is one of such blocks. While the western and south border of the microplate are clearly marked by the San Andreas Fault and its restraining bend, the eastern and northern boundary are more difficult to identify. The southern part of the eastern boundary is clearly marked by the presence of a fairly localized shear zone accommodating ~20% of the North America Pacific plate relative motion, the Eastern California Shear Zone. Moving northward the Walker Lane accommodates the relative displacement on a more diffuse zone and the northern extent of the microplate is not unequivocally identified. Using a compilation of geodetic measurement, we study the motion of the SNGV microplate and the strain accumulated at its borders to quantify to which extent we can really consider the SNGV an independent rigid block with respect to the North American Plate. Preliminary maximum shear strain rate computed using the method of Hackl et al 2009 and available GPS velocity field for the Western United States. Crosses indicate the direction of maximum shear strain rate.

Malservisi, R.; Hackl, M.; La Femina, P. C.; Oldow, J. S.; Geirsson, H.

2010-12-01

138

The Azores-Gibraltar plate boundary: Focal mechanisms, depths of earthquakes, and their tectonic implications  

Microsoft Academic Search

We have analyzed the focal mechanisms and depths of 10 moderately sized earthquakes along the Azores-Gibraltar plate boundary by a variety of methods including formal inversion of the waveform and amplitude of teleseismic P and SH waves, first motion readings, and the identification of depth phases. Our data, together with a compilation of results reported for very large events from

Nina L. Grimison; Wang-Ping Chen

1986-01-01

139

What drives microplate motion and deformation in the northeastern Caribbean plate boundary region?  

NASA Astrophysics Data System (ADS)

north Caribbean plate boundary zone is a broad deformation zone with several fault systems and tectonic blocks that move with different velocities. The indentation by the Bahamas Platform (the "Bahamas Collision") is generally invoked as a cause of this fragmentation. We propose that a second driver of deformation is the western edge of the south dipping Puerto Rico slab moving sideways with the North America plate. The westward motion of the slab edge results in a push on the Caribbean plate farther west. We refer to this second mechanism for deformation as "Slab Edge Push." The motion of the North America plate relative to the Caribbean plate causes both drivers to migrate from east to west. The Bahamas Collision and Slab Edge Push have been operating simultaneously since the Miocene. The question is the relative importance of the two mechanisms. We use mechanical finite element models that represent the two mechanisms from the late Oligocene (30 Ma) to the present. For the present, both models successfully reproduce observed deformation, implying that both models are viable. Back in time the Slab Edge Push mechanism better reproduces observations. Neither mechanism successfully reproduces the observed Miocene counterclockwise rotation of Puerto Rico. We use this rotation to tune a final model that includes fractional contributions of both mechanisms. We find that the Slab Edge Push was the dominant driver of deformation in the north Caribbean plate boundary zone since 30 Ma.

Benthem, Steven; Govers, Rob; Wortel, Rinus

2014-05-01

140

A model of convergent plate margins based on the recent tectonics of Shikoku, Japan  

NASA Technical Reports Server (NTRS)

A viscoelastic finite element plate tectonic model is applied to displacement data for the island of Shikoku, Japan. The flow properties and geometry of the upper portions of the earth are assumed known from geophysical evidence, and the loading characteristics are determined from the model. The nature of the forces acting on the Philippine Sea plate, particularly in the vicinity of the Nankai trough, is determined. Seismic displacement data related to the 1946 Nankaido earthquake are modeled in terms of a thick elastic plate overlying a fluidlike substratum. The sequence of preseismic and seismic displacements can be explained in terms of two independent processes operating on elastic lithospheric plates: a strain accumulation process caused by vertical downward forces acting on or within the lithosphere in the vicinity of the trench, and a strain release process caused by plate failure along a preexisting zone on weakness. This is a restatement of Reid's elastic rebound theory in terms of elastic lithospheric plates.

Bischke, R. E.

1974-01-01

141

Eastern segment of the Azores-Gibraltar line (central-eastern Atlantic) : An oceanic plate boundary with diffuse compressional deformation  

Microsoft Academic Search

New seismic-reflection images across the eastern segment of the Azores-Gibraltar line west of the collisional area between the African and Iberian plates have revealed a complex pattern of compressional deformation involving the Mesozoic oceanic lithosphere. The compressional deformation developed in a region of slow plate convergence and is diffused, at different lithospheric levels, across an area spanning ˜200 km from

R. Sartori; L. Torelli; N. Zitellini; D. Peis; E. Lodolo

1994-01-01

142

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

NASA Astrophysics Data System (ADS)

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.

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

2012-12-01

143

Accretionary margin of north-western Hispaniola: morphology, structure and development of part of the northern Caribbean plate boundary  

USGS Publications Warehouse

Broad-range side-scan sonar (GLORIA) images and single- and multi-channel seismic reflection profiles demonstrate that the margin of north-western Hispaniola has experienced compression as a consequence of oblique North American-Caribbean plate convergence. Two principal morphological or structural types of accretionary wedges are observed along this margin. The first type is characterized by a gently sloping (???4??) sea floor and generally margin-parallel linear sets of sea-floor ridges that gradually deepen towards the flat Hispaniola Basin floor to the north. The ridges are caused by an internal structure consisting of broad anticlines bounded by thrust faults that dip southwards beneath Hispaniola. Anticlines form at the base of the slope and are eventually sheared and underthrust beneath the slope. In contrast, the second type of accretionary wedge exhibits a steeper (???6-16??) sea-floor slope characterized by local slumping and a more abrupt morphological transition to the adjacent basin. The internal structure appears chaotic on seismic reflection profiles and probably consists of tight folds and closely spaced faults. We suggest that changes in sea-floor declivity and internal structure may result from variations in the dip or frictional resistance of the de??collement, or possibly from changes in the cohesive strength of the wedge sediments. The observed pattern of thickening of Hispaniola Basin turbidites towards the insular margin suggests differential southwards tilting of the Hispaniola Basin strata, probably in response to North America-Caribbean plate interactions since the Early Tertiary. Based upon indirect age control from adjacent parts of the northern caribbean plate boundary, we infer a Late Eocene to Early Miocene episode of transcurrent motion (i.e. little or no tilting), an Early Miocene to Late Pliocene period of oblique convergence (i.e. increased tilt) during which the accretionary wedge began to be constructed, and a Late Pliocene to Recent episode of increased convergence (i.e. twice the Miocene to Pliocene tilt), which has led to rapid uplift and erosion of sediment sources on the margin and on Hispaniola, generating a submarine fan at the base of the insular slope. ?? 1992.

Dillon, William P.; Austin, J.A., Jr.; Scanlon, K.M.; Terence, Edgar N.; Parson, L.M.

1992-01-01

144

Experimental investigation of boundary layer transition on a flat plate with C4 leading edge  

NASA Astrophysics Data System (ADS)

This paper considers the effects of freestream turbulence intensity on the boundary layer transition over a range of Reynolds numbers. Bypass mode of transition has been considered using a flat plate with a C4 leading edge, designed to avoid laminar separation. This configuration provides the opportunity to study the effect of a realistic turbomachinery leading edge shape on transition. Hot wire investigations of the boundary layer have been undertaken in order to acquire detailed information about the effect of the freestream conditions on the structure of the boundary layer. This paper concludes with some global observations and comparisons with theoretical predictions and with experimental observations on a more conventional flat plate with a sharp leading edge.

Kalfas, A. I.; Elder, R. L.

145

Measurements of strain at plate boundaries using space based geodetic techniques  

NASA Technical Reports Server (NTRS)

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.

Robaudo, Stefano; Harrison, Christopher G. A.

1993-01-01

146

New Constraints On The Caribbean-South America Plate Boundary From S Wave Receiver Functions  

NASA Astrophysics Data System (ADS)

BOLIVAR (Broadband Ocean-Land Investigation of Venezuela and the Antilles arc Region) was aimed at investigating the interplay between the lithospheric and asthenospheric mantle of the Caribbean and South America plates. We estimate lithospheric thickness from application of the S wave receiver function technique. This reveals lithospheric thinning from 95-105 km depth underneath the Guyana Shield in southern Venezuela to 60-75 km underneath the Caribbean Sea. We observe a comparable thinning on the passive margin transition in eastern Venezuela. Towards the west, the lithosphere-asthenosphere boundary (LAB) shallows to 80 km depth along a NE-SW trending structure bordering the Venezuelan Andes. In addition, the base of the lithosphere beneath the Maracaibo block in NW Venezuela is seen gently dipping towards the southwest. The observed lithospheric structure is consistent with established strike-slip tectonics along the northern boundary of South America. However, we find no evidence for southward subduction of the Caribbean plate as previously suggested. Instead, the boundary is better viewed as the combined motion of three lithospheric blocks: (1) the Caribbean and associated subduction in the Antilles, (2) South America, and (3) the Maracaibo block. The relatively sharp discontinuity in LAB beneath northern Venezuela leads to the conclusion that the Caribbean-South America plate boundary is (1) a structure of lithospheric scale, and (2) a continuous strike-slip plate boundary extending from NE Colombia to Trinidad in NE Venezuela along the Oca-San Sebastian-El Pilar fault zone. This boundary is overprinted in the west by northward translation of the Maracaibo block over the Caribbean.

Landes, M.; Pavlis, G. L.

2008-12-01

147

Receptivity of flat-plate boundary layer in a non-uniform free stream (vorticity normal to the plate)  

NASA Technical Reports Server (NTRS)

Recent progress in both the linear and nonlinear aspects of stability theory has highlighted the importance of the receptivity problem. One of the most unclear aspects of receptivity study is the receptivity of boundary-layer flow normal to vortical disturbances. Some experimental and theoretical results permit the proposition that quasi-steady outer-flow vortical disturbances may trigger by-pass transition. In present work such interaction is investigated for vorticity normal to a leading edge. The interest in these types of vortical disturbances arise from theoretical work, where it was shown that small sinusoidal variations of upstream velocity along the spanwise direction can produce significant variations in the boundary-layer profile. In the experimental part of this work, such non-uniform flow was created and the laminar-turbulent transition in this flow was investigated. The experiment was carried out in a low-turbulence direct-flow wind tunnel T-361 at the Central Aerohydrodynamic Institute (TsAGI). The non-uniform flow was produced by laminar or turbulent wakes behind a wire placed normal to the plate upstream of the leading edge. The theoretical part of the work is devoted to studying the unstable disturbance evolution in a boundary layer with strongly non-uniform velocity profiles similar to that produced by outer-flow vorticity. Specifically, the Tollmien-Schlichting wave development in the boundary layer flow with spanwise variations of velocity is investigated.

Kogan, M. N.

1994-01-01

148

Epidermal ectoderm is required for full elevation and for convergence during bending of the avian neural plate.  

PubMed

Previous studies suggest that bending of the neural plate requires the juxtaposition of neural plate and non-neuroepithelial tissues. The current study examines the role of one of these tissues, the epidermal ectoderm, in bending. Chick blastoderms were harvested from fertile eggs incubated for 24 hr and cultured dorsal-side-up on agar-albumen substrates. In one experiment, a rectangular flap of epidermal ectoderm on one side of each blastoderm was separated from underlying layers and gently reflected onto the area opaca; a fragment of tungsten wire was placed on top of the flap to hold it down and to prevent healing. Embryos were then allowed to develop in a humidified incubator for 2-18 hr. Asymmetric neurulation was observed between the operated and control sides as early as 2 hr after surgery. The amount of asymmetry was quantified in serial transverse sections from embryos collected 8 hr after surgery. Elevation of the lateral edge of the neural plate on the operated side averaged one half to two thirds of that on the control side, and convergence of the operated side around the dorsolateral hinge point toward the dorsal midline did not occur. These results demonstrate that epidermal ectoderm is required for full elevation and for convergence during bending. In another experiment, lateral epidermal ectoderm was removed, leaving only a medial strip consisting of both the epidermal component of the future neural fold and flanking future epidermis. This experiment revealed that although epidermal ectoderm is necessary for full elevation and for convergence of the neural folds, a medial strip of epidermal ectoderm is sufficient to drive bending. Collectively, these results further support the idea that neurulation is a multifactorial process driven by both intrinsic and extrinsic factors acting in concert. PMID:9415425

Hackett, D A; Smith, J L; Schoenwolf, G C

1997-12-01

149

Discovering Plate Boundaries Update: Builds Content Knowledge and Models Inquiry-based Learning  

NASA Astrophysics Data System (ADS)

Discovering Plate Boundaries (DPB) is a jigsaw-structured classroom exercise in which students explore the fundamental datasets from which plate boundary processes were discovered. The exercise has been widely used in the past ten years as a classroom activity for students in fifth grade through high school, and for Earth Science major and general education courses in college. Perhaps more importantly, the exercise has been used extensively for professional development of in-service and pre-service K-12 science teachers, where it simultaneously builds content knowledge in plate boundary processes (including natural hazards), models an effective data-rich, inquiry-based pedagogy, and provides a set of lesson plans and materials which teachers can port directly into their own classroom (see Pringle, et al, this session for a specific example). DPB is based on 4 “specialty” data maps, 1) earthquake locations, 2) modern volcanic activity, 3) seafloor age, and 4) topography and bathymetry, plus a fifth map of (undifferentiated) plate boundary locations. The jigsaw is structured so that students are first split into one of the four “specialties,” then re-arranged into groups with each of the four specialties to describe the boundaries of a particular plate. We have taken the original DPB materials, used the latest digital data sets to update all the basic maps, and expanded the opportunities for further student and teacher learning. The earthquake maps now cover the recent period including the deadly Banda Aceh event. The topography/bathymetry map now has global coverage and uses ice-free elevations, which can, for example, extend to further inquiry about mantle viscosity and loading processes (why are significant portions of the bedrock surface of Greenland and Antarctica below sea level?). The volcanic activity map now differentiates volcano type and primary volcanic lithology, allowing a more elaborate understanding of volcanism at different plate boundaries. The volcanic activity map also now includes seafloor hydrothermal vents to extend the volcanic data set into the oceans. The new maps also more completely represent the polar regions, improving, for example, the students understanding of the ridge system running across the Arctic Sea. We have expanded the teacher’s guide to assist both novice and experienced teachers “see what an Earth Scientist sees” in the data. We have found repeatedly that the real strengths of the DPB activity are that (1) the course materials readily adapt to as well as appropriately challenge all levels of student abilities, leading to very natural differentiated levels of instruction, and (2) students of all levels develop a real ownership in their “plate tectonic” expertise.

Sawyer, D. S.; Pringle, M. S.; Henning, A. T.

2009-12-01

150

Tectonics of the Easter plate  

NASA Technical Reports Server (NTRS)

A new model for the Easter plate is presented in which rift propagation has resulted in the formation of a rigid plate between the propagating and dying ridges. The distribution of earthquakes, eleven new focal mechanisms, and existing bathymetric and magnetic data are used to describe the tectonics of this area. Both the Easter-Nazca and Easter-Pacific Euler poles are sufficiently close to the Easter plate to cause rapid changes in rates and directions of motion along the boundaries. The east and west boundaries are propagating and dying ridges; the southwest boundary is a slow-spreading ridge and the northern boundary is a complex zone of convergent and transform motion. The Easter plate may reflect the tectonics of rift propagation on a large scale, where rigid plate tectonics requires boundary reorientation. Simple schematic models to illustrate the general features and processes which occur at plates resulting from large-scale rift propagation are used.

Engeln, J. F.; Stein, S.

1984-01-01

151

Target Plate Conditions During Stochastic Boundary Operation on DIII-D  

SciTech Connect

A major concern for large tokamaks like ITER is the presence of edge localized modes (ELMs) that repeatedly send large bursts of particles and heat into the divertor plates. Operation with resonant magnetic perturbations (RMP) at the boundary of DIII=D has suppressed ELMs for values of q95 {approx} 3.7. At the target plate, the conditions during ELM suppressed operation for both high and low collisionality are observed by a set of radially distributed Langmuir probes. At high collisionality (n*{approx}1), the target plate particle flux and temperature drops by > 30% during ELM suppression. At low collisionality (n*{approx}0.1), the core density, target plate density, and target plate particle flux drop but the plate electron temperature increases after the ELMs are suppressed. The ELM-suppressed target plate heat flux is nearly the same as the heat flux between ELMs but the (5X higher) transient heat flux peaks due to ELMs are eliminated.

Watkins, J; Evans, T; Moyer, R; Lasnier, C; Rudakov, D

2006-05-15

152

Crustal Structure of the Caribbean-South American Diffuse Plate Boundary: Subduction Zone Migration and Polarity Reversal Along BOLIVAR Profile 64W  

NASA Astrophysics Data System (ADS)

The BOLIVAR (Broadband Ocean-Land Investigation of Venezuela and the Antilles arc Region) project is an NSF funded, collaborative seismic experiment in the southeast Caribbean region. The purpose of the project is to understand the diffuse plate boundary created by the oblique collision between the Caribbean and South American plates. Profile 64W of the BOLIVAR experiment, a 450 km-long, N-S transect onshore and offshore Venezuela located at ~64°W longitude, images the deep crustal structures formed by this collision. The active source components of profile 64W include 300 km of MCS reflection data, 33 coincident OBSs, and 344 land seismic stations which recorded 7500 offshore airgun shots and 2 explosive land shots. Results from the reflection and refraction seismic data along 64W show complex crustal structure across the entire span of the diffuse plate boundary. The onshore portion of 64W crosses the fold and thrust belt of the Serrania del Interior, which formed at ~16 Ma by collision of the Caribbean forearc with the northern South American passive margin. Underlying the Serrania del Interior is a south-vergent, remnant Lesser Antillean subduction zone. As this Lesser Antilles subduction impinged on continental crust, it caused a polarity reversal and jump offshore to the north. Convergence was initially localized in the closure and inversion of the Grenada Basin. However, subduction could not develop because of the ~20-km-thick crust of the Aves Ridge; instead, north-vergent subduction initiated further to the north, where ~12-km-thick Caribbean oceanic crust of the Venezuela Basin began to subduct beneath the Aves Ridge in the Pliocene (~4 Ma) and appears to continue subducting today. Between the remnant subduction zone and the modern one, the El Pilar and Coche dextral strike-slip faults accommodate most of the transform motion of the plate boundary. From the Serrania del Interior to the Aves Ridge, ~260 km of accreted orogenic float comprises the diffuse plate boundary.

Clark, S. A.; Levander, A.; Magnani, M.; Zelt, C. A.; Sawyer, D. S.; Ave Lallemant, H. G.

2005-12-01

153

Plate Borders and Mountain Building  

NSDL National Science Digital Library

This page features animations of four different types of plate boundaries, including one animation of the collision of two pieces of continental crust, forming steep mountain ranges. The animations are all presented in flash, and the plate convergence offers a useful, generic view of orogeny.

Schlumberger Excellence in Educational Development, Inc.

154

Late Cretaceous to mid Eocene plate boundaries in the southwest Pacific  

NASA Astrophysics Data System (ADS)

The late Cretaceous to mid Eocene history of the southwest and southernmost Pacific has been subject to starkly contrasting interpretations, ranging from relative tectonic quiescence with the Lord Howe Rise (LHR) being part of the Pacific plate to a dynamic subduction setting. In the first scenario the Tasman Sea would have formed as a consequence of divergence between the Pacific and Australian plates, whereas in the second scenario it would have formed as a marginal basin associated with subduction. The first scenario is supported by a number of arguments, including a lack of evidence for deformation and tectonic activity in New Zealand during this period and a geodynamic modelling inference, namely that the bend in the Hawaiian-Emperor chain can be better reproduced if the LHR is part of the Pacific plate. The second scenario is supported by regional plate kinematic models reconciling a variety of observations including back-arc basin formation and destruction through time and the history of arc-continent collisions. The primary problem with the first scenario is the use of a plate circuit that leaves relative motion between East and West Antarctica unconstrained, leading to an improbable history of periodic compression and extension. The main problem with the alternative scenario is a lack of sampled late Cretaceous volcanic arc rocks east of the LHR. We analysed available geological and geophysical data to constrain the locations of and movements along the plate boundaries in the southwest and southern Pacific from the late Cretaceous to mid Eocene, and assessed how Pacific plate motion is best quantified during this period. Geological and geophysical evidence suggests that a plate boundary separated the Pacific plate from the LHR. The distribution of lower mantle slab material that is imaged by seismic tomography beneath New Zealand is best explained if subduction occurred to the east of the LHR during the entire late Cretaceous to mid Eocene period. Rocks from ophiolitic nappes in the North Island of New Zealand, New Caledonia and Papua New Guinea show evidence of having formed in a back-arc basin during this period, consistent with a subduction zone near the LHR. Although New Zealand is commonly viewed as tectonically quiescent at this time, deformation at several locations to the east and west of the present-day Alpine Fault suggests that a plate boundary cut through Zealandia during Tasman Sea opening. As the LHR was not attached to the Pacific plate and subduction occurred to the east and north of the LHR we suggest that Pacific plate motion is best quantified using a plate circuit through East and West Antarctica, avoiding this zone of southwest Pacific subduction. Future work should focus on better constraining the location of and motion along the late Cretaceous-mid Eocene plate boundary through New Zealand to enable the use of a plate circuit via Australia.

Matthews, Kara J.; Dietmar Müller, R.; Whittaker, Joanne; Flament, Nicolas; Seton, Maria

2013-04-01

155

The nature of the plate interface and driving forces of deformation in the New Zealand plate-boundary zone - clues from continuous GPS measurements  

NASA Astrophysics Data System (ADS)

New Zealand straddles the boundary between the Australian and Pacific plate. During the Cenozoic, relative plate motion has resulted in a complex pattern of surface faulting and rotation, involving displacements up to 100s kilometres on individual faults. But over periods of decades or less, GPS measurements show a remarkably smooth pattern of velocities. Previous attempts to model the GPS velocity field have invoked a complicated pattern of hypothetical crustal blocks, requiring detailed knowledge of the distribution of the longer term (over ~10 ka) slip rates, 'coupling factors' and geometry of block boundaries, with hundreds of adjustable parameters. We show here that almost the entire plate-boundary continuous GPS velocity field, over the past ~10 years, can be predicted within error from a much simpler model of elastic distortion due to deep slip on a single plate interface, at the relative plate motion rates. This model also predicts the maximum depth of plate locking and tectonic rotations in the overlying crust, but does not require any knowledge of the geometry and rates of surface faulting, or the need to invoke varying 'coupling factors'. In its simplest form, the model has less than 10 adjustable parameters. This way, it can be shown that the smooth GPS velocity field reflects the basic driving forces of plate boundary deformation, where accumulation of slip on the deeper moving part of the plate interface causes a steady build up in tectonic stress in the elastic layer, which will ultimately be relieved during earthquakes by slip on crustal faults.

Lamb, S. H.; Smith, E. G.

2012-12-01

156

Seismicity pattern: an indicator of source region of volcanism at convergent plate margins  

NASA Astrophysics Data System (ADS)

The results of detailed investigation into the geometry of distribution of earthquakes around and below the volcanoes Korovin, Cleveland, Makushin, Yake-Dake, Oshima, Lewotobi, Fuego, Sangay, Nisyros and Montagne Pelée at convergent plate margins are presented. The ISC hypocentral determinations for the period 1964-1999, based on data of global seismic network and relocated by Engdahl, van der Hilst and Buland, have been used. The aim of this study has been to contribute to the solution of the problem of location of source regions of primary magma for calc-alkaline volcanoes spatially and genetically related to the process of subduction. Several specific features of seismicity pattern were revealed in this context. (i) A clear occurrence of the intermediate-depth aseismic gap (IDAG) in the Wadati-Benioff zone (WBZ) below all investigated active volcanoes. We interpret this part of the subducted slab, which does not contain any teleseismically recorded earthquake with magnitude greater than 4.0, as a partially melted domain of oceanic lithosphere and as a possible source of primary magma for calc-alkaline volcanoes. (ii) A set of earthquakes in the shape of a seismically active column (SAC) seems to exists in the continental wedge below volcanoes Korovin, Makushin and Sangay. The seismically active columns probably reach from the Earth surface down to the aseismic gap in the Wadati-Benioff zone. This points to the possibility that the upper mantle overlying the subducted slab does not contain large melted domains, displays an intense fracturing and is not likely to represent the site of magma generation. (iii) In the continental wedge below the volcanoes Cleveland, Fuego, Nisyros, Yake-Dake, Oshima and Lewotobi, shallow seismicity occurs down to the depth of 50 km. The domain without any earthquakes between the shallow seismically active column and the aseismic gap in the Wadati-Benioff zone in the depth range of 50-100 km does not exclude the melting of the mantle also above the slab. (iv) Any earthquake does not exist in the lithospheric wedge below the volcano Montagne Pelée. The source of primary magma could be located in the subducted slab as well as in the overlying mantle wedge. (v) Frequent aftershock sequences accompanying stronger earthquakes in the seismically active columns indicate high fracturing of the wedge below active volcanoes. (vi) The elongated shape of clusters of epicentres of earthquakes of seismically active columns, as well as stable parameters of the available fault plane solutions, seem to reflect the existence of dominant deeply rooted fracture zones below volcanoes. These facts also favour the location of primary magma in the subducting slab rather than in the overlying wedge. We suppose that melts advancing from the slab toward the Earth surface may trigger the observed earthquakes in the continental wedge that is critically pre-stressed by the process of subduction. However, for definitive conclusions it will be necessary to explain the occurrence of earthquake clusters below some volcanoes and the lack of seismicity below others, taking into account the uncertainty of focal depth determination from global seismological data in some regions.

Špi?ák, Aleš; Hanuš, Václav; Van?k, Ji?í

2004-04-01

157

In-Flight Boundary-Layer Transition of a Large Flat Plate at Supersonic Speeds  

NASA Technical Reports Server (NTRS)

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.

Banks, D. W.; Frederick, M. A.; Tracy, R. R.; Matisheck, J. R.; Vanecek, N. D.

2012-01-01

158

The nature of the plate interface and driving force of interseismic deformation in the New Zealand plate-boundary zone, revealed by the continuous GPS velocity field  

NASA Astrophysics Data System (ADS)

New Zealand straddles the boundary between the Australian and Pacific plates. Cenozoic relative plate motion has resulted in a complex pattern of faulting and block rotation, with displacements on individual faults up to hundreds of kilometers. However, over periods of several years, GPS measurements show a remarkably smooth pattern of velocities. We show here using a new method of back slip analysis, that almost the entire plate-boundary continuous GPS velocity field can be predicted within measurement error from a simple model of elastic distortion due to deep slip on a single plate interface (megathrust in the Hikurangi and Putsegur subduction zones or fault through continental lithosphere beneath the Southern Alps) at the relative plate motion rates. This suggests that the main driving force of plate-boundary deformation is slip on the deeper moving part of the plate interface, without buried creep in localized shear zones beneath individual surface faults. The depth at which this deep slip terminates (locking point line) determines the width of deformation. Along the Hikurangi margin, there is also clockwise rotation of ~150 km long segment of the fore arc (Wairoa domain) at 4.5° ± 1 Ma, relative to the Australian Plate, about a pole in western North Island; model residuals in the velocity field are mainly a result of incomplete averaging of the cycle of slow slip events on the plate interface, downdip of the locking point.

Lamb, Simon; Smith, Euan

2013-06-01

159

Diffuse Oceanic Plate Boundaries: Mapping the Relationship Between Angular Velocity and Torque as a Function of Assumed Rheology  

NASA Astrophysics Data System (ADS)

Diffuse plate boundaries comprise about 15% of Earth's surface. The poles of rotation across diffuse oceanic plate boundaries, which are roughly 1,000 to 2,000 km in cross-strike width, tend to lie within the plate boundary themselves. Zatman et al. (2001) showed that this is a predictable consequence of plate geometry and simple physics if component plates are strongly coupled across the diffuse oceanic plate boundaries that separate them. Here we build on the work of Zatman et al. (2001) and of Zatman & Gordon (2003) to construct maps of torque orientation. On these maps we plot the boundary between torque orientations that produce poles of rotation in the diffuse plate boundary and torque orientations that produce poles of rotation outside the diffuse plate boundary. We assume that the upper lithosphere fails at a specific yield strength and that the lower lithosphere deforms by creeping flow. Acting in parallel, the integrated or averaged behavior of these two layers can be approximated as a power-law viscous fluid. The value of the power-law exponent, n, ranges from 3 (if the lower layer dominates) to infinity (if the upper layer dominates). We calculate maps for exponents of 3, 10, 30, and 100. All the maps closely resemble one another, providing further support to the conclusion that the mapping from pole of rotation to torque orientation is insensitive to rheology (Zatman & Gordon 2003). Moreover, the maps show that it is very unlikely (p < 2%) that the pole of rotation will lie outside of the boundary in the along-strike direction. There is a higher probability (p ?20% assuming that all orientations of torque are equally likely) that the pole of rotation will lie outside the boundary in the across-strike direction. Implications will be discussed for the India-Capricorn, Capricorn-Australia, North America-South America, Nubia-Somalia, and Nubia-Eurasia diffuse plate boundaries.

Mutnuri, K.; Gordon, R. G.

2003-12-01

160

Plate boundary forces in the vicinity of Trinidad-the-transition from transpression to transtension in the Southern Caribbean plate boundary zones  

SciTech Connect

Deformation in the southern Caribbean plate boundary zones as recorded in the Northern Range of Trinidad initiated in the Oligocene with northward vergent gravity sliding of Northern Range sediments due to uplift and oversteepening of the previously passive margin by the eastward migration of the Caribbean flexural forebulge. Progressive east-southeast transvergence of the Caribbean Plate with respect to South America overthrust incorporated the Northern Range sediments into the Caribbean accretionary prism, thrusting them south-southeast to produce a Middle Miocene transpressive foreland fold and thrust belt in southern Trinidad. Late Miocene deformation within Trinidad was increasingly dominated by right-lateral strike-slop (RLSS) faulting, at the expense of transpressive compressional features. Right-stepping of RLSS motion initiated the Gulf of Paria and Caroni pull-apart basins, Since Early Pliocene these basins and other areas to the north of Trinidad have undergone north-south extension in addition to east-west trending RLSS. Such extension caused the northward withdrawal of Caribbean terranes from atop of the Northern Range, Resulting in rapid isostatically induced uplift (approximately 0.5 mmyr[sup -1]). This change in deformation style may relate to a hitherto unrecognized shift in the relative motion of the eastern Caribbean Plate with respect to South America: from east-southeast-directed transpression to east-northeast-directed transtension.

Algar, S.T.; Pindell, J.L. (Dartmouth College, Hanover, NH (United States))

1993-02-01

161

Global Stabilization of the von K'arm'an Plate With Boundary Feedback Acting Via Bending Moments Only  

E-print Network

Global Stabilization of the von K'arm'an Plate With Boundary Feedback Acting Via Bending Moments\\Omega be an open bounded domain in R 2 with a sufficiently smooth boundary, \\Gamma. In \\Omega\\Gamma we consider conditions and a control, u, acting through a second order boundary condition (as a moment): w tt \\Gamma fl 2

162

Dike-induced contraction along oceanic and continental divergent plate boundaries  

NASA Astrophysics Data System (ADS)

axis of divergent plate boundaries shows extension fractures and normal faults at the surface. Here we present evidence of contraction along the axis of the oceanic ridge of Iceland and the continental Main Ethiopian Rift. Contraction is found at the base of the tilted hanging wall of dilational normal faults, balancing part of their extension. Our experiments suggest that these structures result from dike emplacement. Multiple dike injection induces subsidence above and uplift to the sides of the dikes; the transition in between is accommodated by reverse faults and subsequent peripheral inward dipping normal faults. Our results suggest that contraction is a direct product of magma emplacement along divergent plate boundaries, at various scales, marking a precise evolutionary stage and initiating part of the extensional structures (extension fractures and normal faults).

Trippanera, D.; Acocella, V.; Ruch, J.

2014-10-01

163

Tectonic plate under a localized boundary stress: fitting of a zero-range solvable model  

E-print Network

We suggest a method of fitting of a zero-range model of a tectonic plate under a boundary stress on the basis of comparison of the theoretical formulae for the corresponding eigenfunctions/eigenvalues with the results extraction under monitoring, in the remote zone, of non-random (regular) oscillations of the Earth with periods 0.2-6 hours, on the background seismic process, in case of low seismic activity. Observations of changes of the characteristics of the oscillations (frequency, amplitude and polarization) in course of time, together with the theoretical analysis of the fitted model, would enable us to localize the stressed zone on the boundary of the plate and estimate the risk of a powerful earthquake at the zone.

Petrova, L

2008-01-01

164

Tectonic plate under a localized boundary stress: fitting of a zero-range solvable model  

E-print Network

We suggest a method of fitting of a zero-range model of a tectonic plate under a boundary stress on the basis of comparison of the theoretical formulae for the corresponding eigenfunctions/eigenvalues with the results extraction under monitoring, in the remote zone, of non-random (regular) oscillations of the Earth with periods 0.2-6 hours, on the background seismic process, in case of low seismic activity. Observations of changes of the characteristics of the oscillations (frequency, amplitude and polarization) in course of time, together with the theoretical analysis of the fitted model, would enable us to localize the stressed zone on the boundary of the plate and estimate the risk of a powerful earthquake at the zone.

L. Petrova; B. Pavlov

2008-01-18

165

Gradual unlocking of plate boundary controlled initiation of the 2014 Iquique earthquake.  

PubMed

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. PMID:25119049

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

166

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

PubMed Central

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

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

2012-01-01

167

Global Stabilization of a Dynamic von K'arm'an Plate With Nonlinear Boundary Feedback  

E-print Network

Global Stabilization of a Dynamic von K'arm'an Plate With Nonlinear Boundary Feedback Mary Ann Horn, \\Gamma. In \\Omega\\Gamma we consider the following von K'arm'an system in the variables w(t; x) and Ã?(w(t; x)) with nonlinear feedback controls, g, f 1 , and f 2 : w tt \\Gamma fl 2 \\Deltaw tt + \\Delta 2 w

168

Tectonic plate under a localized boundary stress: fitting of a zero-range solvable model  

Microsoft Academic Search

We suggest a method of fitting of a zero-range model of a tectonic plate under a boundary stress on the basis of comparison of the theoretical formulae for the corresponding eigenfunctions\\/eigenvalues with the results extraction under monitoring, in the remote zone, of non-random (regular) oscillations of the Earth with periods 0.2-6 h, on the background seismic process, in case of

L. Petrova; B. Pavlov

2008-01-01

169

Unsteady Boundary-Layer Flow over Jerked Plate Moving in a Free Stream of Viscoelastic Fluid  

PubMed Central

This study aims to investigate the unsteady boundary-layer flow of a viscoelastic non-Newtonian fluid over a flat surface. The plate is suddenly jerked to move with uniform velocity in a uniform stream of non-Newtonian fluid. Purely analytic solution to governing nonlinear equation is obtained. The solution is highly accurate and valid for all values of the dimensionless time 0 ? ? < ?. Flow properties of the viscoelastic fluid are discussed through graphs. PMID:24892060

Mehmood, Ahmer; Ali, Asif; Saleem, Najma

2014-01-01

170

Stress in the lithosphere from non-tectonic loads with implications for plate boundary processes  

NASA Astrophysics Data System (ADS)

Stress in the lithosphere from non-tectonic loads is calculated, making use of semi-analytic Fourier models. Sources of non-tectonic stress include coastal lithospheric bending in response to the rise in eustatic sea level since the Last Glacial Maximum, lithospheric rebound and pore pressure changes in response to the intermittent load of Ancient Lake Cahuilla in the Salton trough, stress sustained through the formation and long-term support of local short-wavelength topography, and topography created by the ejecta debris from impact craters on the surface of the icy Galilean satellites. Stresses from time varying surface water loads are calculated along major plate boundaries globally to determine to what extent, if any, these loads influence the major tectonic processes at work in plate boundary regions, such as the earthquake cycle on major faults. It is determined that the stress perturbations from these loads are generally an order of magnitude smaller than the tectonic stress accumulation rate. Their ability to noticeably affect the seismic cycle is therefore restricted to specific circumstances including when the tectonic loading rate is particularly low, such as along secondary plate boundary fault structures, when the nontectonic loading rate is particularly high, such as in the case of catastrophic flooding events, or when the fault in question is already critically stressed to a near-failure level. Stresses from local topography are calculated along the global mid-ocean ridge and along the Chilean subduction megathrust. The predicted orientations of these stresses are compared to a presumed ridge-normal and transform-strike-slip faulting regime or the focal mechanism of a single large earthquake, respectively. Quantitative constraints for the coincident tectonic stresses are subsequently established with implications for the strength of the plate boundary faults and the necessity of particular topographic and bathymetric features.

Luttrell, Karen Marie

171

Thrust -wrench interference tectonics in the Gulf of Cadiz (Africa -Iberia plate boundary in the North-East Atlantic): insights from  

E-print Network

Thrust - wrench interference tectonics in the Gulf of Cadiz (Africa - Iberia plate boundary to a segment of the Africa- Eurasia plate boundary previously described as tectonically diffuse (e.g. Sartori key segment of the Africa-Iberia plate boundary (North- East Atlantic ocean), three main different

Paris-Sud XI, Université de

172

In-Flight Boundary-Layer Transition on a Large Flat Plate at Supersonic Speeds  

NASA Technical Reports Server (NTRS)

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.

Banks, Daniel W.; Fredericks, Michael Alan; Tracy, Richard R.; Matisheck, Jason R.; Vanecek, Neal D.

2012-01-01

173

Plate boundary deformation at the latitude of the Salton Trough - northern Gulf of California (Invited)  

NASA Astrophysics Data System (ADS)

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.

Stock, J. M.

2013-12-01

174

On two-dimensional temporal modes in spatially evolving open flows: the flat-plate boundary layer  

Microsoft Academic Search

Temporal linear stability modes depending on two space directions are computed for a two-dimensional boundary-layer flow along a flat plate. The spatial structure of each individual temporally stable mode is shown to be reminiscent of the spatial exponential growth of perturbations along the flat plate, as predicted by local analyses. It is shown using an optimal temporal growth analysis, that

Uwe Ehrenstein; François Gallaire

2005-01-01

175

Implication of the Central Gulf of California (MX) Earthquake cycle in understanding continental plate boundary rheology  

NASA Astrophysics Data System (ADS)

The Gulf of California is characterized by the development of a highly oblique plate boundary that rifted the Baja California Peninsula from mainland North America through a series of long transform faults and deep basins. Within the central part of Gulf of California 90 % of the relative motion between North America and Pacific plate is localized in a very narrow region between the Baja California peninsula and a chain of islands (in particular Angel de la Guarda and San Lorenzo). In August 2009 and April 2012, two earthquakes (Mw~7) struck the region. The collection of campaign GPS data since 2004 and after the two seismic events, allows an evaluation of the surface deformation during the full earthquake cycle. Here we focus on the surface deformation relative to a rigid Baja California motion (defined by GPS observations along the Peninsula) during the interseismic period before the two seismic events, and the co- and post-seismic period of each earthquake. In particular, we explore the implications of the post-seismic surface deformation in understanding the rheological and mechanical properties underneath the seismogenic layer in a region characterized by a developing plate boundary. a) Interseismic velocity field in a Baja fixed reference frame. b-c) cosesimic displacement fro the 2009 and 2012 seismic events (focal mechanisms from Global CMT web page) Relative position with respect to the first observation of the two stations closest to the coast up to July 1st 2012.

Malservisi, R.; Plattner, C.; Hackl, M.; Suarez Vidal, F.

2012-12-01

176

First epoch geodetic measurements with the Global Positioning System across the northern Caribbean plate boundary zone  

NASA Technical Reports Server (NTRS)

The first geodetic survey across the northern Caribbean plate boundary zone with GPS was conducted in June 1986. Baseline vectors defined by the six-station regional GPS network ranged from 170 to 1260 km in length. Repeatability of independent daily baseline estimates was better than 8 mm plus 1.3 parts in 10 to the 8th of baseline length for horizontal components. The wet tropospheric path delay during the experiment was both high, sometimes exceeding 30 cm at zenith, and variable, sometimes exceeding 5 cm variation over several hours. Successful carrier phase cycle ambiguity resolution (bias fixing) could not be achieved prior to construction of a regional troposphere model. With optimum troposphere treatment and single-day orbital arcs, most biases on baselines were resolved up to about 550 km in length. With multiday orbital arcs most biases in the network were resolved regardless of baseline length. The results suggest that constraints on plate-boundary zone deformation in the Greater Antilles, and on the North America-Caribbean relative plate motion vector, can be obtained with a series of GPS experiments spanning less than 10 and 15 years, respectively.

Dixon, T. H.; Gonzalez, G.; Lichten, S. M.; Katsigris, E.

1991-01-01

177

Late Cenozoic partitioning of oblique plate convergence in the Zagros fold-and-thrust belt (Iran)  

NASA Astrophysics Data System (ADS)

The NW trending Zagros fold-and-thrust belt is affected by two major dextral faults: (1) the NW trending Main Recent Fault that accommodates partitioning of oblique convergence at the rear of the western Zagros and (2) the north trending Kazerun Fault located in the central Zagros. Combined structural and fault kinematics studies and SPOT images analysis have shown a Pliocene kinematic change accompanied by a fault pattern reorganization, which has led to a modification in the accommodation of oblique convergence. Since the late Pliocene, the distributed transpressional deformation operating at the rear of the belt has become partitioned along the newly formed Main Recent Fault. This fault cuts through early Pliocene nappes and transpressional structures by right-laterally reactivating high-angle thrusts. The southeastern termination of the Main Recent Fault connects to the northern termination of Kazerun Fault that consists of three fault zones that end in bent, orogen-parallel splay thrust faults. The Kazerun Fault, together with a series of north to NNW trending inherited basement strike-slip faults, define an orogen-scale fan-shaped fault pattern pointing toward the Main Recent Fault-Kazerun Fault junction. This structural pattern allows slip from along the Main Recent Fault to become distributed by transfer to the longitudinal thrust faults and folds of the Zagros belt, with the fan-shaped fault pattern acting as a horse-tail termination of the Main Recent Fault.

Authemayou, Christine; Chardon, Dominique; Bellier, Olivier; Malekzadeh, Zaman; Shabanian, Esmaeil; Abbassi, Mohammad Reza

2006-06-01

178

Velocity field across the southern Caribbean plate boundary and estimates of Caribbean\\/South-American plate motion using GPS geodesy 1994-2000  

Microsoft Academic Search

Global Positioning System (GPS) observations between 1994 and 2000 at twenty-two sites in the Lesser Antilles and northern South-America indicate that the Caribbean plate, along its southern boundary, slips at a rate of 20.5+\\/-2mm\\/a with an azimuth of N84°+\\/-2°E at 65°W, relative to the South-American plate. East of 68°W, 80% of the dextral slip is contained within a 80-km wide

Omar J. Pérez; Roger Bilham; Rebecca Bendick; José R. Velandia; Napoleón Hernández; Carlos Moncayo; Melvin Hoyer; Mike Kozuch

2001-01-01

179

Paleoseismicity of the North American-Caribbean plate boundary (Septentrional fault), Dominican Republic  

USGS Publications Warehouse

The Septentrional fault zone, the major North American-Caribbean plate-boundary fault in Hispaniola, is a likely source of large earthquakes in the Dominican Republic. An excavation into a Holocene alluvial fan deposited across the fault in the central Cibao Valley, Dominican Republic, provides evidence that it has been at least 430 yr and probably more than 740 yr since the last ground-rupturing earthquake along this segment of the fault. On the basis of these data and published estimates of the plate-tectonic slip rate, it is proposed that the Septentrional fault is a source of high seismic potential in the densely populated and rapidly developing Cibao Valley in the northern Dominican Republic. -Authors

Prentice, C.S.; Mann, P.; Taylor, F.W.; Burr, G.; Valastro, S.

1993-01-01

180

Prehistoric earthquakes on the Caribbean-South American plate boundary, central range fault, Trinidad  

USGS Publications Warehouse

Recent geodetic studies suggest that the Central Range fault is the principal plate-boundary structure accommodating strike-slip motion between the Caribbean and South American plates. Our study shows that the fault forms a topographically prominent lineament in central Trinidad. Results from a paleoseismic investigation at a site where Holocene sediments have been deposited across the Central Range fault indicate that it ruptured the ground surface most recently between 2710 and 550 yr B.P. If the geodetic slip rate of 9-15 mm/yr is representative of Holocene slip rates, our paleoseismic data suggest that at least 4.9 m of potential slip may have accumulated on the fault and could be released during a future large earthquake (M > 7). ?? 2010 Geological Society of America.

Prentice, C.S.; Weber, J.C.; Crosby, C.J.; Ragona, D.

2010-01-01

181

Prehistoric earthquakes on the Caribbean-South American plate boundary, central Range Fault, Trinidad  

USGS Publications Warehouse

Recent geodetic studies suggest that the Central Range fault is the principal plate-boundary structure accommodating strike-slip motion between the Caribbean and South American plates. Our study shows that the fault forms a topographically prominent lineament in central Trinidad. Results from a paleoseismic investigation at a site where Holocene sediments have been deposited across the Central Range fault indicate that it ruptured the ground surface most recently between 2710 and 550 yr B.P. If the geodetic slip rate of 9–15 mm/yr is representative of Holocene slip rates, our paleoseismic data suggest that at least 4.9 m of potential slip may have accumulated on the fault and could be released during a future large earthquake (M > 7).

Prentice, Carol S.; Crosby, Christopher J.; Weber, John C.; Ragona, Daniel

2010-01-01

182

Paleoseismicity of the North American-Caribbean plate boundary (Septentrional fault), Dominican Republic  

NASA Astrophysics Data System (ADS)

The Septentrional fault zone, the major North American-Caribbean plate-boundary fault in Hispaniola, is a likely source of large earthquakes in the Dominican Republic. An excavation into a Holocene alluvial fan deposited across the fault in the central Cibao Valley, Dominican Republic, provides evidence that it has been at least 430 yr and probably more than 730 yr since the last ground-rupturing earthquake along this segment of the fault. On the basis of these data and published estimates of the plate-tectonic slip rate, we propose that the Septentrional fault is a source of high seismic potential in the densely populated and rapidly developing Cibao Valley in the northern Dominican Republic.

Prentice, Carol S.; Mann, Paul; Taylor, F. W.; Burr, G.; Valastro, S.

1993-01-01

183

On the OLP prediction of the unstable modes of the flat plate turbulent boundary layer  

NASA Technical Reports Server (NTRS)

The Orr et al. (OLP) stability analysis is reformulated to yield profiles from hot-wire velocity covariance data in the boundary layer of a flow over a flat plate. The proper orthogonal decomposition theorem (PODT) is used to maximize the mean square of the inner product of the velocity vector with a deterministic candidate vector function in Hilbert space. The OLP formulation couples the PODT for the eddy viscosity with a global extremum principle for the disturbance kinetic energy. Derivation of the governing equations is described analytically, as are the extraction of the mean velocity profile and the eddy viscosity. Finally, techniques for characterizing the dominant mode of the velocity field are introduced and applied to three-dimensional flow over a flat plate. Good agreement is found between the predictions, using laboratory data, and the measured energy and three-dimensional structures of the dominant eddies.

Wadia, A. R.; Payne, F. R.

1981-01-01

184

Flat plate heat transfer for laminar transition and turbulent boundary layers using a shock tube  

NASA Technical Reports Server (NTRS)

Heat transfer results are presented for laminar, transition, and turbulent boundary layers for a Mach number of 0.12 with gas temperatures of 425 K and 1000 K over a flat plate at room temperature. The measurements were made in air for a Reynolds number range of 600 to 6 million. The heat transfer measurements were conducted in a 70-ft long, 4 in. diameter shock tube. Reflecting wedges were used to reflect the incident shock wave to produce a flow Mach number of 0.12 behind the reflected shock wave. Thin film platinum heat gages were mounted on the plate surface to measure the local heat flux. The laminar results for gas temperatures of 425 K to 1000 K agree well with theory. The turbulent results are also close to incompressible theory, with the 1000 K flow case being slightly higher. The transition results lie between the laminar and turbulent predictions.

Brostmeyer, J. D.; Nagamatsu, H. T.

1984-01-01

185

Boundary layer convective heat transfer with pressure gradient using Homotopy Perturbation Method (HPM) over a flat plate  

Microsoft Academic Search

Convective heat transfer equations of boundary layer with pressure gradient over a flat plate are solved using Homotopy Perturbation Method (HPM). This variation method is able to study the effects of Prandtl number (Pr) and pressure gradient (m) on both temperature and velocity distributions in the boundary layer. To this aim, the nonlinear equations of momentum and energy are solved

M. Fathizadeh; F. Rashidi

2009-01-01

186

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)

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.

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

1973-01-01

187

Using GPS, tide gauge and altimetry data to constrain subduction parameters at the Vanuatu plate boundary.  

NASA Astrophysics Data System (ADS)

The Vanuatu subduction zone, Southwest Pacific, combines several features that makes it a particularly useful place to study seismic cycles. The convergence rate is high - approximately 12 cm/yr - and the seismic cycle relatively short. Measurements of interseismic motions are helped by relatively high vertical rates, the close proximity of some islands to the plate interface and the existence of very shallow seamounts on either side of the plate interface. The Vanuatu archipelago is part of the Pacific Ring of Fire: the Australian plate subducts eastward beneath the North Fiji basin, on the western border of the Pacific Plate. High topographic features on the diving plate may contribute to locking of the plates, which can play a major role in the genesis of destructive earthquakes. GPS network points were installed in the early 1990s and the geodesy network has been densified through the years, enabling us to map interseismic horizontal and vertical deformation rates throughout the archipelago. More recently, 8 continuous GPS stations were installed, along with 3 continuous seafloor pressure gauges very near to the plate interface. We show results from GPS data collected from 1996 to 2011, that we re-processed and combined into the ITRF2008 reference frame, and altimetry and seafloor pressure data from 1999 to 2010. The GPS results show that vertical deformation rates vary both across and along the archipelago. We believe that these variations result from variable distance to the plate limit and variable locking parameters. In some areas, subsidence rates are close to one centimeter per year. In the Torres islands (at the northern end of the archipelago) where villagers face recurrent coastal flooding, we showed that this flooding is due more to ground motion than to rise in the absolute sea level, even though the sea-level rise rates are locally high and the islands uplift over the long term. In the Central area of Vanuatu, we augmented the on-land network with two offshore sites using absolute pressure gauges. The sites - Wusi and Sabine Banks - are installed beneath altimetry satellite tracks, Wusi Bank on the over-riding plate and Sabine Bank on the subducting plate. The difference in the pressure records between the sites shows that Wusi Bank subsides by 11 +/- 3 mm/yr with respect to Sabine Bank. We combined the water depths derived from the pressure measurements with altimetry-derived sea-surface heights to tie these heights to a global reference frame: Wusi Bank subsides and Sabine Bank's vertical motion is near zero. Using a 2D elastic model and a finite-element code, we used the gradient of vertical deformation between the coast and the Wusi Bank site to discriminate between possible locked zone geometries. The best simple approximation is a 25° dipping, 30 km long fully locked zone, indicating that stress is currently accumulating west of Santo, Central Vanuatu. The movement of Wusi Bank is a key factor in constraining the dip and length of the locked zone, demonstrating the importance of offshore geodesy measurements.

Ballu, V.; Bouin, M.; Baillard, C.; Calmant, S.; Pelletier, B.; Crawford, W. C.; Kanas, T.; Garaebiti, E.

2012-12-01

188

Experimental study of boundary layer transition on a heated flat plate  

NASA Technical Reports Server (NTRS)

A detailed investigation to the document momentum and thermal development of boundary layers undergoing natural transition on a heated flat plate was performed. Experimental results of both overall and conditionally sampled characteristics of laminar, transitional, and low Reynolds number turbulent boundary layers are presented. Measurements were done in a low-speed, closed-loop wind tunnel with a freestream velocity of 100 ft/s and zero pressure gradient over a range of freestream turbulence intensities from 0.4 to 6 percent. The distributions of skin friction, heat transfer rate, and Reynolds shear stress were all consistent with previously published data. Reynolds analogy factors for momentum thickness Reynolds number, Re(sub theta) less than 2300 were found to be well predicted by laminar and turbulent correlations which accounted for an unheated starting length and uniform heat flux. A small dependence of turbulence results on the freestream turbulence intensity was observed.

Sohn, K. H.; Reshotko, E.; Zaman, K. B. M. Q.

1991-01-01

189

The memory of the accreting plate boundary and the continuity of fracture zones  

USGS Publications Warehouse

A detailed aeromagnetic anomaly map of the Mesozoic seafloor-spreading lineations southwest of Bermuda reveals the dominant magnetic grain of the oceanic crust and the character of the accreting boundary at the time of crustal formation. The magnetic anomaly pattern is that of a series of elongate lobes perpendicular to the fracture zone (flowline) trends. The linear sets of magnetic anomaly peaks and troughs have narrow regions of reduced amplitude anomalies associated with the fracture zones. During the period of Mesozoic geomagnetic polarity reversals (when 1200 km of central North Atlantic seafloor formed), the Atlantic accreting boundary consisted of stationary, elongate, spreading center cells that maintained their independence even though sometimes only minor spatial offsets existed between cells. Normal oceanic crustal structure was formed in the spreading center cells, but structural anomalies and discontinuities characteristic of fracture zones were formed at their boundaries, which parallel flowlines of Mesozoic relative plate motion in the central North Atlantic. We suggest that the memory for a stationary pattern of independent spreading center cells resides in the young brittle lithosphere at the accreting boundary where the lithosphere is weakest; here, each spreading center cell independently goes through its cylce of stress buildup, stress release, and crustal accretion, after which its memory is refreshed. The temporal offset between the peaks of the accretionary activity that takes place within each cell may provide the mechanism for maintaining the independence of adjacent spreading center cells through times when no spatial offset between the cells exists.

Schouten, Hans; Klitgord, Kim D.

1982-01-01

190

Flowfield measurements in a separated and reattached flat plate turbulent boundary layer  

NASA Astrophysics Data System (ADS)

The separation and reattachment of a large-scale, two-dimensional turbulent boundary layer at low subsonic speed on a flat plate has been studied experimentally. The separation bubble was 55 cm long and had a maximum bubble thickness, measured to the height of the mean dividing streamline, of 17 cm, which was twice the thickness of the inlet boundary layer. A combination of laser velocimetry, hot-wire anemometry, pneumatic probing techniques, and flow visualization were used as diagnostics. Principal findings were that an outer inviscid rotational flow was defined which essentially convected over the blockage associated with the inner, viscously dominated bubble recirculation region. A strong backflow region in which the flow moved upstream 100 percent of the time was measured near the test surface over the central 35 percent of the bubble. A laminar backflow boundary layer having pseudo-turbulent characteristics including a log-linear velocity profile was generated under the highly turbulent backflow. Velocity profile shapes in the reversed flow region matched a previously developed universal backflow profile at the upstream edge of the separation region but not in the steady backflow region downstream. A smoke flow visualization movie and hot-film measurements revealed low frequency nonperiodic flapping at reattachment. However, forward flow fraction data at reattachment and mean velocity profiles in the redeveloping boundary layer downstream of reattachment correlated with backward-facing step data when the axial dimension was scaled by the distance from the maximum bubble thickness to reattachment.

Patrick, William P.

1987-03-01

191

Estimation of broadband acoustic power radiated from a turbulent boundary layer-driven reinforced finite plate section due to rib and boundary forces.  

PubMed

Previous papers considered an infinite fluid-loaded plate with parallel line attachments, driven by a wave-number-white pressure excitation invariant in the direction of an attachment, and established the conditions and procedure for estimating the broadband radiated power by assuming the ribs to radiate independently. This paper applies those results to a finite rectangular ribbed plate, and extends the methodology to include the contribution of the plate's boundary support forces to the radiation and the consideration of excitation that varies in the direction parallel to the ribs. The approach is relevant to problems of sound radiation by underwater stiffened steel plates driven by turbulent boundary layer (TBL) pressures, and is also applicable to stiffened circular cylindrical shells when the response is dominated by bending. Comparisons of sample calculations with results of rigorous models validate the approximation. PMID:11931304

Rumerman, M L

2002-03-01

192

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

NASA Astrophysics Data System (ADS)

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.

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

2014-06-01

193

Divergent plate boundaries and crustal spreading on Venus: Evidence from Aphrodite Terra  

NASA Technical Reports Server (NTRS)

The modes of lithospheric heat transfer and the tectonic styles may differ between Earth and Venus, depending on how the high surface temperature (700 K = 430 C), dense and opaque atmosphere (approx. 10 MPa = 100 bars), lack of water oceans, and the other known ways in which Venus differs from Earth, influence basic lithospheric processes, thermal gradient, upper mantle temperature, thermal and chemical evolution, and convection. A fundamental question is whether the lithosphere of Venus is horizontally stable, like the other terrestrial planets, or is mobile like that on Earth. The variety of characteristics, their integrated relationships, and their predictable behavior throughout Western Aphrodite Terra are similar to those features known to occur in association with the terrestrial seafloor at spreading centers and divergent plate boundaries. It is concluded that Western Aphrodite Terra represents the site of crustal spreading centers and divergent plate boundaries. The extent of similar characteristics and processes elsewhere on Venus outside of the 13,000 km long Western and Eastern Aphrodite Terra rise is unknown at the present, but their presence in other areas of the equatorial highlands, suggested from recent analysis, may be tested with forthcoming Magellan data.

Crumpler, L. S.; Head, James W.

1989-01-01

194

A satellite magnetic perspective of subduction zones, large igneous provinces, rifts, and diffuse plate boundary zones  

NASA Astrophysics Data System (ADS)

Large and intermediate-scale tectonic features such as subduction zones, large igneous provinces, rifts, and diffuse plate boundary zones are often seen to have a magnetic signature visible from the perspective of near-Earth magnetic field satellites such as CHAMP and Orsted. Why do these tectonic features have a magnetic signature, while others do not? A new model of the lithospheric field (MF-6, Maus et al., 2008) extending to spherical harmonic degree 120 (333 km wavelength) has been used to evaluate the magnetic state of the lithosphere under the assumption that the magnetization is either induced (with a seismic starting model), or remanent (with a minimum norm approach). Some of the features identified from these images include the Tethyan and NE Siberian diffuse plate boundary zones, the Red Sea rift, and Cretaceous rift basins developed on the West African shield. Almost without exception, subduction zones exhibit a magnetic signature, as do many large igneous provinces. In this talk we discuss some of the new insights this magnetic perspective provides, and speculate on the controls which determine whether tectonic features will be expressed magnetically.

Purucker, M. E.; Whaler, K. A.

2008-12-01

195

Seismic imaging of a plate boundary in the eastern margin of the Japan Sea  

NASA Astrophysics Data System (ADS)

Large earthquakes have frequently occurred in the eastern margin of the Japan Sea (e.g., the 1964 Niigata earthquake (MJMA 7.5), 1983 Nihonkai-Chubu earthquake (MJMA 7.7), 1993 Hokkaido-Nansei-Oki earthquake (MJMA 7.8)), and these earthquakes have caused very strong vibrations, large tsunamis, and serious damage on the coast of the Japan Sea. Nakamura (1983) and Kobayashi (1983) suggested that the eastern margin of the Japan Sea is located along the boundary between the Eurasian Plate and the North America plate. However, since this area has not been identified as one of the priority areas to be investigated, the observation didn't obtain exact evidence of a plate boundary in the eastern margin of Japan Sea. Therefore, we have performed seismic surveys at the eastern margin of the Japan Sea since 2009. Objectives of this study are to reveal structural characteristics around a plate boundary of the Japan Sea with the large earthquakes and understand the tectonics as the geologic background. In 2009-2011, we conducted a multi-channel seismic (MCS) survey and ocean bottom seismometer (OBS) survey around the Yamato basin and the eastern margin of the southern Japan Sea using the R/V KAIREI, JAMSTEC (Japan Agency for Marine-Earth Science and Technology). Survey lines were crooked to avoid the many fishing operations and equipment in the survey area. We shot a tuned airgun array with a spacing of 50 m. This array has a total capacity of 7,800 cubic inches (about 130 liters). The standard air pressure was 2,000 psi (about 14 MPa). During the shooting, we towed a 444-channel hydrophone streamer cable with a 5600-m maximum offset, and the group interval was 12.5 m. The towing depth of the streamer cable was maintained at 12 m below the sea surface using depth controllers. The sampling rate was 2 ms, and the recording length was 15 s. We deployed OBSs, and a refraction survey using an airgun array with a spacing of 200 m. An airgun array in OBS survey used the same configuration as MCS survey. The interval of the OBS deployment was about 5 km or 7 km. We present an outline of the data acquisition and preliminary results of data processing and interpretations in this study. As observed from preliminary results, our imaging are suggested that deformation structure has accompanied past large earthquakes such as the rupture zone of the 1964 Niigata earthquake (MJMA 7.5) and the 2007 Niigata-ken Chuetsu-oki earthquake (MJMA 6.8).

No, T.; Sato, T.; Takahashi, N.; Kodaira, S.; Kaneda, Y.

2011-12-01

196

A Three-Dimensional Seismic Model of the Dead Sea Plate Boundary From Active Source Data  

NASA Astrophysics Data System (ADS)

The Dead Sea fault system is a north-south striking left-lateral shear zone separating the African and Arabian tectonic plates. The southern part of the plate boundary is located within the Dead Sea valley. The valley, much of it below sea level, is surrounded by highlands on both sides, and contains subsurface sedimentary basins, including the large (~150 km long) a deep (6-8 km) Dead Sea basin. A wide-angle seismic reflection and refraction experiment was carried out in the Dead Sea Region in October 2004 to study the deep structure of the plate boundary. The experiment consisted of two perpendicular profiles a 280-km long profile along the valley and the international border between Jordan, Israel and the Palestinian Territories, and a 250 km long profile from Gaza strip to eastern Jordan across the Dead Sea basin. Modeling of the West-East line shows a low velocity zone extending to a depth of 18 km below the basin, which includes >6 km of "syn-rift" sediments (ten Brink et al., GRL, 2006). The lower crust and Moho are not perturbed. The uplift surrounding the Dead Sea Transform also appears to be an upper crustal phenomenon. The shear deformation, associated with the transform plate boundary motion appears, on the other hand, to cut throughout the entire crust (Ibid.). Two-dimensional modeling of the South-North line is more complex due to the fact that sedimentary basins do not occupy the entire width of the valley hence some sources and some receivers are located within the basins whereas others are located outside. This heterogeneous near-surface structure explains why a simple 2-D velocity model does not fit the observed travel times from all shots. Therefore, we are using 3-D travel-time tomography to model the heterogeneous near-surface and deeper structure of the Dead Sea. Preliminary models indicate that some ray-paths from sources near the basin use the edges of the basin as a wave-guide and generate earlier than expected arrivals at receivers near the shot. We find seismic confirmation of sub-basins along the Dead Sea Transform that have been identified using gravity and aeromagnetic surveying (ten Brink, et al., G-cubed, 2007, ten Brink, et al., Geology, 1999), and will present a preliminary model for variations in the crustal structure.

Flores, C. H.; ten Brink, U. S.

2007-12-01

197

16 Years, 16 Cruises, 1.6 Billion Soundings: a Compilation of High-Resolution Multibeam Bathymetry of the Active Plate Boundary Along the Chilean Continental Margin  

NASA Astrophysics Data System (ADS)

Chile, a country stranding the active plate boundary between the South-American and the Nazca Plate is afflicted by recurrent earthquakes and hazardous volcanic eruptions. The strongest earthquake ever recorded occurred here, and volcanic hazards are frequent. Consequently, this area has been studied by geoscientists for many years to improve the understanding of subduction zone processes. Swath bathymetry mapping of the ocean floor has proven to bear a large potential for the interpretation of subduction-related processes, such as tectonic deformation of the marine forearc, release and migration of fluids as well as earthquake-triggered mass wasting. Multibeam bathymetry data of 16 major cruises of German, British, and Chilean research vessels recorded between 1995 and December 2010, in total more than 10,000 data files comprising about 1.6 billion soundings, have now been carefully reprocessed, compiled and merged into a unifying set of high-resolution bathymetric maps of the Chilean continental margin from latitude 40°S to 20°S. The imprint of subsurface processes on the surface morphology is well displayed in the case of the Chilean continental margin. The 3,500 km long Chilean convergent margin is not uniform, as various segments with different tectonic characteristics can be distinguished. Major factors that control margin morphology and thus the style of subduction are (1) relief and structure of the incoming oceanic plate, (2) supply of trench sediment, (3) turbidite transport within the trench, and (4) the input of terrigeneous sediments down the continental slope. A major segment boundary occurs at latitude 32°-33° S where the hotspot-related volcanic chain of Juan Fernandez is presently subducting. South of the area of ridge subduction the trench is filled with turbidites, and accretionary ridges develop across the base of the slope along most of the segment, whereas north of this boundary the turbiditic infill is reduced and subduction erosion is prevailing.

Weinrebe, W.; Flueh, E. R.; Hasert, M.; Behrmann, J. H.; Voelker, D.; Geersen, J.; Ranero, C. R.; Diaz-Naveas, J. L.

2011-12-01

198

Convergence of the 2D Euler- ? to Euler equations in the Dirichlet case: Indifference to boundary layers  

NASA Astrophysics Data System (ADS)

In this article we consider the Euler- ? system as a regularization of the incompressible Euler equations in a smooth, two-dimensional, bounded domain. For the limiting Euler system we consider the usual non-penetration boundary condition, while, for the Euler- ? regularization, we use velocity vanishing at the boundary. We also assume that the initial velocities for the Euler- ? system approximate, in a suitable sense, as the regularization parameter ? ? 0, the initial velocity for the limiting Euler system. For small values of ?, this situation leads to a boundary layer, which is the main concern of this work. Our main result is that, under appropriate regularity assumptions, and despite the presence of this boundary layer, the solutions of the Euler- ? system converge, as ? ? 0, to the corresponding solution of the Euler equations, in L2 in space, uniformly in time. We also present an example involving parallel flows, in order to illustrate the indifference to the boundary layer of the ? ? 0 limit, which underlies our work.

Lopes Filho, Milton C.; Nussenzveig Lopes, Helena J.; Titi, Edriss S.; Zang, Aibin

2015-02-01

199

Experimental investigation on the steady and unsteady disturbances in a flat plate boundary layer  

NASA Astrophysics Data System (ADS)

Recent experiments have shown that miniature vortex generators (MVGs) are coveted devices to stabilize unsteady disturbances in flat plate boundary layers and to delay the onset of turbulence by modulating the base flow in the spanwise direction. The spanwise modulation is a result from the non-modal transient growth of steady and spanwise periodic streamwise vortices being generated by the MVGs. The present experimental investigation aims at studying the transient growth of non-modal disturbances induced by a spanwise periodic array of MVGs and its stabilizing effect on non-linear unsteady disturbances in the boundary layer originating from planar Tollmien-Schlichting (TS) waves. Measurements consist of cross-stream planes at different downstream locations in the boundary layer and a spatio-temporal analysis of different modes of the disturbances is carried out. In the streaky boundary layer generated by the MVGs the fundamental spanwise mode, with the same wavelength as the MVG pairs in the array, and its first harmonic, both undergo transient growth whereas the higher harmonics decay immediately downstream of the array. In the unstable region formed in the wake of the MVG blades, i.e., just downstream of the array, a wide range of spanwise modes contributes to an initial growth in the energy of unsteady disturbances. Similar behavior is observed upstream of branch II position of the neutral stability curve where the unsteady disturbances undergo a second energy growth in the unstable region. It is shown that the spatial gradients of the base flow in the wall-normal and spanwise directions are contributing to the amplification and attenuation of the TS wave disturbances, respectively, in the streaky boundary layer.

Sattarzadeh, Sohrab S.; Fransson, Jens H. M.

2014-12-01

200

Experimental study of boundary layer transition with elevated freestream turbulence on a heated flat plate  

NASA Technical Reports Server (NTRS)

A detailed investigation to document momentum and thermal development of boundary layers undergoing natural transition on a heated flat plate was performed. Experimental results of both overall and conditionally sampled characteristics of laminar, transitional, and low Reynolds number turbulent boundary layers are presented. Measurements were acquired in a low-speed, closed-loop wind tunnel with a freestream velocity of 100 ft/s and zero pressure gradient over a range of freestream turbulence intensities (TI) from 0.4 to 6 percent. The distributions of skin friction, heat transfer rate and Reynolds shear stress were all consistent with previously published data. Reynolds analogy factors for R(sub theta) is less than 2300 were found to be well predicted by laminar and turbulent correlations which accounted for an unheated starting length. The measured laminar value of Reynolds analogy factor was as much as 53 percent higher than the Pr(sup -2/3). A small dependence of turbulent results on TI was observed. Conditional sampling performed in the transitional boundary layer indicated the existence of a near-wall drop in intermittency, pronounced at certain low intermittencies, which is consistent with the cross-sectional shape of turbulent spots observed by others. Non-turbulent intervals were observed to possess large magnitudes of near-wall unsteadiness and turbulent intervals had peak values as much as 50 percent higher than were measured at fully turbulent stations. Non-turbulent and turbulent profiles in transitional boundary layers cannot be simply treated as Blasius and fully turbulent profiles, respectively. The boundary layer spectra indicate predicted selective amplification of T-S waves for TI is approximately 0.4 percent. However, for TI is approximately 0.8 and 1.1 percent, T-S waves are localized very near the wall and do not play a dominant role in transition process.

Sohn, Ki-Hyeon; Reshotko, Eli

1991-01-01

201

Fault Structure Along the North America-Caribbean Plate Boundary in the Dominican Republic  

NASA Astrophysics Data System (ADS)

The Northern Caribbean Plate Boundary Zone is a complex region that has been modified extensively by the relative eastward movement of the Caribbean Plate and the plate's impact with the buoyant Bahama carbonate platform (see Figure). The results include extensive subduction of oceanic crust belonging to the North American Plate, a broad zone of deformation to accommodate strain, the development of several new transform and normal faults to relieve stress after collisions, the formation and rotation of microplates, and the rearrangement and aggregation of crustal fragments into new islands. On 22 September 2003, a large (mW=6.5) earthquake struck the Dominican Republic, causing widespread damage that included partially collapsed buildings and bridges in the cities of Santiago and Puerto Plata and landslides in the mountainous outlying areas. Aftershocks reaching mW=5.1 followed for weeks afterward. This earthquake sequence is the strongest to affect the Dominican Republic since a series of powerful thrust events, including five earthquakes ranging in magnitude from 7.1 to 8.1, occurred between 1943 and 1953. Prior to 1943, significant earthquakes occurred in 1564 (in which the city of Santiago was destroyed), 1783, 1842, 1887, and 1897. Following the 2003 Puerto Plata main shock we deployed 10 broadband seismographs borrowed from IRIS' PASSCAL Instrument Center around the aftershock zone for a period of two months and analyzed the data jointly with data from two permanent seismic networks in the DR. Analyses included estimating a new 1D model of earth structure, re-locating more than 300 aftershocks, producing a 3D tomographic model of the fault zone from phase arrivals, and computing focal mechanisms. We will report the results of these analyses and their implications for regional structure and processes.

Pulliam, J.; Ocasio-Campos, D.; Huerfano-Moreno, V.; von Hillebrandt-Andrade, C.; Camacho, I.; Odonel-Gomez, L.; Payero, J.

2005-12-01

202

Thermochronology and tectonics of the Leeward Antilles: Evolution of the southern Caribbean Plate boundary zone  

USGS Publications Warehouse

Tectonic reconstructions of the Caribbean Plate are severely hampered by a paucity of geochronologic and exhumation constraints from anastomosed basement blocks along its southern margin. New U/Pb, 40Ar/39Ar, apatite fission track, and apatite (U-Th)/He data constrain quantitative thermal and exhumation histories, which have been used to propose a model for the tectonic evolution of the emergent parts of the Bonaire Block and the southern Caribbean Plate boundary zone. An east facing arc system intruded through an oceanic plateau during ~90 to ~87 Ma and crops out on Aruba. Subsequent structural displacements resulted in >80°C of cooling on Aruba during 70–60 Ma. In contrast, exhumation of the island arc sequence exposed on Bonaire occurred at 85–80 Ma and 55–45 Ma. Santonian exhumation on Bonaire occurred immediately subsequent to burial metamorphism and may have been driven by the collision of a west facing island arc with the Caribbean Plate. Island arc rocks intruded oceanic plateau rocks on Gran Roque at ~65 Ma and exhumed rapidly at 55–45 Ma. We attribute Maastrichtian-Danian exhumation on Aruba and early Eocene exhumation on Bonaire and Gran Roque to sequential diachronous accretion of their basement units to the South American Plate. Widespread unconformities indicate late Eocene subaerial exposure. Late Oligocene–early Miocene dextral transtension within the Bonaire Block drove subsidence and burial of crystalline basement rocks of the Leeward Antilles to ?1 km. Late Miocene–recent transpression caused inversion and ?1 km of exhumation, possibly as a result of the northward escape of the Maracaibo Block.

van der Lelij, Roelant; Spikings, Richard A.; Kerr, Andrew C.; Kounov, Alexandre; Cosca, Michael; Chew, David; Villagomez, Diego

2010-01-01

203

Locally similar solutions for hydromagnetic and thermal slip flow boundary layers over a flat plate with variable fluid properties and convective surface boundary condition  

Microsoft Academic Search

This paper presents heat transfer process in a two-dimensional steady hydromagnetic convective flow of an electrically conducting\\u000a fluid over a flat plate with partial slip at the surface of the boundary subjected to the convective surface heat flux at\\u000a the boundary. The analysis accounts for both temperature-dependent viscosity and temperature dependent thermal conductivity.\\u000a The local similarity equations are derived and

M. M. Rahman

204

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

NASA Technical Reports Server (NTRS)

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.

Baltuck, M.; Dixon, T. H.

1984-01-01

205

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

NASA Technical Reports Server (NTRS)

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.

Cook, W. J.

1972-01-01

206

Incorporating rheologic anisotropy in self-consistent models of mantle flow and LPO near plate boundaries  

NASA Astrophysics Data System (ADS)

Flow-induced lattice preferred orientation (LPO) in the upper mantle results in detectable seismic anisotropy, which potentially can be used to map out deformation patterns that would illuminate the interplay between lithosphere, asthenosphere, and melting along plate boundaries. An aspect of mineral texturing that warrants additional study is the rheologic consequences of strong fabric such as can develop due to shear near plate boundaries. Are feedbacks due to enhanced stiffness in local regions sufficient to alter the pattern of mantle flow or melting over 100-km scales? Could ease of slip parallel to a foliation plane develop notable decoupling at the base of the lithosphere? We approach the problem using direct estimates of the local effect of LPO on effective viscosity of a mineral aggregate, which is determined as a tensor that may be anisotropic. This updated viscosity will be employed in subsequent flow and temperature field iterations. Based on our prior experience for flow in the vicinity of an oceanic spreading center, a number of factors can impact the flow solution when anisotropic viscosity is incorporated. Therefore, we carefully tested the effect of several model parameters as we began calculations using the ISAIAH FEM code: boundary conditions, discretization near the base of the lithosphere, viscosities across the lithosphere/asthenosphere boundary, the increment specified for an aggregate to move along its flowpath. Results for these preliminary (isotropic) cases show that robust viscosity tensor calculations can be obtained on meshes where robust flow and temperature fields are solved in a time sufficiently short that the next stage will be computationally viable. The next stage will require tracking aggregates along flowpaths for each iteration, computing the viscosity tensors for the evolved LPO of (Eulerian) model elements, and updating the state variable accordingly. For this presentation, we expect to have results for at least a few intermediate coupling cases, where anisotropic viscosity has been incorporated directly in subsequent ISAIAH flow calculations. These will illustrate the types of impact that LPO-related rheologic anisotropy can have on overall mantle flow pattern and any associated modification to the predicted seismic anisotropy.

Blackman, D. K.; Boyce, D.; Dawson, P.; Castelnau, O.

2013-12-01

207

Singularities of the boundary layer equations and the structure of the flow in the vicinity of the convergence plane on conical bodies  

Microsoft Academic Search

The singularities of the boundary layer equations and the laminar viscous gas flow structure in the vicinity of the convergence\\u000a plane on sharp conical bodies at incidence are analyzed. In the outer part of the boundary layer the singularities are obtained\\u000a in explicit form. It is shown that in the vicinity of a singularity a boundary domain, in which the

V. I. Shalaev

2007-01-01

208

An analytical solution for a multilayered magneto-electro-elastic circular plate under simply supported lateral boundary conditions  

NASA Astrophysics Data System (ADS)

We derive, in this paper, the analytical solution for a three-dimensional transversely isotropic axisymmetric multilayered magneto-electro-elastic (MEE) circular plate under simply supported boundary conditions. The state space vector, the finite Hankel transform and propagating matrix methods are utilized together to obtain the full-field solutions for the MEE plate made of piezoelectric (PE) and piezomagnetic (PM) layers. Numerical examples for three-layered and five-layered PE/PM composites with different stacking sequences and under different loading conditions are presented and discussed. These results can serve as benchmark solutions for future numerical analyses of layered MEE plates.

Wang, R.; Han, Q.; Pan, E.

2010-06-01

209

Instability Investigations in Non-Equilibrium Hypersonic Reacting Flat-Plate Boundary-Layer Flow with DNS  

NASA Astrophysics Data System (ADS)

Non-equilibrium high-speed boundary layers over a flat plate is investigated with Direct Numerical Simulations. A finite difference method of high-order accuracy that has proven its capabilities for laminar-turbulent transition in supersonic boundary-layer flows has been extended for the modeling of thermodynamic coefficients for high- temperature air mixtures as well the handling of the 5 species O, O2 , N, N2 and NO. Vibrational energy is also considered with a separate transport equation. Steady flow calculations show the species distributions and the temperature development in a flat plate boundary layer at a Mach number of 20 at Standard Atmosphere conditions in an altitude of H=50 km. This base flow is then disturbed through period blowing and suction at the wall. The spatial three- imensional disturbance development is presented as well as the species development in the high-speed boundary-layer flow.

Stemmer, C.

2009-01-01

210

The Formation of the Betic-Alboran System in the Iberia-Africa Plate Boundary: a New Kinematic Evolution Model  

NASA Astrophysics Data System (ADS)

Several geodynamic models have been proposed so far to explain the origin and evolution of the Betic-Rif arcuate orogeny and the inner Alboran back-arc basin. Many of these models propose that the Alboran domain underwent a large westward drifting (> 600 km) driven by a subduction rollback, eventually resulting in a symmetric configuration in both the S-Iberia and N-African margins. Alternative models with a more autochthonous component assume that the Oligocene subduction trench extended continuously along the whole Iberian Mediterranean margin from the present Gibraltar arc to the Alps. Common assumptions to all these models are: i) the initial time is about 35 Ma (Eocene-Oligocene), ii) the plate boundary is continuous and non-segmented, iii) the initial subduction polarity is NW-dipping, and iv) the slab must underwent a twisted roll-back to explain the present position of the HP-LT metamorphic rocks involving slab rupture, detachment and tearing. Recent geophysical models based on seismic data, tomography and potential fields draw an arcuate mantle slab restricted below the Betic-Rif orogen, dipping towards the E below the Gibraltar Strait and turning to the SE and S beneath the Betics. In addition, the crust beneath the northern Moroccan margin shows a smooth thinning toward the Alboran basin whereas the southern Iberian margin presents a much sharper thinning. These findings put severe limitations to some of the proposed models and open room for new kinematic proposals. One of the most recent models is based on the following considerations: i) the reconstruction starts in Late Cretaceous times at the onset of northern Africa convergence, ii) displacements and initial configuration are based on plate reconstructions of the Atlantic-Ligurian-Tethys region, and iii) the model assumes that subduction polarity changes laterally from NW-dipping in the Algerian segment to SE-dipping in the Betic-Rif segment. Apart from its simplicity, this model requires a moderate NW to W drifting of the HP-LT metamorphic complexes formed by limited subduction and exhumation, fulfills the imaged crustal and mantle asymmetries, and is compatible with the main geological structures in the region. Cartoon showing the evolution of the Betic-Alboran-Rif system at 9 Ma.

Fernandez, M.; Verges, J.

2013-12-01

211

Plate Tectonics Learning Module  

NSDL National Science Digital Library

This plate tectonics unit was designed to be used with a college course in physical geography. Subject matter covered includes: the development of the theory including Wegener's Continental Drift Hypothesis and the existence of Pangaea, Harry Hess and his work on sea-floor spreading, and the final theory. It points out that global features such as deep oceanic trenches, mid-ocean ridges, volcanic activity, and the location of earthquake epicenters can now be related to the story of plate tectonics, since most geological activity occurs along plate boundaries. Divergent, convergent and transform plate boundaries are discussed in detail. This module contains a study guide and outline notes, study questions, and practice quizzes. One feature of the module is a web exploration section with links to twelve outside sites that augment the instruction.

Haberlin, Rita

212

Present-day kinematics of the plate boundary zone between Africa and Europe, from the Azores to the Aegean  

Microsoft Academic Search

Anticlockwise rotation of Africa relative to Europe around an Euler pole in the eastern Atlantic causes plate convergence in the central Mediterranean towards ~ N20°W at rate considered a priori to be ~ 5-10 mm yr-1. However, previous summaries of the present-day deformation sense in the central Mediterranean are inconsistent with observations in southern Italy. Recent investigations of Italy and

Rob Westaway

1990-01-01

213

Plate Tectonics  

NSDL National Science Digital Library

Students will go over the main points of plate tectonics, including the theory of continental drift, different types of plate boundaries, seafloor spreading, and convection currents. We have been spending time learning about plate tectonics. We have discussed the theory of continental drift, we have talked about the different types of plate boundaries, we have also learned about seafloor spreading and convection currents. Plate Boundary Diagram Now is your chance ...

Rohlfing, Mrs.

2011-02-03

214

Geological and geodynamic investigations of Alaskan tectonics: Responses in the ancient and modern geologic records to oblique plate convergence  

NASA Astrophysics Data System (ADS)

Stratigraphic, structural, and geophysical modeling studies focusing on both the Mesozoic and modern development of southern Alaska aid in understanding the nature of tectonic responses to oblique plate convergence. Analyses of the Lower to Upper (?) Cretaceous Kahiltna assemblage of the western Alaska Range and the Upper Cretaceous Kuskokwim Group of the northern Kuskokwim Mountains provide a stratigraphic record of orogenic growth in southwestern Alaska. The Kahiltna assemblage records dominantly west-directed gravity-flow transport of sediment to the axis of an obliquely closing basin that made up the suture zone between the allochthonous Wrangellia composite terrane and the North American pericratonic margin. Stratigraphic, compositional, and geochronologic analyses suggest that submarine-fan systems of the Kahiltna basin were fed from the subearial suture zone and contain detrital grains derived from both allochthonous and pericratonic sources, thereby implying a relatively close proximity of the island-arc terrane to the North American margin by late Early Cretaceous time. In contrast, Upper Cretaceous strata exposed immediately west of the Kahiltna assemblage record marine deposition during a period of transition from island arc accretion to strike-slip tectonics. The new stratigraphic model presented here recognizes diverse bathyal- to shelfal-marine depositional systems within the Kuskokwim Group that represent distinctive regional sediment entry points to the basin. Collectively, these strata suggest that the Kuskokwim Group represents the waning stages of marine deposition in a long-lived intra-oceanic and continental margin basin. Geodynamic studies focus on the mechanics of contemporary fault systems in southern Alaska inboard of the collisional Yakutat microplate. Finite-element analyses predict that a poorly understood Holocene strike-slip fault in the St. Elias Mountains transfers shear from the Queen Charlotte fault northward to the Denali fault, thereby forming a continuous transform system that accommodates right-lateral motion of the Pacific plate and Yakutat microplate relative to the stable North American craton. Although the best-fit model implies some component of anelastic deformation in the vicinity of the St. Elias Mountains and the western Alaska Range, results imply overall block-like behavior throughout the area of interest.

Kalbas, James L.

215

GEOPHYSICAL RESEARCH LETTERS, VOL. 28, NO. 20, PAGES 4003-4006, OCTOBER 15, 2001 Mantle Control of Plate Boundary Deformation  

E-print Network

of Plate Boundary Deformation Tim Melbourne 1 Don Helmberger 2 Abstract. The seismic wavefield propagating slower uppermost man- tle, with the seismic lithosphere, or lid, measuring less than 5 Km thick]. Unlike teleseismic phases, regional S2 is particularly sen- sitive to lid structure. Propagating along

Miller, M. Meghan

216

MHD mixed convection from a vertical plate embedded in a porous medium with a convective boundary condition  

Microsoft Academic Search

A numerical approach has been used to study the heat and mass transfer from a vertical plate embedded in a porous medium experiencing a first-order chemical reaction and exposed to a transverse magnetic field. Instead of the commonly used conditions of constant surface temperature or constant heat flux, a convective boundary condition is employed which makes this study unique and

O. D. Makinde; A. Aziz

2010-01-01

217

Effect of unsteady wake passing frequency on boundary layer transition on the concave surface of a curved plate  

E-print Network

frequencies. The periodic unsteady flow is generated utilizing an unsteady flow research facility with a rotating cascade of rods positioned upstream of the curved plate. The inlet velocity is measured using a X-wire hot-film probe while the unsteady boundary...

Read, Robert Kevin

2012-06-07

218

Numerical analysis of planar, time-dependent inelastic deformation of plates with cracks by the boundary element method  

SciTech Connect

A boundary element formulation using augmented kernels, for planar time-dependent inelastic deformation problems for bodies with cutouts, has been presented in a companion paper. The primary advantage of this formulation is that the effect of the cutout is incorporated in the kernels and the cutout boundary need not be modelled in a numerical solution procedure. In this paper, the specific kernels for plates with elliptic cutouts are first derived. These kernels are then used to obtain numerical solutions for time-dependent stress fields near stationary crack tips in finite plates. A crack is modelled as a very narrow ellipse and both remote tensile (mode one) and remote shear (mode two) loadings are considered. The deformation of the plate material is assumed to be described either by the equations of power law creep on the combined creep-plasticity constitutive model of Hart.

Morjaria, M.; Mukherjee, S.

1980-02-01

219

Reconstruction convergence and speed enhancement in electrical impedance tomography for domains with known internal boundaries.  

PubMed

An improved approach for electrical impedance tomography (EIT) image reconstruction, based on modifying the forward and inverse solutions, is proposed. In this approach, the EIT forward problem is solved via the finite element method (FEM) using two types of elements. The inverse problem is solved by the modified Newton-Raphson method, whereas the condition number of the Hessian matrix is being monitored. At the early stage of the reconstruction, first-order elements are used, and if the condition number exceeds the allowable limit, the algorithm restarts. Otherwise, if the reconstruction error becomes lower than a predefined threshold, second-order elements are employed in the forward solution in order to preserve the precision of the final results. The latter stage converges in very few iterations. Since the solution speed with the first-order FEM is considerably higher than the second-order FEM, the reconstruction speed improves considerably by this approach, whereas the accuracy of the results is guaranteed by the well-conditioned Hessian matrix. Numerical simulations and experiments are followed by comparisons with other reconstruction methods which demonstrate the reliability and high solution speed of this approach. According to the results, the convergence of the proposed method is significantly improved, and its speed is 2-200 times higher than the previously developed methods with the same level of precision. PMID:20938064

Rezajoo, Saeed; Hossein-Zadeh, Gholam-Ali

2010-11-01

220

North American plate dynamics  

NASA Technical Reports Server (NTRS)

Deformation within the North American plate in response to various tectonic processes is modeled using an elastic finite element analysis. The tectonic processes considered in the modeling include ridge forces associated with the normal thermal evolution of oceanic lithosphere, shear and normal stresses transmitted across transforms, normal stresses transmitted across convergent boundaries, stresses due to horizontal density contrasts within the continent, and shear tractions applied along the base of the plate. Model stresses are calculated with respect to a lithostatic reference stress state. Shear stresses transmitted across transform boundaries along the San Andreas and Caribbean are small, of the order of 5-10 MPa. Also, compressive stresses of the order of 5-10 MPa transmitted across the major transforms improve the fit to the data. Compressive stresses across convergent margins along the Aleutians and the Middle America trench are important.

Richardson, Randall M.; Reding, Lynn M.

1991-01-01

221

The transition from linear to diuse plate boundary in the Azores^Gibraltar region: results from a thin-sheet model  

E-print Network

The transition from linear to di¡use plate boundary in the Azores^Gibraltar region: results from the Azores^Gibraltar region. This plate boundary, which extends from the Azores triple junction The Azores^Gibraltar region contains a major strike^slip structure that extends from the Azores triple

Bird, Peter

222

Propagation of rifting along the Arabia-Somalia Plate Boundary: Into Afar  

NASA Astrophysics Data System (ADS)

It is generally accepted that the Aden ridge has propagated westward from ˜58°E to the western tip of the Gulf of Aden/Tadjoura, at the edge of Afar. Here, we use new tectonic and geochronological data to examine the geometry and kinematics of deformation related to the penetration of that ridge on dry land in the Republic of Djibouti. We show that it veers northward, forming a narrow zone of dense faulting along the northeastern edge of the Afar depression. The zone includes two volcanic rifts (Asal-Ghoubbet and Manda Inakir), connected to one another and to the submarine part of the ridge by transfer zones. Both rifts are composite, divided into two or three disconnected, parallel, NW-SE striking subrifts, all of which appear to have propagated northwestward. In Asal-Ghoubbet as in Manda Inakir, the subrifts appear to have formed in succession, through north directed jumps from subrifts more farther south. At present, the northernmost subrifts (Manda and Dirko Koma) of the Manda Inakir rift, form the current tip of the northward propagating Arabia-Somalia plate boundary in Afar. We account for most observations by a mechanical model similar to that previously inferred for the Gulf of Aden, in which propagation is governed by the intensity and direction of the minimum horizontal principal stress, ?3. We interpret the northward propagation on land, almost orthogonal to that in the gulf, to be related to necking of the Central Afar lithosphere where it is thinnest. Such necking may be a consequence of differential magmatic thickening, greater in the center of the Afar depression where the Ethiopian hot spot enhanced profuse basaltic effusion and underplating than along the edges of the depression. The model explains why the Aden ridge foregoes its WSW propagation direction, constant from ˜58°E to Asal-Ghoubbet. At a smaller scale, individual rifts and subrifts keep opening perpendicular to the Arabia-Somalia (or Danakil-Somalia) motion vector and propagate northwestward. Concurrently, such lithospheric cracks are forced to jump northward, such that the plate boundary remains inside the regional N-S necking zone. Changes of obliquity between the directions of overall and local propagation may account for different segmentation patterns, a small angle promoting long, en échelon subrifts, and a high-angle, smaller, nested, "subrifts within subrifts." The propagation mechanism is thus similar, whether in oceanic or continental lithosphere, the principal change being the overall propagation path, here governed by thickness changes rather than by the geometry in map view as previously inferred for the rest of the Aden ridge. Finally, because the same mechanism has led rifting along the Red Sea to propagate southward and jump to the western edge of Afar, the Arabia-Somalia and Arabia-Nubia plate boundaries tips have missed each other and keep overlapping further, leading to strain transfer by large-scale bookshelf faulting.

Manighetti, I.; Tapponnier, P.; Gillot, P. Y.; Jacques, E.; Courtillot, V.; Armijo, R.; Ruegg, J. C.; King, G.

1998-03-01

223

On the convergence of a finite difference method for a class of singular boundary value problems arising in physiology  

NASA Astrophysics Data System (ADS)

Using Chawla's identity (BIT 29 (1989) 566) a finite difference method based on uniform mesh is described for a class of singular boundary value problems (p(x)y')'=p(x)f(x,y), 0convergence of the method and two physiological problems have also been solved.

Pandey, R. K.; Singh, Arvind K.

2004-04-01

224

Lithospheric evolution of the Pacific-North American Plate Boundary considered in three dimensions  

NASA Astrophysics Data System (ADS)

Tomographic images developed using the combined seismic networks of California and Nevada provide a three-dimensional view into Neogene Pacific-North American plate boundary evolution. Images reveal structures similar in size and spatial distribution to the large-scale structures observed at the surface. A prominent linear anomaly in the mantle is imaged beneath the western foothills to a depth of 70-90 km. Called the Sierran Foothill Anomaly (SFA), this 1-2% high-velocity structure extends the length of the physiographic Sierra Nevada Mountains. Much of the velocity increase is thermal in origin, with a first episode of cooling during the same late-Cretaceous to Paleogene low-angle subduction that affected most of western North America. Post-Laramide resumption of subduction continued chilling the western SFA. Small thrust earthquakes at the contact between the Juan de Fuca slab and the SFA indicate that the contact is still relatively cold to depths approaching 90 km. We propose that this chilled lithospheric section as responsible for the block-like integrity of the core of the Sierra Nevada. The Peninsular Ranges in southern California have also maintained a high degree of integrity, at least until recent times, because they shared a similar batholithic generation and Laramide chilling as the Sierra Nevada. The tomographic image includes other large-scale features. West of the SFA is a low-velocity region interpreted as upwelling mantle filling the window behind the NW-translating Juan de Fuca slab. This low-velocity feature appears to be offset by the San Andreas fault, which would indicate transform relations extend into the mantle. Compression and shortening between the Peninsular Ranges and the Sierra Nevada blocks began when the transform boundary shifted east of the Peninsular Ranges and Baja California around 5.5 Ma. High-velocity structures in the upper mantle developed beneath the Transverse Ranges and the Southern Great Valley (SGV) to accommodate crustal shortening. Alternative explanations for the SGV Anomaly are explored by comparing the volume of proximal sources to the volume of the sinking SGV Anomaly. No local source such as convective overturning of Sierran block eclogitic roots seems adequate to provide the volume needed to explain the anomaly as a purely local feature. Surface and subsurface views of the plate margin are complimentary, but consistent, and each contributes to resolving problems not accessible to the other.

Biasi, Glenn P.

2009-01-01

225

Lithospheric structure beneath the Caribbean- South American plate boundary from S receiver functions  

NASA Astrophysics Data System (ADS)

We have analyzed teleseismic S-wave data recorded by the permanent national seismic network of Venezuela and the BOLIVAR broadband array (Broadband Onshore-offshore Lithospheric Investigation of Venezuela and the Antilles arc Region) deployed from 2003 to 2005. A total of 28 events with Mw > 5.7 occurring at epicentral distances from 55° to 85° were used. We made Sp receiver functions to estimate the rapid variations of lithospheric structure in the southern Caribbean plate boundary region to try to better understand the complicated tectonic history of the region. Estimated Moho depth ranges from ~20 km beneath the Caribbean Large Igneous Provinces to ~50 km beneath the Mérida Andes in western Venezuela and the Sierra del Interior in northeastern Venezuela. These results are consistent with previous receiver functions studies (Niu et al., 2007) and active source profiles (Schmitz et al., 2001; Bezada et al., 2007; Clark et al., 2008; Guedez, 2008; Magnani et al., 2009). Beneath the Maracaibo Block we observe a signal at a depth of 100 km dipping ~24° towards the continent, which we interpret as the top of the oceanic Caribbean slab that is subducting beneath South America from the west. The deeper part of the slab was previously imaged using P-wave tomography (Bezada et al, 2010), and the upper part inferred from intermediate depth seismicity (Malavé and Suarez, 1995). These studies indicate flat slab subduction beneath northern Colombia and northwestern Venezuela with the slab dipping between 20° - 30° beneath Lake Maracaibo. Like others we attribute the flat slab subduction to the uplift of the Mérida Andes (for example Kellogg and Bonini, 1982). In eastern Venezuela beneath the Sierra del Interior we also observe a deep signal that we interpret as deep South American lithosphere that is detaching from the overriding plate as the Atlantic subducts and tears away from SA (Bezada et al., 2010; Clark et al, 2008). The lithosphere-asthenosphere boundary (LAB) is not a continuous feature under the entire region, instead it is seen beneath the Cordillera de la Costa in central Venezuela at ~130 km, also under the Perijá Range and the Sierra del Interior. Under the Guayana Shield we observe two distinct regions with LAB depths at ~150 km depth. We also see the LAB at this depth in places north of the Orinoco River, suggesting the presence of cratonic structures north of the river. These results are in good agreement with the structures observed by Miller et al. (2009) in Rayleigh wave tomography images.

Masy, J.; Levander, A.; Niu, F.

2010-12-01

226

Analysis of and results from the GPS component of the Plate Boundary Observatory  

NASA Astrophysics Data System (ADS)

The first GPS station installed by the Plate Boundary Observatory (PBO) component of the National Science Foundation (NSF) Earthscope program was installed and started operation in January 2004. Since then over 1100 new GPS stations have been installed and combined with over 300 pre-existing GPS stations to form PBO. Analysis of the data from this network is performed daily, with one-day latency, using rapid orbit products from the International GNSS Service (IGS) and weekly, with ~2 week latency, using the final IGS product. A supplemental analysis is also preformed with 12-week latency to add to the final solution data from sites that were not available when the first finals were run. The median weighted root-mean-square (WRMS) scatters of the position results from the combined analyses of these data performed by two different GPS analysis programs, GAMIT at New Mexico Tech and GIPSY at Central Washington University and combined with GLOBK at MIT, are less than 1 mm in North and East (NE) and 3 mm for vertical (U) over monthly durations. The WRMS scatters of the position residuals about linear trends, with offsets for earthquakes and antenna changes removed, from all results processed thus far, ~8 years of data for longest running sites, are ~1.5 mm NE and 4.5 mm U. The top 10% of sites have short period scatters (month duration) of 0.5 mm NE and 1.9 mm U, while the long-term scatters increase to 0.8 mm in NE and 3.3 mm U. The largest RMS sites are generally in volcanic areas and/or affected by snow and ice on the antennas. All of the data from PBO and from an additional 600 GPS sites are being re-processed with data back to 1996 being included in the reprocessing. In this paper, we will present results from this re-processing in terms of secular rates across the Pacific/North America plate boundary and non-secular signals arising from earthquakes (co- and post-seismic deformation) and other natural and human-induced processes.

Herring, T.; King, R. W.; Floyd, M. A.; Murray, M. H.; Melbourne, T. I.; Santillan, V. M.; Mattioli, G. S.; Phillips, D. A.; Puskas, C. M.

2012-12-01

227

Development of an Auto-Convergent Free-Boundary Axisymmetric Equilibrium Solver  

SciTech Connect

The calculation of the magnetic flux given an assumed value for the current profile in axisymmetric toroidal plasmas is essential in studying the effects of various magnetohydrodynamic (MHD) instabilities upon controlled fusion. To this end, an iterative, modular algorithm coupled with a fast, direct elliptic solver for the Grad-Shafranov equation has been used to reconstruct the desired free-boundary equilibrium solution. This free-boundary Grad-Shafranov (FBGS) equilibrium algorithm is modified with the application of the von Hagenow method for determining the flux on the computational boundary, greatly reducing the time cost from O(N3) to O(N2 ln N) machine operations as compared to current Green’s function methods. The inherent variance in implementing the von Hagenow method gives a mean error bound of 0.1 percent with respect to the normal Green’s method. The improvements will allow the grid resolution to be increased efficiently and automatically to reduce the maximum Grad-Shafranov error to values needed for accurate stability calculations on a more effective time scale.

Huang, J.; Menard, J.

2006-01-01

228

Receiver Functions Imaging of the Moho and LAB in the Southern Caribbean plate boundary and Venezuela  

NASA Astrophysics Data System (ADS)

We have made teleseismic Ps and Sp receiver functions from data recorded from 2003 to 2009 by the permanent national seismic network of Venezuela, the BOLIVAR (Broadband Onshore-offshore Lithospheric Investigation of Venezuela and the Antilles arc Region) and WAVE (Western Array for Venezuela) experiments. The receiver functions show rapid variations in Moho and lithosphere-asthenosphere boundary (LAB) depths both across and along the southern Caribbean plate boundary region. We used a total of 69 events with Mw > 6 occurring at epicentral distances from 30° to 90° for the Ps receiver functions, and 43 events with Mw > 5.7 from 55° to 85° to make Sp receiver functions. For CCP stacking we constructed a 3D velocity model from numerous active source profiles (Schmitz et al., 2001; Bezada et al., 2007; Clark et al., 2008; Guedez, 2008; Magnani et al., 2009), from finite-frequency P wave upper mantle tomography model of Bezada et al., (2010) and the Rayleigh wave tomography model of Miller et al., (2009). The Moho ranges in depth from ~25 km beneath the Caribbean Large Igneous Provinces to ~55 km beneath the Mérida Andes in western Venezuela. These results are consistent with previous receiver functions studies (Niu et al., 2007) and the available active source profiles. Beneath the Maracaibo Block in northwestern Venezuela, we observe a strong positive signal at 40 to 60 km depth dipping ~6° towards the continent. We interpret this as the Moho of the Caribbean slab subducting beneath northernmost South America from the west. Beneath northern Colombia and northwestern Venezuela the top of this slab has been previously inferred from intermediate depth seismicity (Malavé and Suarez, 1995), which indicates a slab dipping between 20° - 30° beneath Lake Maracaibo. Our results could indicate that the slab is tearing beneath Lake Maracaibo as suggested previously by Masy et al. (2011). The deeper (> 100 km depth) part of the slab has been imaged using P-wave tomography (Bezada et al, 2010). Like others we attribute the uplift of the Mérida Andes to flat Caribbean slab subduction (for example Kellogg and Bonini, 1982). In central Venezuela beneath the Cordillera de la Costa we observe a positive signal shallower than the Moho at <30 km depth beneath the entire range. We interpret this as a detachment surface beneath Caribbean & arc terranes thrust onto the SA margin (Bezada et al., 2010). The lithosphere-asthenosphere boundary (LAB) beneath the Mérida Andes is shallow, ~65km depth, and parallels the range. In the plate boundary region under the Cordillera de la Costa the lithosphere is also thin, ~65km, beneath the Cariaco basin the lithosphere thickens to 85 km. In the far east under Serranía del Interior the lithosphere is ~75 km. Cratonic lithosphere thickness varies from 85 to 100 km.

Masy, J.; Levander, A.; Niu, F.

2011-12-01

229

The interpretation of crustal dynamics data in terms of plate motions and regional deformation near plate boundaries  

NASA Technical Reports Server (NTRS)

The nature and dynamics of time-dependent deformation along major seismic zones including the influence of irregularities in fault geometry on the earthquake cycle, and the processes contributing to the state of stress and rates of strain in plate interior regions were studied. The principle findings of the research are discussed.

Solomon, Sean C.

1987-01-01

230

Linear stability analysis in compressible, flat-plate boundary-layers  

NASA Astrophysics Data System (ADS)

The stability problem of two-dimensional compressible flat-plate boundary layers is handled using the linear stability theory. The stability equations obtained from three-dimensional compressible Navier-Stokes equations are solved simultaneously with two-dimensional mean flow equations, using an efficient shoot-search technique for adiabatic wall condition. In the analysis, a wide range of Mach numbers extending well into the hypersonic range are considered for the mean flow, whereas both two- and three-dimensional disturbances are taken into account for the perturbation flow. All fluid properties, including the Prandtl number, are taken as temperature-dependent. The results of the analysis ascertain the presence of the second mode of instability (Mack mode), in addition to the first mode related to the Tollmien-Schlichting mode present in incompressible flows. The effect of reference temperature on stability characteristics is also studied. The results of the analysis reveal that the stability characteristics remain almost unchanged for the most unstable wave direction for Mach numbers above 4.0. The obtained results are compared with existing numerical and experimental data in the literature, yielding encouraging agreement both qualitatively and quantitatively.

Özgen, Serkan; K?rcal?, Senem Atalayer

2008-01-01

231

The EarthScope Plate Boundary Observatory: Bringing Low Latency Data From Unimak Island, Alaska  

NASA Astrophysics Data System (ADS)

The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, will complete the installation of a fourteen station GPS network on Unimak Island, Alaska in August, 2008. The primary data communications goal of the project is to design and implement a robust data communications network capable of downloading 15-sec daily GPS files and streaming 1 Hz GPS data, via Ustream, from Unimak Island to three data relay points in the Aleutian chain. As part of the permitting agreement with the landowner, PBO will co-locate the GPS stations with existing USGS seismic stations. The technical challenges involved in optimizing the data communications network for both the GPS data and the seismic data will be presented. From Unimak island, there will be three separate data telemetry paths: 1) West through a radio repeater on Akutan volcano to a VSAT in Akutan village, 2) East through a radio repeater to a T1 connection in Cold Bay, AK, 3) South through a radio repeater to a VSAT at an existing PBO GPS station in King Cove, AK. The difficulties involved in the project include complex network geometries with multiple radio repeaters, long distance RF transmission over water, hardware bandwidth limitations, power limitations, space limitations, as well as working in bear country on an incredibly remote and active volcano.

Feaux, K.; Mencin, D.; Jackson, M.; Gallaher, W.; Pauk, B.; Smith, S.

2008-05-01

232

Hairpin vortices in the transitional and developed turbulence of a flat-plate boundary layer*  

NASA Astrophysics Data System (ADS)

The use of vortex lines to reveal vortical structures in turbulent shear flows has been in disfavor for some time, in spite of their successful use by Kim and Moin (1986, JFM 162) and Rogers and Moin (1987, JFM 176). This is because they are field lines that can be drawn wherever the flow is rotational, regardless of whether a true vortex exists in a part of the field or not. For this reason, it would be better to call them vorticity lines rather than vortex lines. A virtue that such lines have, however, is that the vortical structures they can reveal do not depend on setting a detection threshold, unlike all the vortex identifiers based on the velocity gradient tensor or based on a low pressure criterion. Furthermore, vorticity lines can be used to isolate a single vortical structure. We will show that individual hairpin vortices can be identified using vorticity lines in the transition region at Re?= 500, where turbulent spots merge, and in the developed turbulence at Re?= 1850 within a recent DNS of a flat-plate boundary layer, and that the vortices so identified have quite similar characteristics. These vortices emerge out of sheets of unorganized vorticity in the viscous sublayer. An attempt will be made to follow the temporal and spatial evolution of these vortical structures using simulation files closely separated in time. *CTR 2010 Summer Program research.

Wallace, J.; Wu, X.; Park, I.; Moin, P.

2010-11-01

233

PBO H2O: Plate Boundary Observatory Studies of the Water Cycle  

NASA Astrophysics Data System (ADS)

The EarthScope Plate Boundary Observatory was built to measure the deformation of the North American continent. PBO stations can also be used to measure ground displacements at much higher frequencies (5-Hz) for studies of fault slip during large earthquakes and for warnings of volcanic eruptions. There is also a long history of using atmospheric delays on the GPS signals to estimate precipitable water vapor (for weather and climate studies) and total electron content (space weather studies). Recently the PBO H2O research group has demonstrated that GPS signals that reflect from the nearby environment can be used for water cycle research. These GPS reflections measure how much water is in the top layer of the soil, how much snow is on its surface, and water content of nearby vegetation. Observing and monitoring spatial and temporal changes in the water cycle is critical for both understanding and predicting Earth's climate. Since GPS reflections encompass an area of ~1000 m^2, they provide a spatial footprint that complements satellite systems which sense much larger areas and in situ systems that sense regions < 1 m^2. Water cycle products are produced from PBO data each day and updated on the PBO H2O website.

Larson, K. M.; Small, E. E.; Chew, C. C.; Nievinski, F. G.; Pratt, J.; McCreight, J. L.; Braun, J.; Boniface, K.; Evans, S. G.

2013-12-01

234

Great earthquakes, seismicity gaps and potential for earthquake disaster along the Himalaya plate boundary  

NASA Astrophysics Data System (ADS)

Analysis of the space-time patterns of seismicity in the Himalaya plate boundary has established the existence of three seismic gaps: (1) The "Kashmir gap" lying west of the 1905 Kangra earthquake; (2) the "Central gap", situated between the 1905 Kangra and the 1934 Bihar earthquakes; (3) the "Assam gap" between the 1897 and 1950 Assam earthquakes. This study has shown that the above great earthquakes were preceded as well as followed by long periods (? 19 years) of decreased levels of seismic activity in the epicentral regions. Remarkable decrease in the seismicity following the year 1970 has been observed in the western half of the Central gap as well as in the Assam gap. Local seismic investigation in the Assam gap confirms this feature and the seismicity suggests the existence there of an asperity. The local seismic investigations in Garhwal Himalaya have shown that the small earthquakes are confined to the upper 6-8 km of the crust and may have strike-slip motions. These earthquakes occur in a region where teleseismically recorded events were few.

Khattri, K. N.

1987-06-01

235

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)

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.

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

1993-01-01

236

Nature and distribution of geological domains at the Africa-Eurasia plate boundary off SW Iberia and regional geodynamic implications  

NASA Astrophysics Data System (ADS)

We present a new classification of geological domains at the Africa-Eurasia plate boundary off SW Iberia, together with a regional geodynamic reconstruction spanning from the Mesozoic extension to the Neogene-to-present-day convergence. It is based on seismic velocity and density models along two regional wide-angle seismic transects, one running NW-SE from the Horseshoe to the Seine abyssal plains, and the other running N-S from S Portugal to the Seine Abyssal Plain, combined with previously available information. The seismic velocity and density structure at the Seine Abyssal Plain and the internal Gulf of Cadiz indicates the presence of a highly heterogeneous oceanic crust, similar to that described in ultra-slow spreading centers, whereas in the Horseshoe and Tagus abyssal plains, the basement structure resembles that of exhumed mantle sections identified in the Northern Atlantic margin. The integration of all this new information allows defining the presence of three oceanic domains offshore SW Iberia: (1) the Seine Abyssal Plain domain, generated during the first stages of slow seafloor spreading in the NE Central Atlantic (Early Jurassic); (2) the Gulf of Cadiz domain, made of oceanic crust generated in the Alpine-Tethys spreading system between Iberia and Africa, which was coeval with the formation of the Seine Abyssal Plain domain and lasted up to the North Atlantic continental break-up (Late Jurassic); and (3) the Gorringe Bank domain, mainly made of rocks exhumed from the mantle with little synchronous magmatism, which formed during the first stages of North Atlantic opening. Our models suggest that the Seine Abyssal Plain and Gulf of Cadiz domains are separated by the Lineament South strike-slip fault, whereas the Gulf of Cadiz and Gorringe Bank domains appear to be limited by a deep thrust fault located at the center of the Horseshoe Abyssal Plain. The formation and evolution of these three domains during the Mesozoic is key to understand the sequence of events that occurred during the first stages of opening of the Northern Atlantic.

Martínez-Loriente, Sara; Sallarès, Valentí; Gràcia, Eulàlia; Bartolome, Rafael

2014-05-01

237

Implementation of a python version of a scaled boundary finite element method for plate bending analysis  

E-print Network

Common finite element programs for plate bending analysis are complicated and limited by the common plate theories. Such programs are usually not user-friendly for designers to implement. Lately, Hou Man et al. from the ...

Chen, Lingfeng, M. Eng. Massachusetts Institute of Technology

2014-01-01

238

Wide-angle velocity modeling and receiver functions imaging a lithospheric shear tear in the southeast Caribbean-South America plate boundary  

NASA Astrophysics Data System (ADS)

Two models for slab detachment have been proposed for the lithospheric structure of the northern South America plate boundary with the southeast Caribbean, where westward subduction of oceanic South America transitions to east-west transform between continental South America and the Caribbean plate. In the tensile tear model, oblique convergence causes northwest-dipping subduction, and tension on the subducting slab results in detachment orthogonal to the motion vectors. Conversely, the shear tear model predicts detachment parallel to the motion vectors along a vertical plane, with shear stress focused on the edge of the propagating transform boundary. We present new active-source onshore-offshore wide-angle tomography, integrated with new passive-source receiver function analysis, from profile 64W of the BOLIVAR (Broadband Ocean-Land Investigation of Venezuela and the Antilles arc Region) project. Profile 64W is a 460 km-long, north-south, onshore-offshore reflection/refraction/teleseismic transect located approximately at 64 deg W longitude that extends from the southeastern Caribbean across the Serrania del Interior and into the Maturin basin. The various datasets image deep crustal and upper mantle structure across the entire diffuse plate boundary zone. The active-source components of profile 64W include 33 OBSs and 344 land seismic stations which recorded 7500 offshore airgun shots and 2 chemical explosive land shots. Receiver functions along 64W were picked from hundreds of events at 18 temporary and permanent broadband stations. Close agreement exists between the wide-angle inversion of first arrivals, PmP, and Pn, and receiver function analysis for the Moho conversion, indicating that the Moho deepens northward from 35 km beneath the Guiana shield craton (from receiver functions only) to 45 km beneath the Serrania del Interior; to the north, Moho abruptly shoals to a depth of 25 km. We interpret this step change in Moho depth to be the lower crustal plate boundary between the Caribbean and South America, and coincident with a shear tear through the South American lithosphere. North of the step, Moho depth increases slightly to 28 km beneath Margarita Island, then gradually shallows to 20 km and flattens north of La Blanquilla Island. Thrust faults beneath La Blanquilla and the Serrania del Interior bound the 250 km-wide diffuse plate boundary, the former marking Caribbean underthrusting beneath the remnant arc, the latter marking the frontal thrust of the fold and thrust belt. We hypothesize that isostatic rebound following slab detachment may contribute significantly to the uplift of the Serrania del Interior, which reaches 2500 m elevation, and infer a role in the exhumation of HP/LT metamorphic rocks found along the strike- slip system. We conclude that the Serrania del Interior and Maturin basin do not represent a collisional orogeny and foreland basin, respectively, but are instead resultant from the geodynamic response to the propagating lithospheric shear tear.

Clark, S. A.; Levander, A.; Zelt, C. A.; Niu, F.; Sobiesiak, M.

2007-05-01

239

The interpretation of crustal dynamics data in terms of plate motions and regional deformation near plate boundaries  

NASA Technical Reports Server (NTRS)

The focus of the research was in two broad areas during the most recent 6 month period: the nature and dynamics of time-dependent deformation along major seismic zones, including the influence of irregularities in fault geometry on the earthquake cycles, and the processes contributing to the state of stress and rates of strain in plate interior regions. The principal findings of the research to date are described.

Solomon, Sean C.

1987-01-01

240

Front Cover. (Upper) Perspective view of the Juan de Fuca plate showing plate boundaries and the convergence between the Juan de Fuca and North American plates  

E-print Network

and melting associated with an oceanic spreading center and a subduction zone Northwest 11 Seafloor Geodetic Techniques 12 Seafloor Observatories 15 and hazard of the Cascadia subduction zone. Seafloor geodetic measurements

Wilcock, William

241

Scalar boundary value problems on junctions of thin rods and plates. I. Asymptotic analysis and error estimates  

E-print Network

We derive asymptotic formulas for the solutions of the mixed boundary value problem for the Poisson equation on the union of a thin cylindrical plate and several thin cylindrical rods. One of the ends of each rod is set into a hole in the plate and the other one is supplied with the Dirichlet condition. The Neumann conditions are imposed on the whole remaining part of the boundary. Elements of the junction are assumed to have contrasting properties so that the small parameter, i.e. the relative thickness, appears in the differential equation, too, while the asymptotic structures crucially depend on the contrastness ratio. Asymptotic error estimates are derived in anisotropic weighted Sobolev norms.

R. Bunoiu; G. Cardone; S. A. Nazarov

2014-03-24

242

Large Eddy Simulation of Flow Transition in a Compressible Flat-Plate Boundary Layer at Mach 4.5  

Microsoft Academic Search

Large eddy simulation (LES) has been carried out to investigate the oblique transition process of a flat-plate boundary layer at a free-stream Mach number of M? = 4.5 and a Reynolds number of 10,000 based on the free-stream velocity and inflow displacement thickness. The numerical simulation is performed using a spatial approach to solve a full compressible Navier-Stokes system in

H. Shan; L. Jiang; C. Liu

1999-01-01

243

The effect of periodic unsteady wakes on boundary layer transition and heat transfer on a curved plate  

E-print Network

-wire probes used for data acquisition are laterally traversed using a computer controlled traversing system as shown in Fig 5. The system is mounted vertically on the base plate of the convex wall and uses a linear lead screw to drive an aluminum slider... in this research project. Ilis sound judgement, drive, and commitment to turbomachinery performance research has resulted in an established boundary layer research program. Kevin Read deserves thanks for designing and overseeing the construction of the heat...

Wright, Lance Cole

2012-06-07

244

The EarthScope Plate Boundary Observatory (PBO) Facility: Innovations, Transformations, and Impact  

NASA Astrophysics Data System (ADS)

The word 'transformation' is not used lightly in science. However, the transformative nature of the EarthScope Plate Boundary Observatory facility on the science community is large and measurable. The impact of the creation, execution and delivery of the PBO resulted in radical changes in the way the geodesy community views permanent, continuously operating (and often) real-time GPS and strain networks, open data policies, and the ability for consortium based facilities, such as UNAVCO, to manage and deliver on large National Science Foundation investments. Our presentation will explore these innovations and transformations from the community, facility, and science perspectives. In the genesis of the EarthScope proposal there was a distinct shift away from the PBO being managed and constructed by prominent PI's within the community to a vesting of the responsibility and authority in UNAVCO to execute on behalf of the entire community. This tipping away from individual PI concerns towards a communal behavior allowed the construction of a facility based on broad input from, and equal access for, any member of the geodesy community. The open and transparent nature of EarthScope, including the open data policy for both facility and PI derived data was truly transformative. One of the key tenants of the PBO was strict adherence to not redesigning unless absolutely necessary. For example PBO monumentation and data processing practices were adopted wholesale from the SCIGN project, while the station selection, project management, permitting practices, data downloading, metadata, and, data communications were refactored for optimum use for the broader geodesy community and to scale with the large geography that confronted PBO. The PBO strainmeter network, one of the largest in the world, started by looking at the procedures of 30 years of heterogeneous installations around the word then crafted, created, and amalgamated new drilling, grouting, installation, and data processing procedures that allowed the project to deal with a compressed installation time line and the varying climactic and geological terrains in the Western US. The science that has come from the PBO deployments includes not only estimates of the secular deformation field across important structures in the active Western US but has provided a full kinematic and dynamic picture of the Pacific and North American Plate boundary interaction. The data registered from the PBO network has been used in diverse studies including determination of the asthenospheric density, temperature, and elastic moduli beneath the Western US (Ito and Simons, 2011), snow depth sensing using GPS multipath (Larson and Nievinski, 2013), continuous monitoring of the horizontal displacement gradient tensor field in Southern California (Holt and Shcherbenko, 2013), and using strainmeter data to constrain the magma reservoir beneath the Yellowstone (Luttrell, 2013). There is little doubt that the EarthScope PBO has met and exceeded its science goals, however what is exciting and transformative is the science that has resulted from the signals and the noise found in between these broad science goals.

Jackson, M. E.; Mencin, D.; Feaux, K.

2013-12-01

245

Breaking into the Plate: Seismic and Hydroacoustic Analysis of a 7.6 Mw Oceanic Fracture Zone Earthquake Adjacent to the Central Indian Ridge Plate Boundary  

NASA Astrophysics Data System (ADS)

Where oceanic spreading segments are offset laterally from one another, the differential motion of the plates is accommodated by strike-slip motion along ridge-perpendicular transform faults. Off-axis from the ridge-transform intersection, no differential motion is require, and the fracture zone trace is thought to be inactive except where reactivated by intra-plate stresses. On 15 July 2003, an earthquake with a magnitude of 7.6 Mw occurred near the northern Central Indian Ridge (CIR), the divergent boundary separating the Somalian plate from the Indian and Australian plates. The size of this event places it within the 99th quantile of magnitude for shallow (< 40 km depth) strike-slip events (null axis plunge >45 deg) within the global Harvard CMT catalog. The earthquake's epicenter is near 2.5 deg S, 68.33 deg E, where the CIR is marked by a series of short (<100 km long) right-stepping transforms that offset the northwest trending spreading segments (20 mm/yr). Seismic signals associated with the mainshock and its largest aftershocks were recorded well by land-based seismic networks. Regional seismic phases (Pn, Sn), as well oceanic T-waves, where also recorded at an IMS hydroacoustic station to the north of the Diego Garcia atoll. T-wave signals recorded at Diego Garcia were cross correlated to determine accurate travel time differences. These traveltime differences were used in a plane wave fitting inversion to determine the horizontal slowness components and estimate the back azimuth to the epicenter. Aftershock locations are derived using the azimuthal information and Pn-T traveltime differences. Together, the seismically- and hydroacoustically-derived epicenters show a linear band of aftershocks extending more than 200 km along the off-axis trace of a right stepping transform. We interpret these aftershock events as delineating the length of the mainshock rupture. As the well-constrain hypocenter of the mainshock lies near the western edge of this aftershock zone and the centroid location lies within its eastern portion, the rupture appears to have propagated from the plate boundary, breaking into the Indian plate along the fracture zone. The moment tensor solution for the mainshock event indicates dominantly right-lateral slip with a near vertical nodal plane striking parallel to the trend of the aftershocks. The right-lateral sense of slip opposes the left-lateral slip along the adjacent active transform and is consistent with reactivation due to north-south extension in association with a diffuse plate boundary that separates the Indian and Australian Plates. Coulomb failure modeling indicates that the right-lateral mainshock should promote left-lateral slip on the active portions of neighboring transforms. Consistent with this prediction, the largest aftershock, a 5.6 Mw left-lateral earthquake, is located on the active portion of a transform approximately 150 km northwest of the mainshock rupture. These models also show that left-lateral slip on the adjacent active transform, extending southwest from mainshock rupture, should be inhibited. No aftershock activity is observed along this active transform. Static stress changes will tend to reduce ridge-normal compressive stresses along the portion of the CIR axis to the north of the mainshock, with an increase in ridge-normal compression to the south. This will promote and impede axis-parallel diking events within these respective regions.

Bohnenstiehl, D. R.; Tolstoy, M.; Chapp, E.

2003-12-01

246

A 3-D lithospheric model of the Caribbean-South American plate boundary  

NASA Astrophysics Data System (ADS)

A 3-D structural model of the Caribbean-South American plate boundary was constructed by gravity modeling. The model was constrained by four wide-angle seismic refraction sections, Moho depth estimations from receiver functions, and additionally seismological hypocenters, surface geology, and geodynamic information. Density values were calculated from empirical velocity-density functions, and mineralogical-chemical composition considering specific P/T conditions. We tested different structural models for Western and Eastern Venezuela. In the final model, the fit of the measured and modeled gravity fields for a long Caribbean slab in Western Venezuela was better than the fit obtained for a short one. This interpretation is consistent with the constraining data. The slab is interpreted to extend further to the south beneath Northern Colombia and culminates in the area of the seismic cluster of the Bucaramanga nest. The modeling estimates a slab dip angle under Maracaibo and Mérida Andes of 15°, which increases to 32° below 100 km depth. The dip direction of approx. N150°E ± 5 increases lightly eastward. In Eastern Venezuela, considering its short wavelength, lineaments analyzed from gravity data (by curvature methods and Euler deconvolution) seem to be related to shallow structures and density contrast in the Serranía del Interior and not from a deep detached slab beneath the continental crust. It is deduced from modeling results that this slab configuration has a very small influence on the gravity field. The slab was modeled according to the subduction-transform propagation model with purely westward subduction and a slab break off along a vertical dip-slip tear through the lithosphere.

Sanchez, Javier; Götze, Hans-Jürgen; Schmitz, Michael

2011-10-01

247

Receptivity of Flat-Plate Boundary Layer in a Non-Uniform Free Stream (Vorticity Normal to the Plate)  

NASA Technical Reports Server (NTRS)

Experimental and theoretical studies of low speed leading edge boundary layer receptivity to free-stream vorticity produced by upstream wires normal to the leading edge are discussed. Data include parametric variations in leading edge configuration and details of the incident disturbance field including single and multiple wakes. The induced disturbance amplitude increases with increases in the leading edge diameter and wake interactions. Measurements agree with the theory of M. E. Goldstein.

Kogan, M. N.; Shumilkin, V. G.; Ustinov, M. V.; Zhigulev, S. V.

1999-01-01

248

The interpretation of crustal dynamics data in terms of plate motions and regional deformation near plate boundaries  

NASA Technical Reports Server (NTRS)

During our participation in the NASA Crustal Dynamics Project under NASA contract NAS-27339 and grant NAG5-814 for the period 1982-1991, we published or submitted for publication 30 research papers and 52 abstracts of presentations at scientific meetings. In addition, five M.I.T. Ph.D. students (Eric Bergman, Steven Bratt, Dan Davis, Jeanne Sauber, Anne Sheehan) were supported wholly or in part by this project during their thesis research. Highlights of our research progress during this period include the following: application of geodetic data to determine rates of strain in the Mojave block and in central California and to clarify the relation of such strain to the San Andreas fault and Pacific-North American plate motions; application of geodetic data to infer post seismic deformation associated with large earthquakes in the Imperial Valley, Hebgen Lake, Argentina, and Chile; determination of the state of stress in oceanic lithosphere from a systematic study of the centroid depths and source mechanisms of oceanic intraplate earthquakes; development of models for the state of stress in young oceanic regions arising from the differential cooling of the lithosphere; determination of the depth extent and rupture characteristics of oceanic transform earthquakes; improved determination of earthquake slip vectors in the Gulf of California, an important data set for the estimation of Pacific-North American plate motions; development of models for the state of stress and mechanics of fold-and-thrust belts and accretionary wedges; development of procedures to invert geoid height, residual bathymetry, and differential body wave travel time residuals for lateral variations in the characteristic temperature and bulk composition of the oceanic upper mantle; and initial GPS measurements of crustal deformation associated with the Imperial-Cerro Prieto fault system in southern California and northern Mexico. Full descriptions of the research conducted on these topics may be found in the Semi-Annual status Reports submitted regularly to NASA over the course of this project and in the publications listed.

Solomon, Sean C.

1991-01-01

249

Plate Tectonics: Plate Interactions  

NSDL National Science Digital Library

This Science Object is the fourth of five Science Objects in the Plate Tectonic SciPack. It identifies the events that may occur and landscapes that form as a result of different plate interactions. The areas along plate margins are active. Plates pushing against one another can cause earthquakes, volcanoes, mountain formation, and very deep ocean trenches. Plates pulling apart from one another can cause smaller earthquakes, magma rising to the surface, volcanoes, and oceanic valleys and mountains from sea-floor spreading. Plates sliding past one another can cause earthquakes and rock deformation. Learning Outcomes:? Explain why volcanoes and earthquakes occur along plate boundaries. ? Explain how new sea floor is created and destroyed.? Describe features that may be seen on the surface as a result of plate interactions.

National Science Teachers Association (NSTA)

2006-11-01

250

The turbulent boundary layer on a porous plate: An experimental study of the heat transfer behavior with adverse pressure gradients  

NASA Technical Reports Server (NTRS)

An experimental investigation of the heat transfer behavior of the near equilibrium transpired turbulent boundary layer with adverse pressure gradient has been carried out. Stanton numbers were measured by an energy balance on electrically heated plates that form the bottom wall of the wind tunnel. Two adverse pressure gradients were studied. Two types of transpiration boundary conditions were investigated. The concept of an equilibrium thermal boundary layer was introduced. It was found that Stanton number as a function of enthalpy thickness Reynolds number is essentially unaffected by adverse pressure gradient with no transpiration. Shear stress, heat flux, and turbulent Prandtl number profiles were computed from mean temperature and velocity profiles. It was concluded that the turbulent Prandtl number is greater than unity in near the wall and decreases continuously to approximately 0.5 at the free stream.

Blackwell, B. F.; Kays, W. M.; Moffat, R. J.

1972-01-01

251

Shape sensitivity analysis of the energy integrals for the Timoshenko-type plate containing a crack on the boundary of a rigid inclusion  

NASA Astrophysics Data System (ADS)

An equilibrium problem for an elastic Timoshenko-type plate containing a rigid inclusion is considered. On the interface between the elastic plate and the rigid inclusion, there is a vertical crack. Inequality-type boundary conditions are imposed at the crack faces to guarantee mutual nonpenetration. By using a sufficiently smooth perturbation determined in the middle plate plane, the variation of plate geometry is specified. The formula of the derivative of the plate energy functional with respect to the perturbation parameter is deduced.

Lazarev, N.

2015-01-01

252

Upper mantle structure beneath the Caribbean-South American plate boundary from surface wave tomography  

E-print Network

-slip fault system along the northern coast of Venezuela, illustrating the differences between the South beneath the South American plate. In eastern Venezuela, linear crustal low velocities are associated the buoyant continental South American plate offshore of northeastern Venezuela. The continental lithosphere

Niu, Fenglin

253

Active Pacific North America Plate boundary tectonics as evidenced by seismicity in the oceanic lithosphere offshore Baja California, Mexico  

NASA Astrophysics Data System (ADS)

Pacific Ocean crust west of southwest North America was formed by Cenozoic seafloor spreading between the large Pacific Plate and smaller microplates. The eastern limit of this seafloor, the continent-ocean boundary, is the fossil trench along which the microplates subducted and were mostly destroyed in Miocene time. The Pacific-North America Plate boundary motion today is concentrated on continental fault systems well to the east, and this region of oceanic crust is generally thought to be within the rigid Pacific Plate. Yet, the 2012 December 14 Mw 6.3 earthquake that occurred about 275 km west of Ensenada, Baja California, Mexico, is evidence for continued tectonism in this oceanic part of the Pacific Plate. The preferred main shock centroid depth of 20 km was located close to the bottom of the seismogenic thickness of the young oceanic lithosphere. The focal mechanism, derived from both teleseismic P-wave inversion and W-phase analysis of the main shock waveforms, and the 12 aftershocks of M ˜3-4 are consistent with normal faulting on northeast striking nodal planes, which align with surface mapped extensional tectonic trends such as volcanic features in the region. Previous Global Positioning System (GPS) measurements on offshore islands in the California Continental Borderland had detected some distributed Pacific and North America relative plate motion strain that could extend into the epicentral region. The release of this lithospheric strain along existing zones of weakness is a more likely cause of this seismicity than current thermal contraction of the oceanic lithosphere or volcanism. The main shock caused weak to moderate ground shaking in the coastal zones of southern California, USA, and Baja California, Mexico, but the tsunami was negligible.

Hauksson, Egill; Kanamori, Hiroo; Stock, Joann; Cormier, Marie-Helene; Legg, Mark

2014-03-01

254

Estimating Fault Slip Rates and Deformation at Complex Strike-Slip Plate Boundaries  

NASA Astrophysics Data System (ADS)

Modeling GPS velocity fields in seismically active regions worldwide indicates deformation can be efficiently and usefully described as relative motions among elastic, fault-bounded crustal blocks. These models are providing hundreds of new decadal fault slip rate estimates that can be compared with the (much smaller) independent Holocene (<10 ka) to late Quaternary (<125 ka) rates obtained by geological methods. Updated comparisons show general agreement but a subset of apparently significant outliers. Some of these outliers have been discussed previously and attributed either to a temporal change in slip rate or systematic error in one of the estimates. Here we focus particularly on recent GPS and geologic results from southern California and discuss criteria for assessing the differing rates. In southern California (and elsewhere), subjective choices of block geometry are unavoidable and introduce significant uncertainties in model formulation and in the resultant GPS fault slip rate estimates. To facilitate comparison between GPS and geologic results in southern California we use the SCEC Community Fault Model (CFM) and geologic slip rates tabulated in the 2008 Uniform California Earthquake Rupture Forecast (UCERF2) report as starting points for identifying the most important faults and specifying the block geometry. We then apply this geometry in an inversion of the SCEC Crustal Motion Model (CMM4) GPS velocity field to estimate block motions and intra-block fault slip rates and compare our results with previous work. Here we use 4 criteria to evaluate GPS/geologic slip rate differences. First: Is there even-handed evaluation of random and systematic errors? ‘Random error' is sometimes subjectively estimated and its statistical properties are unknown or idealized. Differences between ~equally likely block models introduces a systematic error into GPS rate estimates that is difficult to assess and seldom discussed. Difficulties in constraining the true initiation date of offset of geomorphic markers by faulting can introduce uncertainties much larger than quoted random errors. Second: Are rate estimates obtained by more than one geodetic or geologic method? For example, agreement between GPS and InSAR slip rate estimates on the Altyn Tagh and Haiyuan faults of Tibet make the geodetic estimates more reliable. Similarly, dating of multiple offset markers of differing age across these faults supports the consistency of the geologic rate estimates. Third: Is proposed rate change mechanism consistent with examples of changes in style and rate of deformation preserved in the geologic record? For example, temporal evolution of the multi-stranded San Andreas system during the past 5-10 Ma (Powell & Weldon 1992; Graymer et al. 2002) indicates activation and deactivation of different faults within the system accompanied by consequent changes in fault slip rate and/or creation of new crustal blocks. Fourth: Is there a quantitative analysis of mechanism proposed to explain rate change? Candidate mechanisms meriting quantitative analysis include (1) changes in frictional resistance of faults and creation of new fractures due to progressive rotation of irregularly shaped blocks, (2) episodic subduction of buoyant lithosphere, and (3) changes in the plate geometry (and so the forces acting) at major continent/ocean plate boundaries (e.g. Late Cenozoic migration of Mendocino triple junction off California). In most parts of southern California—for example, north of the San Andreas Big Bend and SE of Los Angeles--our block geometry closely resembles that assumed in previous studies (McCaffrey 2005 JGR; Meade & Hager 2005 JGR; Becker et al. 2005 GJI). In these regions GPS slip rates can be reliably estimated and values for individual faults generally agree from one study to another and are also consistent with geologic estimates. However, there is no consensus on block geometry in the Transverse Ranges, Los Angeles Basin and Central Mojave Desert, where CFM faults are densely distributed, UCERF2 slip rates on sever

Thatcher, Wayne; Murray-Moraleda, Jessica

2010-05-01

255

The Plate Boundary Observatory: Current status and plans for the next five years  

NASA Astrophysics Data System (ADS)

UNAVCO currently operates and maintains the NSF-funded Plate Boundary Observatory (PBO), which is the geodetic facility of EarthScope. PBO was designed and built from 2003 to 2008 with $100M investment from the NSF Major Research Equipment and Facilities Construction (MREFC) Program. UNAVCO operated and maintained PBO under a Cooperative Agreement (CA) with NSF from 2008 to 2013 and will continue PBO O&M for the next five years as part of the new Geodesy Advancing Geosciences and EarthScope (GAGE) Facility. PBO is largest continuous GPS and borehole geophysical network in the Americas, with 1100 continuous Global Positioning System (cGPS) sites, including several with multiple monuments, 79 boreholes, with 75 tensor strainmeters, 78 short-period, 3-component seismometers, and pore pressure sensors at 23 sites. PBO also includes 26 tiltmeters deployed at volcanoes in Alaska, Mt St Helens, and Yellowstone caldera and 6 long-baseline laser strainmeters. Surface meteorological sensors are collocated at 154 GPS sites. UNAVCO provides high-rate (1 Hz), low-latency (<1 s) GPS data streams (RT-GPS) from 382 stations in PBO. UNAVCO has delivered over 62 Tb of geodetic data to the EarthScope community since its PBO's inception in 2004. Over the past year, data return for the cGPS component of PBO is 98%, well above the data return metric of 85% set by the NSF, a result of efforts to upgrade power systems and communications infrastructure. In addition, PBO has set the standard for the design, construction, and operation of other multi-hazard networks across the Americas, including COCONet in the Caribbean region and TLALOCNet in Mexico. Funding to support ongoing PBO O&M has declined from FY2012 CA levels under the new GAGE Facility. The implications for data return and data quality metrics as well as replacement of aging PBO GPS instruments with GNSS-compatible systems are as yet unknown. A process to assess the cost of specific PBO components, data rates, enhanced capabilities, and method of delivery (i.e. continuous streams vs. archived files) relative to their scientific value will be proposed. In addition, options to partner with other federal mission-oriented agencies and possible commercial ventures also will be discussed. 1100 station PBO continuous GPS Network.

Mattioli, G. S.; Feaux, K.; Meertens, C. M.; Mencin, D.; Miller, M.

2013-12-01

256

The Plate Boundary Observatory Borehole Strainmeter Program: Overview of Data Analysis and Products  

NASA Astrophysics Data System (ADS)

The PBO borehole strainmeter network is now the largest in the US with 19 strainmeters installed along the Western US Plate Boundary: 14 in the Pacific North West and 5 in Anza, Southern California. With five drilling crews operating though October 2006 the network should grow to 28 strainmeters by December 2006. The areas include Parkfield and Mt St. Helens, PBO's first strainmeter installation in a volcanic region. PBO strainmeter sites are multi-instrumented. Seismic, pore pressure, atmospheric pressure, rainfall and temperature data are measured at almost all sites. Tiltmeters will also be installed at some sites. The strainmeters record at 20-sps, 1-sps and 10-minute interval and are downloaded hourly. The 1-sps data are sent to the NCEDC and IRIS DMC within a few minutes of being retrieved from the strainmeter. The data are archived in SEED format and can be viewed and analyzed with any SEED handling software. PBO's Borehole Strainmeter Analysis Center (BSMAC) in Socorro, NM, produces processed strain data every 10 to 14 days. The data are stored in XML format giving the user the option to use PBO edits or to work with unedited data. The XML file contains time series corrections for the atmospheric pressure, the Earth tides and borehole effects. Every 3 months the data are reviewed and the borehole trends and tidal signal are re- estimated to form the best possible processed data set. PBO reviewed the quality of the data collected by the first 8 strainmeters in a workshop in January 2006. The group discussed coring, examined the borehole trends, tidal signal, and a PSD analysis of data from each strainmeter. A second workshop, focusing on data analysis and in-situ calibration, will take place in October 2006. The UNAVCO strainmeter web page (http://pboweb.unavco.org) provides links to the raw and processed data and is a source for information on data formats, links to software and instrument documentation. An XML log file for each strainmeter provides a history of firmware upgrades and details anything that might affect data quality. A homepage has been developed for each strainmeter where plots of strain and state-of-health data can be viewed. UNAVCO has provided training in processing strainmeter data both at the BSMAC and through short courses. In June 2006 UNAVCO hosted the joint GPS and Strainmeter Short course where the topics of data analysis, calibration, hydrological signals and noise models where taught using PBO data. The next UNAVCO strainmeter course is planned for summer 2007.

Hodgkinson, K.; Anderson, G.; Hasting, M.; Hoyt, B.; Jackson, M.; Lee, E.; Matykiewicz, J.; Mencin, D.; Persson, E.; Smith, S.; Torrez, D.; Wright, J.

2006-12-01

257

Studying the active deformation of distributed plate boundaries by integration of GNSS networks  

NASA Astrophysics Data System (ADS)

In the last decade GNSS networks installed for different purposes have proliferated in Italy and now provide a large amount of data available to geophysical studies. In addition to the existing regional and nation-wide scientific GNSS networks developed by ASI (http://geodaf.mt.asi.it), INGV (http://ring.gm.ingv.it) and OGS (http://crs.inogs.it/frednet), a large number (> 400) of continuously-operating GPS stations have been installed in the framework of regional and national networks, both publicly-operated and commercial, developed to provide real-time positioning capability to surveyors. Although the quality of the data and metadata associated to these stations is generally lower with respect to the "scientific" CGPS stations, the increased density and redundancy in crustal motion information, resulting in more than 500 stations with more than 2.5 years of observations, significantly increase the knowledge of the active deformation of the Italian territory and provides a unique image of the crustal deformation field. The obtained GPS velocity field is analysed and various features ranging from the definition of strain distribution and microplate kinematics within the plate boundary, to the evaluation of tectonic strain accumulation on active faults are presented in this work. Undeforming, aseismic regions (Sardinia, Southern Apulia) provide test sites to evaluate the lower bound on the accuracy achievable to measure tectonic deformation. Integration of GNSS networks significantly improves the resolution of the strain rate field in Central Italy showing that active deformation is concentrated in a narrow belt along the crest of the Apennines, consistently with the distribution of the largest historical and recent earthquakes. Products derived from dense GPS velocity and strain rate fields include map of earthquake potential developed under the assumption that the rate of seismic moment accumulation measured from geodesy distributes into earthquake sizes that follow a truncated Gutenberg-Richter distribution of given b-value and Mmax. The advantage is that, being purely strain-rate based, geodetic models of earthquake potentials require few subjective constraints. In addition, the maps have well-defined error bounds and the approach may apply over regions where poor fault informations are available. This approach provides independent verification of the rates of deformation in regions where geologists have documented faults and allows to evaluate the consistency of the contemporary deformation field and the historical earthquake record. We believe that GNSS networks integration represents an important reality in the framework of the EPOS infrastructure and we strongly support the idea of an European research approach to data sharing among the scientific community.

D'Agostino, Nicola; Avallone, Antonio; Cecere, Gianpaolo; D'Anastasio, Elisabetta

2013-04-01

258

The Earthscope Plate Boundary Observatory Alaska Region an Overview of Network Operation, Maintenance and Improvement  

NASA Astrophysics Data System (ADS)

UNAVCO has now completed its third year of operation of the 138 continuous GPS stations, 12 tiltmeters and 31 communications relays that comprise the Alaska Region of the Earthscope Plate Boundary Observatory. Working in Alaska has been challenging due to the extreme environmental conditions encountered and logistics difficulties. Despite these challenges we have been able to complete each summer field season with network operation at 95% or better. Throughout the last three years we have analyzed both our successes and failures to improve the quality of our network and better serve the scientific community. Additionally, we continue to evaluate and deploy new technologies to improve station reliability and add to the data set available from our stations. 2011 was a busy year for the Alaska engineering team and some highlights from last year's maintenance season include the following. This spring we completed testing and deployment of the first Inmarsat BGAN satellite terminal for data telemetry at AC60 Shemya Island. Shemya Island is at the far western end of the Aleutian Islands and is one of the most remote and difficult to access stations in the PBO AK network. Until the installation of the BGAN, this station was offline with no data telemetry for almost one year. Since the installation of the BGAN in early April 2011 dataflow has been uninterrupted. This year we also completed the first deployments of Stardot NetCamSC webcams in the PBO Network. Currently, these are installed and operational at six GPS stations in Alaska, with plans to install several more next season in Alaska. Images from these cameras can be found at the station homepages linked to from the UNAVCO website. In addition to the hard work put in by PBO engineers this year, it is important that we recognize the contributions of our partners. In particular the Alaska Volcano Observatory, the Alaska Earthquake Information Center and others who have provided us with valuable engineering assistance and data telemetry in several locations. With their help we have reduced the number of stations that require manual data download to six in the entire Alaska network getting us closer to our goal of 100% auto data archival for the Alaska network.

Enders, M.; Boyce, E. S.; Bierma, R.; Walker, K.; Feaux, K.

2011-12-01

259

2011 Operations and Maintenance Activities in the East Region of UNAVCO's Plate Boundary Observatory  

NASA Astrophysics Data System (ADS)

2011 marked Year 3 of Operations and Maintenance of the Plate Boundary Observatory (PBO). In the East Region of PBO, it was a year characterized by several major projects as well as scheduled ongoing maintenance activities. The most significant major project was a USGS/ARRA funded communications upgrade in Yellowstone National Park. This upgrade consisted of bringing 8 existing PBO stations within the Yellowstone volcanic region to near real-time communications. This work will be completed on time and in collaboration with the National Park Service. The upgrade promises to provide much faster latency for invaluable data being recorded for one of the most geodetically critical regions of the current PBO network. Another significant ongoing project in the East Region has been supporting the community that continues to use PBO data. In particular, support of Kristine Larson (Univ of CO) both in installing webcams at PBO sites for monitoring snow depth as well as supporting vegetative surveys at current PBO sites. Similarly, the East Region responded promptly to the community with requests for data quality issues that are station hardware related, including replacing GPS antennae and receivers. With regards to ongoing operations and maintenance projects, reasons for site visits in 2011 were dominated by two significant situations: battery replacement and CDMA modem swaps. 83 site visits were required as part of the Operations and Maintenance strategic battery plan of 5 year battery replacements. This proved to be a considerable challenge due to the scale and geography of the scheduled replacements- the sites were spread throughout the entire network, east to west and north to south. 20 station visits were required due to a Verizon upgrade of the older Alltel network purchased by Verizon. These stations are predominantly in the Rocky Mountain region, but often times had limited access to due weather. Overall, despite record snowfalls throughout the west, state of health in the East Region was consistently over 95% operational; a testament to past network-hardening and current vigilance and hard work. The east region looks forward to a successful 2012 campaign.

Dittmann, T.; Feaux, K.; Kasmer, D.; Jenkins, F.; Mencin, D.

2011-12-01

260

Thermochronology of mid-Cretaceous dioritic granulites adjacent "Big Bend" in Australia-Pacific plate boundary, northern South Island, New Zealand  

NASA Astrophysics Data System (ADS)

The Western Fiordland Orthogneiss (WFO), situated south-east of the Australian-Pacific plate boundary (Alpine Fault), southern South Island, New Zealand is the largest suite of plutonic rocks intruded into the Pacific margin of Gondwana during the final stages of arc plutonism preceding break-up of the supercontinent in the Late Cretaceous. Dextral motion of c. 480 km along the Alpine Fault during the Cenozoic has offset originally contiguous Pacific Gondwana margin rocks in northern and southern South Island. The Glenroy Complex in northern South Island, west of the Alpine Fault is dominated by two-pyroxene+hornblende granulite facies monzodioritic gneisses. U-Pb zircon geochronological and geochemical data indicate the Glenroy Complex was emplaced between 128-122 Ma and is a correlative of the WFO. The Glenroy Complex forms the lower-most block bounded by an east-dipping set of imbricate thrusts that developed during the late Cenozoic to the west of the largest S-shaped restraining bend ("Big Bend") in the Alpine Fault. New 40Ar/39Ar and fission-track thermochronological data, combined with previous geological field-mapping, demonstrate that the Glenroy Complex cooled rapidly (c. 30° C/Ma) after emplacement and granulite facies metamorphism (c. 850°C) at c. 120 Ma, through c. 550 °C by c. 110-100 Ma. The average cooling rate during the Late Cretaceous-Cenozoic was relatively slow, and initial exposure in the late Early Miocene (c. 16 Ma) was followed by reburial to c. 3-4 km (c. 80-100 °C) before final exhumation post-Pliocene. This thermal history is similar to the WFO, which cooled rapidly through c. 350 °C during mid-Cretaceous continental extension, followed by slow cooling during the Late Cretaceous and Cenozoic until development of the Australian-Pacific boundary through New Zealand facilitated rapid, exhumation-related cooling from c. 240 °C at c. 20 Ma and final exhumation post-10 Ma (Davids, 1999). However, the Glenroy Complex cooled at a faster rate in the Paleogene-early Neogene and was at the surface (before reburial) at least 5 Ma earlier than the WFO. These differences are in part considered to reflect the influence of the Big Bend, which caused relatively early localised exhumation of the Glenroy Complex by local 'pop-up' mechanisms during a time when there was no significant component of overall convergence across the Pacific-Australian plate boundary and the Alpine Fault was dominantly strike-slip.

Sagar, M.; Seward, D.; Heizler, M. T.; Palin, J. M.; Toy, V. G.; Tulloch, A. J.

2012-12-01

261

Plate motions: fundamentals  

E-print Network

lithospheric plates" · Plate tectonics = a kinematic theory ­ Rigid plates (no intraplate deformation") · Convergent = subductions ("trenches") · Strike-slip = transform faults · Plate tectonics describesPlate motions: fundamentals · Assume a pie-shaped wedge plate B, rotating around E (=rotation pole

Déverchère, Jacques

262

North America-Pacific plate boundary, an elastic-plastic megashear - Evidence from very long baseline interferometry  

NASA Technical Reports Server (NTRS)

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.

Ward, Steven N.

1988-01-01

263

Blood flow modelling in stented arteries: new convergence results of first order boundary layers and wall-laws for a rough Neumann-Laplace problem  

E-print Network

Stents are medical devices designed to modify blood flow in aneurysm sacs, in order to prevent their rupture. They can be considered as a locally periodic rough boundary. In order to approximate blood flow in arteries and vessels of the cardio-vascular system containing stents, we use multi-scale techniques to construct boundary layers and wall laws. Simplifying the flow we turn to consider a 2-dimensional Poisson problem that conserves essential features related to the rough boundary. Then, we investigate convergence of boundary layer approxi- mations and the corresponding wall laws in the case of Neumann type boundary conditions at the inlet and outlet parts of the domain. The difficulty comes from the fact that correctors, for the boundary layers near the rough surface, may introduce error terms on the other por- tions of the boundary. In order to correct these spurious oscillations, we introduce a vertical boundary layer. Trough a careful study of its behavior, we prove rigorously decay estimates. We then...

Bonnetier, Eric; Milisic, Vuk

2008-01-01

264

Effects of thermal radiation and viscous dissipation on boundary layer flow of nanofluids over a permeable moving flat plate  

NASA Astrophysics Data System (ADS)

The effects of suction, viscous dissipation, thermal radiation and thermal diffusion are numerically studied on a boundary layer flow of nanofluids over a moving flat plate. The partial differential equations governing the motion are transformed into ordinary differential equations using similarity solutions, and are solved using the Runge-Kutta-Fehlberg method with the shooting technique. The effects of nanoparticle volume fraction, the type of nanoparticles, the radiation parameter, the Brinkman number, the suction/injection parameter and the relative motion of the plate on the nanofluids velocity, temperature, skin friction and heat transfer characteristics are graphically presented and then discussed quantitatively. A comparative study between the previously published and the present results in a limiting sense reveals excellent agreement between them.

Motsumi, T. G.; Makinde, O. D.

2012-10-01

265

Seismic Anisotropy, Deformation, Stress and Faulting in the crust and mantle at the New Zealand Plate Boundary (Invited)  

NASA Astrophysics Data System (ADS)

We summarize measurements of seismic anisotropy and its relation to fault zone structure in the crust and mantle of New Zealand, which sits on the NE/SW striking transpressional boundary region between the Pacific and Australian plates. In the North Island, the Pacific Plate subducts obliquely under the Australian Plate while in the South Island, the Australian plate subducts obliquely under the Pacific Plate. These two subduction zones are joined by the transpressional Alpine Fault. Seismic anisotropy measured with shear wave splitting of SKS and deep teleseismic S arrivals of on-shore stations yield mostly plate-boundary-parallel fast directions (phi) and delay times (dt) ranging on the order of 1.5 to 2.5 seconds, suggesting broad scale shear deformation in the crust, lithosphere and asthenosphere. Asthenospheric shear may be considered as trench-parallel flow below the North Island. Delay times are even higher (up to 4.5 s) in the back-arc Central Volcanic Region (CVR), an area of active extension, and decrease sharply to zero at its western boundary. These values have been interpreted as caused by melt bands in the CVR giving way to a region that has been stripped of lithosphere. South of the CVR the back-arc is in compression and splitting is nearly constant at 1.6 s, except for higher delay times up to 3 s in the southeastern North Island. Abrupt lateral changes in delay time in the North Island have been attributed to strong, shallow anisotropy in the crust and mantle wedge, but some contamination from isotropic velocity changes may also affect the delay times. An ocean bottom seismometer (OBS) deployment off the South Island shows that plate-boundary parallel anisotropy, interpreted as the limit of shear deformation, reaches to 100 km on either side of the Alpine Fault, changing to nearly E-W at the eastern-most land stations and at most of the offshore east coast stations. Southern OBS and land stations yield more northerly fast directions, suggesting rotation of anisotropic axes and either alignment with asthenospheric flow parallel to the absolute plate motion, or small strain at an angle of about 45 degrees to the shear plane. Frequency-dependence of delay times is apparent for teleseismic S, ScS and local S phases, with smaller periods yielding smaller delay times. The higher frequency waves also yield more scatter in delay times as well as fast directions. However, spatial averaging and delay time tomography of local S phases yield consistent results, with regions of high anisotropy near known fault zones and fault-zone parallel anisotropy in many areas, suggesting fault zone mineralization or shearing near the fault zone controls some anisotropy. In many other areas, shear wave splitting of local earthquakes is parallel to the maximum horizontal stress direction (SHmax) as measured by focal mechanism inversions, suggesting that aligned, fluid-filled cracks control anisotropy in the shallow crust away from faults. For aftershocks of the E-W striking 2010 M=7.1 Darfield earthquake in the Canterbury Plains in the east-central South Island, a spatial rotation of both fast directions and SHmax occurs. Far from the fault plane, SHmax and phi are at 116+-18 degrees, but earthquakes increasingly near to the fault trace yield increasingly E-W SHmax. This suggests the fault is either weak, or the stress rotated after the earthquake.

Savage, M. K.; Karalliyadda, S.; Zietlow, D. W.; Holt, R. A.; Sheehan, A. F.; Townend, J.; Stern, T. A.

2013-12-01

266

Selective control of neuronal cluster size at the forebrain/midbrain boundary by signaling from the prechordal plate.  

PubMed

Within the vertebrate embryonic neural plate, the first neuronal clusters often differentiate at the border of patterning identities. Whether the information inherent in the intersection of patterning identities alone controls all aspects of neuronal cluster development (location, identity, and size) is unknown. Here, we focus on the cluster of the medial longitudinal fascicle (nMLF) and posterior commissure (nPC), located at the forebrain/midbrain (fore/mid) boundary, to address this issue. We first identify expression of the transcription factor Six3 as a common and distinct molecular signature of nMLF and nPC neurons in zebrafish, and we use this marker to monitor mechanisms controlling the location and number of nMLF/nPC neurons. We demonstrate that six3 expression is induced at the fore/mid boundary in pax2.1/no-isthmus and smoothened/slow muscle omitted mutants, where identities adjacent to the six3 cluster are altered; however, in these mutants, the subpopulation of six3-positive cells located within the mispatterned territory is reduced. These results show that induction of the six3 cluster is triggered by the information derived from the intersection in patterning identities alone, whereas correct cluster size depends, in a modular manner, on the identities themselves. The size of the six3 cluster is also controlled independently of neural tube patterning: we demonstrate that the prechordal plate (PCP) is impaired in mixer/bonnie and clyde mutants and that this phenotype secondarily results in an increased production of six3-positive cells at the fore/mid boundary, without correlatively affecting patterning in this area. Thus, a signaling process originating from the PCP distinguishes between neural patterning and the control of six3 cluster size at the fore/mid junction in vivo. Together, our results suggest that a combination of patterning-related and -unrelated mechanisms specifically controls the size of individual early neuronal clusters within the anterior neural plate. PMID:12889061

Tallafuss, Alexandra; Adolf, Birgit; Bally-Cuif, Laure

2003-08-01

267

Consolidation patterns during initiation and evolution of a plate-boundary decollement zone: northern Barbados accretionary prism  

USGS Publications Warehouse

Borehole logs from the northern Barbados accretionary prism show that the plate-boundary decollement initiates in a low-density radiolarian claystone. With continued thrusting, the decollement zone consolidates, but in a patchy manner. The logs calibrate a three-dimensional seismic reflection image of the decollement zone and indicate which portions are of low density and enriched in fluid, and which portions have consolidated. The seismic image demonstrates that an underconsolidated patch of the decollement zone connects to a fluid-rich conduit extending down the decollement surface. Fluid migration up this conduit probably supports the open pore structure in the underconsolidated patch.

Moore, J.C.; Klaus, A.; Bangs, N.L.; Bekins, B.; Bucker, C.J.; Bruckmann, W.; Erickson, S.N.; Hansen, O.; Horton, T.; Ireland, P.; Major, C.O.; Moore, G.F.; Peacock, S.; Saito, S.; Screaton, E.J.; Shimeld, J.W.; Stauffer, P.H.; Taymaz, T.; Teas, P.A.; Tokunaga, T.

1998-01-01

268

Coupled effects of director orientations and boundary conditions on light induced bending of monodomain nematic liquid crystalline polymer plates  

NASA Astrophysics Data System (ADS)

A photo-chromic liquid crystal polymers (LCPs) is a smart material for large light-activated variation or bending to transfer luminous energy into mechanical energy. We study the light induced behavior by modeling planar and homeotropic nematic network polymer plates. We effectively illustrate some reported experimental outcomes and theoretically predict some possible bending patterns. This paper constructs an understanding between the bending behaviors and interactions among the alignments, aspect ratios and boundary conditions, etc. Our work provides information on optimizing light induced bending in the process of micro-opto-mechanical system (MOMS) design.

You, Yue; Xu, Changwei; Ding, Shurong; Huo, Yongzhong

2012-12-01

269

Stability of GNSS Monumentation: Analysis of Co-Located Monuments in the Plate Boundary Observatory  

NASA Astrophysics Data System (ADS)

Geodetic-quality permanent GNSS stations have used a number of different monumentation styles for the purpose of ensuring that the motions of the GNSS antenna reflect those of the Earth's crust while minimizing non-tectonic motions near the surface. Monuments range from simple masts drilled into building roofs or bedrock that cost a few hundred dollars to machine-drilled-braced monuments in soil that cost tens of thousands. Monument stability can depend on their design, the construction techniques used to install them, and the local surface geology where they are installed. Previous studies have separately investigated pairs of identical monuments at a single site, monument type variations using global statistical analysis, and multiple monument styles at a single site. Despite these efforts, the stability of different styles of monumentation in similarly varying geologic conditions has not been adequately determined. Errors in GPS measurements can be dominated by error sources unrelated to the movement of the monument with respect to the Earth's crust, thus making it difficult to isolate monument instability. Contributions from GPS measurement error unrelated to monument stability include, but are not limited to: satellite orbits, satellite clocks, tropospheric delay, and ionospheric delay, antenna phase center variations, near-field multipath, far-field multipath. Installing multiple monuments with small antenna separations at a given test location can help to reduce GPS measurement errors. To increase the understanding of monument stability of various monument styles in diverse geologic conditions UNAVCO has constructed two additional monuments at five existing Plate Boundary Observatory stations during the past year. Deep drilled-braced, short drilled-braced, and single mast type monuments were installed at sites with bedrock at the surface; deep drilled-braced, short driven-braced and pillar type monuments were installed at sites with alluvium or soil at the surface. Sites were selected that comprised a variety of geographic, hydrologic, and geologic conditions. The resulting set of 10-meter spaced monument triangles will yield valuable information regarding the stability of their types in different settings. Data collected from PBO Multi-Monument Experiment are being analyzed using a variety of methods. Each site is characterized using quality-control parameters such as multipath, signal-to-noise and previously determined seasonal variations. High-precision processing by the PBO Analysis Centers with GAMIT and GIPSY software packages using regional and global schemes yield time-series with millimeter-level that determine noise content, overall site stability relative to other PBO sites and differential motions between the individual monuments. Sub-millimeter results from UNAVCO's short-baseline processing efforts will be presented showing further details of monument performance site characterization including the effects of varying elevation cutoff angle and modeling of monument-dependent noise.

Blume, F.; Berglund, H. T.; Feaux, K.; Dittmann, S. T.; Walls, C. P.; Austin, K. E.; Mattioli, G. S.

2013-12-01

270

What can we Learn From Small Non-Recoverable Strains at Plate Boundaries?  

NASA Astrophysics Data System (ADS)

Background seismicity carries often overlooked information about how the crust responds to plate motions. Integrating focal mechanisms for background seismicity with (1) geologic observations, and (2) geodetic constraints, is critical to establishing a better understanding of both the rock record and contemporary deformation. Treating the crust as a micropolar continuum it is possible to constrain not only the orientations and relative magnitudes of the principal strains but also the vorticity of crustal blocks with respect to the large-scale continuum. We show the utility of this approach with examples from the Cascadia margin and the Coso Range (within the Eastern California shear zone). In the upper crust of the Cascadia margin, seismogenic strain appears to be dominated by accommodation of motion of the Oregon forearc block. This suggests that the shallow crust is responding to long-term motion of the Oregon forearc rather than the interseismic locking of the subduction megathrust. In the area west of Mt. Rainier, this response is marked by non-zero relative vorticity in a regime of N-S shortening and crustal thickening. To date, geologic studies necessary to evaluate the significance of this vorticity have not been completed. In contrast within the Coso Range of California, seismogenic strain at Wild Horse Mesa indicates a component of relative vorticity that is broadly consistent with paleomagnetically constrained finite rotations of the ca. 3 Ma lava flows that compose the mesa. This area is centered at a right-releasing step in the Eastern California shear zone and thus is experiencing active transtension. Stratigraphic constraints have been used to suggest that significant dextral shearing in this region initiated ca. 3.5-2 Ma. The seismogenic response to transtension is depth-dependent plane strain with crustal thinning above 5 km and horizontal dextral shearing from 5-8 km. Both structural levels indicate subhorizontal E-W maximum stretching. Relative vorticity at deeper levels is consistent with down-viewed clockwise rotation, in accord with paleomagnetic results. Relative vorticity at shallower levels is consistent with E tilting of crustal blocks, which has not been resolved paleomagnetically. In addition, micropolar modeling of outcrop-scale brittle faults exposed in the eastern part of Wild Horse Mesa shows subhorizontal maximum stretching directions that are in general agreement with those determined for contemporary deformation. At 90% confidence, bootstrap models suggest a sense of block rotation that is in accord with that evident from the paleomagnetic data, as well as prolate strain, consistent with transtension. The latter finding suggests that the time-integrated record of shearing captures the contemporary, depth dependent plane strains as a 3-dimensional deformation. These rocks, in fact, record evidence for partitioning of strain at fine spatial scales with faults that record crustal thinning and crustal thickening intimately mixed with the more dominant strike-slip faults. In total, the neotectonic record of non-recoverable strain at Wild Horse Mesa is in accord with (1) expectations based on the current boundary conditions, and (2) models for the formation of the youthful Eastern California shear zone. The faults that provide this record are invariably limited to the outcrop scale, and are interpreted to be akin to the structures that accommodate contemporary background seismicity. These small structures therefore appear to provide an important link between understanding the rock record and contemporary non-recoverable deformation.

Lewis, J. C.; Pluhar, C. J.

2003-12-01

271

EarthScope: Cyberinfrastructure to access Plate Boundary Observatory data products and services  

NASA Astrophysics Data System (ADS)

The wealth of data from geodetic observing systems, especially the Plate Boundary Observatory (PBO), presents major data management challenges. The challenges are driven by ingenious new uses of Global Positioning System (GPS) data, demands for higher-rate, lower latency data, the need for continued access and long term preservation of archival data, the expansion of data users into other science, engineering and commercial arenas, and the growth of enhanced products that expand the utility of the data. To meet these challenges, UNAVCO has established a comprehensive suite of data services encompassing sensor network data operations, data product generation (through the activities of partners at Massachusetts Institute of Technology, Central Washington University, New Mexico Institute of Mining and Technology, and the University of California, San Diego - UCSD), data management, access and archiving, and advanced cyberinfrastructure. PBO sensor systems include 1,100 continuously operating GPS stations, 79 borehole geophysical sites (with a combination of strainmeters, tiltmeters, seismometers, pore pressure gauges, and meteorological sensors), and 6 long baseline strainmeters. Imaging data acquired for EarthScope include large volumes of satellite synthetic aperture radar (SAR) and airborne LiDAR data. Core data products such as daily GPS position time series and derived crustal motion velocities have been augmented with real-time data streams and positions calculated every second from 367 PBO stations. Higher rate (5 Hz) data files are available for applications such as GPS seismology. Efforts are underway with UCSD to integrate GPS and accelerometers at a subset of PBO sites to increase the reliability and capability of the observations. These observations have utility for research and hazards mitigation. Ingenious methods of GPS data analysis, developed by the University of Colorado and the University Corporation for Atmospheric Research, measure snow depth, near surface soil moisture, and vegetation. Along with atmospheric water vapor estimates, these products are expanding the utility of the data into atmospheric, environmental, ecological and soil sciences. Another new PBO product, hydrologic loading models derived from the NASA Global Land Data Assimilation System, is available for correcting GPS time series and hydrologic studies. To facilitate discovery and access of these extensive, diverse, and distributed data collections, UNAVCO has led collaborative efforts to develop web services and federated query capabilities for GPS, LiDAR and SAR. These services form the foundations for global integration projects such as EarthCube, GEO Geohazard Supersites and Natural Laboratories, and COOPEUS. In order to further curation and enhance access and processing capabilities, UNAVCO is exploring cloud computing and storage with UCSD and Amazon that will increase capacity over the next five years. Finally, with the rich set of data and services offered from PBO comes the need to help users better understand data techniques, observations, and quality. To serve this need, UNAVCO is enhancing online resources and, with its community partners, will continue to develop technical short courses and workshops.

Meertens, C. M.; Mattioli, G. S.; Miller, M.; Boler, F. M.; Crosby, C. J.; Mencin, D.; Phillips, D. A.; Snett, L.

2013-12-01

272

Crustal structure of a transform plate boundary: San Francisco Bay and the central California continental margin  

USGS Publications Warehouse

Wide-angle seismic data collected during the Bay Area Seismic Imaging Experiment provide new glimpses of the deep structure of the San Francisco Bay Area Block and across the offshore continental margin. San Francisco Bay is underlain by a veneer (<300 m) of sediments, beneath which P wave velocities increase rapidly from 5.2 km/s to 6.0 km/s at 7 km depth, consistent with rocks of the Franciscan subduction assemblage. The base of the Franciscan at-15-18 km depth is marked by a strong wide-angle reflector, beneath which lies an 8- to 10-km-thick lower crust with an average velocity of 6.75??0.15 km/s. The lower crust of the Bay Area Block may be oceanic in origin, but its structure and reflectivity indicate that it has been modified by shearing and/or magmatic intrusion. Wide-angle reflections define two layers within the lower crust, with velocities of 6.4-6.6 km/s and 6.9-7.3 km/s. Prominent subhorizontal reflectivity observed at near-vertical incidence resides principally in the lowermost layer, the top of which corresponds to the "6-s reflector" of Brocher et al. [1994]. Rheological modeling suggests that the lower crust beneath the 6-s reflector is the weakest part of the lithosphere; the horizontal shear zone suggested by Furlong et al. [1989] to link the San Andreas and Hayward/Calaveras fault systems may actually be a broad zone of shear deformation occupying the lowermost crust. A transect across the continental margin from the paleotrench to the Hayward fault shows a deep crustal structure that is more complex than previously realized. Strong lateral variability in seismic velocity and wide-angle reflectivity suggests that crustal composition changes across major transcurrent fault systems. Pacific oceanic crust extends 40-50 km landward of the paleotrench but, contrary to prior models, probably does not continue beneath the Salinian Block, a Cretaceous arc complex that lies west of the San Andreas fault in the Bay Area. The thickness (10 km) and high lower-crustal velocity of Pacific oceanic crust suggest that it was underplated by magmatism associated with the nearby Pioneer seamount. The Salinian Block consists of a 15-km-thick layer of velocity 6.0-6.2 km/s overlying a 5-km-thick, high-velocity (7.0 km/s) lower crust that may be oceanic crust, Cretaceous arc-derived lower crust, or a magmatically underplated layer. The strong structural variability across the margin attests to the activity of strike-slip faulting prior to and during development of the transcurrent Pacific/North American plate boundary around 29 Ma. Copyright 1996 by the American Geophysical Union.

Holbrook, W.S.; Brocher, T.M.; ten Brink, U.S.; Hole, J.A.

1996-01-01

273

Secular and annual hydrologic effects from the Plate Boundary Observatory GPS network  

NASA Astrophysics Data System (ADS)

The Plate Boundary Observatory (PBO) GPS network is providing accurate and spatially coherent vertical signals that can be interpreted in terms of hydrological loading and poroelastic effects from both natural and anthropogenic changes in water storage. Data used for this analysis are the precise coordinate time series produced on a daily basis by PBO Analysis Centers at New Mexico Institute of Mining and Technology and at Central Washington University and combined by the Analysis Center Coordinator at the Massachusetts Institute of Technology. These products, as well as derived velocity solutions, are made freely available from the UNAVCO Data Center in Boulder. Analysis of secular trends and annual variations in the time series was made using the analysis software of Langbein, 2008. Spatial variations in the amplitude and phase of the annual vertical component of motion allow for identification of anthropogenic effects due to water pumping, irrigation, and reservoir lake variations, and of outliers due to instrumental or other local site effects. Vertical annual signals of 8-10 mm peak-to-peak amplitude are evident at stations in the mountains of northern and central California and the Pacific Northwest. The peak annual uplift is in October and is correlated to hydrological loading effects. Mountainous areas appear to be responding elastically to the load of the water contained in surface soil, fractures, and snow. Vertical signals are highest when the water load is at a minimum. The vertical elastic hydrologic loading signal was modeled using the 0.25 degree community NOAH land-surface model (LSM) and generally fits the observed GPS signal. Addition comparisons will be made using the Mosaic LSM and the NOAA “Leaky Bucket” hydrologic model. In contrast to mountain stations that are installed principally in bedrock, stations in the valleys of California are installed in sediments. Observations from these stations show greater spatial variability ranging from almost no detectable annual signal to very large, 20-30 mm, vertical amplitudes that reach a maximum in March. Vertical signals in the valleys are the result of poroelastic effects induced by groundwater variations caused by pumping for irrigation or other purposes and are highest when groundwater is at maximum recharge level. Secular trends in the vertical time series show 1-3 mm/yr of subsidence across the western U.S. In areas of groundwater pumping the rates are up to several cm/yr showing subsidence as pumping exceeds annual recharge over a multi-year time period. In the mountainous areas where hydrologic loading is evident in the annual signals, secular trends show uplift of 1-3 mm/yr possibly due to regional drought and decreased overall water volumes that result in less load and vertical uplift. Overall, these results illustrate the potential of using GPS data to constrain hydrological models. In return, accurate hydrologic loading models will be needed to better measure and detect vertical tectonic motions at the mm-level.

Meertens, C. M.; Wahr, J. M.; Borsa, A. A.; Jackson, M. E.; Herring, T.

2009-12-01

274

PBO Nucleus Project Status: Integration of 209 Existing GPS Stations into the Plate Boundary Observatory  

NASA Astrophysics Data System (ADS)

Tectonic and earthquake research in the US has experienced a quiet revolution over the last decade precipitated by the recognition that slow-motion faulting events can both trigger and be triggered by regular earthquakes. Transient motion has now been found in essentially all tectonic environments, and the detection and analysis of such events is the first-order science target of the EarthScope Project. Because of this and a host of other fundamental tectonics questions that can be answered only with long-duration geodetic time series, the incipient 1100-station EarthScope Plate Boundary Observatory (PBO) network has been designed to leverage 445 existing continuous GPS stations whose measurements extend back over a decade. The irreplaceable recording history of these stations will accelerate EarthScope scientific return by providing the highest possible resolution. This resolution will be used to detect and understand transients, to determine the three-dimensional velocity field (particularly vertical motion), and to improve measurement precision by understanding the complex noise sources inherent in GPS. The PBO Nucleus project supports the operation, maintenance and hardware upgrades of a subset of the six western U.S. geodetic networks until they are subsumed by PBO. Uninterrupted data flow from these stations will effectively double the time-series length of PBO over the expected life of EarthScope, and has created, for the first time, a single GPS-based geodetic network in the US. The other existing sites remain in operation under support from non-NSF sources (e.g. the USGS), and EarthScope continues to benefit from their continued operation On the grounds of relevance to EarthScope science goals, geographic distribution and data quality, 209 of the 432 existing stations were selected as the nucleus upon which to build PBO. Conversion of these stations to a PBO-compatible mode of operation was begun under previous funding, and as a result data now flow directly to PBO archives and processing centers while maintenance, operations, and meta-data requirements are continue to be upgraded to PBO standards. At the end of this project all 209 stations will be fully incorporated into PBO, meeting all standards for new PBO construction including data communications and land use permits. Funds for operation of these stations have been included in planned budgets for PBO after the construction phase ends and PBO begins an operational phase in 2008. At this time work on the project is apporixmately 80% complete, with over 90% of the stations having been upgraded. The data from these stations serve a much larger audience than just the few people who work to keep them operating. This project is now collecting the data that will be used by the next generation of solid-earth researchers for at least two decades. Educational modules are being developed by a team of researchers, educators, and curriculum development professionals, and are being disseminated through regional and national workshops. An interactive website provides the newest developments in tectonics research to K-16 classrooms.

Blume, F.; Meertens, C.; Anderson, G.; Eriksson, S.; Boyce, E.

2007-12-01

275

PBO Nucleus Project Status: Integration of 209 Existing GPS Stations into the Plate Boundary Observatory.  

NASA Astrophysics Data System (ADS)

Tectonic and earthquake research in the US has experienced a quiet revolution over the last decade precipitated by the recognition that slow-motion faulting events can both trigger and be triggered by regular earthquakes. Transient motion has now been found in essentially all tectonic environments, and the detection and analysis of such events is the first-order science target of the EarthScope Project. Because of this and a host of other fundamental tectonics questions that can be answered only with long-duration geodetic time series, the incipient 1400-station EarthScope Plate Boundary Observatory (PBO) network has been designed to leverage 432 existing continuous GPS stations whose measurements extend back over a decade. The irreplaceable recording history of these stations is accelerating EarthScope scientific return by providing the highest possible resolution. This resolution will be used to detect and understand transients, to determine the three-dimensional velocity field (particularly vertical motion), and to improve measurement precision by understanding the complex noise sources inherent in GPS. The PBO Nucleus project supports the operation, maintenance and hardware upgrades of a subset of the six western U.S. geodetic networks until they are subsumed by PBO. Uninterrupted data flow from these stations will effectively double the time-series length of PBO over the expected life of EarthScope, and has created, for the first time, a single GPS-based geodetic network in the US. The other existing sites remain in operation under support from non-NSF sources (e.g. the USGS), and EarthScope continues to benefit from their continued operation. On the grounds of relevance to EarthScope science goals, geographic distribution and data quality, 209 of the 432 existing stations were selected as the nucleus upon which to build PBO. Conversion of these stations to a PBO-compatible mode of operation was begun under previous funding, and as a result data now flow directly to PBO archives and processing centers while maintenance, operations, and meta-data requirements are continuing to be upgraded to PBO standards. At the end of this project all 209 stations will be fully incorporated into PBO, meeting all standards for new PBO construction including data communications and land use permits. Funds for operation of these stations have been included in planned budgets for PBO after the construction phase ends and PBO begins an operational phase in 2008. To date approximately 150 of the 209 stations have been completely upgraded, and data flow from all stations is incorporated into the PBO data analysis flow. The community has only begun to understand the pervasive effects of transient creep, and its societal consequences remained largely unexplored. For example, one open question is whether slow faulting pervasively moderates earthquake nucleation. The existence of slow earthquakes will impact seismic hazards estimation, since these transients are now known to `absorb' a significant component of total slip in some regions and trigger earthquakes in others. The data from these stations serve a much larger audience than just the few people who work to keep them operating. This project is now collecting the data that will be used by the next generation of solid-earth researchers for at least two decades. Educational modules are being developed by a team of researchers, educators, and curriculum development professionals, and are being disseminated through regional and national workshops. An interactive website provides the newest developments in tectonics research to K-16 classrooms.

Blume, F.; Prescott, W.; Anderson, G.; Eriksson, S.; Feldl, N.

2006-12-01

276

Stress Transfer Processes during Great Plate Boundary Thrusting Events: A Study from the Andaman and Nicobar Segments  

NASA Astrophysics Data System (ADS)

The response of subduction zones to large earthquakes varies along their strike, both during the interseismic and post-seismic periods. The December 26, 2004 earthquake nucleated at 3° N latitude and its rupture propagated northward, along the Andaman-Sumatra subduction zone, terminating at 15°N. Rupture speed was estimated at about 2.0 km per second in the northern part under the Andaman region and 2.5 - 2.7 km per second under southern Nicobar and North Sumatra. We have examined the pre and post-2004 seismicity to understand the stress transfer processes within the subducting plate, in the Andaman (10° - 15° N ) and Nicobar (5° - 10° N) segments. The seismicity pattern in these segments shows distinctive characteristics associated with the outer rise, accretionary prism and the spreading ridge, all of which are relatively better developed in the Andaman segment. The Ninety East ridge and the Sumatra Fault System are significant tectonic features in the Nicobar segment. The pre-2004 seismicity in both these segments conform to the steady-state conditions wherein large earthquakes are fewer and compressive stresses dominate along the plate interface. Among the pre-2004 great earthquakes are the 1881 Nicobar and 1941 Andaman events. The former is considered to be a shallow thrust event that generated a small tsunami. Studies in other subduction zones suggest that large outer-rise tensional events follow great plate boundary breaking earthquakes due to the the up-dip transfer of stresses within the subducting plate. The seismicity of the Andaman segment (1977-2004) concurs with the steady-state stress conditions where earthquakes occur dominantly by thrust faulting. The post-2004 seismicity shows up-dip migration along the plate interface, with dominance of shallow normal faulting, including a few outer rise events and some deeper (> 100 km) strike-slip faulting events within the subducting plate. The September 13, 2002, Mw 6.5 thrust faulting earthquake at Diglipur (depth: 21 km) and the August 10, 2009, Mw 7.5 normal faulting earthquake near Coco Island (depth: 22 km), within the northern terminus of the 2004 rupture are cited as examples of the alternating pre and post earthquake stress conditions. The major pre and post 2004 clusters were associated with the Andaman Spreading Ridge (ASR). In the Nicobar segment, the most recent earthquake on June 12, 2010, Mw 7.5 (focal depth: 35 km) occurred very close to the plate boundary, through left lateral strike-slip faulting. A segment that does not feature any active volcanoes unlike its northern and southern counterparts, this part of the plate boundary has generated several right lateral strike-slip earthquakes, mostly on the Sumatra Fault System. The left-lateral strike-slip faulting associated with the June 12 event on a nearly N-S oriented fault plane consistent with the trend of the Ninety East ridge and the occasional left-lateral earthquakes prior to the 2004 mega-thrust event suggest the involvement of the Ninety East ridge in the subduction process.

Andrade, V.; Rajendran, K.

2010-12-01

277

Capacity Design of Intermediate Horizontal Boundary Elements of Steel Plate Shear Walls  

E-print Network

with the exception of plastic hinges at their ends when the infill plates fully yield under seismic loading. However presents analytical models for estimating the design forces for intermediate HBEs to reliably achieve capacity design. Those models combine the assumed plastic mechanism with a linear beam model

Bruneau, Michel

278

Plate motion  

SciTech Connect

The motion of tectonic plates on the earth is characterized in a critical review of U.S. research from the period 1987-1990. Topics addressed include the NUVEL-1 global model of current plate motions, diffuse plate boundaries and the oceanic lithosphere, the relation between plate motions and distributed deformations, accelerations and the steadiness of plate motions, the distribution of current Pacific-North America motion across western North America and its margin, plate reconstructions and their uncertainties, hotspots, and plate dynamics. A comprehensive bibliography is provided. 126 refs.

Gordon, R.G. (USAF, Geophysics Laboratory, Hanscom AFB, MA (United States))

1991-01-01

279

The Plate Boundary Observatory Cascadia Network: Development and Installation of a Large Scale Real-time GPS Network  

NASA Astrophysics Data System (ADS)

The EarthScope Plate Boundary Observatory (PBO), through a NSF-ARRA supplement, has enhanced the geophysical infrastructure in in the Pacific Northwest by upgrading 232 Plate Boundary Observatory GPS stations to allow the collection and distribution of high-rate (1 Hz), low-latency (<1 s) data streams (RT-GPS). These upgraded stations supplemented the original 100 RT-GPS stations in the PBO GPS network. The addition of the new RT-GPS sites in the Pacific Northwest should spur new volcano and earthquake research opportunities in an area of great scientific interest and high geophysical hazard. Streaming RT-GPS data will enable researchers to detect and investigate strong ground motion during large geophysical events, including a possible plate-interface earthquake, which has implications for earthquake hazard mitigation. A total of 282 PBO stations were upgraded and added to the UNAVCO real-time GPS system, along with addition of 22 new meteorological instruments to existing PBO stations. Extensive testing of BGAN satellite communications systems has been conducted to support the Cascadia RT-GPS upgrades and the installation of three BGAN satellite fail over systems along the Cascadia margin will allow for the continuation of data flow in the event of a loss of primary communications during in a large geophysical event or other interruptions in commercial cellular networks. In summary, with these additional upgrades in the Cascadia region, the PBO RT-GPS network will increase to 420 stations. Upgrades to UNAVCO's data infrastructure included evaluation and purchase of the Trimble Pivot Platform, servers, and additional hardware for archiving the high rate data. UNAVCO staff is working closely with the UNAVCO community to develop data standards, protocols, and a science plan for the use of RT-GPS data.

Austin, K. E.; Blume, F.; Berglund, H. T.; Dittman, T.; Feaux, K.; Gallaher, W. W.; Mattioli, G. S.; Mencin, D.; Walls, C. P.

2013-12-01

280

Interplate strain, wide plate margin deformation, intraplate strain: The GPS analysis spectrum  

Microsoft Academic Search

Global Positioning System (GPS) data from southern Central America and northwestern South America collected during 1991, 1994, 1996, and 1998 reveal wide plate boundary deformation and escape tectonics occurring along an 1400 km length of the North Andes; locking of the subducting Nazca plate, strain accumulation in the Ecuador-Colombia forearc; ongoing collision of the Panama arc and Colombia; and convergence

Robert Anthony Trenkamp

2003-01-01

281

Plate Tectonics  

NSDL National Science Digital Library

This interactive Flash explores plate tectonics and provides an interactive map where users can identify plate boundaries with name and velocities as well as locations of earthquakes, volcanoes, and hotspots. The site also provides animations and supplementary information about plate movement and subduction. This resource is a helpful overview or review for introductory level high school or undergraduate physical geology or Earth science students.

Smoothstone; Company, Houghton M.

282

Normal faulting at convergent plate boundaries: Mylonitic extensional fabrics in the Franciscan subduction complex in Del Puerto Canyon, California, revisited  

Microsoft Academic Search

Using a strain and rotation analysis we tested the hypotheses that top-east mylonitic extensional structures in the uppermost Franciscan subduction complex in Del Puerto Canyon, California, accomplished exhumation of the Franciscan blueschists. We found no evidence of strongly noncoaxial deformation, instead our data indicate overall coaxial deformation in the proposed zone of mylonitic extensional deformation. There are no extensional strains,

Uwe Ring; Peter P. Richter

2004-01-01

283

Thermochronology and tectonics of the Leeward Antilles: Evolution of the southern Caribbean Plate boundary zone  

Microsoft Academic Search

Tectonic reconstructions of the Caribbean Plate are severely hampered by a paucity of geochronologic and exhumation constraints from anastomosed basement blocks along its southern margin. New U\\/Pb, 40Ar\\/39Ar, apatite fission track, and apatite (U-Th)\\/He data constrain quantitative thermal and exhumation histories, which have been used to propose a model for the tectonic evolution of the emergent parts of the Bonaire

Roelant van der Lelij; Richard A. Spikings; Andrew C. Kerr; Alexandre Kounov; Michael Cosca; David Chew; Diego Villagomez

2010-01-01

284

Turbulent Friction in the Boundary Layer of a Flat Plate in a Two-Dimensional Compressible Flow at High Speeds  

NASA Technical Reports Server (NTRS)

In the present report an investigation is made on a flat plate in a two-dimensional compressible flow of the effect of compressibility and heating on the turbulent frictional drag coefficient in the boundary layer of an airfoil or wing radiator. The analysis is based on the Prandtl-Karman theory of the turbulent boundary later and the Stodola-Crocco, theorem on the linear relation between the total energy of the flow and its velocity. Formulas are obtained for the velocity distribution and the frictional drag law in a turbulent boundary later with the compressibility effect and heat transfer taken into account. It is found that with increase of compressibility and temperature at full retardation of the flow (the temperature when the velocity of the flow at a given point is reduced to zero in case of an adiabatic process in the gas) at a constant R (sub x), the frictional drag coefficient C (sub f) decreased, both of these factors acting in the same sense.

Frankl, F.; Voishel, V.

1943-01-01

285

800,000Year Record of Plate Boundary Earthquakes in the Atacama Desert, Northern Chile  

Microsoft Academic Search

Coseismic cracks preserved in the hyper-arid Atacama Desert of Northern Chile provide a unique record of the seismic history of the modern Andean forearc, which has generated the largest earthquakes on earth. Loveless et al. (2009) mapped more than 50,000 cracks on satellite imagery and, based on boundary element modeling, suggested that they indicate repeated rupture of approximately the same

A. M. Baker; L. A. Owen; J. Rech; R. W. Allmendinger

2010-01-01

286

Streamwise turbulence intensity formulation for flat-plate boundary layers Ivan Marusic and Gary J. Kunkel  

E-print Network

round jets with highly disturbed nozzle-exit boundary layers Phys. Fluids 24, 105107 (2012) Particle variable scaling. That is, u2 f z , where u is the stream- wise component of the fluctuating velocity variable scaling alone is insufficient. The major difficulty in drawing firm conclusions has been

Marusic, Ivan

287

Transients in Pacific/North American Plate Boundary Deformation: Synthesis and Modeling of GPS and Borehole Strain Observations  

NASA Technical Reports Server (NTRS)

This is the Final Technical Report on research conducted between 1 June 1997 and 14 September 2001 entitled "Transients in Pacific/North American plate boundary deformation: Synthesis and modeling of GPS and borehole strain observations." As the project title implies, our effort involved a geodetic study of strain transients, i.e., temporal variations in deformation rates, that occur within plate boundary zones and their relationship to earthquakes and plate motions. Important transients occur during and following large earthquakes, and there are also strain transients not apparently associated with earthquakes. A particularly intriguing class of transients, for which there is a modest but growing list of examples, are preseismic anomalies. Such earthquake precursors, if further documented and understood, would have obvious importance for earthquake hazard mitigation. Because the timescales for these diverse transients range over at least 6 orders of magnitude (minutes to years), no single geodetic technique is optimum. We therefore undertook a systematic synthesis of Global Positioning Satellite (GPS) and borehole strainmeter data in three areas in California where there are adequate numbers of both types of instruments (or their equivalent): the San Francisco Bay region (within the Bay Area Regional Deformation network), southern California (within the Southern California Integrated GPS Network), and Parkfield (where a two-color laser system provides a proxy for continuous GPS measurements). An integral component of our study was the elucidation of the physical mechanisms by which such transients occur and propagate. We therefore initiated the development of multiple forward models, using two independent approaches. In the first, we explored the response to specified earthquake slip in viscoelastic models that incorporated failure criteria and the geometry of major faults in California. In the second approach, we examined the dynamical response of a complex rheological medium to the application of a far-field stress imposed by plate motions. The forward models were used both to gain insight into the range of strain transients to be expected under different assumed mechanical conditions and to develop representations for strain fields that allow GPS, borehole, and other strain data to be combined in a self-consistent, yet well-determined, manner. The models also provided a basis for hypothesis testing, by which data from a strain transient well characterized by GPS and borehole observations were utilized to distinguish among competing candidates for the causative physical mechanism and the governing physical characteristics. During the three years of this project, continued to a fourth year through a no-cost extension of the grant, we published 14 papers and presented or co-authored 37 papers at national scientific meetings.

Solomon, Sean C.; Frey, H. V. (Technical Monitor)

2002-01-01

288

Compositional and fluid pressure controls on the state of stress on the Nankai subduction thrust: A weak plate boundary  

NASA Astrophysics Data System (ADS)

We show that both fault mineralogy and regional excess fluid pressure contribute to low resolved shear stresses on the Nankai subduction plate boundary off southwest Japan. Ring and direct shear tests indicate that saturated clay minerals in the fault possess intrinsically low residual friction coefficients ( ?r) at stress levels between 1.0 and 40 MPa. The direct shear ?r values for purified smectite are ˜0.14±0.02, for illite ˜0.25±0.01, and for chlorite 0.26±0.02 (for point load velocities of 0.0001 mm/s). These clay minerals dominate the Nankai subduction décollement zone. Illite (plus quartz) is mechanically important in the altered incoming Muroto section and the predicted décollement ?r should lie between 0.2 and 0.32. This low residual strength, together with elevated fluid pressure, limits shear stresses to below ˜4 MPa within the frontal ˜50 km of the subduction system, consistent with the low wedge taper in this region. A higher wedge taper off the Ashizuri peninsula indicates basal shear stresses rise slightly along strike towards this region. Our analysis indicates lower fluid pressures must predominantly be responsible because only small second order along strike variations in ?r are predicted to occur as a result of variations in smectite and total clay content. These variations should be further reduced at depth under the wedge as smectite is diagenetically altered to illite. However, our data suggest the low ?r values of the clay-rich décollement still limit shear stresses to between ˜17 and 29 MPa within the frontal ˜50 km of the wedge, consistent with other estimates of plate boundary weakness. Indeed, we propose that it should be expected that subduction plate boundaries like Nankai will be weak because of the intrinsic presence of clay-rich faults and moderate fluid overpressures. Our data do not support the hypothesis that the smectite-to-illite reaction directly controls the onset of seismogenic behavior deep in the Nankai system because there is already a mechanical dominance of illite (rather than smectite) in the shallow décollement zone, and we find all the clay phases tend to velocity strengthen. However, temperature-activated clay diagenesis and dehydration may cause secondary changes in the fault properties and state of stress across the up-dip limit of the seismogenic zone.

Brown, K. M.; Kopf, A.; Underwood, M. B.; Weinberger, J. L.

2003-09-01

289

Seismic and gravity constraints on the nature of the basement in the Africa-Eurasia plate boundary: New insights for the geodynamic evolution of the SW Iberian margin  

NASA Astrophysics Data System (ADS)

present a new classification of geological domains at the Africa-Eurasia plate boundary off SW Iberia, together with a regional geodynamic reconstruction spanning from the Mesozoic extension to the Neogene-to-present-day convergence. It is based on seismic velocity and density models along a new transect running from the Horseshoe to the Seine abyssal plains, which is combined with previously available geophysical models from the region. The basement velocity structure at the Seine Abyssal Plain indicates the presence of a highly heterogeneous, thin oceanic crust with local high-velocity anomalies possibly representing zones related to the presence of ultramafic rocks. The integration of this model with previous ones reveals the presence of three oceanic domains offshore SW Iberia: (1) the Seine Abyssal Plain domain, generated during the first stages of slow seafloor spreading in the NE Central Atlantic (Early Jurassic); (2) the Gulf of Cadiz domain, made of oceanic crust generated in the Alpine-Tethys spreading system between Iberia and Africa, which was coeval with the formation of the Seine Abyssal Plain domain and lasted up to the North Atlantic continental breakup (Late Jurassic); and (3) the Gorringe Bank domain, made of exhumed mantle rocks, which formed during the first stages of North Atlantic opening. Our models suggest that the Seine Abyssal Plain and Gulf of Cadiz domains are separated by the Lineament South strike-slip fault, whereas the Gulf of Cadiz and Gorringe Bank domains appear to be limited by a deep thrust fault located at the center of the Horseshoe Abyssal Plain.

Martínez-Loriente, Sara; Sallarès, Valentí; Grácia, Eulália; Bartolome, Rafael; Dañobeitia, Juan José; Zitellini, Nevio

2014-01-01

290

Isla Guadalupe, a Plate Boundary Observatory Remote GPS System: What's Next in PBO-Mexico?  

NASA Astrophysics Data System (ADS)

As a join project between scientific and technical personnel from Southern California Integrated GPS Network, the University NAVSTAR Consortium, Nanometrics Inc, and CICESE, we installed a VSAT remote communications on Isla Guadalupe in support of data telemetry from a cluster of GPS, meteorological and seismic instrumentation. This Mexican island located between 28\\deg53' and 29\\deg 11'N and 118\\deg 13' to 118\\deg 22'W, lies too far from the main land to allow regular radio link. The station now in operation (GUAX) is near of the early GEOMEX site (GUAD), which recent GPS survey mode result show, is fully located on the Pacific plate within the prediction (1 mm/yr N and 2 mm/yr E) of both the geophysical (NNR-NUVEL1-A) and geodetic (ITRF2000) Plate Tectonic models. Thus, GUAX serve as an important clue to accurately monitor the plate's motion, as well as a reference for studies of California Borderland deformation. During the last 5 years we have built two more sites in northern Baja California: SPMX (1998) and CORX (2000); these together with the IGS station in Ensenada (CICE established in 1995 and replaced by CIC1 in 1999), became part of SCIGN-SOPAC (http://sopac.ucsd.edu, www.scign.org). In Mexico the major organizations working with GPS are INEGI (15 sites) and UNAM (different groups: 20-25 sites). Other State Universities and agencies are increasingly using permanent GPS stations for diverse purposes. It seems that in order to achieve our commitment for PBO-Mexico we must to follow the PGGA/SCIGN/CSRC waybill.

Gonzalez Garcia, J.

2003-12-01

291

Hypersonic Laminar Boundary Layer Velocimetry with Discrete Roughness on a Flat Plate  

NASA Technical Reports Server (NTRS)

Laminar boundary layer velocity measurements are made on a 10-degree half-angle wedge in a Mach 10 flow. Two types of discrete boundary layer trips were used to perturb the boundary layer gas. The first was a 2-mm tall, 4-mm diameter cylindrical trip. The second was a scaled version of the Orbiter Boundary Layer Transition (BLT) Detailed Test Objective (DTO) trip. Both 1-mm and 2.5-mm tall BLT DTO trips were tested. Additionally, side-view and plan-view axial boundary layer velocity measurements were made in the absence of these tripping devices. The free-stream unit Reynolds numbers tested for the cylindrical trips were 1.7x10(exp 6)/m and 3.3x10(exp 6)/m. The free-stream unit Reynolds number tested for the BLT DTO trips was 1.7x10(exp 6)/m. The angle of attack was kept at approximately 5-degrees for most of the tests resulting in a Mach number of approximately 8.3. These combinations of unit Reynolds numbers and angle of attack resulted in laminar flowfields. To study the precision of the measurement technique, the angle of attack was varied during one run. Nitric-oxide (NO) molecular tagging velocimetry (MTV) was used to obtain averaged axial velocity values and associated uncertainties. These uncertainties are as low as 20 m/s. An interline, progressive scan CCD camera was used to obtain separate images of the initial reference and shifted NO molecules that had been tagged by the laser. The CCD configuration allowed for sub-microsecond sequential acquisition of both images. The maximum planar spatial resolution achieved for the side-view velocity measurements was 0.07-mm in the wall-normal direction by 1.45-mm in the streamwise direction with a spatial depth of 0.5-mm. For the plan-view measurements, the maximum planar spatial resolution in the spanwise and streamwise directions was 0.69-mm by 1.28-mm, respectively, with a spatial depth of 0.5-mm. Temperature sensitive paint (TSP) measurements are provided to compliment the velocity data and to provide further insight into the behavior of the boundary layers. The experiments were performed at the NASA Langley Research Center 31-Inch Mach 10 Air tunnel.

Bathel, Brett; Danehy, Paul M.; Inman, Jennifer A.; Watkins, A. Neal; Jones, Stephen B.; Lipford, William E.; Goodman, Kyle Z.; Ivey, Christopher B.; Goyne, Christopher P.

2010-01-01

292

Dynamics of the pacific-north american plate boundary in the western united states  

PubMed

The vertically averaged deviatoric stress tensor field within the western United States was determined with topographic data, geoid data, recent global positioning system observations, and strain rate magnitudes and styles from Quaternary faults. Gravitational potential energy differences control the large fault-normal compression on the California coast. Deformation in the Basin and Range is driven, in part, by gravitational potential energy differences, but extension directions there are modified by plate interaction stresses. The California shear zone has relatively low vertically averaged viscosity of about 10(21) pascal.seconds, whereas the Basin and Range has a higher vertically averaged viscosity of 10(22) pascal.seconds. PMID:10657292

Flesch; Holt; Haines; Shen-Tu

2000-02-01

293

Coherent structures in the boundary layer of a flat thick plate  

NASA Astrophysics Data System (ADS)

We use POD and EPOD (extended POD) analysis to extract the main features of the flow over a thick flat plate simulated with an LES. Our goal is to better understand the coupling between the velocity field and the surface pressure field. We find that POD modes based on the full velocity and energy fields contain both flapping and shedding frequencies. Pressure modes are found to be uniform in the spanwise direction and the most intense variations take place at the mean reattachment point. Velocity modes educed from the pressure modes with EPOD are seen to correspond to eddies shed by the recirculation bubble. xml:lang="fr"

Podvin, Bérengère; Fraigneau, Yann; Tenaud, Christian; Daru, Virginie

2014-06-01

294

Resistance of plate motion due to continental deformation (Invited)  

NASA Astrophysics Data System (ADS)

Convergent plate margins that produce high mountains often induce deformation that extends for hundreds to thousands kilometers inboard of the plate boundary. Buoyancy forces that are derived from this thickened, elevated continental crust are commonly thought to resist further convergence and contribute to changes in plate rates as the balance of forces on a plate boundary evolves. For orogens that develop broad plateau-style topography, the strength of the deforming continent and the distance over which it deforms may also contribute to plate forces, although this forcing has rarely been considered. For example, the post-collisional slowing of India with respect to Eurasia challenges the role of topography as the cause of decreasing convergence rates and instead favors the role of deforming a confined mantle lithosphere as the cause of slowing. Here, geologic evidence suggests that compressional deformation began at the distal extent of the orogen when continental collision initiated and that the majority of deformation since has remained localized along what can be considered to be a stationary boundary. As post-collisional convergence continued, convergence rates have declined exponentially as did the distance across the intervening region of deformation. The decline in rate and distance occurred in tandem such that the bulk average strain rate across the orogen remained constant and is equal to the modern strain rate determined by GPS. For both linear and non-linear constitutive relationships, a constant average strain rate implies constant average stress (or constant forcing). A constant force per unit length of the plate boundary might be explained by the viscous resistance of the deforming continental mantle lithosphere, as opposed to a change in forces that would be expected from the buoyancy of the evolving high topography. A viscous resistance of the continental lithosphere has not previously been considered as a type of plate forcing, and the Indo-Asia orogen may offer one extreme example of such. Other examples include the ongoing Arabian-Eurasia continental collision and the ocean-continent subduction beneath South America, where exponentially decreasing convergence rates and mountain building are also observed. Long-lived, far-field deformation in the Arabian example may provide analogous to the Tibet case where decreasing convergence rates follow a decrease over which that convergence is absorbed by continental deformation. Unlike Tibet and Arabia, the outward expansion of deformation away from the plate boundary in the Andean orogen suggests that bulk strain rates must have decreased through time. Possibly, such differences may be related to time-dependent rheologic changes associated with subduction-related magmatism, changes in the frictional resistance along the plate contact, or the diminished role of viscous resistance in subduction settings compared to their continental collision counterpart.

Clark, M. K.

2013-12-01

295

Wide-angle seismic constraints on the evolution of the deep San Andreas plate boundary by Mendocino triple junction migration  

USGS Publications Warehouse

Recent wide-angle seismic observations that constrain the existence and structure of a mafic layer in the lower crust place strong constraints on the evolution of the San Andreas plate boundary system in northern and central California. Northward migration of the Mendocino Triple Junction and the subducted Juan de Fuca lithospheric slab creates a gap under the continent in the new strike-slip system. This gap must be filled by either asthenospheric upwelling or a northward migrating slab attached to the Pacific plate. Both processes emplace a mafic layer, either magmatic underplating or oceanic crust, beneath the California Coast Ranges. A slab of oceanic lithosphere attached to the Pacific plate is inconsistent with the seismic observation that the strike-slip faults cut through the mafic layer to the mantle, detaching the layer from the Pacific plate. The layer could only be attached to the Pacific plate if large vertical offsets and other complex structures observed beneath several strike-slip faults are original oceanic structures that are not caused by the faults. Otherwise, if oceanic slabs exist beneath California, they do not migrate north to fill the growing slab gap. The extreme heat pulse created by asthenospheric upwelling is inconsistent with several constraints from the seismic data, including a shallower depth to the slab gap than is predicted by heat flow models, seismic velocity and structure that are inconsistent with melting or metamorphism of the overlying silicic crust, and a high seismic velocity in the upper mantle. Yet either the Pacific slab model or the asthenospheric upwelling model must be correct. While the mafic material in the lower crust could have been emplaced prior to triple junction migration, the deeper slab gap must still be filled. A preexisting mafic layer does not reduce the inconsistencies of the Pacific slab model. Such material could, however, compensate for the decrease in mafic magma that would be produced if asthenospheric upwelling occurred at a lower temperature. These low temperatures, however, may be inconsistent with asthenospheric rheology.

Hole, J.A.; Beaudoin, B.C.; Henstock, T.J.

1998-01-01

296

Noise of a turbulent boundary layer flow over smooth and rough plates at low mach numbers  

Microsoft Academic Search

The spectral levels of the quadrupole noise generated by a boundary layer flow over a smooth surface are calculated. Explicit\\u000a dependences of the noise levels on the Reynolds number are obtained for the low-frequency and high-frequency ranges. It is\\u000a shown that the logarithmic zone of the velocity profile is responsible for the region of the quadrupole noise spectrum with\\u000a a

A. V. Smol’yakov

2001-01-01

297

An experimental and theoretical investigation of instabilities in hypersonic flat plate boundary layer flow  

Microsoft Academic Search

As part of an investigation on hypersonic boundary layer transition, the first successful instantaneous hot-wire and fluctuating pressure measurements have been conducted in the Ludwieg-tube facility of DLR at a free-stream Mach number of M?=5. The disturbance amplitudes [root-mean-square (RMS) values] of the fluctuations of Pitot pressure and mass flow are smaller than the values measured in conventional, i.e., continuously

Volker Wendt; Martin Simen; Ardeshir Hanifi

1995-01-01

298

Crustal Buoyancies Dominate over Plate Boundary Effects in the U.S. Basin and Range: The Requirement of Weak Faults  

NASA Astrophysics Data System (ADS)

We model the long-term dynamics of the seismogenic layer within the plate boundary zone of western North America, where the relevant time scale is 105 -- 106 years. We utilize a forward dynamic modeling approach, where the body force distributions, inferred lateral variations in effective viscosity, power-law behavior, and the known far-field velocity boundary conditions are defined. Body forces are the differences in gravity potential energy per unit area (GPE), calculated by performing depth integration of vertical stress from the surface down to a common depth reference (20 km below sea level). In our treatment of the seismogenic layer, depth-integrated viscosities are proportional to the assumed long-term friction on faults (expected deviatoric stress at fault failure) and inversely proportional to the long-term strain rates (the known fault slip rates). The velocity boundary conditions are defined using PA-NA, CO-NA, RI-NA, and JF-NA plate motion estimates. Self-consistent dynamic strain rate tensor solutions to the force-balance equations were solved for and scored with kinematic strain rate tensor and velocity fields of western North America, obtained from a large set of highly detailed Quaternary fault observations (e.g., United States Geologic Survey Quaternary fault and fold data base of the United States). We use fault data from present-day to 750 ka to investigate models using a range of long-term fault friction coefficients from 0.02 -- 1.0 under hydrostatic pore pressure conditions. Evaluation of fitness of the dynamic solutions to deformation indicators is achieved using two different measures. In one measure, the forward dynamic strain rate tensor styles are scored by misfit to the kinematic strain rate tensor styles inferred from Kostrov summation of Quaternary fault observations. In a second measure, the dynamic model velocity fields are scored via reduced chi-square misfit with the long-term kinematic model velocity field defined by Quaternary fault observations. Models constructed with low fault friction coefficients (? < 0.20) achieve a vastly superior fit to Quaternary fault observations than do models with intermediate or high fault friction coefficients. Successful models require a weak and distributed fault fabric in which the deviatoric stresses associated with internal crustal buoyancies in the Basin and Range Province dominate over deviatoric stresses associated with velocity boundary conditions. The deformation field in western North America therefore suggests and supports the premise of a sufficiently dense fabric of faults that possess low long-term friction coefficients of 0.10--0.20.

Klein, E. C.; Holt, W. E.; Flesch, L. M.; Haines, A. J.

2008-12-01

299

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

PubMed

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. PMID:25343360

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

2014-01-01

300

Fluctuating pressures measured beneath a high-temperature, turbulent boundary layer on a flat plate at Mach number of 5  

NASA Technical Reports Server (NTRS)

Fluctuating pressures were measured beneath a Mach 5, turbulent boundary layer on a flat plate with an array of piezoresistive sensors. The data were obtained with a digital signal acquisition system during a test run of 4 seconds. Data sampling rate was such that frequency analysis up to 62.5 kHz could be performed. To assess in situ frequency response of the sensors, a specially designed waveguide calibration system was employed to measure transfer functions of all sensors and related instrumentation. Pressure time histories were approximated well by a Gaussian prohibiting distribution. Pressure spectra were very repeatable over the array span of 76 mm. Total rms pressures ranged from 0.0017 to 0.0046 of the freestream dynamic pressure. Streamwise, space-time correlations exhibited expected decaying behavior of a turbulence generated pressure field. Average convection speed was 0.87 of freestream velocity. The trendless behavior with sensor separation indicated possible systematic errors.

Parrott, Tony L.; Jones, Michael G.; Albertson, Cindy W.

1989-01-01

301

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

PubMed Central

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

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

2014-01-01

302

Boundary-layer transition extent measurements on a cone and flat plate at Mach 3.5  

NASA Technical Reports Server (NTRS)

Wide excursions of the boundary-layer transition region are expected to occur on the X-30 National Aerospace Plane (NASP) due to the high Mach number, high temperature, and low density environment experienced during flight. Undesirable features of the transition region, such as the peak heat transfer rate, make it important to understand transition region physics. The current study investigates transition extent in 2D and axisymmetric bounday-layer flows. Surface-pitot and recovery temperature data obtained on a cone and flat plate at Mach 3.5 in the Supersonic Low-Disturbance Pilot Tunnel at NASA Langley are presented. Results show the effects of the unit Reynolds number, freestream disturbances, and nose/leading-edge bluntness on the extent of transition.

Chen, Fang-Jenq

1993-01-01

303

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

PubMed

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. PMID:23577156

Bachok, Norfifah; Ishak, Anuar; Pop, Ioan

2013-01-01

304

Combined regional gravity model of the Andean convergent subduction zone and its application to lithospheric modelling in active plate margins  

NASA Astrophysics Data System (ADS)

Comparison of global GOCE gravity models with terrestrial gravity data reveals large systematic differences in South America, which can be attributed to a low data quality of the terrestrial data. Correspondingly, these large inconsistencies are also reflected when comparing GOCE models with pre-GOCE combined global models such as EGM2008. Therefore, it could be assumed that lithospheric models of the study region, which did not yet include GOCE, are also affected with long to medium wavelength errors. In a joint effort of geodesy and geophysics, a regional gravity field model for the Andean convergent subduction zone is computed as a combination of satellite gravity data from GOCE and GRACE, terrestrial gravity data of the study region, as well as satellite altimetry in the adjacent Pacific ocean. In a first step, the ground data (gravity anomalies and associated heights) are validated against external information, such as global GOCE gravity models (within the limited spectral band captured by the global models), and ACE2 digital terrain model regarding the height information attached to the terrestrial gravity data base. For the validation of ground gravity data, the high-frequency signal content (mainly contained in terrestrial data) is reduced consistently by a topographic-isostatic reduction. The optimum combination of terrestrial gravity anomalies and GOCE satellite gravity is achieved by Least Squares Collocation, taking - as much as possible - error information of the input data into account. Also the omission error related to non-resolved high-frequency gravity signal of the satellite data is considered adequately. As a result, not only a combined regional gravity field model, but also associated error information is derived. The resulting model is validated against external gravity data and also regarding plausibility of geophysical interpretation. Finally, lithospheric density modelling applying the IGMAS+ software is performed based on this new gravity field model, and the resulting density model is compared to a model of the pre-GOCE area, thus evaluating the impact of GOCE on geophysical modelling of the lithosphere. It will be shown that artefacts in EGM2008 could be identified and eliminated especially in regions with no or very poor terrestrial data. Therefore, we conclude that with this regional gravity field model large-to medium-scale lithospheric modelling of the whole Andes region has now become possible.

Pail, Roland; Hosse, Michael; Horwath, Martin; Gutknecht, Ben; Holzrichter, Nils

2014-05-01

305

Boundary Layer Convergence Induced by Strong Winds across a Midlatitude THOMAS KILPATRICK, NIKLAS SCHNEIDER, AND BO QIU  

E-print Network

-integrated divergence in the warm-to-cold case. The turbulent stress divergence term changes over a shorter length scale KILPATRICK, NIKLAS SCHNEIDER, AND BO QIU Department of Oceanography, and International Pacific Research-induced MABL convergence is explored here with the Weather Research and Forecasting mesoscale model

Qiu, Bo

306

Evolutionary process of Beppu Bay in central Kyushu, Japan: a quantitative study of the basin-forming process controlled by plate convergence modes  

NASA Astrophysics Data System (ADS)

This integrated tectonic study reveals the basin-forming and deforming processes on an active margin. Southwest Japan (SWJ) is an island arc under the influence of oblique subduction of the Philippine Sea plate, which has provoked dextral slips on the arc-bisecting Median Tectonic Line (MTL). Plio-/Pleistocene sediments in Beppu Bay, a tectonic depression at the westernmost portion of the MTL, are categorized into lower (5 ~ 0.7 Ma), upper (0.7 ~ 0.3 Ma), and an auxiliary uppermost (0.3 Ma ~ present) unit in ascending order. Detailed seismic interpretation demonstrates that major structures in the deep interior of the basin are an older half-graben under a strong N-S extensional regime and a younger pull-apart sag that developed in a right-stepping part of the MTL as a result of late Quaternary-enhanced strike-slip rates on the fault. Sediments within the pull-apart have been deformed by later inversion events as a contraction phase arose. Conspicuous deformation of the hanging wall of the low-angle detachment of the basin was successfully reproduced by numerical modeling. Based on a discrete element method, this suggests that structural differences in the deformed sedimentary layers are caused by differences in the dip angles of the faults. Remarkable temporal changes in tectonic regimes around Beppu Bay and other areas of SWJ are probably related to transient modes of convergence, including the migration of the Euler pole, of the Philippine Sea plate since ca. 6 Ma.

Itoh, Yasuto; Kusumoto, Shigekazu; Takemura, Keiji

2014-12-01

307

Deformation record of 4-d accommodation of strain in the transition from transform to oblique convergent plate margin, southern Alaska (Invited)  

NASA Astrophysics Data System (ADS)

Crustal deformation at the transition from a dextral transform to subduction in the northern Cordillera is complicated by both the bend of the margin and the presence of low-angle subduction of an oceanic plateau, the Yakutat microplate, into the 'corner'. The dextral Denali Fault system located ~400 km inboard of the plate margin shows a similar transition from a dominantly strike-slip to transpressional regime as it curves to the west. Thermochronologic and structural studies in both areas indicate crustal response through the transition region is highly varied along and across strike. Previous thermochronology along the Fairweather fault SE of the St. Elias bend shows the most rapid exhumation occurs in close proximity to the fault, decreasing rapidly away from it. Enkelmann et al. (2010) and more recent detrital zircon FT (Falkowski et al., 2013 AGU abstract) show rapid and deep exhumation concentrated in the syntaxis, but over a fairly broad area continuing north beyond the Fairweather fault. Although the region is dominantly under ice, borders of the rapidly exhuming region appear to be previously identified major high-angle faults. This suggests that structures controlling the extreme exhumation may have significant oblique slip component, or, if flower structure, are reverse faults, and the region may be exhuming by transpression, with a significant component of pure shear. Southwest of the syntaxis, where convergence dominates over strike-slip, thin-skinned fold-and-thrust belts in the Yakutat microplate strata account for the shortening. The long-term record of convergence in this area is more cryptic due to sediment recycling through deep underplating and/or limited exhumation by upper crustal shortening, but a wide range of thermochronologic studies suggests that initial exhumation in the region began ~ 30 Ma and most rapid exhumation in the syntaxis began ~ 5 Ma. In the eastern Alaska Range a significant component of strike-slip, in addition to convergence, has been accommodated along the Denali Fault since E. Miocene. Southeast of the bend there is little evidence of convergence across the fault and Quaternary slip is ~12-13.5 mm/year. The eastern restraining bend of the Denali fault is much broader than the syntaxis and dextral slip continues at rates of ~10 mm/year, but the rock response to increasing obliquity is similar. Low and moderate-T cooling histories determined from a wide range of isotopic systems on minerals from bedrock show exhumation strongly localized on the north side of the high-angle Denali fault, south of the Hines Creek fault, since ~25 Ma. The structural record in ductilely deformed rocks from the most highly exhumed regions shows transpressive deformation over a few km wide region, but above the brittle-ductile transition strain becomes highly partitioned and is accommodated by thrust and normal faults on the north side of the bend. A connector fault between the Fairweather and Totschunda-Denali fault systems has been speculated on but it is not clear whether a single through-going fault is expressed at the surface. Any connector is likely a relatively young structure compared to the Fairweather and Denali systems' histories of long-lived oblique convergence. Overall, in both regions high-angle faults appear to be critical for controlling the location of major deep-seated and/or long-lived exhumation, and deformation at these geometrical complexities is dominated by transpression.

Roeske, S.; Benowitz, J.; Enkelmann, E.; Pavlis, T. L.

2013-12-01

308

Heat exchange in boundary layer on permeable plate at injection and combustion  

NASA Astrophysics Data System (ADS)

The peculiarities of the heat and mass exchange in a laminar boundary layer with combustion at the injection of the fuel mixture H2/N2 through the permeable surface are considered. It is shown that at a certain value of the injection parameter, the value of the heat flux into the wall averaged over the length has a maximum. An analytic estimate is proposed for determining the maximum heat flux at the combustion depending on the injection intensity. The obtained relations agree with the results of experimental studies and numerical modelling.

Lukashov, V. V.; Terekhov, V. V.; Hanjali?, K.

2014-12-01

309

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)

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.

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

1996-01-01

310

Low heat flow inferred from >4Gyr zircons suggests Hadean plate boundary interactions  

NASA Astrophysics Data System (ADS)

The first ~600 million years of Earth history (the `Hadean' eon) remain poorly understood, largely because there is no rock record dating from that era. Detrital Hadean igneous zircons from the Jack Hills, Western Australia, however, can potentially provide insights into the conditions extant on our planet at that time. Results of geochemical investigations using these ancient grains have been interpreted to suggest the presence of a hydrosphere and continental crust before 4Gyr. An underexploited characteristic of the >4Gyr zircons is their diverse assemblage of mineral inclusions. Here we present an examination of over 400 Hadean zircons from Jack Hills, which shows that some inclusion assemblages are conducive to thermobarometry. Our thermobarometric analyses of 4.02-4.19-Gyr-old inclusion-bearing zircons constrain their magmatic formation conditions to about 700°C and 7kbar. This result implies a near-surface heat flow of ~75mWm-2, about three to five times lower than estimates of Hadean global heat flow. As the only site of magmatism on modern Earth that is characterized by heat flow of about one-quarter of the global average is above subduction zones, we suggest that the magmas from which the Jack Hills Hadean zircons crystallized were formed largely in an underthrust environment, perhaps similar to modern convergent margins.

Hopkins, Michelle; Harrison, T. Mark; Manning, Craig E.

2008-11-01

311

Influence of boundary stress singularities on the vibration of clamped and simply-supported sectorial plates with arbitrary radial edge conditions  

NASA Astrophysics Data System (ADS)

This paper extends previous studies made for sectorial plates having re-entrant (i.e., interior) corners causing stress singularities, to provide accurate frequencies when the circular edge is either clamped or simply-supported. An extensive review of the literature is also given herein spanning nearly the past two decades explaining the free vibration characteristics of sectorial plates. In this work, the classical Ritz method is employed with two sets of admissible functions assumed for the transverse vibratory displacements. These sets include: (1) mathematically complete algebraic-trigonometric polynomials which guarantee convergence to exact frequencies as sufficient terms are retained and (2) corner functions which account for the bending moment singularities at the re-entrant vertex corner of the radial edges having arbitrary edge conditions. Extensive convergence studies summarized herein confirm that the corner functions substantially enhance the convergence and accuracy of non-dimensional frequencies for sectorial plates having either a clamped or hinged circumferential edge and various combinations of clamped, hinged, and free conditions on the radial edges. Accurate (to at least four significant figure) frequencies and normalized contours of the transverse vibratory displacement are presented for the spectra of sector angles [90°, 180° (semi-circular), 270°, 300°, 330°, 350°, 355°, 360° (complete circular)] causing a re-entrant vertex corner of the radial edges. For sector angles of 360°, a clamped-clamped, clamped-hinged, clamped-free, hinged-free or free-free radial crack ensues. One general observation is the substantial reduction in the first six frequencies as the sector angle increases for all plates, except in the first two modes of plates having free-free radial edges.

McGee, O. G.; Kim, J. W.; Kim, Y. S.

2010-12-01

312

What on Earth is Plate Tectonics?  

NSDL National Science Digital Library

This abbreviated explanation of the subject of plate tectonics is divided into several parts. The first section, entitled Into the Earth, describes the crust, mantle and core of the Earth, while the next section shows a world map with the plates delineated. The section called Action at the Edges uses text and diagrams to explain what is occurring at the plate boundaries. Links lead to a detailed discussion of converging boundaries including ocean-ocean, ocean-continental, and continental-continental. A wide range illustration shows both surface and cross-section views of plate interaction and a link leads to a similar diagram with labels. In the Moving through Time section, a series of color-coded maps is shown, illustrating the relative position of the continents over the past 650 million years. The last section shows a paleogeographic reconstruction of the Earth and explains how paleomagnetism, magnetic anomalies, paleobiogeography, paleoclimatology, and geologic history are used to create it.

313

Vibration of skewed cantilever plates and helicoidal shells  

NASA Technical Reports Server (NTRS)

Theoretical vibration frequencies and mode shapes are obtained for skewed plates and helicoidal shells with a cantilever boundary. Using Hamilton's law of varying action, a power series solution is developed to obtain converged numerical results for the five lowest frequencies. Effects of geometrical variables such as aspect ratio, sweep angle and shell radius to thickness ratio are investigated. Accuracy of the solution method is substantiated by comparison with existing skewed plate spherical cap, and conical shell results.

Beres, D. P.; Bailey, C. D.

1975-01-01

314

Caribbean plate tectonics  

NSDL National Science Digital Library

This illustration available at Wikimedia Commons shows the plate tectonic setting in the Caribbean. Plate boundaries are color-coded by margin type and plate motions are noted with direction and magnitude in mm/yr.

Sting; Commons, Wikimedia

315

Physical Optics Curved-Boundary Dielectric Plate Scattering Formulas for an Accurate and Efficient Electromagnetic Characterization of a Class of Natural Targets  

Microsoft Academic Search

Closed-form representations of the physical optics (PO) field scattered in the far zone by plane penetrable dielectric angular sectors of arbitrary opening angle featuring a conical-section boundary are derived in terms of incomplete cylindrical functions (ICFs). The proposed expressions, possibly in combination with PO formulas for the scattering from polygonal plates, allow one to evaluate the scattering from flat dielectric

Andrea Vallecchi

2008-01-01

316

On MHD boundary-layer flow and mass transfer past a vertical plate in a porous medium with constant heat flux  

Microsoft Academic Search

Purpose – The hydromagnetic mixed convection flow of an incompressible viscous electrically conducting fluid and mass transfer over a vertical porous plate with constant heat flux embedded in a porous medium is investigated. Design\\/methodology\\/approach – Using the Boussinesq and boundary-layer approximations, the fluid equations for momentum, energy balance and concentration governing the problem are formulated. These equations are solved numerically

O. D. Makinde

2009-01-01

317

Direct numerical simulation methods of hypersonic flat-plate boundary layer in thermally perfect gas  

NASA Astrophysics Data System (ADS)

High-temperature effects alter the physical and transport properties of air such as vibrational excitation in a thermally perfect gas, and this factor should be considered in order to compute the flow field correctly. Herein, for the thermally perfect gas, a simple method of direct numerical simulation on flat-plat boundary layer is put forward, using the equivalent specific heat ratio instead of constant specific heat ratio in the N-S equations and flux splitting form of a calorically perfect gas. The results calculated by the new method are consistent with that by solving the N-S equations of a thermally perfect gas directly. The mean flow has the similarity, and consistent to the corresponding Blasius solution, which confirms that satisfactory results can be obtained basing on the Blasius solution as the mean flow directly in stability analysis. The amplitude growth curve of small disturbance is introduced at the inlet by using direct numerical simulation, which is consistent with that obtained by linear stability theory. It verified that the equation established and the simulation method is correct.

Jia, WenLi; Cao, Wei

2014-01-01

318

Present-Day Kinematics of the Central Mediterranean Plate Boundary Region from Large GPS Network Analysis Using the Ambizap Algorithm  

NASA Astrophysics Data System (ADS)

The large, recent increase of continuous GPS (CGPS) stations in the Central Mediterranean plate boundary zone offers the opportunity to study in detail the present-day kinematics of this actively deforming region. CGPS data from scientific and commercial networks in the Italian region is now available from more than 350 stations, including more than 130 from the RING network deployed by the Istituto Nazionale di Geofisica e Vulcanologia. The RING stations all have high quality GPS monuments and are co- located with broadband or very broadband seismometers and strong motion sensors. The analysis presented here also uses far-field data to provide reference frame control, bringing the total to over 580 CGPS stations. GPS ambiguity resolution of such a large amount of data presents a serious challenge in terms of processing time. Many scientific GPS data processing software packages address this problem by dividing the network into several clusters. In contrast, this analysis uses the new Ambizap GPS processing algorithm (Blewitt, 2008) to obtain unique, self-consistent daily ambiguity-fixed solutions for the entire network. Ambizap allows for a rapid and multiple reanalysis of large regional networks such the one presented in this work. Tests show that Ambizap reproduces solutions from time-prohibitive full-network ambiguity resolution to much less than 1 mm. Single station GPS data are first processed with the GIPSY-OASIS II software by the precise point positioning (PPP) strategy (Zumberge et al., 1997) using JPL products from ftp://sideshow.jpl.nasa.gov. Integer ambiguity resolution is then applied using Ambizap. The resulting daily solutions are aligned to the ITRF2005 reference frame. Then, using the CATS software (Williams, 2007), time series are cleaned to remove outliers and are analyzed for their noise properties, linear velocities, periodic signals and antenna jumps. Stable plate reference frames are realized by minimizing the horizontal velocities at more than 70 and 20 sites on the Eurasia and Nubia plates, respectively. The daily RMS scatter for the east coordinates (derived from PPP) in this frame is typically in the range 2-4 mm before applying Ambizap, and 1-2 mm after applying Ambizap. The solutions are then evaluated with regard to the numerous scientific motivations behind this project, ranging from the definition of strain distribution and microplate kinematics within the plate boundary, to the evaluation of tectonic strain accumulation on active faults. References: Blewitt, G. (2008), Fixed-point theorems of GPS carrier phase ambiguity resolution and their application to massive network processing: 'Ambizap', J. Geophys. Res., doi:10.1029/2008JB005736, in press. Williams, S.D.P. (2007), CATS: GPS coordinate time series analysis software, GPS solut., doi:10.1007/s10291-007-0086-4 Zumberge, J. F., M. B. Heflin, D. C. Jefferson, M. M. Watkins, and F. H. Webb (1997), Precise point positioning for the efficient and robust analysis of GPS data from large networks, J. Geophys. Res., 102, 5005-501

D'Anastasio, E.; D'Agostino, N.; Avallone, A.; Blewitt, G.

2008-12-01

319

Integration of the Plate Boundary Observatory and Existing GPS Networks in Southern California: A Multi Use Geodetic Network  

NASA Astrophysics Data System (ADS)

The ultra-stable GPS monument design developed by Southern California Geodetic Network (SCIGN) in the late 1990s demonstrates sub-millimeter errors on long time series where there are a high percentage of observations and low multipath. Following SCIGN, other networks such as PANGA and BARGEN have adopted the monument design for both deep drilled braced monuments (DDBM = 5 legs grouted 10.7 meters into bedrock/stratigraphy) and short drilled braced monuments (SDBM = 4 legs epoxied 2 meters into bedrock). A Plate Boundary Observatory (PBO) GPS station consists of a "SCIGN" style monument and state of the art NetRS receiver and IP based communications. Between the years 2003-2008 875 permanent PBO GPS stations are being built throughout the United States. Concomitant with construction of the PBO the majority of pre-existing GPS stations that meet stability specifications are being upgraded with Trimble NetRS and IP based communications to PBO standards under the EarthScope PBO Nucleus project. In 2008, with completed construction of the Plate Boundary Observatory, more than 1100 GPS stations will share common design specifications and have identical receivers with common communications making it the most homogenous geodetic network in the World. Of the 875 total Plate Boundary Observatory GPS stations, 211 proposed sites are distributed throughout the Southern California region. As of August 2007 the production status is: 174 stations built (81 short braced monuments, 93 deep drilled braced monuments), 181 permits signed, 211 permits submitted and 211 station reconnaissance reports. The balance of 37 stations (19 SDBM and 18 DDBM) will be built over the next year from Long Valley to the Mexico border in order of priority as recommended by the PBO Transform, Extension and Magmatic working groups. Fifteen second data is archived for each station and 1 Hz as well as 5 Hz data is buffered to be triggered for download in the event of an earthquake. Communications equipment includes CDMA Proxicast modems, Hughes Vsat, Intuicom 900 MHz Ethernet bridge radios and several "real-time" sites use 2.4 GHz Wilan radios. Ultimately, 125 of the existing former-SCIGN GPS stations will be integrated into the So Cal region of PBO, of which 25 have real-time data streams. At the time of this publication the total combined Southern California region has over 40 stations streaming real-time data using both radios and CDMA modems. The real-time GPS sites provide specific benefits beyond the standard GPS station: they can provide a live correction for local surveyors and can be used to trigger an alarm if large displacements are recorded. The cross fault spatial distribution of these 336 GPS stations in the seismically active southern California region has the grand potential of augmenting a strong motion earthquake early warning system.

Walls, C.; Blume, F.; Meertens, C.; Arnitz, E.; Lawrence, S.; Miller, S.; Bradley, W.; Jackson, M.; Feaux, K.

2007-12-01

320

Measuring present-day strain rates along the Fish Lake Valley fault system, Pacific-North America plate boundary  

NASA Astrophysics Data System (ADS)

A fundamental issue in modern tectonics is the degree to which spatial and temporal variations exist in strain accumulation and release along evolving plate boundaries. The eastern California shear zone (ECSZ) is located east of the San Andreas fault and contains a complex network of structures that accommodate ~25% of the relative displacement between the Pacific and North American plates. Geodetic data indicate strain accumulation at a rate of 12±2 mm/yr along four main structures in the ECSZ. The Death Valley-Fish Lake Valley fault, the prominent and longest fault in the ECSZ at ~300km, is observed to be the fastest slipping fault in the region storing elastic strain at a rate of 3-8 mm/yr. Recently determined long-term slip rates (103 - 106 year timescale) indicate a pattern of decreasing velocity moving north through Fish Lake Valley (FLV) from ~6 mm/yr to zero, presumably because strain is transferred onto extensional faults located to the east. This study intends to determine the short-term (decadal timescale) GPS-derived displacement fields along the FLV fault to test whether spatial patterns of geodetic and geologic rates are consistent through time. In a series of two GPS campaigns in 2010 and 2011, eleven geodetic monuments, spaced 15-20 km apart, were surveyed in and around FLV. In addition, campaign data from previous surveys has been acquired from UNAVCO. The combined data sets are used to calculate the relative motion along the fault. Modern strain rates will be presented in comparison to published long-term rates.

Johnson, C. W.; Frankel, K. L.; Newman, A. V.; Lifton, Z. M.

2011-12-01

321

Earthquake-cycle models of the Pacific-North America plate boundary at Point Reyes, California  

NASA Astrophysics Data System (ADS)

At Point Reyes, California, about 36 mm/yr of Pacific-North America relative plate motion is accommodated by (from west to east) the San Andreas, Rodgers Creek, Napa and Green Valley faults. We have developed a suite of viscoelastic earthquake cycle models which take into account the timing and recurrence intervals of large earthquakes on these faults, and are calibrated to the current GPS velocity field. We infer a locking depth of about 12 km for all four faults, consistent with previous analyses of local hypocenter depths (e.g., d'Alessio et al, 2005). Low-viscosity viscous shear zones appear to be required for our models to fit the GPS velocities. In order to fit the high surface velocity gradient across this set of faults, the effective viscosity for the lower crust and mantle must exceed 10^20 Pa s. A modest contrast in effective viscosity of the lower crust and upper mantle across the San Andreas Fault, with higher viscosity values (at least 5 x 10^20 Pa s) to the east, is also indicated. In the region between the Rodgers Creek Fault and the Green Valley Fault, GPS data indicate a higher strain rate than our models can explain. Even after shifting the entire Green Valley Fault slip rate (9 mm/yr) westward to the Napa Fault, the misfit is not eliminated. Double-difference hypocenter data (Waldhauser and Schaff, 2008) suggest the presence of another fault zone between the Napa Fault and the Green Valley Fault, and that all three of these faults dip toward the west. This offsets their deep, creeping extensions several km from their surface traces. A preliminary model with a suitably offset, deep Green Valley Fault extension cuts the WRSS misfit to GPS site velocities by over a factor of two. Since non-vertical fault dips are often missed in seismic studies (e.g. Fuis et al., 2008), creeping shear zones at depth may routinely be offset by several kilometers from their surface traces, unless alternate evidence of their position at depth is available (e.g. Shelly et al., 2009). This may lead to incorrect inferences of material asymmetry, or errors in the attribution of slip rates to closely spaced, active faults.

Vaghri, A.; Hearn, E. H.

2011-12-01

322

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)

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.

Sivells, James C; Deters, Owen J

1946-01-01

323

Regional provenance study of Eocene clastic sedimentary rocks within the South America-Caribbean plate boundary zone using detrital zircon geochronology  

NASA Astrophysics Data System (ADS)

Previous on- and offshore studies have postulated that the Caribbean plate has translated hundreds of kilometers eastward during the Cenozoic along strike-slip and oblique thrust faults bounding the northern margin of the continental South America plate. Two previously proposed tectonic-sedimentary models to explain the complex linkages between plate motions and sedimentation within the broad plate boundary zone include: 1) eastward bulldozing by the Caribbean plate of a single, large point source, thick Eocene proto-Maracaibo deltaic system of northwestern South America, over 1000 km to the east and incorporation of these continentally derived sediments into the ˜ 12-km-thick Barbados accretionary prism along the leading edge of the Caribbean plate; and 2) eastward bulldozing by less than 300 km of smaller point and line sources of Eocene and younger clastic sediments derived from erosion of the Guyana shield located in north-central and northeastern South America. We test both models by sampling eight Eocene localities that span a 1200-km-length of the plate boundary zone from the proto-Maracaibo delta in western Venezuela to Barbados Island in the subaerial part of the large accretionary prism bounding the eastern margin of the Caribbean plate. Ages of 972 single grains from samples at these eight localities support the multiple-source model, in which the Barbados prism was partly constructed from the bulldozing and incorporation of smaller point and line sources derived from older-than 1500 Ma crustal provinces of the Precambrian Guyana shield in central and northeastern South America. Eocene clastic sediments of the proto-Maracaibo delta derived from Paleozoic and Precambrian crustal provinces in northwestern South America are distinct in their ranges of detrital zircon ages from the ranges of the Guyana shield sources to the east.

Xie, Xiangyang; Mann, Paul; Escalona, Alejandro

2010-03-01

324

Strain accumulation controls failure of a plate boundary zone: Linking deformation of the Central Andes and lithosphere mechanics  

NASA Astrophysics Data System (ADS)

We make use of observations on orogenic strain accumulation and deformation partitioning in the Central Andes to explore the backarc strength evolution at the lithospheric scale. In plan view, the Altiplano-Puna plateaux experienced rapid initial increase of surface area undergoing active deformation during the Cenozoic. Beyond the maximum lateral extent reached around 10-15 Ma (40-50% of entire proto-Andes undergoing deformation) at 10-20% total strain, rapid localization initiated at the eastern flank of the Altiplano (Inter- and Subandean thrust belt) but not at the Puna latitude. Localization was associated with a significant increase in bulk shortening rate. Average fault slip rates equally increased by an order of magnitude following a protracted period of stable average rates. Estimates of strength evolution based on force balance calculations and critical wedge analysis suggest significant backarc weakening driving this change after the Middle Miocene. Strain accumulation led to localization and weakening with development of a detachment propagating through crust and upper mantle. We find that lithosphere-scale failure resulting from strain weakening beyond a critical strain threshold (c. 20%) and fault coalescence with formation of a weak detachment in shales (effective coefficient of friction < 0.1) plays a key role in the evolution of the Andes. Strain-related lithosphere weakening appears to dominate over the impact of external forcing mechanisms, such as variations of plate convergence, mantle-assisted processes, or erosion. Comparison of these orogen-scale observations with experimental rock rheology indicates substantial similarity of deformation behavior with similar weakening thresholds across a wide range of scales.

Oncken, O.; Boutelier, D.; Dresen, G.; Schemmann, K.

2012-12-01

325

Crustal structure and fluid migration studies in the southwestern Taiwan convergent zone using seismic tomography  

Microsoft Academic Search

The presence of bottom simulating reflections (BSRs) is well established observationally in the offshore region of the southwestern Taiwan. The geochemical and geologic setting in a convergent plate boundary exerts specific controls on the formation of a BSR and the inferred distribution of gas hydrates. Along the southern Taiwan active margin, BSR phases could be detected both across and along

W. Cheng; T. K. Wang; S. Hsu; C. Lee; C. Liu

2010-01-01

326

Plume Capture by Divergent Plate Motions: Implications for the Distribution of Hotspots, Geochemistry of Mid-Ocean Ridge Basalts, and Heat Flux from the Core-Mantle Boundary  

NASA Astrophysics Data System (ADS)

The coexistence of mantle plumes with plate-scale flow is problematic in geodynamics. Significant problems include the fixity of hotspots with respect to plate motions, the spatial distribution and duration of hotspots, the geophysical and geochemical signatures of plume-ridge interactions, and the relation between mantle plumes and heat flux across the core-mantle boundary. We present results from laboratory experiments aimed at understanding the effects of an imposed large-scale circulation on thermal convection at high Rayleigh number (up to 109) in a fluid with a strongly temperature-dependent viscosity. In a large tank, a layer of corn syrup is heated from below while being stirred by large-scale flow due to the opposing motions of a pair of conveyor belts immersed in the syrup at the top of the tank. Three regimes are observed, depending on the velocity ratio V of the imposed horizontal flow velocity to the rise velocity of plumes ascending from the hot boundary. When V<<1, large scale circulation has a negligible effect and convective upwelling occurs as randomly-spaced axisymmetric plumes that interact with one another. When V>10, plume instabilities are suppressed entirely and the heat flux from the hot lower boundary is carried by a central sheet-like upwelling. At intermediate V, ascending plumes are advected along the bottom boundary layer, and the heat flux from the boundary is found to scale (according to a simple boundary layer theory) with V and the ratio of the viscosity of cold fluid above the thermal boundary layer to the viscosity of the hottest fluid in contact with the bottom boundary. For large viscosity ratios (10-100), only about 1/5th or less of the total heat flux from the hot boundary layer is carried by plume instabilities, even for modest imposed horizontal flow velocities (V of order 1). When applied to Earth, our results suggest that plate-scale flow focuses ascending mantle plumes toward mid-ocean ridges, and that plumes may be entirely captured by sufficiently rapid upwelling flow beneath ridges. This behavior may explain why hotspots are more abundant near slow-spreading ridges than near fast ridges. Such a model also predictes, in apparent accord with geochemical observations, that while slow ridges exhibit more variable isotopic and trace element signatures than fast ridges, their average signatures should be about the same. The laboratory experiments further suggest that plumes originating at the core-mantle boundary (CMB) may carry only a small fraction of the total CMB heat flux, the remainder being swept away by large-scale mantle flow associated with plate-scale convection.

Jellinek, A. M.; Richards, M. A.

2001-12-01

327

Plio-Quaternary paleostresses in the Atlantic passive margin of the Moroccan Meseta: Influence of the Central Rif escape tectonics related to Eurasian-African plate convergence  

NASA Astrophysics Data System (ADS)

The Atlantic Moroccan Meseta margin is affected by far field recent tectonic stresses. The basement belongs to the variscan orogen and was deformed by hercynian folding and metamorphism followed by a post-Permian erosional stage, producing the flat paleorelief of the region. Tabular Mesozoic and Mio-Plio-Quaternary deposits locally cover the Meseta, which has undergone recent uplift, while north of Rabat the subsidence continues in the Gharb basin, constituting the foreland basin of the Rif Cordillera. The Plio-Quaternary sedimentary cover of the Moroccan Meseta, mainly formed by aeolian and marine terraces deposits, is affected by brittle deformations (joints and small-scale faults) that evidence that this region - considered up to date as stable - is affected by the far field stresses. Striated faults are recognized in the oldest Plio-Quaternary deposits and show strike-slip and normal kinematics, while joints affect up to the most recent sediments. Paleostress may be sorted into extensional, only affecting Rabat sector, and three main compressive groups deforming whole the region: (1) ENE-WSW to ESE-WNW compression; (2) NNW-SSE to NE-SW compression and (3) NNE-SSW compression. These stresses can be attributed mainly to the NW-SE oriented Eurasian-African plate convergence in the western Mediterranean and the escape toward the SW of the Rif Cordillera. Local paleostress deviations may be related to basement fault reactivation. These new results reveal the tectonic instability during Plio-Quaternary of the Moroccan Meseta margin in contrast to the standard passive margins, generally considered stable.

Chabli, Ahmed; Chalouan, Ahmed; Akil, Mostapha; Galindo-Zaldívar, Jesús; Ruano, Patricia; Sanz de Galdeano, Carlos; López-Garrido, Angel Carlos; Marín-Lechado, Carlos; Pedrera, Antonio

2014-07-01

328

New c. 270 kyr strike-slip and uplift rates for the southern Alpine Fault and implications for the New Zealand plate boundary  

NASA Astrophysics Data System (ADS)

Along 100 km of the Alpine Fault, major valleys and glacial deposits can be matched across an 8000 m dextral offset. We use paleontologic and stratigraphic age constraints to date c. 270 ka marine sediments uplifted to 600 m elevation and overlying c. 270 ka glacial deposits related to the 8000 m dextral offset. These constraints yield a fault-proximal Australian plate uplift rate of 2.6 (-0.5/+0.4) mm/yr and an Alpine Fault dextral slip rate of 29.6 (-2.5/+4.5) mm/yr. Our rates resolve an apparent along-strike drop in strike-slip rate and instead support a relatively constant along-strike dextral slip rate of ˜28 mm/yr (˜80% of current Australian-Pacific plate boundary motion). We argue that the rate of dextral slip on the southern Alpine Fault has been relatively constant over the last ?3.5 myr, and that ductile fault processes may rate-limit the fault from accommodating a progressively higher percentage of plate boundary motion through time (i.e., the fault reached maturity long ago). The spatiotemporally constant strike-slip rate of the southern Alpine Fault and a previously published paleoseismic record of near-regular earthquake recurrence both characterize the Alpine Fault as a mature plate boundary fault zone that behaves in a constant way with behavior predictable over timescales of thousands and hundreds of thousands of years.

Barth, N. C.; Kulhanek, D. K.; Beu, A. G.; Murray-Wallace, C. V.; Hayward, B. W.; Mildenhall, D. C.; Lee, D. E.

2014-07-01

329

The Plate Boundary Observatory Permanent Global Positioning System Network on Augustine Volcano Before and After the 2006 Eruption  

USGS Publications Warehouse

In September of 2004, UNAVCO and the National Science Foundation (NSF) funded EarthScope Plate Boundary Observatory (PBO) installed five permanent Continuous Global Positioning System (CGPS) stations on Augustine Volcano, supplementing one existing CGPS station operated by the Alaska Volcano Observatory. All six CGPS stations proved crucial to scientists for detecting and monitoring the precursory deformation of the volcano beginning in early May 2005, as well as for monitoring the many subsequent small inflationary and deflationary episodes that characterized the 2006 eruption. Following the eruption, in September of 2006, PBO added six additional permanent CGPS stations. The 2006 eruption and its precursors were the first significant activity of the volcano in 20 years and the PBO CGPS network provided an unprecedented opportunity to monitor and detect volcanic ground deformation on an erupting Alaskan stratovolcano. Data from the new CGPS stations coupled with the existing seismic stations provided scientists with the first real opportunity to use geodetic data and real time seismic data to assess the volcanic hazards before, during, and after an Alaskan eruption.

Pauk, Benjamin A.; Jackson, Michael; Feaux, Karl; Mencin, David; Bohnenstiehl, Kyle

2010-01-01

330

The effect of elastic boundary conditions on the dynamic response of rectangular plates. M.S. Thesis  

NASA Technical Reports Server (NTRS)

Natural frequencies and forced steady-state harmonic response for the vibration of uniform rectangular plates with edges elastically restrained against rotation and transverse translation are addressed. A single mode Rayleigh-Ritz solution is derived using functions that describe the normal modes of vibration of a beam whose ends are elastically restrained. The finite element solution is obtained for comparison. MACSYMA symbolic manipulation system is implemented as an aid to the mathematical rigor of the Ritz approach, and NASTRAN finite element code is used to model the mechanical system. Comparisons are made to published results and the solutions of this study are found to give lower frequencies for some values of boundary restraint. Steady-state harmonic amplitudes of displacement and acceleration are found to agree favorably for the two solutions. Low predictions of steady-state strain from NASTRAN result in some cases when compared to the Ritz values. Finally, a subjective assessment is made about the merit of using MACSYMA and NASTRAN.

Brewer, Terry K.

1988-01-01

331

NO excitation and thermal non-equilibrium within a flat plate boundary layer in an air plasma  

NASA Astrophysics Data System (ADS)

Optical emission spectroscopy experiments are carried out by recording the radiation from the ? transitions of nitrogen monoxide in an air inductively coupled plasma in interaction with a water-cooled metallic flat plate at moderate pressure. The calibrated results allow to derive the vibrational and rotational temperatures of the NO( A 2 ? +) excited state as well as its densities in the free jet and within the boundary layer by comparison with calculated spectra. Those results are compared with previous ones concerning temperatures and densities of the ground states of the majority species (N2, O2 and NO) that were obtained by laser techniques. As for the NO( X 2 ?) ground state, vibration and rotation of the excited state are found out of equilibrium. The NO( A 2 ? +) excited state is found to be populated by an energy transfer from the metastable N2(A3\\varSigma +u). The steady state of the plasma allows using this property to derive N2(A3\\varSigma +u) densities and N2 electronic excitation temperatures. Close to the wall, a production of excited NO by a catalytic process is also considered involving N2(A3\\varSigma +u) as source of adsorbed atoms. The present results confirm that the kinetic temperature cannot be compared to the rotational temperature derived from optical emission spectroscopy in such plasma conditions.

Studer, D.; Boubert, P.; Vervisch, P.

2010-11-01

332

3-D electromagnetic imaging of a Palaeozoic plate-tectonic boundary segment in SW Iberian Variscides (S Alentejo, Portugal)  

NASA Astrophysics Data System (ADS)

In SW Iberian Variscides, the boundary between the South Portuguese Zone (SPZ) and the Ossa Morena Zone (OMZ) corresponds to a major tectonic suture that includes the Beja Acebuches Ophiolite Complex (BAOC) and the Pulo do Lobo Antiform Terrane (PLAT). Three sub-parallel and approximately equidistant MT profiles were performed, covering a critical area of this Palaeozoic plate-tectonic boundary in Portugal; the profiles, running roughly along an NE-SW direction, are sub-perpendicular to the main Variscan tectonic features. Results of the three-dimensional (3-D) modelling of MT data allow to generate, for the first time, a 3-D electromagnetic imaging of the OMZ-SPZ boundary, which reveals different conductive and resistive domains that display morphological variations in depth and are intersected by two major sub-vertical corridors; these corridors coincide roughly with the NE-SW, Messejana strike-slip fault zone and with the WNW-ESE, Ferreira-Ficalho thrust fault zone. The distribution of the shallow resistive domains is consistent with the lithological and structural features observed and mapped, integrating the expected electrical features produced by igneous intrusions and metamorphic sequences of variable nature and age. The development in depth of these resistive domains suggests that: (1) a significant vertical displacement along an early tectonic structure, subsequently re-taken by the Messejana fault-zone in Late-Variscan times, has to be considered to explain differences in deepness of the base of the Precambrian-Cambrian metamorphic pile; (2) hidden, syn- to late-collision igneous bodies intrude the meta-sedimentary sequences of PLAT; (3) the roots of BAOC are inferred from 12 km depth onwards, forming a moderate resistive band located between two middle-crust conductive layers extended to the north (in OMZ) and to the south (in SPZ). These conductive layers overlap the Iberian Reflective Body (evidenced by the available seismic reflection data) and are interpreted as part of an important middle-crust décollement developed immediately above or coinciding with the top of a graphite-bearing granulitic basement.

Vieira da Silva, N.; Mateus, A.; Monteiro Santos, F. A.; Almeida, E. P.; Pous, J.

2007-12-01

333

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)

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.

Gupta, R. N.

1972-01-01

334

The migration of plate boundaries in SE Sicily: Influence on the large-scale kinematic model of the African promontory in southern Italy  

NASA Astrophysics Data System (ADS)

A detailed field mapping, coupled with structural analyses and morphological investigation, has been carried out along the northern and western borders of the Hyblean Plateau (SE Sicily), in order to define the nature and the kinematics of a major Quaternary fault belt. This, here designed as the Scicli Line Fault Belt, is composed of two N50 oriented extensional basins that, linked by a regional N10 trending transfer zone, originated during the Early Pleistocene and experienced, since the Late Quaternary, a positive tectonic inversion. In both the two stages of deformation, the Scicli Line Fault Belt has been characterised by displacement-rate comparable with the relative velocities measured between the distinct plates composing the central Mediterranean region. In the period going from 1.5-1.2 to 0.85 Ma, the fault belt accommodated the entire divergence between Adria and Nubia. At present, the Scicli Line Fault Belt absorbs most of the Nubia-Eurasia convergence, while the western divergent margin of the Adria microplate has jumped to the eastern and the southern margins of the Hyblean Plateau, along the Late Quaternary Siculo-Calabrian Rift Zone. The off-shore prolongation of the two tectonic boundaries of the Hyblean Plateau has been recognised in the Sicily Channel, where they are both interrupted by a WNW-ESE oriented dextral fault. According to our reconstruction, the Hyblean Plateau represents an isolated lithospheric block, whose evolution can be related to the propagation of the western divergent margin of the Adria microplate, accompanied with the southward migration of the triple junction between Eurasia, Nubia and Adria. In this new large-scale kinematic picture, the GPS velocity measured in the Hyblean region, at the permanent site of NOTO, is actually representative of the local kinematics, rather than of the entire African promontory of southern Italy. This implies a correction of previous regional kinematic models based on combination of GPS vectors. In particular, our data constrain a new interpretation both for the kinematics along the E-W oriented Nubia-Eurasia margin, dominated by prevalent dextral deformation rather than reverse motions, and for the intraplate deformation in the Sicily Channel, within the Africa promontory, which would be dominated by a roughly N110° oriented extension. This conclusion has implication also on the mechanism and the origin of the Pantelleria-Linosa-Malta Rift that is here interpreted as a transtensive feature developed along a major transform fault, rather than the result of passive rifting induced by the Nubia-Eurasia collision, as it is currently interpreted.

Catalano, S.; De Guidi, G.; Romagnoli, G.; Torrisi, S.; Tortorici, G.; Tortorici, L.

2008-03-01

335

New insights into North America-Pacific plate boundary deformation from Lake Tahoe, Salton Sea and Southern Baja California  

E-print Network

to the Pacifi c Plate: Tectonics, v. 8, p. 99-115. Stock,c North America plate tectonics of the Neogene southwesternplate motion partitioning and the transition to seafl oor spreading in the Gulf of California: Tectonics,

Brothers, Daniel Stephen

2009-01-01

336

Permeability in sediments and their role in large slip near the surface of the plate boundary fault in the Japan Trench  

NASA Astrophysics Data System (ADS)

Fluid transport properties such as permeability, porosity, and specific storage are significant parameters that affect earthquake dynamic process. Thermal pressurization model (Mitsui et al., 2012, Earth and Planetary Science Letters) and shallow strong patch model (Kato and Yoshida, 2011, Geophysical Research Letters) were proposed to explain the giant earthquake in the Tohoku area, and transport property around the plate boundary fault is an important factor that impact on both models. Therefore we measured the transport properties of shallow sediments sampled around the plate boundary near the Japan Trench in the IODP expedition 343 at confining pressures up to 40 MPa. The permeabilities of samples from the shallow plate boundary fault at 820 mbsf were very low at 10 -20 m2, equivalent to a hydraulic diffusivity of 10-10 m2/s. Permeability in the core of the fault zone at the plate boundary were lower than those in the immediately overlying and underling sediments and the surrounding intact sediment, suggesting that the plate boundary fault can act as a barrier for fluid flow. Low permeability and high specific storage in the shallow plate boundary fault create a strong potential for dynamic fault weakening due to fluid pressurization with frictional heating, even when the initial shear stress is low. Our investigation supports the hypothesis that thermal pressurization on the fault plane induced the extremely large slip in the shallow part of the subduction zone during the Tohoku earthquake. As the fault zone has a lower permeability than the surrounding sediments and a higher clay content, pore pressure generation at depth by dehydration of clay minerals can explain formation of the shallow strong patch on the fault more reasonably than continuous fluid influx from the subducting oceanic crust proposed by Yoshida and Kato (2011, Geophysical Research Letters). Although there are many possible mechanisms of fault weakening, thermal pressurization can act relatively efficiently as slip begins, even at shallow depths. Therefore thermal pressurization is the most likely trigger mechanism for the large shallow displacement of the Tohoku earthquake.

Tanikawa, W.; Hirose, T.; Mukoyoshi, H.; Tadai, O.; Lin, W.

2013-12-01

337

Modulation of mantle plumes and heat flow at the core mantle boundary by plate-scale flow: results from laboratory experiments  

NASA Astrophysics Data System (ADS)

We report results from analog laboratory experiments, in which a large-scale flow is imposed upon natural convection from a hot boundary layer at the base of a large tank of corn syrup. The experiments show that the subdivision of the convective flow into four regions provides a reasonable conceptual framework for interpreting the effects of large-scale flow on plumes. Region I includes the area of the hot thermal boundary layer (TBL) that is thinned by the large-scale flow, thereby suppressing plumes. Region II encompasses the critically unstable boundary layer where plumes form. Region III is the area above the boundary layer that is devoid of plumes. Region IV comprises the area of hot upwelling and plume conduits. Quantitative analysis of our experiments results in a scaling law for heat flux from the hot boundary and for the spatial extent of plume suppression. When applied to the Earth's core-mantle boundary (CMB), our results suggest that large-scale mantle flow, due to sinking lithospheric plates, can locally thin the TBL and suppress plume formation over large fractions of the CMB. Approximately 30% of heat flow from the core may be due to increased heat flux from plate-scale flow. Furthermore, CMB heat flux is non-uniformly distributed along the CMB, with large areas where heat flux is increased on average by a factor of 2. As a consequence, the convective flow pattern in the outer core may be affected by CMB heat-flux heterogeneity and sensitive to changes in plate-scale mantle flow. Because of plume suppression and 'focusing' of hot mantle from the CMB into zones of upwelling flow, plume conduits (hotspots) are expected to be spatially associated with lower-mantle regions of low seismic velocities, inferred as hot upwelling mantle flow.

Gonnermann, Helge M.; Jellinek, A. Mark; Richards, Mark A.; Manga, Michael

2004-09-01

338

On the convergence of a finite difference method for a class of singular boundary value problems arising in physiology  

Microsoft Academic Search

Using Chawla's identity (BIT 29 (1989) 566) a finite difference method based on uniform mesh is described for a class of singular boundary value problems (p(x)y?)?=p(x)f(x,y),0

R. K Pandey; Arvind K Singh

2004-01-01

339

Using high-resolution aeromagnetic survey to map tectonic elements of plate boundaries: An example from the Dead Sea Fault  

NASA Astrophysics Data System (ADS)

The Dead Sea Fault (DSF) is a transform plate boundary between the African and the Arabian plates. The 200-km-long DSF segment between the Gulf of Aqaba/Elat and the Dead Sea, which has the morphology of a rift valley, shows little seismic activity, and its surface trace is only intermittently visible. High-resolution magnetic data were collected in October 2003 aboard a Jordanian military helicopter flying at an altitude of 100 m over the southern 120-km-long section of this fault segment. The survey was part of a US-AID Middle Eastern Regional Cooperation project between Jordanian, Israeli, Palestinian, and American scientists. Data were collected along rift-perpendicular lines spaced 300 m apart, requiring frequent crossings between Israeli and Jordanian air spaces. The data were gridded at 75 m interval following resolution tests, reduced to pole, and incorporated into a GIS together with elevation, geology, and gravity maps to facilitate interpretation. The main findings of the magnetic survey are the absence of magnetic anomalies crossing the rift valley, and the presence of a rift-parallel regional lineament corresponding to the active trace of the DSF. The lineament extends NNE as an almost continuous trace from Elat, Israel, to the eastern side of the valley 5 km north of Rahmeh. Jordan. Another fault trace located 2-3 km to the west may overlap and continue NNE through Gebel A-Risha, and into the central Arava/Araba valley, where it is visible on the surface. Alternatively, the two traces may be connected. If an offset between the two traces exists, it may be small enough to allow an earthquake rupture to propagate across the offset, and generate an earthquake with a moment magnitude of up to 7.5. Traces of buried faults in the central Arava/Araba valley that were previously active in the DSF system, are visible as abrupt terminations of an area of short wavelength magnetic anomalies. These anomalies probably represent shallow subsurface magmatic intrusions. The closest exposed intrusion is dated at 20.7 Ma, shortly before the development of the DSF. Other anomalies can be traced at the edges of our survey area and are likely related to Precambrian outcrops along the rift shoulders. Comparison of the magnetic and the sparser land-gravity data shows the same general azimuth of the magnetic lineament and of the segmented fault system as derived from the gravity and a surprisingly good coincidence between local gravity and magnetic anomalies over the Timna pull-apart basin, owing perhaps to the sensitivity of the high-resolution magnetic data to the thickness of the sedimentary cover.

Al-Zoubi, A. S.; ten Brink, U. S.; Rybakov, M.; Rotstein, Y.

2004-12-01

340

New constraints on timing of India-Asia collision from plate kinematic and seismic observations in the Equatorial Indian Ocean  

Microsoft Academic Search

The far-field signature of the India-Asia collision and history of uplift in Tibet is recorded by sediment input into the Indian Ocean and the strain accumulation history across the diffuse plate boundary between the Indian and Capricorn plates. We describe the history of India-Capricorn convergence from updated estimates of India-Somalia-Capricorn plate rotations and observations derived from seismic reflection data. New

J. M. Bull; C. Demets; K. S. Krishna; D. J. Sanderson; S. Merkouriev

2010-01-01

341

Parallel and convergent processing in grid cell, head-direction cell, boundary cell, and place cell networks  

PubMed Central

The brain is able to construct internal representations that correspond to external spatial coordinates. Such brain maps of the external spatial topography may support a number of cognitive functions, including navigation and memory. The neuronal building block of brain maps are place cells, which are found throughout the hippocampus of rodents and, in a lower proportion, primates. Place cells typically fire in one or few restricted areas of space, and each area where a cell fires can range, along the dorsoventral axis of the hippocampus, from 30?cm to at least several meters. The sensory processing streams that give rise to hippocampal place cells are not fully understood, but substantial progress has been made in characterizing the entorhinal cortex, which is the gateway between neocortical areas and the hippocampus. Entorhinal neurons have diverse spatial firing characteristics, and the different entorhinal cell types converge in the hippocampus to give rise to a single, spatially modulated cell type—the place cell. We therefore suggest that parallel information processing in different classes of cells—as is typically observed at lower levels of sensory processing—continues up into higher level association cortices, including those that provide the inputs to hippocampus. WIREs Cogn Sci 2014, 5:207–219. doi: 10.1002/wcs.1272 PMID:24587849

Brandon, Mark P; Koenig, Julie; Leutgeb, Stefan

2014-01-01

342

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

PubMed Central

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

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

2014-01-01

343

Effect of double stratification on mixed convection boundary layer flow of a nanofluid past a vertical plate in a porous medium  

NASA Astrophysics Data System (ADS)

The effect of thermal and mass stratification on mixed convection boundary layer flow over a vertical flat plate embedded in a porous medium saturated by a nanofluid has been investigated. The vertical plate is maintained at uniform and constant heat, mass and nanoparticle fluxes, and the behavior of the porous medium is described by the Darcy model. The model considered for nanofluids incorporates the effects of Brownian motion and thermophoresis. In addition, the thermal energy equations include regular diffusion and cross-diffusion terms. A suitable coordinate transformation is introduced, and the obtained system of non-similar, coupled and non-linear partial differential equations is solved numerically. The influence of pertinent parameters on the non-dimensional velocity, temperature, concentration and nanoparticle volume fraction are discussed. In addition, the variation of heat, mass and nanoparticle transfer rates at the plate are exhibited graphically for different values of physical parameters.

Srinivasacharya, D.; Surender, Ontela

2015-01-01

344

Geologic observations of the northern boundary of the Caribbean plate across central America as seen by Seasat and SIR-A  

NASA Technical Reports Server (NTRS)

The radar data analyzed here extend from the Amatique Bay (Golfo de Honduras) in the northeast to the Pacific Ocean (Puenta Remedios) in the southwest. Space Shuttle Imaging Radar (SIR-A) data-take 18 overlaps the principal part of the Seasat mosaic. SIR-A data make possible more observations over the Central American Cordillera, where strong layover limited the amount of information obtained by Seasat. The radar coverage delineates the principal strike-slip faults of the region (Cuilco-Chixoy-Polochic, Motagua and Jocotan), which have acted as the Caribbean-Americas plate boundary. It also demarcates volcanic terranes related to subduction of the Cocos Plate under the Caribbean Plate. Within pumice fields of the Tertiary volcanic belt, the use of two Seasat look directions (rev 759 and rev 1211), in conjunction with SIR-A data, makes possible some rock discrimination.

Rebillard, P.; Dixon, T.; Farr, T.

1982-01-01

345

The 11 December, 1995 earthquake (Mw=6.4): Implications for the present-day relative motion on the Rivera-Cocos plate boundary  

Microsoft Academic Search

The 11 December, 1995 earthquake is the largest and best constrained instrumentally recorded event which has occurred on the Rivera-Cocos plate boundary. The reported focal mechanism for this event indicates almost pure strike-slip faulting with nodal planes oriented north-south and east-west. A visual inspection shows that the seismograms recorded world-wide strongly suggest a directivity effect indicative of a rupture propagating

Gerardo Suárez; David Escobedo; William Bandy; Javier F. Pacheco

1999-01-01

346

Characteristic seismic activity in the subducting plate boundary zone off Kamaishi, northeastern Japan, revealed by precise hypocenter distribution analysis using ocean-bottom seismometers  

Microsoft Academic Search

High seismic activity prevails along the plate boundary to the east of northeastern Japan. To understand how this seismic activity is related to subduction process, hypocenter locations are re-determined using data obtained over 6 years by fiber-cabled permanent ocean bottom seismometers off Kamaishi. The double-difference method is adopted to obtain the relative location in more detail. As a result of

T. Okada; K. Sakoda; T. Matsuzawa; R. Hino; A. Hasegawa; S. Sakai; T. Kanazawa

2004-01-01

347

Jurassic Oceanic Remnants In The Siuna Area (NE-Nicaragua) - Tracing The Chortis- Caribbean Paleo-plate Boundary  

NASA Astrophysics Data System (ADS)

The southern limit of the Chortis Block has been commonly placed along a line between the Santa Elena Peninsula (Costa Rica) and the Hess Escarpment (Eastern Caribbean). However, we have mapped extensive occurrences of ultramafic and mafic rocks, associated with Jurassic radiolarites in the Siuna area. These are in conflict with the current plate tectonic schemes. In the area S and NE of Siuna, we observe three tectono-stratigraphic units: 1. A pre-Cretaceous, subduction-related melange outcropping in a 30 x 5 km sized erosional window. Serpentinite is a (tectonic) matrix for a variety of mappable blocks grouped into the following categories: Gabbros and peridotites preserving original cumulate textures, greenstones, epidote-bearing greenschists, barroisite-bearing metamafics that partially contain garnet+clinopyroxene inclusions, phengite-schists, blue- green amphibole-rich metacherts, detrital quartzites, radiolarian cherts, black shales and Mn-radiolarites- bearing Middle and Late Jurassic Radiolaria. Blocks with greenschists and higher pressure metamorphic facies appear to be concentrated in the central part of the window. In some blocks, greenstones (mainly altered metabasalts) are associated with ribbon-bedded radiolarites and siliceous shales suggesting an original sedimentary contact of sediments on the oceanic crust. This melange resembles (though more polymict) the subduction melanges of the Franciscan and indicates that the Siuna area exposes part of a major suture zone between the Chortis Block and the Caribbean Large Igneous Province (CLIP). 2. Thin-bedded calcareous hemipelagites yielding Aptian/Albian planktonic Foraminifera rest unconformably on the oceanic melange. Distal volcaniclastic turbitites are interbedded. The sequence contains shallow upsections into thick bedded limestones, in which andesitic flows may be intercalated. Well rounded/sorted and imbricated volcanic pebble conglomerates sometimes intervene between the andesites and fossiliferous, massive shallow water limestones (Atima Formation known in the Chortis stratigraphy). Apparently, andesitic flows became eroded in a high energy/beach environment that gave way to a shallow carbonate bank. We interpret this succession as a passage from a distal forearc basin into an island arc situation with local emergence of basaltic to andesitic volcanoes. 3. An andesitic to dacitic volcanic cover is represented by pyroclastic flows and tuffs intruded by small sub- volcanic, hornblende-rich andesite bodies. All previously described units are affected by large intrusive bodies of diorites and granodiorites of Late Cretaceous-Paleocene ages. The presence of oceanic remnants in NE Nicaragua may radically change the current concepts of plate boundaries in the area. The boundary between the Palaeozoic-Mesozoic continental Chortis Block and the CLIP is commonly placed as far south as the Costa Rica/Nicaragua border. A suture zone was interpreted to be aligned with the EW-trending Santa Elena Fault and the Hess Escarpment, based on outcrops of serpentinites that are found along the San Juan River (Costa Rica/Nicaragua border). However, newly discovered outcrops of serpentinites and oceanic sediments far north of the San Juan River may connect to the Siuna area suggesting that Tertiary and Quaternary volcanics of Nicraragua may hide extensive oceanic terranes.

Flores, K.; Baumgartner, P. O.; Skora, S.; Baumgartner, L.; Baumgartner-Mora, C.; Rodriguez, D.

2006-12-01

348

Investigating crustal deformation associated with the North America-Pacific plate boundary in southern California with GPS geodesy  

NASA Astrophysics Data System (ADS)

The three largest earthquakes in the last 25 years in southern California occurred on faults located adjacent to the southern San Andreas fault, with the M7.3 1992 Landers and M7.1 1999 Hector Mine earthquakes occurring in the eastern California shear zone (ECSZ) in the Mojave Desert, and the M7.2 2010 El Mayor-Cucapah earthquake occurring along the Laguna Salada fault in northern Baja California, Mexico. The locations of these events near to but not along the southern San Andreas fault (SSAF) is unusual in that the last major event on the SSAF occurred more than 300 years ago, with an estimated recurrence interval of 215 +/- 25 years. The focus of this dissertation is to address the present-day deformation field along the North America-Pacific plate boundary in southern California and northern Baja California, through the analysis of GPS data, and elastic block and viscoelastic earthquake models to determine fault slip rates and rheological properties of the lithosphere in the plate boundary zone. We accomplish this in three separate studies. The first study looks at how strain is partitioned northwards along-strike from the southern San Andreas fault near the Salton Sea. We find that estimates for slip-rates on the southern San Andreas decrease from ~23 mm/yr in the south to ~8 mm/yr as the fault passes through San Gorgonio Pass to the northwest, while ~13-18 mm/yr of slip is partitioned onto NW-SE trending faults of the ECSZ where the Landers and Hector Mine earthquakes occurred. This speaks directly to San Andreas earthquake hazards, as a reduction in the slip rate would require greater time between events to build up enough slip deficit in order to generate a large magnitude earthquake. The second study focuses on inferring the rheological structure beneath the Salton Trough region. This is accomplished through analysis of postseismic deformation observed using a set of the GPS data collected before and after the 2010 El Mayor-Cucapah earthquake. By determining the slip-rates on each of the major crustal faults prior to the earthquake, we are able to model the pre-earthquake velocity field for comparison with velocities measured using sites constructed post-earthquake. We then determine how individual site velocities have changed in the 3 years following the earthquake, with implications for the rate at which the lower crust and upper mantle viscously relax through time. We find that the viscosity of the lower crust is at least an order of magnitude higher than that of the uppermost mantle, and hypothesize that this is due to mafic material emplaced at the base of the crust as the spreading center developed beneath the Salton Trough since about 6 Ma. The final study investigates crustal deformation and fault slip rates for faults in the northern Mojave and southern Walker Lane regions of the ECSZ. Previous geodetic studies estimated slip-rates roughly double those inferred via geological dating methods in this region for NW striking strike-slip faults, but significantly smaller than geologic estimates for the Garlock fault. Through construction of a detailed elastic block model, which selects only active fault structures, and applying a new, dense GPS velocity field in this region, we are able to estimate slip-rates for the strike-slip faults in the ECSZ that are much closer to those reported from geology.

Spinler, Joshua C.

349

Current Status of Nankai Earthquake Forecasting System based on Sequential Data Assimilation of the Slip on the Plate Boundary  

NASA Astrophysics Data System (ADS)

Interplate earthquake cycles are expressed by spatiotemporal variation of slip and slip deficit on plate interfaces. Hence, we can approximate changes in fault stress during earthquake cycles through the kinematic dislocation model in the simplified medium. By combining fault stress based on the elastic dislocation with a friction law, we can derive mathematical formulations obeying the evolution of fault slips. Actually, it has been shown that many phenomena in plate boundaries can be explained by results of numerical integration of mathematical models. Moreover, the distribution of slips on the plate interface can be presumed from the crustal deformation obtained by some instruments (e.g. GNSS or submarine pressure gage etc.). Thus, owing to developments of models for fault slips and observation networks, it is possible to predict the evolution of fault slips through the combination of model and observation. However, there are many difficulties to realize the prediction of the evolution of fault slips; Mathematical models of earthquakes are nonlinear ones with many DOFs, even though they are highly simplified. Besides, observation always contains an error, and observation sites are limited to the earth's surface. Moreover, the precise observation data are only available for recent several decades which is much shorter than a great interplate earthquake cycle. In such situation, the observation is not enough to obtain a deterministic prediction. Hence, we must prepare many simulation results (scenarios) with possible conditions. Then, for crustal deformations associated with whole scenarios, the fitness to observation is checked. Based on the fitness, likelihoods of scenarios are calculated, and each scenario is weighted by the likelihood value. Thus, the extrapolation of the ensemble of weighted scenarios should be regarded as the prediction of fault slips. To predict anticipated Nankai earthquakes in southwestern Japan, we have so far advanced the construction of the forecasting system in Nankai region based on the above concept. For investigating Nankai earthquake scenarios comprehensively, the simultaneous simulation of many conditions is performed using K computer. Moreover, for the implementation of ensemble prediction, we adopt Sequential Importance Sampling which is a kind of the data assimilation technique. Now, observation data (vertical component of GEONET) is taken from a database weekly, and using 22 sites in the Pacific coast of southwestern Japan, the likelihood of each scenario is evaluated. Results indicate that for scenarios with high likelihood, predicted horizontal deformation at GEONET sites and vertical deformation at the DONET sites are well consistent with the observation, though horizontal components of GEONET data and DONET data are not included in current data assimilation. This means the scenarios evaluated here are valid for the recent deformation data. Hence, as a next step for improving the forecasting system, we are planning to incorporate other data which characterize earthquake cycles (e.g. recurrence times, occurrence timing of past earthquakes etc.) to sequential assimilation.

Hyodo, M.; Nakata, R.; Ariyoshi, K.; Hori, T.; Kaneda, Y.

2013-12-01

350

Slip rate and earthquake recurrence along the central Septentrional fault, North American-Caribbean plate boundary, Dominican Republic  

USGS Publications Warehouse

The Septentrional fault zone (SFZ) is the major North American-Caribbean, strike-slip, plate boundary fault at the longitude of eastern Hispaniola. The SFZ traverses the densely populated Cibao Valley of the Dominican Republic, forming a prominent scarp in alluvium. Our studies at four sites along the central SFZ are aimed at quantifying the late Quaternary behavior of this structure to better understand the seismic hazard it represents for the northeastern Caribbean. Our investigations of excavations at sites near Rio Cenovi show that the most recent ground-rupturing earthquake along this fault in the north central Dominican Republic occurred between A.D. 1040 and A.D. 1230, and involved a minimum of ???4 m of left-lateral slip and 2.3 m of normal dip slip at that site. Our studies of offset stream terraces at two locations, Rio Juan Lopez and Rio Licey, provide late Holocene slip rate estimates of 6-9 mm/yr and a maximum of 11-12 mm/yr, respectively, across the Septentrional fault. Combining these results gives a best estimate of 6-12 mm/yr for the slip rate across the SFZ. Three excavations, two near Tenares and one at the Rio Licey site, yielded evidence for the occurrence of earlier prehistoric earthquakes. Dates of strata associated with the penultimate event suggest that it occurred post-A.D. 30, giving a recurrence interval of 800-1200 years. These studies indicate that the SFZ has likely accumulated elastic strain sufficient to generate a major earthquake during the more than 800 years since it last slipped and should be considered likely to produce a destructive future earthquake.

Prentice, C.S.; Mann, P.; Pena, L.R.; Burr, G.

2003-01-01

351

Friction properties of the plate boundary megathrust beneath the frontal wedge near the Japan Trench: an inference from topographic variation  

NASA Astrophysics Data System (ADS)

The 2011 Tohoku-Oki earthquake (Mw 9.0) produced a fault rupture that extended to the toe of the Japan Trench. The deformation and frictional properties beneath the forearc are keys that can help to elucidate this unusual event. In the present study, to investigate the frictional properties of the shallow part of the plate boundary, we applied the critically tapered Coulomb wedge theory to the Japan Trench and obtained the effective coefficient of basal friction and Hubbert-Rubey pore fluid pressure ratio (?) of the wedge beneath the lower slope. We extracted the surface slope angle and décollement dip angle (which are the necessary topographic parameters for applying the critical taper theory) from seismic reflection and refraction survey data at 12 sites in the frontal wedges of the Japan Trench. We found that the angle between the décollement and back-stop interface generally decreases toward the north. The measured taper angle and inferred effective friction coefficient were remarkably high at three locations. The southernmost area, which had the highest coefficient of basal friction, coincides with the area where the seamount is colliding offshore of Fukushima. The second area with a high effective coefficient of basal friction coincides with the maximum slip location during the 2011 Tohoku-Oki earthquake. The area of the 2011 earthquake rupture was topographically unique from other forearc regions in the Japan Trench. The strain energy accumulation near the trench axis may have proceeded because of the relatively high friction, and later this caused a large slip and collapse of the wedge. The location off Sanriku, where there are neither seamount collisions nor rupture propagation, also has a high coefficient of basal friction. The characteristics of the taper angle, effective coefficient of basal friction, and pore fluid pressure ratio along the Japan Trench presented herein may contribute to the understanding of the relationship between the geometry of the prism and the potential for generating seismo-tsunamigenic slips.

Koge, Hiroaki; Fujiwara, Toshiya; Kodaira, Shuichi; Sasaki, Tomoyuki; Kameda, Jun; Kitamura, Yujin; Hamahashi, Mari; Fukuchi, Rina; Yamaguchi, Asuka; Hamada, Yohei; Ashi, Juichiro; Kimura, Gaku

2014-12-01

352

Monitoring the terrestrial water cycle with reflected GPS signals recorded by the Plate Boundary Observatory Network (Invited)  

NASA Astrophysics Data System (ADS)

Data from NSF's EarthScope Plate Boundary Observatory (PBO), and similar GPS networks worldwide, can be used to monitor the terrestrial water cycle. GPS satellites transmit L-band microwave signals, which are strongly influenced by water at the surface of the Earth. GPS signals take two different paths: (1) the 'direct' signal travels from the satellite to the antenna; (2) the 'reflected' signal interacts with the Earth's surface before travelling to the antenna. The direct signal is used by geophysicists to measure the position of the antenna. By analyzing these GPS data over multiple years, the motion of the site can be estimated. The effects of reflected signals are generally ignored by geophysicists because they are small. This is not happenstance, as significant effort has been made to design and deploy a GPS antenna that suppresses ground reflections. Our group has developed a new remote sensing technique to retrieve terrestrial water cycle variables from GPS data. We extract the water cycle products from signal strength data that measures the interference between the direct and reflected GPS signals. The sensing footprint is intermediate in scale between in situ observations and most remote sensing measurements. Snow depth, soil moisture, and an index of vegetation water content are estimated from data collected at over 400 PBO sites. The products are updated daily and are available online. Validation studies show that retrieved products are of sufficient quality to be used in a variety of applications. In order to improve the resolution of GPS water cycle products, we are also developing a new sensor especially designed to measure reflected GPS signals. This will yield a more sensitive instrument that costs an order of magnitude less than existing geodetic-quality GPS systems. Such a technology would have broad applications in both research and agricultural settings.

Small, E. E.; Larson, K. M.; Braun, J.; Chew, C. C.; McCreight, J. L.

2013-12-01

353

Monitoring the terrestrial water cycle with reflected GPS signals recorded by the Plate Boundary Observatory Network (Invited)  

NASA Astrophysics Data System (ADS)

Data from NSF's EarthScope Plate Boundary Observatory (PBO), and similar GPS networks worldwide, can be used to monitor the terrestrial water cycle. GPS satellites transmit L-band microwave signals, which are strongly influenced by water at the surface of the Earth. GPS signals take two different paths: (1) the 'direct' signal travels from the satellite to the antenna; (2) the 'reflected' signal interacts with the Earth's surface before travelling to the antenna. The direct signal is used by geophysicists to measure the position of the antenna. By analyzing these GPS data over multiple years, the motion of the site can be estimated. The effects of reflected signals are generally ignored by geophysicists because they are small. This is not happenstance, as significant effort has been made to design and deploy a GPS antenna that suppresses ground reflections. Our group has developed a new remote sensing technique to retrieve terrestrial water cycle variables from GPS data. We extract the water cycle products from signal strength data that measures the interference between the direct and reflected GPS signals. The sensing footprint is intermediate in scale between in situ observations and most remote sensing measurements. Snow depth, soil moisture, and an index of vegetation water content are estimated from data collected at over 400 PBO sites. The products are updated daily and are available online. Validation studies show that retrieved products are of sufficient quality to be used in a variety of applications. In order to improve the resolution of GPS water cycle products, we are also developing a new sensor especially designed to measure reflected GPS signals. This will yield a more sensitive instrument that costs an order of magnitude less than existing geodetic-quality GPS systems. Such a technology would have broad applications in both research and agricultural settings.

Small, E. E.; Larson, K. M.; Braun, J.; Chew, C. C.; McCreight, J. L.

2011-12-01

354

Slip rate and earthquake recurrence along the central Septentrional fault, North American-Caribbean plate boundary, Dominican Republic  

NASA Astrophysics Data System (ADS)

The Septentrional fault zone (SFZ) is the major North American-Caribbean, strike-slip, plate boundary fault at the longitude of eastern Hispaniola. The SFZ traverses the densely populated Cibao Valley of the Dominican Republic, forming a prominent scarp in alluvium. Our studies at four sites along the central SFZ are aimed at quantifying the late Quaternary behavior of this structure to better understand the seismic hazard it represents for the northeastern Caribbean. Our investigations of excavations at sites near Rio Cenovi show that the most recent ground-rupturing earthquake along this fault in the north central Dominican Republic occurred between A.D. 1040 and A.D. 1230, and involved a minimum of ˜4 m of left-lateral slip and 2.3 m of normal dip slip at that site. Our studies of offset stream terraces at two locations, Rio Juan Lopez and Rio Licey, provide late Holocene slip rate estimates of 6-9 mm/yr and a maximum of 11-12 mm/yr, respectively, across the Septentrional fault. Combining these results gives a best estimate of 6-12 mm/yr for the slip rate across the SFZ. Three excavations, two near Tenares and one at the Rio Licey site, yielded evidence for the occurrence of earlier prehistoric earthquakes. Dates of strata associated with the penultimate event suggest that it occurred post-A.D. 30, giving a recurrence interval of 800-1200 years. These studies indicate that the SFZ has likely accumulated elastic strain sufficient to generate a major earthquake during the more than 800 years since it last slipped and should be considered likely to produce a destructive future earthquake.

Prentice, Carol S.; Mann, Paul; PeñA, Luis R.; Burr, G.

2003-03-01

355

Numerical approaches to the evaluation of foreland basin in an active convergence boundary for CO2 sequestration  

NASA Astrophysics Data System (ADS)

Greenhouse gas control has become one of the most critical environmental issues since last two decades. Since then, underground geological storage has been recognized as an important technique for CO2 mitigation. The geological reservoirs can trap CO2 by a number of mechanisms, including stratigraphic and structural trapping, hydrodynamic trapping and geochemical trapping. However, the detailed evaluation on capacity of reservoir formation, sealing caprock and stability of geological environment should be carefully made when consider a potential site as CO2 reservoir. IPCC suggested that potential sites located in active plate margin must be carefully evaluated on an individual basis. However, Cenozoic foreland basin is one of the most dominant tectonic units in the west Pacific margin, including the study area (Taiwan), and is naturally characterized by many preferred features for geological CO2 storage. Accordingly, in this study, foreland basin will be assessed in both aspects of a conceptual framework and an individual local case with a full-scale numerical model. The foreland basin along Taiwan Orogeny can be subdivided into two basins (Taihsi Basin and Tainan Basin) by Peikang High region. Taihsi Basin is a preferred potential storage due to considerable thickness of sandstone in the range of injection depth. Accordingly, a detailed geological profile across the Taihsi Basin has been established with magnetotelluric and seismic reflection surveys in a preliminary study, which were used for evaluating the Taihsi Basin and estimating the amount of CO2 sequestration under various geological scenarios in this study. The results demonstrate that the north part of Taihsi Basin were less faulted and folded and is the most favor potential site. The injected CO2 naturally migrates toward the Taiwan Strait due to the gentle dipping; and, CO2 will finally reach the forebulge of the basin in about twenty thousand years. In addition, the reservoir formation is truncated by a thick clay formation in front of the forebulge. The CO2 can be eventually trapped in the wedge sealed by the clay formation.

He, Sinda

2013-04-01

356

Deep Seismic Reflection Images across a Major Reactivated Fracture Zone in the Wharton Basin: Implications for the Location of the Plate Boundary between India and Australia  

NASA Astrophysics Data System (ADS)

The equatorial Indian Ocean has long been recognized to be hosting extensive "intra-plate" deformation. To west of the Ninety-East Ridge (NER), The Central Indian Ocean Basin is characterized by N-S compression in a broad region with E-W trending folds and high-angle reverse faulting. To the east of NER in the Wharton Basin, deformation mainly occurs along reactivated N5°E-trending oceanic fracture zones with left-lateral strike-slip motion. Near longitude 93°E in the Wharton Basin runs a major reactivated fracture zone, along which the epicenters of the two recent Mw=8.6 and Mw=8.2 strike-slip earthquakes of April 11, 2012, and an Mw=7.2 foreshock that occurred in January 2012 are aligned. The April 11 events are the largest known oceanic events occurring away from the main plate boundaries. They ruptured a 20-40 km thick section of the oceanic lithosphere, i.e. down to depths at which no direct images of fault zones have been obtained so far. Deep seismic reflection data acquired in the Mw=8.6 earthquake rupture zone ~100 km north of the epicenter shows the presence of sub-Moho reflectivity down to 37 km depth in the oceanic mantle. We interpret these events as reflections off the earthquake-generating fault plane in the oceanic mantle, in accordance with results suggesting that brittle deformation of the oceanic lithosphere extends well into the mantle down to the 600°C isotherm. The fracture zone near 93°E separates lithospheres of contrasting crustal thicknesses (3.5-4.5 km versus 6 km) with a 10 Ma age difference, and therefore seems to act as a rheological boundary. We find that the deep reflections could originate from either a plane trending approximately N105°E, at high angle to the fracture zone, or from the fracture zone itself if the dip of the fault surface decreases from nearly vertical in the sediments to about 45° in the oceanic mantle. We propose that this fracture zone is a major tectonic boundary in the Wharton Basin, and that the three 2012 earthquakes ruptured a large section of it as part of a poorly-defined diffuse plate boundary between the Indian and Australian plates, with slip occurring on this re-activated N-S fracture zone and on fossil E-W spreading-related faults. Over 1000 km of this plate boundary could have ruptured since the great 2004 Sumatra earthquake.

Carton, H. D.; Singh, S. C.; Hananto, N. D.; Martin, J.; Djajadihardja, Y. S.; Udrekh, U.; Franke, D.; Gaedicke, C.

2012-12-01

357

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

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

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

2013-01-01

358

Using EarthScope Construction of the Plate Boundary Observatory to Provide Locally Based Experiential Education and Outreach  

NASA Astrophysics Data System (ADS)

EarthScope is an NSF-funded, national science initiative to explore the structure and evolution of the North American continent and to understand the physical processes controlling earthquakes and volcanoes. This large-scale experiment provides locally based opportunities for education and outreach which engage students at various levels and the public. UNAVCO is responsible for the Plate Boundary Observatory (PBO) component of EarthScope. PBO includes the installation and operations and maintenance of large networks of Global Positioning Satellite (GPS), strainmeter, seismometer, and tiltmeter instruments and the acquisition of satellite radar imagery, all of which will be used to measure and map the smallest movements across faults, the magma movement inside active volcanoes and the very wide areas of deformation associated with plate tectonic motion. UNAVCO, through its own education and outreach activities and in collaboration with the EarthScope E&O Program, uses the PBO construction activities to increase the understanding and public appreciation of geodynamics, earth deformation processes, and their relevance to society. These include programs for public outreach via various media, events associated with local installations, a program to employ students in the construction of PBO, and development of curricular materials by use in local schools associated with the EarthScope geographic areas of focus. PBO provides information to the media to serve the needs of various groups and localities, including interpretive centers at national parks and forests, such as Mt. St. Helens. UNAVCO staff contributed to a television special with the Spanish language network Univision Aquí y Ahora program focused on the San Andreas Fault and volcanoes in Alaska. PBO participated in an Education Day at the Pathfinder Ranch Science and Outdoor Education School in Mountain Center, California. Pathfinder Ranch hosts two of the eight EarthScope borehole strainmeters in the Anza region to study the area between the San Andreas Fault and the San Jacinto Fault. The event provided an opportunity for the Pathfinder Ranch to unveil the instruments and describe the important science behind the project to the school's students, staff, and board members. The two strainmeters will be used as a teaching tool for several years as hundreds of students filter through Pathfinder school. UNAVCO sponsors a summer PBO Student Field Assistant Program designed to give students from a variety of educational backgrounds the opportunity get involved in the construction of the EarthScope PBO project. The goal of the program is to excite students about the geodetic sciences through direct work experience. Over the summers of 2005 and 2006, PBO sponsored a total of 11 student assistants who helped to install GPS and strainmeter stations and to perform operations and maintenance tasks. PBO plans to expand this program in 2007 by including student assistants in our data management and strainmeter data processing activities. In August, 2006, UNAVCO led a group of scientists, teachers, and curriculum developers to identify key scientific concepts of EarthScope research and how they can be translated into the Earth Science classroom at the middle and high school levels. The focus was on the Cascadia region. A feature of the workshop was to use PBO and USArray data in the classroom.

Jackson, M.; Eriksson, S.; Barbour, K.; Venator, S.; Mencin, D.; Prescott, W.

2006-12-01

359

Seismic Tomography of the Southern California Plate Boundary Region from Noise-Based Rayleigh and Love Waves  

NASA Astrophysics Data System (ADS)

We use cross-correlations of ambient seismic noise between pairs of 158 broadband and short-period sensors to investigate velocity structure over the top 5-10 km of the crust in the Southern California plate boundary region around the San Jacinto Fault Zone (SJFZ). From the 9-component correlation tensors associated with all station pairs we derive dispersion curves of Rayleigh and Love wave group velocities. The dispersion results are inverted first for Rayleigh and Love waves group velocity maps on a 1.5 × 1.5 km2 g