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1

Slip partitioning along major convergent plate boundaries  

Microsoft Academic Search

Along plate boundaries characterized by oblique convergence, earthquake slip vectors are commonly rotated toward the normal of the trench with respect to predicted plate motion vectors. Consequently, relative plate motion along such convergent margins must be partitioned between displacements along the thrust plate interface and deformation within the forearc and back-arc regions. The deformation behind the trench may take the

Guang Yu; Steven G. Wesnousky; Göran Ekström

1993-01-01

2

Plate Tectonics: Diverging, Converging, and Transform Boundaries  

NSDL National Science Digital Library

In this lesson, students will learn to distinguish the different layers of the Earth, observe the effects of plate movements, and explore the reasons for earthquakes and volcanoes. They will label and measure the thicknesses of each layer of the Earth (lithosphere, asthenosphere, etc.) and record their results, construct models from sand and clay to illustrate what happens at the three types of plate boundaries (transform, diverging, and converging), and investigate convergent plate boundaries to see which scenarios may create earthquakes and/or volcanoes.

3

Analogue models of obliquely convergent continental plate boundaries  

Microsoft Academic Search

Analogue models are used to examine crustal-scale faulting at obliquely convergent continental plate boundaries. A uniform Coulomb material is deformed with basal kinematic boundary conditions to model two obliquely convergent lithospheric plates. The mantle part of one plate is assumed to detach from its overriding crust and then be subducted beneath the other plate. The obliquity of the collision is

David R. Burbidge; Jean Braun

1998-01-01

4

On the geometry of convergent plate boundaries  

Microsoft Academic Search

Previous studies of plate dynamics suggest that, at consuming plate boundaries, driving forces (negative buoyancy) acting on the slab are counterbalanced by viscous forces, proportional to the consumption velocity and resisting the downgoing motion into the mantle. New observations on the geometry of subduction zones may help test this equilibrium theory. A condition for local equilibrium of the driving and

Gilles Peltzer

1981-01-01

5

Geodetic analysis of motion at a convergent plate boundary  

Microsoft Academic Search

A simplistic model of the superficial interaction between two lithospheric plates would comprise two rigid bodies separated by a linear discontinuity. Where continental crust straddles an obliquely convergent boundary, however, as in New Zealand, extensive deformation can be seen over a zone several hundred kilometres in width. Past analyses of repeated geodetic surveys have indicated that shear-strain may be occurring

W. I. Reilly

6

Analogue models of obliquely convergent continental plate boundaries  

NASA Astrophysics Data System (ADS)

Analogue models are used to examine crustal-scale faulting at obliquely convergent continental plate boundaries. A uniform Coulomb material is deformed with basal kinematic boundary conditions to model two obliquely convergent lithospheric plates. The mantle part of one plate is assumed to detach from its overriding crust and then be subducted beneath the other plate. The obliquity of the collision is assumed to remain constant throughout the deformation. Experiments are run with obliquities ranging from pure convergence (low obliquity) to pure strike slip (high obliquity). Reverse faults are observed for all obliquities with a nonzero convergent component. By contrast, only collisions with a large amount of strike slip motion exhibit wrench faulting. In experiments dominated by their convergent component, the strike slip motion is totally accommodated by oblique slip along the reverse faults. Strain partitioning between reverse faults and wrench faults is only observed for experiments run above a certain critical partitioning obliquity. Prom the observed initial faults, we can deduce the change in orientation in the principal stress triad as the obliquity is changed. We propose that the initial direction of maximum compressive stress (?1) rotates horizontally as the obliquity is changed, which in turn affects the geometry of the initial faults formed in the material. In the case of reverse faults, the rotation increases their dip measured along the direction of pure convergence. The relative magnitude of the minimum horizontal stress and the vertical stress determine whether reverse faults or strike slip faults are the first to form. Although long term deformation is more difficult to analyze, a simple relationship for the angle at which strain partitioning occurs is derived.

Burbidge, David R.; Braun, Jean

1998-07-01

7

The proximity of hotspots to convergent and divergent plate boundaries  

SciTech Connect

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

Weinstein, S.A.; Olson, P.L. (Johns Hopkins Univ., Baltimore, MD (USA))

1989-05-01

8

Recent geodynamic evolution of convergent plate margins and the reconstruction of fossil plate boundaries  

Microsoft Academic Search

Summary  The discovery of paleoplates buried in the upper mantle leads to an interpretation of the subduction as a discontinuous process running in cycles and shifting the place of its operation in or against the direction of ocean floor spreading. This mechanism explains the distribution of calc-alkaline volcanism of different age in fossil convergent plate boundaries. The establishment of regular spatial

Václav Hanuš; Ji?í Van?k

1995-01-01

9

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.

10

The role of near-trench extension at convergent plate boundaries  

Microsoft Academic Search

Knowledge of how convergent plate boundary coupling in the seismogenic zone controls the nucleation of subduction zone earthquakes is fundamental to assess seismic risks. Increased data at convergent margins has revealed the complexity of the earthquake cycle through the detection of strain-release processes like episodic tremors and slip events, low frequency earthquakes, afterslip, slip heterogeneity along the fault plane. The

P. Vannucchi

2009-01-01

11

Viscous flow and deformation of regional metamorphic belts at convergent plate boundaries  

Microsoft Academic Search

Viscous flow and deformation of a Newtonian fluid between rigid boundaries have been modeled for investigating deformation of a forearc wedge and a regional metamorphic belt as a weak deforming zone between the plates at convergent boundaries. Three types of analytic formulations together with numerical formulations for a Newtonian fluid with a constant viscosity are used for investigating various flows

Hikaru Iwamori

2003-01-01

12

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.

13

Oblique Convergence under Increasing Plate-Boundary Curvature: Pliocene-Holocene Partitioned Transtension in the Eastern Hellenic Forearc  

Microsoft Academic Search

Deformation of an overriding plate varies along the strike of a convergent plate boundary whose curvature is greater than that of the Earth. For the Hellenic plate boundary, not only do relative plate-convergence vectors vary spatially along strike, but the subduction-zone curvature has increased temporally as the trench migrated south-southwestward since Early Miocene time. Structural mapping\\/kinematic analyses, tectonostratigraphy, and chronostratigraphy

K. L. Kleinspehn; J. H. Ten Veen

2001-01-01

14

Segmentation of convergent plate boundary in eastern Taiwan observed by Persistent SAR Interferometry  

NASA Astrophysics Data System (ADS)

Rapid convergence between the Eurasian plate and the Philippine Sea plate in eastern Taiwan consumed around 30 mm^-1 of the 82 mm^-1 of the continuous convergence between these two plates. The force has produced prominent landscape and frequent seismicity along this collisional boundary. Because of the obliquity of the arc-continent collision, the northern part of the Luzon arc collided first with the Eurasian continental margin and the collision propagated southward with the southern tip of Taiwan only emerged very recently. As a result, the convergent rates vary along the strike of the Longitudinal Valley which was designated as the suture of the two collided plates. In this research, we focus on the spatial variation in the surface deformation along the collisional boundary. Nineteen Envisat ASAR radar images from Track 461, frame 3123 and 3141 were used to extract surface deformation signals from the plate suture. We applied PSI (Persistent Scatterer InSAR) to the area of study, which spans from Hualien city to Taitung city, to observe the surface displacements in the Longitudinal Valley. Our investigation indicates that the Longitudinal Valley can be divided into at least three segments in terms of relative changes in ranges between the approaching Coastal Range and the Longitudinal Valley. Comparison between PSI and leveling results indicates that PSI may be slightly under-estimated the magnitude of velocity relative to the ones derived from leveling.

Yen, J.; Chang, C.

2011-12-01

15

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

Microsoft Academic Search

We investigate microseismic activity at the convergent plate boundary of the Hellenic subduction zone on- and offshore south-eastern\\u000a Crete with unprecedented precision using recordings from an amphibian seismic network. The network configuration consisted\\u000a of up to eight ocean bottom seismometers as well as five temporary short-period and six permanent broadband stations on Crete\\u000a and surrounding islands. More than 2,500 local

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

2010-01-01

16

The role of near-trench extension at convergent plate boundaries  

NASA Astrophysics Data System (ADS)

Knowledge of how convergent plate boundary coupling in the seismogenic zone controls the nucleation of subduction zone earthquakes is fundamental to assess seismic risks. Increased data at convergent margins has revealed the complexity of the earthquake cycle through the detection of strain-release processes like episodic tremors and slip events, low frequency earthquakes, afterslip, slip heterogeneity along the fault plane. The processes controlling the earthquake cycle and their interactions are still far from being understood; improved understanding will require better characterization of the fault zone. Here we compare in-situ observations from two major subduction zones drilled by ODP and IODP (Costa Rica Trench and Nankai Trough) with a well-preserved fossil convergent plate boundary zone in the Northern Apennines of Italy. At all three sites, deformation in the region above and at the updip limit of the seismogenic zone is dominated by extension and normal faulting (i.e. maximum principal stress is oriented sub-vertically). Episodes of reverse shearing are also present, but occur with less intensity, alternating with extension. Ocean Drilling Program Legs 170 and 205 offshore Costa Rica provide structural observations of the frontal part of the upper plate and décollement at about 2 km from the trench. Analysis of drilled cores reveals the presence of normal faults cutting the frontal part of the upper plate. Normal faults are also seen from seismic reflection to develop along all the forearc (about 60 km from the trench). The décollement damage zone is a few tens of meters in width; it develops mainly within frontal prism material. A clear cm-thick fault core is observed 1.6 km from the trench. Both the upper plate and the décollement damage zone show the co-existence of two distinct fracturing processes in which extension fracturing is frequent in the upper part of the damage zone farthest from the fault core, while both extension and shear fracturing occur approaching the fault core. Recent drilling at Nankai has confirmed sub-horizontal extension in the upper plate there by observation of core-scale normal faulting (Lewis et al., 2008) and anelastic strain recovery determination (Byrne et al., 2008). In the fossil erosive megathrust system preserved in the Apennines, two décollements are simultaneously active at the roof and base of the subduction channel. The uppermost (nonseismogenic) portion of the megathrust appears to alternate between tensional and compressional modes of failure during the seismic cycle along the deeper portions of the megathrust. The presence of extensional strain along the plate boundary of convergent margins indicates that the décollements are able to transmit lithostatic loads. This implies their weak nature until at least intermediate (~3 km) depths where, in the fossil example, the basal décollement became partially locked. Fluid pressure cycles have not yet been well established at the frontmost part of convergent margins. Where the coexistence of extensional and shear fracturing is present, it seems to be best explained by fluid pressure variations in response to variations of the compressional regime during the seismic cycle. Byrne ,T., et al. (2008), In Situ Stress Determinations from Anelastic Strain Recovery (ASR): Preliminary Results and Comparisons to Borehole Breakout and Core-scale Fault Data from IODP Expeditions 314, 315 and 316 to the Nankai Trough, Eos Trans. AGU, 89(53), Fall Meet. Suppl., Abstract T22B-05 Lewis, J. et al. (2008), Subhorizontal Extension of the Upper Plate at NantroSEIZE Sites C0001 and C0002, Eos Trans. AGU, 89(53), Fall Meet. Suppl., Abstract T31B-2005

Vannucchi, P.

2009-04-01

17

Plate convergence measured by GPS across the Sundaland/Philippine Sea Plate deformed boundary: the Philippines and eastern Indonesia  

NASA Astrophysics Data System (ADS)

The western boundary of the Philippine Sea (PH) Plate in the Philippines and eastern Indonesia corresponds to a wide deformation zone that includes the stretched continental margin of Sundaland, the Philippine Mobile Belt (PMB), extending from Luzon to the Molucca Sea, and a mosaic of continental blocks around the PH/Australia/Sunda triple junction. The GPS GEODYSSEA data are used to decipher the present kinematics of this complex area. In the Philippines, the overall scheme is quite simple: two opposing rotations on either side of the left-lateral Philippine Fault, clockwise to the southwest and counterclockwise to the northeast, transfer 55 per cent of the PH/Sundaland convergence from the Manila Trench to the northwest to the Philippine Trench to the southeast. Further south, 80 per cent of the PH/Sunda convergence is absorbed in the double subduction system of the Molucca Sea and less than 20 per cent along both continental margins of northern Borneo. Finally, within the triple junction area between the Sundaland, PH and Australia plates, from Sulawesi to Irian Jaya, preferential subduction of the Celebes Sea induces clockwise rotation of the Sulu block, which is escaping toward the diminishing Celebes Sea oceanic space from the eastward-advancing PH Plate. To the south, we identify an undeformed Banda block that rotates counterclockwise with respect to Australia and clockwise with respect to Sundaland. The kinematics of this block can be defined and enable us to compute the rates of southward subduction of the Banda block within the Flores Trench and of eastward convergence of the Makassar Straits with the Banda block. The analysis made in this paper confirms that this deformation is compatible with the eastward motion of Sundaland with respect to Eurasia determined by the GEODYSSEA programme but is not compatible with the assumption that Sundaland belongs to Eurasia, as was often assumed prior to this study.

Rangin, C.; Le Pichon, X.; Mazzotti, S.; Pubellier, M.; Chamot-Rooke, N.; Aurelio, M.; Walpersdorf, Andrea; Quebral, R.

1999-11-01

18

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

19

Mountain Building At Convergent Plate Boundaries: A Three-dimensional Geodynamic Model  

Microsoft Academic Search

Most of the worldSs major mountain belts have formed at convergent plate bound- aries. The major driving forces include tectonic indentation and basal shear, which are largely balanced by the gravitational buoyancy force arising from lateral density vari- ations within the orogen and mantle thermal perturbations, and resisting stresses in the surrounding lithosphere. The crustal deformation is controlled by lithospheric

Q. Liu; M. Yang; Y. Li

2002-01-01

20

3-D Simulation of Tectonic Loading at Convergent Plate Boundary Zones: Internal Stress Fields in Northeast Japan  

Microsoft Academic Search

The evidence of east-west compression in northeast Japan has been reported by many investigators on the basis of geodetic,\\u000a geologic and geomorphic data, but its origin still remains far from understood. In the present study we have proposed a mechanical\\u000a model of tectonic loading at convergent plate boundary zones, and demonstrated its validity through the numerical simulation\\u000a of internal stress

Chihiro Hashimoto; Mitsuhiro Matsu'ura

2006-01-01

21

Recent and present-day stresses in the Granada Basin (Betic Cordilleras): Example of a late Miocene-present-day extensional basin in a convergent plate boundary  

Microsoft Academic Search

The diffuse convergent boundary between the Eurasian and African plates in the western Mediterranean is associated with a seismicity zone more than 300 km wide. Although the two plates are converging NW-SE, the Betic and Rif Cordilleras contain extensional structures that have been active since the Miocene. The extensional tectonics in the region, which occurred simultaneously with the uplift of

J. Galindo-Zaldívar; A. Jabaloy; I. Serrano; J. Morales; F. González-Lodeiro; F. Torcal

1999-01-01

22

The behavior of a convergent plate boundary - Crustal deformation in the South Kanto district, Japan  

Microsoft Academic Search

The northwesternmost part of the Sagami trough, a part of the Philippine Sea-Eurasian plate boundary, was ruptured during the great South Kanto earthquake in 1923. Very extensive and frequent geodetic measurements of crustal deformation have been made in the South Kanto district since the 1890's, and these constitute the most complete data set on crustal movements in the world. These

C. H. Scholz; Teruyuki Kato

1978-01-01

23

Plate convergence measured by GPS across the Sundaland\\/Philippine Sea Plate deformed boundary: the Philippines and eastern Indonesia  

Microsoft Academic Search

The western boundary of the Philippine Sea (PH) Plate in the Philippines and eastern Indonesia corresponds to a wide deformation zone that includes the stretched continental margin of Sundaland, the Philippine Mobile Belt (PMB), extending from Luzon to the Molucca Sea, and a mosaic of continental blocks around the PH\\/Australia\\/Sunda triple junction. The GPS GEODYSSEA data are used to decipher

C. Rangin; X. Le Pichon; S. Mazzotti; M. Pubellier; N. Chamot-Rooke; M. Aurelio; Andrea Walpersdorf; R. Quebral

1999-01-01

24

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

Microsoft Academic Search

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

W. F. Giggenbach; Y. Sano; H. Wakita

1993-01-01

25

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  

Microsoft Academic Search

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

W. F. Giggenbach; Y. Sano; H. Wakita

1993-01-01

26

Imaging the ascent path of fluids and partial melts at convergent plate boundaries by geophysical characteristics  

NASA Astrophysics Data System (ADS)

During the last decades many investigations were carried out at active continental margins to understand the link between the subduction of the fluid saturated oceanic plate and the process of ascent of fluids and partial melts forming a magmatic system that leads to volcanism at the earth surface. For this purpose structural information are needed about the slap itself, the part above it, the ascent paths as well as the storage of fluids and partial melts in the mantle and the crust above the down going slap up to the volcanoes on the surface. If we consider statistically the distance between the trench and the volcanic chain as well as the inclination angle of the down going plate, then the mean value of the depth distance down to the Wadati Benioff zone results of approximately 100 kilometers. Surprisingly, this depth range shows pronounced seismicity at most of all subduction zones. Additionally, mineralogical investigations in the lab have shown that the diving plate is maximal dehydrated around 100 km depth because of temperature and pressure conditions at this depth range. However, assuming a vertical fluid ascent there are exceptions. For instance at the Sunda Arc beneath Central Java the vertical distance results in approximately 150 km. But, in this case seismic investigations have shown that the fluids do not ascend vertically, but inclined even from a source area at around the 100 km depth. The ascent of the fluids and the appearance of partial melts as well as the distribution of these materials in the crust can be proved by seismic and seismological methods. With the seismic tomography these areas are imaged by lowered seismic velocities, high Vp/Vs ratios, as well as increased attenuation of seismic shear waves. But, to explore plate boundaries large and complex amphibious experiments are required, in which active and passive seismic investigations should be combined. They have to recover a range from before the trench to far behind the volcanic chain, to provide under favorable conditions information down to a depth of 150 km. In particular the record of the natural seismicity and its distribution allows the three-dimensional imaging of the entire crust and lithosphere structure above the Wadati Benioff zone with the help of tomographic procedures, and therewith the entire ascent path region of the fluids and melts, which are responsible for volcanism. The seismic velocity anomalies detected so far are within a range of a few per cent to more than 30% reduction. In the lecture findings of different subduction zones are compared and discussed.

Luehr, B. G.; Koulakov, I.; Kopp, H.; Rabbel, W.; Zschau, J.

2011-12-01

27

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

28

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 ...

29

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 ...

30

Characterizing Plate Boundaries  

NSDL National Science Digital Library

To prepare for this exercise students read about the processes that operate at plate boundaries and how they are related to the distinct patterns of seismicity, volcanism, surface elevations (e.g., ridges versus trenches), and seafloor ages characteristic of different boundary types. During the week the assignment is available online, students have access to: (1) an index map that locates three boundaries they are to study; and (2) four maps from Sawyer's Discovering Plate Boundaries website that provide the data mentioned above. Student tasks are to: (1) document patterns in each type of data along the three targeted boundaries; and (2) use these observations in conjunction with their understandings of the processes that operate along different types of boundaries to decide whether each of the targeted sites is most likely to be a divergent, convergent, or shear boundary. This activity gives students practice in map reading, interpreting the likely tectonic setting of a boundary by pulling together constraints from several types of data, and collaborating with their classmates in an online environment. The activity also provides a foundation for understanding a wide range of phenomena that are discussed later in the semester in the context of plate tectonic processes. Teaching Tips Adaptations that allow this activity to be successful in an online environment Sawyer's Discovering Plate Boundaries is a jigsaw exercise in which students collaboratively develop an empirical classification of plate boundaries by first studying an individual data set (e.g., seismicity) and then working as part of a multidisciplinary team to develop a composite classification for the boundaries of a single plate using several types of data. In order for the classification to be truly empirical, students are not introduced to the "traditional" classification of plate boundaries till the end of the exercise. In adapting this assignment to the online environment I have: (1) asked students to prepare by becoming familiar with the standard classification of plate boundaries and the processes that operate at them; (2) limited their work to three targeted boundaries of different types; and (3) provided guidance about which features to look for in the each data set. I have found that these modifications help online students, who often work alone "on their own schedules", to avoid getting "lost" and frustrated with the assignment and to compensate for the lack of collaborative input they would receive in a classroom setting. Elements of this activity that are most effective The success of this exercise is really seems to depend on how well a student follows the directions. If a student learns about the geologic differences among plate boundaries, makes careful observations, and thoughtfully compares his or her observations to the expected patterns he or she typically does quite well based on answers to the follow-up questions. If, on the other hand, a student simply looks up the types of the targeted boundaries on a map and then attempts to "back out" the observations that he or she thinks should fit, the result is often inconsistency and a poor score on the questions. (I can often tell which approach a student is taking based on the queries they post to the discussion board, but rarely seem to be able to get those who are trying to work backwards through the assignment to change direction.) Recommendations for other faculty adapting this activity to their own course: To date my experience developing an engaging online exercise to help students learn the principles of plate tectonics has only been partly successful. I think that having such an exercise is critical, however, because this topic provides the framework for so much of what we learn in the geosciences. Based on my efforts to adapt elements of Discovering Plate Boundaries to an online environment I would offer three recommendations. (1) Provide examples. Confronted with an unfamiliar map students are sometimes confused when asked to decide if seafloor age, for example, is uniform or variable along the length of a boundary. Showing them what you mean using snapshots from a map can often clear questions like this up quickly. Similarly, for written work a single example that gives them a clear sense of "what you're looking for" and can often head off a lot of questions. (2) Choose the boundaries you ask students to study carefully. The scarcity of documented volcanism along a mid-ocean ridge or the burial of seafloor age belts by sediment along a trench can result in student observations that are correct, but problematic for correctly assessing the nature of a boundary. (3) Stay on top of student questions and comments, and be prepared to make well-publicized "mid-course corrections" if something you thought was clear turns out to be misunderstood. These minor corrections happen naturally in face-to-face classes but can require real diligence to catch and correct in the online environment.

Hirt, Bill

31

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

32

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

33

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.

34

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

35

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.

Harwood, Cara

36

Discovering Plate Boundaries  

NSDL National Science Digital Library

Students are initially assigned to one of four maps of the world: Seismology, Volcanology, Geochronology or Topography. They are also given a map of the world's plate boundaries and are asked to classify the boundaries based upon the data from their assigned map. Students are then assigned to a tectonic plate, such that each plate group contains at least one "expert" on each map. As a group, they must classify their plate's boundaries using data from all four maps. Recent volcanic and seismic events are discussed in the plate tectonic context. Has minimal/no quantitative component Uses geophysics to solve problems in other fields

Henning, Alison

37

Large tectonic rotations since the Early Miocene in a convergent plate-boundary zone, South Island, New Zealand  

Microsoft Academic Search

A palaeomagnetic study in part of the New Zealand plate-boundary zone provides new constraints on the temporal and spatial distribution of Neogene and Quaternary tectonic rotations. Thermal demagnetization of samples from Cretaceous basaltic dykes, Palaeocene-Oligocene micritic limestone, and Miocene and Pliocene siltstones in the Marlborough region, South Island, have defined stable, high-temperature magnetic components, which are interpreted as the primary

Sara Vickery; Simon Lamb

1995-01-01

38

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.

2011-05-09

39

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.

40

ConcepTest: Convergent Boundary  

NSDL National Science Digital Library

The figures below show the location of a plate boundary (dashed line) and the distribution of earthquake foci (filled circles). The color of the filled circle indicates the depth of the earthquake focus. Given the ...

41

Secular, Transient and Seasonal Crustal Movements in Japan from a Dense GPS Array: Implication for Plate Dynamics in Convergent Boundaries  

Microsoft Academic Search

Japanese nationwide dense array of Global Positioning System has been yielding large amount of crustal movement data in Japan over the last decade. In this article, I review its contribution to our knowledge of crustal dynamics in a subduction zone. Secular velocity field provides information on rigid plate motion and coupling on the plate interface, and allows us to discuss

Kosuke Heki

42

Plate Boundary Forces at Subduction Zones: Effects of Plate Bending and Back-Arc Orogeny on Global Plate Motions  

Microsoft Academic Search

Deformation of both subducting and overriding at convergent plate boundaries tends to dissipate energy that would otherwise be used to drive plate motions. For subducting plates, the magnitude of the bending deformation is not known because of poor constraints on slab strength. For overriding plates, back-arc orogeny results from upper plate shortening and frictional stresses on the plate interface that

C. P. Conrad; B. J. Meade; B. Wu; A. Heuret; C. Lithgow-Bertelloni; S. Lallemand

2008-01-01

43

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

44

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

45

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

46

Low cloud boundaries coincident with oceanic convergences  

Microsoft Academic Search

Low stratus cloud was present over the cool water on the southern and western sides of the Subtropical Convergence east of New Zealand during two airborne infrared radiation thermometer surveys made on 2 April and 17–18 November 1969. The alignment of the northern boundary of such cloud with the Subtropical Convergence, and of cloud boundaries elsewhere with other areas having

R. A. Heath

1973-01-01

47

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

48

ConcepTest: EQs at Convergent Boundaries  

NSDL National Science Digital Library

The figures below show the location of a plate boundary (red line) and the distribution of earthquake epicenters (filled black circles). The size of the filled circle indicates the earthquake magnitude. Given the ...

49

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

50

The Arabia-India plate boundary unveiled  

Microsoft Academic Search

Since the advent of Plate Tectonics, tectonic plate boundaries were explored on land as at sea for search of active faults where the destructive energy of earthquakes is released. Yet, some plate boundaries, less active or considered as less dangerous to humankind, escaped general attention and remained unknown to a large extent. Among them, the boundary between two major tectonic

M. Fournier; N. R. Chamot-Rooke; M. Rodriguez; C. Petit; P. Huchon; M. Beslier; B. Hazard

2009-01-01

51

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

52

Tertiary palaeogeography and tectonostratigraphic evolution of the Northern and Southern Peri-Tethys platforms and the intermediate domains of the African–Eurasian convergent plate boundary zone  

Microsoft Academic Search

The increasing effects of African–Eurasian convergence during the Tertiary resulted in the uplift and emergence of the Northern and Southern Peri-Tethys platforms. Palaeogeographic maps covering six selected time slices, including the Middle Eocene, late Early Oligocene, late Early Miocene, early Middle Miocene, early Late Miocene and Middle to Late Pliocene illustrate that environmental and depositional differentiations on the northern platform

Johan E. Meulenkamp; Wim Sissingh

2003-01-01

53

Spatial variation of the crustal stress field along the Ryukyu-Taiwan-Luzon convergent boundary  

Microsoft Academic Search

We applied an improved stress inversion method to a comprehensive data set of earthquake focal mechanisms to depict the pattern of crustal stress along the western convergent boundary of the Philippine Sea plate. Our results indicate that the crustal stress along the Ryukyu fore arc is segmented with boundaries at or near the places of seamount subduction, including the Tokara

Wen-Nan Wu; Honn Kao; Shu-Kun Hsu; Chung-Liang Lo; How-Wei Chen

2010-01-01

54

Bolivar: Crustal Structure of the Caribbean-South America plate boundary at 70W  

Microsoft Academic Search

The Caribbean-South America plate boundary is characterized by tectonic transpression with oblique convergence. The ~ 20 mm\\/yr eastward displacement of the Caribbean plate, with respect to a fixed South America causes the plate boundary to have a dominant right-lateral strike-slip component, accommodated by the San Sebastian-El Pilar fault system. To the west, relative plate motion is complicated by the northeastward

M. C. Guedez; C. A. Zelt; B. M. Magnani; A. Levander

2006-01-01

55

Three-dimensional mechanics of Yakutat convergence in the southern Alaskan plate corner  

NASA Astrophysics Data System (ADS)

Three-dimensional numerical models are used to investigate the mechanical evolution of the southern Alaskan plate corner where the Yakutat and the Pacific plates converge on the North American plate. The evolving model plate boundary consists of Convergent, Lateral, and Subduction subboundaries with flow separation of incoming material into upward or downward trajectories forming dual, nonlinear advective thermal/mechanical anomalies that fix the position of major subaerial mountain belts. The model convergent subboundary evolves into two teleconnected orogens: Inlet and Outlet orogens form at locations that correspond with the St. Elias and the Central Alaska Range, respectively, linked to the East by the Lateral boundary. Basins form parallel to the orogens in response to the downward component of velocity associated with subduction. Strain along the Lateral subboundary varies as a function of orogen rheology and magnitude and distribution of erosion. Strain-dependent shear resistance of the plate boundary associated with the shallow subduction zone controls the position of the Inlet orogen. The linkages among these plate boundaries display maximum shear strain rates in the horizontal and vertical planes where the Lateral subboundary joins the Inlet and Outlet orogens. The location of the strain maxima shifts with time as the separation of the Inlet and Outlet orogens increases. The spatiotemporal predictions of the model are consistent with observed exhumation histories deduced from thermochronology, as well as stratigraphic studies of synorogenic deposits. In addition, the complex structural evolution of the St Elias region is broadly consistent with the predicted strain field evolution.

Koons, P. O.; Hooks, B. P.; Pavlis, T.; Upton, P.; Barker, A. D.

2010-08-01

56

Feedback between mountain belt growth and plate convergence  

Microsoft Academic Search

While it is generally assumed that global plate motions are driven by the pattern of convection in the Earth's mantle, the details of that link remain obscure. Bouyancy forces associated with subduction of cool, dense lithosphere at zones of plate convergence are thought to provide significant driving force, but the relative magnitudes of other driving and resisting forces are less

Giampiero Iaffaldano; Hans-Peter Bunge; Timothy H. Dixon

2006-01-01

57

Question of the Day: Plate Boundary Characteristics  

NSDL National Science Digital Library

What kind of plate tectonic process or boundary would you expect if you find a seafloor region with: 1. A long, narrow linear or gently curving deep valley, earthquakes to depths of several hundred km, and ...

58

METRIC TENSOR ESTIMATES, GEOMETRIC CONVERGENCE, AND INVERSE BOUNDARY PROBLEMS  

Microsoft Academic Search

Three themes are treated in the results announced here. The rst is the regularity of a metric tensor, on a manifold with boundary, on which there are given Ricci curvature bounds, on the manifold and its boundary, and a Lipschitz bound on the mean curvature of the boundary. The second is the geometric convergence of a (sub)sequence of manifolds with

MICHAEL ANDERSON; ATSUSHI KATSUDA; YAROSLAV KURYLEV; MATTI LASSAS; MICHAEL TAYLOR

59

Feedback between mountain belt growth and plate convergence  

NASA Astrophysics Data System (ADS)

While it is generally assumed that global plate motions are driven by the pattern of convection in the Earth's mantle, the details of that link remain obscure. Bouyancy forces associated with subduction of cool, dense lithosphere at zones of plate convergence are thought to provide significant driving force, but the relative magnitudes of other driving and resisting forces are less clear, as are the main factors controlling long-term changes in plate motion. The ability to consider past as well as present plate motions provides significant additional constraints, because changes in plate motion are necessarily driven by changes in one or more driving or resisting forces, which may be inferred from independent data. Here we present for the first time a model that explicitly links global mantle convection and lithosphere models to infer plate motion changes as far back as Miocene time. By accurately predicting observed convergence rates over the past 10 m.y., we demonstrate that surface topography generated at convergent margins is a key factor controlling the long-term evolution of plate motion. Specifically, the topographic load of large mountain belts and plateaus consumes a significant amount of the driving force available for plate tectonics by increasing frictional forces between downgoing and overriding plates.

Iaffaldano, Giampiero; Bunge, Hans-Peter; Dixon, Timothy H.

2006-10-01

60

Tectonics of the Jurassic-Early Cretaceous magmatic arc of the north Chilean Coastal Cordillera (22°-26°S): A story of crustal deformation along a convergent plate boundary  

Microsoft Academic Search

The tectonic evolution of a continental magmatic arc that was active in the north Chilean Coastal Cordillera in Jurassic-Early Cretaceous times is described in order to show the relationship between arc deformation and plate convergence. During stage I (circa 195-155 Ma) a variety of structures formed at deep to shallow crustal levels, indicating sinistral arc-parallel strike-slip movements. From deep crustal

Ekkehard Scheuber; Gabriel Gonzalez

1999-01-01

61

Tectonics of the Jurassic-Early Cretaceous magmatic arc of the north Chilean Coastal Cordillera (22°-26°S): A story of crustal deformation along a convergent plate boundary  

NASA Astrophysics Data System (ADS)

The tectonic evolution of a continental magmatic arc that was active in the north Chilean Coastal Cordillera in Jurassic-Early Cretaceous times is described in order to show the relationship between arc deformation and plate convergence. During stage I (circa 195-155 Ma) a variety of structures formed at deep to shallow crustal levels, indicating sinistral arc-parallel strike-slip movements. From deep crustal levels a sequence of structures is described, starting with the formation of a broad belt of plutonic rocks which were sheared under granulite to amphibolite facies conditions (Bolfin Complex). The high-grade deformation was followed by the formation of two sets of conjugate greenschist facies shear zones showing strike-slip and thrust kinematics with a NW-SE directed maximum horizontal shortening, i.e., parallel to the probable Late Jurassic vector of plate convergence. A kinematic pattern compatible to this plate convergence is displayed by nonmetamorphic folds, thrusts, and high-angle normal faults which formed during the same time interval as the discrete shear zones. During stage II (160-150 Ma), strong arc-normal extension is revealed by brittle low-angle normal faults at shallow levels and some ductile normal faults and the intrusion of extended plutons at deeper levels. During stage III (155-147 Ma), two reversals in the stress regime took place indicated by two generations of dikes, an older one trending NE-SW and a younger one trending NW-SE. Sinistral strike-slip movements also prevailed during stage IV (until ˜125 Ma) when the Atacama Fault Zone originated as a sinistral trench-linked strike-slip fault. The tectonic evolution of the magmatic arc is interpreted in terms of coupling and decoupling between the downgoing and overriding plates. The structures of stages I and IV suggest that stress transmission due to seismic coupling between the plates was probably responsible for these deformations. However, decoupling of the plates occurred possibly due to a decrease in convergence rate resulting in extension and the reversals of stages II and III.

Scheuber, Ekkehard; Gonzalez, Gabriel

1999-10-01

62

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

63

Tectonic mélange as fault rock of subduction plate boundary  

NASA Astrophysics Data System (ADS)

An assemblage of quantitative data sets is examined to evaluate tectonic mélange as a plate boundary fault rocks in subduction zone. The research object is the latest Cretaceous Mugi mélange in the Shimanto Belt, southwest Japan. Systematic age younging from pelagic to terrigenous through hemipelagic sediments is well-documented even though original stratigraphy is disrupted. Systematic shear fabric consistent with ancient plate convergence is reconstructed. The mélange was formed at temperatures of ~ 130-200 °C by cataclastic comminution of sandstone layers accompanied by tensile cracking, and plastic deformation and the dehydration of clayey shale matrix, with subsequent peeling off and underplating of the oceanic basement.The temperature setting for the Mugi mélange indicates around the up-dip limit of the seismogenic zone, therefore includes various fault rocks suggestive of earthquake fault; pseudotachylyte, fluidized ultracataclasite with heating evidence, amorphous silica and so on. These suggest that fluid induced lubrication was dominated. Localized cataclastic shear, which is a candidate of small earthquake or very low frequency earthquake, is also recognized especially in sandstone blocks dominated portion in mélange. These observations are consistent with the mélange being a fault rock along the plate boundary that records various types of earthquakes in a subduction zone. The quantitative examination of the Mugi mélange suggests several criteria to define the tectonic mélange of the plate boundary fault in subduction zone from other mélanges in orogenic belt.

Kimura, Gaku; Yamaguchi, Asuka; Hojo, Megumi; Kitamura, Yujin; Kameda, Jun; Ujiie, Kohtaro; Hamada, Yohei; Hamahashi, Mari; Hina, Shoko

2012-09-01

64

A fast convergent iterative boundary element method on PVM cluster  

Microsoft Academic Search

This paper reports a fast convergent boundary element method on a Parallel Virtual Machine (PVM) (Geist et al., PVM: Parallel Virtual Machine, A Users' Guide and Tutorial for Networked Parallel Computing. MIT Press, Cambridge, 1994) cluster using the SIMD computing model (Single Instructions Multiple Data). The method uses the strategy of subdividing the domain into a number of smaller subdomains

N. Mai-Duy; P. Nguyen-Hong; T. Tran-Cong

1998-01-01

65

Plate Tectonics: From Plate Boundary Zone Tectonics To Extensive Intraplate Tectonics  

Microsoft Academic Search

Plates makes up earth's surface, and tectonic activity is generally concentrated on plate boundary zones. In restrict meaning, plate tectonics of the earth is regarded as mixture of plate boundary zone tectonics and extensive intraplate tectonics. For example, the Asian continent never behaves as rigid plate that was deformed extensively when the Indian continent collided with it. I infer that

M. Ishikawa

2004-01-01

66

The Role of Plate Boundaries in Degassing: Dynamic Mantle Models  

NASA Astrophysics Data System (ADS)

In recent years, the geodynamical community has put forth a number of models which examine the chemical evolution of the mantle with respect to noble gases. These models are able to satisfy general constraints such as heat flow and overall degassing rate, but have difficulty in reproducing the noble gas isotopic heterogeneity observed in oceanic basalts. Such models generally employ a free slip surface boundary condition and thus lack the formation of sharp and long-lived zones of convergence and divergence that are associated with subduction zones and mid-oceanic ridges. This makes it difficult in the models to distinguish mid-oceanic ridge volcanism from ocean island volcanism. Model approximations of plate tectonics include the prescription of a kinematic surface boundary condition, or by using an advanced rheological description with imposed weak zones or a finite yield strength criterion. Here, we use another approach, which is based on the force balance method by Gable (JGR, 1991). This is essentially an advanced kinematic boundary condition in which segments of constant boundary velocity are prescribed in a way that is dynamically consistent with the overall convective flow. By doing this, we explicitly link degassing to zones of plate divergence in our model, thereby consistently following the degassing associated with mid ocean ridge volcanism. Our model simulates mantle convection by the numerical solution of the time dependent Boussinesq equations on a two dimensional cylindrical finite element mesh, with mantle noble gas inventories discritized to a large number of passive tracers. We present the results from a suite of model runs with temperature- and pressure-dependent viscosity, and with a variable number of plates.

Brandenburg, J.; van Keken, P. E.; Ballentine, C. J.; Hauri, E. H.

2004-12-01

67

Florida: A Jurassic transform plate boundary  

NASA Astrophysics Data System (ADS)

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

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

1984-09-01

68

Characterizing the southeast Caribbean-South American plate boundary at 64°W  

Microsoft Academic Search

The crustal and lithospheric structure of the northern South America plate boundary with the southeast Caribbean has been the focus of many studies. In this region, westward subduction of (Atlantic) oceanic South America transitions to east-west transform between continental South America and the Caribbean plate. Previous models invoke a poorly-constrained component of north-south convergence between the Caribbean and continental South

Stephen Anthony Clark

2007-01-01

69

Boundary element analysis of shear deformable stiffened plates  

Microsoft Academic Search

In this paper a boundary element formulation for analysis of shear deformable stiffened plates is presented. The formulation is derived by coupling boundary element formulation of shear deformable plate and two-dimensional plane stress elasticity. Both concentric and eccentric stiffeners have been considered. The interaction forces between stiffeners and the plate are treated as either line distribution or area distribution of

P. H. Wen; M. H. Aliabadi; A. Young

2002-01-01

70

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

71

Development of transtensional and transpressive plate boundaries due to noncircular (cycloid) relative plate motion  

SciTech Connect

The trace of a transform fault commonly is assumed to be circular and concentric with the finite relative motion of the plates adjacent to the fault. These assumptions have led to controversy as the transform fault label has been applied to the San Andreas fault in California because the San Andreas fault is neither circular nor concentric with the motion of the Pacific plate relative to the North American plate. The assumption of circular relative plate motion over a finite time interval is not generally valid. When finite relative plate motion is not circular, the length and orientation of a transform fault must change through time. The length and orientation of ridge-ridge transform faults in oceanic crust evolve through the migration, propagation, and abandonment of ridge segments. Transform faults that bound continental crust evolve differently than do transform faults along mid-ocean ridges because continental transform faults typically do not have ridges at both ends and because of the rheological differences between oceanic and continental crust. Along continent-continent transform faults in which the initial displacement is entirely strike slip, later displacements will be progressively more divergent or convergent (i.e., transtensive or transpressive). Transtension can result in the development of deep basins with high heat flow. Transpression can result in folding, reverse faulting, and decoupling of the crust from its lower crustal or mantle lithosphere in the region adjacent to the transform fault. Regardless of whether the transform boundary becomes transtensional or transpressional, the boundary evolves from a discrete transform fault to a broader, structurally complex accommodation zone (sensu lato).

Cronin, V.S. (Univ. of Wisconsin, Milwaukee (USA))

1990-05-01

72

Influence of exhumation on the structural evolution of transpressional plate boundaries: An example from the Southern Alps, New Zealand  

Microsoft Academic Search

Concentration of erosional activity along transpressional plate boundaries can significantly alter the pattern of mechanical behavior through the influence of exhumation on crustal strength. Three-dimensional numerical modeling of an obliquely convergent orogen shows that a single oblique plate-bounding structure is stable if asymmetric erosion patterns, such as those observed in orographic mountain belts, pertain, and if Earth's crust has a

Peter O. Koons; Richard J. Norris; Dave Craw; Alan F. Cooper

2003-01-01

73

Origin of production gases from convergent plate margins  

SciTech Connect

Molecular and isotopic composition of hydrocarbon production gases from four convergent plate margins have been measured. New Zealand is represented by two gases from the Taranaki basin in the back arc of the active Tonga-Kermadec subduction system. Gases from Barbados and Taiwan are from forearc locations in the active Lesser Antilles system and relict northern Manila Trench system. Philippine gases from offshore Palawan are associated with the Palawan Trough. Gases from Taiwan, the Maiu field in New Zealand, and the Nido field in Palawan have very high /sup 3/He//sup 4/He ratios, indicating considerable mantle input of helium to the gas reservoirs. Variations in /sup 3/He//sup 4/He ratios in neighboring fields are quite striking and suggest localized sources for the mantle components. Possible sources include shallow igneous bodies and fractures or faults tapping a direct mantle source. Measurements of helium isotope ratios in hydrocarbon production gases have been compiled and show a striking association of mantle helium with gases from subduction zones in contrast to deep subsided or rifted sedimentary basins. The dynamics of the subduction process, involving the interaction of upper mantle and crustal rocks, is apparently responsible for the injection of volatile mantle components into reservoired gases. Current exploration techniques are based on maturation and gas migration theories developed from the study of subsiding sedimentary basins. At convergent margins, such technique may have to be amended to include the effects of subduction dynamics on the source, maturation, and migration of hydrocarbons.

Jeffrey, A.W.A.; Poreda, R.J.; Gwilliam, W.J.; Kaplan, I.R.; Craig, H.

1987-05-01

74

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

Microsoft Academic Search

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

R. G. Gordon; S. Zatman

2001-01-01

75

Polarization Anisotropy Along the Anatolian African Plate Boundary  

NASA Astrophysics Data System (ADS)

This study focuses on mantle flow beneath and around the Anatolian plate using measurements of seismic anisotropy. Observations of shear wave splitting across the Anatolian plate have a NE-SW fast direction and lag time similar to that observed from temporary broadband stations within the plate, indicating that the anisotropic fabric may be relatively uniform throughout the upper mantle beneath the Anatolian plate. The extensive young basaltic volcanism, regional travel time tomography, and regional phase attenuation tomography all indicate that the lithospheric mantle beneath most of the Anatolian plate has largely been removed or is very thin. Unless exceptionally high anisotropy exists in the thinned lithosphere, the main contribution to the observed delay times (of order 1 s) must therefore be asthenospheric and thus reflect recent asthenospheric flow patterns. One exception appears to be a change in the fast direction across a region of concentrated extension in western Anatolia. We observe a change in the orientation of the splitting that is consistent with the direction of crustal extension. The African-Anatolian plate boundary is made up of two very different convergent margins: the Hellenic arc to the west and the Cyprian arc to the east. There is substantial evidence that the Hellenic arc is retreating and the Cyprian arc is relatively stationary. Furthermore, both earthquake hypocenters and tomographic models indicate that the Cyprian angle of subduction is much less steep than the subduction occurring along the Hellenic arc. This substantial geometric difference implies that there is a tear or gap in the subduction of African oceanic lithosphere beneath the Anatolian plate along what is called the Isparta Angle. We are investigating mantle dynamics and mantle flow around and through this possible tear in the lithosphere. We will use a combination of seismic tomographic methods (surface wave, body wave, and attenuation) as well as neotectonics studies to help constrain the extent, timing and amount of deformation in and around the Isparta angle. We have initiated this study by deploying another array of seismometers across the western Cyprean arc and extending to the easternmost Hellenic arc and the Burdur fault zone. We will combine these stations with a number of newly established permanent stations in the region to map the asthenospheric flow through this possible stab tear.

Sandvol, E.; Polat, G.; Lough, A.; Sahin, S.; Turkelli, N.

2006-12-01

76

BEHAVIOUR OF NON-LINEAR FLOW AND APPLICATION OF NEURAL NETWORK IN CONVERGING BOUNDARIES  

Microsoft Academic Search

The objective of this study is to develop NNCF (Neural Network on Convergent Flow) models on “Convergent Flow Through Homogeneous Porous Media” to predict the friction factor (fk) and Reynolds number (Rk) for different (Cw) values, when the media is packed in convergent boundaries. This paper presents the results of experiments conducted on Convergent flow permeameter using crushed rock of

P. Rama Mohan Rao; N. Bhanu Prakasham Reddy

2003-01-01

77

A diffuse plate boundary model for Indian Ocean tectonics  

Microsoft Academic Search

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

D. A. Wiens; Charles DeMets; R. G. Gordon; Seth Stein; Don Argus; Joseph F. Engeln; Paul Lundgren; Dan Quible; Carol Stein; Stuart Weinstein; Dale F. Woods

1985-01-01

78

Mapping Plate Boundaries with Reference to Mean Gravity Anomalies.  

National Technical Information Service (NTIS)

A global chart showing plate boundaries as defined by the 1 degree x 1 degree mean free air gravity anomaly holdings of the Dept. of Defense Gravity Library is presented. The chart confirms and, in some cases, redefines the plate boundaries as now delinea...

L. E. Wilcox

1974-01-01

79

Identifying Plate Tectonic Boundaries for a Virtual Ocean Basin  

NSDL National Science Digital Library

Students observe a virtual ocean basin and two adjacent continental margins. From the characteristics of the sea floor and adjacent land, students infer where plate boundaries might be present. They then predict where earthquakes and volcanoes might occur. Finally, they draw their inferred plate boundaries in cross section.

Reynolds, Stephen

80

On the effect of damage and healing from a two-phase damage theory perspective in generating narrow plate boundaries  

NASA Astrophysics Data System (ADS)

The generation of plate tectonics from mantle convection requires shear localization in order to form narrow, weak zones that separate the broad, strong plate interiors. Two-phase damage theory provides a theoretical framework to describe the failure and weakening that leads to shear localization. Two-phase damage theory allows for the development of damage to be manifested in two distinct ways: void generation associated with dilation of the matrix and increasing the fineness of the mixture (e.g. grain size reduction). This work will examine the application of two-phase damage theory to the problem of generating plate-like behavior from mantle convection, as well as investigating the influence of the rheology in simpler flow systems (i.e. simple shear). Our objective is to determine how successful the different manifestations of damage are at producing plate-like behavior in a more sophisticated simulation than previously examined. Our results suggest that divergent and convergent plate boundaries undergo localization in different physical regimes. Convergent plate boundaries are most sensitive to grain size reducing mechanisms, while divergent plate boundaries respond significantly to the interplay of advection and healing. Our results also suggest that allowing for both forms of damage (void and fineness) to work in tandem enables another regime of localization for both convergent and divergent plate boundaries. A series of scaling analyses have been developed to categorize and comprehend the range of behaviors seen in the numerical results.

Landuyt, W.; Bercovici, D.; Ricard, Y.

2006-12-01

81

Discovering Plate Boundaries, A Data-Rich Inquiry-Based Classroom Exercise for Teaching Plate Tectonic Boundary Processes  

Microsoft Academic Search

Discovering Plate Boundaries is a classroom exercise based on 4 world maps containing earthquake, volcano, topography, and seafloor age data. A 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

D. S. Sawyer

2005-01-01

82

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

Microsoft Academic Search

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

Amanda Gail Beardsley

2007-01-01

83

On the frequency-magnitude distribution of converging boundaries  

NASA Astrophysics Data System (ADS)

The occurrence of the last mega-thrust earthquake in Japan has clearly remarked the high risk posed to society by such events in terms of social and economic losses even at large spatial scale. The primary component for a balanced and objective mitigation of the impact of these earthquakes is the correct forecast of where such kind of events may occur in the future. To date, there is a wide range of opinions about where mega-thrust earthquakes can occur. Here, we aim at presenting some detailed statistical analysis of a database of worldwide interplate earthquakes occurring at current subduction zones. The database has been recently published in the framework of the EURYI Project 'Convergent margins and seismogenesis: defining the risk of great earthquakes by using statistical data and modelling', and it provides a unique opportunity to explore in detail the seismogenic process in subducting lithosphere. In particular, the statistical analysis of this database allows us to explore many interesting scientific issues such as the existence of different frequency-magnitude distributions across the trenches, the quantitative characterization of subduction zones that are able to produce more likely mega-thrust earthquakes, the prominent features that characterize converging boundaries with different seismic activity and so on. Besides the scientific importance, such issues may lead to improve our mega-thrust earthquake forecasting capability.

Marzocchi, W.; Laura, S.; Heuret, A.; Funiciello, F.

2011-12-01

84

Boundary knot method: A meshless, exponential convergence, integration-free, and boundary-only RBF technique  

Microsoft Academic Search

Based on the radial basis function (RBF), non-singular general solution and dual reciprocity principle (DRM), this paper presents an inheretnly meshless, exponential convergence, integration-free, boundary-only collocation techniques for numerical solution of general partial differential equation systems. The basic ideas behind this methodology are very mathematically simple and generally effective. The RBFs are used in this study to approximate the inhomogeneous

W. Chen

2000-01-01

85

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

86

Statistical tests of additional plate boundaries from plate motion inversions  

Microsoft Academic Search

The application of the F-ratio test, a standard statistical technique, to the results of relative plate motion inversions has been investigated. The method tests whether the improvement in fit of the model to the data resulting from the addition of another plate to the model is greater than that expected purely by chance. This approach appears to be useful in

Seth Stein; R. G. Gordon

1984-01-01

87

Tectonics of the Hjort region of the Macquarie Ridge Complex, southernmost Australian-Pacific plate boundary, southwest Pacific Ocean  

NASA Astrophysics Data System (ADS)

The Hjort Ridge, Trench, and Plateau comprise the southernmost portion of the Macquarie Ridge Complex (MRC), the Australian-Pacific plate boundary south of New Zealand. The MRC is an ideal location to study deformation and structural development at an obliquely convergent plate boundary involving oceanic lithosphere. This dissertation documents structures and processes in the Hjort region associated with incipient subduction, an outstanding problem in plate tectonics. I investigated the evolution of the plate boundary from ˜33 Ma to the present day, concentrating on the active and recent structural development. Interpretations are based on analyses of recently collected geophysical data in the Hjort region, including swath bathymetry, reflectivity, seismic reflection, gravity, magnetics, and seismicity. The Australian plate is actively underthrusting the Pacific plate along the Hjort Trench, but self-sustaining subduction does not appear to have commenced. Transpression along the length of the plate boundary has been accommodated by lithospheric flexure, strike slip faulting, and geographically limited underthrusting. A consistent relationship exists between the convergence angle and the amount of dynamically supported topography; up to 50 km of convergence has been accommodated by flexure forming ridges and troughs. A continuous, strike slip fault accommodates oblique convergence along the length of the boundary. Where angles of convergence are highest (>20°), underthrusting is observed in addition. Gravity modeling and seismicity suggest ˜50 km of underthrusting in the southern Hjort Trench, but only define an eastwardly dipping Australian slab to about 20 km depth. Lithosphere underthrust in the southern trench is translated subparallel to the ˜N-trending boundary, limiting the eastward extent of underthrust slab. Reconstructions of the plate boundary since 33.3 Ma show that the Antarctic-Australian-Pacific triple junction migrated southward with respect to the Australian plate resulting in the present day curved plate boundary. Migration resulted in lengthening of the dextral transform fault connecting the Macquarie Ridge and Southeast Indian Ridge spreading centers and shortening of the easternmost ridge-segment of latter spreading center. The MRC in the Hjort region changed from a dextral transform into an obliquely convergent zone of incipient subduction.

Meckel, Timothy Ashworth

88

In situ evidence for dextral active motion at the Arabia-India plate boundary  

NASA Astrophysics Data System (ADS)

The Arabia-India plate boundary-also called the Owen fracture zone-is perhaps the least-known boundary among large tectonic plates. Although it was identified early on as an example of a transform fault converting the divergent motion along the Carlsberg Ridge to convergent motion in the Himalayas, its structure and rate of motion remains poorly constrained. Here we present the first direct evidence for active dextral strike-slip motion along this fault, based on seafloor multibeam mapping of the Arabia-India-Somalia triple junction in the northwest Indian Ocean. There is evidence for ~12km of apparent strike-slip motion along the mapped segment of the Owen fracture zone, which is terminated to the south by a 50-km-wide pull-apart basin bounded by active faults. By evaluating these new constraints within the context of geodetic models of global plate motions, we determine a robust angular velocity for the Arabian plate relative to the Indian plate that predicts 2-4mmyr-1 dextral motion along the Owen fracture zone. This transform fault was probably initiated around 8 million years ago in response to a regional reorganization of plate velocities and directions, which induced a change in configuration of the triple junction. Infrequent earthquakes of magnitude 7 and greater may occur along the Arabia-India plate boundary, unless deformation is in the form of aseismic creep.

Fournier, Marc; Chamot-Rooke, Nicolas; Petit, Carole; Fabbri, Olivier; Huchon, Philippe; Maillot, Bertrand; Lepvrier, Claude

2008-01-01

89

Structural Configuration of the Northwestern Caribbean Plate Boundary.  

National Technical Information Service (NTIS)

The interpretation of 6,700 km of magnetic total intensity lines collected between the Cayman Trough and coastal Honduras indicates that two distinct systems of transcurrent faults control the configuration of the northwestern Caribbean plate boundary. A ...

P. R. Pinet

1971-01-01

90

Calibrated Plate Boundary Observatory Borehole Strainmeter Data  

NASA Astrophysics Data System (ADS)

The Plate Boundary Observatory (PBO), funded by NSF as part of the Earthscope program and installed and maintained by UNAVCO, includes 75 borehole strainmeters (BSMs), which makes it one of the largest strainmeter arrays in the world. Co-located with seismometers, and embedded within the PBO continuous GPS network, the strainmeters expand the bandwidth of the Observatory enabling the capture of signals with periods of days to minutes. Six years after installation of the first strainmeter, over 70% of the network is in compression and over 85% of the instruments have a strong signal to noise ratio in the M2 tidal band. UNAVCO's BSM engineers ensure the network usually collects over 95% percent of possible data. UNAVCO makes the BSM Level 0 (raw) and Level 2 (processed) data products available to the community via the Northern California Earthquake Data Center (NCEDC), the IRIS DMC and UNAVCO's own web site. Processed BSM data includes gauge, areal, differential and tensor shear strains plus data edits and time series corrections for barometric pressure, earth tides, ocean load and borehole trends. Before strain data can be incorporated into a geophysical model with confidence, however, an instrument response must be found that relates the gauge measurements to the regional strains (i.e., an in-situ calibration is needed). In this presentation we describe the method UNAVCO will use to calibrate PBO strainmeters using earth tides as a reference signal and assuming an anisotropic instrument setting. The calibrated data will be released in a simple delimited ASCII format and will be included with the processed data set that is currently updated every 24 hours. In addition to the 5-minute Level 2 data set, UNAVCO will include the calibrated areal and shear strains at 1-sps for significant events anywhere in the world as part of its Special Event series. In order to meet Earthscope goals of data transparency and processing repeatability, the expanded processed data sets will include a summary of the calibration method, tidal observations, predictions upon which the calibrations are based and the strain matrix used to generate the areal and shear data. This presentation will also describe the new file naming convention that will allow the user to 1.) select a preferred calibration method for their data and 2.) allow UNAVCO the flexibility of including new methods of calibration in the future.

Hodgkinson, K. M.; Mencin, D.; Borsa, A. A.; Fox, O.; Gallaher, W. W.; Gottlieb, M. H.; Henderson, D. B.; Johnson, W.; Pyatt, C.; Van Boskirk, L.

2011-12-01

91

AN EXPERIMENTAL STUDY ON THE EFFECT OF CONVERGING BOUNDARY ON FLOW THROUGH POROUS MEDIA  

Microsoft Academic Search

Flow behaviour through porous media with converging boundaries is analysed theoretically and the modifications in the Forchheimer equation needed to incorporate the effect of convergence are brought out. An experimental investigation on the effect of convergence factors on the resistance law relating friction factor (fR) and Reynolds number (RR) using the hydraulic radius as the characteristic length was carried out

N. Bhanu Prakasham Reddy

2005-01-01

92

Vibration of mindlin plates using boundary characteristic orthogonal polynomials  

Microsoft Academic Search

The vibration analysis of shear deformable plates formulated on the basis of first order Mindlin theory is presented. The displacement and rotational functions of the plates are approximated by sets of boundary characteristic orthogonal polynomials. The ease of generation and manipulation of these polynomial functions greatly enhances the computational efficiency of the numerical method. The energy functional of the shear

K. M. Liew; K. C. Hung; M. K. Lim

1995-01-01

93

Relationship between the present-day stress field and plate boundary forces in the Pacific Northwest  

USGS Publications Warehouse

The relationship between plate boundary forces and the observed stress field in the Pacific Northwest is established using numerical models of continental deformation. Because the orientation of the greatest horizontal principal stress throughout the Pacific Northwest differs considerably from the direction of convergence between the Juan de Fuca and North American plates, the relationship between the stress field and forces acting along the subduction zone has been unclear. To address this relationship, a two-dimensional finite element model developed by Bird [1989] is used that incorporates critical aspects of continental deformation such as a stratified rheology and interaction between thermal and mechanical components of deformation. Boundary conditions are specified in terms of either velocity or shear traction, depending on whether the computed shear stress at the plate boundary is less than or exceeds, respectively, a prescribed limit. Shear-stress limits on the subduction and transform plate boundaries are independently varied to determine the relative effect of forces along these boundaries on intraplate deformation. Results from this study indicate that the shear stress limit of both subduction and transform boundaries is low, and that the intraplate stress field is attributed, in part, to the normal component of relative plate motion along the transform boundaries. However, the models also indicate that although the subduction zone fault is weak, a minimum shear strength ( ??? 10 MPa) for the fault is necessary to explain the observed stress field. The balance among forces along the tectonic boundaries of North America results in a surprising degree of variation in the present-day stress field.

Geist, E. L.

1996-01-01

94

Sharp Lithosphere-asthenosphere Boundaries of Oceanic Plates  

Microsoft Academic Search

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

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

2008-01-01

95

The Plate Boundary Observatory Borehole Network: Combining Geodetic, Seismic and Environmental Data to Understand Plate Boundary Deformation  

Microsoft Academic Search

The Plate Boundary Observatory (PBO), the geodetic component of the NSF-funded Earthscope program, is designed to capture the continuous three-dimensional deformation field across the western US plate boundary. Installed and maintained by UNAVCO, the observatory currently consists of over 1100 continuously operating GPS stations and 79 borehole installations. PBO boreholes are multi-instrumented sites containing a combination of strainmeters, seismometers, pore

K. M. Hodgkinson; D. Mencin; D. B. Henderson; A. A. Borsa; W. Johnson; M. H. Gottlieb; E. van Boskirk; W. Gallaher; O. Fox; J. Smith; M. E. Jackson

2010-01-01

96

Viscoelastic Postseismic Rebound to Strike-Slip Earthquakes in Regions of Oblique Plate Convergence.  

National Technical Information Service (NTIS)

According to the slip partitioning concept, the trench parallel component of relative plate motion in regions of oblique convergence is accommodated by strike-slip faulting in the overriding continental lithosphere. The pattern of postseismic surface defo...

S. C. Cohen

1999-01-01

97

Analytical treatment of boundary integrals in direct boundary element analysis of plate bending problems  

Microsoft Academic Search

A direct-type Boundary Element Method (BEM) for the analysis of simply supported and built-in plates is employed. The integral equations due to a combined biharmonic and harmonic governing equations are first established. The boundary integrals developed are then evaluated analytically. The domain integrals due to external body forces are also transformed over the boundary and subsequently evaluated analytically. Thus, it

G. Karami; J. Zarrinchang; B. Foroughi

1994-01-01

98

Micro\\/nano sliding plate problem with Navier boundary condition  

Microsoft Academic Search

For Newtonian flow through micro or nano sized channels, the no-slip boundary condition does not apply and must be replaced by a condition which more properly reflects surface roughness. Here we adopt the so-called Navier boundary condition for the sliding plate problem, which is one of the fundamental problems of fluid mechanics. When the no-slip boundary condition is used in

Miccal T. Matthews; James M. Hill

2006-01-01

99

Micro\\/nano sliding plate problem with Navier boundary condition  

Microsoft Academic Search

.  For Newtonian flow through micro or nano sized channels, the no-slip boundary condition does not apply and must be replaced\\u000a by a condition which more properly reflects surface roughness. Here we adopt the so-called Navier boundary condition for the\\u000a sliding plate problem, which is one of the fundamental problems of fluid mechanics. When the no-slip boundary condition is\\u000a used in

Miccal T. Matthews; James M. Hill

2006-01-01

100

Radiocarbon evidence for extensive plate-boundary rupture about 300 years ago at the Cascadia subduction zone  

Microsoft Academic Search

THE Cascadia subduction zone, a region of converging tectonic plates along the Pacific coast of North America, has a geological history of very large plate-boundary earthquakes1,2, but no such earthquakes have struck this region since Euro-American settlement about 150 years ago. Geophysical estimates of the moment magnitudes (Mw) of the largest such earthquakes range from 8 (ref. 3) to 9

Alan R. Nelson; Brian F. Atwater; Peter T. Bobrowsky; Lee-Ann Bradley; John J. Clague; Gary A. Carver; Mark E. Darienzo; Wendy C. Grant; Harold W. Krueger; Rodger Sparks; Thomas W. Stafford; Minze Stuiver

1995-01-01

101

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

NASA Astrophysics Data System (ADS)

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 plate tectonics by increasing frictional forces between downgoing and overriding plates. Here we use this insight to pose a new tectonic inverse problem and to infer the growth of mountain belts from a record of past plate convergence. We introduce the automatic differentiation method, which is a technique to produce derivative code free of truncation error by source transformation of the forward model. We apply the method to a publicly available global tectonic thin-shell model and generate a simple derivative code to relate Nazca/South America plate convergence to gross topography of the Andes mountain belt. We test the code in a search algorithm to infer an optimal paleotopography of the Andes 3.2 m.y. ago from the well-known history of Nazca/South America plate convergence. Our modeling results are in excellent agreement with published estimates of Andean paleotopography and support the notion of strong feedback between mountain belt growth and plate convergence.

Iaffaldano, Giampiero; Bunge, Hans-Peter; Bücker, Martin

2007-08-01

102

Characterizing the southeast Caribbean-South American plate boundary at 64°W  

NASA Astrophysics Data System (ADS)

The crustal and lithospheric structure of the northern South America plate boundary with the southeast Caribbean has been the focus of many studies. In this region, westward subduction of (Atlantic) oceanic South America transitions to east-west transform between continental South America and the Caribbean plate. Previous models invoke a poorly-constrained component of north-south convergence between the Caribbean and continental South America, predicting that the westward subduction transitions to northwest-dipping subduction beneath the Serrania del Interior. These models predict that continental crust extends north of the Venezuela coast beneath the Leeward Antilles remnant arc islands, and that the Leeward Antilles are accreting onto South America. The results presented in this dissertation determine instead that the dextral strike-slip system along the Venezuelan coast cuts near-vertically through the crust and offsets the Moho. The strike-slip system fundamentally defines the plate boundary, deriving from a shear tear through the entire lithosphere that is actively propagating north of the Paria peninsula. This shear tear detaches subducting oceanic crust from buoyant continental crust along the weakened, former passive margin. Thrust faults flanking the strike-slip system to the north and south dip systematically toward the plate boundary. These faults have been previously interpreted as delineating a 300 km-wide diffuse plate boundary zone, caused by oblique convergence partitioned into orthogonal thrust and strike-slip displacements. Instead, these faults are driven largely by vertical rather than horizontal tectonics, and are the result of the geodynamic response to the shear tear.

Clark, Stephen Anthony

103

Paleomagnetic Quantification of Neogene Block Rotations within an Active Transtensional Plate Boundary, Baja California, Mexico  

Microsoft Academic Search

Compared to oceanic plate boundaries which are generally narrow zones of deformation, continental plate boundaries appear as widespread areas with complex and poorly understood kinematics. Motion of crustal blocks within these ``diffuse plate boundaries'' causes rather small-scale lithospheric deformation within the boundary zone, while the main plates behave more rigid. Complex deformation patterns of interacting terranes separated by a variety

J. Weber; P. J. Umhoefer; J. A. Pérez Venzor; V. Bachtadse

2009-01-01

104

Feedback between mountain belt growth and plate convergence revealed by forward and inverse tectonic models  

NASA Astrophysics Data System (ADS)

While it is generally assumed that global plate motions are driven by the pattern of convection in the Earth's mantle, the details of that linkage remain obscure. Bouyancy forces associated with subduction of cool, dense lithosphere at zones of plate convergence are thought to provide significant driving force, but the relative magnitudes of other driving and resisting forces are less clear. The ability to consider past as well as present plate motions provides significant additional constraints, because changes in plate motion are necessarily driven by changes in one or more driving or resisting forces, which may be inferred from independent data. Here we first exploit the capabilities of forward tectonic models of the Andean region to infer plate motion changes as far back as Miocene time. By accurately predicting observed convergence rates between Nazca and South America plates over the last 10 Myrs, we demonstrate for the first time that the topographic load of the Andes increases frictional forces between downgoing and overriding plates and thus consumes a significant amount of the driving force available for plate tectonics. This result suggests a strong feedback between mountain belt growth and plate convergence. We then test this notion by performing a numerical inversion of the same model. We use the Automatic Differentiation approach to generate a derivative code that relates convergence of the Nazca/South America plates to gross topography of the Andes mountain belt. We test the derivative code in a simple search algorithm to infer an optimal paleotopography of the Andes at 3.2 m.y. from the well-known history of Nazca/South America plate convergence. Our modeling result is in good agreement with independent published estimates of Andean paleotopography.

Iaffaldano, G.; Bunge, H.; Dixon, T. H.; Buecker, M.

2006-12-01

105

Strong plate coupling along the Nazca\\/South America convergent margin  

Microsoft Academic Search

The force balance in plate tectonics is fundamentally important, but poorly known. Much information on the dynamics is embedded in the record of past and present plate velocities, featured with long- as well as short- term variations, but a precise budget, in particular of resistive coupling forces along convergent margins, is hard to come by. Building on substantial, yet separate

G. Iaffaldano; H. Bunge

2007-01-01

106

Dynamical boundary control for elastic plates of general shape  

NASA Astrophysics Data System (ADS)

The control of transverse vibrations of elastic plates of general shape by feedback boundary control is formulated as an abstract evolution equation. Because the control acts locally on the boundary, which possesses a flanged rim with inertial properties of mass and bending moment, the analysis concerns dynamical controllability and stabilizability of a hybrid system. By the approach of energy decay inequalities and Hoermander's global uniqueness theorem, it is shown that the system is strongly stabilizable by a locally supported damping feedback of boundary velocity and boundary angular velocity, and hence the system is approximately controllable.

Markus, Lawrence; You, Yuncheng

1993-07-01

107

Convergence of the boundary control for the wave equation in domains with holes of critical size  

Microsoft Academic Search

In this paper, we consider the homogenization of the exact control- lability problem for the wave equation in periodically perforated domain with holes of critical size. We show that the boundary control converges to the boundary control of the homogenized system under the assumption that the perforations are uniformly away from the boundary.

A. K. Nandakumaran

2002-01-01

108

Stress fields of the overriding plate at convergent margins and beneath active volcanic arcs.  

PubMed

Tectonic stress fields in the overriding plate at convergent plate margins are complex and vary on local to regional scales. Volcanic arcs are a common element of overriding plates. Stress fields in the volcanic arc region are related to deformation generated by subduction and to magma generation and ascent processes. Analysis of moment tensors of shallow and intermediate depth earthquakes in volcanic arcs indicates that the seismic strain field in the arc region of many convergent margins is subhorizontal extension oriented nearly perpendicular to the arc. A process capable of generating such a globally consistent strain field is induced asthenospheric corner flow below the arc region. PMID:17774792

Apperson, K D

1991-11-01

109

Evolution of the Plate Boundary Through New Zealand since 25 Ma Implications for the Development of the Alpine Fault  

NASA Astrophysics Data System (ADS)

The current plate boundary configuration through New Zealand of a (transpressional) continental transform linking two convergent/subduction zones initiated approximately 25 Ma. Its present configuration, kinematics, and patterns of deformation are reasonably well constrained, although the tectonic history of boundary is less clear. In particular, the extent, geometry, location, and deformational behavior of the plate boundary linking the Hikurangi and Puysegur subduction regimes the proto-Alpine Fault (AF) plate boundary structure prior to approximately 10 Ma is not well understood. Combining plate reconstructions, patterns of basin evolution and volcanism recording the southward migration of Hikurangi subduction, and plate kinematics through time allow us to place important constraints on the development of the proto-Alpine fault plate boundary through the Miocene. Results include (1) a substantial volume of crustal material must have been removed along the proto- AF adjacent/within the present North Island, implying transpression along that segment of the plate boundary in the Middle Miocene and the development of a Southern Alps-like orogen bounding the eastern margin of the present-day North Island; (2) Hikurangi margin forearc terranes were likely originally part of the Pacific plate (i.e. east of the proto-AF) and have been sequentially captured by the Australian plate in a manner similar to present capture by Australia of the Marlborough terranes in the northern South Island; (3) remnants of the proto-AF structures should lie inboard of these forearc terranes and may be associated with faults of the North Island Axial Ranges; and (4) the proto-AF plate boundary may have had different geometry, orientation, and attitude from the current Alpine Fault through the South Island characteristics that are in part controlled by the structure and mechanical properties of the Australia plate margin. This analysis implies that the Alpine Fault system was transpressional throughout much of its history and not only post-Miocene as is normally assumed.

Furlong, K. P.; Kamp, P. J.

2006-12-01

110

Feedback Between Mountain Belt Growth and Plate Convergence Revealed by Forward and Inverse Tectonic Models  

NASA Astrophysics Data System (ADS)

While it is generally assumed that global plate motions are driven by the pattern of convection in the Earth's mantle, the details of that linkage remain obscure. Bouyancy forces associated with subduction of cool, dense lithosphere at convergent zones are thought to provide significant driving force, but the relative magnitudes of other driving and resisting forces are less clear. The ability to consider past as well as present plate motions provides significant additional constraints, because changes in plate motion must be necessarily driven by changes in one or more driving or resisting forces, which may be inferred from independent data. Here we first exploit the capabilities of forward global tectonic models focused on the Andean region to infer plate motion changes as far back as Miocene time. By accurately predicting observed convergence rates between Nazca and South America plates over the past 10 Myrs, we demonstrate that the topographic load of the Andes increases resistive forces between downgoing and overriding plates and thus consumes a significant amount of the driving force available for plate tectonics. This result suggests a strong feedback between mountain belt growth and plate convergence. We then test this notion by performing a numerical inversion of the same model. We use the Automatic Differentiation approach to generate a derivative code that relates convergence of the Nazca/South America plates to gross topography of the Andes mountain belt. We test the derivative code in a simple search algorithm to infer an optimal paleotopography of the Andes at 3.2 Myrs from the well-known history of Nazca/South America plate convergence. Our modeling result is in good agreement with independent published estimates of Andean paleotopography.

Iaffaldano, G.; Buecker, M.

2009-05-01

111

The accommodation of Arabia-Eurasia plate convergence in Iran  

Microsoft Academic Search

Continental convergence between Arabia and Eurasia is taken up by distributed deformation in Iran. At wavelengths large compared with the thickness of the lithosphere this deformation is best described by a continuous velocity field. The only quantitative source of information on the spatial distribution of strain rates within Iran is the record of earthquakes. We find that we can reproduce

James Jackson; John Haines; William Holt

1995-01-01

112

Fluxes of mantle and subducted carbon along convergent plate boundaries  

Microsoft Academic Search

The potential impact of increases in atmospheric CO2 is a topic of considerable controversy. Even though volcanic emission of CO2 may be very small as compared to anthropogenic emissions, evaluation of natural degassing of CO2 is important for any model of the geochemical C cycle and evolution of the Earth's atmosphere. We report here the mantle C flux in subduction

Yuji Sano; Stanley N. Williams

1996-01-01

113

A Great Earthquake Rupture Across a Rapidly Evolving Three-Plate Boundary  

NASA Astrophysics Data System (ADS)

On 1 April 2007 a great, tsunamigenic earthquake (moment magnitude 8.1) ruptured the Solomon Islands subduction zone at the triple junction where the Australia and Solomon Sea-Woodlark Basin plates simultaneously underthrust the Pacific plate with different slip directions. The associated abrupt change in slip direction during the great earthquake drove convergent anelastic deformation of the upper Pacific plate, which generated localized uplift in the forearc above the subducting Simbo fault, potentially amplifying local tsunami amplitude. Elastic deformation during the seismic cycle appears to be primarily accommodated by the overriding Pacific forearc. This earthquake demonstrates the seismogenic potential of extremely young subducting oceanic lithosphere, the ability of ruptures to traverse substantial geologic boundaries, and the consequences of complex coseismic slip for uplift and tsunamigenesis.

Furlong, Kevin P.; Lay, Thorne; Ammon, Charles J.

2009-04-01

114

Convergence of a boundary value difference equation for computing periodic solutions of neutral delay differential equations  

Microsoft Academic Search

We prove numerical stability and convergence of a finite difference scheme for computing asymptotically stable and unstable periodic solutions of the linear neutral delay differential equation by a periodic boundary value approach

K. Engelborghs; E. J. Doedelb

2001-01-01

115

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

USGS Publications Warehouse

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

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

1990-01-01

116

Cocos Ridge Collision as a Driver for Plate Boundary Deformation in the Western Caribbean  

NASA Astrophysics Data System (ADS)

The subduction and collision of bathymetric highs can result in geodynamic changes along convergent plate boundaries, including intense upper plate deformation, increases in mechanical coupling and seismicity, migration and or cessation of volcanism and formation of forearc terranes. But how extensive can the deformation associated with these features be and what are the implications for the long-term formation and evolution of plate boundary zones? Plate boundary evolution and upper plate deformation in southern Central America associated with Cocos Ridge collision is well studied and indicates, 1) migration of the volcanic arc toward the backarc northwest of and cessation of volcanism directly inboard the ridge, 2) uplift of the Cordillera de Talamanca inboard the ridge, 3) shortening across the forearc Fila Costena fold and thrust belt, and 4) outer forearc uplift above and flanking the ridge. Recent geodynamical modeling of Cocos Ridge collision, combined with the results of kinematic block models for the Central American margin, suggests the ridge drives northwest-directed forearc motion from central Costa Rica northwest to the Cocos - Caribbean (Central American forearc block) - North America triple junction, greatly increasing the spatial scale of deformation. Upperplate deformation of the Central American margin to the southeast of the Cocos Ridge in Panama was not investigated in these models. We investigate the dynamics of Cocos Ridge collision along the entire Central American margin and the implications on plate boundary evolution with a new geodynamic model of ridge collision. Our model results are compared to a new GPS derived horizontal velocity field for Central America and preliminary results indicate that the Cocos Ridge drives the Panamanian isthmus into northern South America (i.e., the North Andes block).

La Femina, P. C.; Govers, R. M.; Geirsson, H.; Kobayashi, D.

2011-12-01

117

Bolivar: Crustal Structure of the Caribbean-South America plate boundary at 70W  

NASA Astrophysics Data System (ADS)

The Caribbean-South America plate boundary is characterized by tectonic transpression with oblique convergence. The ~ 20 mm/yr eastward displacement of the Caribbean plate, with respect to a fixed South America causes the plate boundary to have a dominant right-lateral strike-slip component, accommodated by the San Sebastian-El Pilar fault system. To the west, relative plate motion is complicated by the northeastward tectonic escape of the Maracaibo block along the Bocono and Santa Marta strike-slip faults, and the shortening between North and South America. The convergence rate between the Maracaibo block and the Caribbean has been estimated to be ~ 2 mm/yr. The multidisciplinary BOLIVAR project seeks to understand the complex plate interaction of the Caribbean- South American diffuse plate boundary. We hypothesize that this may be a site of continental growth by island arc accretion of the Leeward Antilles onto South America. The active-seismic component of the project, completed in June 2004, concentrated along five main onshore-offshore profiles extending from the Caribbean basin to the front of the fold and thrust belts of Venezuela. Seismic refraction data were acquired as well as coincident multi-channel seismic (MCS) lines in the offshore sections. We present results from seismic reflection and wide-angle refraction data along a 450 km-long onshore- offshore north-south striking profile at 70 degrees west longitude. Refraction data were used to develop 2-D velocity models from independent and simultaneous traveltime inversion of first arrivals and PmP reflections from 40 Ocean Bottom Seismometers (OBS) and about ~ 80 land recorders. A coincident MCS profile was processed and interpreted independently. Offshore western Venezuela the Caribbean plate is anomalously thick ~ 15 km. The velocity model from wide-angle data is well correlated with the structures interpreted in the reflection data; in particular in the upper and middle crust of the Southern Caribbean Deformed Belt, the Falcon Basin and the Aruba Rise. High- velocity anomalies are spatially associated with the strike-slip Oca-Ancon fault in the region. Underthrusting of the Caribbean plate beneath the South America plate is inferred from the presence of low velocity sediments beneath the South Caribbean Deformed Belt over a distance of 75-100 km.

Guedez, M. C.; Zelt, C. A.; Magnani, B. M.; Levander, A.

2006-12-01

118

The Earthscope Plate Boundary Observatory Akutan Alaskan Volcano Network Installation  

Microsoft Academic Search

During June and July of 2005, the Plate Boundary Observatory (PBO) installed eight permanent GPS stations on Akutan Volcano, in the central Aleutian Islands of Alaska. PBO worked closely with the Alaska Volcano Observatory and the Magmatic Systems Site Selection working group to install stations with a spatial distribution to monitor and detect both short and long term volcanic deformation

B. Pauk; M. Jackson; D. Mencin; J. Power; W. Gallaher; A. Basset; K. Kore; Z. Hargraves; T. Peterson

2005-01-01

119

Stress accumulation and release at complex transform plate boundaries  

Microsoft Academic Search

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 and the results suggest that the San

David Verdonck; Kevin P. Furlong

1992-01-01

120

Stress accumulation and release at complex transform plate boundaries  

Microsoft Academic Search

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

David Verdonck; Kevin P. Furlong

1992-01-01

121

The Magmatic Component of the Plate Boundary Observatory  

Microsoft Academic Search

The Plate Boundary Observatory (PBO) component of the NSF-funded Earthscope program has a significant complement of instruments devoted to the study of magmatic systems. There are ten target areas: Akutan, Unimak, Augustine, Mt St Helens, Long Valley, Yellowstone, Lake Tahoe, Medicine Lake, Mt Lassen, and Mt Shasta that include 22 borehole strainmeters, 22 borehole seismometers, 26 borehole tiltmeters and 110

D. Mencin; M. Jackson; M. Lisowski; K. Feaux; G. Andersen; K. Bohnenstiehl; K. Hodgkinson; B. Coyle; B. Friesen; B. Pauk; C. Walls; C. Meertens

2007-01-01

122

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

123

Do variations in Arabian plate lithospheric structure control deformation in the Arabian-Eurasian convergence zone?  

Microsoft Academic Search

The Arabian plate has been converging with Eurasia for 20-30 Ma, currently at 2-3 cm\\/year. Convergence is manifested differently along strike, with collision and tectonic escape in the west (Anatolia) and subduction of Arabia beneath Eurasia in the east (Iran). The reason for these differences may reflect the greater density of the Arabian lithosphere in the east relative to that

Robert J Stern; Peter R Johnson

2008-01-01

124

Turbulent flow in converging nozzles, part one: boundary layer solution  

Microsoft Academic Search

The boundary layer integral method is used to investigate the development of the turbulent swirling flow at the entrance region\\u000a of a conical nozzle. The governing equations in the spherical coordinate system are simplified with the boundary layer assumptions\\u000a and integrated through the boundary layer. The resulting sets of differential equations are then solved by the fourth-order\\u000a Adams predictor-corrector method.

R. Maddahian; B. Farhanieh; B. Firoozabadi

2011-01-01

125

Oblique Plate Convergence, Margin Truncation and Deformation, Block Rotation, Faulting and Extension/Compression in the Pacific Active Margin and Magmatic Arc of Mexico  

NASA Astrophysics Data System (ADS)

Tectonic evolution at convergent plate boundaries is dominated by plate subduction and mainly controlled by variables such as subduction dip and rate, convergence direction and age of subducted lithosphere. However, there are several examples where deformation appears more complex and extends into the margin interior. Along Western North America, plate convergence since Late Mesozoic has involved complex processes, with the margin characterized by several tectonic blocks and far-traveled terranes with distinct tectonic and stratigraphic records. Large-scale tectonic transport has been documented by paleomagnetic and tectonic studies. Transport has been in the form of accretion to the margin after convergence of the oceanic plate and/or by lateral motion of margin slivers. The large-scale construction of the margin and continental deformation has left a complex record where tectonic deformation with faulting, block rotations, extension and compression has been documented far away into the continental interior. In southern Mexico, plate convergence occurs along the Middle America trench where the Cocos and Rivera oceanic plates are being subducted. Southern Mexico presents characteristics of a composite truncated continental margin, with the trench containing Miocene and younger sediments. Along the margin and the magmatic arc represented by the Trans-Mexican volcanic belt, the region is characterized by structural features which have been interpreted in terms of extensional/compressional tectonics related to wide deformation, oblique convergence and plate reorganizations. Here we discuss the paleomagnetic and geophysical data in terms of regional deformation of the margin and magmatic arc. Aeromagnetic anomalies show apparent regional arcute patterns suggestive of vertical-axis rotation of the margin. The paleomagnetic data show less-clear patterns, which in some areas can be related to lateral faulting, extension/compression and rotation.

Fucugauchi, J. U.

2008-05-01

126

A convergent scheme for boundary control of the heat equation  

Microsoft Academic Search

The terminal state in the considered heat equation problem depends continuously on the initial state and the boundary data. For a specified terminal state, the considered problem can be viewed as a control problem in which the control is provided by the boundary data. A description is presented of an algorithm which, in the event that such a control is

W. C. Chewning; Thomas I. Seidman

1977-01-01

127

Geological record of fluid flow and seismogenesis along an erosive subducting plate boundary.  

PubMed

Tectonic erosion of the overriding plate by the downgoing slab is believed to occur at half the Earth's subduction zones. In situ investigation of the geological processes at active erosive margins is extremely difficult owing to the deep marine environment and the net loss of forearc crust to deeper levels in the subduction zone. Until now, a fossil erosive subduction channel-the shear zone marking the plate boundary-has not been recognized in the field, so that seismic observations have provided the only information on plate boundary processes at erosive margins. Here we show that a fossil erosive margin is preserved in the Northern Apennines of Italy. It formed during the Tertiary transition from oceanic subduction to continental collision, and was preserved by the late deactivation and fossilization of the plate boundary. The outcropping erosive subduction channel is approximately 500 m thick. It is representative of the first 5 km of depth, with its deeper portions reaching approximately 150 degrees C. The fossil zone records several surprises. Two décollements were simultaneously active at the top and base of the subduction channel. Both deeper basal erosion and near-surface frontal erosion occurred. At shallow depths extension was a key deformation component within this erosive convergent plate boundary, and slip occurred without an observable fluid pressure cycle. At depths greater than about 3 km a fluid cycle is clearly shown by the development of veins and the alternation of fast (co-seismic) and slow (inter-seismic) slip. In the deepest portions of the outcropping subduction channel, extension is finally overprinted by compressional structures. In modern subduction zones the onset of seismic activity is believed to occur at approximately 150 degrees C, but in the fossil channel the onset occurred at cooler palaeo-temperatures. PMID:18256668

Vannucchi, Paola; Remitti, Francesca; Bettelli, Giuseppe

2008-02-01

128

Discovering plate boundaries: Laboratory and classroom exercises using geodetic data to develop students' understanding of plate motion  

Microsoft Academic Search

To introduce the concept of plate boundaries, typical introductory geology exercises include students observing and plotting the location of earthquakes and volcanoes on a map to visually demarcate plate boundaries. Accompanying these exercises, students are often exposed to animations depicting the movement of Earth's tectonic plates over time. Both of these teaching techniques are very useful for describing where the

S. E. Olds

2010-01-01

129

Dynamic Plate Boundaries and Restored Synthetic Isochrons: The Indispensable Tools To Constrain Plate Tectonic Models  

NASA Astrophysics Data System (ADS)

We developed a plate tectonics 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 have been constructed through time by adding/removing oceanic material symbolized by syntethic isochrones, to ma- jor continents and terranes. These oceanic isochrons have been constructed through time in order to define the location of the spreading ridges and to restore subducted ocean basins. To simplify the process we worked with a symmetrical sea floor spread- ing for the main oceans (Paleo- and NeoTethys). Driving forces like slab pull and slab buoyancy were used to constrain the evolution of paleo-oceanic domains. This ap- proach offers a good control on the sea floor spreading and plate kinematics. This new method represents a distinct departure from classical continental drift reconstructions, which are not constrained due to the lack of plate boundaries. This model allows a more comprehensive analysis of the development of the Tethyan realm in space and time. In particular, the relationship between the Variscan and the Cimmerian cycles in the Mediterranean-Alpine realm is clearly illustrated by numerous maps. For the Alpine cycle, the relationship between the Alpides senso stricto and the Tethysides is also explicable in terms of plate tectonic development of the Alpine Tethys-Atlantic domain versus the NeoTethys domain.

Borel, G. D.; Stampfli, G. M.

130

Free, transverse vibrations of thin plates with discontinuous boundary conditions  

NASA Astrophysics Data System (ADS)

Vibrations of circular and rectangular plates clamped on part of the boundary and simply supported along the remainder are analyzed by means of a method of perturbation of boundary conditions. This approach appears to be simple and straightforward, giving excellent results for the first mode and its versatility permits to extend it to higher modes of vibration without difficulty. Furthermore, it is shown that the fundamental frequency coefficient can also be determined using a modified Galerkin approach and very simple polynomial coordinate functions which yield good engineering accuracy.

Febbo, M.; Vera, S. A.; Laura, P. A. A.

2005-03-01

131

Boundary effects on the vibration statistics of a random plate  

NASA Astrophysics Data System (ADS)

This paper considers the estimation of statistics of displacement of a vibrating rectangular plate with random wave scatterers. The influence of uncertainty is investigated using point impedance theory. Coherent boundary effects are seen, which decrease when the number of scatterers increases. The boundary effect is investigated using images and the first side and corner reflections are found to be a minimum requirement to estimate the spatial correlation. Statistics for point driven response are investigated under the assumption that the statistics of the natural frequencies follow those of the Gaussian Orthogonal Ensemble (GOE). The estimates are compared with Monte Carlo simulation results, and they show good agreement.

Choi, Wonjae; Langley, Robin S.; Woodhouse, Jim

2013-02-01

132

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

133

BOLIVAR & GEODINOS: Investigations of the Southern Caribbean Plate Boundary  

Microsoft Academic Search

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

A. Levander; M. Schmitz

2006-01-01

134

Owen Fracture Zone: The Arabia-India plate boundary unveiled  

NASA Astrophysics Data System (ADS)

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

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

2011-02-01

135

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

136

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

137

Projection Method I : Convergence and Numerical Boundary Layers  

Microsoft Academic Search

This is the first of a series of papers on the subject of projection methods for viscous incompressible flow calculations. The purpose of these papers is to provide a thorough understanding of the numerical phenomena involved in the projection methods, particularly when boundaries are present, and point to ways of designing more efficient, robust and accurate numerical methods based on

Weinan E; Jian-Guo Liu

1968-01-01

138

Stability and convergence of boundary value methods for solving ODE  

Microsoft Academic Search

we review some recent approaches to the numerical solution of ODE. They are based on the solution of IVP (Initial Value Problem) by means of suitable BVM (Boundary Value Methods). A discussion of their properties of stability and covergence is presented along with their practical construction. The advantages of such methods with respect to IVP methods consist in a higher

P. Marzulli; D. Trigiante

1995-01-01

139

Convergence acceleration for boundary value problems with singularities using the E-algorithm  

Microsoft Academic Search

In the present work we use the E-algorithm to accelerate the convergence of finite-difference schemes for ordinary differential equations. As a model, a boundary-value problem for a second-order differential equation is considered, where the right-hand side may have different kinds of singularities. An asymptotic error expansion is obtained, enabling the use of the E-algorithm to accelerate the convergence. The applicability

Pedro M. Lima; Mário M. Graça

1995-01-01

140

Birth of a Plate Boundary: Detailed thermochronological constraint of Cenozoic Plate Boundary Evolution in the South Island of New Zealand  

Microsoft Academic Search

Detailed thermochronological investigations of individual samples collected west of the Alpine Fault zone in New Zealand provide new insight into the spatial distribution of early Australian-Pacific (AUS-PAC) plate boundary evolution that is not preserved elsewhere in the modern orogenic system of the South Island. Internally consistent cooling histories, derived through combination of 40Ar-39Ar, fission track and (U-Th)\\/He analyses of a

G. E. Batt; M. A. Cottam; S. L. Baldwin

2004-01-01

141

Discovering Plate Boundaries, A Data-Rich Inquiry-Based Classroom Exercise for Teaching Plate Tectonic Boundary Processes  

NASA Astrophysics Data System (ADS)

Discovering Plate Boundaries is a classroom exercise based on 4 world maps containing earthquake, volcano, topography, and seafloor age data. A 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. We have used it successfully with middle school, high school, and college major and non-major earth science classes, as well as with pre-service and in-service teachers. The exercise takes three to four 50 minute class periods to complete and involves the students making presentations to one another in small groups and 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 the way it does. While the materials are accessible on the web (http://terra.rice.edu/plateboundary/ and through http://www.dlese.org ), the actual exercise is not based on student access to the Web and is not dependent on classroom technology equipment.

Sawyer, D. S.

2005-12-01

142

Intraplate Deformation Adjacent to the Macquarie Ridge South of New Zealand - The Tectonic Evolution of a Complex Plate Boundary  

Microsoft Academic Search

The response of lithospheric plate boundaries to rapid changes in plate motions provide constraints used to determine the manner in which transitions in plate motions and plate boundary configurations can occur. In the case of the Australia - Pacific plate boundary in the Macquarie Ridge region south of New Zealand a substantial change in plate motions has occurred since the

G. P. Hayes; K. P. Furlong

2007-01-01

143

Upper plate controls on deep subduction, trench migrations and deformations at convergent margins  

NASA Astrophysics Data System (ADS)

Thus far, relatively simplistic models of free subduction, in which the trench and plate motions are emergent features completely driven by the negative buoyancy of the slab, have investigated the dynamics of a single, isolated subducting plate. Here we extend such models to incorporate an overriding plate and present the results of how such an overriding plate feedbacks into the dynamics of free subduction. In this study, we address three fundamental aspects of these dynamics: 1) how does the presence of an overriding plate change the force balance at the convergent margins? 2) How are the forces from deep subduction propagated to the surface? And 3) what controls the stress regime in a system of coupled upper and subducting plates and how is it expressed in the deformations and plate motions? In general, we find that the evolution of subduction zones is strongly controlled by both the interactions between the slab and the upper-lower mantle discontinuity as well as the strength of the upper plate. When either the subducting or upper plates are unable to move, subduction motions are steady-state and partitioned entirely into either slab rollback or plate advance, respectively. When conditions favour a quasi-stationary trench, subducted lithosphere can form into a pile with multiple recumbent folds of slab material atop the lower mantle. Alternating between forwards- and backwards-draping slab, the corresponding horizontal trench motions at the surface are frontward and rearward, respectively, resulting in either a compressive or extensional regime in the back-arc. Time-dependent forcing arising from the slab piling behaviour can have a feedback with upper plate and produce strongly non-steady state, intermittent phases of upper plate deformation as those commonly observed on Earth. Two types of discontinuous back-arc strain evolution are identified: (1) periodic, when recurrent phases of strain over finite durations are accommodated by (viscous) stretching/thickening of the plate, and (2) episodic, when upper plate deformation localizes (plastic strain) and allows for punctuated episodes. These phases can include extension, quiescence, and compression, giving rise to a large variety of possible tectonic evolutions. The models presented here provide insight into the dynamics behind the non-steady state evolution of subduction, which can help unravel seemingly erratic motions of major convergent margins and back-arc deformations around the Pacific and Indian Oceans during the Cenozoic.

Sharples, W.; Capitanio, F. A.; Stegman, D.; Moresi, L. N.

2009-12-01

144

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

145

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.

146

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

Microsoft Academic Search

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.

R. G. Gordon; J. Royer

2005-01-01

147

Magnetohydrodynamic Boundary Layer Flow Past a Flat Plate  

NASA Astrophysics Data System (ADS)

The Carrier-Greenspan equations footnote H.P. Greenspan and G.F. Carrier, J. Fluid Mech. 6, 77 (1959) for the magnetohydrodynamic boundary layer flow past a flat plate are considered. Group theoretical arguments are used to deduce the asymptotic properties of the solution. A perturbative procedure due to Bender et. al. footnote C.M. Bender, K.M. Milton, S.S. Pensky and L.M. Simmons Jr., J. Math. Phys. 30, 1447 (1989) is used to find an approximate analytic solution of the Carrier-Greenspan equations which confirms the asymptotic properties given above.

Rollins, David; Shivamoggi, Bhimsen

1997-11-01

148

Cenozoic evolution of the Africa-Eurasia plate boundary west of Strait of Gibraltar: mechanical models based on kinematic constraints  

NASA Astrophysics Data System (ADS)

In an effort to identify the source of the 1755 Lisbon earthquake and find the missing link in the Africa-Eurasia plate boundary, extensive surveying has been going on in the Gulf of Cadiz between the Gloria Fault and the Rif-Tell boundary. The main tectonic structures in the region are(1) the allochthonous wedge of the Gulf of Cadiz and (2) a network of cross-cutting NE-SW thrusts and WNW-ESE dextral strike-slip faults. Absence of evidence for a continuous morphological frontier, combined with dispersed seismicity around the most important active thrusts, support the hypothesis that the plate boundary offshore SW Iberia corresponds to a broad (~200 km wide) zone of distributed deformation which accommodates the Africa-Eurasia convergence through dextral strike-slip along the WNW-ESE faults and synchronous oblique westwards thrusting along the NNE-SSW faults. Recently, a new swath bathymetry compilation revealed a new set of linear sub-parallel WNW-ESE trending vertical faults, estimated to be only 2 Ma old, beginning at the end of the Gloria Fault and running on for more than 600 km in the direction of the Rif-Tell plate boundary. On the whole they form a 40 km wide dextral shear band that coincides with a small circle centred on the pole of rotation of Africa with respect to Eurasia. Accordingly this fault system has been interpreted as a precursor to the formation of a new transcurrent Africa-Eurasia plate boundary. Now, if this is a new developing plate boundary the question is why is it so incipient? In fact we should ask what has been the configuration and evolution of the boundary between Africa and Eurasia in the past. Kinematic models for the motions of Africa and Iberia relative to Eurasia hold the key to the history of this plate boundary. The most recent models envisage 3 main phases in the Iberia-Africa movement during the Cenozoic: (1) between An 13 and An 6 Iberia was firmly attached to Africa in such a way that N-S compressive stresses were transmitted across the boundary causing broad intraplate deformation; (2) between An 6 and An 5 decoupling between Iberia and Africa was driven by the westward displacement of the Alboran-Betics-Rif domain; and (3) From An5 to present day Iberia is attached to Eurasia and only the westernmost parts of Iberia and Moroco are still mechanically coupled. In this study we aim to explore how the evolving plate boundary conditions throughout the Cenozoic affected the formation and/or reactivation of the main tectonic structures presently found in the Gulf of Cadiz. For that purpose we use 3D finite element models representing the three phases of the Cenozoic history of the Eurasia-Africa plate boundary. Both the convergence between the African and Iberia plates as the westward drift of the Alboran domain are considered. The plate boundary itself is defined as a set of cross-cutting cohesive zones oriented along the dominant observed structural trends. The precise locations where faults develop, among all areas modelled as cohesive zones, are determined as part of the solution. The characteristics of the fault network evolution sheds light on the configuration of the plate boundary and help to understand its present character.

Neves, M. L.; Monteiro, C.; Matias, L. M.; Rosas, F.; Terrinha, P.

2009-12-01

149

Kinematics of the Western Africa-Eurasia plate boundary from focal mechanisms and GPS data  

NASA Astrophysics Data System (ADS)

The Western Mediterranean displays a complex pattern of crustal deformation distributed along tectonically active belts developed in the framework of slow oblique plate convergence. We used earthquake and Global Positioning System (GPS) data to study the present-day kinematics and tectonics of the Africa-Eurasia plate boundary in this region. Crustal seismicity and focal mechanisms, analysed in terms of seismic moment release and seismic deformation, outline the geometry of major seismic belts and characterize their tectonics and kinematics. Continuous GPS data have been analysed to determine Euler vectors for the Nubian and Eurasian plates and to provide the global frame for a new Mediterranean GPS velocity field, obtained by merging continuous and campaign observations collected in the 1991-2005 time span. GPS velocities and displacements predicted by the Nubia-Eurasia rotation pole provide estimates of the deformation accommodated across the tectonically active belts. The rather simple deformation occurring in the Atlantic region, characterized by extension about perpendicular to the Middle Atlantic and Terceira ridges and right-lateral motion along the Gloria transform fault, turns into a complex pattern of deformation, occurring along broader seismic belts, where continental lithosphere is involved. Our analysis reveals a more complex fragmentation of the plate boundary than previously proposed. The roughly E-W trending mainly compressive segments (i.e. southwestern Iberia, northern Algeria and southern Tyrrhenian), where plate convergence is largely accomodated across rather localized deformation zones, and partially transferred northward to the adjacent domains (i.e. the Algero-Balearic and Tyrrhenian basins), are interrupted by regions of more distributed deformation (i.e. the Rif-Alboran-Betics, Tunisia-Libya and eastern Sicily) or limited seismicity (i.e. the Strait of Sicily), which are characterized by less homogeneous tectonics regimes (mainly transcurrent to extensional). In correspondence of the observed breaks, tectonic structures with different orientation interfere, and we find belts with only limited deformation (i.e. the High and Middle Atlas, the Tunisian Atlas and the offshore Tunisia-Libya belt) that extends from the plate boundary into the Nubian plate, along pre-existing tectonic lineaments. Our analysis suggest that the Sicilian-Pelagian domain is moving independently from Nubia, according to the presence of a right-lateral and extensional decoupling zone corresponding to the Tunisia-Libya and Strait of Sicily deformation zone. Despite the space variability of active tectonic regimes, plate convergence still governs most of the seismotectonic and kinematic setting up to the central Aeolian region. In general, local complexities derive from pre-existing structural features, inherited from the tectonic evolution of the Mediterranean region. On the contrary, along Calabria and the Apennines the contribution of the subducted Ionian oceanic lithosphere and the occurrence of microplates (i.e. Adria) appear to substantially modify both tectonics and kinematics. Finally, GPS data across the Gibraltar Arc and the Tyrrhenian-Calabria domain support the hypothesis that slab rollback in these regions is mostly slowed down or stopped.

Serpelloni, E.; Vannucci, G.; Pondrelli, S.; Argnani, A.; Casula, G.; Anzidei, M.; Baldi, P.; Gasperini, P.

2007-06-01

150

Flat plate turbulent boundary-layer control using vertical LEBUs  

NASA Astrophysics Data System (ADS)

Necessity of aerodynamic drag reduction of aircrafts and other moving objects stimulates researchers for finding out new means of the near-wall turbulence control. In [1] it has been found that the vertical positioning of the LEBUs in boundary layer can be much more efficient compared to the conventional horizontal one, although, according to the same authors, the devices were far from being optimized. Present work is focused upon the study of possibility of turbulent skin-friction reduction using flow-aligned vertical LEBUs, the LEBUs being mounted perpendicular to the flat plate surface in nominally gradient-free incompressible turbulent boundary layer. The Reynolds number based on the momentum thickness of the boundary layer at the LEBUs' position was 1099. All measurements were performed using a computer-controlled automated system of space/time hot wire visualization of mean and fluctuating components of the velocity field. The system provided accuracy not worse than approximately ±2 µm along x, y, and z coordinates. Local skin friction C f in the regular (unmodified) shear flow was determined from the condition of the best correspondence between measured and and classic velocity coefficient profiles in the region of the law of the wall functionality U^+ = A log y+ + B with known coefficients A and B. In the modified boundary layer C f was determined by the mean velocity gradient at the wall (partial U/partial y)_{y=0}. The measurement technique is given in more detail in [2].

Kornilov, V. I.; Boiko, A. V.

151

Experiments on the turbulent boundary layer on a flat plate in the wake of another flat plate  

Microsoft Academic Search

Experiments were conducted on the development of the turbulent boundary layer on a flat plate which was located in the wake of another flat plate. The investigation covered six cases in which the distance between the plates and the momentum thickness of the upstream wake were varied. The results show that the mean velocity and longitudinal fluctuation in the outer

S. Sundaram; K. S. Yajnik

1990-01-01

152

Seismotectonics and recent evolution of the Eurasia-North America Plate Boundary in Northeastern Russia  

NASA Astrophysics Data System (ADS)

In contrast to oceanic plate boundaries which are usually well defined by earthquake locations and magnetic anomalies, the present and past kinematics of plate boundaries in the continents remains problematic in many settings. One particularly vexing such boundary is the one that separates Eurasia from North America in Northeast Russia. In the earliest plate models it was evident that the mid-Atlantic spreading ridge continues in the Arctic as the Gakkel ridge which then runs almost perpendicularly into the continental shelf of Russia in the Laptev sea. On the shelf, and further south on land, the narrow belt of seismicity that is found along the Gakkel ridge broadens into a diffuse swath of earthquakes which is in places more than 800 km wide and extends along the Chersky Range towards the coast of the Okhotsk sea and northern Kamchatka The fact that the Okhotsk sea is aseismic but is surrounded by seismic belts has to lead the interpretation that it is an independent microplate that lies between the Eurasian, North American, Pacific and Amur plates (Cook et al., 1986).Unravelling the kinematics of the Eurasia-Okhotsk-North America Plate boundaries has proven difficult. This is in part due to the paucity of geological and geophysical data from this remote region, and to the fact that the Eurasia-North America pole of rotation lies in close vicinity to the plate boundary itself. Cook et al. (1986), using earthquake slip vectors, placed the current pole of rotation near the Lena river delta, that is, in the area where Eurasia-North America plate boundary comes on shore ). As a consequence, spreading along the Gakkel ridge north of the pole of rotation, should change into convergence or strike-slip to the south depending on the orientation of the boundary. Making specific predictions for fault kinematics in the area has been hampered by the fact that different geophysical and geodetic data-sets have yielded different locations for the Eurasia-North America pole of rotation (Cook et al. 1986; Rowley and Lottes, 1988; De Mets, 1990; Imaev et al., 2000; Kogan et al., 2000). Focal mechanism solutions are predominantly left-lateral and thrust along the Chersky seismic belt, that is, the northern boundary of the Okhotsk plate and right-lateral along its western boundary leading Riegel et al.(1993) to the conclusion that the Okhotsk plate is being extruded to the south. Furthermore, it has been shown on the basis of North Atlantic magnetic and gravity data, that the position of the Eurasia-North America pole of rotation moved significantly over that last 60 my so that the portion of the plate boundary in Northeast Russia changed from predominantly convergent until the Late Cretaceous to divergent until the Early Eocene, followed by various degrees of transpression during the rest of the Cenozoic (Gaina et al., 2002).On the shelf of the Laptev Sea, the Gakkel Ridge gives way to four major continental rift branches with up to 10 km of sedimentary fill spanning from the Late Cretaceous to Recent (Drachev, 1999). Earthquakes are most numerous along the southern margin of the rift system in the Lena delta region and have normal and strike-slip focal mechanism solutions (Imaev et al., 2000). On land, several branches of the rift system overprint the northern termination of the Mesozoic Verkhoyansk fold-and-thrust belt and the accreted arc terranes which are found in its hinterland (Parfenov et al., 1995). Focal mechanism solutions in this area shift from extentional to the north to compressional and strike-slip to the south. The plate boundary continues to the southeast across the Omoloi depression and then follows the trend of major mountain ranges and intermontane basins in the area: the Chersky and Moma ranges and the Moma basin. The Chersky Range, which has the highest topographic elevations in Northeast Russia (3947 m), has a complex history of Mesozoic and Cenozoic deformation (Parfenov and Gaiduk, 2001). The highest peaks are underlain by late Jurassic granite batholiths. Late Oligocene-Miocene deposits along the middle Indigirk

Imaev, V. S.; Imaeva, L. P.; Kozmin, B. M.; Fujita, K. T.; Mackey, K. G.

2009-04-01

153

Visual Abilities and Misconceptions About Plate Tectonics  

Microsoft Academic Search

Diagrams, drawings, and pictures are prototypical representations of concepts. Students' drawings of their concepts of convergent plate boundaries provided an efficient means of discovering some widely held misconceptions. Over 600 general education students' drawings of continent -continent convergent boundaries reveal two common misconceptions. Approximately one-third drew a continent-continent convergent boundary with concave slabs of continental crust as one might imagine

Duncan F. Sibley

154

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

155

Tsunami Signals Recorded By Plate Boundary Observatory Borehole Strainmeters  

NASA Astrophysics Data System (ADS)

The Plate Boundary Observatory (PBO), the geodetic component of the US National Science Foundation funded Earthscope program, is designed to capture the continuous three-dimensional deformation field across the western United States plate boundary. Installed and maintained by UNAVCO, the observatory currently consists of over 1100 continuous GPS sites, 6 long-baseline laser strainmeters and 75 borehole strainmeters. PBO borehole strainmeters have recorded the arrival of tsunamis generated by the 2009 M8.0 Samoa, 2010 M8.8 Chile and 2011 M9.0 Tohoku earthquakes on the Pacific coast of North America. In our analysis of the strain data we find the following: the tsunami arrival times recorded by the strainmeters are consistent with those recorded by nearby tide-gauges, the data are of sufficient quality to compare the frequency content of the tidal signal in the days before and after the tsunami and, the strain measurements are comparable with those predicted by theory. In each case the strain measurements can be translated to water height estimates which are within centimeters of those recorded by tide gauges. It is possible that borehole strainmeters could play a role in providing a land-based, continuous, high-rate tsunami measurement system.

Hodgkinson, K.; Mencin, D.; Borsa, A.; Henderson, B.; Johnson, W.

2012-04-01

156

Movies of Finite Deformation within Western North American Plate Boundary Zone  

NASA Astrophysics Data System (ADS)

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

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

2004-12-01

157

Plate Tectonics  

NSDL National Science Digital Library

This site contains 25 questions on the topic of plate tectonics, which covers the development of the theory, crustal movements, geologic features associated with tectonics, and plate boundaries (convergent, divergent, transform). This is part of the Principles of Earth Science course at the University of South Dakota. Users submit their answers and are provided immediate verification.

Heaton, Timothy

158

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

159

The Development of the San Andreas Plate Boundary through Northern California: Insights from GPS, Crustal Structure, and Lithospheric Modeling  

NASA Astrophysics Data System (ADS)

The San Andreas plate boundary lengthens in the wake of the Mendocino triple junction (MTJ), and over the last ca. 7-10 Ma it has developed into a localized plate boundary shear zone between the North America and Pacific plates. The pathway from a diffuse deformation swath to a few major fault related plate boundary structures reflects the interplay of thermal and deformational processes acting on the inherited structures of the Cascadia forearc. Furlong and Govers (1998) proposed the Mendocino Crustal Conveyor (MCC) model (supported by numerical modeling) that argued for temporal and spatial variations in lithospheric deformation in association with MTJ passage, which have led to the formation of the main plate boundary structures. The general concept of faults developing and eventually coalescing into a primary plate boundary structure after MTJ passage serves as the framework for most tectonic and geodetic analyses of the fault system. What has been less well understood or quantified is specifically how the fault systems form, what drives fault localization, and how does the concomitant crustal evolution play a role in the plate boundary development. The substantial augmentation of the geodetic data for northern California through a combination of campaign and most recently (through the PBO component of EarthScope) continuous GPS observations in concert with seismological analyses of crustal structure now allows us to test, calibrate, and refine the MCC model. Specifically, the (1) crustal thickening at and north of the MTJ, predicted by MCC processes, is clearly seen in the crustal velocity and GPS derived strain fields, (2) the approx, E-W extent of MCC deformation is delineated by the GPS data to occur primarily through the core of the northern Coast Ranges - consistent with the topographic and fluvial evolution of the region, (3) compatible with seismic observations, the GPS data imply that the upper crust is only a minor participant in the MCC crustal thinning that occurs approximately 200 km south of the MTJ (i.e. ca. 4-5 million years after MTJ passage), and (4) development of the precursor faults to the San Andreas plate boundary structures appear to be driven by the combination of MCC crustal deformation and the development of localized shear within the MTJ-formed slab window. Further structural complexities arise in developing these precursor faults in the upper crust with its pre- existing convergent margin structures, which are either overprinted or reactivated as a result of their orientation and segmentation. The addition of GPS observations to the existing catalog of geophysical and tectonic characteristics of the northern San Andreas system allow us to place the transition from a mature convergent margin to an active translational plate boundary into a physically constrained framework. The MCC model of plate boundary evolution is consistent with these kinematic and structural constraints and thus provides a useful framework model for unraveling the processes that drive the development of the San Andreas plate boundary after MTJ passage and the cessation/removal of subduction from the western margin of North America.

Furlong, K. P.; Williams, T.; Hayes, G. P.

2007-12-01

160

Natural Frequencies and Mode Shapes of a Square Plate with Discontinuous Boundary Conditions.  

National Technical Information Service (NTIS)

The natural frequencies and mode shapes are theoretically determined for a simply supported square plate with discontinuous boundary conditions created by clamping segments of the boundary. Two different clamping configurations are investigated: (1) parti...

J. E. Marsh

1971-01-01

161

The Plate Boundary Observatory: Community Focused Web Services  

NASA Astrophysics Data System (ADS)

The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three-dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, PBO will install 852 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser strainmeters, as well as manage data for 209 previously existing continuous GPS stations. UNAVCO provides access to data products from these stations, as well as general information about the PBO project, via the PBO web site (http://pboweb.unavco.org). GPS and strainmeter data products can be found using a variety of channels, including map searches, text searches, and station specific data retrieval. In addition, the PBO construction status is available via multiple mapping interfaces, including custom web based map widgets and Google Earth. Additional construction details can be accessed from PBO operational pages and station specific home pages. The current state of health for the PBO network is available with the statistical snap-shot, full map interfaces, tabular web based reports, and automatic data mining and alerts. UNAVCO is currently working to enhance the community access to this information by developing a web service framework for the discovery of data products, interfacing with operational engineers, and exposing data services to third party participants. In addition, UNAVCO, through the PBO project, provides advanced data management and monitoring systems for use by the community in operating geodetic networks in the United States and beyond. We will demonstrate these systems during the AGU meeting, and we welcome inquiries from the community at any time.

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

2006-12-01

162

Convergence of boundary and body information in the visual processing of aspect ratio  

Microsoft Academic Search

We used DOG ellipses and outlined ellipses that contained, respectively, only low-frequency and only high-frequency information about aspect ratio. Cross-adaptation (i.e., adapt DOG\\/test outline and adapt outline\\/test DOG) produced aspect ratio aftereffects. Conclusion: Spatial information encoded in terms of the body of the stimulus and in terms of the boundary of the stimulus have substantially converged before the information-processing stage

D. Regan; M. P. Regan; D. Harnanansingh

2006-01-01

163

A convergent boundary integral method for three-dimensional water waves  

Microsoft Academic Search

We design a boundary integral method for time-dependent, three- dimensional, doubly periodic water waves and prove that it converges with O(h3) accuracy, without restriction on amplitude. The moving surface is rep- resented by grid points which are transported according to a computed velocity. An integral equation arising from potential theory is solved for the normal ve- locity. A new method

J. Thomas Beale

2001-01-01

164

Paleomagnetic constraints on Cenozoic deformation along the northwest margin of the Pacific-Australian plate boundary zone through New Zealand  

NASA Astrophysics Data System (ADS)

New Zealand straddles the boundary between the Australian and Pacific plates, a zone of oblique continental convergence and transform motion. The actively deforming region offers a unique opportunity to study the dynamics of deformation, including vertical-axis rotation of rigid blocks within a transcurrent plate boundary zone. We present and interpret paleomagnetic data from three new and three previously published sites from the NW part of the South Island (NW Nelson region), where sedimentary strata dated between 36 and 10 Ma overlie the crystalline Paleozoic basement assemblages of the Gondwana margin. Compared with reference directions from the Australian apparent polar wander path, none of the results provide evidence of post-Eocene vertical-axis rotation. This suggests that for the past 36 Myr NW Nelson has remained a strong, coherent block that has moved as a contiguous part of the Australian plate. This is in marked contrast to the strongly rotated nature of more outboard accreted terranes to the east. For example, the Hikurangi Margin in the North Island (NW of the Alpine Fault) and the Marlborough region in the NE of the South Island (SE of the Alpine Fault), have both undergone diverse clockwise rotations of up to 140° since the early Paleogene. The NW tip of the South Island seems to have acted as a rigid backstop relative to these more complex oroclinal deformations. We infer that, because of its relatively stiff bulk rheology, it has not been drawn into the distributed plate boundary rotational deformation associated with the New Zealand Orocline.

Turner, Gillian M.; Michalk, Daniel M.; Little, Timothy A.

2012-02-01

165

Historical and modern seismotectonics of the Indian plate with an emphasis on its western boundary with the Eurasian plate  

Microsoft Academic Search

The western edge of the Indian plate is a transform plate boundary similar to the San Andreas Fault in that it lies mostly on land, has a similar expected slip rate, accommodates restraining bends, and contains segments that may slip aseismically by surface creep. Tectonic models of the western edge of India must also account for the absence of significant

W. M. Szeliga

2010-01-01

166

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

167

Distributed Plate Boundary Deformation Across the San Andreas Fault System, Central California  

Microsoft Academic Search

Plate boundaries are now recognized as broad zones of complex deformation as opposed to narrow zones with discrete offsets. When assessing how plate boundary deformation is accommodated, both spatially and temporally, it is therefore crucial to understand the relative contribution of the discrete and distributed components of deformation. The creeping segment of the San Andreas fault is an ideal location

M. Dyson; S. J. Titus; C. Demets; B. Tikoff

2007-01-01

168

Convergence  

NASA Astrophysics Data System (ADS)

Call for Papers: Convergence

Guest Editors: Thomas E. Darcie, University of Victoria Robert Doverspike, AT&T Martin Zirngibl, Lucent Technologies

Coordinating Associate Editor: Steven K. Korotky, Lucent Technologies

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, 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

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

    2005-01-01

169

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

Microsoft Academic Search

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

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

2009-01-01

170

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

171

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

172

Geodynamic Evolution of the Nubia-Arabia-Somalia Plate Boundary System  

Microsoft Academic Search

We present a geodynamic scenario for the evolution of the Nubia (Nu)-Arabia (Ar)-Somalia (So) plate boundary system that is based on new geodetic constraints on the kinematics of active deformation, and published estimates of the timing of regional tectonic processes. This scenario supports two, long debated, principal hypotheses for plate dynamics, 1) plate motions are driven primarily by sinking of

R. E. Reilinger; S. McClusky; P. Vernant; G. Ogubazghi; S. Fisseha; A. Arrajehi; R. O. Bendick; J. Sholan

2009-01-01

173

License plate detection method using vertical boundary pairs and geometric relationships  

Microsoft Academic Search

License plate detection and recognition is a crucial and difficult issue for an ITS (Intelligent Transportation System). This paper proposes a robust license plate detection method using vertical boundary pairs and geometric relationships. The proposed method first tries to find a candidate region for a license plate region or character, if a candidate if found, then it estimates the candidate

Liang Li; Youngjoon Han; Hernsoo Hahn

2010-01-01

174

Three-dimensional modeling of the behavior of the oblique convergent boundary of southeast Taiwan: friction and strain partitioning  

Microsoft Academic Search

The Longitudinal Valley Fault (LVF) of eastern Taiwan is the plate boundary between the Philippine Sea plate and Eurasian plate. Analyses of triangulation networks showed that two distinct deformation zones coexist: thrusting prevails between the Pinanshan Conglomerate massif and the Central Range to the west, while strike-slip dominates between the Pinanshan massif and the Coastal Range to the east. Crustal

Jyr-Ching Hu; J. Angelier; C. Homberg; Jian-Cheng Lee; Hao-Tsu Chu

2001-01-01

175

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

176

Plate boundary re-organization in the western Mediterranean  

NASA Astrophysics Data System (ADS)

The TOPO-EUROPE ESF Collaborative Research Project TOPOMED addresses an intriguing process of plate boundary re-organization, considered to be active in the western Mediterranean region. The opening of the Algero-Provencal Basin (between Spain, Corsica-Sardinia and NW Africa) by roll-back of the African lithosphere, led to collision of the migrating arc-trench system with the NW African (Maghrebian) continental margin, in the M. Miocene. TOPOMED investigates the hypothesis that this event prompted the subsequent and probably still ongoing evolution of the Calabrian Arc in the east, and possibly that of the Gibraltar Arc in the west. In this contribution we focus on the role of STEP faults (Subduction-Transform-Edge-Propagators [Govers and Wortel, EPSL 2005]) in the evolution of the arcs. Furthermore, seismic activity along the margins of NW Africa and northern Sicily indicates the possibility that a new subduction zone is being formed, accommodating the continuing ~ N-S motion between Africa and Eurasia (Europe) after arc-continent collision. The postulated processes involved are subduction polarity reversal and subduction initiation along a STEP fault. The Mediterranean setting offers unique opportunities to study the arcs’ evolution and the subduction initiation process in a natural setting. We explore the differences between the margins’ settings on the basis of observations and report on numerical modeling results pertaining to the inferred processes of subduction initiation.

Wortel, M. J.; Govers, R. M.; Baes, M.

2010-12-01

177

Tidal calibration of plate boundary observatory borehole strainmeters  

NASA Astrophysics Data System (ADS)

The Plate Boundary Observatory, the geodetic component of the EarthScope program, includes 74 borehole strainmeters installed in the western United States and on Vancouver Island, Canada. In this study, we calibrate 45 of the instruments by comparing the observed M2 and O1 Earth tides with those predicted using Earth tide models. For each strainmeter, we invert for a coupling matrix that relates the gauge measurements to the regional strain field assuming only that the measured strains are linear combinations of the regional areal and shear strains. We compare these matrices to those found when constraints are imposed which require the coupling coefficients to lie within expected ranges for this strainmeter design. Similar unconstrained and constrained coupling matrices suggest the instrument is functioning as expected as no other coupling matrix can be found that better reduces the misfit between observed and predicted tides when the inversion is unconstrained. Differences imply a coupling matrix with coefficients outside typical ranges gives a better fit between the observed and predicted tides. We find that 22 of the strainmeters examined have coupling matrices for which there is little difference between the constrained and unconstrained inversions. If we allow a greater divergence in the shear coupling coefficients and consider the possibility that one gauge may not function as expected, the discrepancies between the unconstrained and constrained coupling matrices are resolved for a subset of the remaining strainmeters. Our results also indicate that most of the strainmeters are less sensitive to areal strain than expected from theory.

Hodgkinson, Kathleen; Langbein, John; Henderson, Brent; Mencin, Dave; Borsa, Adrian

2013-01-01

178

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

179

Investigating the influence of plate boundary motion on mantle thermal evolution using 3D convection models  

NASA Astrophysics Data System (ADS)

A number of studies examining the influence of plates on mantle convection have concluded that planform and temperature are strongly influenced by the plate geometry (i.e., plate boundary locations). However, the small number of 3D studies that have modelled evolving plate geometries over substantial periods (greater than a mantle transit time) indicate that mantle planform may not correlate well with plate geometry in systems featuring plate evolution. Indeed, conceptual models such as a fixed hotspot reference frame of mantle-plume origin require a certain degree of decoupling of the location of deep mantle thermal features from the motion and geometry of the plates. In order to properly assess the influence of plate-like surface motion on mantle convection, we investigate convecting systems featuring plates with boundaries that move at comparable speeds to the velocities associated with convection driven flow in the mantle. Plate velocities in our calculations are time-dependent and use a force-balance method to ensure that the plate motion neither drives nor resists the convection. We compare the evolution of the surface and basal heat flow and changes in convection planform in two sets of calculations in which simple plate geometries change with time while plate velocity responds dynamically to the evolving driving forces in the plate-mantle system. The numerical models feature polygon-shaped plates (either 9 or 4) resulting in a surface characterized by piece-wise continuous uniform velocities corresponding to each plate interior. In the first study we compare the difference in evolution of pairs of models featuring 9 plates in a 6x6x1 system. We compare cases where plate boundaries are held fixed with cases where the plate boundaries evolve dynamically in response to motion of the plate triple junctions. In addition to thermal evolution we examine the time-dependence of the plate velocities in these models. Our second set of calculations uses 4x4x1 solution domains and prescribes the evolution of four plates. The influence of the plate boundary motion on the convection is compared in models featuring different viscosity profiles.

Lowman, J. P.; Stein, C.; King, S. D.; Trim, S.

2009-12-01

180

The Plate Boundary Observatory: Data Management Progress and Highlights  

NASA Astrophysics Data System (ADS)

The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three- dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, UNAVCO will install 880 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser strainmeters by October 2008, as well as manage data for 209 previously existing continuous GPS stations and one laser strainmeter through the PBO Nucleus project and 11 GPS stations installed by the USArray segment of EarthScope. As of 1 September 2007, UNAVCO had completed 680 PBO GPS stations and had upgraded 89% of the planned PBO Nucleus stations. Most of these stations return data to the UNAVCO Boulder Network Operations Center (NOC) on a daily basis, with about 40 stations returning data on an hourly basis. Overall, the combined PBO and Nucleus network has now provided almost 350 GB of raw standard rate data, which are routinely processed by the PBO GPS Analysis Centers, at Central Washington University and the New Mexico Institute of Mining and Technology, and the PBO GPS Analysis Center Coordinator at MIT. These groups create a range of GPS products, including station position time series, GPS velocity vectors, and related information. As of September 2007, these centers processed data on a daily basis from about 920 stations; typical position uncertainties are under 1.5 mm horizontally and 4 mm vertically. All PBO GPS data products are archived at and available from the UNAVCO Facility, with a second archive at the IRIS Data Management Center (DMC). All these products may be accessed via the PBO web page at http://pboweb.unavco.org/gps_data. As part of PBO, UNAVCO will also install and operate the largest borehole seismic and strainmeter networks in North America, as well as tiltmeters and laser strainmeters. As of September 2007, 41 PBO borehole stations had been installed and three laser strainmeter stations were operating. Seismic data flow in real time to the Boulder NOC for initial quality checks, and then to the IRIS DMC for final quality checks, archiving, and distribution; all PBO seismic data flow is via the Antelope software suite. Strainmeter data flow hourly and daily to the Boulder NOC and then to the Borehole Strainmeter Analysis Center in Socorro, New Mexico, and the Laser Strainmeter Analysis Center at the University of California, San Diego. These groups transform the raw strainmeter observations into cleaned individual strain gauge components; time series of shear, areal, and linear strain; and related products. All strainmeter data products are archived at and available from the Northern California Earthquake Data Center and the IRIS DMC, in both the native raw formats and SEED format; all seismic data products are archived at and available from the IRIS DMC, in SEED format. By September 2007, the PBO seismic network had provided more than 200 GB of raw data, and the PBO strainmeter network had provided almost 100 GB of raw data. Please visit http://pboweb.unavco.org/strain_data for more information on data products from the PBO strainmeter and seismic networks.

Anderson, G.; Blackman, B.; Eakins, J.; Hodgkinson, K.; Matykiewicz, J.; Boler, F.; Beldyk, M.; Henderson, B.; Hoyt, B.; Lee, E.; Persson, E.; Smith, J.; Torrez, D.; Wright, J.; Jackson, M.; Meertens, C.

2007-12-01

181

The Plate Boundary Observatory: Data Management Progress and Highlights  

NASA Astrophysics Data System (ADS)

The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three-dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, UNAVCO will install 852 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser strainmeters, as well as manage data for 209 previously existing continuous GPS stations through the PBO Nucleus project. As of 1 September 2006, the PBO GPS network was halfway completed with 426 stations installed, of which 400 have returned data, and PBO handled data flow for 120 PBO Nucleus stations. Most of these stations return data to the UNAVCO Boulder Network Operations Center (NOC) on a daily basis, with 16 returning data on an hourly basis. Overall, the combined PBO and Nucleus networks had returned almost 150 GB of raw GPS data as of September 2006. These data are then processed by the PBO GPS Analysis Centers, at Central Washington University and the New Mexico Institute of Mining and Technology, and the PBO GPS Analysis Center Coordinator at MIT. These groups create a range of GPS products, including station position time series, GPS velocity vectors, and related information. As of September 2006, these centers processed data on a daily basis from about 590 stations; typical position uncertainties are under 1.5 mm horizontally and 4 mm vertically. All PBO GPS data products are archived at and available from the UNAVCO Facility, with a second archive at the IRIS Data Management Center (DMC). All these products may be accessed via the PBO web page at http://pboweb.unavco.org/?pageid=88. As part of PBO, UNAVCO will also install and operate the largest borehole seismic and strainmeter networks in North America, as well as tiltmeters and laser strainmeters. As of September 2006, 19 PBO borehole stations had been installed and two laser strainmeter stations were operating, with a total of 28 borehole stations and 3 laser strainmeters expected by the end of 2006. Seismic data flow in real time to the Boulder NOC for initial quality checks, and thence to the IRIS DMC for final quality checks, archiving, and distribution; all PBO seismic data flow is via the Antelope software suite. Strainmeter data flow hourly and daily to the Boulder NOC and thence to the Borehole Strainmeter Analysis Center in Socorro, New Mexico, and the Laser Strainmeter Analysis Center at the University of California, San Diego. These groups transform the raw strainmeter observations into cleaned individual strain gauge components; time series of shear, areal, and linear strain; and related products. All strainmeter data products are archived at and available from the Northern California Earthquake Data Center and the IRIS DMC, in both the native raw formats and SEED format; all seismic data products are archived at and available from the IRIS DMC, in SEED format. By September 2006, the PBO seismic network had provided 60 GB of raw data, and the PBO strainmeter network had provided 27.5 GB of raw data. Please visit http://pboweb.unavco.org/?pageid=89 for more information on data products from the PBO strainmeter and seismic networks.

Anderson, G.; Eakins, J.; Hodgkinson, K.; Matykiewicz, J.; Boler, F.; Beldyk, M.; Hoyt, B.; Lee, E.; Persson, E.; Torrez, D.; Wright, J.; Jackson, M.; Prescott, W.

2006-12-01

182

The Earthscope Plate Boundary Observatory Akutan Alaskan Volcano Network Installation  

NASA Astrophysics Data System (ADS)

During June and July of 2005, the Plate Boundary Observatory (PBO) installed eight permanent GPS stations on Akutan Volcano, in the central Aleutian Islands of Alaska. PBO worked closely with the Alaska Volcano Observatory and the Magmatic Systems Site Selection working group to install stations with a spatial distribution to monitor and detect both short and long term volcanic deformation in response to magmatic intrusions at depth and magma migration through the volcano's conduit system. All eight of the GPS stations were installed by PBO field crews with helicopter support provided by Evergreen Helicopters and logistical support from the Trident Seafood Corporation, the City of Akutan, and the Akutan Corporation. Lack of roads and drivable trails on the remote volcanic island required that all equipment be transported to each site from the village of Akutan by slinging gear beneath the helicopter and internal loads. Each station installed on the volcano consists of a standard short braced GPS monument, two solar panels mounted to an inclined structure, and a six foot high Plaschem enclosure with two solar panels mounted to one of the inclined sides. Each Plaschem houses 24 6 volt batteries that power a Trimble NetRS GPS receiver and one or two Intuicom radios. Data from each GPS receiver is telemetered directly or through a repeater radio to a base station located in the village of Akutan that transmits the data over the internet to the UNAVCO data archive at ftp://data-out.unavco.or/pub/PBO_rinex where it is made freely available to the public.

Pauk, B.; Jackson, M.; Mencin, D.; Power, J.; Gallaher, W.; Basset, A.; Kore, K.; Hargraves, Z.; Peterson, T.

2005-12-01

183

The Influence of Evolving Plate Boundaries in 3D Mantle Convection Simulations  

NASA Astrophysics Data System (ADS)

A variety of mantle convection simulations featuring model plates have shown that plate-like surface motion strongly influences underlying convection patterns, surface heat flux, system temperature and plume stability. However, plate boundaries move at comparable speeds to the velocities associated with convection driven flow in the mantle, therefore the shapes and sizes of the tectonic plates change considerably in just one mantle transit time. In order to properly assess the influence of plate-like surface motion on mantle convection, it is thus necessary to investigate convection in systems featuring evolving plate geometries. In the calculations presented here we investigate the behaviour of systems featuring both evolving plate velocities and shapes. The plate velocities evolve so that the shear stress on the base of each of the finite thickness high viscosity plates sums to zero at all times, to ensure that the plates neither drive nor resist the convection. We compare the evolution of the surface and basal heat flow and changes in convection planform in two sets of calculations in which simple plate geometries change with time while plate velocity responds dynamically to the evolving driving forces in the plate-mantle system. The models feature either 4 or 9 polygon-shaped plates resulting in a surface characterised by piece-wise continuous uniform velocities corresponding to each plate interior. In the first study we compare the difference in evolution of a pair of models featuring 9 plates in a 6×6×1 system. In one calculation the plate boundaries are held fixed and in the second the plate boundaries evolve dynamically in response to motion of the plate geometry triple junctions. In addition to thermal evolution we compare the time-dependence of the plate velocities in these models. In a second set of calculations using 4×4×1 solution domains we prescribe the evolution of four plates, rotating the initial plate geometry through 90 degrees at a constant rate in each experiment. The influence of the plate boundary motion on the convection is compared in models featuring different viscosity profiles.

Lowman, J. P.; Stein, C.; Trim, S.; King, S. D.

2009-05-01

184

Convergence!  

NSDL National Science Digital Library

Some math teachers find themselves confronted by students who ask, "Why do we have to learn this?" or "When am I going to use it?" These are vexing questions for sure, and one suggestion might be to incorporate the history and development of the field of mathematics into the formal study of the subject. That is exactly what a dedicated team of individuals at the Mathematical Association of America (MAA) and the National Council of Teachers of Mathematics decided to do when they created the online magazine, Convergence. The magazine contains a wide range of materials for educators, including animated mathematical demonstrations that can be downloaded for classroom use and discussions of particular problems from an historical context. On the magazine's homepage, visitors can view featured articles, take a look over the "Critic's Corner", and use the "Show Me" search engine to look for new and compelling additions.

185

Scattered waves from low-frequency earthquakes and plate boundary structure in northern Cascadia  

NASA Astrophysics Data System (ADS)

use 3-D waveform modeling of LFEs (low-frequency earthquakes) to investigate their relation to plate boundary structure along a linear transect in northern Cascadia. To account for crustal velocity heterogeneity, a smoothed 3-D model of subduction zone structure is assembled that incorporates constraints from regional tomographic and plate boundary models. Scattered phases within LFE waveforms are identified based on synthetic predictions that incorporate thrust mechanisms aligned parallel to a dipping plate boundary atop a high-Vp/Vs low-velocity zone (LVZ). Scattering for near-vertical paths is dominated by S-to-P/S-to-S reflections/conversions from the LVZ. The modeling suggests that LFEs lie at or very close to the plate boundary and that the LVZ structure is laterally heterogeneous but broadly consistent with results from teleseismic analysis.

Nowack, Robert L.; Bostock, Michael G.

2013-08-01

186

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

187

On the boundary conditions for transversely isotropic piezoelectric plates  

Microsoft Academic Search

By invoking the theorem of work reciprocity for piezoelectric media, necessary conditions, which the prescribed edge data of the plate must fulfill in order that it should generate a decaying state within the plate, are established through generalizing the method proposed by Gregory and Wan. These decaying state conditions for the case of axisymmetric deformation of a transversely isotropic piezoelectric

S. P. Xu; Y. Gao; W. Wang

2007-01-01

188

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

NASA Astrophysics Data System (ADS)

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 evolution of paleo-oceanic domains. This approach offers good control of sea-floor spreading and plate kinematics. This new method represents a distinct departure from classical continental drift reconstructions, which are not constrained, due to the lack of plate boundaries. This model allows a more comprehensive analysis of the development of the Tethyan realm in space and time. In particular, the relationship between the Variscan and the Cimmerian cycles in the Mediterranean-Alpine realm is clearly illustrated by numerous maps. For the Alpine cycle, the relationship between the Alpides senso stricto and the Tethysides is also explicable in terms of plate tectonic development of the Alpine Tethys-Atlantic domain versus the NeoTethys domain.

Stampfli, G. M.; Borel, G. D.

2002-02-01

189

Halfway There: An EarthScope Plate Boundary Observatory Progress Report  

Microsoft Academic Search

The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three-dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, UNAVCO will install 852 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser strainmeters

M. Jackson; G. Anderson; F. Blume; B. Coyle; K. Feaux; B. Friesen; K. Hafner; M. Hasting; W. Johnson; D. Mencin; B. Pauk; D. Phillips; C. Walls; W. Prescott

2006-01-01

190

Pore fluid pressures, porosity, and permeability of the Cascadia subduction zone plate boundary  

Microsoft Academic Search

The strength and seismogenic behavior of subduction zone plate boundaries depend critically on pore fluid pressure. Integrated over time, large amounts of H2O are released from subducting plates by tectonic compaction at shallow depths and by metamorphic dehydration reactions at deeper depths. In the Cascadia subduction zone, beneath southern Vancouver Island, converted teleseismic waves reveal anomalously high Poisson's ratios (average

S. M. Peacock; N. I. Christensen; M. G. Bostock; P. Audet

2009-01-01

191

Direct drag measurements in a turbulent flat-plate boundary layer with turbulence manipulators  

Microsoft Academic Search

The effect of turbulence manipulators on the turbulent boundary layer above a flat plate has been investigated. These turbulence manipulators are often referred to as Large Eddy Break Up (LEBU) devices. The basic idea is that thin blades or airfoils are inserted into the turbulent flow in order to reduce the fluctuating vertical velocity component v' above the flat plate.

T. B. Lynn; D. W. Bechert; D. A. Gerich

1995-01-01

192

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

Microsoft Academic Search

Transient tectonic deformation has long been noted within ~100km of plate boundary fault zones and within active volcanic regions, but it is unknown whether transient motions also occur at larger scales within plates. Relatively localized transients are known to occur as both seismic and episodic aseismic events, and are generally ascribed to motions of magma bodies, aseismic creep on faults,

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

2006-01-01

193

Transient Particle Deposition in a Boundary Layer of Impulsive Flow Over a Flat Plate.  

National Technical Information Service (NTIS)

The transport and deposition of fine particles in a boundary layer of impulsive flow over a flat plate have been examined by numerical methods. The transient impulsive flow over a flat plate is solved by a vortex sheet method and the particle transport eq...

J. N. Chung

1987-01-01

194

Natural convection in a square cavity due to thermally active plates for different boundary conditions  

Microsoft Academic Search

This work deals with the study of natural convection cooling of thermally active plates placed inside an air filled cavity at the center, with two different boundary conditions imposed on the cavity walls. By an active plate we mean one that is hotter due to isothermal heating or inherent heat generation. The walls of the cavity are subjected to either

A. K. Abdul Hakeem; S. Saravanan; P. Kandaswamy

2011-01-01

195

How does a lithospheric plate boundary adapt to changes in plate motion? An example from South Island of New Zealand  

NASA Astrophysics Data System (ADS)

Since ~ 20 Ma the plate boundary along the Alpine Fault in South Island of New Zealand has undergone substantial changes. The combination of movement of the Eulerian pole describing the Pacific-Australian relative motion with the southern migration of the Hikurangi subduction zone has changed the conditions along the Alpine Fault to progressively more transpressive. On a crustal scale this change has been accommodated by crustal thickening and the creation of the Southern Alps, on the full lithospheric scale it is still not clear how these changes in plate motion are accommodated. At shallow to middle level where the lithosphere is predominantly brittle these changes of motion are normally accommodated through strain partitioning along preexisting weakness (faults) and/or through crustal thickening. Within the ductile regime, the plate boundary shear may reorient along a more favorable direction (a typical behavior for a linear viscous flow) or it may localize along a preexisting weak shear zone with lithospheric thickening (typical for power law rheology). Here we use a FEM to simulate the evolution of the Southern Alps and to analyze the effects of the coupling between ductile and brittle lithosphere (in particular the presence of a fault), the effects of boundary conditions (southern migration of the subduction) and of the rheology (linear vs. power law) on the localization of the flow in the ductile part of the lithosphere and how the lithospheric scale plate boundary adapts to the new tectonic regime.

Malservisi, R.; Govers, R.; Furlong, K. P.

2006-12-01

196

Vibration Characteristics of Functionally Graded Plates with Non-Ideal Boundary Conditions  

Microsoft Academic Search

An analytical investigation is carried out to determine the vibration behavior of functionally graded plates with non-ideal boundary conditions. The plate has three edges simply supported while the other edge has a small non-zero deflection and moment. The effective material properties are estimated by the Mori-Tanaka scheme. The classical plate theory is employed to obtain the frequency equation. The proposed

M. M. Najafizadeh; J. Mohammadi; P. Khazaeinejad

2012-01-01

197

The Boundary Layer on a Flat Plate in Anisotropic Magnetohydrodynamics.  

National Technical Information Service (NTIS)

It is demonstrated that when calculating the boundary layer, despite the presence of thermal flow due to Larmor precession of electrons, it is possible to consider the temperature at the limit of the boundary layer as fixed. For this purpose the problem o...

V. B. Varanov A. G. Kukilovskii G. A. Lyubimov

1965-01-01

198

Historical seismicity and implications for diffuse plate convergence in the northeast Indian Ocean  

NASA Astrophysics Data System (ADS)

Large historical earthquakes provide constraints on the geographical extent and kinematics of the slow, diffuse plate boundary extending from the Central Indian Ridge to the Sumatra Trench. The fault parameters of pre-1963 earthquakes are derived using a grid search for the best fit between observed and synthetic body waveforms, surface wave spectral amplitudes, and polarity and polarization constraints, and location uncertainties are determined using a bootstrap resampling method. The March 9, 1928 Ninetyeast Ridge (M 7.7) event shows left lateral strike-slip faulting along a plane approximately coincident with the orientation of the Ninetyeast Ridge. Two small events which occurred at the location of the 1928 event in 1980 show focal mechanisms nearly identical to that determined for the 1928 earthquake and apparently reactivated the same fault. The 1928 waveforms can also be fit by a thrust faulting solution with ENE striking fault planes, but a variety of evidence, including the recent strike-slip earthquakes at the same location, suggest the strike-slip solution. These earthquakes are located along the western scarp of the ridge and do not represent reactivation of the Ninetyeast Fracture Zone to the east of the edifice, which was a major plate boundary in the early Cenozoic. The January 23, 1949 (M 6.75) and March 22, 1955 (M 7.0) Wharton Basin earthquakes, although only 350 km apart, show different strike-slip and thrust faulting mechanisms. All earthquakes show a regionally consistent pattern of horizontal compressional stress, which changes from NW-SE in the Wharton Basin to N-S in the Central Indian Basin. The compressional axes are oriented perpendicular to linear gravity anomalies associated with lithospheric flexure, indicating little change in stress orientation since the onset of folding. Seismic deformation along the diffuse boundary consists of sinistral strike-slip faulting associated with N-S features such as the Ninetyeast Ridge and the 86°E fracture zone, and thrust or reverse faulting in regions between fracture zones. Assuming transform motion, the approximate slip rate along the northern Ninetyeast Ridge calculated from the summed moments of earthquakes is 2.8 mm/yr. This value is an order of magnitude less than previous estimates, and suggests that at most only a small fraction of the current relative plate motion (˜7 mm/yr) occurs along the ridge. The geographic distribution of seismicity suggests that the Wharton Basin east of the Ninetyeast Ridge is nearly as seismically active as the Central Indian Basin to the west. This result, along with observed long wavelength gravity anomalies in the Wharton Basin, indicates that the India-Australia plate boundary intersects the Sumatra Trench along a diffusely deforming region several thousand kilometers long, rather than along a discrete transform zone.

Petroy, David E.; Wiens, Douglas A.

1989-09-01

199

ConcepTest: Cross-Section of Plate Boundaries  

NSDL National Science Digital Library

The map below shows the plate configurations along the western margin of North America. Which of the four diagrams on the right best represents a cross section through the outer layers of Earth along the line X-Y?

200

ConcepTest: Cross-Sections of Plate Boundaries  

NSDL National Science Digital Library

The map below shows the plate configurations along the western margin of North America. Which of the four diagrams on the right best represents a cross section through the outer layers of Earth along the line X-Y?

201

Mixed convection boundary layer flow of a micropolar fluid on a horizontal plate  

Microsoft Academic Search

Summary A boundary layer analysis is presented to study the effects of buoyancy-induced streamwise pressure gradients on laminar forced convection heat transfer to micropolar fluids from a horizontal plate. A numerical solution of the transformed boundary layer equations has been carried out for different values of the buoyancy and material parameters. A discussion is provided for the effect of the

R. S. R. Gorla

1995-01-01

202

Active boundary control of a rectangular plate using smart modal sensors  

NASA Astrophysics Data System (ADS)

This paper deals with active boundary control (ABC) of a rectangular plate using feedforward control. Conventionally, boundary conditions dominating the fundamental properties of a structure are obtained a priori. If it is possible to control the boundary conditions of a structure, its structural characteristics may be altered as wished. The ABC presented in this work enables one to generate the desired boundary conditions at a designated area on a target plate. Firstly, the principle of the ABC where the system is described using the transfer matrix method is presented. Then, the optimal feedforward control law for producing the desired boundary conditions on the plate is derived. It is found that, as a result of applying the ABC on an edge of the plate, global generation of a quiet zone around the edge can be achieved. Numerical simulations are conducted where the fundamental properties of the ABC system are investigated. In addition, implementation of the ABC using distributed parameter polyvinylidene fluoride film (PVDF) sensors introduced for modal filtering is discussed. Finally, experiments are carried out to demonstrate the validity of the ABC when generating a desired boundary condition at the target location, creating a global quiet zone within the target region of the plate.

Kaizuka, Tsutomu; Tanaka, Nobuo

2006-10-01

203

Accelerated plate tectonics.  

PubMed

The concept of a stressed elastic lithospheric plate riding on a viscous asthenosphere is used to calculate the recurrence interval of great earthquakes at convergent plate boundaries, the separation of decoupling and lithospheric earthquakes, and the migration pattern of large earthquakes along an arc. It is proposed that plate motions accelerate after great decoupling earthquakes and that most of the observed plate motions occur during short periods of time, separated by periods of relative quiescence. PMID:17799689

Anderson, D L

1975-03-21

204

From Slab Window to Plate Boundary: Making the San Andreas Fault System  

NASA Astrophysics Data System (ADS)

The development of the San Andreas fault system in the wake of the Mendocino Triple Junction (MTJ) serves as a principal example of processes involved in developing a new plate boundary structure in a slab window environment. The general concepts of slab window formation with MTJ migration, patterns of crustal deformation, and the subsequent development of the major strands of the plate boundary within the shallow slab window corridor are well documented. What is less well understood about the formation of this plate boundary system are the roles of spatial and temporal variations in crustal structure, and slab window volcanics (the northern California Coast Range volcanic centers) in localizing the crustal deformation, constraining the position of the plate boundary fault system, and explaining the slip history of various fault strands along the plate boundary. In particular, we argue that there is a swath or corridor of northern Coast Ranges within which the crust undergoes northward-migrating rapid thinning (aided by the effects of emplaced asthenospheric mantle), whose western margin becomes the Ma'acama/Rodgers Creek/Hayward system. This has specific consequences for both the kinematics of the fault system and the development of slab window volcanism. The localization of upper crustal strain into discrete fault systems (e.g. the Ma'acama and Bartlett Springs Faults) and the initiation of slab-window volcanism are spatially (and thus likely genetically) linked. Such interactions between the emplacement of slab window volcanism, its impact on crustal structure and deformation, and the resulting development of plate boundary fault systems are likely not restricted solely to the San Andreas evolution, but may have played important roles in the development of other segments of the circum-Pacific plate boundary.

Furlong, K. P.

2006-12-01

205

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

NASA Astrophysics Data System (ADS)

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

Stock, J. M.

2011-12-01

206

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

Microsoft Academic Search

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

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

1993-01-01

207

Geometrical Non-Linear Steady State, Forced, Periodic Vibration of Plates, Part i: Model and Convergence Studies  

NASA Astrophysics Data System (ADS)

A model for the steady state, geometrically non-linear, periodic vibration of thin rectangular plates under harmonic external excitation is presented. The equations of motion in the time domain are derived by applying the principle of virtual work and the hierarchical finite element method (HFEM). These equations are transformed into the frequency domain by the harmonic balance method (HBM) and are solved by a continuation method. The convergence properties of the model are discussed by applying it to isotropic and to composite laminated plates.

Ribeiro, P.; Petyt, M.

1999-10-01

208

Dynamic thermal stresses in a nonhomogeneous plate caused by rapid heating of its plane boundary  

NASA Astrophysics Data System (ADS)

This paper is concerned with the dynamic treatment of a transient thermoelastic problem for an infinite plate with arbitrarily prescribed temperature field. The material of the structure is continuously nonhomogeneous with thermal and mechanical properties varying linearly with the thickness of the plate. The curvilinear characteristics in the space-time plane are transformed into straight lines of equal slope so that the numerical errors can be minimized. The problem is then solved using appropriate characteristic equations on boundaries while using more convenient explicit finite-difference approximations at all other points in the transformed space-time plane. The numerical calculations are carried out for the propagation and reflection of thermal stress waves in a nonhomogeneous plate subjected to ramp type heating on one of the plane boundaries while the other plane boundary is maintained at a constant temperature.

Sumi, Naobumi

1993-07-01

209

Mixed convection over a horizontal plate: self-similar and connecting boundary-layer flows  

Microsoft Academic Search

The boundary-layer flow over a horizontal plate is considered. In case that the heat transfer is limited to the leading edge of the plate two similarity solutions exist, if the buoyancy parameter is above a critical value. By an asymptotic expansion with respect to buoyancy parameters near the critical value it is shown that steady-state (non-similar) solutions connecting both similarity

Herbert Steinruck

1995-01-01

210

Mean profile of a high-Reynolds-number smooth-flat-plate turbulent boundary layer  

Microsoft Academic Search

Although smooth-flat-plate turbulent boundary layers (TBLs) have been studied for nearly a century, measurements at Reynolds numbers typical of marine & aerospace transportation systems are scarce. Experimental results at momentum-thickness Reynolds numbers (Re) up to 150,000 from the US Navy W.B. Morgan Large Cavitation Channel using a polished 12.9-m-long flat-plate test model at water flow speeds up to 20 m\\/s

David R. Dowling; Ghanem F. Oweis; Eric S. Winkel; James M. Cutbirth; Steven L. Ceccio; Marc Perlin

2010-01-01

211

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

NASA Astrophysics Data System (ADS)

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 mantle, allowing us to relate the measurements (i.e., strain and strain rate) to the driving forces. The surface velocity field across two active plate boundaries was measured using high precision GPS geodesy and a combination of analytical elastic half-space models and numerical finite element modeling techniques were used to estimate lithospheric and fault parameters. The surface velocity field and modeling results for southern Iceland indicate that this divergent plate boundary has a complex pattern of strain accumulation due to its propagating nature. Strain accumulation is partitioned between the Western and Eastern Volcanic zones, whereby the spreading rate increases and decreases to the southwest, respectively. The surface velocity field and modeling results for the Central America, indicate that collision of the aseismic Cocos Ridge results in high degrees of coupling along the plate boundary. Strain is distributed in the upper plate across the forearc and back arc, resulting in terrane migration away from, and orogeny and subduction polarity reversal inboard of the rigid indenter.

Lefemina, Peter Christopher

212

Convergent boundaries and related igneous and metamorphic complexes in caledonides of Central Asia  

NASA Astrophysics Data System (ADS)

Fragments of the crystalline complexes where Vendian metamorphism of moderate and elevated pressure predated Early Paleozoic metamorphism have been established in the accretionary-collisional domain of the eastern segment of the Central Asian Foldbelt (Early Caledonian superterrane of Central Asia). The geodynamic setting of the Vendian (˜560-570 Ma) South Hangay metamorphic belt located in the junction zone of the Baydrag Block and the Late Riphean (˜665 Ma) ophiolite complex of the Bayanhongor Zone is considered. The origination of this belt was related to the formation of the convergent boundary in the framework of the Zabhan microcontinent about 570 Ma ago. At the same time, an island-arc complex was formed in the paleo-oceanic domain. Metamorphism of elevated pressure indicates that Vendian structures with sufficiently thick continental crust were formed in the framework of the continental blocks. Vendian metamorphism is also established in the Tuva-Mongolia Massif and the Kan Block of the Eastern Sayan. These data show that the Late Baikalian stage predated the evolution of the Early Caledonian superterrane of Central Asia. The development of its accretionary-collisional structure was accompanied by Late Cambrian-Early Ordovician low-pressure regional metamorphism. Granulite-facies conditions were reached only at the deep levels of the accretionary-collisional edifice. The outcrops of crystalline complexes in the southern framework of the Caledonian paleocontinent are regarded as fragments of the Early Paleozoic Central Mongolian metamorphic belt.

Kozakov, I. K.; Sal'Nikova, E. B.; Yarmolyuk, V. V.; Kozlovsky, A. M.; Kovach, V. P.; Azimov, P. Ya.; Anisimova, I. V.; Lebedev, V. I.; Enjin, G.; Erdenejargal, Ch.; Plotkina, Yu. V.; Fedoseenko, A. M.; Yakovleva, S. Z.

2012-01-01

213

Ridge reorientation mechanisms: Macquarie Ridge Complex, Australia-Pacific plate boundary  

NASA Astrophysics Data System (ADS)

The Macquarie Ridge Complex portion of the Australia-Pacificplate boundary south of New Zealand provides a unique, completerecord of a 60°-90° change in spreading directionsince 40 Ma that resulted in the transition from a spreadingcenter to a transform plate boundary. Marine geophysical datashow that during reorientation, most ridge segments completelydisappeared and all shortened. Additionally, modification ofnewly created crust caused differences in widths of correlativespreading segment corridors on the two plates. We propose twomodels for ridge reorientation that explain the observed spreadingfabric and arcuate fracture zone relationships. Nonrigid platedeformation was accommodated by failing and propagating spreadingridge segments (rifts) and transfer of crust between platesduring the gradual reorientation of the spreading axes.

Mosher, Sharon; Massell Symons, Christina

2008-02-01

214

Seismic Structure, Crustal Architecture and Tectonic Evolution of the Anatolian-African Plate Boundary and the Cenozoic Orogenic Belts  

NASA Astrophysics Data System (ADS)

The modern Anatolian-African plate boundary is represented by a north-dipping subduction zone that is part of a broad domain of regional convergence between Eurasia and Afro-Arabia since the latest Mesozoic. A series of collisions between Gondwana-derived ribbon continents and trench-rollback systems in the Tethyan realm produced nearly E-W-trending, subparallel mountain belts with high elevation and thick orogenic crust in this region. Ophiolite emplacement, terrane stacking, high-P and Barrovian metamorphism, and crustal thickening occurred during the accretion of these microcontinents into the upper plates of Tethyan subduction rollback systems during the late Cretaceous-early Eocene. Continued convergence and oceanic lithospheric subduction within the Tethyan realm were punctuated by slab breakoff events following the microcontinental accretion episodes. Slab breakoff resulted in asthenospheric upwelling and partial melting, which facilitated post-collisional magmatism along and across the suture zones. Resumed subduction and slab rollback-induced upper plate extension triggered a tectonic collapse of the thermally weakened orogenic crust in Anatolia in the late Oligocene-Miocene. This extensional phase resulted in exhumation of high-P rocks and medium- to lower-crustal material leading to the formation of metamorphic core complexes in the hinterland of the young collision zones. The geochemical character of the attendant magmatism has progressed from initial shoshonitic and high-K calc-alkaline to calc-alkaline and alkaline affinities through time, as more asthenosphere-derived melts found their way to the surface with insignificant degrees of crustal contamination. The occurrence of discrete high-velocity bodies in the mantle beneath Anatolia, as deduced from lithospheric seismic velocity data, supports our Tethyan slab breakoff interpretations. Pn velocity and Sn attenuation tomography models indicate that the uppermost mantle is anomalously hot and thin, consistent with the existence of a shallow asthenosphere beneath the collapsing Anatolian orogenic belts and widespread volcanism in this region. The sharp, north-pointing cusp (Isparta Angle) between the Hellenic and Cyprus trenches along the modern Anatolian-African plate boundary corresponds to a subduction-transform edge propagator (STEP) fault, which is an artifact of a slab tear within the downgoing African lithosphere.

Dilek, Y.; Sandvol, E.

2009-04-01

215

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

216

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

217

Delamination growth of laminated circular plates under in-plane loads and movable boundary conditions  

NASA Astrophysics Data System (ADS)

An investigation is made on interlaminar delamination growth of composite laminated circular plates under in-plane loads and movable delamination boundary conditions. A four-dissociated-region model is developed on the basis of von-Karman plate theory. The model is geometrically nonlinear and the laminated circular plate considered is subjected to axisymmetrical delamination. The effects of transverse shear deformation and contact effect of the delamination on the laminated plates are taking into account in the development of the governing equations of the laminated circular pates with random axisymmetrical delamination. The formulas for describing the total energy release rate and its individual mode components along the delamination front are also derived with considerations of Griffith criterion for fracture. Based on the model established, the delamination growth is numerically studied; and the influences of the parameters such as delamination radii and depths, together with material properties of the plates on the energy release rate are analyzed in detail.

Chen, Deliang; Dai, Liming

2013-11-01

218

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

219

Turbulent boundary layer pressure field-induced vibrations in a thin flexible plate under water  

NASA Astrophysics Data System (ADS)

Two point turbulent boundary layer pressure spectra at the wall were determined empirically in a low noise water tunnel. The measured pressure spectra were used in a linear theory to predict the response of a thin stainless steel rectangular plate attached to the water tunnel. The predicted responses were found to agree well with the measured responses of the plate. The in-situ plate response characteristics were also determined empirically by driving the plate separately at several points with a miniature shaker and measuring its response with accelerometers mounted on the plate. The accuracy of the predicted response was found to be controlled by the accuracy of the plate modal model. Due to the reverberant acoustic field in the water tunnel and a complicated supporting structure, the plate modal model could be determined only approximately. The plate modal damping factors were very high, its resonance frequencies were close and the associated mode shapes were complex. These factors made it very difficult to accurately determine the plate modal properties. The wall pressure spectra were also measured for the case when a step discontinuity was present in the wall. These spectra were markedly different from those measured on a smooth wall.

Narayan, Nilabh

1989-06-01

220

Geodynamic Evolution of the Nubia-Arabia-Somalia Plate Boundary System  

NASA Astrophysics Data System (ADS)

We present a geodynamic scenario for the evolution of the Nubia (Nu)-Arabia (Ar)-Somalia (So) plate boundary system that is based on new geodetic constraints on the kinematics of active deformation, and published estimates of the timing of regional tectonic processes. This scenario supports two, long debated, principal hypotheses for plate dynamics, 1) plate motions are driven primarily by sinking of oceanic lithosphere at subduction zones, and 2) the lithosphere is strong in relation to plate boundaries and drag forces on the base of the lithosphere (and likely, resisting forces associate with continental collision). 1) During the Late Oligocene (~30 Ma), domal uplift of the Afar region due to the Afar hot spot caused regional extension and the initial development of the Afar Triple Junction (TJ) along pre-existing zones of weakness; 2) The So-Nu plate boundary, East African Rift (EAR), developed at a slow rate due to the absence of boundary-normal extensional stresses (i.e., no subduction “pulling” the So Plate), slow motion that continues to the present; 3) Larger extensional stresses across the Nu-Ar and Ar-So boundaries (Red Sea and Gulf of Aden) due to active subduction of the Neotethys ocean lithosphere beneath Eu caused more rapid extension of these early rifts, with full scale continental rifting beginning ~ 25-30 Ma; 4) Between 16 - 11 Ma full ocean rifting in the Gulf of Aden caused a decrease in the forces transmitted to the So and Nu plates, causing slowing of the Nu and So plates with respect to Eu and Ar, and (possibly) an additional component of N-S oriented extension across the Red Sea; 5) Around this time (~10 Ma), activity shifted from the Gulf of Suez to the DSF system in the N Red Sea, and the Danakil Block in the southern Red Sea began rotating with respect to Nu and Ar, both changes related to the change in Nu-Ar relative motion; and 6) The balance of forces on the plate system have remained roughly unchanged since ~10 Ma, as have relative plate motions.

Reilinger, R. E.; McClusky, S.; Vernant, P.; Ogubazghi, G.; Fisseha, S.; Arrajehi, A.; Bendick, R. O.; Sholan, J.

2009-12-01

221

Relating rapid plate-motion variations to plate-boundary forces in global coupled models of the mantle\\/lithosphere system: Effects of topography and friction  

Microsoft Academic Search

Recent high-resolution models of past plate motions and their comparison with plate motion models inferred from space geodetic techniques reveal a number of short-term variations in global plate velocities over the past 10 Myrs. Such variations serve as powerful probe into the nature and magnitude of plate boundary forces, because they are unlikely to originate from changes in mantle buoyancy forces,

Giampiero Iaffaldano; Hans-Peter Bunge

2009-01-01

222

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

NASA Astrophysics Data System (ADS)

The shear wave velocity structure of the crust and upper mantle beneath the Caribbean-South American boundary was determined by analysis of fundamental mode Rayleigh waves in the 20-100s band that were recorded at the BOLIVAR/GEODINOS stations between 2003-2005. The 84 station array included 1 GSN station, 27 PASSCAL broadband (BB) seismographs, 15 OBSIP BB instruments and 8 Rice BB seismometers, as well as 34 BB stations of the Venezuelan national seismological network. Earthquakes in the distance range 20° to 60°, with magnitudes greater than 5.1, were used to invert for the upper mantle structure using the method of Forsyth and Li (2005). The model contains lateral variations that primarily correspond to tectonic provinces and plate boundaries. A clear linear velocity change parallels the plate bounding strike-slip fault systems along the northern coast of Venezuela, illustrating the differences between the continental lithosphere of the South American plate and the lithosphere of the Caribbean large igneous province. At depths up to 120 km beneath the Venezuelan Andes and the Maracaibo block there is evidence of underthrusting of the Caribbean plate a few hundred kilometers inland, but there is no other evidence of subduction of the Caribbean plate beneath the South American plate. Shallow low velocities associated with the basins near the coast are clearly imaged, as are higher velocities in the crust and upper mantle associated with the Guayana shield in southeastern Venezuela. The subducting Atlantic plate is imaged beneath the Antilles Arc as a shear tear where the subducting Atlantic plate tears away from the buoyant continental plate at the western end of the Caribbean-South American plate boundary. A low velocity "column" at the edge of the tear may be associated with asthenospheric flow from the Lesser Antilles arc mantle wedge. The complex structure of the plate boundary is best imaged and interpreted with three-dimensional modeling. We have combined the surface wave model, receiver functions, relocated local seismicity, and interpretations from active source profiling to more completely understand the geometry and upper mantle structure of the region.

Miller, M. S.; Niu, F.; Levander, A.

2007-12-01

223

The EarthScope Plate Boundary Observatory Response to the 2006 Augustine Alaskan Volcanic Eruption  

Microsoft Academic Search

During September of 2006, UNAVCO installed five permanent Plate Boundary Observatory (PBO) GPS stations on Augustine Volcano, in the lower Cook Inlet of Alaska. The installations were done at the request of the PBO Magmatic Systems committee in response to the January 11, 2006 eruption of Augustine Volcano. Prior to the eruption, PBO installed five permanent GPS stations on Augustine

B. Pauk; K. Feaux; M. Jackson; B. Friesen; M. Enders; A. Baldwin; K. Fournier; A. Marzulla

2006-01-01

224

Crustal and upper mantle investigations of the Caribbean-South American plate boundary  

Microsoft Academic Search

The evolution of the Caribbean --- South America plate boundary has been a matter of vigorous debate for decades and many questions remain unresolved. In this work, and in the framework of the BOLIVAR project, we shed light on some aspects of the present state and the tectonic history of the margin by using different types of geophysical data sets

Maximiliano J. Bezada

2010-01-01

225

Analysis of Blasius Equation for Flat-plate Flow with Infinite Boundary Value  

Microsoft Academic Search

This paper applies the homotopy perturbation method (HPM) to determine the well-known Blasius equation with infinite boundary value for Flat-plate Flow. We study here the possibility of reducing the momentum and continuity equations to ordinary differential equations by a similarity transformation and write the nonlinear differential equation in the state space format, and then solve the initial value problem instead

M. O. Miansari; M. E. Miansari; A. Barari; G. Domairry

2010-01-01

226

Dynamics of a bubbly turbulent boundary layer along a surface piercing flat plate  

NASA Astrophysics Data System (ADS)

The behaviour of a bubble-laden turbulent boundary layer has been studied experimentally in an open channel water flow with Reynolds number up to 10^6. A poly-dispersed bubble cloud with mean diameter around 200 ? m is injected at the leading edge of a vertical, surface piercing flat plate. The high void fraction bubble layer rises along the plate, developing a Kelvin Helmholtz type instability due to the vertical shear. As a result of this instability, streamwise vorticity is generated that combines with the vertical vorticity associated with the boundary layer, tilting the vortex lines. Bubbles are, for the most part, confined to the boundary layer and accumulate as they interact with the turbulent structures present in this type of flows. The flow at the junction between the flat plate and the free surface is also studied in the presence of bubbles. An streamwise submerged vortex is observed, in agreement with previous studies of single phase junction flows. Vorticity originated by the bouyancy-driven instability of the bubbly layer is convected away from the plate when it reaches the surface, and reconects with the streamwise vortex. Thus, the vortex gains strength and starts to accumulate bubbles stripped from the boundary layer, becoming a dominant feature of the flow.

Aliseda, Alberto; Lasheras, Juan C.

2003-11-01

227

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

228

Initial and boundary conditions in multidimensional wave digital filter algorithms for plate vibration  

Microsoft Academic Search

Recently, multidimensional wave digital filter (MDWDF) structures have been proposed for the modeling of plate vibration problems. In this paper, we discuss how initial and boundary conditions may be properly embedded into such an algorithm in terms of the state quantities that are an integral part of the algorithm. Due to the essential feature of fully-local interconnectivity in the MDWDF

Chien-Hsun Tseng; Stuart Lawson

2004-01-01

229

Energy spectra of velocity pulsations in a turbulent boundary layer on a penetrable plate  

Microsoft Academic Search

Results of measurements of the pulsation characteristics of a turbulent boundary layer on a flat penetrable plate, in a range of variation of the parameters of in-blow from 0 to 20, are presented. It is shown that for supercritical in-blows close to the surface there exists a zone in which the energy spectra of velocity pulsations do not vary as

A. I. Alimpiev; V. N. Mamonov; B. P. Mironov

1973-01-01

230

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

Microsoft Academic Search

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

A. I. Kalfas; R. L. Elder

1993-01-01

231

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

232

An upward turbulent bubbly boundary layer along a vertical flat plate  

Microsoft Academic Search

The structure of an upward wall-bounded bubbly flow is investigated in the simple case of a turbulent boundary layer developing on a vertical flat plate. The data reported is part of a research program currently under progress. They concern the void fraction distribution, the wall shear stress, and the mean liquid velocity profiles. It is shown that depending on their

E. Moursali; J. L. Marié; J. Bataille

1995-01-01

233

Boundary conditions and mode jumping in the buckling of a rectangular plate  

Microsoft Academic Search

We show that mode jumping in the buckling of a rectangular plate may be explained by a secondary bifurcation — as suggested by Bauer et al. [1] — when “clamped” boundary conditions on the vertical displacement function are assumed. In our analysis we use the singularity theory of mappings in the presence of a symmetry group to analyse the bifurcation

David Schaeffer; Martin Golubitsky

1979-01-01

234

EDGE-CRACKED PLATE WITH ONE FREE AND ONE CONSTRAINED BOUNDARY SUBJECTED TO SUDDEN CONVECTIVE COOLING  

Microsoft Academic Search

The transient thermal stress edge crack problem for an elastic strip with free and fully constrained boundaries is considered. The plate is suddenly subjected to convective cooling on the face containing the edge crack while the other face is insulated. The solution of the problem is obtained by using the superposition technique results in a singular integral equation that is

Abd El-Fattah A. Rizk

1994-01-01

235

Linkage Between Chaos Dynamics and the Onset of Turbulence in a Flat Plate Transitional Boundary Layer  

Microsoft Academic Search

An experiment was performed to investigate the onset of turbulence in a flat plate boundary layer. The correlation dimension was calculated from the experimental data by means of chaos dynamics and the existence of the strange attractor was shown in the transitional processes. Therefore, the transitional processes to turbulence have been classified by not only the instability theory but also

R. Q. Li

2005-01-01

236

Post-rifting stress relaxation at the divergent plate boundary in Northeast Iceland  

NASA Astrophysics Data System (ADS)

INTERACTION of the elastic lithosphere with the underlying anelastic asthenosphere causes strain to propagate along the Earth's surface in a diffusion-like manner following tectonism at plate boundaries. This process transfers stress between adjacent tectonic segments and influences the temporal tectonic pattern along a plate boundary. Observations of such strain transients have been rare, and have hitherto been confined to strike-slip and underthrusting plate boundaries1. Here we report the observation of a strain transient at the divergent (spreading) plate boundary in Iceland. A Global Positioning System survey undertaken a decade after an episode of dyke intrusion accompanying several metres of crustal spreading reveals a spatially varying strain field with the expected diffusion-pulse shape and an amplitude three times greater than the 5.7 cm that would be expected from the average spreading rate2. A simple one-dimensional model with a thin elastic layer overlying a viscous layer fits the data well and yields a stress diffusivity of 1.1 á+/-0.3 m2s-1. Combined with struc-tural information from magnetotelluric measurements, this implies a viscosity of 0.3-2 × 1019 Pa s-a value comparable to that derived for Iceland from post-glacial rebound23, but low compared with estimates for mantle viscosity obtained elsewhere3.

Foulger, G. R.; Jahn, C.-H.; Seeber, G.; Einarsson, P.; Julian, B. R.; Heki, K.

1992-08-01

237

An appraisal of 'flat plate' closure for the approximate solution of boundary layer problems  

Microsoft Academic Search

The usefulness of zero pressure gradient, flat plate closure relations in providing approximate solutions for the boundary layer momentum and energy integral equations is examined. Expressions are obtained for skin friction, surface heat transfer rate and local Reynolds analogy factor under general compressible flow conditions. For laminar flows the predictions are compared with well known similarity solutions, with some exact

D. I. A. Poll; C. M. Hellon

1987-01-01

238

The Plate Boundary Observatory (PBO) Network in the PNW region of the United States  

Microsoft Academic Search

The Pacific Northwest Region (PNW) of the United States contains a variety of geologic regions and tectonic problems. These include the Cascadia Subduction Zone, Mt. St. Helens and the transition to the Basin and Range province. Since September of 2003, the Plate Boundary Observatory (PBO), which is part of the larger NSF-funded EarthScope project, has been installing a network of

K. Hafner; K. Austin; K. Feaux; M. Jackson; K. Fengler; S. Doelger

2007-01-01

239

The kinematics of a transition from subduction to strike-slip: An example from the central New Zealand plate boundary  

NASA Astrophysics Data System (ADS)

We develop a kinematic model for the transition from subduction beneath the North Island, New Zealand, to strike-slip in the South Island, constrained by GPS velocities and active fault slip data. To interpret these data, we use an approach that inverts the kinematic data for poles of rotation of tectonic blocks and the degree of interseismic coupling on faults in the region. Convergence related to the Hikurangi subduction margin becomes very low offshore of the northern South Island, indicating that in this region the majority of the relative plate motion has been transferred onto faults within the upper plate, as suggested by previous studies. This result has implications for understanding the likely extent of subduction interface earthquake rupture in central New Zealand. Easterly trending strike slip faults (such as the Boo Boo fault) are the key features that facilitate the transfer of strike-slip motion from the northern South Island faults further north into the southern North Island and onto the Hikurangi subduction thrust. Our results also indicate that the transition from rapid forearc rotation adjacent to the Hikurangi subduction margin to a strike-slip dominated plate boundary (with negligible vertical-axis rotation) in the South Island occurs via a crustal-scale hinge or kink in the upper plate, compatible with paleomagnetic and structural geological data. Despite the ongoing tectonic evolution of the central New Zealand region, our study highlights a remarkable consistency between data sets spanning decades (GPS), thousands of years (active faulting data), and millions of years (paleomagnetic data and bedrock structure).

Wallace, L. M.; Barnes, P.; Beavan, J.; van Dissen, R.; Litchfield, N.; Mountjoy, J.; Langridge, R.; Lamarche, G.; Pondard, N.

2012-02-01

240

Stability of flat plate boundary layer over monolithic viscoelastic coatings  

NASA Astrophysics Data System (ADS)

It is well known that compliant coatings of a wetted surface can affect the stability of hydrodynamic flows. The mechanism of this influence is related to viscoelastic properties of the coatings particularly to their reaction on the disturbing impact. However, the majority of corresponding studies are devoted to investigation of the effect of soft compliant coatings which are unpractical. Moreover, up to now only model computations of flow stability over the compliant coatings have been performed, as experimental data on viscoelastic properties (the modulus of elasticity E characterizing the elastic features, and the loss tangent ? characterizing the viscous or damping features) as functions of frequency for the coatings promising from the point of view of their practical application have been absent. Such data were obtained only last years for some materials (silicon rubbers) in a series of studies [1-3]. The coatings are prospective first of all because of their adequate stiffness (about 1 MPa). In the present paper, results of computations of boundary layer stability performed for the first time for the flow developed over compliant coatings with real properties.

Boiko, A. V.; Kulik, V. M.

2012-07-01

241

Simulating the San Andreas Plate Boundary System: Progress and Prospects  

NASA Astrophysics Data System (ADS)

Computing the hazard posed by the next large earthquake on the San Andreas fault is best carried out with a simulation-based approach. Here we discuss a numerical simulation, Virtual California, that includes many of the physical processes known to be important in earthquake dynamics. These include elastic interactions among the faults in the model, driving at the correct plate tectonic rates, and frictional physics on the faults using the physics obtained from laboratory models with parameters consistent with the occurrence of historic earthquakes. We report progress on a variety of problems relating to the construction and use of increasingly realistic models for earthquakes on the San Andreas fault system, which will be required as the Working Group on California Earthquake Probabilities moves into its next phase of hazard and risk analysis. One of the important issues is to construct a fault system model based upon current WGCEP data. Here we use Deformation Model 2.2 ( http://www.relm.org/models/WGCEP/ ) to produce the most realistic model to date. We also have more fine-scale versions of previous models, including one model having 3 x 2**12 fault elements. While previous versions of Virtual California used only vertical strike slip faults, we are now incorporating dipping rectangular faults having arbitrary rake anble into the model as well. Versions of the basic code are available in Fortran, C, and object-oriented C++. One of the issues that we have encountered is the existence of a dynamical instability that arises as a direct result of the basic interactions between the fault elements, combined with the requirement that the long term slip rate on all fault elements match the observed field-derived average. Using these new models and simulations, we are engaged in novel types of data assimilation, using a method of "scoring" the simulation in comparison to observed paleoseismic data. In this paper, we summarize these results and discuss the implications for numerical forecasting methods

Rundle, P. B.; Rundle, J. B.; Yakovlev, G.; Fernandez, J.; Shcherbakov, R.; Turcotte, D. L.; Donnellan, A.; Field, N.; Grant, L.; Tiampo, K. F.; van Aalsburg, J.; Kellogg, L. H.

2006-12-01

242

Seismic wave conversion near the upper boundary of the Pacific plate beneath the Kanto district, Japan  

NASA Astrophysics Data System (ADS)

A detailed structure of the Pacific plate beneath the Kanto district, Japan, was studied by the use of conspicuous SP converted waves that are generated near the upper boundary of the Pacific plate. These SP waves are observed for earthquakes occurring in the lower plane of the double seismic zone of the subducted Pacific plate. The location of the conversion interface is estimated by inverting the observed TSP - P times. 293 seismic traces recorded at 42 stations for 49 earthquakes are used for analysis. The conversion interface is located above the upper seismic plane of the double seismic zone and is equivalent to the upper boundary of the Pacific plate within the estimated uncertainty. In general, the conversion interface coincides well with the zone of low-angle thrust-fault-type earthquakes in the entire area studied. Comparison with the result of 3-D tomographic inversion reveals that the conversion interface is probably located in the low-velocity layer on the top of the Pacific plate, which is interpreted as the oceanic crust of the Pacific plate.

Ohmi, Shiro; Hori, Sadaki

2000-04-01

243

Frozen-plasma boundary-layer flows over adiabatic flat plates  

NASA Astrophysics Data System (ADS)

The boundary-layer equations for a partially ionized frozen flow over a flat plate has been solved using a new approach in which the problem is reduced from a two-point boundary value problem to a Cauchy problem, thus offering a simple, stable, and relatively inexpensive solution technique. The method is applied to a strong shock-induced argon flow over an adiabatic flat plate. The dependence of the flow inside the boundary layer on the Prandtl number Pr, and Lewis number Le, and on the exponential dependence n of the density viscosity product on the temperature are explored, and it is found that while Pr and n strongly affect the obtained flow field, the influence of Le is negligibly small.

Ben-Dor, G.; Igra, O.; Rakib, Z.

1984-07-01

244

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.

245

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

246

Relocations and Rupture Processes of Large Plate Boundary Earthquakes in Fiordland, South Island, New Zealand  

NASA Astrophysics Data System (ADS)

The geometry, development and kinematics of the Alpine fault system depend to a large extent on the structure and behavior of the Australian Plate as it subducts beneath and translates past the Pacific Plate in southern New Zealand. Understanding the interactions between the Australian and Pacific Plates at the Fiordland subduction zone is a key component of understanding the evolution of the Alpine fault. Here we analyze a series of moderate-to-large earthquakes that have occurred over the past ~15 years in the Fiordland region, near the southern termination of the Alpine Fault. We combine surface wave relocations, finite fault modeling and source time function estimation to more accurately determine the locations and sense of rupture of these events and to analyze what they tell us about the interactions between the two plates. Preliminary results of the precise earthquake relocations describe a broad (~100km), east-west distribution of events around the Australia:Pacific plate boundary, suggesting that not all of these events occurred on the subduction interface. Furthermore, if the large Mw7.2 August 2003 event is located (in an absolute sense) close to the surface trace of the plate boundary (as is often assumed), then most of these events must be located outboard of the subduction trench (akin to the 1985 Mw6.2 and 2004 Mw7.1 earthquakes) and thus do not represent subduction processes. Further analysis of these relocations, in combination with rupture process information revealed through finite fault modeling and source time function estimation of larger events, helps place these plate-boundary associated events into the proper Alpine Fault tectonic framework.

Hayes, G. P.; Furlong, K. P.; Ammon, C. J.; Zeng, Y.

2006-12-01

247

Plate-Tectonic Analysis of Shallow Seismicity: Apparent Boundary Width, beta-Value, Corner Magnitude, Coupled Lithosphere Thickness, and Coupling in 7 Tectonic Settings  

NASA Astrophysics Data System (ADS)

A new plate model [Bird, 2003, G3, 10.1029/2001GC000252] is used to analyze the mean seismicities of 7 types of plate boundary (CRB continental rift boundary, CTF continental transform fault, CCB continental convergent boundary, OSR oceanic spreading ridge, OTF oceanic transform fault, OCB oceanic convergent boundary, SUB subduction zone). We compare the plate-like (non-orogen) regions of model PB2002 with the CMT catalog to select apparent boundary half-widths, and then assign 95% of shallow earthquakes to one of these settings. A tapered Gutenberg-Richter model of the frequency/moment relation is fit to the subcatalog for each setting by maximum-likelihood. Best-fitting ? values range from 0.53 to 0.92, but all 95%-confidence ranges are consistent with a common value of 0.61-0.66. To better determine some corner magnitudes we expand the subcatalogs by: (1) inclusion of orogens; and (2) inclusion of years 1900-1975 from the catalog of Pacheco and Sykes [1992]. Combining both earthquake statistics and the plate-tectonic constraint on moment rate, corner magnitudes include: CRB 7.64-.26+.76, CTF 8.01-.21+.45, CCB 8.46-.39+.21, OCB 8.04-.22+.52, and SUB 9.58-.46+.48. Coupled lithosphere thicknesses are found to be: CRB 3.0-1.4+7.0 km; CTF 8.6-4.1+11 km; CCB 18-11+? km; OSR 0.13-0.09+.13 km for normal-faulting and 0.40-.21+? km for strike-slip; OTF 12-7.1+?, 1.6-0.5+1.4, and 1.5-0.6+1.2 km at low, medium, and high velocities; OCB 3.8-2.3+13.7 km, and SUB 18.0-10.8+? km. Generally high coupling of subduction and continental plate boundaries suggests that here all seismic gaps are dangerous unless proven to be creeping. Generally low coupling within oceanic lithosphere suggests a different model of isolated seismic asperities surrounded by large seismic gaps which may be permanent.

Bird, P.; Kagan, Y. Y.

2003-12-01

248

Discovering plate boundaries: Laboratory and classroom exercises using geodetic data to develop students' understanding of plate motion  

NASA Astrophysics Data System (ADS)

To introduce the concept of plate boundaries, typical introductory geology exercises include students observing and plotting the location of earthquakes and volcanoes on a map to visually demarcate plate boundaries. Accompanying these exercises, students are often exposed to animations depicting the movement of Earth’s tectonic plates over time. Both of these teaching techniques are very useful for describing where the tectonics plates have been in the past, their shapes, and where the plates are now. With the integration of data from current geodetic techniques such as GPS, InSAR, LiDAR, students can learn that not only have the tectonic plates moved in the past, but they are moving, deforming, and changing shape right now. Additionally, GPS data can be visualized using time scales of days to weeks and on the scale of millimeters to centimeters per year. The familiar temporal and spatial scales of GPS data also help students understand that plate tectonics is a process that is happening in the present and can ease the transition to thinking about processes that are typically described using deep time, a very difficult concept for students to grasp. To provide a more robust learning environment, UNAVCO has been incorporating high-precision GPS data into free, place-based, data-rich learning modules for educators and students in introductory Earth science courses at secondary and undergraduate levels. These modules integrate new scientific discoveries related to crustal deformation and explore applications of GPS, LiDAR, and InSAR techniques to research. They also provide students with case studies highlighting the process of scientific discovery, providing context and meaning. Concurrent to these efforts, tools to visualize the inter-relationships of geophysical and geologic processes, structures, and measurements including high-precision GPS velocity data are an essential part of the learning materials. Among the suite of visualization tools that UNAVCO has made available, the Jules Verne Voyager (JVV) interactive map tools are available online and are very well received by educators in introductory Earth science courses. In response to requests for easily accessible and usable data, UNAVCO built the Data for Educators webpage, incorporating an embedded Google Map with GPS locations and providing current GPS time series plots and downloadable data from the Plate Boundary Observatory. To extend and update the datasets available to our community, UNAVCO has developed a GPS velocity viewer using Google Maps technology and provides a learning- focused KMZ combining geophysical data sets for Google-Earth. By combining near real-time geodetic data with modern visualization tools into inquiry-based learning resources, students are deepening their understanding about the active nature of plate margins and gain a solid foundation for learning future concepts. UNAVCO is a non-profit, membership-governed consortium funded by the National Science Foundation and NASA.

Olds, S. E.

2010-12-01

249

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

250

Seismic evidence for sharp lithosphere-asthenosphere boundaries of oceanic plates.  

PubMed

The mobility of the lithosphere over a weaker asthenosphere constitutes the essential element of plate tectonics, and thus the understanding of the processes at the lithosphere-asthenosphere boundary (LAB) is fundamental to understand how our planet works. It is especially so for oceanic plates because their relatively simple creation and evolution should enable easy elucidation of the LAB. Data from borehole broadband ocean bottom seismometers show that the LAB beneath the Pacific and Philippine Sea plates is sharp and age-dependent. The observed large shear wave velocity reduction at the LAB requires a partially molten asthenosphere consisting of horizontal melt-rich layers embedded in meltless mantle, which accounts for the large viscosity contrast at the LAB that facilitates horizontal plate motions. PMID:19390042

Kawakatsu, Hitoshi; Kumar, Prakash; Takei, Yasuko; Shinohara, Masanao; Kanazawa, Toshihiko; Araki, Eiichiro; Suyehiro, Kiyoshi

2009-04-24

251

On boundary layer and interior equations for higher-order theories of plates  

NASA Astrophysics Data System (ADS)

Several shear-deformation plate theories of symmetric laminated plates with transversely isotropic layers are reviewed and the governing equations of these theories are then recast into two equations: one for the interior of the domain and the other for the edge-zone or the boundary layer. For the first time it is shown that the governing equations of the third-order shear-deformation theory of Reddy result in a sixth-order interior equation and a second-order edge-zone equation. It is also demonstrated that in bending and stability problems, and under certain conditions in dynamic problems, the contribution of the edge-zone equation is identically zero for a simply-supported plate. The pure-shear frequencies of a plate according to different theories are determined and compared.

Nosier, Asghar; Reddy, J. N.

252

Late Cretaceous\\/early Tertiary convergence between the Indian and Arabian plates recorded in ophiolites and related sediments  

Microsoft Academic Search

Remnants of ocean floor forming the Eastern Ophiolite Belt in Oman and the Western Ophiolite Belt in Pakistan have a common plate-tectonic history culminating in emplacement at the Cretaceous\\/Tertiary boundary. Fragments of ocean floor in these two belts have ages between 150 and 65 Ma and recorded tectonic events in the early Indian Ocean at 150 Ma, 130-120 Ma, 110-100

E. Gnos; A. Immenhauser; Tj. Peters

1997-01-01

253

A revised estimate of Pacific-North America motion and implications for Western North America Plate boundary zone tectonics  

Microsoft Academic Search

For the past 20 years, much effort has been directed to determining the present-day relative motion of the Pacific and North American plates using two independent approaches. One uses geologic observations and geodetic measurements along the San Andreas Fault and other faults in the plate boundary zone. The other is based on plate motion models that incorporate spreading rates from

Charles DeMets; Richard G. Gordon; Seth Stein; Donald F. Argus

1987-01-01

254

Intraplate deformation adjacent to the Macquarie Ridge south of New Zealand—The tectonic evolution of a complex plate boundary  

Microsoft Academic Search

The distribution of relocated seismicity and the evolving shape of fracture zones through time in the oceanic crust of the Australian Plate adjacent to the Australia:Pacific plate boundary south of New Zealand are used to constrain the deformation of this region of the Australian Plate, here called the Puysegur Block. Relocated seismicity reveals a broad distribution of earthquakes in the

Gavin P. Hayes; Kevin P. Furlong; Charles J. Ammon

2009-01-01

255

Boundary layer flow for a nanofluid over a flat plate with a convective boundary condition  

NASA Astrophysics Data System (ADS)

The steady flow over a static plate immersed in three different nanofluids (CuO-water, Al2O3-water, TiO2-water) with the bottom surface of the plate is heated by convection is investigated numerically. Similarity solutions for the flow and thermal fields are possible if the convective heat transfer from the hot fluid on the lower surface of the plate varies like x-1/2, where x is the distance from the leading edge. The governing partial differential equations are first transformed into a system of ordinary differential equations, before being solved numerically. The results indicate that the inclusion of nanoparticles into the base fluid produces an increase in the skin friction coefficient and the heat transfer rate at the surface. The rate of heat transfer in the Al2O3-water nanofluid is found to be higher than the rate of heat transfer in the CuO-water and TiO2-water nanofluids.

Mansur, Syahira; Ishak, Anuar

2013-09-01

256

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

PubMed

Transient tectonic deformation has long been noted within approximately 100 km of plate boundary fault zones and within active volcanic regions, but it is unknown whether transient motions also occur at larger scales within plates. Relatively localized transients are known to occur as both seismic and episodic aseismic events, and are generally ascribed to motions of magma bodies, aseismic creep on faults, or elastic or viscoelastic effects associated with earthquakes. However, triggering phenomena and systematic patterns of seismic strain release at subcontinental (approximately 1,000 km) scale along diffuse plate boundaries have long suggested that energy transfer occurs at larger scale. Such transfer appears to occur by the interaction of stresses induced by surface wave propagation and magma or groundwater in the crust, or from large-scale stress diffusion within the oceanic mantle in the decades following clusters of great earthquakes. Here we report geodetic evidence for a coherent, subcontinental-scale change in tectonic velocity along a diffuse approximately 1,000-km-wide deformation zone. Our observations are derived from continuous GPS (Global Positioning System) data collected over the past decade across the Basin and Range province, which absorbs approximately 25 per cent of Pacific-North America relative plate motion. The observed changes in site velocity define a sharp boundary near the centre of the province oriented roughly parallel to the north-northwest relative plate motion vector. We show that sites to the west of this boundary slowed relative to sites east of it by approximately 1 mm yr(-1) starting in late 1999. PMID:16810252

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

2006-06-29

257

Paleomagnetic Quantification of Neogene Block Rotations within an Active Transtensional Plate Boundary, Baja California, Mexico  

NASA Astrophysics Data System (ADS)

Compared to oceanic plate boundaries which are generally narrow zones of deformation, continental plate boundaries appear as widespread areas with complex and poorly understood kinematics. Motion of crustal blocks within these “diffuse plate boundaries” causes rather small-scale lithospheric deformation within the boundary zone, while the main plates behave more rigid. Complex deformation patterns of interacting terranes separated by a variety of active faults are the consequence. To study the dynamic implications of boundary zone deformation, the southern part of the Baja California peninsula, Mexico (Baja) has been chosen as target for a detailed paleomagnetic study. In combination with geodetic measurements it is tried to characterize rigid block rotations and temporal changes in rotation rates. Up to now, little paleomagnetic work directed toward vertical axis rotations has been done in Baja California, despite its location in a major active transtensional zone. To address this problem, a total of 501 cores from 63 sites in the southern part of Baja - including sites on San José Island, San Francisco Island and Cerralvo Island - has been taken from volcanic and sedimentary rocks covering the last 25 million years in time. The analysis of paleomagnetic declinations and comparison to coeval data from North America and stable areas of Baja California allow evaluating the long-term kinematics of the region and the effects of oblique-rifting in the Gulf of California to the east. Nearly all sampled sites indicate vertical axis rotation up to 30-40 degrees with an average of about 20-25 degrees. Depending on the location these rotations have been either clockwise or counter-clockwise and are correlated with the opening of the Gulf of California and the translation of the Baja California peninsula to the North. Results of the paleomagnetic investigation are compared to geodetic data of the last few years in order to address the problem how strain is partitioned within a complex network of faults and how rates of rotation change with time.

Weber, J.; Umhoefer, P. J.; Pérez Venzor, J. A.; Bachtadse, V.

2009-12-01

258

A visual study of vortex-induced subcritical instability on a flat plate laminar boundary layer  

NASA Astrophysics Data System (ADS)

This paper reports results of our experimental investigation on flow instability on a flat plate laminar boundary layer caused by a ``captive'' vortex migrating far outside the boundary layer. Results show that the sign of the circulation associated with the vortex is the main determinant for the severity of the boundary layer instability. A captive vortex with an opposite sign to that of the unperturbed shear layer vorticity causes a breakdown ahead of it, while the one with the same sign as the unperturbed shear layer vorticity gives rise to weaker excitation trailing it. Additional parameters that influence the flow instability are the strength and distance of the vortical disturbance from the boundary layer, as well as the translational speed of the vortex. These experimental results compliment the corresponding theoretical analysis of Sengupta et al. (J Fluid Mech 493:277-286, 2003).

Lim, T. T.; Sengupta, T. K.; Chattopadhyay, M.

259

MHD free convective boundary layer flow of a nanofluid past a flat vertical plate with Newtonian heating boundary condition.  

PubMed

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

2012-11-15

260

The band gaps of plate-mode waves in one-dimensional piezoelectric composite plates: polarizations and boundary conditions.  

PubMed

Theoretical studies are presented for the band structures of plate-mode waves in a one-dimensional (1-D) phononic crystal plate consisting of piezoelectric ceramics placed periodically in an epoxy substrate. The dependences of the widths and starting frequencies of first band gaps (FBG) on the filling fraction and the thickness to lattice pitch ratio are calculated for different polarizations of piezoelectric ceramics under different electric boundary conditions, i.e., short circuit (SC) and open circuit (OC). We found that the FBG always is broadened by polarizing piezoelectric ceramics, and the FBG widths with SC always are larger than that with OC for the same polarization. Our research shows that there are three critical parameters which determine the FBG: the polarized directions, the filling fraction, and the ratio of the plate thickness to the lattice pitch, respectively. Therefore, we can control the width and starting frequency of the FBG in the engineering according to need by choosing these parameters of the system. PMID:17718332

Zou, Xin-Ye; Chen, Qian; Cheng, Jian-Chun

2007-07-01

261

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

262

Comparison of turbulence models for the natural convection boundary layer along a heated vertical plate  

NASA Astrophysics Data System (ADS)

A numerical code for solving the boundary-layer equations is used to evaluate the performance of various turbulence models for the natural convection boundary layer along a heated vertical plate. The Cebeci-Smith (1974) model yields wall-heat transfer and turbulent viscosity values that are lower than the experimental values, while the standard k-epsilon model with wall functions for k and epsilon yields high wall-heat transfer values and resonable velocity and temperature profiles. Low-Reynolds-number k-epsilon models provide accurate wall-heat transfer results.

Henkes, R. A. W. M.; Hoogendoorn, C. J.

1989-01-01

263

The Theory of Plate Tectonics  

NSDL National Science Digital Library

This is a brief overview of the Theory of Plate Tectonics. According to the theory, the Earth's surface layer, or lithosphere, consists of seven large and 18 smaller plates that move and interact in various ways. Along their boundaries, they converge, diverge, and slip past one another, creating the Earth's seismic and volcanic activities. These plates lie atop a layer of partly molten rock called the asthenosphere. The plates can carry both continents and oceans, or exclusively one or the other. The site also explains interaction at the plate boundaries, which causes earthquakes, volcanoes and other forms of mountain building.

264

The Theory of Plate Tectonics  

NSDL National Science Digital Library

This is a brief overview of the Theory of Plate Tectonics. According to the theory, the Earth's surface layer, or lithosphere, consists of seven large and 18 smaller plates that move and interact in various ways. Along their boundaries, they converge, diverge, and slip past one another, creating the Earth's seismic and volcanic activities. These plates lie atop a layer of partly molten rock called the asthenosphere. The plates can carry both continents and oceans, or exclusively one or the other. The site also explains interaction at the plate boundaries, which causes earthquakes, volcanoes and other forms of mountain building.

Oberrecht, Kenn

2007-03-28

265

Dynamic role of tectonic mélange during interseismic process of plate boundary mega earthquakes  

NASA Astrophysics Data System (ADS)

Tectonic mélange has a key role in subduction zones because its thick pile forms the plate boundary itself; therefore, the plate boundary process is nearly identical to the mélange-forming process. We examined three tectonic mélanges in the Shimanto Belt in southwest Japan to decipher their progressive deformation process with subduction, especially within the seismogenic zone. Here we report detailed observation of sandstone blocks and the strain history of the shale matrix of a sediment-dominated tectonic mélange. The necessity of tectonic mélange accompanying fossil seismogenic décollement is unveiled. Several deformation processes continue by turn until the depth of the down-dip limit of the seismogenic zone is reached. The results support the space-time partition of deformation in terms of seismic behavior and suggest a possible candidate for a geological consequence of recently observed slow earthquakes.

Kitamura, Yujin; Kimura, Gaku

2012-09-01

266

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

267

Active faulting south of the Himalayan Front: Establishing a new plate boundary  

Microsoft Academic Search

New tectonic uplifts south of the Salt Range Thrust and Himalayan Front Thrust (HFT) represent an outward step of the plate boundary from the principal tectonic displacement zone into the Indo-Gangetic Plain. In Pakistan, the Lilla Anticline deforms fine-grained overbank deposits of the Jhelum River floodplain 15 km south of the Salt Range. The anticline is overpressured in Eocambrian non-marine strata.

Robert S. Yeats; V. C. Thakur

2008-01-01

268

BOLIVAR: Crustal Structure of the Caribbean-South America Plate Boundary at 65W  

Microsoft Academic Search

We describe a ~550 km long, N-S oriented, onshore-offshore profile that crosses the SE Caribbean plate boundary at approximately 65W longitude. The profile is one of the principal seismic reflection and refraction transects acquired in 2004 as part of the Broadband Ocean and Land Investigation of Venezuela and the Antilles arc Region (BOLIVAR) experiment. The transect starts ~330 km offshore

M. Bezada; M. Magnani; C. A. Zelt; A. Levander; M. Schmitz

2007-01-01

269

Transpression, displacement partitioning, and exhumation in the eastern Caribbean\\/South American plate boundary zone  

Microsoft Academic Search

The Caribbean\\/South American plate boundary zone in northeastern Venezuela is a transpressive orogenic belt consisting from north to south of a nascent subduction zone (South Caribbean deformed belt), a volcanic arc (Leeward Antilles arc), a ``hinterland'' with high-pressure (P)\\/low temperature (T) metamorphic rocks (Cordillera de la Costa belt), and a southern nonmetamorphic, foreland fold and thrust belt (Serranía del Interior).

Hans G. Avé Lallemant

1997-01-01

270

Transpression, displacement partitioning, and exhumation in the eastern Caribbean \\/ South American plate boundary zone  

Microsoft Academic Search

The Caribbean\\/South American plate boundary zone in northeastern Venezuela is a transpressive orogenic belt consisting from north to south of a nascent subduction zone (South Caribbean deformed belt), a volcanic arc (Leeward Antilles arc), a “hinterland” with high-pressure (P)\\/low temperature (T) metamorphic rocks (Cordillera de la Costa belt), and a southern nonmetamorphic, foreland fold and thrust belt (Serranía del Interior).

Hans G. Avé Lallemant

1997-01-01

271

The Baja California Borderland and the Neogene Evolution of the Pacific-North American Plate Boundary  

Microsoft Academic Search

New observational data on Neogene faulting in the borderland of Baja California places important constraints on tectonic models for the evolution of the Pacific-North American (P-NA) plate boundary and rifting in the Gulf of California. Neogene faults in the borderland range from strike slip to normal slip and accommodate integrated transtension. Most have east-facing escarpments and likely reactivate the former

J. M. Fletcher; B. W. Eakins

2001-01-01

272

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

Microsoft Academic Search

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

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

2011-01-01

273

Deep structural setting of the North American-Caribbean plate boundary in eastern Guatemala  

Microsoft Academic Search

Two-dimensional inverse gravity modeling is presented to help determine the deep structural framework of the left-lateral Polochic-Motagua fault systems. They represent a major segment of the North American-Cari- bbean plate boundary. These seismically active tectonic lineaments, crossing broadly E-W Guatemala, are super- imposed over a narrow suture where slices of ophiolitic assemblages crop out. Within the principal displacement zone of

E. Lodolo; M. Menichetti; M. Guzmán-Speziale; G. Giunta; C. Zanolla

2009-01-01

274

Cenozoic plate boundary evolution in the South Island of New Zealand: New thermochronological constraints  

Microsoft Academic Search

Thermochronological investigations of samples collected west of the Alpine Fault zone provide new insight into the early development of the Australian-Pacific (AUS-PAC) plate boundary through New Zealand that is not preserved elsewhere in the modern orogenic system of the South Island. The 40Ar\\/39Ar, fission track, and (U-Th)\\/He ages for these samples span the Cenozoic and provide direct constraints on the

Geoffrey E. Batt; Suzanne L. Baldwin; Michael A. Cottam; Paul G. Fitzgerald; Mark T. Brandon; Terry L. Spell

2004-01-01

275

Receiver function study of the crustal structure of the southeastern Caribbean plate boundary and Venezuela  

Microsoft Academic Search

We have investigated crustal thickness and composition across the southeastern Caribbean plate boundary with the receiver function technique. We used teleseismic data recorded by a temporary broadband array deployed under the BOLIVAR project and the permanent national seismic network of Venezuela. We used the primary P-to-S conversion and crustal reverberations to estimate crustal thickness and average crustal VP\\/VS ratio over

Fenglin Niu; Tammy Bravo; Gary Pavlis; Frank Vernon; Herbert Rendon; Maximiliano Bezada; Alan Levander

2007-01-01

276

Update on Plate Boundary Observatory (PBO) Activities in the PNW Region  

Microsoft Academic Search

As of September 2005 The Plate Boundary Observatory (PBO), part of the larger NSF-funded EarthScope project, is completing year 2 in the installation phase of 875 continuously operating GPS instruments in the Western United States. The Pacific Northwest (PNW) region will install 149 continuous GPS stations by the end of 2008. These sites are distributed along the fore and back-arc

K. Hafner

2005-01-01

277

Preservation of contrasting geothermal gradients across the Caribbean-North America plate boundary (Motagua Fault, Guatemala)  

NASA Astrophysics Data System (ADS)

Strike-slip plate boundaries juxtapose crustal blocks that may have different geodynamic origins and therefore different thermal structures. Thermo-kinematic modeling of this type of strike-slip plate boundary predicts an asymmetric signature in the low-temperature thermochronologic record across the fault. Age-elevation profiles of zircon (U-Th)/He ages across the Motagua Fault, a 500 km long segment of the transform boundary between the North American and Caribbean plates, document a sharp cooling age discontinuity across the fault. This discontinuity could be interpreted as a difference in denudation history on each side of the fault. However, a low-relief Miocene erosional surface extends across the fault; this surface has been uplifted and incised and provides a geomorphic argument against differential denudation across the fault. By integrating magmatic, volcanic, and heat flow data, age-elevation profiles, and thermo-kinematic modeling, we propose that large horizontal displacement along the Motagua Fault has offset a persistent geothermal asymmetry across the fault and explains both the age discontinuities and the age-elevation patterns. This study illustrates how thermochronology can be used to detect large strike-slip displacements and more generally opens new perspectives in understanding the impact of nonuniform thermal structures on thermochronologic results.

Simon-Labric, Thibaud; Brocard, Gilles Y.; Teyssier, Christian; Beek, Peter A.; Fellin, Maria Giuditta; Reiners, Peter W.; Authemayou, Christine

2013-07-01

278

Boundary layer analysis for two-dimensional slot jet impingement on inclined plates  

SciTech Connect

The laminar boundary layer flow when a two-dimensional slot jet impinges on a flat plate at some angle is analyzed theoretically. The conservation equations in primitive variables are solved using a finite-difference technique. The computed results at 0 and 90 deg angle of impingement are in perfect agreement with standard solutions available in the literature. The influence of the angle of impingement on the velocity and temperature profiles is studied. The presence of a stagnation point when the plate is not parallel to the oncoming jet is found to affect considerably the local Nusselt number and skin friction coefficient. These parameters attain very large values close to the stagnation point at small angles of impingement. However, far from the stagnation point, they approach values corresponding to a flat plate at zero incidence, irrespective of the angle of jet impingement.

Garg, V.K.; Jayaraj, S. (Indian Institute Technology, Kanpur (India))

1988-08-01

279

Null controllability of von Karman thermoelastic plates under the clamped or free mechanical boundary conditions  

NASA Astrophysics Data System (ADS)

In this paper, we provide results of local and global null controllability for 2-D thermoelastic systems, in the absence of rotational inertia, and under the influence of the (nonLipschitz) von Karman nonlinearity. The plate component may be taken to satisfy either the clamped or higher order (and physically relevant) free boundary conditions. In the accompanying analysis, critical use is made of sharp observability estimates which obtain for the linearization of the thermoelastic plate (these being derived in [G. Avalos, I. Lasiecka, The null controllability of thermoelastic plates and singularity of the associated minimal energy function, J. Math. Anal. Appl. 294 (2004) 34-61] and [G. Avalos, I. Lasiecka, Asymptotic rates of blowup for the minimal energy function for the null controllability of thermoelastic plates: The free case, in: Proc. of the Conference for the Control of Partial Differential Equations, Georgetown University, Dekker, in press]). Moreover, another key ingredient in our work to steer the given nonlinear dynamics is the recent result in [A. Favini, M.A. Horn, I. Lasiecka, D. Tataru, Addendum to the paper: Global existence, uniqueness and regularity of solution to a von Karman system with nonlinear boundary dissipation, Differential Integral Equations 10 (1997) 197-200] concerning the sharp regularity of the von Karman nonlinearity.

Avalos, George

2006-06-01

280

Transitional and turbulent flat-plate boundary layers with heat transfer  

NASA Astrophysics Data System (ADS)

We report on our direct numerical simulation of two incompressible, nominally zero-pressure-gradient flat-plate boundary layers from momentum thickness Reynolds number 80 to 1950. Heat transfer between the constant-temperature solid surface and the free-stream is also simulated with molecular Prandtl number=1. Throughout the entire flat-plate, the ratio of Stanton number and skin-friction St/Cfdeviates from the exact Reynolds analogy value of 0.5 by less than 1.5%. Turbulent Prandtl number t peaks at the wall. Preponderance of hairpin vortices is observed in both the transitional and turbulent regions of the boundary layers. In particular, the internal structure of merged turbulent spots is hairpin forest; the internal structure of infant turbulent spots is hairpin packet. Numerous hairpin vortices are readily detected in both the near-wall and outer regions of the boundary layers up to momentum thickness Reynolds number 1950. This suggests that the hairpin vortices in the turbulent region are not simply the aged hairpin forests convected from the upstream transitional region. Temperature iso-surfaces in the companion thermal boundary layers are found to be a useful tracer in identifying hairpin vortex structures.

Wu, Xiaohua; Moin, Parviz

2010-11-01

281

A Model of Convergent Plate Margins Based on the Recent Tectonics of Shikoku, Japan  

Microsoft Academic Search

Displacements generated by a (viscoelastic finite element) plate tectonic model are compared with and found to be compatible with geodetic survey data taken on the island of Shikoku, Japan. The model indicates that prior to the 1946 Nankaid0 earthquake, large vertical displacements occurred along the continental slope, increasing in magnitude toward and approaching a maximum of 7 m at the

Richard Edward Bischke

1974-01-01

282

Effect of Surfactant Additives on Generation and Development of Laminar Boundary Layer on a Flat Plate  

NASA Astrophysics Data System (ADS)

The effect of surfactant solutions on laminar boundary layer over a flat plate has been investigated at Re < 15.3×103 by measuring the velocity profile using a PIV system. It was clarified that the boundary layer thickness of surfactant solutions increases significantly compared to that of tap water. In the upstream region of the leading edge, the boundary layer (or the stagnation area) has already been generated and the thickness of this area is already large. In the downstream region, the velocity profiles of all surfactant concentrations at the near-wall region, are similar, but not identical, to that of tap water. At the far-wall region of the boundary layer, the velocity profile is significantly different. For higher surfactant concentrations, the velocity profile describes like S-shape profile, which is greatly different from that of lower concentration. When the Reynolds number increases, the velocity profile of the surfactant solution gradually develops. The dependence of the boundary layer thickness of the surfactant solution on the distance downstream from the leading edge is similar to that of tap water. Consequently, the surfactant gives large effect for not only development of the boundary layer but also the generation of it.

Ogata, Satoshi; Fujita, Takeshi

283

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

SciTech Connect

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

Speed, R.C. (Northwestern Univ., Evanston, IL (United States)); Larue, D.K. (Univ. of Puerto Rico, Mayaguez (Puerto Rico))

1991-03-01

284

A parametric study of boundary layer receptivity for an acoustic wave/porous plate interaction  

NASA Astrophysics Data System (ADS)

An analysis is made of the coupling of a plane sound wave in the incompressible limit to the growth of Tollmien-Schlichting waves in a laminar, parallel boundary layer over a flat plate containing a porous strip. The strip is a receptivity site and links the Blasius layer to a fluid-filled cavity that can act as a resonator. The receptivity problem is modeled with the linearized Navier-Stokes equations describing the boundary layer and the sound wave and is solved with numerical integration and Fourier transformation techniques. Values of the receptivity coefficient are presented as functions of selected flowfield and geometric variables which define the problem. Conclusions are drawn with regard to combinations of parameters that lead to local maximum and minimum values of the receptivity coefficient, which has relevance to the more general problem of boundary layer transition control.

Pal, A.; Bower, W. W.; Meyer, G. H.

285

Leading-edge receptivity of a hypersonic boundary layer on a flat plate  

NASA Astrophysics Data System (ADS)

Experimental investigations of the boundary layer receptivity, on the sharp leading edge of a at plate, to acoustic waves induced by two-dimensional and three- dimensional perturbers, have been performed for a free-stream Mach number M[infty infinity] = 5.92. The fields of controlled free-stream disturbances were studied. It was shown that two-dimensional and three-dimensional perturbers radiate acoustic waves and that these perturbers present a set of harmonic motionless sources and moving sources with constant amplitude. The disturbances excited in the boundary layer were measured. It was found that acoustic waves impinging on the leading edge generate Tollmien Schlichting waves in the boundary layer. The receptivity coefficients were obtained for several radiation conditions and intensities. It was shown that there is a dependence of receptivity coefficients on the wave inclination angles.

Maslov, A. A.; Shiplyuk, A. N.; Sidorenko, A. A.; Arnal, D.

2001-01-01

286

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

Microsoft Academic Search

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

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

2000-01-01

287

Influence of convergent plate boundaries on upper mantle flow and implications for seismic anisotropy  

Microsoft Academic Search

Shear-wave splitting observations in the region of the upper mantle enveloping subduction zones have been interpreted as showing extensive regions of trench-parallel flow, despite the difficulty of reconciling such behavior with a sound model based on the forces that drive mantle motion. To gain insight into the observations, we systematically investigate flow patterns around the cold downwelling sheets associated with

Julian P. Lowman; Laura T. Pinero-Feliciangeli; J.-Michael Kendall; M. Hosein Shahnas

2007-01-01

288

Paleocurrents beside an obliquely convergent plate boundary (Sulaiman foldbelt, southwestern Himalayas, west-central Pakistan)  

Microsoft Academic Search

Cretaceous to Holocene paleocurrents at the north and south ends of the Sulaiman Range show flow trending westward, then variably eastward, southward, and finally eastward. Pre-orogenic Cretaceous shelf sandstones show dispersal to the southwest, north-northwest, and west-southwest off the craton. However, Paleocene marine sandstones in the south spread east-southeast, and early Eocene deltaic sandstones in the north spread southeast and

A. Waheed; N. Ahmad

1988-01-01

289

From subduction to collision: Control of deep processes on the evolution of convergent plate boundary  

Microsoft Academic Search

Using laboratory experiments, we investigate the dynamics of the collisional process that follows the closure of an oceanic basin. The evolution of these experiments systematically shows four successive episodes of deformation, which correspond to (1) the initiation of oceanic subduction, (2) a mature period of oceanic subduction, (3) an episode of continental subduction, during which the trench absorbs all the

Vincent Regard; Claudio Faccenna; Joseph Martinod; Olivier Bellier; Jean-Charles Thomas

2003-01-01

290

Continental Collision and the STEP-wise Evolution of Convergent Plate Boundaries: From Structure to Dynamics  

Microsoft Academic Search

Particularly interesting stages in the evolution of subduction zones are the two main transient stages: initiation and termination.\\u000a In this contribution the focus is on the second of these: terminal stage subduction, often triggered by continental collision\\u000a or arc-continent collision. The landlocked basin setting of the Mediterranean region, in particular the western-central Mediterranean,\\u000a provides unique opportunities to study terminal stage

Rinus Wortel; Rob Govers; Wim Spakman

291

Overriding plate structure of the Nicaragua convergent margin: Constraints on the limits of the seismogenic zone and the 1992 tsunami earthquake  

NASA Astrophysics Data System (ADS)

We present two 2D seismic velocity models of the Nicaragua convergent erosional margin along perpendicular WAS profiles acquired in the rupture area of the 1992 tsunami earthquake. The models focus on the structure of the upper plate and the geometry of the plate boundary interface. In the trench-perpendicular profile (NIC20), the basement shows increasing velocity from top to bottom and from the trench towards the coast. In the absence of an accretionary wedge, the velocity gradient reflects a progressive decrease in the degree of rock fracturing of the Mesozoic igneous basement, from almost complete disaggregation at < 4 km from the trench to aseismic ridge-like crustal rocks at ~75 km, where the upper plate is ~20±0.5 km-thick. Upper mantle-like velocities are obtained at a depth of ~10 km beneath the ~5 km-thick Sandino basin, which means that the mantle wedge is shallow and extends up to ~90 km from the trench. The trench-parallel profile (NIC125) is similar in terms of velocity structure and depth of the inter-plate boundary (18±0.5 km). It displays a laterally-uniform structure, indicating that the NIC20 model is representative of the upper plate structure along the whole rupture area of the 1992 earthquake. A mismatch between the WAS inter-plate reflector and that imaged along coincident MCS profiles can be explained by a velocity anisotropy of 17±2%, probably related with locally-enhanced rock fracturing and fluid percolation. The updip limit of the seismogenic zone is difficult to define based on regional seismicity and aftershock distribution because the aftershocks nucleate up to the trench. The frontal part of the overriding plate is probably too fractured to store elastic energy, unless the presence of local asperities makes it conditionally stable. The downdip limit (~25 km depth), defined by an abrupt decrease in the number of aftershocks and by a gap in the regional seismicity, occurs near the tip of the mantle wedge, indicating that it is probably controlled by the presence of a serpentinized mantle wedge right beneath the Sandino basin. The hypocenter of the 1992 main shock is not particularly shallow (~21 km), but seismological data indicate that it triggered sub-events in the conditionally stable area. One of these sub-events occurred near the SE limit of the rupture zone, which is the area of maximum inferred co-seismic slip and seafloor displacement and the place where MCS data have revealed the presence of a subducted seamount. Given that sediments are absent on top of the subducting seamount, we hypothesize that the seismic rupture is controlled by the nature of the basement rocks. In this case the average rupture velocity of this sub-event would be 1.4-1.7 km/s, and the rigidity 9-14 GPa, consistent with estimations based on seismological data analysis. Thus, the slow propagation and long duration of the 1992 tsunami earthquake could be explained by rupture propagating within the fractured, conditionally stable part the crystalline basement and not into the sediments.

Melendez, A.; Sallares, V.; Prada, M.; Ranero, C. R.; McIntosh, K. D.; Grevemeyer, I.

2011-12-01

292

USArray observations of quasi-Love surface wave scattering: Orienting anisotropy in the Cascadia plate boundary  

NASA Astrophysics Data System (ADS)

Quasi-Love (QL) surface wave anomalies are observed along multiple great circle paths crossing the Pacific and through the mid-ocean ridge and subduction zone associated with the Juan de Fuca plate. The long-period QL waves observed on the USArray component of EarthScope arrive immediately after the fundamental Love wave arrival, suggesting that the QL waves were generated close to USArray and near the plate boundary. The dense USArray network allows the analysis of the azimuthal dependence of the QL surface wave scattering to determine the horizontal anisotropic axes of symmetry in Earth's upper mantle. We focus on the location, 42.5°N and 127.5°W just offshore of the southern Oregon coastline near the Gorda Ridge, and we analyze the QL scattering along 14 different great circle paths crossing through this location. We low-pass filter the data to suppress overtones and crustal effects. QL amplitude and polarity constrains an anisotropic axis of symmetry that correlates well with the hot spot referenced Juan de Fuca plate motion and regional shear wave splitting. QL observations at multiple periods (50, 75, 100, 150, and 200 s) suggest a maximum Love-to-Rayleigh scattering at 100 s period, which is consistent with anisotropic lateral gradients in the asthenosphere beneath the Juan de Fuca and Gorda plates. Our observations do not follow the predictions of slab rollback and suggest the entrainment of asthenosphere with the overriding Juan de Fuca and Gorda plates.

Rieger, D. M.; Park, J.

2010-05-01

293

CONVERGENCE OF A BOUNDARY INTEGRAL METHOD FOR 3-D WATER WAVES  

Microsoft Academic Search

We prove convergence of a modified point vortex method for time- dependent water waves in a three-dimensional, inviscid, irrotational and incompress- ible fluid. Our stability analysis has two important ingredients. First we derive a leading order approximation of the singular velocity integral. This leading order approximation captures all the leading order contributions of the original velocity integral to linear stability.

Thomas Y. Hou; Pingwen Zhang

2002-01-01

294

Boundary layer development on a semi-infinite suddenly heated vertical plate  

NASA Astrophysics Data System (ADS)

The flow resulting from suddenly heating a semi-infinite, vertical wall immersed in a stationary fluid has been described in the following way: at any fixed position on the plate, the flow is initially described as one-dimensional and unsteady, as though the plate is doubly infinite; at some later time, which depends on the position, a transition occurs in the flow, known as the leading-edge effect (LEE), and the flow becomes two-dimensional and steady. The transition is characterized by the presence of oscillatory behaviour in the flow parameters, and moves with a speed greater than the maximum fluid velocities present in the boundary layer. A stability analysis of the one-dimensional boundary layer flow performed by Armfield & Patterson (1992) showed that the arrival times of the LEE determined by numerical experiment were predicted well by the speed of the fastest travelling waves arising from a perturbation of the initial one-dimensional flow. In this paper, we describe an experimental investigation of the transient behaviour of the boundary layer on a suddenly heated semi-infinite plate for a range of Rayleigh and Prandtl numbers. The experimental results confirm that the arrival times of the LEE at specific locations along the plate, relatively close to the leading edge, are predicted well by the Armfield & Patterson theory. Further, the periods of the oscillations observed following the LEE are consistent with the period of the maximally amplified waves calculated from the stability result. The experiments also confirm the presence of an alternative mechanism for the transition from one-dimensional to two-dimensional flow, which occurs in advance of the arrival of the LEE at positions further from the leading edge.

Patterson, John C.; Graham, Tasman; Schöpf, Wolfgang; Armfield, S. W.

2002-02-01

295

Model representation of boundary-layer convergence triggering deep convection over complex terrain: A case study from COPS  

NASA Astrophysics Data System (ADS)

An isolated thunderstorm from the Convective and Orographically-induced Precipitation Study in southwest Germany and east France in 2007 is analyzed. On July 15, deep convection developed east of the Black Forest crest, although convective available potential energy (CAPE) was only moderate and convective inhibition (CIN) was high. Data analysis revealed that convection was triggered by updrafts penetrating the capping inversion of the planetary boundary layer as a result of low-level convergence. Although the numerical weather prediction model COSMO-DE of the German Weather Service (2.8 km grid resolution) simulated a convergence line and the evolution of a line of low clouds in good agreement with radar and satellite observations, no precipitating deep convection developed from this line of clouds. For an improved representation of orographic effects, simulations with a finer grid resolution of 1 km were performed. Despite almost optimal conditions, i.e. moderate amount of CAPE and almost vanishing CIN, the updrafts required to overcome CIN were not reached in both model configurations. Although both simulations did not initiate deep convection, the results suggest that in an air mass convection situation without mid-tropospheric forcing, the simulated location and timing of convergence lines with coexistent large values of CAPE and low values of CIN can be used as diagnostic parameters for deep convection nowcasting.

Barthlott, Christian; Schipper, Janus Willem; Kalthoff, Norbert; Adler, Bianca; Kottmeier, Christoph; Blyth, Alan; Mobbs, Stephen

2010-02-01

296

Quasi-simultaneous interaction method for solving 2D boundary layer flows over plates and airfoils  

NASA Astrophysics Data System (ADS)

This paper studies unsteady 2D boundary layer flows over dented plates and a NACA 0012 airfoil. An inviscid flow is assumed to exist outside the boundary layer and is solved iteratively with the boundary layer flow together with the interaction method until a matching solution is achieved. Hereto a quasi-simultaneous interaction method is applied, in which the integral boundary layer equations are solved together with an interaction-law equation. The interaction-law equation is an approximation of the external flow and based on thin-airfoil theory. It is an algebraic relation between the velocity and displacement thickness. The interaction-law equation ensures that the eigenvalues of the system of equations do not have a sign change and that no singularities occur. Three numerical schemes are used to solve the boundary layer flow with the interaction method. These are: a standard scheme, a splitting method and a characteristics solver. All schemes use a finite difference discretization. The three schemes yield comparable results for the simulations carried out. The standard scheme is deviating most from the splitting and characteristics solvers. The results show that the eigenvalues remain positive, even in separation. As expected, the addition of the interaction-law equation prevents a sign change of the eigenvalues. The quasi-simultaneous interaction scheme is applicable to the three numerical schemes tested.

Bijleveld, H. A.; Veldman, A. E. P.

2012-11-01

297

The turbulent boundary layer and wake of an aligned flat plate  

NASA Astrophysics Data System (ADS)

A theoretical study of the turbulent boundary layer and symmetric wake of an aligned flat plate is described. A specific turbulence model is taken throughout, namely the Cebeci-Smith (1974) one, although at the high Reynolds numbers of interest the wake results are found subsequently to be influenced hardly at all by the precise details of the model, so that there is a ready generalization. The two-tiered wake implied by the analysis is rather different from the two-tiered boundary layer. The inner tier of the wake is thicker than the boundary layer's inner tier and, associated with this, the 'logarithmic' zone present in the boundary layer upstream is absent in the wake, being replaced by a 'cuspidal' zone just outside the inner-wake tier due to the reduction in shear stresses. Local interactive regions near the trailing edge show how the erosion of the logarithmic behavior takes place relatively fast, being virtually complete on entry into the full wake. The agreement between the theory, experiments and previous computations for the boundary layer and full wake is found to be good quantitatively as well as qualitatively, encouraging the use of the present approach in other contexts such as turbulent separation.

Neish, A.; Smith, F. T.

298

GPS and tectonic evidence for a diffuse plate boundary at the Azores Triple Junction  

NASA Astrophysics Data System (ADS)

We use GPS, bathymetric/structural, and seismic data to define the pattern of present deformation along the northern half of the Azores plateau, where the Nubia–Eurasia plate boundary terminates at the axis of the Mid-Atlantic Ridge (MAR). New and existing campaign GPS velocities from the Azores islands reveal extension oblique to a series of en échelon volcanic ridges occupied by Terceira, S. Jorge, Pico, and Faial islands. In a frame of reference defined by 69 continuous GPS stations on the Eurasia plate, Terceira Island moves 2±1 mm/yr away from Eurasia, consistent with the island's location within the Terceira Rift and plate boundary structure. The volcanic ridges south of the Terceira Rift move toward WSW at progressively faster rates, reaching a maximum of 3.5±0.5 mm/yr (2-?) for the Pico/Faial volcanic ridge. The hypothesis that the Terceira Rift accommodates all Nubia–Eurasia plate motion is rejected at high confidence level based on the motions of sites on S. Jorge Island just west of Terceira Rift. All of the islands move relative to the Nubia plate, with Pico Island exhibiting the slowest motion, only 1±0.5 mm/yr (2-?). Detailed bathymetry from the interior of the hypothesized Azores microplate reveals faults that crosscut young MAR seafloor fabric. These observations and the GPS evidence for distributed deformation described above argue against the existence of a rigid or semi-rigid Azores microplate, and instead suggest that Nubia–Eurasia plate motion is accommodated by extension across a ˜140-km-wide zone east of the MAR axis, most likely bounded to the north by the northern shoulder of the Terceira Rift. The MAR spreading rate along the western end of the Azores deformation zone (˜38.5°N–39.5°N) is intermediate between the Eurasia–North America rate measured at 39.5°N and the Nubia–North America rate measured at 38.5°N, consistent with the joint conclusions that the Nubia–Eurasia boundary is broad where it intersects the MAR, and the Azores Triple Junction is diffuse rather than discrete.

Marques, F. O.; Catalão, J. C.; DeMets, C.; Costa, A. C. G.; Hildenbrand, A.

2013-11-01

299

The boundary between the Indian and Asian tectonic plates below Tibet.  

PubMed

The fate of the colliding Indian and Asian tectonic plates below the Tibetan high plateau may be visualized by, in addition to seismic tomography, mapping the deep seismic discontinuities, like the crust-mantle boundary (Moho), the lithosphere-asthenosphere boundary (LAB), or the discontinuities at 410 and 660 km depth. We herein present observations of seismic discontinuities with the P and S receiver function techniques beneath central and western Tibet along two new profiles and discuss the results in connection with results from earlier profiles, which did observe the LAB. The LAB of the Indian and Asian plates is well-imaged by several profiles and suggests a changing mode of India-Asia collision in the east-west direction. From eastern Himalayan syntaxis to the western edge of the Tarim Basin, the Indian lithosphere is underthrusting Tibet at an increasingly shallower angle and reaching progressively further to the north. A particular lithospheric region was formed in northern and eastern Tibet as a crush zone between the two colliding plates, the existence of which is marked by high temperature, low mantle seismic wavespeed (correlating with late arriving signals from the 410 discontinuity), poor Sn propagation, east and southeast oriented global positioning system displacements, and strikingly larger seismic (SKS) anisotropy. PMID:20534567

Zhao, Junmeng; Yuan, Xiaohui; Liu, Hongbing; Kumar, Prakash; Pei, Shunping; Kind, Rainer; Zhang, Zhongjie; Teng, Jiwen; Ding, Lin; Gao, Xing; Xu, Qiang; Wang, Wei

2010-06-07

300

The boundary between the Indian and Asian tectonic plates below Tibet  

PubMed Central

The fate of the colliding Indian and Asian tectonic plates below the Tibetan high plateau may be visualized by, in addition to seismic tomography, mapping the deep seismic discontinuities, like the crust-mantle boundary (Moho), the lithosphere-asthenosphere boundary (LAB), or the discontinuities at 410 and 660 km depth. We herein present observations of seismic discontinuities with the P and S receiver function techniques beneath central and western Tibet along two new profiles and discuss the results in connection with results from earlier profiles, which did observe the LAB. The LAB of the Indian and Asian plates is well-imaged by several profiles and suggests a changing mode of India-Asia collision in the east-west direction. From eastern Himalayan syntaxis to the western edge of the Tarim Basin, the Indian lithosphere is underthrusting Tibet at an increasingly shallower angle and reaching progressively further to the north. A particular lithospheric region was formed in northern and eastern Tibet as a crush zone between the two colliding plates, the existence of which is marked by high temperature, low mantle seismic wavespeed (correlating with late arriving signals from the 410 discontinuity), poor Sn propagation, east and southeast oriented global positioning system displacements, and strikingly larger seismic (SKS) anisotropy.

Zhao, Junmeng; Yuan, Xiaohui; Liu, Hongbing; Kumar, Prakash; Pei, Shunping; Kind, Rainer; Zhang, Zhongjie; Teng, Jiwen; Ding, Lin; Gao, Xing; Xu, Qiang; Wang, Wei

2010-01-01

301

The 2000 Mw 6.8 Uglegorsk earthquake and regional plate boundary deformation of Sakhalin from geodetic data  

Microsoft Academic Search

Interseismic GPS velocities in Sakhalin indicate that the island moves to the west at 3–4 mm\\/yr with respect to the Eurasian plate, which is about half of the relative Eurasia - North America plate convergence rate. GPS measurements across the central Sakhalin fault system provide evidence of compressive and strike-slip strain accumulation at a rate ?3 mm\\/yr. Coseismic vertical displacements

M. G. Kogan; R. Bürgmann; N. F. Vasilenko; C. H. Scholz; R. W. King; A. I. Ivashchenko; D. I. Frolov; G. M. Steblov; Ch. U. Kim; S. G. Egorov

2003-01-01

302

On convergence on the boundary of the unit ball in dual space  

Microsoft Academic Search

In this paper some results that are known for extreme points of the unit ball in dual space are carried over to a more general case, namely to the case of the boundary of the ball ( B is the boundary of the unit ballB in the space dual toX if everyx X achieves its maximum value onB at some

V. I. Rybakov

1996-01-01

303

Pointwise Convergence on the Boundary in the Denjoy-Wolff Theorem  

Microsoft Academic Search

If $\\\\phi$ is an analytic selfmap of the disk (not an elliptic automorphism)\\u000athe Denjoy-Wolff Theorem predicts the existence of a point $p$ with $|p|\\\\leq 1$\\u000asuch that the iterates $\\\\phi_{n}$ converge to $p$ uniformly on compact subsets\\u000aof the disk. Since these iterates are bounded analytic functions, there is a\\u000asubset of the unit circle of full linear measure

Pietro Poggi-Corradini

2010-01-01

304

Nonlinear bending analysis of shear deformable functionally graded plates subjected to thermo-mechanical loads under various boundary conditions  

Microsoft Academic Search

Nonlinear bending analysis of shear deformable functionally graded plates subjected to thermo-mechanical loads and under various boundary conditions is presented. Theoretical formulations are based on Reddy's higher order shear deformation plate theory and include the thermal effects due to temperature rise. Material properties are assumed to be temperature-dependent and graded in the thickness direction according to a power law distribution

J. Yang; H.-S. Shen

2003-01-01

305

Triple diffusive free convection along a horizontal plate in porous media saturated by a nanofluid with convective boundary condition  

Microsoft Academic Search

Abstract The steady triple diffusive boundary layer free convection flow past a horizontal flat plate embedded in a porous medium filled by a water-based nanofluid and two salts is investigated numerically. The plate is assumed to be convectively cooled by a surrounding fluid. It is assumed that there is no nanoparticle flux at the surface and the effect of thermophoresis

Z. H. Khan; W. A. Khan; I. Pop

2013-01-01

306

Mixed convection boundary layer flow over a horizontal plate with thermal radiation  

NASA Astrophysics Data System (ADS)

The effects of thermal radiation and thermal buoyancy on the steady, laminar boundary layer flow over a horizontal plate is investigated. The plate temperature is assumed to be inversely proportional to the square root of the distance from the leading edge. The set of similarity equations is solved numerically, and the solutions are given for some values of the radiation and buoyancy parameters for Prandtl number unity. It is found that dual solutions exist for negative values of the buoyancy parameter, up to certain critical values. Beyond these values, the solution does no longer exist. Moreover, it is found that there is no local heat transfer at the surface except in the singular point at the leading edge. The radiation parameter is found to increase the local Stanton number.

Ishak, Anuar

2009-12-01

307

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

308

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

309

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).

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

2010-01-01

310

An influence on eigenvibrations in resonators of anisotropy of boundary surface of piezoelectric plate with variable convexity  

Microsoft Academic Search

The report addresses an analysis of the transversely varying thickness modes in a piezoelectric resonator caused by the convex anisotropic boundary surface in a piezoelectric plate. We show that the anisotropy of the boundary surface greatly influences the frequency spectrum of the eigenvibrations of the resonator. The relations to calculate the frequency spectrum and the relative amplitudes of the vibrations

S. S. Nedorezov; O. Yu. Shmaliy; Yu. S. Shmaliy; B. Dulmet

2003-01-01

311

Plate tectonics and offshore boundary delimitation: Tunisia-Libya case at the International Court of Justice  

NASA Astrophysics Data System (ADS)

The first major offshore boundary dispute where plate tectonics constituted a significant argument was recently brought before the International Court of Justice by Libya and Tunisia concerning the delimitation of their continental shelves. Libya placed emphasis on this concept to determine natural prolongation of its land territory under the sea. Tunisia contested use of the entire African continental landmass as a reference unit and views geography, geomorphology and bathymetry as relevant as geology. The Court pronounced that “It is the outcome, not the evolution in the long-distant past, which is of importance.” Moreover, it is the present-day configuration of coasts and seabed that are the main factors, not geology.

Stanley, Daniel Jean

1982-03-01

312

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

313

Crustal strain rate patterns of the western North America Plate boundary  

NASA Astrophysics Data System (ADS)

The knowledge of the crustal strain rate tensor provides a description of geodynamic processes such as fault strain accumulation. We use interpolation of GPS geodetic measurements to derive the regional strain rate field for selected regions within the western North America plate boundary. We applied the interpolation scheme to data from the Eastern California Shear Zone, the Mendocino triple junction region, and the transition from the Sierra block to the Pacific North West. Our results allow us to define regions of localization of the strain rate at the northern end of the San Andrea Fault system and within the boundary between the Sierra Nevada and Basin and Range. These results help to understand the way in which strain is accommodated in the Sierra/Pacific North West transition. The results will be compared with geologic and tectonic observation of the region.

Hackl, M.; Malservisi, R.; Furlong, K.; Kirby, E.

2009-04-01

314

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. ?? 1982.

Schouten, H.; Klitgord, K. D.

1982-01-01

315

Numerical investigation of transition control of a flat plate boundary layer  

NASA Astrophysics Data System (ADS)

A numerical model has been developed for investigating boundary layer transition control for a three-dimensional flat plate boundary layer. Control of a periodically forced boundary layer in an incompressible fluid is studied using surface heating techniques. The spatially evolving boundary layer is simulated. The Navier-Stokes and energy equations are integrated using a fully implicit finite difference/spectral method. The Navier-Stokes equations are in vorticity-velocity form and are coupled with the energy equation through the viscosity dependence on temperature. Both passive and active methods of control by surface heating are investigated. In passive methods of control, wall heating is employed to alter the stability characteristics of the mean flow. Both uniform and nonuniform surface temperature distributions are studied. In the active control investigations, temperature perturbations are introduced locally along finite heater strips to directly attenuate the instability waves in the flow. A feedback control loop is employed in which a downstream sensor is used to monitor wall shear stress fluctuations. A receptivity study is performed to study how localized temperature perturbations are generated into Tollmien-Schlichting waves. It is shown that narrow heater strips are more receptive in that they maximize the amplitude level of the disturbances in the flow. It is also found that the local temperature fluctuations cause mainly a strong normal gradient in spanwise vorticity.

Kral, Linda Dee

316

A Reference Crustal and Plate-Boundary Velocity Model of Japan  

NASA Astrophysics Data System (ADS)

The study of velocity structure using earthquake data has been remarkably progressed by development of seismic observation networks, improvement of the methodology, and increase in processing power. Recent studies on 3D velocity structures have produced tomographic images with resolution of a few kilometers (e.g., Matsubara et al., 2005; Nakamichi et al., 2007). In addition to these traveltime analyses, waveform studies such as receiver function analyses have been developed to image the configuration of continental Moho and oceanic plate boundaries (e.g., Yamauchi et al., 2003; Shiomi et al., 2004). Reflection and refraction surveys with controled sources have also been providing information on 2D and 3D velocity structures (e.g., Sato et al., 2005; Special Project for Earthquake Disaster Mitigation in Urban Areas). Thus, plenty of structural property models exist over the Japan islands, but the validity of an individual model is confined to its study area. Therefore, it is essential to build a reference crustal and plate-boundary velocity model for the whole Japan by combining them all together. If this sort of reference velocity model over the Japan islands is available under a unified criterion, it will be valuable for many fields of seismology and Earth sciences. We here construct a reference crustal and plate-boundary velocity model of Japan by integrating 2D models from seismic profiling and receiver functions, 3D models of seismic tomography, and other geophysical data such as gravity anomalies. The goal of this study is to construct a 3D laterally heterogeneous seismic velocity structure model, which clarifies the topography of the Conrad and Moho discontinuities and shapes of the oceanic plates, like the SCEC Unified Velocity Model (e.g., Magistrale et al., 1996). We first make a preliminary Japan model by compiling information on the topography of the Conrad and Moho discontinuities and subducting plates. To this end, we collect 2D seismic velocity models obtained by seismic profiling of reflection/refraction surveys and receiver function analyses, and then integrate them to a 3D velocity model, using complementary information on 3D structures, such as 3D boundary shapes obtained by travel time and gravity anomaly analyses. At this stage, maintaining local structural continuity is a key challenge in the process. We also have to clarify major tectonic features such as the Median Tectonic Line and the Itoigawa-Shizuoka Tectonic Line, and consider the continuity between land-based and offshore models. The integrated 3D reference model will improve the reliability of strong ground motion prediction. Improvements will be the most critical for large-scale ground motion simulations for plate-boundary earthquakes in the Nankai and Tokai regions, which can cause strong shaking in major metropolitan areas of Japan. So, this modeling should be one of the most essential parts of earthquake damage mitigation in Japan.

Ishise, M.; Koketsu, K.; Miyake, H.

2007-12-01

317

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

318

RRS DISCOVERY Cruise 161, 15 August (227)-19 September (262) 1986. Portuguese Ocean-Continent Boundary, Plate Boundaries West of Iberia and Seismic Structure of Sediments Off Madeira.  

National Technical Information Service (NTIS)

The cruise had three main objectives: to study the ocean-continent transition zone on the western margin of Portugal; to study the Azores-Gibraltar plate-boundary and past plate-boundaries of the Iberian plate; and to conduct experiments east of Madeira t...

R. B. Whitmarsh

1986-01-01

319

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

320

The quest for the Africa-Eurasia plate boundary west of the Strait of Gibraltar  

NASA Astrophysics Data System (ADS)

The missing link in the plate boundary between Eurasia and Africa in the central Atlantic is presented and discussed. A set of almost linear and sub parallel dextral strike-slip faults, the SWIM Faults, that form a narrow band of deformation over a length of 600 km coincident with a small circle centred on the pole of rotation of Africa with respect to Eurasia, was mapped using a new swath bathymetry compilation available in the area offshore SW Portugal. These faults connect the Gloria Fault to the Rif-Tell Fault Zone, two segments of the plate boundary between Africa and Eurasia. The SWIM faults cut across the Gulf of Cadiz, in the Atlantic Ocean, where the 1755 Great Lisbon earthquake, M ~ 8.5-8.7, and tsunami were generated, providing a new insight on its source location. SWIM is the acronym of the ESF EuroMargins project "Earthquake and Tsunami hazards of active faults at the South West Iberian Margin: deep structure, high-resolution imaging and paleoseismic signature".

Zitellini, N.; Gràcia, E.; Matias, L.; Terrinha, P.; Abreu, M. A.; DeAlteriis, G.; Henriet, J. P.; Dañobeitia, J. J.; Masson, D. G.; Mulder, T.; Ramella, R.; Somoza, L.; Diez, S.

2009-04-01

321

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

322

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

323

Fluctuation transfer velocity measurement in a boundary layer around a thin edge plate using dynamic PIV  

NASA Astrophysics Data System (ADS)

The dynamic (time resolved) PIV (particle imaging velocimetry) measurement technique was applied to high-speed gas flow in a narrow channel with an obstacle. The boundary layer was visualized with a high-speed APX RS camera and an Nd:YLF high repetition double-pulse laser. Nitrogen gas seeded with oil particles using Laskine nozzle flows through a 10 × 10 mm2 square channel with Reynolds numbers of 11 000 and 34 000. Although a sufficient quantity of images was difficult to capture for the Re = 34 000 flow to visualize the vortex evolution in time for the time resolved analysis of the boundary layer, large scale structures of turbulence at the edge of the thin plate are clearly visualized in the temporal domain. Fluctuation transfer velocities in the boundary layer were measured employing the whole field two-point velocity correlation. It is proposed that dynamic PIV can open a way of measuring the fluctuation transfer velocities in the whole flow target area simultaneously for high-speed turbulent flows even in small scales.

Erkan, N.; Ishikawa, M.; Okamoto, K.

2006-06-01

324

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

NASA Astrophysics Data System (ADS)

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

2010-12-01

325

Numerical investigation on convergence of boundary knot method in the analysis of homogeneous Helmholtz, modified Helmholtz, and convection–diffusion problems  

Microsoft Academic Search

This paper concerns a numerical study of convergence properties of the boundary knot method (BKM) applied to the solution of 2D and 3D homogeneous Helmholtz, modified Helmholtz, and convection–diffusion problems. The BKM is a new boundary-type, meshfree radial function basis collocation technique. The method differentiates from the method of fundamental solutions (MFS) in that it does not need the controversial

W. Chen; Y. C. Hon

2003-01-01

326

Subduction Geometry at the Southeastern Caribbean Plate Boundary Inferred from BOLIVAR Receiver-function Images  

NASA Astrophysics Data System (ADS)

The eastward motion of the Caribbean plate since late Paleocene has resulted in a progressive detachment of the oceanic lithosphere from the continent South American plate. The detachment process is, however, poorly understood. At least two very different models have been proposed. The tensile tear model invokes a break-off of the northward descending slab following the collision of the two plates while the shear tear model suggests a near vertical dip-slip detachment at the two plates? boundary, the El-Pilar fault. Mapping the subducted oceanic lithosphere beneath the southeastern Caribbean is thus crucial to understanding the dominant process controlling the regional tectonics. In this study we mapped the presence of the cold subducted oceanic lithosphere in the transition zone by investigating the topography of the 410-km and 660- km seismic discontinuities. The two discontinuities are believed to be caused by temperature sensitive phase transitions of mantle minerals. We generated 1662 receiver functions from seismograms of 112 earthquakes recorded by the BOLVIAR (Broadband Ocean-Land Investigations of Venezuela and the Antilles arc Region) seismic array. The array consists of 35 temporary broadband stations, 13 temporary broadband ocean bottom seismometers, and 35 permanent stations of the national seismic network of Venezuela. We applied the common-conversion-point (CCP) stacking technique to the receiver-function data to image the P to S conversion events and their lateral variations beneath the array. P to S time moveout were calculated with 3D crustal and mantle velocity models. A 4th root stacking technique was employed to boost coherent signals in the data. Beneath the southeastern Caribbean, the 410-km is featured by a narrow (~200 km laterally) 20 km uplift with a NS trending centering at 64° west, while the 660-km is depressed broadly (> ~400 km) with a moderate amount of ~15 km, a scenario that is more consistent with westward descending of the oceanic South American plate. We also found a thick transition zone beneath the Falcon region in northwestern Venezuela, which probably is associated with the subducted Cocos plate. A flat 410-km was observed beneath the Guayana shield, suggesting that the shield has a stable moderate deep keel which has little effect on the underlying transition zone.

Huang, J.; Niu, F.; Ni, S.

2008-12-01

327

EarthScope Plate Boundary Observatory Data in the College Classroom (Invited)  

NASA Astrophysics Data System (ADS)

The Plate Boundary Observatory (PBO) is the geodetic component of the EarthScope project, designed to study the 3-D strain field across the active boundary zone between the Pacific and North American tectonics plates in the western United States. All PBO data are freely available to scientific and educational communities and have been incorporated into a variety of activities for college and university classrooms. UNAVCO Education and Outreach program staff have worked closely with faculty users, scientific researchers, and facility staff to create materials that are scientifically and technically accurate as well as useful to the classroom user. Availability of processed GPS data is not new to the geoscience community. However, PBO data staff have worked with education staff to deliver data that are readily accessible to educators. The UNAVCO Data for Educators webpage, incorporating an embedded Google Map with PBO GPS locations and providing current GPS time series plots and downloadable data, extends and updates the datasets available to our community. Google Earth allows the visualization GPS data with other types of datasets, e.g. LiDAR, while maintaining the self-contained and easy-to-use interface of UNAVCO’s Jules Verne Voyager map tools, which have multiple sets of geological and geophysical data. Curricular materials provide scaffolds for using EarthScope data in a variety of forms for different learning goals. Simple visualization of earthquake epicenters and locations of volcanoes can be used with velocity vectors to make simple deductions of plate boundary behaviors. Readily available time series plots provide opportunities for additional science skills, and there are web and paper-based support materials for downloading data, manipulating tables, and using plotting programs for processed GPS data. Scientists have provided contextual materials to explore the importance of these data in interpreting the structure and dynamics of the Earth. These data and their scientific context are now incorporated into the Active Earth Display developed by IRIS. Formal and informal evaluations during the past five years have provided useful data for revision and on-line implementation.

Eriksson, S. C.; Olds, S. E.

2009-12-01

328

BOLIVAR: Crustal Structure of the Caribbean-South America Plate Boundary at 65W  

NASA Astrophysics Data System (ADS)

We describe a ~550 km long, N-S oriented, onshore-offshore profile that crosses the SE Caribbean plate boundary at approximately 65W longitude. The profile is one of the principal seismic reflection and refraction transects acquired in 2004 as part of the Broadband Ocean and Land Investigation of Venezuela and the Antilles arc Region (BOLIVAR) experiment. The transect starts ~330 km offshore northern Venezuela and crosses the plate boundary from the stable Caribbean (CAR) plate to the stable South America (SA) continent crossing the El Pilar continental strike-slip fault system. High quality multi-channel seismic (MCS) reflection data were acquired along the 330 km offshore portion of the profile. The airgun shots from the MCS vessel and two land shots were also recorded by 7 OBS's and 514 single channel land receivers for wide-angle analysis. We have analyzed the wide-angle data using a tomographic inversion of first arrival travel times to obtain upper and mid-crustal P wave velocities, followed by simultaneous inversion of PmP and Pn to obtain Moho depth and lower crustal and upper mantle P wave velocities. The P-Wave velocity model was converted to density using a 5th order polynomial fit to global experimental data, and the calculated gravity response was compared to an observed gravity curve resulting from averaging a swath 50 km wide about the profile. The calculated gravity response fits the observed locations and wavelengths of local highs and lows well, although the anomaly amplitudes do not fit exactly using the automatic velocity-density conversion. The model suggests a Caribbean crust that is over 10 km thick and shows South American crust of variable thickness ranging from 30 to 40 km. Structures imaged in the model include the Cariaco trough offshore, a sedimentary basin that reaches a depth of ~9 km; and the Espino Graben onshore, that reaches a maximum depth of ~8 km. The MCS data image the stable CAR plate and the thrusting of the CAR plate under the South Caribbean Deformed Belt (SCDB) prism. The accretionary prism is highly deformed although the seismic data suggest limited recent tectonic activity: The frontal thrust faults are draped by an apron of recent sediments, mostly deformed by slumping above the steepest slope of the prism. Wide-angle data corroborate a limited amount of thrusting of the CAR plate under the Leeward Antilles arc region. To the south, the reflection data cross the El Pilar continental strike-slip system along the northern edge of the Cariaco basin. At this longitude the dextral strike-slip system accommodates ~50% of the strike-slip displacement between the CAR and SA plate and is characterized by transtensional motion. The Cariaco basin appears as a narrow, deep trough, bounded to the north by the nearly vertical El Pilar strike slip fault, which juxtaposes crustal rocks with an average velocity of 5.7 km/s against sedimentary sequences with an average velocity of 3.0 km/s.

Bezada, M.; Magnani, M.; Zelt, C. A.; Levander, A.; Schmitz, M.

2007-12-01

329

Evolution of retreating subduction boundaries formed during continental collision  

Microsoft Academic Search

Retreating subduction boundaries, formed where the rate of subduction exceeds the rate of overall plate convergence, appear to be commonly developed features within regions of early or incomplete continent-continent collision. They are characterized by regional extension within the overriding plate, and at their leading edge, by thin-skinned arcuate thrust belts that are concave toward the overriding plate. As is illustrated

Leigh H. Royden

1993-01-01

330

Evolution of retreating subduction boundaries formed during continental collision  

Microsoft Academic Search

Retreating subduction boundaries, formed where the rate of subduction exceeds the rate of overall plate convergence, appear to be commonly developed features within regions of early or incomplete continent-continent collision. They are characterized by regional extension within the overriding plate and, at their leading edge, by thin-skinned arcuate thrust belts that are concave towards the overriding plate. As is illustrated

Leigh H. Royden

1993-01-01

331

Crustal structure of the South American–Caribbean plate boundary at 67°W from controlled source seismic data  

Microsoft Academic Search

We present the results of new seismic reflection and wide-angle data across the SE Caribbean plate boundary. The 550 km long N–S profile crosses the structures involved in the active 55 Ma long continent-arc oblique collision between the Caribbean (CAR) and the South American (SA) plate. From the north to the south these structures include the accretionary prism, the extinct

Maria Beatrice Magnani; Colin A. Zelt; Alan Levander; Michael Schmitz

2009-01-01

332

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

Microsoft Academic Search

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

A. S. Al-Zoubi; M. Rybakov; Y. Rotstein

2004-01-01

333

Magmatism at the Eurasian–North American modern plate boundary: Constraints from alkaline volcanism in the Chersky Belt (Yakutia)  

Microsoft Academic Search

The Chersky seismic belt (NE-Russia) forms the modern plate boundary of the Eurasian?North American continental plate. The geodynamic evolution of this continent?continent setting is highly complex and remains a matter of debate, as the extent and influence of the Mid-Arctic Ocean spreading center on the North Asian continent since the Eocene remains unclear. The progression from a tensional stress regime

Cornelius Tschegg; Michael Bizimis; David Schneider; Vyacheslav V. Akinin; Theodoros Ntaflos

2011-01-01

334

Plate boundary forces are not enough: Second and third-order stress patterns highlighted in the World Stress Map database  

Microsoft Academic Search

The World Stress Map Project compiles a global database of contemporary tectonic stress information of the Earth's crust. Early releases of the World Stress Map Project demonstrated the existence of first-order (plate-scale) stress fields controlled by plate boundary forces and second-order (regional) stress fields controlled by major intraplate stress sources such as mountain belts and zones of widespread glacial rebound.

Oliver Heidbach; John Reinecker; Mark Tingay; Birgit Müller; Blanka Sperner; Karl Fuchs; Friedemann Wenzel

2007-01-01

335

A mixed problem of plate bending for doubly connected domains with partially unknown boundaries in the presence of cyclic symmetry  

NASA Astrophysics Data System (ADS)

This paper addresses the problem of plate bending for a doubly connected body with outer and inner boundaries in the form of regular polygons with a common center and parallel sides. The neighborhoods of the vertices of the inner boundary are equal full-strength smooth arcs symmetric about the rays coming from the vertices to the center, but have unknown positions. Rigid bars are attached to the linear parts of the boundary. The plate bends by the moments applied to the middle point bars. The unknown arcs are free from external stresses. The same problem of plate bending is considered for a regular hexagon weakened by a full-strength hole. Using the methods of complex analysis, the analytical image of Kolosov-Muskhelishvili’s complex potentials (characterizing an elastic equilibrium of the body), the plate deflection and unknown parts of its boundary are determined under the condition that the tangential normal moment on that plate takes a constant value. Numerical analyses are also performed and the corresponding graphs are constructed.

Odishelidze, N.; Criado-Aldeanueva, F.

2010-10-01

336

Stability of the laminar boundary layer on a permeable flat plate with uniform blowing  

NASA Astrophysics Data System (ADS)

The effect of increased uniform blowing on the stability of the laminar boundary-layer flow over a permeable plate is investigated theoretically on the basis of experimental data obtained by thermal anemometry and interferometry (Eroshenko et al., 1972 and 1980). Sample interferograms and velocity profiles for blowing parameters 0, 0.28, 0.64, 0.2, and 1.13 are shown; a linear stability analysis based on a modified version of the Orr-Sommerfeld equation is performed; and the results are compared with other theoretical analyses and with experimental data in graphs. Qualitative agreement is found with experiments in a plot of critical Reynolds number as a function of the blowing intensity.

Eroshenko, V. M.; Zaichik, L. I.; Klimov, A. A.; Pershukov, V. A.

1984-07-01

337

Diffuse Oceanic Plate Boundaries, Plate Non-Rigidity, True Polar Wander, and Motion Between Hotspots: Results From Investigations of Marine Magnetic Anomalies  

NASA Astrophysics Data System (ADS)

Marine magnetic anomalies due to seafloor spreading record reversals of Earth's magnetic field and the orientation of the paleomagnetic field. They can be used to make precise estimates of relative plate motion and of the apparent polar wander of oceanic plates. In this talk I will present the results of several studies that include analyses of marine magnetic anomalies. A new set of geologically current relative plate angular velocities, termed MORVEL, has been determined in part from 1696 rates of seafloor spreading estimated from marine magnetic anomalies (DeMets, Gordon, & Argus 2009). The MORVEL set of angular velocities supersede those of NUVEL-1A (DeMets et al. 1994). A new feature of MORVEL is the assumed existence of many diffuse oceanic plate boundaries, such as that between the Indian and Capricorn plates. An important result from MORVEL is that several plate circuits fail closure, that is, the relative plate angular velocities summed around the circuit differ significantly from zero as would be expected if all the plates are rigid. Thus, it appears that at least some plates are not rigid. The most dramatic example of plate circuit non-closure is for the Pacific-Nazca-Cocos plate circuit, which encloses the Galapagos triple junction and fails to close by a stunning 14 ± 5 mm/yr (95% confidence limits). Part of the observed non-rigidity is likely due to predictable horizontal thermal contraction as oceanic lithosphere cools and subsides (Kumar & Gordon 2009). I will present simple illustrations of the velocity field within a plate expected from horizontal thermal contraction and speculate on how it may relate to observed plate circuit non-closures. The shapes of magnetic anomalies due to seafloor spreading contain valuable information about the location of the paleomagnetic pole, especially for the Pacific plate for which oriented rock samples are scarce. Particularly useful are Pacific-Farallon magnetic anomaly crossings near the paleo-equator. I use results from anomaly 12r (32 Ma, Horner-Johnson & Gordon 2009) to illustrate the value of these data. The results show that the hotspots in the Pacific basin have moved in unison with those in the Indian and Atlantic basins relative to the spin axis, a process most simply interpreted as true polar wander. Plate reconstructions based on fits of magnetic anomalies are used to place limits of 0 to 10 mm/yr on the rate that hotspots in the Pacific basin move relative to hotspots in other basins over the past 50 Ma (Koivisto, Andrews, & Gordon, 2009).

Gordon, R. G.

2009-05-01

338

Geomorphic Response to Crustal Evolution of the Plate Boundary, northern California  

NASA Astrophysics Data System (ADS)

The Coast Ranges in northern California are located within a developing transform plate boundary (San Andreas-Maacama-Bartlett Springs strike slip faults) and experience a crustal evolution driven by the migration of the Mendocino Triple Junction. How the landscape responds to the evolution of this plate boundary, however, is uncertain. Here, we analyze channel longitudinal profiles developed throughout the Coast Ranges to investigate the link between surface and deeper-seated processes. In particular, we focus on a crustal transition zone centered around the Little Lake Valley (Willits). Using the USGS 10m DEM to extract longitudinal stream profiles, we identify knickpoints and their spatial positions, calculate channel steepnesses and concavities, and analyze the pattern of knickpoint migration to explore possible driving mechanisms for landscape evolution. Our results reveal two first-order “domains” in the Coast Ranges. West of the Maacama fault system, drainages exhibit smooth, concave-up profiles with no discernable knickpoints. Preservation of relict patches of a high-elevation, low-relief landscape along the drainage divide between these coastal streams and inland watersheds (Eel and Russian Rivers) is consistent with progressive emergence of this region from below sea level, as indicated by relict shallow marine deposits (Ohlson Ranch Formation). East of the divide, tributaries of the Russian and Eel rivers exhibit knickpoints that separate downstream reaches of high gradient from lower-gradient headwater reaches. These are interpreted to reflect a transient increase in incision rates following either 1) stream capture, or 2) local vertical movements along the Maacama fault system. An example of this is found in the region east of Little Lake Valley, drainages are beheaded along the range front fault bounding the eastern side of the valley, suggesting relatively recent west-side down displacement along this fault system. Overall, our analysis suggests that vertical motions along the nascent Maacama fault system are superimposed upon a longer-wavelength pattern of deformation and differential rock uplift that are attributed to the Mendocino crustal conveyor.

Shi, X.; Kirby, E.; Furlong, K. P.

2009-12-01

339

Logistical Support for the Installation of the Plate Boundary Observatory GPS and Borehole Strainmeter Networks  

NASA Astrophysics Data System (ADS)

The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three- dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, UNAVCO will install 880 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser strainmeters by October 2008. Such a broad network presents significant logisitical challenges, including moving supplies, equipment, and personnel around 6 million square kilometers, and this requires accurate tracking and careful planning. The PBO logistics chain includes the PBO headquarters at UNAVCO in Boulder, Colorado and five regional offices in the continental United States and Alaska, served by dozens of suppliers spread across the globe. These offices are responsible for building and maintaining sites in their region. Most equipment and supplies first arrive in Boulder, where they are tagged and entered into a UNAVCO-wide equipment database, assembled and quality checked as necessary, and sent on to the appropriate regional office. Larger items which are costly to store and ship from Boulder, such as batteries or long sections of stainless steel pipe and bar required for monuments, are shipped directly from the supplier to each region as needed. These supplies and equipment are also tracked through the ordering, delivery, installation, and maintenance cycle via Earned Value Management techniques which allow us to meet NSF and other Federal procurement rules. Early prototypes and assembly configurations aid the development of material and supply budgets. A thorough understanding of Federal procurement rules at project start up is critical as the project moves forward.

Kurnik, C.; Austin, K.; Coyle, B.; Dittmann, T.; Feaux, K.; Friesen, B.; Johnson, W.; Mencin, D.; Pauk, B.; Walls, C.

2007-12-01

340

Data Access and Web Services at the EarthScope Plate Boundary Observatory  

NASA Astrophysics Data System (ADS)

The EarthScope Plate Boundary Observatory (PBO) at UNAVCO, Inc., part of the NSF-funded EarthScope project, is designed to study the three-dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, PBO will install 880 continuous GPS stations, 103 borehole strainmeter stations, and five laser strainmeters, as well as manage data for 209 previously existing continuous GPS stations and one previously existing laser strainmeter. UNAVCO provides access to data products from these stations, as well as general information about the PBO project, via the PBO web site (http://pboweb.unavco.org). GPS and strainmeter data products can be found using a variety of access methods, incuding map searches, text searches, and station specific data retrieval. In addition, the PBO construction status is available via multiple mapping interfaces, including custom web based map widgets and Google Earth. Additional construction details can be accessed from PBO operational pages and station specific home pages. The current state of health for the PBO network is available with the statistical snap-shot, full map interfaces, tabular web based reports, and automatic data mining and alerts. UNAVCO is currently working to enhance the community access to this information by developing a web service framework for the discovery of data products, interfacing with operational engineers, and exposing data services to third party participants. In addition, UNAVCO, through the PBO project, provides advanced data management and monitoring systems for use by the community in operating geodetic networks in the United States and beyond. We will demonstrate these systems during the AGU meeting, and we welcome inquiries from the community at any time.

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

2007-12-01

341

Recording Plate Boundary Deformation Processes Around The San Jacinto Fault, California  

NASA Astrophysics Data System (ADS)

The San Jacinto Fault is one of the major faults which form the San Andreas Fault System in southern California. The fault, which lies to the west of the San Andreas, is one of the most active in the region. While strain rates are higher along the San Andreas, 23-37 mm/yr compared to 12-22 mm/yr along the San Jacinto, there have been 11 earthquakes of M6 and greater along the San Jacinto in the past 150 years while there have been none of this magnitude on the San Andreas in this region. UNAVCO has installed an array of geodetic and seismic instruments along the San Jacinto as part of the Plate Boundary Observatory (PBO). The network includes 25 GPS stations within 20 km of the surface trace with a concentration of borehole instrumentation in the Anza region where there are nine boreholes sites. Most of the borehole sites contain a GTSM21 4-component strainmeter, a Sonde-2 seismometer, a MEMS accelerometer and a pore pressure sensor. Thus, the array has the capability to capture plate boundary deformation processes with periods of milliseconds (seismic) to decades (GPS). On July 7th 2010 a M5.4 earthquake occurred on the Coyote Creek segment of the fault. The event was preceded by a M4.9 earthquake in the same area four weeks earlier and four earthquakes of M5 and greater within a 20 km radius of the epicenter in the past 50 years. In this study we will present the signals recorded by the different instrument types for the July 7th 2010 event and will compare the coseismic displacements recorded by the GPS and strainmeters with the displacement field predicted by Okada [1992]. All data recorded as part of the PBO observatory are publically available from the UNAVCO, the IRIS Data Management Center and the Northern California Earthquake Data Center.

Hodgkinson, K.; Mencin, D.; Borsa, A.; Fox, O.; Walls, C.; Van Boskirk, E.

2012-04-01

342

Compressibility effect in two-phase flow and its application to flow metering with orifice plate and convergent-divergent nozzle  

SciTech Connect

The effect of solution gas on the 2-phase flow behavior through an orifice plate and a convergent- divergent nozzle has been investigated with regard to the flow metering of compressible 2-phase mixtures. A proper thermodynamics approach to consider more accurately the compressibility effect in an accelerated 2-phase flow, in particular that through an orifice and Laval's nozzle in the presence of the solution gas, has been developed. From this approach an equation of state of mixture was derived and used in determining the orifice equation. An analysis of flow behavior has been performed and several illustrative plots were presented in order to evaluate the gas solubility effect in the flow metering with an orifice plate or a convergent-divergent nozzle. A delimitation between critical and noncritical flow has been established in terms of measured parameters and a relationship between the critical pressure and gas-liquid mass ratio was shown.

Pascal, H.

1983-12-01

343

Direct measurements of turbulent boundary layer wall pressure wavenumber-frequency spectra on smooth and riblet-coated plates  

Microsoft Academic Search

Measurements of the fluctuating wall pressure space-time field were made with a linear array of 48 hydrophones beneath a fully developed turbulent boundary layer of water on a flat plate. Autospectra, cross-spectra, and wavenumber-frequency spectra were calculated from digitized hydrophone signals. Boundary layer parameters were estimated from streamwise velocity profiles that were measured with a laser doppler anemometry system and

Bruce Matthew Abraham

2000-01-01

344

Experimental study of the stability of boundary-layer flow along a heated, inclined plate  

NASA Astrophysics Data System (ADS)

Experiments are conducted to study the longitudinal vortices that develop in the boundary layer on the upper surface of an inclined, heated plate. An isothermal plate in water is inclined at angles ranging from 20 to 60 degrees (from the vertical) while the temperature difference is varied from 2 to 23°C. A double-pass Schlieren system is used to visualize the vortices and particle image velocimetry (PIV) is used to measure velocities. In addition, a unique method is developed such that both the Schlieren visualization and PIV can be performed simultaneously. The wavelengths of the vortices and the critical modified Reynolds numbers (R˜) for the onset, merging, and breakup of the vortices are determined from Schlieren images for Pr=5.8. The critical values for R˜ and the critical wavelengths are compared to results of previous experiments and stability analyses. The spatial growth rates of vortices are determined by using the PIV measurements to determine how the circulation in the vortices grows with distance from the leading edge. This is the first time that the growth rate of the vortices have been found using velocity measurements. These spatial growth rates are compared to the results of Iyer & Kelly (1974) and found to be in general agreement. By defining a suitable circulation threshold, the critical R˜ for the onset of the vortices can be found from the growth curves.

Zuercher, E. J.; Jacobs, J. W.; Chen, C. F.

1998-07-01

345

Crustal and upper mantle investigations of the Caribbean-South American plate boundary  

NASA Astrophysics Data System (ADS)

The evolution of the Caribbean --- South America plate boundary has been a matter of vigorous debate for decades and many questions remain unresolved. In this work, and in the framework of the BOLIVAR project, we shed light on some aspects of the present state and the tectonic history of the margin by using different types of geophysical data sets and techniques. An analysis of controlled-source traveltime data collected along a boundary-normal profile at ˜65°W was used to build a 2D P-wave velocity model. The model shows that the Caribbean Large Igenous Province is present offshore eastern Venezuela and confirms the uniformity of the velocity structure along the Leeward Antilles volcanic belt. In contrast with neighboring profiles, at this longitude we see no change in velocity structure or crustal thickness across the San Sebastian - El Pilar fault system. A 2D gravity modeling methodology that uses seismically derived initial density models was developed as part of this research. The application of this new method to four of the BOLIVAR boundary-normal profiles suggests that the uppermost mantle is denser under the South American continental crust and the island arc terranes than under the Caribbean oceanic crust. Crustal rocks of the island arc and extended island arc terranes of the Leeward Antilles have a relatively low density, given their P-wave velocity. This may be caused by low iron content, relative to average magmatic arc rocks. Finally, an analysis of teleseismic traveltimes with frequency-dependent kernels produced a 3D P-wave velocity perturbation model. The model shows the structure of the mantle lithosphere under the study area and clearly images the subduction of the Atlantic slab and associated partial removal of the lower lithosphere under northern South America. We also image the subduction of a section of the Caribbean plate under South America with an east-southeast direction. Both the Atlantic and Caribbean subducting slabs penetrate the mantle transition zone, affecting the topography of the 410-km and 660-km discontinuities.

Bezada, Maximiliano J.

346

Cretaceous to Paleogene speed-up and slow-down of India-Asia relative plate convergence: the roles of mantle plumes and continental collision  

NASA Astrophysics Data System (ADS)

Most authors prefer an age of collision around 50 Ma between the Tethyan Himalayas -northernmost continental remnants of the Indian plate - and Asia. A popular argument to support this age is a dramatic slow-down of the India-Asia convergence rate from ~18 to ~5 cm/yr between 50 and 35 Ma, interpreted to result from subduction of continental lithosphere at the collision zone. However, an equally dramatic increase of the India-Asia convergence rate occurred between 65 and 50 Ma, from ~8 to 18 cm/yr. The causes of this increase are not well understood, but may reflect the dynamic influence of sublithospheric mantle flow on the India motion. Arrival of hot mantle plumes (e.g. the Deccan plume at ~65 Ma) may both increase the potential gravitational energy of a plate and impose lateral mantle flow accelerating the plate, especially when it contains a thick continental lithospheric root. If the processes responsible for the acceleration ceases to exist, this may generate a slow-down even without a collision. Here we provide estimates of the India-Asia convergence using the India-Eurasia plate circuit. The analysis of reconstruction errors shows that the speed-up and slow-down are robust, with minor variations in peak convergence velocities depending on the choice of North America-Eurasia rotations. We use two numerical codes to assess the kinematic effects of the arrival of a mantle plume at 65 Ma below India on the convergence rates. The numerical models suggest that the arrival of the plume may indeed lead to a 3-4 cm/yr increase in the convergence rate followed by a gradual slow-down with decreasing plume activity, if no changes in the lithosphere-asthenosphere coupling are assumed. However, the plume arrival is likely to weaken the asthenosphere-lithosphere coupling, leading to a more effective slab-pull effect, which may potentially generate larger a driving force, comparable with the observed 65-50 Ma acceleration. In contrast, the sudden slow-down starting at 50 Ma can not be attributed to a decrease in plume forcing, and is best explained by an increase of resisting forces generated by the arrival of continental lithosphere in the subduction zone.

van Hinsbergen, D. J.; Steinberger, B. M.; Doubrovine, P. V.; Gassmöller, R.

2010-12-01

347

Effects of Mesh Motion on the Stability and Convergence of ALE Based Formulations for Moving Boundary Flows  

NASA Astrophysics Data System (ADS)

This paper investigates the effects of mesh motion on the stability of fluid-flow equations when written in an Arbitrary Lagrangian-Eulerian frame for solving moving boundary flow problems. Employing the advection-diffusion equation as a model problem we present a mathematical proof of the destabilizing effects induced by an arbitrary mesh motion on the stability and convergence of an otherwise stable scheme. We show that the satisfaction of the so-called geometric conservation laws is essential to the development of an identity that plays a crucial role in establishing stability. We explicitly show that the advection dominated case is susceptible to growth in error because of the motion of the computational grid. To retain the bound on the growth in error, the mesh motion techniques need to account for a domain based constraint that minimizes the relative mesh velocity. Analysis presented in this work can also be extended to the Navier-Stokes equations when written in an ALE frame for FSI problems.

Masud, Arif

2006-09-01

348

The INGV National Earthquake Centre research infrastructure to study the plate boundary deformation in the Central Mediterranean  

Microsoft Academic Search

To understand the complex kinematics within the plate boundary zone between Africa and Eurasia in the central Mediterranean, INGV installed a monitoring system based on broad-band seismometers, CGPS and strong motion sensors, most of them co-located in the same site. Established since early '80 with some tens of short period seismometers and analogue transmission, now the monitoring system consists of

Giulio Selvaggi; Salvatore Mazza; Alberto Delladio; Gianpaolo Cecere; Roberto Devoti

2010-01-01

349

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

Microsoft Academic Search

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

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

2008-01-01

350

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

Microsoft Academic Search

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

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

2007-01-01

351

Seismic Images and Magnetic Evidence of The Late Jurassic To Early Cretaceous Africa-eurasia Plate Boundary Off SW Iberia  

NASA Astrophysics Data System (ADS)

During the last decades numerous studies have investigated the structure of the West Iberia non-volcanic continental margin. However, the nature of the crust off SW Iberia is still poorly understood, because of sparse geophysical and geological data coverage. Here we present a 275-km-long multichannel seismic reflection profile, line AR01, acquired in E-W direction across the Horseshoe Abyssal Plain, to partially fill the gap of information in the margin. Line AR01 runs across the inferred plate boundary between the Iberian and the African plates during the opening of the Central Atlantic Ocean. The boundary separates crust formed during or soon after continental rifting of the SW Iberian margin from normal seafloor spreading oceanic crust of the Central Atlantic Ocean. Line AR01 has been processed and pre-stack depth migrated to show the tectonic structure of the crust across the paleo plate boundary. A zone of large basements highs bounded by landward-dipping reflections that penetrate to depths of 15-18 km, marks a change in the character of the basement structure and relief from east to west. In this study we integrate pre-stack depth migration images of line AR01 with potential field data to show that the change in basement structure occurs across the fossil plate boundary separating African oceanic crust of the M series (M22-M16) to the west from the transitional crust of the Iberian margin to the east.

Rovere, M.; Ranero, C. R.; Zitellini, N.; Sartori, R.; Torelli, L.

352

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

Microsoft Academic Search

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

Steven N. Ward

1988-01-01

353

BOLIVAR: Crustal Structure Across the Caribbean-South American Plate Boundary at 70W: Results from Refraction and Reflection Data  

Microsoft Academic Search

The active-seismic component of the BOLIVAR project (Broadband Ocean and Land Investigations of Venezuela and the Antilles arc Region) was completed in June 2004. Among the goals of BOLIVAR is to study the structure of the South America-Caribbean plate boundary as a site of likely continental growth by island arc accretion of the Leeward Antilles arc to the South American

M. C. Guedez; C. A. Zelt; M. B. Magnani; A. Levander; G. L. Christeson; D. S. Sawyer

2005-01-01

354

Analytical Investigation of a Fourth-order Boundary Value Problem in Deformation of Beams and Plate Deflection Theory  

Microsoft Academic Search

In this research, variational iteration method and homotopy perturbation method are applied to solve a nonlinear fourth order boundary value problem. These problems used as mathematical models in viscoelastic inelastic flows and deformation of beams and plate deflection theory. Comparison is made between the exact solutions and the results of the Variational Iteration Method (VIM) and Homotopy Perturbation Method (HPM).

A. J. Choobbasti; A. Barari; F. Farrokhzad; D. D. Ganji

2008-01-01

355

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

356

Geodetic Constraints on the Rigidity and Eastern Boundary of the Sierra Nevada Micro-Plate, from Mohawk Valley to Southern Walker Lane  

Microsoft Academic Search

The Sierra Nevada - Great Valley (SNGV) micro-plate has long been recognized as a tectonically rigid, though mobile, entity within the Pacific - North America plate boundary zone. The motion of the SNGV relative to stable North America (and the Colorado Plateau) provides the kinematic boundary condition for, and perhaps drives, the deformation in the Basin and Range Province (BRP)

C. W. Kreemer; W. C. Hammond; G. Blewitt

2009-01-01

357

Geodynamics of flat-slab subduction, sedimentary basin development, and hydrocarbon systems along the southern Alaska convergent plate margin  

Microsoft Academic Search

Combining field-based geologic studies and numerical modeling provides a robust tool for evaluating the geodynamics of convergent margins. Southern Alaska is arguably the most tectonically active part of the convergent margin of western North America. This conceptual approach has been used to interpret the modern basin dynamics, as well as key stages in the Cenozoic development of this region, including

Emily S Finzel

2010-01-01

358

How do long-offset oceanic transforms adapt to plate motion changes? The example of the Western Pacific-Antarctic plate boundary  

NASA Astrophysics Data System (ADS)

Oceanic transform faults respond to changes in the direction of relative plate motion. Studies have shown that short-offset transforms generally adjust with slight bends near the ridge axis, while long-offset ones have a remarkably different behavior. The western Pacific-Antarctic plate boundary highlights these differences. A set of previously unpublished seismic profiles, in combination with magnetic anomaly identifications, shows how across a former, ~1250 km long transform (the Emerald Fracture Zone), plate motion changes have produced a complex geometric readjustment. Three distinct sections are recognized along this plate boundary: an eastern section, characterized by parallel, multiple fault strand lineaments; a central section, shallower than the rest of the ridge system, overprinted by a mantle plume track; and a western section, organized in a cascade of short spreading axes/transform lineaments. This configuration was produced by changes that occurred since 30 Ma in the Australia-Pacific relative plate motion, combined with a gradual clockwise change in Pacific-Antarctic plate motion. These events caused extension along the former Emerald Fracture Zone, originally linking the Pacific-Antarctic spreading ridge system with the Southeast Indian ridge. Then an intra-transform propagating ridge started to develop in response to a ~6 Ma change in the Pacific-Antarctic spreading direction. The close proximity of the Euler poles of rotation amplified the effects of the geometric readjustments that occurred along the transform system. This analysis shows that when a long-offset transform older than 20 Ma is pulled apart by changes in spreading velocity vectors, it responds with the development of multiple discrete, parallel fault strands, whereas in younger lithosphere, locally modified by thermal anisotropies, tensional stresses generate an array of spreading axes offset by closely spaced transforms.

Lodolo, Emanuele; Coren, Franco; Ben-Avraham, Zvi

2013-03-01

359

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

360

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

361

Analysis of eccentrically stiffened plates with mixed boundary conditions using differential quadrature method  

Microsoft Academic Search

Differential quadrature solution for the flexural analysis of eccentrically stiffened plates subjected to transverse uniform loads is presented. In-plane forces in the plate are considered to take into account the axial stiffness of the plate and the interaction between the beams and the plate due to the eccentricity. Torsional and shear stiffnesses of the beams are also considered. The analysis

Zahid A Siddiqi; Anant R Kukreti

1998-01-01

362

Effects of Triple Junction Plate Boundary Geometry on Mantle Thermal Structure and Crustal Production  

NASA Astrophysics Data System (ADS)

Plate boundary geometry likely has an important influence on crustal production at mid-ocean ridges. Many studies have explored the effects of geometrical features such as transform offsets and oblique ridge segments on mantle flow and melting. This investigation calculates how triple junction geometry may influence the generation of oceanic crust. An earlier study (Georgen and Lin 2002) suggested that the effects of a ridge-ridge- ridge configuration are most pronounced under the branch with the slowest spreading rate. Thus, we create a three-dimensional, finite element, variable viscosity numerical model that incorporates thermal buoyancy and focuses on the slowest-diverging ridge. First, we employ a model geometry similar to the Southwest Indian Ridge near the Rodrigues Triple Junction in the central Indian Ocean. Within 100 km of the triple junction, axial temperatures at depths within the partial melting zone are predicted to increase by ~40 deg. C, and crustal thickness is calculated to increase by 1 km. We also explore how varying spreading rate magnitude affects triple junction dynamics. Consistent with Georgen and Lin (2002), variable-viscosity flow models for calculations where all spreading rates are greater than the Rodrigues-like case (i.e., with plate kinematics similar to those observed around the Galapagos Triple Junction) predict little influence of the triple junction geometry on the thermal structure of the slowest-spreading ridge. However, when ridge divergence rates are all relatively slow (i.e., with plate kinematics similar to those observed around the Azores Triple Junction), significant along-axis increases in mantle temperature and crustal thickness are calculated. At depths within the partial melting zone, temperatures are predicted to increase by ~150 deg. C, similar to the excess temperatures associated with mantle plumes. Likewise, crustal thickness is calculated to increase by approximately 6.5 km over the 200 km of ridge closest to the triple junction. These results could imply that some component of the excess volcanism observed in geologic settings such as the Terceira Rift may be attributed to the effects of triple junction geometry, although the important influence of features like nearby hotspots (e.g., the Azores hotspot) cannot be evaluated without additional numerical modeling.

Georgen, J. E.

2007-12-01

363

NanTroSEIZE: Sampling and Monitoring Plate Boundary Fault Processes of the Nankai Subduction Zone  

NASA Astrophysics Data System (ADS)

The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) is a a long-term effort to image, sample, and instrument the up-dip portion of a subduction megathrust in a location where great earthquakes repeatedly occur. It comprises a series of geophysical surveys, including 3D seismic reflection, a transect of drilled boreholes, and a long-term borehole observatory component. The objective is to elucidate the strain accumulation and release in the region transitional between the presumed aseismic accretionary wedge and the locked portion of the megathrust. The main operational goal of the science plan is to sample and instrument key faults in several locations spanning the transition from those dominated by frictionally stable, aseismic or quasi-seismic processes, vs. those hypothesized to be frictionally locked (seismogenic) faults of the megathrust system, testing hypotheses for the spatial and temporal patterns of fault locking. From 2007 through the end of 2010, the NanTroSEIZE science team has achieved many of its primary goals during 6 expeditions with D/V Chikyu. Completed drill sites to date comprise penetrations ranging from 200 m to more than 1600 m below the sea floor, including IODP’s first riser-drilled borehole. We have sampled and made in situ measurements on the faults and wall rocks of both the frontal thrust and out-of-sequence splay faults in the accretionary system, the sedimentary section of the subducting plate, and the thick forearc basin sedimentary record and underlying older subduction complex in the hanging wall of the main plate interface. Major results so far include: (a) evidence for strongly localized, likely co-seismic fault slip to within a few hundred meters of the sea floor at the trench and in an out-of-sequence splay fault, (b) the distribution of present-day and paleo-stress orientations across the transect showing evidence for tectonic control coupled with time-varying stress magnitudes, (c) an absence of evidence for focused fluid channeling along the principal shallow fault systems, and (d) the event-punctuated nature of the tectonic history of the subduction system governed by subducted topography. Extensive downhole measurements and a 2-ship VSP experiment have further documented stress, pressure, rock strength, and elastic properties. The first long-term monitoring instruments are now in place in a sealed borehole, recording pore pressure and temperature. Expedition 326 in 2010 completed the first 800 meters of casing for the main riser hole targeted at drilling to ~ 7000 m below the sea bed across the faults of the main plate boundary, then placing long-term monitoring instruments into both deep and shallow sealed borehole observatories.

Tobin, H. J.; Kinoshita, M.; Iodp Expedition 314/315/316/319/322 Scientists

2010-12-01

364

Ridge Reorientation Mechanisms and Tectonic Processes Along the Macquarie Ridge Complex Portion of the Australia-Pacific Plate Boundary  

NASA Astrophysics Data System (ADS)

Analysis of side scan, bathymetry, magnetic anomaly and gravity data for the Macquarie Ridge Complex portion of the Australia-Pacific plate boundary south of New Zealand documents an ~100o change in spreading direction between 40 and 6 Ma prior to truncation by the present day transform fault. We present a reconstruction that correlates arcuate fracture zones on the Australian and Pacific plates and compare them to synthetic flowlines generated from 32 Ma to 6 Ma using the most recently resolved poles. Our analysis shows that this major change in spreading direction, caused by continuous migration of the proximal pole of rotation since 33 Ma, resulted in dynamic interaction and transfer of crust between the two plates, consistent with continuous transpression. In our reconstruction area, spreading following rifting was initially accommodated by 7 ridge segments ranging in width from 40 to 125km and offset by 7-25km. By the end of spreading, only three narrower segments, 5 to 50km in width offset by 117-160 km, were still active. Synthetic flowlines predict 80% shortening of the combined ridge segment widths approaching the plate boundary to maintain strain compatibility, whereas only 69% shortening is observed. Regionally available side scan and bathymetry data show an overall "Zed" pattern and fanning spreading fabric within regions of high curvature, indicating differential asymmetric spreading during gradual reorientation of spreading axes. However, away from the rifted margins, the width of crust between correlative fracture zones on the two plates differs, requiring crustal modification after spreading. This modification, the decreasing width and complete disappearance of ridge segments approaching the present day plate boundary, plus seafloor morphology and magnetic anomaly patterns, all support ridge (rift) propagation into preexisting crust. Comparison of individual fracture zones with corresponding synthetic flowlines show them nearly identical closest to rifted margins and diverging with less curvature approaching the plate boundary. Modification of fracture zones by shearing during transform motion since 6 Ma is not likely because fracture zones show less deflection into the plate boundary than the synthetic flowlines. Thus, spreading ridge segments responded to the large change in orientation by a combination of gradual rotation and unidirectional propagation into adjacent crust, decreasing the predicted curvature magnitude, coupled with faster failing of the opposite end of the ridge, thereby decreasing the width of the spreading segments.

Symons, C. M.; Mosher, S.

2006-12-01

365

Watching structural and geodynamic features of a plate boundary: Peceneaga-Camena Fault  

NASA Astrophysics Data System (ADS)

The Peceneaga - Camena Fault represents one of the major lithosphere contacts on the Romanian territory. Its nature and dynamics have been subject to many geological and geophysical researches since the beginning of the 20th century. Based on geophysical evidence some authors consider PCF as a plate boundary, the strike-slip contact between the Moesian Micro-Plate (MoP) and East European Plate (EEP). Deep seismic soundings along the international line II had revealed its trans-crustal nature, with a 10 km step at both Conrad and Moho discontinuities. It is likely that the geodynamic evolution of this major tectonic accident is tightly connected to the opening of the W Black Sea basin. Seismic tomography studies have outlined strong fingerprints of the W Black Sea opening within its NW inland. In depth extension of PCF may be clearly seen within the tomography images down to more than 150 km. It seems that lithosphere expelled by the rifting split MoP into several compartments by creating or reactivating a NW trending major fault system to which the PCF belongs. After the W Black Sea rifting ended its evolution, the geodynamic engine in the area seems to be the active rifting in the SW Arabian Plate (red Sea and Aden Bay) pushing northward the Arabian Plate by about 48 mm/yr, and further on, pushing a MoP segment towards the Carpathians. Under this pushing, the above-mentioned MoP compartments move towards the Carpathians, staying together by friction. However, when tectonic forces overcome the friction, the slivers may relatively slip each other, thus generating earthquakes along their wedges. The presence of some scarce seismicity along PCF seems to confirm the idea. To check up the above mentioned geodynamic scenario, a geodetic experiment has been imagined to monitor PCF flanks displacement. Two Leica TC 1201 total stations were installed on the southern flank of PCF (belonging to MoP) in order to measure the distance to a laser reflector installed on the northern PCF flank (within the neighbouring EEP). Each instrument measures the distance to the reflector every 6 seconds and records minute averages of the observations. This way time series related to movements of the PCF compartments were acquired and stored in a computer database. To diminish the record noise, mainly due to the temperature variation and terrestrial tides, some filtering techniques were applied to data in order to better reveal the existent trends. The analysis made lead to some interesting conclusions: (i) PCF is a geodynamical active contact, which explains earthquakes presence along it; (ii) flanks displacements are irregular in both speed and strike; (iii) according to the records, PCF has behaved both as a right-lateral and / or left-lateral contact. The results are fully consistent with the geodynamic model connected to W Black Sea evolution. When the PCF northern compartment escapes toward Carpathians, PCF appears as a left-lateral fault. On the opposite, if the southern compartment is moving under the action of tectonic forces, then PCF appears as right-lateral fault. These conclusions may provide important constraints for interpreting GPS data obtained during epoch campaigns.

Besutiu, L.; Zlagnean, L.

2009-04-01

366

GPS Installation Progress in the Northern California Region of the Plate Boundary Observatory  

NASA Astrophysics Data System (ADS)

The Plate Boundary Observatory (PBO) is the geodetic component of the National Science Foundation (NSF) funded Earthscope Project. The final PBO GPS network will comprise 1100 continuously operating GPS stations installed throughout the Western US and Alaska. There are 448 Stations planned for California with 231 of these in Northern California (NCA). This poster will present a progress report and highlights of GPS installations in NCA over the past year up until the end of the five year project. In the fifth year of the project (beginning 10/1/2007 and ending 10/1/2008), we installed 40 additional stations for a total of 231 stations. The stations installed include; 8 station installed at Lassen Volcanic National Park, 2 additional stations built around Mount Shasta (8 total), 3 stations built in Yosemite National Park, 2 in the Mendocino National Forest, and 2 stations in Tahoe National Forest. The higher elevations stations required modification for use in areas of high snow load and high wind. Data from these stations are available from the UNAVCO archive. In addition to the installations, there was a gradual shift of resources from installation to the operation and maintenance aspects of the growing GPS network. Telemetry priorities moved from individual stations telemetry solutions to grouped telemetry solutions to increase efficiency and reduce costs.

Basset, A.; Coyle, B.; Williams, T.; Mann, D.; Finn, D.; Feaux, K.

2008-12-01

367

Three-dimensional stability by global modes in the flat plate boundary-layer flow  

NASA Astrophysics Data System (ADS)

The stability of the flat-plate boundary-layer flow is studied by means of three-dimensional eigenmodes of the linearized Navier--Stokes equations obtained by linearization about the steady state. The disturbance variables are approximated using a Fourier--Chebyshev collocation technique in inhomogeneous directions. Given the large size of the generalized eigenvalue problem we employ Arnoldi iterations using |ARPACK|. By expanding the flow disturbance variables in the basis of eigenmodes the growth potential is revealed by the computation of the optimal initial condition. This yields a low-dimensional model of the flow and a unified view on its stability characteristics. We discuss three different mechanisms associated with the non-normality of the operator: The lift-up mechanism is a componentwise non-normality where momentum is transferred from the spanwise to the streamwise velocity component. The Orr mechanism provides, through structures leaning against the shear, an efficient way of obtaining short time growth while borrowing energy from the mean flow, transferring momentum from the streamwise component to the wall-normal component. The TS mechanism is related to the streamwise non-normality where initial disturbances are located upstream and wavepacket propagation leads to a large energy gain downstream.

Åkervik, Espen; Brandt, Luca; Henningson, Dan S.

2007-11-01

368

The Baja California Borderland and the Neogene Evolution of the Pacific-North American Plate Boundary  

NASA Astrophysics Data System (ADS)

New observational data on Neogene faulting in the borderland of Baja California places important constraints on tectonic models for the evolution of the Pacific-North American (P-NA) plate boundary and rifting in the Gulf of California. Neogene faults in the borderland range from strike slip to normal slip and accommodate integrated transtension. Most have east-facing escarpments and likely reactivate the former east-dipping accretionary complex. Numerous lines of evidence indicate that Neogene faults are still active and accomplish a significant component ( ~1-5 mm/yr) of Pacific-North American shearing. Quaternary volcanoes are found offshore and along the Pacific coastal margin, Quaternary marine terraces are warped and uplifted as high as 200 masl. Many of the offshore faults have fresh escarpments and cut Holocene sediments. Extensive arrays of Quaternary fault scarps are found throughout the coastal region and in Bahia Magdalena they are clearly associated with major faults that bound recently uplifted islands. A prominent band of seismicity follows the coast and eight earthquakes (Ms>5.0) were teleseismically recorded between 1973 and 1998. This evidence for active shearing indicates that the Baja microplate has not yet been completely transferred to the Pacific plate. The best lithologic correlation that can be used to define the total Neogene slip across the borderland faults is the offset between the Magdalena submarine fan and its Baja source terrane. The distal facies of the fan drilled during DSDP leg 63 is dominated by mudstone and siltstone that contain reworked Paleogene cocoliths derived from strata correlative with the Tepetate formation found throughout the borderland and fine-grained sandstone derived from a source terrane of granitoid basement. The Middle Miocene La Calera formation of the Cabo trough is one of many granitoid-clast syn-rift alluvial deposits that could form the continental counterpart of the submarine fan near the mouth of the proto-gulf. However, regardless of the exact source, the Magdalena fan must have been transported beyond a major submarine canyon system south of Todos Santos by 13.5 Ma when sedimentation rates significantly diminished. This places a maximum of { ~}200 km total slip on the borderland faults since 13.5 Ma. Alternatively, all components of the Magdalena fan could have been derived from reworking Cenozoic strata within the borderland. The sandstone facies could be derived from the Oligocene El Cien Fm., which is a granitoid clast conglomerate that overlies the Tepetate Fm. and crops out ~100 km west of La Paz. If true, the total slip across borderland faults may be only a few tens of kilometers. Key structural relations along the submarine Tosco-Abreojos fault system support this lower slip estimate including: relatively short ({ ~}30 km width) pull-apart basins, correlative strata on either side of the fault, and a strong pattern of splaying, which indicates a lateral termination only { ~}50 km to the SE of the Magdalena fan. These new observations require significant modifications to existing tectonic models, which usually assign { ~}300 km of offset to the borderland. Lower finite slip estimates suggest that the borderland may not have formed the main P-NA plate boundary and long-term Neogene slip rates need not be significantly different from Quaternary slip rates. Lower finite slip estimates also allow stronger correlations between Farallon derived microplates and the patterns of Neogene faulting, volcanism, topographic variations, and surface heat flow in the overlying continental crust of Baja California.

Fletcher, J. M.; Eakins, B. W.

2001-12-01

369

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

370

Seismic images and magnetic signature of the Late Jurassic to Early Cretaceous Africa-Eurasia plate boundary off SW Iberia  

NASA Astrophysics Data System (ADS)

Over the last two decades numerous studies have investigated the structure of the west Iberia continental margin, a non-volcanic margin characterized by a broad continent-ocean transition (COT). However, the nature and structure of the crust of the segment of the margin off SW Iberia is still poorly understood, because of sparse geophysical and geological data coverage. Here we present a 275-km-long multichannel seismic reflection (MCS) profile, line AR01, acquired in E-W direction across the Horseshoe Abyssal Plain, to partially fill the gap of information along the SW Iberia margin. Line AR01 runs across the inferred plate boundary between the Iberian and the African plates during the opening of the Central Atlantic ocean. The boundary separates crust formed during or soon after continental rifting of the SW Iberian margin from normal seafloor spreading oceanic crust of the Central Atlantic ocean. Line AR01 has been processed and pre-stack depth migrated to show the tectonic structure of the crust across the palaeo plate boundary. This boundary is characterized by a 30-40-km-wide zone of large basements highs related to landward-dipping reflections, which penetrate to depths of 13-15 km, and it marks a change in the character of the basement structure and relief from east to west. In this study, we have used pre-stack depth migrated images, the velocity model of line AR01 and magnetic data available in the area to show that the change in basement structure occurs across the fossil plate boundary, separating African oceanic crust of the M series (M21-M16) to the west from the transitional crust of the Iberian margin to the east.

Rovere, M.; Ranero, C. R.; Sartori, R.; Torelli, L.; Zitellini, N.

2004-08-01

371

Numerical modelling of the upper mantle anisotropy beneath a migrating strike-slip plate boundary: the San Andreas Fault system  

NASA Astrophysics Data System (ADS)

We performed forward modelling of seismic anisotropy beneath a migrating strike-slip plate boundary to: (1) test if such a geodynamic context might explain teleseismic shear-wave splitting data in the vicinity of the central part of the San Andreas Fault, and (2) constrain the power of such data to unravel vertical and lateral variations in deformation patterns in the upper mantle. The modelling involves five steps: (1) thermo-mechanical modelling, using a finite-element code, of the deformation field, (2) viscoplastic self-consistent modelling of the resulting olivine and pyroxene crystal preferred orientations, (3) calculation of the elastic tensors for different domains of the finite elements (FE) model, (4) forward modelling of seismic wave propagation through the model using ray theory, finite-frequency theory, and a full wave approach, and (5) performing splitting measurements on the synthetic seismograms. SKS splitting data in central California are best fitted by a model with a hotter geotherm within 60 km of the plate boundary accounting for the opening of an asthenospheric window due to the northward migration of the Mendocino Triple Junction. The westward motion of the plate boundary cannot however explain the rotation of fast polarisations east of the San Andreas Fault in central California. Comparison between modelled and measured individual shear-wave splitting also implies that the homogeneity of the 2-layer models accounting for the observations in the vicinity of the San Andreas Fault indicates a sharp transition between lithospheric and asthenospheric deformations beneath this plate boundary. The ability of different synthetic approaches to localize horizontally and vertically the plate boundary-related deformation differs significantly. Splitting data on ray theory synthetics closely follow variations in olivine crystal preferred orientations in the model. In contrast, splitting analysis on full-wave synthetics, which should be more representative of actual long period SKS waves, results in smooth lateral variations of the anisotropy; the location and width of the plate boundary may only be retrieved by comparing fast polarisation profiles obtained using a multichannel analysis on waves with different periods.

Bonnin, Mickael; Tommasi, Andréa; Hassani, Riad; Chevrot, Sébastien; Wookey, James; Barruol, Guilhem

2013-04-01

372

Propagation of rifting along the Arabia-Somalia Plate Boundary: The Gulfs of Aden and Tadjoura  

NASA Astrophysics Data System (ADS)

The localization and propagation of rifting between Arabia and Somalia are investigated by assessing the deformation geometry and kinematics at different scales between the eastern Gulf of Aden and the Gulf of Tadjoura, using bathymetric, magnetic, seismological, and structural evidence. Large-scale, southwestward propagation of the Aden ridge, markedly oblique to the Arabia-Somalia relative motion vector, began about 30 Myr ago between the Error and Sharbithat ridges. It was an episodic process, with stages of rapid propagation, mostly at rates >10 cm/yr, interrupted by million year pauses on transverse discontinuities coinciding with rheological boundaries between different crustal provinces of the Arabia-Somalia plate. The longest pause was at the Shukra-El Sheik discontinuity (?45°E), where the ridge tip stalled for ?13 Myr, between ?17 and ?4 Ma. West of that discontinuity, rifting and spreading took place at an azimuth (?N25°±10°E) and rate (1.2±0.3 cm/yr) different from those of the global Arabia-Somalia motion vector (?N39°, ?1.73 cm/yr), implying an additional component of movement (N65°±10°E, 0.7±0.2 cm/yr) due to rotation of the Danakil microplate. At Shukra-El Sheik, the typical oceanic ridge gives way to a narrow, WSW trending axial trough, resembling a large fissure across a shallow shelf. This trough is composed of about eight rift segments, which result from normal faulting and fissuring along N110°-N130°E trends. All the segments step to the left southwestward, mostly through oblique transfer zones with en échelon normal faults. Only two segments show clear, significant overlap. There is one clear transform, the Maskali fault, between the Obock and Tadjoura segments. The latter segment, which encroaches onland, is composed of two parallel subrifts (Iboli, Ambabbo) that propagated northwestward and formed in succession. The most recent, southwestern subrift (Ambabbo) represents the current tip of the Aden ridge. We propose a mechanical model in which the large-scale propagation of the ridge followed a WSW trending zone of maximum tensile stress, while the small-scale propagation of its NW trending segments was dictated by the orientation of that stress. Oblique propagation was a consequence of passive lithospheric necking of the Arabia-Somalia plate along its narrow section, in map view, between Socotra and the kink of the Red Sea-Ethiopian rift, above the Afar plume. Individual ridge segments oriented roughly perpendicular to plate motion, like lithospheric cracks, were forced to jump southward because of confinement within the necking zone. Self-sustaining, plate-scale necking may explain why the Aden ridge did not connect with the Red Sea through Bab El Mandeb but continued straight into Afar.

Manighetti, Isabelle; Tapponnier, Paul; Courtillot, Vincent; Gruszow, Sylvie; Gillot, Pierre-Yves

1997-02-01

373

Character of the Caribbean-Gônave-North America plate boundaries in the upper mantle based on shear-wave splitting  

NASA Astrophysics Data System (ADS)

We present new shear-wave splitting measurements of SKS, SKKS, PKS, and sSKS phases from eight stations in the northern Caribbean. Prior to this work, shear-wave splitting analysis of the northern Caribbean boundary was only evaluated at a station in Puerto Rico. Stations that lie within several tens of kilometers of microplate boundaries have mean fast polarization directions parallel to the boundary and have delay times greater than 1 s. Stations more than several tens of kilometers away from microplate boundaries show no evidence for an anisotropic upper mantle. Stations in Cuba and Jamaica have fast axes oriented ˜100° with delay times of ˜1.5 s, indicating that the east-striking left-lateral strike-slip faults that define the north and south boundaries of the Gônave microplate continue into the upper mantle. A station located in Antigua, where the North America plate subducts beneath the Caribbean plate, has a high degree of splitting with the fast axis parallel to the trench. Based on our results, the deformation related to the presence of microplates in the northern Caribbean extends into the upper mantle.

Benford, B.; Tikoff, B.; DeMets, C.

2012-12-01

374

Analytical Investigation of a Fourth-order Boundary Value Problem in Deformation of Beams and Plate Deflection Theory  

NASA Astrophysics Data System (ADS)

In this research, variational iteration method and homotopy perturbation method are applied to solve a nonlinear fourth order boundary value problem. These problems used as mathematical models in viscoelastic inelastic flows and deformation of beams and plate deflection theory. Comparison is made between the exact solutions and the results of the Variational Iteration Method (VIM) and Homotopy Perturbation Method (HPM). The results reveal that these methods are very effective and simple. In this survey, it will be shown that these methods can also be used for solving nonlinear boundary value problems.

Choobbasti, A. J.; Barari, A.; Farrokhzad, F.; Ganji, D. D.

375

Sub-slab mantle flow parallel to the Caribbean plate boundaries: Inferences from  

Microsoft Academic Search

article i nfo Upper-mantle deformation near the margins of the Caribbean plate is investigated using observations of shear-wave splitting in teleseismic and local shear phases. The Caribbean plate is almost stationary in the hot-spot reference frame and is wedged between the North America, South America, Nazca and Cocos plates; collisional belts and major shear zones encircle the plate. Data from

L. T. Piñero-Feliciangeli; J.-M. Kendall

376

Natural frequencies and mode shapes of elliptic plates with boundary characteristic orthogonal polynomials as assumed shape functions  

NASA Astrophysics Data System (ADS)

The natural frequencies and natural modes of vibration of uniform elliptic plates with clamped, simply supported and free boundaries are investigated using the Rayleigh-Ritz method. A modified polar coordinate system is used to investigate the problem. Energy expressions in the Cartesian coordinate system are transformed into the modified polar coordinate system. Boundary characteristic orthogonal polynomials in the radial direction, and trigonometric functions in the angular direction are used to express the deflection of the plate. These deflection shapes are classified into four basic categories, depending on their symmetrical or antisymmetrical properties about the major and minor axes of the ellipse. The first six natural modes in each of the above categories are presented in the form of contour plots.

Rajalingham, C.; Bhat, R. B.; Xistris, G. D.

1993-07-01

377

Aerodynamic optimization of the flat-plate leading edge for experimental studies of laminar and transitional boundary layers  

NASA Astrophysics Data System (ADS)

This work is concerned with the design of a leading edge for a flat-plate model used to study laminar and transitional boundary layers. For this study, the flow over the complete boundary-layer model, including leading edge, flat section, and trailing-edge flap, is modeled. The effect of important geometrical features of the leading edge on the resulting pressure distribution, starting from the well-known symmetric modified super ellipse, is investigated. A minimal pressure gradient on the measurement side of the plate is achieved using an asymmetrical configuration of modified super ellipses, with a thickness ratio of 7/24. An aerodynamic shape optimization is performed to obtain a novel leading edge shape that greatly reduces the length of the non-zero pressure gradient region and the adverse pressure gradient region compared to geometries defined by ellipses. Wind tunnel testing is used to validate the numerical solutions.

Hanson, Ronald E.; Buckley, Howard P.; Lavoie, Philippe

2012-10-01

378

A Geodetic Strain Rate Model for the Pacific-North American Plate Boundary, western United States  

NASA Astrophysics Data System (ADS)

We present a model of crustal strain rates derived from GPS measurements of horizontal station velocities in the Pacific-North American plate boundary in the western United States. The model reflects a best estimate of present-day deformation from the San Andreas fault system in the west to the Basin and Range province in the east. Of the total 2,846 GPS velocities used in the model, 1,197 are derived by ourselves, and 1,649 are taken from (mostly) published results. The velocities derived by ourselves (the "UNR solution") are estimated from GPS position time-series of continuous and semi-continuous stations for which data are publicly available. We estimated ITRF2005 positions from 2002-2011.5 using JPL's GIPSY-OASIS II software with ambiguity resolution applied using our custom Ambizap software. Only stations with time-series that span at least 2.25 years are considered. We removed from the time-series continental-scale common-mode errors using a spatially-varying filtering technique. Velocity uncertainties (typically 0.1-0.3 mm/yr) assume that the time-series contain flicker plus white noise. We used a subset of stations on the stable parts of the Pacific and North American plates to estimate the Pacific-North American pole of rotation. This pole is applied as a boundary condition to the model and the North American - ITRF2005 pole is used to rotate our velocities into a North America fixed reference frame. We do not include parts of the time-series that show curvature due to post-seismic deformation after major earthquakes and we also exclude stations whose time-series display a significant unexplained non-linearity or that are near volcanic centers. Transient effects longer than the observation period (i.e., slow viscoelastic relaxation) are left in the data. We added to the UNR solution velocities from 12 other studies. The velocities are transformed onto the UNR solution's reference frame by estimating and applying a translation and rotation that minimizes the velocities at collocated stations. We removed obvious outliers and velocities in areas that we identified to undergo subsidence likely due to excessive water pumping. For the strain rate calculations we excluded GPS stations with anomalous vertical motion or annual horizontal periodicity, which are indicators of local site instability. First, we used the stations from the UNR solution to create a Delaunay triangulation and estimated the horizontal strain rate components (and rigid body rotation) for each triangle in a linear least-squares inversion using the horizontal velocities as input. Some level of spatial damping was applied to minimize unnecessary spatial variation in the model parameters. The strain rates estimates were then used as a priori strain rate variances in a method that fits continuous bi-cubic Bessel spline functions through the velocity gradient field while minimizing the weighted misfit to all velocities. A minimal level of spatial smoothing of the variances was applied. The strain rate tensor model is shown by contours of the second invariant of the tensor, which is a measure of the amplitude that is coordinate frame independent. We also show a map of the tensor style and of the signal-to-noise ratio of the model.

Kreemer, C.; Hammond, W. C.; Blewitt, G.; Holland, A. A.; Bennett, R. A.

2012-04-01

379

Halfway There: An EarthScope Plate Boundary Observatory Progress Report  

NASA Astrophysics Data System (ADS)

The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three-dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, UNAVCO will install 852 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser strainmeters by October 2008, acquire radar imagery and geochronology as well as manage data for 209 previously existing continuous GPS stations through the PBO Nucleus project. As of September 2006, UNAVCO had completed half the PBO GPS stations, with 426 installed and data returned from 400 stations, and 60% of the PBO Nucleus stations have been upgraded. Highlights of the past year's work include the expansion of the Alaska subnetwork to nearly 70 continuously-operating stations, including coverage of Akutan and Augustine volcanoes and reconnaissance for future installations on Unimak Island; the installation of nine new stations on Mt. St. Helens; and the arrival of 33 permits for station installations on BLM land in Nevada. The Augustine network provided critical data on magmatic and volcanic processes associated with the 2005-2006 volcanic crisis, and is now being expanded to a total of 11 stations. Please visit http://pboweb.unavco.org/?pageid=3 for further information on PBO GPS network construction activities. UNAVCO is also installing and operating the largest borehole seismic/strainmeter network in North America, as well as tiltmeters and laser strainmeters. As of September 2006, 19 PBO borehole stations had been installed and two laser strainmeter stations were operating, with a total of 28 borehole stations and 3 laser strainmeters expected by the end of 2006. In response to direction from the EarthScope community, UNAVCO has installed a dense network of six stations along the San Jacinto Fault near Anza, California. During the fall of 2006, the first borehole stations will be installed on Mt. St. Helens, along with the first PBO borehole tiltmeters, and work will begin to densify the network near Parkfield. Please visit http://pboweb.unavco.org/?pageid=8 for more information on PBO strainmeter network construction progress. The combined PBO/Nucleus GPS network has now provided almost 150 GB of raw data, with special downloads of more than 15 GB of high-rate GPS data following the March 2006 Koryakia, Russia and May 2006 Tonga earthquakes. These GPS data are processed routinely to generate data products including station position time series, velocity vectors, and related information, and all data products are available from the UNAVCO Facility archive. The PBO seismic network seismic network has provided 60 GB of raw data, which are available from the IRIS Data Management Center (DMC). The PBO strainmeter network has provided nearly 30 GB of raw data, available in both raw native format and SEED format from the Northern California Earthquake Data Center and the IRIS DMC, along with higher-level products such as cleaned strain time series and related information. Please visit http://pboweb.unavco.org/?pageid=88 and http://pboweb.unavco.org/?pageid=89 for more information on PBO GPS and strainmeter/seismic data products.

Jackson, M.; Anderson, G.; Blume, F.; Coyle, B.; Feaux, K.; Friesen, B.; Hafner, K.; Hasting, M.; Johnson, W.; Mencin, D.; Pauk, B.; Phillips, D.; Walls, C.; Prescott, W.

2006-12-01

380

Estimation of fracture parameters and stress field for edge cracks in finite elastically graded plates using boundary collocation  

Microsoft Academic Search

Summary  The fracture parameters, stress intensity factor and T-stress are obtained for edge cracks aligned along the gradient in finite\\u000a size elastically graded plates using the technique of boundary collocation. A scheme for extending the recently derived crack\\u000a tip stress field for elastically graded materials is proposed. Using this extended stress field, the fracture parameters are\\u000a evaluated for edge cracks subjected

V. Parameswaran; S. Sharma

2006-01-01

381

The EarthScope Plate Boundary Observatory (PBO) High-rate Real-time Cascadia network  

NASA Astrophysics Data System (ADS)

As part of the 2009 American Recovery and Reinvestment Act (ARRA), NSF is investing in onshore-offshore instrumentation to support studies of the Cascadia margin. EarthScope's Plate Boundary Observatory (PBO) will upgrade all 232 of its GPS stations in the Pacific Northwest to high-rate sampling and real-time telemetry and provide streaming data from this network to the public for scientific research, education, and hazard monitoring. This effort expands UNAVCO’s real-time GPS operations beyond its current pilot project of 100 stations to include a comprehensive regional network that spans the states of Washington and Oregon, and extends south into California to the Mendocino triple junction. By blanketing the Pacific Northwest with real-time GPS coverage, the NSF is hoping to create a natural laboratory in an area of great scientific interest and high geophysical hazard in order to spur new volcano and earthquake research opportunities. Streaming high-rate data in real-time will enable researchers to routinely analyze for strong ground motion monitoring and earthquake hazards mitigation. For stations with collocated meteorological instruments, met data will be streamed as well, opening the possibility for combined GPS/met processing in real time by the atmospheric community. Finally, the new funding also expands opportunities for research using high-rate GPS data from a large-aperture network, since 1 Hz streams will be permanently archived and freely available via FTP. PBO will provide 1Hz-streaming data in BINEX, RTCM2.3 and RTCM 3.0 formats via the NTrip protocol, from servers located at UNAVCO headquarters in Boulder, CO. Data latency will vary according to the telemetry deployed at each station, but is expected to range from 0.5~2.0 seconds given recent improvements in PBO's real-time streaming capabilities.

Jackson, M. E.; Austin, K. E.; Borsa, A. A.; Eriksson, S. C.; Feaux, K.; Williams, T. B.

2009-12-01

382

Low-latency high-rate GPS data from the EarthScope Plate Boundary Observatory  

NASA Astrophysics Data System (ADS)

Real-time processing of high rate GPS data can give precise (e.g., 5-10 mm for data recorded once per second) recordings of rapid volcanic and seismic deformation. GPS is also an inertial sensor that records ground displacement with very high dynamic range, which allows the use of high rate GPS as a strong-motion seismometer. Such processing applied to low-latency streams of high sample rate GPS provide an emerging tool for earthquake, volcano, and tsunami geodesy and early warning. UNAVCO, as part of the EarthScope Plate Boundary Observatory project, is developing a system to provide such streams from some PBO and other UNAVCO-operated GPS stations, which we call UStream. UStream will be based on the Ntrip standard, a widely used protocol for streaming GNSS data over the Internet. Remote GPS stations will provide a stream of BINEX data at 1 sample/sec to an Ntrip server at UNAVCO's Boulder offices, while at the same time recording data locally in the event of communications failure. Once in Boulder, the data will be forked into three output streams: BINEX files stored at the UNAVCO archive and streams of data in BINEX and RTCM format. These data will flow to an Ntrip broadcaster that will distribute data to Ntrip clients, which can be anything from epoch-by-epoch processing systems to external data archiving systems. Data will flow through this system with no artificial latency and will be freely available to the community for use in scientific research.

Anderson, G.; Jackson, M.; Meertens, C.; Stark, K.

2007-05-01

383

High-Resolution LiDAR Topography of the Plate-Boundary Faults in Northern California  

NASA Astrophysics Data System (ADS)

GeoEarthScope acquired more than 1500 square km of airborne LiDAR data in northern California, providing high-resolution topographic data of most of the major strike-slip faults in the region. The coverage includes the San Andreas Fault from its northern end near Shelter Cove to near Parkfield, as well as the Rodgers Creek, Maacama, Calaveras, Green Valley, Paicines, and San Gregorio Faults. The Hayward fault was added with funding provided by the US Geological Survey, the City of Berkeley, and the San Francisco Public Utilities Commission. Data coverage is typically one kilometer in width, centered on the fault. In areas of particular fault complexity the swath width was increased to two kilometers, and in selected areas swath width is as wide as five kilometers. A five-km-wide swath was flown perpendicular to the plate boundary immediately south of Cape Mendocino to capture previously unidentified faults and to understand off-fault deformation associated with the transition zone between the transform margin and the Cascadia subduction zone. The data were collected in conjunction with an intensive GPS campaign designed to improve absolute data accuracy and provide quality control. Data processing to classify the LiDAR point data by return type allows users to filter out vegetation and produce high-resolution DEMs of the ground surface beneath forested regions, revealing geomorphic features along and adjacent to the faults. These data will allow more accurate mapping of fault traces in regions where the vegetation canopy has hampered this effort in the past. In addition, the data provide the opportunity to locate potential sites for detailed paleoseismic studies aimed at providing slip rates and event chronologies. The GeoEarthScope LiDAR data will be made available via an interactive data distribution and processing workflow currently under development.

Prentice, C. S.; Phillips, D. A.; Furlong, K. P.; Brown, A.; Crosby, C. J.; Bevis, M.; Shrestha, R.; Sartori, M.; Brocher, T. M.; Brown, J.

2007-12-01

384

Receptivity of the boundary layer over a flat plate with different leading-edge geometries: Numerical simulations  

NASA Astrophysics Data System (ADS)

The receptivity to freestream oscillations of the laminar boundary layer over a semi-infinite flat plate of finite thickness is simulated numerically. The incompressible flow past the flat plate is computed by solving the full Navier-Stokes equations in general curvilinear coordinates. A finite-difference method which is second-order accurate in space and time is used. Spatial and temporal developments of the Tollmien-Schlichting wave in the boundary layer, due to small-amplitude time-harmonic oscillations of the freestream velocity that closely simulate a sound wave traveling parallel to the plate for incompressible flow, are observed. The effect of leading-edge geometry is studied by using leading edges with different aspect ratios. The boundary layer over the flat plate with a sharper elliptic leading edge is found to be less receptive. A new leading-edge geometry, a modified super-ellipse, which provides continuous curvature at the juncture with the flat plate, is used to study the effect of continuous curvature and inherent pressure gradient on receptivity. It is found that receptivity magnitude depends on how rapid the pressure gradient changes along the wall, and for a given aspect ratio, there is an optimum variation of the leading-edge curvature for minimum receptivity. Moreover, the phase of the instability wave is determined by the location of the maximum adverse-pressure gradient along the wall. The threshold of linearity of the instability-wave response with respect to the freestream amplitude is investigated. The applicability of the linearized form of disturbance equations for this receptivity problem is also demonstrated.

Lin, Nay

385

Convergence of Wnt and FGF signals in the genesis of posterior neural plate through activation of the Sox2 enhancer N-1.  

PubMed

The expression of the transcription factor gene Sox2 precisely marks the neural plate in various vertebrate species. We previously showed that the Sox2 expression prevailing in the neural plate of chicken embryos is actually regulated by the coordination of five phylogenetically conserved enhancers having discrete regional coverage, among which the 420-bp long enhancer N-1, active in the node-proximal region, is probably involved directly in the genesis of the posterior neural plate. We investigated the signaling systems regulating this enhancer, first identifying the 56-bp N-1 core enhancer (N-1c), which in a trimeric form recapitulates the activity of the enhancer N-1. Mutational analysis identified five blocks, A to E, that regulate the enhancer N-1c. Functional analysis of these blocks indicated that Wnt and FGF signals synergistically activate the enhancer through Blocks A-B, bound by Lef1, and Block D, respectively. Fgf8b and Wnt8c expressed in the organizer-primitive streak region account for the activity in the embryo. Block E is essential for the repression of the enhancer N-1c activity in the mesendodermal precursors. The enhancer N-1c is not affected by BMP signals. Thus, Wnt and FGF signals converge to activate Sox2 expression through the enhancer N-1c, revealing the direct involvement of the Wnt signal in the initiation of neural plate development. PMID:16354715

Takemoto, Tatsuya; Uchikawa, Masanori; Kamachi, Yusuke; Kondoh, Hisato

2005-12-14

386

Generalization of the Twist-Kirchhoff Theory of Plate Elements to Arbitrary Quadrilaterals and Assessment of Convergence.  

National Technical Information Service (NTIS)

We generalize the recently introduced twist-Kirchhoff theory of rectangular plate elements to arbitrary quadrilateral elements. A key feature is the use of Raviart-Thomas vector-field approximations for rotations. To preserve continuity of the normal comp...

H. A. Santos J. A. Evans T. J. Hughes

2011-01-01

387

Rupture behavior of a moderate earthquake (MW 5.9, April 2006) and its close relation with the 2003 Chengkung earthquake (MW 6.8) at the southern termination of the plate boundary, southeast Taiwan  

NASA Astrophysics Data System (ADS)

The Taiwanese orogen is the result of the active and vigorous collision between the Eurasian and the Philippine Sea plates. In this strong convergence context, a one month-long earthquake sequence composed of two mainshocks of magnitude 6 occurred in April 2006 in the Taitung area. The first mainshock (T1) mobilized a structure just west to the plate boundary, while the second one (T2) is located on the other side. In order to retrieve the exact fault geometry of T2, we inverted waveforms from stations located at local and teleseismic distances. We performed a grid search on strike and dip (each strike-dip couple defining a geometry) considering the source as a point source then as an extended source. In the last case, a simple average over stations misfit failed to isolate a precise geometry. To overcome this problem, we used a more statistical approach on the distribution of misfits to define the best geometry. Comparing the best model to local structures, it appears the generative fault was the plate boundary that rotates from a strike pointing at N20°E north of the event to N0°E in T2 area with an identical eastward dip of 35°. For this model, the fault slip inversion provides a critical slip of 3.5 cm above which slip, rake and rupture time are constrained with uncertainties of 29%, 14° and 0.47 s respectively. The average slip along the rupture was 20 cm with a maximum of 46 ± 13 cm. The movement was inverse with a minor left-lateral component similar to the faulting behavior of the plate boundary. In addition, the slip pattern of T2 is contained within the southern portion of the deepest segment of the plate boundary and at the edge of the rupture area of the 2003 Chengkung earthquake (MW 6.8), a large event also generated by the plate boundary but 2.5 years earlier. After 1 s of aseismic spreading, the rupture propagated seismically and circularly outward before being stopped by the fault bending.

Mozziconacci, Laetitia; Huang, Bor-Shouh; Delouis, Bertrand; Lee, Jian-Cheng; Lee, Shiann-Jong

2013-10-01

388

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

389

Real time data from the Plate Boundary Observatory continuous GPS network  

NASA Astrophysics Data System (ADS)

EarthScope's Plate Boundary Observatory (PBO) runs a network of 1,100 continuous GPS stations in North America and has the potential to be a major provider of real-time GPS data for scientific research, hazard monitoring and survey control. PBO is planning to implement real time data flow for its three volcanic subnetworks (at Mt. Saint Helens and Alaksa's Akutan and Unimak Islands) to maximize the return of scientifically important data in the event of an eruption that destroys the installations. GPS sites with collocated instruments for meteorological measurement are also targeted for both GPS and met data streaming in the near future. On a larger scale, the USGS and a handful of academic institutions are doing research on integrating GPS into earthquake early warning (EEW) networks. The implementation of GPS- based EEW will involve real time streaming from GPS sites on major faults and in areas of high seismic hazard, and PBO is partnering with the USGS to help develop the first implementation of this early warning capability. Finally, planning is underway to develop open statewide real time networks to serve surveying communities and the general public, and PBO is positioned to be a key data provider for these efforts as well. PBO has been operating a pilot program to provide real-time GPS streams to the public from 75+ stations from the Salton Sea to Alaska. PBO's streaming data is provided exclusively via the NTrip protocol, from servers located at UNAVCO headquarters in Boulder, CO. The formats supported are BINEX and RTCM 2.3 at 1 second sampling, with RTCM 3.0 to be added in the near future. Access to PBO data streams is currently unrestricted and users are free to rebroadcast these streams provided they do not charge for these services. Our experience with this program indicates that we are technically capable of streaming real time GPS data from most of our network using existing telemetry, although PBO's IT infrastructure would have to be upgraded to support an expansion of the current system.

Borsa, A. A.; Jackson, M.; Feaux, K.; Mencin, D.; Smith, S.; Smith, J.; Torres, D.; Snett, L.

2008-12-01

390

The EarthScope Plate Boundary Observatory (PBO) High-rate Real-time Cascadia network  

NASA Astrophysics Data System (ADS)

As part of the 2009 American Recovery and Reinvestment Act (ARRA), NSF is investing in onshore-offshore instrumentation to support studies of the Cascadia margin. EarthScope's Plate Boundary Observatory (PBO) is upgrading 232 of its GPS stations in the Pacific Northwest to high-rate sampling and real-time telemetry and providing streaming data from this network to the public for scientific research, education, and hazard monitoring. This effort expands UNAVCO’s real-time GPS operations beyond its original pilot project of 100 stations to include a comprehensive regional network that spans the states of Washington and Oregon, and extends south into California to the Mendocino triple junction. By blanketing the Pacific Northwest with real-time GPS coverage, the NSF is hoping to create a natural laboratory in an area of great scientific interest and high geophysical hazard in order to spur new volcano and earthquake research opportunities. Streaming high-rate data in real-time will enable researchers to routinely analyze for strong ground motion monitoring and earthquake hazards mitigation. At stations with collocated meteorological instruments, met data is being streamed as well, opening the possibility for combined GPS/met processing in real time by the atmospheric community. Funding for field upgrades provide for the installation of 3G capable modems or high speed data radios, as well as for updating the power at each location. Finally, the new funding also expands opportunities for research using high-rate GPS data from a large-aperture network, since 1 Hz streams will be permanently archived and freely available via FTP. PBO deployed new data distribution software in June 2010, to which stations being added soon after field upgrades have been completed. PBO is currently providing 1Hz-streaming data in BINEX, RTCM2.3 and RTCM 3.0 formats via the NTrip protocol, from servers located at UNAVCO headquarters in Boulder, CO. Data latency varies according to the telemetry deployed at each station, but typically ranges from 0.5~2.0 seconds given recent improvements in PBO's real-time streaming capabilities and advances in the communications infrastructure.

Austin, K. E.; Borsa, A. A.; Feaux, K.; Jackson, M. E.; Williams, T. B.

2010-12-01

391

Real Time Data From the Plate Boundary Observatory Continuous GPS Network  

NASA Astrophysics Data System (ADS)

EarthScope's Plate Boundary Observatory (PBO) runs a network of 1,100 continuous GPS stations in North America and has the potential to be a major provider of real-time GPS data for scientific research, hazard monitoring and survey control. PBO is planning to implement real time data flow for its three volcanic subnetworks (at Mt. Saint Helens and Alaksa's Akutan and Unimak Islands) to maximize the return of scientifically important data to detect the onset of eruptive activity. GPS sites with collocated instruments for meteorological measurement are also targeted for both GPS and met data streaming in the near future. On a larger scale, the USGS and a handful of academic institutions are doing research on integrating GPS into earthquake early warning (EEW) networks. The implementation of GPS-based EEW will involve real time streaming from GPS sites on major faults and in areas of high seismic hazard, and PBO is partnering with the USGS to help develop the first implementation of this early warning capability. Finally, planning is underway to develop open statewide real time networks to serve surveying communities and the general public, and PBO is positioned to be a key data provider for these efforts. PBO has been operating a pilot program to provide real-time GPS streams to the public from 75+ stations from the Salton Sea to Alaska. PBO's streaming data is provided exclusively via the NTrip protocol, from servers located at UNAVCO headquarters in Boulder, CO. The formats supported are BINEX and RTCM 2.3 at 1 second sampling, with RTCM 3.0 to be added in the near future. Access to PBO data streams is currently unrestricted and users are free to rebroadcast these streams provided they do not charge for these services. Our experience with this program indicates that we are technically capable of streaming low-latency, real time GPS data from most of our network using existing telemetry, although PBO's IT infrastructure would have to be upgraded to support an expansion of the current system.

Jackson, M.; Borsa, A.; Feaux, K.; Walls, C.; Mencin, D.

2009-05-01

392

Building a Global Data Network for Studies of Earth Processes at the World's Plate Boundaries  

NASA Astrophysics Data System (ADS)

The international geoscience community is engaged in scientifically aligned goals to understand the fundamental processes of crustal formation, modification and destruction at the Earth's plate boundaries through broad multi- disciplinary initiatives such as the InterRidge and InterMARGINS programs. These programs involve the collection of unique data sets during oceanic and terrestrial expeditions and subsequent laboratory work conducted by research institutions around the globe. These international research efforts would benefit significantly if data collections maintained as national efforts could be better linked and broader access were initiated. At present there are no formal agreements within these programs for data sharing between foreign partners. A workshop was convened in May 2007, jointly sponsored and funded by MARGINS, InterMARGINS, InterRidge, Ridge2000, the US National Science Foundation, and the German project "The Future Ocean", to explore current opportunities and challenges for international data exchange to support marine geoscience research broadly. Participants from 14 countries discussed technological, organizational, and cultural issues for building a global data network and agreed on a set of recommendations regarding science user needs, data documentation, data publication, metadata interoperability, and opportunities and obstacles for international data sharing. They underscored that (1) open public access to data is fundamental to verifiable scientific progress; (2) uniform best practices and standards for data acquisition, data submission to data centers, and data publication need to be developed and used routinely within the international community, facilitated by tools that automate metadata acquisition in the field and in the lab; (3) the proliferation of metadata standards needs to be minimized to achieve a uniform approach for scientific metadata building upon the work of existing community-based projects; (4) data centers should expose their data resources via web services to enable data access through programmatic interfaces and expand options for data analysis and visualization; (5) international programs and bodies such as GEOSS, eGY, and ICSU should be leveraged to promote an initiative for a global data network; (6) a dedicated task group is needed to advance the implementation of a global data network along with special interest groups to share experience and solutions on issues concerning metadata and interfaces. Several immediate next steps were identified to initiate the implementation of these recommendations.

Lehnert, K. A.; Carbotte, S.; Tsuboi, S.; Weinrebe, W.

2007-12-01

393

Crustal Thickness Variations Along the Southeastern Caribbean Plate Boundary From Teleseismic and Active Source Seismic Data  

NASA Astrophysics Data System (ADS)

Insight into the topography of the Moho discontinuity beneath Venezuela has been progressively gained since the 1990's through seismic refraction studies carried out in the south and east of the country. More recently, both active and passive, land and marine seismic data were acquired by the U.S. BOLIVAR and Venezuelan GEODINOS projects to understand accretion processes and mechanisms for continental growth. The passive component includes an 18-month deployment of 27 PASSCAL broadband seismographs, a 12-month deployment of 15 OBSIP broadband instruments and an ongoing deployment of 8 Rice broadband seismometers. Additionally, data from the 34 BB stations of the national seismic network of Venezuela and the GSN SDV station, give a seismic dataset from 84 stations covering an area of ~750,000 km2. The active component includes 4 onshore-offshore refraction/wide angle reflection profiles as well as the recording of airgun blasts from offshore seismic lines by BB stations in mainland Venezuela and the Leeward Antilles. This abundance of datasets allows us to estimate Moho depths using different methods such as receiver functions, and forward and inverse modeling of wide-angle datasets, but also poses the challenge of reconciling the different values obtained to achieve robust results. Generally the active source and receiver function estimates are close to one another. We present a composite crustal thickness map showing a highly variable crustal thicknesses ranging from 15 km beneath the Caribbean LIP, to ~55 km beneath eastern Venezuela. Crustal thickness is strongly correlated with geologic terranes, but not always as expected. The thickest crust is found to exist in the east of the country, beneath the sedimentary basins north of the Orinoco River where depth to Moho exceeds 50 km. Crustal thickness beneath most of the Precambrian Guayana Shield is fairly constant at ~38 km . In contrast, we observe relatively thin (~25-30 km) crust in the eastern and western coastal mountains, suggesting a significant portion of the high topography of the costal mountain ranges has a dynamic origin. Crustal thickness changes of more than 10km are observed crossing the coast in the plate boundary zone, but are not always directly associated with the surface expression of the strike-slip fault system.

Bezada, M. J.; Niu, F.; Baldwin, T. K.; Pavlis, G.; Vernon, F.; Rendón, H.; Zelt, C. A.; Schmitz, M.; Levander, A.

2006-12-01

394

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

395

Update on Plate Boundary Observatory (PBO) Activities in the PNW Region  

NASA Astrophysics Data System (ADS)

As of September 2005 The Plate Boundary Observatory (PBO), part of the larger NSF-funded EarthScope project, is completing year 2 in the installation phas