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1

Faulting within the Pacific plate at the Mariana Trench: Implications for plate interface coupling and subduction of hydrous minerals  

NASA Astrophysics Data System (ADS)

investigate faulting within the incoming Pacific plate at the Mariana subduction trench to understand stresses within the bending plate, regional stresses acting upon the plate interface, and the extent of possible faulting-induced mantle serpentinization. We determine accurate depths by inverting teleseismic P and SH waveforms for earthquakes occurring during 1990-2011 with Global Centroid Moment Tensor (GCMT) solutions. For earthquakes with Mw 5.0+, we determine centroid depths and source time functions and refine the fault parameters. Results from Central Mariana indicate that all earthquakes are extensional and occur at centroid depths down to 11 km below the Moho. At the Southern Mariana Trench, extensional earthquakes continue to 5 km below the Moho. One compressional earthquake at 34 km below the seafloor suggests stronger plate interface coupling here. In addition, we model the stress distribution within the Pacific plate along two bathymetric profiles extending seaward from the Mariana subduction trench axis to better understand whether our earthquake depth solutions match modeled scenarios for plate bending under applied external forces. Results from our flexure models match the locations of extensional and compressional earthquakes and suggest that the Pacific plate at Southern Mariana is experiencing larger, compressional stresses, possibly due to greater interplate coupling. Additionally, we conclude that if extensional faulting promotes the infiltration of water into the subducting plate mantle, then the top 5-15 km of the Pacific plate mantle are partially serpentinized, and a higher percentage of serpentinization is located near the Central Mariana trench where extensional events extend deeper.

Emry, Erica L.; Wiens, Douglas A.; Garcia-Castellanos, Daniel

2014-04-01

2

Imaging megathrust zone and Yakutat/Pacific plate interface in Alaska subduction zone  

NASA Astrophysics Data System (ADS)

We image the subducted slab underneath a 450 km long transect of the Alaska subduction zone. Dense stations in southern Alaska are set up to investigate (1) the geometry and velocity structure of the downgoing plate and their relation to slab seismicity, and (2) the interplate coupled zone where the great 1964 (magnitude 9.3) had greatest rupture. The joint teleseismic migration of two array datasets (MOOS, Multidisciplinary Observations of Onshore Subduction, and BEAAR, Broadband Experiment Across the Alaska Range) based on teleseismic receiver functions (RFs) using the MOOS data reveal a shallow-dipping prominent low-velocity layer at ~25-30 km depth in southern Alaska. Modeling of these RF amplitudes shows a thin (3-6.5 km) low-velocity layer (shear wave velocity less than 3 km/s), which is ~20-30% slower than normal oceanic crustal velocities, between the subducted slab and the overriding North America plate. The observed low-velocity megathrust layer (with Vp/Vs ratio exceeding 2.0) may be due to a thick sediment input from the trench in combination of elevated pore fluid pressure in the channel. The subducted crust below the low-velocity channel has gabbroic velocities with a thickness of 11-15 km. Both velocities and thickness of the low-velocity channel abruptly increase as the slab bends in central Alaska, which agrees with previously published RF results. Our image also includes an unusually thick low-velocity crust subducting with a ~20 degree dip down to 130 km depth at approximately 200 km inland beneath central Alaska. The unusual nature of this subducted segment has been suggested to be due to the subduction of the Yakutat terrane. Subduction of this buoyant crust could explain the shallow dip of the thrust zone beneath southern Alaska. We also show a clear image of the Yakutat and Pacific plate subduction beneath the Kenai Peninsula, and the along-strike boundary between them at megathrust depths. Our imaged western edge of the Yakutat terrane, at ~30-42 km depth in the central Kenai along the megathrust, aligns with the western end of the geodetically locked patch with high slip deficit, and coincides with the boundary of aftershock events from the 1964 earthquake. It seems plausible that this sharp change in the nature of the downgoing plate controls the slip distribution of great earthquakes on this plate interface.

Kim, Y.; Abers, G. A.; Li, J.; Christensen, D. H.; Calkins, J. A.

2012-12-01

3

Imaging megathrust zone and Yakutat/Pacific plate interface in Alaska subduction zone  

NASA Astrophysics Data System (ADS)

We image the subducted slab underneath a 450 km long transect of the Alaska subduction zone. Dense stations in southern Alaska are set up to investigate (1) the geometry and velocity structure of the downgoing plate and their relation to slab seismicity, and (2) the interplate coupled zone where the great 1964 (magnitude 9.3) had greatest rupture. The joint teleseismic migration of two array datasets (MOOS, Multidisciplinary Observations of Onshore Subduction, and BEAAR, Broadband Experiment Across the Alaska Range) based on teleseismic receiver functions (RFs) using the MOOS data reveal a shallow-dipping prominent low-velocity layer at ~25-30 km depth in southern Alaska. Modeling of these RF amplitudes shows a thin (<6.5 km) low-velocity layer (shear wave velocity of ~3 km/s), which is ~20-30% slower than normal oceanic crustal velocities, between the subducted slab and the overriding North American plate. The observed low-velocity megathrust layer (with P-to-S velocity ratio (Vp/Vs) exceeding 2.0) may be due to a thick sediment input from the trench in combination of elevated pore fluid pressure in the channel. The subducted crust below the low-velocity channel has gabbroic velocities with a thickness of 11-12 km. Both velocities and thickness of the low-velocity channel abruptly increase as the slab bends in central Alaska, which agrees with previously published RF results. Our image also includes an unusually thick low-velocity crust subducting with a ~20 degree dip down to 130 km depth at approximately 200 km inland beneath central Alaska. The unusual nature of this subducted segment has been suggested to be due to the subduction of the Yakutat terrane. We also show a clear image of the Yakutat and Pacific plate subduction beneath the Kenai Peninsula, and the along-strike boundary between them at megathrust depths. Our imaged western edge of the Yakutat terrane, at 25-30 km depth in the central Kenai along the megathrust, aligns with the western end of the geodetically locked patch with high slip deficit, and coincides with the boundary of aftershock events from the 1964 earthquake. It seems plausible that this sharp change in the nature of the downgoing plate controls the slip distribution of great earthquakes on this plate interface.

Kim, Y.; Abers, G. A.; Li, J.; Christensen, D. H.; Calkins, J. A.

2013-05-01

4

Alaska Megathrust 2: Imaging the megathrust zone and Yakutat/Pacific plate interface in the Alaska subduction zone  

NASA Astrophysics Data System (ADS)

image the slab underneath a 450 km long transect of the Alaska subduction zone to investigate (1) the geometry and velocity structure of the downgoing plate and their relationship to slab seismicity and (2) the interplate coupled zone where the great 1964 earthquake (Mw 9.2) exhibited the largest amount of rupture. The joint teleseismic migration of two array data sets based on receiver functions (RFs) reveals a prominent, shallow-dipping low-velocity layer at ~25-30 km depth in southern Alaska. Modeling of RF amplitudes suggests the existence of a thin layer (Vs of ~2.1-2.6 km/s) that is ~20-40% slower than underlying oceanic crustal velocities, and is sandwiched between the subducted slab and the overriding plate. The observed megathrust layer (with Vp/Vs of 1.9-2.3) may be due to a thick sediment input from the trench in combination with elevated pore fluid pressure in the channel. Our image also includes an unusually thick low-velocity crust subducting with a ~20° dip down to 130 km depth at ~200 km inland beneath central Alaska. The unusual nature of this subducted segment results from the subduction of the Yakutat terrane crust. Our imaged western edge of the Yakutat terrane aligns with the western end of a geodetically locked patch with high slip deficit, and coincides with the boundary of aftershock events from the 1964 earthquake. It appears that this sharp change in the nature of the downgoing plate could control the slip distribution of great earthquakes on this plate interface.

Kim, YoungHee; Abers, Geoffrey A.; Li, Jiyao; Christensen, Douglas; Calkins, Josh; Rondenay, Stéphane

2014-03-01

5

Earthscope Science Target: Temporal and Spatial Patterns of Silent Earthquake Recurrence Along the Cascadia Plate Interface From the Pacific Northwest Geodetic Array  

NASA Astrophysics Data System (ADS)

Earthscope proposes to observe the deforming plate margin over a broad range of temporal scales using seismology, strain meters, continuous GPS geodesy, and paleoseismology. The recent discovery of the periodic recurrence of creep events on the deep Cascadia plate interface point to the potential and synergistic strength of such integrated data sets. Over the last decade, GPS observations have revealed that deep creep events recur with a 14.5 month periodicity, originating in the northern Puget Sound region and sweeping both along strike and up-dip. To date, the Cascadia events have only been detected by GPS; observed periodicity poises us to optimize Earthscope to observe these phenomena across their full frequency range. The Pacific Northwest Geodetic Array (PANGA) characterizes active deformation along the Cascadia margin using an array of continuous GPS stations that monitor a range of temporal and spatial scales. The displacement fields and propagation signatures for four transient deformation events since 1998 have been mapped in a complete four-dimensional sense; baseline results from as early as 1992 suggest at least an additional four such events. These periodic events nucleate in northern Puget Sound and result in characteristic offsets at Alberthead near Victoria, B.C. but differ in their geographic extent and propagation sequence. An analysis of the displacement fields for each event is consistent with several centimeters of movement along the subduction zone interface between the Juan de Fuca and North American plates. Strain release along the deeper plate contact within the Cascadia subduction zone in the Pacific Northwest is not continuous. In the north, episodic creep front propagation is observed in periodic slow earthquakes and in southern Washington and farther south, a more sporadic record reveals similar events, but without the striking periodicity observed to the north. Several subtle events south of the arch in the Juan de Fuca slab share diagnostic features of such creep episodes: discrete reversals in subduction-parallel contraction and propagation patterns that persist over weeks at individual stations and sweep through the network with coherent propagation fronts.

Miller, M.; Johnson, D. J.; Melbourne, T.; Sumner, W. Q.

2002-12-01

6

Pliocene change in Pacific-plate motion  

Microsoft Academic Search

The absolute motion of the Pacific plate has been nearly constant during the past 15 Myr, but Epp1 recognized that some change took place between 15 Myr and the present, and tentatively chose 1 Myr for the time of the change. Cox and Engebretson2 found a change in Pacific absolute motion based on hotspot tracks and a change in Pacific-Antarctic

Fred F. Pollitz

1986-01-01

7

Deformations of the northwestern Pacific plate  

NASA Astrophysics Data System (ADS)

The style and age of deformations of the sedimentary cover and basaltic basement in the northwestern basin of the Pacific Ocean were studied based on seismic data coordinated with the results of deep-water drilling. The deformations are widespread not only on the oceanic slope of the trench as a plate boundary, but also within the plate especially close to the large Hokkaido, Tuscarora, and Seismikov fracture zones and the Hokkaido Swell. The most intense deformation took place at the Pliocene-Quaternary boundary. Abundant diapirs related to the plastic serpentinite layer at base of the crust indicate that gravity tectonics primarily develops here.

Patrikeev, V. N.

2013-09-01

8

Reconciling late Neogene Pacific absolute and relative plate motion changes  

Microsoft Academic Search

New models of Pacific absolute plate motion relative to hot spots and models of relative plate motion involving the Pacific plate all agree there was a significant change in the late Neogene (Chron 3A, ?5.89 Ma), reflecting a more northerly absolute motion than previously determined. As Pacific absolute plate motion became slightly more northerly, left-stepping transform segments came under compression.

Paul Wessel; Loren W. Kroenke

2007-01-01

9

Focal Mechanisms and Plate Tectonics of the Southwest Pacific  

Microsoft Academic Search

Ninety-six new focal mechanisms were determined for earthquakes on the belt of seismic activity separating the Pacific and Australian plates. The direction of convergence of these plates varies from Ntg-SW to E-W. The Australian plate underthrusts the Pacific plate to the ENE under the Solomon and New Hebrides islands and overthrusts the Pacific to the east along the Tonga-Kermadec arc

Tracy Johnson; Peter Molnar

1972-01-01

10

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

Microsoft Academic Search

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

William R. Keller

2005-01-01

11

Warping and cracking of the Pacific plate by thermal contraction  

Microsoft Academic Search

Lineaments in the gravity field and associated chains of volcanic ridges are widespread on the Pacific plate but are not yet explained by plate tectonics. Recent studies have proposed that they are warps and cracks in the plate caused by uneven thermal contraction of the cooling lithosphere. We show that the large thermoelastic stress produced by top-down cooling is optimally

David Sandwell; Yuri Fialko

2004-01-01

12

GPS determination of current Pacific North American plate motion  

Microsoft Academic Search

Global Positioning System (GPS) data, collected by campaign-style GPS experiments at five sites along the Gulf of California in 1996 and 1998, determine a locally based estimate for current relative motion between the Pacific and North American plates. At the mouth of the Gulf of California, the Pacific plate moves 50.4 ± 3.4 mm\\/yr, along an azimuth of N59.0°W ±

Kyle Antonelis; Daniel J. Johnson; M. Meghan Miller; Randy Palmer

1999-01-01

13

Pacific Rim and Pacific Plate Tectonism Associated With the Hawaiian Emperor Bend  

NASA Astrophysics Data System (ADS)

Widespread Pacific Rim and Pacific plate tectonism both appear to be closely associated with a pronounced change in Pacific absolute plate motion (APM) that occurred about 43 Ma as revealed by the Hawaiian Emperor Bend. In the Western Pacific prior to the change, as the Pacific plate moved toward the north, Proto Izu -- Bonin -- Mariana (IBM) subduction was already occurring by 49 Ma, perhaps as early as 52 Ma near the northern end of the Proto IBM, evidenced by the emplacement of boninites in the forearc (Cosca et al., 1998). If the Philippine Basin -- Pacific plate circuit is traced though the Coral Sea basin after closing the Ayu and Sorel troughs, it is evident that the alignment of the Proto IBM (Kyushu -- Palau) subduction zone roughly paralleled the Pacific APM during the initiation of subduction. At ~ 43 Ma, Proto-IBM Trench subduction rapidly increased, possibly causing the major change in Pacific (and Australia) APM that produced the prominent bend in the Hawaiian-Emperor chain. This change also produced a the minor bend in the Louisville chain, as the Pacific plate began to move west-northwestward, as well as at least five more noticeable bends in other seamount chains across the Central Pacific. In the Northeastern Pacific, the expansive magmatic activity, which occurred during the early stage of Aleutian Arc growth between 55--50 Ma, began to wane between 45 and 40 Ma (Scholl et al., 1987). After the 43 Ma change in Pacific APM, the Aleutian subduction zone began to accommodate dextral slip at its western end, as well as continuing convergence at its eastern end. To the south, in the Eastern Pacific, Ridge propagation began about 43 Ma both north and south of the Murray FZ (extending southward to the Clarion FZ). Much farther to the south, changes are also apparent in the Pacific -- Antarctic spreading pattern at ~43 Ma. In the Central Pacific, following the 43 Ma change in Pacific plate motion, intraplate subduction began along the Manus -- North Solomon -- Vitiaz (Melanesian) Trench, which was aligned parallel to the post 43 Ma Pacific APM. Subduction was heralded by metamorphic events in the Solomon Islands' Florida Group and Eastern Belt Islands that occurred between ~44 and ~35 Ma (Neef and McDougal, 1976), after which the earliest Lemau Intrusives were emplaced between 38 and 32 Ma in New Ireland (Stewart and Sandy, 1988) near the western end of the Melanesian Arc. To the southwest, on the Australia Plate, the Louisiade Plateau also formed over the Lord Howe Hotspot about 43 Ma as a concomitant change in Australia APM also occurred.

Sterling, A.; Kroenke, L. W.; Wessel, P.; Harada, Y.

2002-12-01

14

ConcepTest: Pacific Plate Motion  

NSDL National Science Digital Library

Review the map of the plates below and predict which pair of locations is moving closer together as a result of plate tectonics? a. Bombay and Sydney b. Hawaii and Tokyo c. New York and London d. Cape Town and ...

15

Diffuse interseismic deformation across the Pacific North America plate boundary  

Microsoft Academic Search

Crustal movements and deformation within the diffuse Pacific North America (Pa-NA) plate boundary are dominated by the right-lateral motion between the two plates. By using the Pa-NA pole of rotation (PoR) spherical coordinate system, we decompose observed crustal movements into parallel and normal components to the Pa-NA plate motion. We transformed the 840 velocity vectors of the Southern California Earthquake

Shimon Wdowinski; Bridget Smith-Konter; Yehuda Bock; David Sandwell

2007-01-01

16

Spatial and temporal evolution of the subducting Pacific plate structure along the western Pacific margin  

Microsoft Academic Search

Tomographic images of the subducting Pacific plate beneath the Izu-Bonin-Mariana arc illustrate a progression of geometries from shallow dipping to vertical from north to south along the arc. Recent advances in technology and inversion techniques have improved resolution of slab structure beneath the western Pacific island arcs, but reasons for the variation in geometry and morphology are still poorly understood.

M. S. Miller; B. L. N. Kennett; V. G. Toy

2006-01-01

17

Spatial and temporal evolution of the subducting Pacific plate structure along the western Pacific margin  

Microsoft Academic Search

(1) Tomographic images of the subducting Pacific plate beneath the Izu-Bonin-Mariana arc illustrate a progression of geometries from shallow dipping to vertical from north to south along the arc. Recent advances in technology and inversion techniques have improved resolution of slab structure beneath the western Pacific island arcs, but reasons for the variation in geometry and morphology are still poorly

M. S. Miller; B. L. N. Kennett; V. G. Toy

2006-01-01

18

What controls the seismogenic plate interface in subduction zones?  

NASA Astrophysics Data System (ADS)

The greatest earthquakes occur on the seismogenic plate interface of subduction zones. We need to understand what controls the updip and downdip edges of this seismogenic zone. For the circum-Pacific subduction zones that generate great earthquakes, the downdip edge is at a depth of about 40 km, but with significant variations. Several mechanisms might control this transition from seismogenic to aseismic slip. Tichelaar and Ruff [1993] argue that one or two critical temperatures can explain the global observations. The model with two critical temperatures invokes two different upper plate rock types, crust and mantle rocks. In this paper, we investigate the correlation between the location of the downdip edge with the location of the coastline. We find a statistically significant correlation between these two variables for the major circum-Pacific subduction zones. Is this correlation a coincidence, or is it indicative of deeper fundamental processes? We offer a simple unifying explanation: the intersection of the overlying plate's Moho with the top of the subducting slab determines both the downdip edge of the seismogenic zone, and the coastline above. This explanation implies that rocks in the subduction zone mantle wedge are aseismic.

Ruff, Larry J.; Tichelaar, Bart W.

19

Swimming Across the Pacific: A Swimming Interface for Virtual Reality  

Microsoft Academic Search

We have created a new locomotion interface for swimming and floating in a virtual ocean in a VR environment as part of our Swimming Across the Pacific (SAP) artwork1. The artwork is motivated by Alzek Mische's Swimming Across the Atlantic (Mishe 1982) performed in 1982. In the SAP artwork, we swim across the Pacific Ocean using the swim- ming apparatus

Sidney Fels; Yuichiro Kinoshita; Tzu-Pei Grace Chen; Yasufumi Takama; Kenji Funahashi; Ashley Gadd

20

The Australia-Pacific boundary and Cenozoic plate motions in the SW Pacific: Some constraints from Geosat data  

Microsoft Academic Search

Finite poles of Australia-Pacific rotation are calculated using a three-plate (Australia-Antarctica-Pacific) model and published Geosat data analyses of the Indian and Pacific Oceans (GEOS-3P solution). Features identified on maps of Geosat data from SW of New Zealand are used to determine a new best fit finite pole for the prerift (mid Eocene; ~45 Ma) configuration of the Australia-Pacific plate boundary

Rupert Sutherland

1995-01-01

21

Tectonic implications of post-30 Ma Pacific and North American relative plate motions  

Microsoft Academic Search

The Pacific plate moved northwest rela- tive to North America since 42 Ma. The rapid half rate of Pacific-Farallon spread- ing allowed the ridge to approach the con- tinent at about 29 Ma. Extinct spreading ridges that occur offshore along 65% of the margin (Lonsdale, 1991) document that fragments of the subducted Farallon slab became captured by the Pacific plate

Tom Parsons

22

Relative motions of the Australian, Pacific and Antarctic plates estimated by the Global Positioning System  

Microsoft Academic Search

Global Positioning System (GPS) measurements spanning approximately 3 years have been used to determine velocities for 7 sites on the Australian, Pacific and Antarctic plates. The site velocities agree with both plate model predictions and other space geodetic techniques. We find no evidence for internal deformation of the interior of the Australian plate. Wellington, New Zealand, located in the Australian-Pacific

Kristine M. Larson; Jeff Freymueller

1995-01-01

23

Pacific-North America Plate Tectonics of the Neogene Southwestern United States: An Update  

Microsoft Academic Search

We use updated rotations within the Pacific-Antarctica-Africa-North America plate circuit to calculate Pacific-North America plate reconstructions for times since chron 13 (33 Ma). The direction of motion of the Pacific plate relative to stable North America was fairly steady between chrons 13 and 4, and then changed and moved in a more northerly direction from chron 4 to the present

Tanya Atwater; Joann Stock

1998-01-01

24

Trans-Pacific Bathymetry Survey crossing over the Pacific, Antarctic, and Nazca plates  

NASA Astrophysics Data System (ADS)

Multibeam bathymetric data reveals seafloor fabrics, i.e. abyssal hills and fracture zones, distribution of seamounts and/or knolls and are usually smaller than the detectable size by global prediction derived from satellite altimetry. The seafloor depths combined with shipboard gravity data indicate the structure of oceanic lithosphere, thermal state, and mantle dynamics and become more accurate data set to estimate fine-scale crustal structures and subsurface mass distribution. We present the ~22000 km long survey line from the northeast Japan through to the equator at the mid-Pacific on to the southwest Chilean coast collected during the JAMSTEC R/V Mirai MR08-06 Leg-1 cruise in January-March 2009. The cruise was as a part of SORA2009 (Abe, 2009 Cruise report) for geological and geophysical studies in the southern Pacific, and was an unprecedented opportunity to collect data in the regions of the Pacific Ocean where it has been sparsely surveyed using state-of-the-art echo-sounding technology. Our multibeam bathymetric and shipboard gravity survey track crossed over the Pacific, the Antarctic, and the Nazca plates, and covered lithospheric ages varying from zero to 150 Ma. Strikes of lineated abyssal hills give critical evidences for future studies of the plate reconstruction and tectonic evolution of the old Pacific Plate because magnetic lineations are unconstrained on the seafloor in the Cretaceous magnetic quiet (125-80 Ma) zone. Consecutive trends of lineated abyssal hills and fracture zones indicate stable tectonic stress field originated from the Pacific Antarctic Ridge (PAR) and the Chile Ridge spreading systems. The seafloor fabric morphology revealed a clear boundary between the PAR and the Chile Ridge domains. The observed bathymetric boundary is probably a part of a trace of the Pacific-Antarctic-Farallon (Nazca) plate's triple junction. The result will be constraint for future studies of the plate reconstruction and tectonic evolution of the PAR, the Chile Ridge, and the Antarctic Plate. Fluctuation of the seafloor fabric strikes on Chile Ridge off-ridge flank suggests instability of tectonic stress field. The seafloor fabric may be largely influenced by the tectonic structure of offsets at fracture zones system separated by short ridge segments. The offset length by fracture zones is short at the flank. The offset of fracture zone increases with age decrease due to ridge jumps (Bourgois et al., 2000 JGR) or change in spreading rates (Matsumoto et al., 2013 Geochem. J.). The dominant stress may vary spatially or temporally, during the fracture zone evolution. Abyssal hills elongated in the direction originated from the Chile Ridge system and fracture zones having long offset lengths distinctly bisect at right angles. We also detected many small seamounts and knolls superimposed on the seafloor fabrics. These are considered to be constructed by excess magmatism at a mid-ocean ridge or intra-plate volcanism.

Abe, N.; Fujiwara, T.

2013-12-01

25

Fast Paleogene Motion of the Pacific Hotspots from Revised Global Plate Circuit Constraints  

NASA Technical Reports Server (NTRS)

Major improvements in late Cretaceous-early Tertiary Pacific-Antarctica plate reconstructions, and new East-West Antarctica rotations, allow a more definitive test of the relative motion between hotspots using global plate circuit reconstructions with quantitative uncertainties.

Raymond, C.; Stock, J.; Cande, S.

2000-01-01

26

Relative Velocities of the Pacific, North America and Cocos Plates in the Middle America Region.  

National Technical Information Service (NTIS)

Relative velocities of crustal plates are used for the first time to test the conventional assumption that such plates are rigid. Spreading rates derived from magnetic anomaly data, fracture zone trends, and earthquake mechanisms at the Pacific-North Amer...

R. L. Larson C. G. Chase

1969-01-01

27

Pacific-North America plate motions - New results from very long baseline interferometry  

NASA Technical Reports Server (NTRS)

The state of Pacific-North America plate interaction is updated using newest VLBI measurements and newly developed rigid plate tectonic models. Particular attention is given to examining the extent of relative motion between the Pacific plate and the North America plate as measured from their stable interiors, the evidence of Pacific plate deformation off the central California coast, and the distribution of path integrated deformaton east of the San Andreas fault. The information obtained on these questions is discussed in the framework of implications for lithospheric rheology and earthquake hazard.

Ward, Steven N.

1990-01-01

28

Azimuthal anisotropy layering and plate motion in the Pacific Ocean  

NASA Astrophysics Data System (ADS)

We recently developed a three dimensional radially and azimuthally anisotropic model of the upper mantle in north America, using a combination of long-period 3-component surface and overtone waveforms, and SKS splitting measurements (Yuan and Romanowicz, 2010, Yuan et al., 2011). We showed that azimuthal anisotropy is a powerful tool to detect layering in the upper mantle, revealing two domains in the cratonic lithosphere, separated by a sharp laterally varying boundary in the depth range 100-150 km, which seems to coincide with the mid-lithospheric boundary (MLD) found in receiver function studies. Contrary to receiver functions, azimuthal anisotropy also detects the lithosphere-asthenosphere boundary (LAB) as manifested by a change in the fast axis direction, which becomes quasi-parallel to the absolute plate motion below ~250 km depth. A zone of stronger azimuthal anisotropy is found below the LAB both in the western US (peaking at depths of 100-150km) and in the craton (peaking at a depth of about 300 km). Here we show preliminary attempts at expanding our approach to the global scale, with a specific goal of determining whether such an anisotropic LAB can also be observed in the Pacific ocean. We started with our most recent global upper mantle radially anisotropic shear velocity model, determined using the Spectral Element Method (SEMum2; French et al., this meeting). We augment the corresponding global surface wave and overtone dataset (period range 60 to 400 s) with deep events and shorter period body waves, in order to ensure optimal deeper depth (>250km) anisotropy recovery due to the paucity of shear wave splitting measurements in the oceans. Our preliminary results, which do not yet incorporate SKS splitting measurements, look promising as they confirm the layering found previously in North America, using a different, global dataset and starting model. In the Pacific, our study confirms earlier azimuthal anisotropy results in the region (e.g. Smith et al. 2004; Maggi et al. 2006) that the shallow upper mantle beneath the ocean basin is strongly stratified. Our results further illustrate that 1) a shallow anisotropy domain (~100 km) is present, which is high in velocity and has in general a northward anisotropy direction where the plate is old (>80 Ma); and 2) there is a deeper domain (100-200 km) with stronger anisotropy, which correlates spatially with the low velocity zone and has a fast axis direction in good agreement with the absolute plate motion direction (HS3 NUVEL-1A). The boundary between the anisotropy domains clearly follows the age progressive deepening of the fast velocity in the shallow domain, suggesting an oceanic LAB that separates the Pacific lithosphere and the underlying asthenosphere.

Yuan, H.; Romanowicz, B. A.

2012-12-01

29

Circum-arctic plate accretion - Isolating part of a pacific plate to form the nucleus of the Arctic Basin  

USGS Publications Warehouse

A mosaic of large lithospheric plates rims the Arctic Ocean Basin, and foldbelts between these plates contain numerous allochthonous microplates. A new model for continental drift and microplate accretion proposes that prior to the late Mesozoic the Kula plate extended from the Pacific into the Arctic. By a process of circumpolar drift and microplate accretion, fragments of the Pacific basin, including parts of the Kula plate, were cut off and isolated in the Arctic Ocean, the Yukon-Koyukuk basin in Alaska, and the Bering Sea. ?? 1980.

Churkin, Jr. , M.; Trexler, Jr. , J. H.

1980-01-01

30

Improved Absolute Plate Motion Modeling in the Pacific  

NASA Astrophysics Data System (ADS)

In studies of Relative Plate Motion (RPM), the model constraints are conjugate magnetic isochrons identified in marine magnetic anomalies. The model is a finite rotation that rotates an isochron on plate A such that the rotated segment matches the conjugate isochron on plate B. Chang (1987; 1988) solved for such rotations using nonlinear spherical regression and developed statistical confidence regions for the resulting rotations. Because conjugate data can be optimally superimposed using a single, finite rotation it was natural to define the model in terms of total reconstruction rotations. In studies of Absolute Plate Motion (APM), the constraints are the surface expressions of hotspot seamount chains and their measured ages. The traditional approach is to model coeval segments of seamount chains as small circles about stage poles of rotation found by minimizing the distances from each seamount to its locally best-fitting, small circle about a candidate pole. The opening angles are typically found by trial and error. Given the age range of a particular set of copolar segments, opening rates can be determined. Because the data portray small circles, it was natural to define the model in terms of stage rotations. The traditional APM modelling approach has many limitations, including (1) shorter segments, possibly reflecting APM changes, are difficult to identify and correlate across several chains; (2) short small-circle segments become indistinguishable from great circles and hence reliable poles cannot be determined; (3) without easily identifiable kinks between chain segments, ages are needed to make the correlation and these are often lacking; and (4) unlike RPM modelling, no rigorous approach for estimating APM uncertainties exists. However, Wessel and Kroenke (1997) developed a method to derive optimal hotspot locations from seamount data if the APM is known, whereas Harada and Hamano (2000) introduced a technique to determine total reconstruction rotations if hotspot locations are known. We improve the modelling of APM by combining these two complimentary methods into a self-consistent hybrid technique. The hybrid technique allows us to determine (1) the best location for hotspots, (2) a high-resolution APM model, and (3) covariance matrices for each rotation. We present the first self-consistent Pacific APM with confidence regions for each rotation pole and reconstructed points. The new model is contrasted with traditional models, and the implications of the model for drift within the Pacific hotspot group and the origin of the Hawaii-Emperor bend is addressed.

Wessel, P.; Harada, Y.; Kroenke, L. W.

2004-12-01

31

Plate motion controls on back-arc spreading. [Cenozoic movement in Western Pacific  

NASA Technical Reports Server (NTRS)

The motions of the subducting and the overriding plates influence the spatial and temporal distribution of back-arc spreading. Cenozoic plate motions in hot spot-fixed and no-net-rotation reference frames were studied with attention to correlations between changes in motion and episodes of back-arc spreading in the western Pacific. The results suggest that major back-arc opening occurs when both the overriding plate retreats from the trench in an absolute sense and the subducting plate undergoes a significant speed-up. Neither phenomenon alone is sufficient to initiate spreading. Three major plate velocity increases can be identified in the Cenozoic: (1) the Pacific plate 5-9 Ma; (2) the Indian plate at 27 Ma; and (3) the Pacific plate at 43 Ma, due to its shift from northerly to more westerly motion. At the present time, the Indian and Philippine are the only overriding plates that are retreating from their Pacific trenches and back-arc spreading occurs only on these two retreating plates. Although the Indian plate has been retreating for at least 25 Ma, back-arc spreading began only following the Pacific plate speed-up 5-9 Ma. Earlier, during the Indian plate speed-up, no overriding plates were retreating strongly and no back-arc spreading epsiodes are preserved from this time. For the earliest Pacific plate shift at 43 Ma, the Eurasian plate was not advancing, thus creating the only favorable plate kinematic conditions in the Cenozoic for back-arc basin formation in this region. It is unclear whether extension in the Japan Sea is a result of these conditions.

Fein, J. B.; Jurdy, D. M.

1986-01-01

32

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

33

Relative motions of the Australian, Pacific and Antarctic plates estimated by the Global Positioning System  

NASA Technical Reports Server (NTRS)

Global Positioning System (GPS) measurements spanning approximately 3 years have been used to determine velocities for 7 sites on the Australian, Pacific and Antarctic plates. The site velocities agree with both plate model predictions and other space geodetic techniques. We find no evidence for internal deformation of the interior of the Australian plate. Wellington, New Zealand, located in the Australian-Pacific plate boundary zone, moves 20 +/- 5 mm/yr west-southwest relative to the Australian plate. Its velocity lies midway between the predicted velocities of the two plates. Relative Euler vectors for the Australia-Antarctica and Pacific-Antarctica plates agree within one standard deviation with the NUVEL-1A predictions.

Larson, Kristine M.; Freymueller, Jeff

1995-01-01

34

Explosive bonding of plates with diffusion barrier interfaces  

NASA Astrophysics Data System (ADS)

Composite plates, with and without, ``waves'' were made using improved explosive welding techniques. Oriented heat treatment of one surface of a steel-titanium composite introduces brittle intermetallic material at the specific interface. Currently, we are investigating methods to minimize this layer. While ``waveless'' interfaces revealed minimum intermetallic material; failure of the bond during ballistic impact necessitated production of a semi-compatible diffusion barrier using a fine layer of pure metal. Methods of producing composite plates with different interlayer materials and the effect of variables in optimizing the bond quality is presented. .

Joshi, V. S.; Banks, M. L.; Krebsbach, J.

2000-04-01

35

Explosive Bonding of Plates with Diffusion Barrier Interfaces  

NASA Astrophysics Data System (ADS)

Composite plates, with and without, “waves” were made using improved explosive welding techniques. Oriented heat treatment of one surface of a steel-titanium composite introduces brittle intermetallic material at the specific interface. Currently, we are investigating methods to minimize this layer. While “waveless” interfaces revealed minimum intermetallic material; failure of the bond during ballistic impact necessitated production of a semi-compatible diffusion barrier using a fine layer of pure metal. Methods of producing composite plates with different interlayer materials and the effect of variables in optimizing the bond quality will be presented.

Joshi, Vasant; Banks, Marvin; Krebsbach, John

1999-06-01

36

Quantifying the forces needed for the rapid change of Pacific plate motion at 6 Ma  

NASA Astrophysics Data System (ADS)

Studies have documented several rapid changes along the Pacific-North American, Pacific-Antarctic and Pacific-Australian plate boundaries in latest Miocene to earliest Pliocene time consistent with a sudden clockwise rotation of Pacific plate velocity relative to hotspots during this period. We test the hypothesis that this change in plate motion was initiated by cessation of subduction along the northern Melanesian arc due to the collision between the arc and the Ontong Java plateau. This hypothesis has long been formulated but never tested quantitatively. We use a geomechanical model of the lithosphere to determine the changes in plate boundary forces that are necessary to obtain the observed change in the Pacific plate motion. Our model results show that the change in motion can be explained by a clockwise rotation of the slab-related (basal-strength) component of plate driving force. The change of slab-related force from a post-6 Ma to a pre-6 Ma setting is perpendicular to the arc and points towards the Australian plate. The force per unit length is in the range of currently accepted values for subduction zones. Since there have been no other relevant changes at subduction zones along the Pacific plate boundary during the latest Miocene, we relate this change in slab-related force to the former southward-dipping Pacific plate slab along the northern Melanesian arc system which is now detached. Our model results suggest that rapid changes in plate motion can be triggered by slab detachment, with consequences for plate boundary processes even at great distances from the event.

Austermann, Jacqueline; Ben-Avraham, Zvi; Bird, Peter; Heidbach, Oliver; Schubert, Gerald; Stock, Joann M.

2011-07-01

37

Laser shockwave technique for characterization of nuclear fuel plate interfaces  

NASA Astrophysics Data System (ADS)

The US National Nuclear Security Agency is tasked with minimizing the worldwide use of high-enriched uranium. One aspect of that effort is the conversion of research reactors to monolithic fuel plates of low-enriched uranium. The manufacturing process includes hot isostatic press bonding of an aluminum cladding to the fuel foil. The Laser Shockwave Technique (LST) is here evaluated for characterizing the interface strength of fuel plates using depleted Uranium/Mo foils. LST is a non-contact method that uses lasers for the generation and detection of large amplitude acoustic waves and is therefore well adapted to the quality assurance of this process. Preliminary results show a clear signature of well-bonded and debonded interfaces and the method is able to classify/rank the bond strength of fuel plates prepared under different HIP conditions.

Perton, M.; Lévesque, D.; Monchalin, J.-P.; Lord, M.; Smith, J. A.; Rabin, B. H.

2013-01-01

38

Laser Shockwave Technique For Characterization Of Nuclear Fuel Plate Interfaces  

SciTech Connect

The US National Nuclear Security Agency is tasked with minimizing the worldwide use of high-enriched uranium. One aspect of that effort is the conversion of research reactors to monolithic fuel plates of low-enriched uranium. The manufacturing process includes hot isostatic press bonding of an aluminum cladding to the fuel foil. The Laser Shockwave Technique (LST) is here evaluated for characterizing the interface strength of fuel plates using depleted Uranium/Mo foils. LST is a non-contact method that uses lasers for the generation and detection of large amplitude acoustic waves and is therefore well adapted to the quality assurance of this process. Preliminary results show a clear signature of well-bonded and debonded interfaces and the method is able to classify/rank the bond strength of fuel plates prepared under different HIP conditions.

James A. Smith; Barry H. Rabin; Mathieu Perton; Daniel Lévesque; Jean-Pierre Monchalin; Martin Lord

2012-07-01

39

Break-up spots: Could the Pacific open as a consequence of plate kinematics?  

Microsoft Academic Search

The South Central Pacific is the location of an abnormal concentration of intraplate volcanism. Noting that this volcanism is present from the Kermadec Tonga trench to the Easter microplate and forms a wide east–west channel, we propose to explain its occurrence in relation to the Pacific plate geometry and kinematics. We construct 2D numerical models of stress and strain within

Valérie Clouard; Muriel Gerbault

2008-01-01

40

A revised kinematic model for the relative motion between Pacific oceanic plates and North America since the Late Cretaceous  

Microsoft Academic Search

The convergence between the Pacific, Farallon, and Kula oceanic plates and the North American plate has provided a driving force for tectonic processes that have shaped the western margin of North America. Yet reconstructions of plate motion in the Pacific basin have traditionally relied on the assumption of fixed hot spots. In the last decade, substantial Cretaceous to Paleogene motion

Pavel V. Doubrovine; John A. Tarduno

2008-01-01

41

Late Cretaceous to mid Eocene plate boundaries in the southwest Pacific  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

42

Tectonic implications of post-30 Ma Pacific and North American relative plate motions  

USGS Publications Warehouse

The Pacific plate moved northwest relative to North America since 42 Ma. The rapid half rate of Pacific-Farallon spreading allowed the ridge to approach the continent at about 29 Ma. Extinct spreading ridges that occur offshore along 65% of the margin document that fragments of the subducted Farallon slab became captured by the Pacific plate and assumed its motion proper to the actual subduction of the spreading ridge. This plate-capture process can be used to explain much of the post-29 Ma Cordilleran North America extension, strike slip, and the inland jump of oceanic spreading in the Gulf of California. Much of the post-29 Ma continental tectonism is the result of the strong traction imposed on the deep part of the continental crust by the gently inclined slab of subducted oceanic lithosphere as it moved to the northwest relative to the overlying continent. -from Authors

Bohannon, R. G.; Parsons, T.

1995-01-01

43

Marine Magnetic Anomaly and Magnetization of Oceanic Plate around the Japan Trench in the Northwestern Pacific  

Microsoft Academic Search

We have newly collected dense magnetic data around the Japan Trench in the northwestern Pacific. We present characteristics of the complied magnetic anomaly and crustal magnetization variation. The Pacific Plate in the study area has a series of parallel magnetic anomalies (Japanese Lineation Set), identified as chron M14-M7 (140-127 Ma). These anomalies are well lineated, in the direction of WSW-ENE,

T. Fujiwara; A. Obi; Y. Noda; Y. Kido; M. Nakanishi; N. Hirano; N. Abe; Y. Ogawa

2005-01-01

44

The cretaceous dynamics of the pacific plate and stages of magmatic activity in Northeastern Asia  

Microsoft Academic Search

The dynamics of the Pacific Plate is recorded in the systematic variation of location and the 40Ar-39Ar age of seamounts in the western Pacific from 120 to 65 Ma ago. The seamounts are grouped into three linear zones as long\\u000a as 5000 km. The seamounts become younger in the southeastern direction along the strike of these zones. Correlation between\\u000a age

A. A. Stepashko

2006-01-01

45

Crustal structure and seismicity distribution adjacent to the Pacific and North America plate boundary in southern California  

NASA Astrophysics Data System (ADS)

New three-dimensional (3-D) VP and VP/VS models are determined for southern California using P and S-P travel times from local earthquakes and controlled sources. These models confirm existing tectonic interpretations and provide new insights into the configuration of geological structures at the Pacific-North America plate boundary. The models extend from the U.S.-Mexico border in the south to the southernmost Coast Ranges and Sierra Nevada in the north and have a 15-km horizontal grid spacing and an average vertical grid spacing of 4 km, down to 22 km depth. The heterogeneity of the crustal structure as imaged by VP and VP/VS models is larger within the Pacific plate than the North American plate. Similarly, the relocated seismicity deepens and shows more complex 3-D distribution in areas of the Pacific plate exhibiting compressional tectonics. The models reflect mapped changes in the lithology across major geological terranes such as the Mojave Desert, the Peninsular Ranges, and the Transverse Ranges. The interface between the shallow Mono of the Continental Borderland and the deep Moho of onshore California forms a broad zone to the north beneath the western Transverse Ranges, Ventura basin, and the Los Angeles basin and a narrow zone to the south, along the Peninsular Ranges. The near-surface increase in velocity, from the surface to up to 8 km depth, is rapid and has a logarithmic shape for stable blocks and mountain ranges but is slow with a linear shape for sedimentary basins. At midcrustal depths a rapid increase in VP is imaged beneath the sediments of the large sedimentary basins, while beneath the adjacent mountain ranges the increase is small or absent.

Hauksson, Egill

2000-06-01

46

Seamounts, knolls and petit spots on the NW Pacific Plate represent intra-plate volcanism from the Cretaceous to present  

NASA Astrophysics Data System (ADS)

Most of seamounts of the western Pacific formed before 70 Ma in the so-called West Pacific Seamount Province (WPSP) which is characterized by relatively short seamount chains maybe indicating a significant short-lived hotspot system (Koppers et al., 2003). As for the NW Pacific Plate offshore of Northeast Japan, the Joban and Japanese Seamount Trail are also composed of middle Cretaceous seamounts, which are erupted on the northern margin of WPSP. The 120 to 100 Ma seamounts in the Joban seamount chain do not show a middle Cretaceous hotspot track, whereas the Japanese seamount chain shows a well-established ENE to WSW trend in this age range. On the other hand, the unnamed knolls, which are well-circular and flat-topped in shape, are scattered on the NW Pacific Plate and are not aligned to any volcanic chains. These were correspond to eruptive ages of 70 Ma based on Ar-Ar ages of a second volcanic event in the NW Pacific. As the last stage, we should note that Hirano et al. (2006) reported the 0-1, 2, 4.2, 6.0 and 8.6 Ma volcanoes, called petit spots, in the Japan Trench on the outer-rise system. The petit spot volcanoes imply episodic eruptions of magma over a distance of 600 km of plate motion on the flexural Pacific Plate before its subduction but with low volumes of magma production. The volume of volcanic edifice of the petit spot volcanoes certainly is several orders of magnitude less than the Cretaceous seamounts and knolls. Therefore, we can interpret that the petit spot volcanoes are not related to any mantle plumes and hotspots. Evidence includes the geochemical data and the tectonic alignment of the volcanoes which show that the petit spot lavas escaped along fractures in the lithosphere and were sourced from small pockets of asthenospheric melts. The bathymetric map and sidescan sonar imagery of the ocean-ward slope in the Tonga Trench also shows a possible presence of young volcanoes. Such small volcanoes, therefore, may be ubiquitous on the ocean floor, where incipient melts in the asthenosphere can be squeezed out by tectonic forces associated with plate flexure of outer-rise.

Hirano, N.; Nakanishi, M.; Koppers, A. A.

2007-12-01

47

Uncertainties in the relative positions of the Australia, Antarctica, Lord Howe, and Pacific plates since the late cretaceous  

Microsoft Academic Search

We determined parameters that describe finite rotations and their uncertainity regions for relative plate motion at the spreading centers between the Pacific and Antarctic plates, between Australia and Antarctica, and between the Lord Howe Rise and Australia. We combined these to yield a range of possible finite rotations describing the relative positions of the Pacific, Australia, Antarctica, and Lord Howe

Joann Stock; Peter Molnar

1982-01-01

48

Rheology of the plate interface - the rock record  

NASA Astrophysics Data System (ADS)

Models of subduction zones generally assume deformation to be localized into a comparatively narrow interplate shear zone. The cool crust of the subducted lithosphere, from which heat is additionally withdrawn by endothermic dehydration reactions, implies a cool geotherm for this region of interplate deformation. For localization of viscous flow in a region of low temperatures, specific material properties, environmental conditions, and mechanisms of deformation are prerequisite. As details on material behaviour cannot be predicted from models based on geophysical observations, the record of high pressure - low temperature (HP-LT) metamorphic rocks, probably being exhumed in a subduction channel, represents the only source of information on activated deformation mechanisms and typical stresses along the plate interface at depth. The record of blueschist facies metabasalts from the Franciscan Complex (California), of eclogite facies serpentinites from the Western Alps (Italy), and of eclogite facies micaschist from the Eastern Alps (Austria) invariably indicates that crystal plastic deformation of all minerals is subordinate. Instead, viscous flow at HP-LT metamorphic conditions is primarily by dissolution precipitation creep (DPC). Interphase boundaries act as preferred sites of dissolution. Prominent local sinks include strain shadows, dilatant fractures, and veins. Incongruent DPC is coupled with mineral reactions. DPC still predominates during the earlier stages of exhumation. Taking such observations to be representative for subducted material deformed at low temperatures along the plate interface between about 30 and 80 km depth, and exhumed without significant overprint within a weak subduction channel, the following is concluded: (1) Crystal plastic deformation and dislocation creep play no major role in long term viscous flow. (2) The absence of crystal plastic deformation all along the burial and exhumation path poses an upper bound to long term stress at the plate interface. (3) Long term deformation is essentially by dissolution precipitation creep at very low stress. (4) An aqueous fluid phase is present throughout. (5) Low stress implies little shear heating, hence supports a cool geotherm. (6) Inhomogeneous deformation to very high finite strain, controlled by contrasting rock properties, can lead to block-in-matrix structures and formation of a tectonic mélange, which may be a characteristic result of interplate deformation in the field of DPC. (7) Combined with the high strain rates expected for localized deformation between the plates, a very low viscosity of material in the interplate shear zone at depths between about 30 and 80 km is predicted.

Wassmann, S.; Stöckhert, B.

2012-04-01

49

Role of the eastern California shear zone in accommodating Pacific-North American plate motion  

Microsoft Academic Search

The newly recognized Eastern California shear zone (ECSZ) of the Mojave Desert-Death Valley region has played a major, but previously underappreciated role in accommodating the dextral shear between the Pacific and North American plates in late Cenozoic time. Comparison of integrated net slip along the shear zone with motion values across the entire transform boundary indicates that between 9% and

Roy K. Dokka; Christopher J. Travis

1990-01-01

50

The cretaceous dynamics of the pacific plate and stages of magmatic activity in Northeastern Asia  

NASA Astrophysics Data System (ADS)

The dynamics of the Pacific Plate is recorded in the systematic variation of location and the 40Ar-39Ar age of seamounts in the western Pacific from 120 to 65 Ma ago. The seamounts are grouped into three linear zones as long as 5000 km. The seamounts become younger in the southeastern direction along the strike of these zones. Correlation between age and location of seamounts allows division of the history of their formation into three stages. The rate of seamount growth was relatively low (2-4 cm/yr) during the first and the third stages within the intervals of 120-90 and 85-65 Ma, whereas during the second stage (90-85 Ma), the seamounts were growing very fast (80-100 cm/yr). In the midst of this stage, at ˜87 Ma ago, the magmatic activity increased abruptly. The dynamics of seamount building is in good agreement with (1) pulses in the development of the Ontong Java, Manihiki, and Caribbean-Colombian oceanic plateaus; (2) the age of spreading acceleration in the mid-Cretaceous; and (3) the short period when the Izanagi Plate ceased to exist and the Kula Plate was formed. The variation of the seamounts’ age and location is in consistence with the hypothesis of diffuse extension of the Pacific Plate in the course of its motion with formation of impaired zones of decompression melting. The direction of extension (325°-340° NW) calculated from the strike of seamount zones is consistent with the path of the Pacific Plate (330° NW) in the Late Cretaceous. The immense perioceanic volcanic belts were formed at that time along the margin of the Asian continent. The Okhotsk-Chukchi Peninsula Belt extends at a right angle to the compression vector. Three stages of this belt’s evolution are synchronous with the stages of seamount formation in the Pacific Plate. The delay in the origination of the East Sikhote-Alin Volcanic Belt and its different orientation were caused by counterclockwise rotation of the vector of convergence of oceanic and continental plates in the mid-Cretaceous. At the same time, i.e., 95-85 Ma ago, the volcanic activity embraced the entire continental margin and the tin granites were emplaced everywhere in eastern Asia. This short episode (90 ± 5 Ma) corresponds to the mid-Cretaceous maximum of compression of the continental margin, and its age fits a culmination in extension of the Pacific Plate well.

Stepashko, A. A.

2006-05-01

51

Plate-like” subsidence of the East Pacific Rise–South Pacific superswell system  

Microsoft Academic Search

In previous studies the removal of small-scale features such as seamounts and oceanic islands from bathymetry has revealed a large and unusually shallow region in the South Pacific Ocean, which, at 3000 km wide and up to 1 km high, has been dubbed a “superswell.” These studies use statistical techniques based on finding the modal depth of the bathymetry. Such

J. K. Hillier; A. B. Watts

2004-01-01

52

Overview on the Plate Boundaries Along the Western Mexican Pacific Margin  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

53

Subduction of the Western Pacific Plate underneath Northeast China: Implications of numerical studies  

NASA Astrophysics Data System (ADS)

The geodynamic process of the deep subduction of the western Pacific Plate underneath Northeast China is critical for understanding the extensional events and volcanism in Northeast China. Understanding of this process depends on: (1) the initial time of the subduction, (2) the trench retreat velocity during the subduction process, (3) the contribution of Indian-Eurasian collision and Pacific-Eurasian subduction to extensional events in the northeast of China. However, information on these three issues is very limited. We use several regional models to gain insight into these three issues. Each of the models includes temperature-dependent viscosity structures, and distinct velocity patterns at the surface. Our results show that the subduction of the Pacific Plate under the Eurasian plate started most probably around 70 Ma. To be consistent with the tomography under Northeast China, trench retreat must be included in the models, with a rate less than 45 km/Ma that has been estimated in the past. We suggest that the extension events in the northeast China are attributed to Indian-Eurasian collision and Pacific-Eurasian subduction according to the velocity evolution in our models.

Zhu, Guizhi; Shi, Yaolin; Tackley, Paul

2010-01-01

54

Pacific Plate slab pull and intraplate deformation in the early Cenozoic  

NASA Astrophysics Data System (ADS)

Large tectonic plates are known to be susceptible to internal deformation, leading to a range of phenomena including intraplate volcanism. However, the space and time dependence of intraplate deformation and its relationship with changing plate boundary configurations, subducting slab geometries, and absolute plate motion is poorly understood. We utilise a buoyancy driven Stokes flow solver, BEM-Earth, to investigate the contribution of subducting slabs through time on Pacific Plate motion and plate-scale deformation, and how this is linked to intraplate volcanism. We produce a series of geodynamic models from 62 to 42 Ma in which the plates are driven by the attached subducting slabs and mantle drag/suction forces. We compare our modelled intraplate deformation history with those types of intraplate volcanism that lack a clear age progression. Our models suggest that changes in Cenozoic subduction zone topology caused intraplate deformation to trigger volcanism along several linear seafloor structures, mostly by reactivation of existing seamount chains, but occasionally creating new volcanic chains on crust weakened by fracture zones and extinct ridges. Around 55 Ma subduction of the Pacific-Izanagi ridge reconfigured the major tectonic forces acting on the plate by replacing ridge push with slab pull along its north-western perimeter, causing lithospheric extension along pre-existing weaknesses. Large scale deformation observed in the models coincides with the seamount chains of Hawaii, Louisville, Tokelau, and Gilbert during our modelled time period of 62 to 42 Ma. We suggest that extensional stresses between 72 and 52 Ma are the likely cause of large parts of the formation of the Gilbert chain and that localised extension between 62 and 42 Ma could cause late-stage volcanism along the Musicians Volcanic Ridges. Our models demonstrate that early Cenozoic changes in Pacific plate driving forces only cause relatively minor changes in Pacific absolute plate motions, and cannot be responsible for the Hawaii-Emperor Bend (HEB), confirming previous interpretations that the 47 Ma HEB does not reflect an absolute plate motion event.

Butterworth, N. P.; Müller, R. D.; Quevedo, L.; O'Connor, J. M.; Hoernle, K.; Morra, G.

2014-01-01

55

Constraints on Pacific plate kinematics and dynamics with global positioning system measurements  

NASA Technical Reports Server (NTRS)

A measurement program designed to investigate kinematic and dynamic aspects of plate tectonics in the Pacific region by means of satellite observations is proposed. Accuracy studies are summarized showing that for short baselines (less than 100 km), the measuring accuracy of global positioning system (GPS) receivers can be in the centimeter range. For longer baselines, uncertainty in the orbital ephemerides of the GPS satellites could be a major source of error. Simultaneous observations at widely (about 300 km) separated fiducial stations over the Pacific region, should permit an accuracy in the centimeter range for baselines of up to several thousand kilometers. The optimum performance level is based on the assumption of that fiducial baselines are known a priori to the centimeter range. An example fiducial network for a GPS study of the South Pacific region is described.

Dixon, T. H.; Golombek, M. P.; Thornton, C. L.

1985-01-01

56

Roles of plate locking and block rotation in the tectonics of the Pacific Northwest  

Microsoft Academic Search

The Pacific Northwest has potential for huge megathrust earthquakes. The influence of plate locking in the Cascadia subduction zone dominates crustal deformation off the shores of Washington and Oregon, but does not much affect areas far from the trench. The maximum principal strain rate epsilon 1 is -0.013 +\\/- 0.007 mustrain\\/yr in the Olympic Peninsula, 0.007 +\\/- 0.005 mustrain\\/yr in

Zuoli Ning

2003-01-01

57

Propagation of the Hawaiian-Emperor volcano chain by Pacific plate cooling stress  

USGS Publications Warehouse

The lithosphere crack model, the main alternative to the mantle plume model for age-progressive magma emplacement along the Hawaiian-Emperor volcano chain, requires the maximum horizontal tensile stress to be normal to the volcano chain. However, published stress fields calculated from Pacific lithosphere tractions and body forces (e.g., subduction pull, basal drag, lithosphere density) are not optimal for southeast propagation of a stress-free, vertical tensile crack coincident with the Hawaiian segment of the Hawaiian-Emperor chain. Here we calculate the thermoelastic stress rate for present-day cooling of the Pacific plate using a spherical shell finite element representation of the plate geometry. We use observed seafloor isochrons and a standard model for lithosphere cooling to specify the time dependence of vertical temperature profiles. The calculated stress rate multiplied by a time increment (e.g., 1 m.y.) then gives a thermoelastic stress increment for the evolving Pacific plate. Near the Hawaiian chain position, the calculated stress increment in the lower part of the shell is tensional, with maximum tension normal to the chain direction. Near the projection of the chain trend to the southeast beyond Hawaii, the stress increment is compressive. This incremental stress field has the form necessary to maintain and propagate a tensile crack or similar lithosphere flaw and is thus consistent with the crack model for the Hawaiian volcano chain.?? 2007 The Geological Society of America.

Stuart, W. D.; Foulger, G. R.; Barall, M.

2007-01-01

58

The Hawaiian-Emperor Bend: A Record of Pronounced Change in Pacific Absolute Plate Motion  

NASA Astrophysics Data System (ADS)

Following the development of the hot spot hypothesis (Morgan, 1971) there was almost unanimous agreement that the Hawaiian-Emperor Bend (HEB) was the archetypal example of a large change in absolute plate motion (APM) recorded by hot spot volcanism. Lately, however this conviction has come under renewed scrutiny. Norton (1995) analyzed the geological evidence for contemporaneous tectonic activity and found none, arguing instead that the HEB was a "nonevent" caused by southward drift of the Hawaiian plume. Earlier studies had argued that it was impossible to fit all Pacific hotspot trails without invoking drift (Molnar and Stock, 1987). Recent fluid dynamic modeling, suggesting southeast-ward drift of the Hawaiian plume (Steinberger and O'Connell, 1997), supports that view and is in accord with sparse paleomagnetic data. African APM models, when projected via the Antarctica plate circuit into the Pacific, fail to reproduce the HEB, suggesting that the HEB does not reflect APM changes (Cande et al., 1995). Finally, the lack of a major reorganization of the Pacific-Farallon ridge system following the HEB event seems to imply that no large APM change took place (Atwater, 1989). Collectively, these arguments put the fixed hotspot hypothesis on the defensive. Despite these arguments, we wish to point out several facts that caution against the quick dismissal of a fixed hotspot frame of reference for the Pacific. First, and contrary to Norton's conclusions, there are significant tectonic precursors that appear to be directly related to the HEB event. Second, modeling of the Pacific APM using both hotspotting (Wessel and Kroenke, 1997) and polygon finite rotations (Harada and Hamano, 2000) does allow numerous chains to be fit simultaneously without invoking hotspot drift. In particular, we find geometrical suggestions of several seamount trail bends apparently coeval with the HEB; however, lack of radiometric dates precludes firm determinations. Third, the differential motion (DM) vectors associated with the HEB plate motion change are approximately normal to the Vancouver-Pacific spreading axis at that time. If the DM vectors can be considered proxies for stresses, then they imply there would be no reason for the ridge to reorient itself significantly. Further south, along the Pacific-Farallon ridge, the small angular difference between the DM vectors and the spreading direction may have initiated numerous propagating rifts around Chron 19. The area where the largest DM occurs coincides with the oldest part of the Western Pacific. Here, the plate was already old and mechanically strong and no deformation can be found orthogonal to the DM directions. Fourth, the large dispersion of paleo-latitudes, the possibility of magnetic terrain effects, and potentially unrecognized tectonic deformation may leave room for alternative explanations such as true polar wander. Finally, although we cannot rule out the possibility that the Pacific hotspots group has moved together, it is our belief that some of the mismatch between Pacific and Africa APM derives from incomplete parameterization of the global plate circuit.

Wessel, P.; Kroenke, L. W.; Harada, Y.; Sterling, A.

2002-12-01

59

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

National Technical Information Service (NTIS)

This is the Final Technical Report on research conducted between 1 June 1997 and 14 September 2001 entitled 'Transients in Pacific/North American plate boundary deformation: Synthesis and modeling of GPS and borehole strain observations.' As the project t...

S. C. Solomon

2002-01-01

60

Numerical simulation of shock waves in linear-elastic plates with curvilinear boundaries and material interfaces  

Microsoft Academic Search

An existing numerical scheme of bicharacteristics for linear-elastic, rectangular plates under in-plane impact loading is extended to plates with curvilinear boundaries. In order to validate the employed concept, numerical computations are compared with analytical and experimental results for plates with circular shaped boundaries. Focusing phenomena induced by reflection and refraction at curved outer boundaries and material interfaces are studied.

R. J. Niethammer; K.-S. Kim; J. Ballmann

1995-01-01

61

Petrologic Aspects of Seamount and Guyot Volcanism on the Ancestral Mesozoic Pacific Plate: a Review  

NASA Astrophysics Data System (ADS)

Hundreds of large seamounts and guyots are widely scattered almost in a "shotgun-blast" arrangement in an area about the size of the United States west of the Mississippi River on the Mesozoic Pacific plate between the Mariana Trench and the Gilbert Islands. Most of these formed between ~160-100 Ma while the Pacific plate was surrounded by spreading ridges and growing outward in all directions. There is little to no indication that the seamounts and guyots formed along linear seamount chains; existing radiometric-age data show no age progressions. The volcanoes appear to have formed in response to a uniform stress configuration across the plate, which was either not moving or moving very slowly at the time (1, 2), much like the modern Antarctic plate. When the growing plate started to encounter subduction systems in the western Pacific at ~90 Ma, consistent stress patterns began to develop, and the broad linear Gilbert and Line volcanic ridge systems began to form. Even then, however, considerable overlapping of volcanism occurred, and only the most general age progressions are evident in existing data. Petrologic data from samples obtained from dozens of volcanic summits by dredging and beneath several carbonate platforms by drilling reveal considerable diversity in development of differentiated alkalic magmatic lineages rooted in diverse parental basaltic rocks. These include transitional, alkalic and basanitic compositions, with differentiates of hawaiite, mugearite, trachyte and one phonolite. Many of the basaltic rocks are partly to significantly transformed by alteration under oxidative conditions (dredged rocks) and both oxidative and non-oxidative conditions (drilled rocks). This can make estimations of mantle geochemical provenance difficult. Nevertheless, the province has been linked by backtracking techniques to the modern SOPITA region of the South Pacific (3), and its rocks show enrichments in trace elements and isotopic characteristics similar to lavas from the Cook-Austral, Marquesas, Society, and Samoan linear volcanic chains. Significantly, Hawaiian- type tholeiite has not been sampled in the region, and the diversity of basaltic rocks and differentiates has always been high. Even unusual potassic nephelinites (K2O > Na2O) with phenocrysts of kaersutitic amphibole or phlogopite occur in the Wake and Line Seamounts. These resemble lavas of portions of the East African Rift, but also have counterparts in the Samoan and Society chains, and resemble very young basalts obtained on the outer trench swell of the Pacific plate near Japan. I suggest that variably and often strongly enriched material was originally supplied to the shallow upper mantle beneath a broad region of the Pacific plate during the Mesozoic; that partial melts of this material were subsequently tapped along major fracture systems that developed to form linear island chains as stress configurations changed on the Pacific plate; and that narrow plume conduits of ascending mantle have never figured in the emplacement of the broadly distributed enriched SOPITA volcanoes. 1) Natland, J. H., and Winterer, E.L., 2005, GSA Spec. Paper 388: 687-710. 2) Larson, R.L., et al., 1992, Proc. ODP, Sci Results, 129: p. 615-631; 3) Staudigel, H., et al., 1991, EPSL, 102: 24-44.

Natland, J. H.

2007-12-01

62

Imaging the Hikurangi Plate interface region, with improved local-earthquake tomography  

NASA Astrophysics Data System (ADS)

The properties of the plate interface region influence plate coupling and rupture behaviour during large earthquakes. Plate coupling varies greatly along the Hikurangi subduction zone in the southern half of the North Island, New Zealand, and heterogeneous material properties can be examined with the well-recorded seismicity. For this study, we have used a modified velocity inversion to incorporate earthquake differential times from selected groups of distributed earthquakes, which improves the spatial resolution of features in the lower crust, and sharpens velocity gradients. Data are selected from temporary deployments and the permanent GeoNet network, which has expanded in the last decade. The resulting 3-D velocity model shows that the overlying plate exhibits patterns related to geologic terranes. The Rakaia terrane has low Vp/Vs and high Vp, and is spatially related to the zone of strong plate coupling. Seismicity occurs throughout the overlying plate, and extends to the plate interface without a lower crustal aseismic zone. The Wairarapa-Waewaepa fault zone may form the updip limit of strong coupling in future plate interface earthquakes. The crust of the subducting plate is characterized by abundant seismicity and is bounded by strong velocity gradients. Low-velocity zones above the plate interface are indicated from 30 to 50 km depth. Seismic velocities near the plate interface show an excellent correlation with the distribution of plate coupling, and provide insight into what controls such coupling. The plate interface has the highest Vp/Vs (>1.85) and sharpest Vp/Vs gradient in the region of strongest coupling, consistent with the suggestion that strong coupling is related to the inability of fluid to cross the plate interface. In regions of recurrent slow slip, Vp/Vs is still high, but the gradient of Vp/Vs near the plate interface is much broader, suggesting movement of fluid across the plate interface. The area of deep slow slip corresponds to the most extensive high Vp/Vs mantle region above the slab.

Eberhart-Phillips, Donna; Reyners, Martin

2012-08-01

63

Nazca absolute plate motion and Pacific basin inter-hotspot motion  

NASA Astrophysics Data System (ADS)

Historically, hotspots have been used to define a fixed reference frame for plate motions: however, since hotspots are rooted within a dynamically convecting mantle, it is hard to believe that the fixity is absolute and instead slow motion between hotspots are expected to be occurring. Thus "how slow" is the central issue that needs to be addressed. Harada and Hamano (2000) and Harada and Wessel (2003, in prep.) showed that the mean speed since 70Ma for inter-hotspot motion within the Pacific plate is less than 4 or 5 mm per year. Recently, Steinberger (2002) suggested a numerical model for westward motion of the Easter hotspot at several cm per year relative to the Hawaii and Louisville hotspots. To test his hypothesis we dredged more than 70 sites along the Nazca Ridge and Easter Seamount Chain during the Drift expedition, Leg 6, of the R/V Revelle and dated more than 20 samples using the Ar/Ar method to examine the motion of the Easter hotspot relative to the Pacific hotspots. To estimate the positions and ages of the Easter hotspot track on the Nazca plate, we needed a good model of the absolute motion of the Nazca plate (Nazca APM) and present location of the Easter hotspot. For the modeling of the Nazca APM, we combined several existing models of Pacific APM with Pacific-Nazca relative motions (Pac-Naz RPM) determined from magnetic anomalies, and investigated the differences of these Nazca APM models. To determine the present location of the Easter hotspot, we applied the hot-spotting technique (Wessel and Kroenke, 1997) using the Nazca APM models, and then examined the differences in the optimal CVA locations. Because the hot-spotting technique can predict the present position of a hotspot without using any age data, we could test the modeled ages of the theoretical hotspot track by comparing them with observed ages of the hotspot track. The present position of the Easter hotspot is found to be near Salas y Gomez Island, not Easter Island. Although there are some dispersion owing to the various Nazca APM models used, the result shows that the position and ages of the modeled hotspot track well explain the observed geometry and ages, and there appears to be no systematic difference with time or distance from the present position. The suggested speed for inter-hotspot motion between the Easter and the Pacific hotspots would therefore be less than 10 mm per year.

Harada, Y.; Wessel, P.; Naar, D.; Wilder, D.; Duncan, R. A.; Mahoney, J. J.; Johnson, K. T.; Pyle, D. G.; Ray, J. S.

2003-04-01

64

Evaluating Cenozoic equatorial sediment deposition anomalies for potential paleoceanographic and Pacific plate motion applications  

NASA Astrophysics Data System (ADS)

If equatorial sediments form characteristic deposits around the equator, they may help to resolve the amount of northwards drift of the Pacific tectonic plate. Relevant to this issue, it has been shown that 230Th has been accumulating on the equatorial seabed faster than its production from radioactive decay in the overlying water column during the Holocene (Marcantonio et al. in Paleoceanography 16:260-267, 2001). Some researchers have argued that this reflects the deposition of particles with adsorbed 230Th carried by bottom currents towards the equator ("focusing"). If correct, this effect may combine with high pelagic productivity, which is also centered on the equator, to yield a characteristic signature of high accumulation rates marking the paleoequator in older deposits. Here we evaluate potential evidence that such an equatorial feature existed in the geological past. Seismic reflection data from seven meridional transects suggest that a band of equatorially enhanced accumulation of restricted latitude was variably developed, both spatially and temporally. It is absent in the interval 14.25-20.1 Ma but is well developed for the interval 8.55-14.25 Ma. We also examined eolian dust accumulation rate histories generated from scientific drilling data. A dust accumulation rate anomaly near the modern equator, which is not obviously related to the inter-tropical convergence zone, is interpreted as caused by focusing. Accumulation rates of Ba and P2O5 (proxies of export production) reveal a static equatorial signature, which suggests that the movement of the Pacific plate over the period 10-25 Ma was modest. The general transition from missing to well-developed focusing signatures around 14.25 Ma in the seismic data coincides with the mid-Miocene development of the western boundary current off New Zealand. This current supplies the Pacific with deep water from Antarctica, and could therefore imply a potential paleoceanographic or paleoclimatic origin. At 10.05-14.25 Ma, the latitudes of the seismic anomalies are up to ~2° different from the paleoequator predicted by Pacific plate-hotspot models, suggesting potentially a small change in the hotspot latitudes relative to the present day (although this inference depends on the precise form of the deposition around the equator). The Ba and P2O5 anomalies, on the other hand, are broadly compatible with plate models predicting slow northward plate movement over 10-25 Ma.

Mitchell, Neil C.; Dubois, Nathalie

2014-03-01

65

Marine magnetic anomaly and magnetization of subducting Pacific Plate around the Japan Trench  

NASA Astrophysics Data System (ADS)

We studied marine magnetic anomaly in the northwestern margin of the Pacific Plate off Japan to examine whether the magnetic anomaly varies due to tectonic phenomenon caused by the plate subduction. For the sake of this study, we newly collected magnetic data aboard JAMSTEC cruises in the seaward area where was sparsely surveyed, and made a magnetic anomaly map by compilation of our data, data published by Geological Survey of Japan, and data from NGDC. The seafloor of the seaward slope of the Japan Trench is characterized by a series of parallel magnetic anomalies (Japanese Lineation Set) during M11-M7 (135-127 Ma). The anomalies are well lineated and have high-amplitudes of ~500-1000 nT peak-to-trough. The amplitudes of the anomalies gradually decay to the landward from the trench axis associated with the plate subduction. Equivalent magnetization was calculated from the magnetic anomaly to correct for effects of seafloor topography and increasing depth of subducting plate. Densely distributed seismic survey profiles in the study area enabled us to constrain the depth of the plate. On the seaward trench slope from the trench axis to a distance of ca. 100 km, horst-graben structure is developed and large steps grow associated with plate bending and normal faulting, which would cause some kind of destruction and mechanical disorganization of the magnetic layer by faulting. However, the magnetization is not influenced apparently there. The magnetization gradually decreases as the plate subduction proceeded. The apparent decay could reflect destruction and mechanical disorganization and/or chemical demagnetization of the topmost part of the oceanic crust along the plate boundary. The magnetization in reverse polarity decays larger than that in normal polarity. The result is indicative of reduction of remanence in the oceanic crust and induced magnetization possibly due to serpentinized uppermost mantle.

Fujiwara, T.

2013-12-01

66

Reconstructing Ontong Java Nui: Implications for Pacific absolute plate motion, hotspot drift and true polar wander  

NASA Astrophysics Data System (ADS)

The Taylor (2006) hypothesis suggesting a common origin for the Ontong Java, Manihiki, and Hikurangi large igneous provinces provides an opportunity for a quantitative reconstruction and reassessment of the Ontong Java-Louisville hotspot connection. Our plate tectonic reconstructions of the three plateaus into Ontong Java Nui, or greater Ontong Java, combined with models for Pacific absolute plate motion (APM), allow an analysis of this connection. A new survey of the central Ellice Basin confirms easterly fracture zones, northerly abyssal hill fabric, as well as an area of sigmoidally-southeast-trending fracture zones associated with a late-stage spreading reorientation. From the fracture zone trends we derive new rotation poles for a two-stage model of Ellice Basin opening between the Ontong Java and Manihiki Plateaus. We use these and a single stage pole for separation of the Manihiki and Hikurangi Plateaus, together with three different Pacific APMs, to reconstruct the Ontong Java Nui super plateau back to 123 Ma and compare its predicted location with paleolatitude data obtained from the Ontong Java and Manihiki plateaus. Discrepancies between our Ontong Java Nui reconstructions and Ontong Java and Manihiki paleolatitudes are largest for the fixed Pacific hotspot APM. Assuming a Louisville hotspot source for Ontong Java Nui, remaining disparity between Ontong Java Nui's paleo-location at 123 Ma and published paleomagnetic latitudes for Ontong Java plateau imply that 8°-19° of Louisville hotspot drift or true polar wander may have occurred since the formation of Ontong Java Nui. However, the older portions of the Pacific APMs could easily be biased by a similar amount, making a firm identification of the dominant source of misfit difficult. Prior studies required a combined 26° of hotspot drift, octupole bias effects, and true polar wander just to link the Ontong Java Plateau to Louisville. Consequently, we suggest the super plateau hypothesis and our new reconstructions have considerably strengthened the case for a Louisville plume origin for Ontong Java Nui.

Chandler, Michael T.; Wessel, Paul; Taylor, Brian; Seton, Maria; Kim, Seung-Sep; Hyeong, Kiseong

2012-05-01

67

North American-Pacific relative plate motion in southern California from interferometry  

NASA Technical Reports Server (NTRS)

VLBI measurements of baselines crossing the San Andreas fault zone in southern California have provided observational constraints on rates of elastic tectonic strain accumulation. The single site located near this fault (the JPL site) moves in a direction concordant with the Pacific plate motion vector but at approximately half the net rate relative to North America. This motion agrees approximately in amount with geologically determined displacement rates on the San Andreas fault alone but not with the local strike of the fault. When considered together with complementary geodetic data, these results suggest a complex relation between the short-term accumulation of elastic strain and its permanent accommodation on existing faults.

Lyzenga, G. A.; Golombek, M. P.

1986-01-01

68

Seismic velocity structure of the subducting Pacific plate in the Izu-Bonin region  

SciTech Connect

Observed travel time residual data from a spatially dense seismic network above deep earthquakes in the Izu-Bonin region are compared with 3D ray tracing calculations. The data are inconsistent with a homogeneous slab model and consistent with a heterogenous slab model with regional velocity variations. The residual data can be explained by a model that has a velocity gradient within the slab. In the subducting Pacific plate, the velocity near the center of the slab is faster than that near the upper boundary, and gradually decreases toward the bottom of the plate. A model with a velocity decrease of 3 percent, as predicted by a thermal profile, explains the observed data. 52 refs.

Iidaka, Takashi; Mizoue, Megumi; Suyehiro, Kiyoshi (Tokyo Univ. (Japan))

1992-10-01

69

Structural Setting and Post-miocene Evolution of The Antarctic/pacific Plate Boundary Close To The Macquarie Triple Junction.  

NASA Astrophysics Data System (ADS)

The southern sector of the SW Pacific Ocean, south of 60S, is one of the less inves- tigated areas of our planet, although is a key point for studying the kinematics and the tectonic interactions of three major plates, Antarctic, Pacific and Australian, as they meet at the Macquarie Triple Junction (MTJ). Satellite-derived images of the ocean floor constitute the only morphostructural data-set available to date for this remote re- gion. Free-air gravity anomaly, as well as predicted-topography maps, outline a great complexity, and an overall geometrical and structural variability. The Pacific-Antarctic boundary SE of the MTJ is formed by a sequence of short ridge axes, dissected by a set of close-spaced fracture zones. This configuration is probably related to a recent (late Miocene) plate reorganization, that caused transtension across an abandoned trans- form/transcurrent boundary, and the formation of a "leaky transform system", which subsequently developed in well organized, equally-spaced ridge/transform segments. A focused re-processing of multichannel seismic reflection profiles acquired in this area during the early '90, in conjunction with more recent geomagnetic data, allow us to depict the post-Miocene evolution of this sector of the Antarctic/Pacific plate boundary. Data analysis led to the conclusion that two major deformation processes have contributed to shape the plate boundary in this region, convergence and strike-slip tectonics. They were probably active during different phases and/or in combination. Although teleseismic data show that the present-day boundary is dominated by exten- sional deformations, evidence of compressions are observed SE of the MTJ, along the westernmost Pacific-Antarctic margin. This suggests an unexpected structural conti- nuity between the present-day Pacific/Australian margin north of the MTJ (the Hjort Trench and the southern part of the Macquarie Ridge Complex), and a wide sector of the Pacific plate along the Pacific/Antarctic boundary.

Gasperini, L.; Fabretti, P.; Lodolo, E.

70

The geochemical fingerprint of serpentinite- and crust-dominated plate-interface settings: some tectonic implications  

NASA Astrophysics Data System (ADS)

The interface between converging plates is made of kilometre-thick domains where slab and upper plate mantle materials are tectonically slicied within a matrix dominated either by (meta)sedimentary/crustal rocks or by serpentinite. The latter may correspond to supra-subduction mantle altered by uprising slab fluids. Once formed, these plate-interface domains act as hydrated low-viscosity layers where tectonic stress and fluid-mediated mass transfer are strongly focussed. Here we present the geochemical study of two plate-interface environments: (1) serpentinite-rich, represented by the high-pressure serpentinites of the Ligurian Alps (Erro-Tobbio and Voltri Units); (2) sediment-dominated top slab mélange, represented by de-serpentinized garnet peridotite and chlorite harzburgite bodies (hosting eclogite and metarodingite) embedded in paragneiss and micaschist from Cima di Gagnone (Adula Unit, Central Alps). The Ligurian serpentinites derive from oceanic and wedge mantle tectonically coupled and dragged to depth during Alpine subduction: they may represent the hydrated precursors of the Cima di Gagnone peridotites. The B, Pb and Sr isotopic composition of the above sets of rocks helps defining tectonic and mass transfer processes during accretion of slab and suprasubduction mantle rocks in plate-interface domains, and to retrieve the imprint of fluids from these settings, which that ultimately affect arc magmatism. The serpentinized peridotites from Erro-Tobbio (ET) show high B (10-30 ppm), delta11B (10-25 per mil), B/Nb ratio (>380) and limited enrichment in 206Pb/204Pb (18.17-18,51) and 87Sr/86Sr (0.7046- 0.7060). Scambelluri & Tonarini (2012) interpreted the B and Sr isotopic imprint of ET as representative of upper plate mantle altered by slab-fluids. The B contents (up to 30 ppm), delta11B (18-30 per mil), B/Nb ratio (>900) and 206Pb/204Pb (18.09-18.22) of the Voltri serpentinites are similar to ET. Their 87Sr/86Sr (0.7079 to 0.7105) is higher than ET. The garnet peridotite and harzburgite from Gagnone have low B (up to 9 ppm), low B/Nb (<100) and high Pb and Sr isotopic ratios (206Pb/204Pb up to 18.84; 87Sr/86Sr 0.7124). Eclogite and HP metarodingite in the Gagnone peridotite show comparable values. The host metasediments and gneiss show higher B (6-16 ppm), 206Pb/204Pb (up to 18.98) and 87Sr/86Sr (0.7275). than peridotites and mafic rocks. All the Gagnone rocks have negative delta11B (ultramafic and mafic rocks = 0 to -10 per mil; country rocks = -3 to -12 per mil). The Gagnone peridotites reveal geochemical mixing between ultramafic and host crustal reservoirs. Considering that these peridotites derive from serpentinized protoliths, we expect that the initial high 11B of serpentinites was modified by two combined processes: (1) serpentine dehydration, releasing heavy B to fluids, and (2) exchange between ultramafic rocks and sediment-derived subduction fluids during burial and exhumation. The geochemical signature of the Voltri serpentinites is indicative of interaction with slab fluids enriched in heavy B-rich and in crust-derived components, such as in mantle rocks which evolved atop of the subducting slab. This implies that the slices of the downgoing slab are emplaced early during their burial history atop of the subducting plate. The geochemical signature of peridotites and host metasediments from Gagnone, points to significant exchange between ultramafic bodies and host rocks during prograde subduction prior to peak metamorphism. This again indicates accretion to the plate interface of slab and wedge materials during an early stage of subduction. Moreover, Voltri and Gagnone represent distinct reservoirs, showing positive versus negative delta11B. Serpentinite-dominated settings, like Voltri, produce high B and 11B fluids which can explain 11B-enrichment of much Pacific arcs. Differently, the sediment- and gneiss-dominated Gagnone mélange shows high B, negative ?11B, high radiogenic Pb and Sr: fluids released from such a mélange fit the composition of lavas from convergent margins affecte

Cannaò, Enrico; Scambelluri, Marco; Agostini, Samuele; Tonarini, Sonia

2014-05-01

71

Reconstruction of Pacific-Nazca Plates, Nazca Ridge, and Easter Seamount Chain  

NASA Astrophysics Data System (ADS)

Relative plate motion history since 30 Ma between the Pacific and Nazca (Farallon) plates has been constrained by available seafloor magnetic anomaly data and a two-minute grid of predicted bathymetry. These data are used to create a new plate reconstruction based on finite and stage poles of rotation and radiometric ages along the Easter-Salas y Gomez-Nazca Ridge volcanic lineament. An iterative process of anomaly identifications, pole calculations and anomaly rotations was used to test for self-consistency in the interpretation. The new identified magnetic isochrons (10y, 7y, 6c, 5d, 5b, 5aa, 5o, 4a, and 3a) and the predicted tectonic history provide an improved understanding between chrons 7y (24.73 Ma) and 3 (4.18 Ma). However, the finite poles for 6c and 5d are poorly constrained. Eleven stage poles were calculated using the nine finite poles and two published instantaneous Euler vectors for the 1o and 2a isochrons. The stage poles indicate full-spreading rates increased from about 175 mm/yr to about 205 mm/yr after the break-up of the Farallon plate, and then have slowed to about 145 mm/yr. The tectonic reconstruction indicates two major southward propagating events, the first starting by 28 Ma and terminating by 18 Ma. The second starting in association with breakup of the Farallon plate around 24 Ma and terminating by about 11 Ma. Lithosphere was transferred from Nazca to Pacific during the first event and in the opposite sense during the second. Development of the Mendoza microplate east of the second propagator occurred at about 20 Ma and this dual spreading process appears to have lasted until about 15 Ma. Radiometric ages, geochemical data, relative and absolute motion models presented at the Nice AGU meeting by Duncan et al., Ray et al., Wilder et al., and Harada et al. indicate that since 30 Ma: 1) a hotspot located near Salas y Gomez Island does not require significant motion of the hotspot with respect to the Hawaiian hotspot; 2) that this hotspot has generated similar proportions of OIB vs. MORB end-member compositions in most samples collected east of Salas y Gomez; and 3) that the change of plate motion velocity was primarily accommodated by the combination of propagating rifts and microplate formation, including a rapid clockwise rotation of spreading direction and rapid increase in spreading rate, followed by a subsequent decline until present.

Naar, D. F.; Wilder, D. T.; Duncan, R. A.; Wessel, P.; Harada, Y.; Mahoney, J. J.; Ray, J. S.; Johnson, K. T.

2003-12-01

72

The collective behavior and spacing of adiabatic shear bands in the explosive cladding plate interface  

Microsoft Academic Search

Large assemblages (?150) of adiabatic shear bands (ASBs) on the titanium side in the titanium\\/mild steel explosive cladding plate interface were investigated. The change of spacing and length of ASBs initiating at the wavy interface was characterized as periodic and the behavior of ASBs was organized. The observed shear band spacing was compared with existing theories based on a perturbation

Y. Yang; B. F. Wang; B. Hu; K. Hu; Z. G. Li

2005-01-01

73

Subduction zone dynamics in the SW Pacific plate boundary region constrained from high-precision Pb isotope data  

NASA Astrophysics Data System (ADS)

This study presents high-precision Pb isotope data obtained by MC-ICP-MS for lavas from the Solomon island arc that covers ca. 1000 km of the SW Pacific plate boundary. Following a reversal of subduction polarity, the presence of the old subducted Pacific oceanic crust, and the presently subducting Indian-Australian plate beneath the entire island arc is confirmed by geophysical and geochemical evidence. New high-precision Pb isotope data now permit to distinguish more clearly between Indian and Pacific-type subduction components in this complex plate tectonic constellation. The values range from 206Pb/ 204Pb = 18.345 to 18.845, 207Pb/ 204Pb = 15.498 to 15.545, and 208Pb/ 204Pb = 38.120 to 38.372, indicating the absence of pelagic sediments in the sub-arc mantle. These data reveal a predominance of subduction components derived from ancient subduction of the Pacific plate. In contrast, lavas with Indian-type Pb isotope signatures are confined to the central New Georgia Group of the Solomon Islands, where the young Woodlark Ridge spreading centre is currently subducting. All other Solomon arc segments with a lower geothermal gradient have apparently not yet been overprinted by younger subduction components over the past 6 Myrs. Moreover, trace element and Pb isotope data for Woodlark Ridge basalts show that subduction components from the fossil Pacific slab have locally modified the source of Woodlark Basin lavas. Altogether, our study highlights the potential of high-resolution Pb isotope measurements to distinguish between Indian and Pacific-type subduction components along the SW Pacific plate boundary.

Schuth, Stephan; König, Stephan; Münker, Carsten

2011-11-01

74

Imaging the Hikurangi Plate Interface Region, with Improved Local-Earthquake Tomography  

NASA Astrophysics Data System (ADS)

The properties of the plate interface region influence the rupture behavior (coupling) of the plate interface in large earthquakes. Plate coupling varies greatly along the Hikurangi subduction zone in the southern half of the North Island, New Zealand, and material heterogeneity can be examined with the well-recorded seismicity. We have modified the Simul velocity inversion program to incorporate earthquake differential times from selected groups of distributed earthquakes, which improves the spatial resolution of features in the lower crust region, and sharpens velocity gradients. Data are selected from temporary deployments and the permanent Geonet network, which has expanded in the last decade. The 3-D velocity model shows that the overlying plate exhibits patterns related to geologic terranes, and a sharp gradient in Vp/Vs occurs across the Wairarapa-Waewaepa fault zone. The Rakaia terrane has low Vp/Vs and high Vp, and is spatially related to the zone of strong plate coupling. The crust of the subducting plate is shown by abundant seismicity and is bounded by strong velocity gradients. Low-velocity zones above the plate interface are indictated from 30 to 50-km depth. The plate interface has moderately high Vp/Vs at all depths, and the highest Vp/Vs (>1.85) and sharpest Vp/Vs gradient correspond to the strongest coupling. A region of high Vp/Vs located downdip of the locked area corresponds to the Manawatu slow slip region. Seismicity occurs throughout the overlying plate, and extends to the plate interface without a lower crustal aseismic zone. Most of the deeper seismicity in the overlying plate is in a zone underlying the Wairarapa-Waewaepa fault zone near the border of the strongly locked area. This may indicate numerous small splay faults off of the plate interface. The subducted slab mantle has high velocity, Vp 8.5-9.3 km/s, and large areas of high Vp/Vs. The slab mantle includes low Vp zones consistent with a linear feature which is parallel to structural features of the Hikurangi Plateau and thus may represent long-term oceanic plate structure rather than current subduction processes.

Eberhart-Phillips, D. M.; Reyners, M.; Bannister, S. C.

2011-12-01

75

On gravity from SST, geoid from Seasat, and plate age and fracture zones in the Pacific  

NASA Technical Reports Server (NTRS)

A composite map produced by combining 90 passes of SST data show good agreement with conventional GEM models. The SEASAT altimeter data were deduced and found to agree with both the SST and GEM fields. The maps are dominated (especially in the east) by a pattern of roughly east-west anomalies with a transverse wavelength of about 2000 km. Comparison with regional bathymetric data shows a remarkedly close correlation with plate age. Most anomalies in the east half of the Pacific could be partly caused by regional differences in plate age. The amplitude of these geoid or gravity anomalies caused by age differences should decrease with absolute plate age, and large anomalies (approximately 3 m) over old, smooth sea floor may indicate a further deeper source within or perhaps below the lithosphere. The possible plume size and ascent velocity necessary to supply deep mantle material to the upper mantle without complete thermal equilibration was considered. A plume emanating from a buoyant layer 100 km thick and 10,000 times less viscous than the surrounding mantle should have a diameter of about 400 km and must ascend at about 10 cm/yr to arrive still anomalously hot in the uppermost mantle.

Marsh, B. D.; Marsh, J. G.; Williamson, R. G. (principal investigators)

1984-01-01

76

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

77

Nicoya earthquake rupture anticipated by geodetic measurement of the locked plate interface  

NASA Astrophysics Data System (ADS)

The Nicoya Peninsula in Costa Rica is one of the few places on Earth where the seismically active plate interface of a subduction zone is directly overlaid by land rather than ocean. At this plate interface, large megathrust earthquakes with magnitudes greater than 7 occur approximately every 50 years. Such quakes occurred in 1853, 1900 and 1950, so another large earthquake had been anticipated. Land-based Global Positioning System (GPS) and seismic measurements revealed a region where the plate interface was locked and hence accumulated seismic strain that could be released in future earthquakes. On 5 September 2012, the long-anticipated Nicoya earthquake occurred in the heart of the previously identified locked patch. Here we report observations of coseismic deformation from GPS and geomorphic data along the Nicoya Peninsula and show that the magnitude 7.6 Nicoya earthquake ruptured the lateral and down-dip extent of the previously locked region of the plate interface. We also identify a previously locked part of the plate interface, located immediately offshore, that may not have slipped during the 2012 earthquake, where monitoring should continue. By pairing observations of the spatial extent of interseismic locking and subsequent coseismic rupture, we demonstrate the use of detailed near-field geodetic investigations during the late interseismic period for identifying future earthquake potential.

Protti, Marino; González, Victor; Newman, Andrew V.; Dixon, Timothy H.; Schwartz, Susan Y.; Marshall, Jeffrey S.; Feng, Lujia; Walter, Jacob I.; Malservisi, Rocco; Owen, Susan E.

2014-02-01

78

Depth of the decoupling plate interface and thermal structure under arcs  

NASA Astrophysics Data System (ADS)

Subduction proceeds as thrust movements at the boundary between the subducting plate and the rigid overlying plate. At depth below this mechanically decoupling plate interface, the subducting plate couples with the overlying mantle, and flow is induced in the mantle wedge. This induced flow is the main factor that controls thermal structure under arcs. Depth of this decoupling to coupling transition at the plate interface is estimated from observed surface heat flow in the northeastern Japan arc using a two-dimensional numerical simulation of thermal structure. The estimated depth is about 70 km. The termination depth of thrust earthquakes agrees well with the depth of the coupling transition, which indicates that these earthquakes occur at the decoupling plate interface. The mechanism of this decoupling plate interface is discussed in this paper. It is believed that water associated with the subducting oceanic crust reduces the frictional stress at the plate interface and thrust movement thus becomes possible. Petrological studies show that dehydration reaction in the subducting oceanic crust terminate at about 2.0 GPa and have little temperature dependence. Termination depths of thrust earthquakes estimated from seismic studies are nearly the same (60 to approximately 80 km) for various arcs. This indicates that depth of the decoupling to coupling transition is controlled by the termination depth of dehydration reaction in the subducting oceanic crust. Across-arc heat flow profiles observed in various subduction zones show similar features; heat flow is very low in the forearc region and increases steeply at the volcanic front. Considering that the depth of the slab is about 100 km at the volcanic from for various arcs, this heat flow feature is closely related to the depth of the slab. Thus it is concluded that thermal structure under arcs is mainly controlled by the depth of the pressure dependent dehydration reactions in the subducting oceanic crust.

Furukawa, Yoshitsuga

1993-11-01

79

Cenozoic geological and plate tectonic evolution of SE Asia and the SW Pacific: computer-based reconstructions, model and animations  

Microsoft Academic Search

A plate tectonic model for the Cenozoic development of the region of SE Asia and the SW Pacific is presented and its implications are discussed. The model is accompanied by computer animations in a variety of formats, which can be viewed on most desktop computers. GPS measurements and present seismicity illustrate the high rates of motions and tectonic complexity of

Robert Hall

2002-01-01

80

Roles of plate locking and block rotation in the tectonics of the Pacific Northwest  

NASA Astrophysics Data System (ADS)

The Pacific Northwest has potential for huge megathrust earthquakes. The influence of plate locking in the Cascadia subduction zone dominates crustal deformation off the shores of Washington and Oregon, but does not much affect areas far from the trench. The maximum principal strain rate epsilon 1 is -0.013 +/- 0.007 mustrain/yr in the Olympic Peninsula, 0.007 +/- 0.005 mustrain/yr in the Puget Sound, -0.005 +/- 0.005 mustrain/yr at Mt. Rainier, -0.004 +/- 0.005 mustrain/yr along the northern Oregon coast, and 0.011 +/- 0.006 mustrain/yr in central Oregon. The minimum principal strain rate epsilon2 is -0.083 +/- 0.008 mustrain/yr N56°E in the Olympic Peninsula, -0.034 +/- 0.007 mustrain/yr N63°E in the Puget Sound, -0.020 +/- 0.006 mustrain/yr N53°E at Mt. Rainier, -0.051 +/- 0.014 mustrain/yr N85°E along the northern Oregon coast, and -0.010 +/- 0.006 mustrain/yr N71°E in central Oregon. A new model of plate locking on the Cascadia subduction zone is similar to a model (1997). The uncertainty of the widths of the locked and transition zone in the model is about 25km--40km. Guided by computed site velocities, seismicity patterns, heat flow, volcanic data, and geological structures, we find it is necessary to divide the crust in the Pacific Northwest into separate moving blocks. We have analyzed a model in which the Oregon block is separated from the Washington block at latitude 46°. The Washington block has been further divided into 5-subblocks, three in the forearc and two in eastern Washington. We remove contributions of JDF plate locking from the site velocity field and determine a rotation pole and a strain rate for each sub-block. We conclude that Juan de Fuca plate locking has little direct effect on crustal earthquake occurrence in the Pacific Northwest (except for periodic megathrust earthquakes). In the Oregon block, plate locking and rigid block rotation are sufficient to explain GPS observations and the lower rate of seismicity in Oregon. The Washington block is more. The southwestern Washington sub-blocks have higher rotation rates and smaller residual strain rates than the northern sub-blocks. The Olympic sub-block shows the greatest north-south compression (0.017 mustrain/yr). The Puget Lowland sub-block and Mt. Rainier sub-block are shortening along a NNE direction, roughly consistent with the direction of maximum principal stress from fault plane solutions. The overall north-south shortening across the Puget Sound is 3mm/yr, sufficient to generate M7+ earthquakes in the future. NS compression dominates eastern Washington near Yakima which is also consistent with principal stress directions derived from fault plane solutions. Northeast Washington sub-block is currently poorly constrained by GPS data. As western Washington is pushed northward against the British Columbia, block rotation in Oregon is slowed down in Washington and the motion produces NS compression in northern Washington. The sub-blocks in southwestern WA act as a transition zone between Oregon and British Columbia. Residual strain rate is proportional to crustal seismicity. The great variation of residual strain rate in WA compared to Oregon may explain their crustal seismicity difference. GPS derived velocities in NE Washington are still too uncertain to determine the details of block rotation and strain rate there.

Ning, Zuoli

81

Volcanisms and Earthquakes Related to the Pacific Plate Subduction in Northeast Asia  

NASA Astrophysics Data System (ADS)

It is very known that an integrated plate system displays in Northeast Asia from the Pacific Plate subduction zone via arc islands and back-arc basin to the continental margin with rifting system. Based on this geological background many huge earthquakes and volcanic eruptions occurred in this area from the Mesozoic to the present such as Fujiyama Volcano in Japan, Cheju Volcano in South Korea, Changbaishan Volcano in China and M 7.3 deep focus earthquake in Wangqing, Northeast China of June 28,2002, M9 earthquake in Northeast Japan of March 11,2011 and so on. Now it is tectonic active phase in the Northeast Asia, even in the globe. The Changbaishan Volcano is huge volcanic group with some 12-103 km2 area and hundreds volcanic cones crossed the boundary between China and Korea covered 41° -42.5° latitude north and 127° -129° longitude east. It is among largest active and dangerous volcanoes on the Globe and composed of three main volcanoes (eruptive centers): Tianchi(2755 m a.s.l.), Wangtian'e (2438m a.s.l.) and South Paotaishan (2434m a.s.l.), which distribution assumes as tripod. These three eruptive centers have similar magma system and different ages. They were built from the Early Miocene to the Recent by basaltic flow as lava plateau, trachyte composing of volcanic cones and pyroclastic deposits covering the tops of the mountains and other places. Tianchi volcano is younger than others. According to historic documents the largest eruption of Tianchi volcano occurred in 1014-1019 AD., after that there were still several eruptions until 1903 AD. The frequencies of Changbaishan volcanic eruptions corresponded to those of the Pacific, especially Japan. There is systematic magma evolution from basic basalt, intermediate trachyte to acid pantellerite with 87Sr/86Sr 0.704771-0.710096, 143Nd/144Nd 0.512487-0.512602, which indicated that the magma derived from rich mantle. Geophysical data reveal a buried magmatic reservoir is lying below the volcanoes. Recently, the west Pacific fire ring is very active accompanied with frequent volcanic eruptions and earthquakes; the earthquake frequency and intensity and geochemical anomaly also obviously strengthen in the surrounding of Changbaishan volcanoes. It reveals that volcanic activity and possibility of re-eruption is going to strengthen. Therefore we must put attention to volcanic action.

Liu, J.; Chen, X.

2012-04-01

82

Subduction of the Pacific Plate Beneath the Kamchatka: Volcanism and Tectonic Earthquakes  

NASA Astrophysics Data System (ADS)

The results of studying subduction process of the Pacific plate beneath the Kamchatka and related processes are described. The focal mechanism solutions estimated from Centroid Moment Tensor (CMT) catalog and sequence of the largest earthquakes occurred in Kamchatka were used to asses velocity of subducted slab. The boundary of contact for subducted slab is determined at a depth of 30-70 km, and is considered as a plane at azimuth 217° and with a dip angle of 25°. The rate of subduction estimated from CMT mechanisms yields V=0.9 cm/yr for southern zone (south of Shipunsky Cape), and V=1.4 cm/yr for central zone (from Shipunsky Cape to Kronotsky Cape). The largest coupled consistent earthquakes recorded from 1737 were used for analysis. The results show, that for the southern area V=6.6 - 7.1 cm yr (two couples), and for the central part V=6.6 cm yr. The estimated value of velocity for the creep part of subducted slab is about 5 to 15 per cent of the bulk velocity. The Pacific plate subducts at a rate of 8 cm yr. Series of GPS observations conducted from 1997 up to 2007 were used to estimate the rate at which Kamchatka is deformed under the effect of the subducted slab (along-slab direction). The average values of rate and velocity variations versus the average rate were estimated response to permanent GPS station PETR. It was shown that the motion at BKI (Bering) regardless KlU (Klyuchi) is uneven: variations of velocity reach up to 30 per cent (at average running window of 1 year). There are about 28 active volcanoes in Kamchatka that provide intensive volcanic activity in this region. The volcanoes produce about 16-17% of magmatic rocks erupted by all volcanoes in the Earth. Over the past 5 years, eruptions of Sheveluch, Klyuchevskoy, Bezymianny, Karymsky, and Mutnovsky volcanoes have occurred. Although many of these volcanoes are in sparsely populated areas, they lie adjacent to the heavily North Pacific air routes between North America, Europe and Asia. The Institute of Volcanology and Seismology (IVS) of the Russian Academy of Sciences (RAS) and Kamchatka Branch of Geophysical Survey (KB GS) of RAS monitor and study Kamchatka's hazardous volcanoes, to forecast and record eruptive activity, and implement public safety measures. To meet its mission, the IVS and KB GS maintains a volcano monitoring network to detect signs of volcanic unrest; conducts basic geological, geophysical, and geochemical investigations of Kamchakan volcanoes; and provides accurate and timely warnings of imminent activity to local, state and federal agencies.

Gordeev, E. I.

2008-12-01

83

Slow earthquakes associated with fault healing on a serpentinized plate interface  

PubMed Central

Slow earthquakes that occur at subduction zones are distinct from regular earthquakes in terms of their slip behavior. We consider this difference to relate to localized hydration reactions at the plate interface that influence the frictional properties. The results of laboratory friction experiments indicate that simulated serpentine faults are characterized by a low healing rate and large slip-weakening distance compared with unaltered dry fault patches. These results are consistent with the slip mechanism of slow earthquakes, indicating that a locally serpentinized plate interface could trigger slow earthquakes, assisted by pore pressure build-up, whereas unaltered dry patches that remain strongly coupled are potential sites of regular earthquakes.

Katayama, Ikuo; Iwata, Mutsumi; Okazaki, Keishi; Hirauchi, Ken-ichi

2013-01-01

84

Paleomagnetism of Midway Atoll lavas and northward movement of the Pacific plate  

USGS Publications Warehouse

Two deep drill holes through the reef limestones of Midway Atoll penetrated 120 m and 19 m of basaltic lavas that were dated by the KAr method at 18 my. Inclinations of natural remanent magnetization have been measured in 173 specimens cut from 57 core samples from 13 of the lava flows. The mean paleomagnetic inclination is 27.6?? ?? 6.8??, corresponding to a paleolatitude of 14.7?? ?? 4.2??. The present latitude of Midway is 28??, suggesting a northward component of motion of the Pacific plate of approximately 13?? or 1400 km in the last 18 my. The paleolatitude of Midway is thus not significantly different from the present latitude (19??) of the active volcanic island of Hawaii. The paleomagnetic data from the Midway basalts thus support the hypothesis of Wilson and Morgan that volcanic heat sources are fixed with respect to the Earth's mantle below the asthenosphere and their apparent migration with time is due to plate motion. ?? 1972.

Gromme, S.; Vine, F. J.

1972-01-01

85

Geodetic evidence for low coupling on the Hellenic subduction plate interface  

NASA Astrophysics Data System (ADS)

We develop a block model for the Aegean and surrounding areas, constrained by Global Positioning System (GPS), in order to investigate the degree of coupling on the Hellenic subduction interface (i.e., the fraction of the motion across the plate boundary accommodated by elastic strain accumulation). We use previously published models, and seismicity to define the geometry of the interface separating the down-going Nubian slab from the overriding Aegean. This model provides a good fit to the GPS observations; for the ˜200,000 km2 Aegean block the wrms of the residual velocities is 1.4 mm/yr for 80 GPS velocity estimates, approximately the 95% level of the GPS velocity uncertainties. We investigate the degree of coupling on the seismically active plate interface, the Hellenic trench splay fault (believed to be the source of the 365 AD Great Crete Earthquake and Tsunami), and the Kephalonia transform fault by comparing the modeled GPS residual velocity field for a range of coupling values. The GPS observations are almost insensitive to coupling on the Kephalonia transform fault, because of the vertical dip of the fault that creates interseismic deformation only close to the fault where few GPS sites exist. The absence of resolvable shortening of the leading edge of the Aegean Plate precludes coupling of more than 0.2 (20% of the full Nubia-Aegean convergence rate) on the modeled plate interface. Because of the shallow dip of the plate interface and trench splay fault, and high rate of convergence, if these boundaries were fully coupled, high elastic strain rates would be expected to extend well into the overriding Aegean plate. Based on our preferred value for the degree of coupling (0.1), and assuming characteristic earthquake behavior, we estimate a recurrence time for great earthquakes with slip similar to that for the 365 Crete event of 5700-8300 yr, consistent with the absence of subsequent great earthquakes on this segment of the subduction zone.

Vernant, Philippe; Reilinger, Robert; McClusky, Simon

2014-01-01

86

Accelerated subduction of the Pacific Plate after mega-thrust earthquakes: evidence from GPS and GRACE  

NASA Astrophysics Data System (ADS)

Interplate thrust earthquakes are often followed by afterslips (Heki et al., 1997; Miyazaki et al., 2004; Ozawa et al., 2012). They let the fore-arc move slowly trenchward and accelerate plate convergence. Accelerated convergence of the oceanic side (including ocean floor and slab) has been suggested by changes of focal mechanisms of earthquakes within oceanic plates after mega-thrust events, i.e. change from trench-normal compression to tension in outer rise regions, and from down-dip tension to compression in intermediate depths (Lay et al., 1989). However, landward acceleration of the oceanic plate has never been observed geodetically due to the scarcity of appropriate islands on oceanic plates near trenches. The westward velocity of GPS stations in NE Japan show gradient decreasing from east to west reflecting the E-W compressional stress built up by the inter-plate coupling. We found that such coupling significantly enhanced after the 2003 Tokachi-Oki earthquake (Mw8.0), Hokkaido, in the segments adjacent to the ruptured fault. The coupling was further enhanced after the 2011 Tohoku-Oki earthquake (Mw9.0). Movement of the ocean floor benchmark after the 2011 event suggests that the current (i.e. 2011-2012) subduction of the Pacific Plate is about three times as fast as the geological average, e.g. NUVEL-1 (DeMets et al., 1990). Such a temporary acceleration of the subduction would be a response of the subducting slab to the sudden decrease of interplate coupling (decoupling); because slab-pull and ridge-push cannot change, viscous traction has to increase to recover the force balance. We will present a simple physical model assuming a thin low-viscosity layer on the slab surface that has enabled such a rapid adjustment. The accelerated subduction would account for high regional interplate seismicity after mega-thrust earthquakes, especially successive ruptures of remote segments, e.g. the 2003 Tokachi-Oki, 2006 Kuril, and 2011 Tohoku-Oki earthquakes. GRACE satellite gravimetry revealed coseismic gravity drops in the back-arc regions due to the dilatation of island arc lithosphere for the 2004 Sumatra-Andaman (Han et al., 2005), 2010 Maule (Heki and Matsuo, 2010), and 2011 Tohoku-oki (Matsuo and Heki, 2011) earthquakes. Postseismic slow gravity increase centered in the fore-arc region was first found for the 2004 Sumatra-Andaman earthquake (Ogawa and Heki, 2007). Here we show that similar postseismic gravity increases also followed the other two mega-thrust earthquakes. We assume that they also reflect accelerating subduction of oceanic plates, i.e. episodic convergence at the boundary propagates into oceanic plate interior by stress diffusion (Bott and Dean, 1973), and postseismic thickening of the coseismically thinned lithosphere causes the on-going gravity increases.

Heki, K.; Mitsui, Y.; Matsuo, K.; Tanaka, Y.

2012-12-01

87

Seismic structure of the North Pacific oceanic crust prior plate bending at the Alaska subduction zone  

NASA Astrophysics Data System (ADS)

Seismic reflection profiles across North Pacific oceanic Plate reveal the internal structure of a mature oceanic crust (42-56Ma) formed at fast (70mm/yr, half rate) to intermediate (28mm/yr, half rate) spreading rates. Data used in this study were collected with the R/V Langseth in summer 2011 as part of the ALEUT (Alaska Langseth Experiment to Understand the megathrust) program. MCS data were acquired with two 8-km streamers and a 6600 cu. in. air gun array. We collected a series of profiles across the subduction zone system but also across the preexisting structures of the oceanic crust before being affected by subduction zone processes. Additionally, two 400-km OBS refraction lines were shot coincident with MCS profiles. The multi-channel seismic (MCS) data across oceanic crust formed at fast spreading rates contain abundant bright reflectors mostly confined in the lower crust above the Moho discontinuity and dipping predominantly toward the paleo-ridge. Along these profiles, the Moho discontinuity is observed as a bright event with remarkable lateral continuity. The lengths of the dipping reflectors are on the order of 5-km, with apparent dips between 10 and 30°. These reflectors represent discrete events, with spacing between 0.3 to 5 km without any obvious regularity. These dipping events appear to sole out within the middle crust (1 to 1.5 s beneath basement) and most of them terminate at the Moho. The Moho is much weaker or absent on the northern profiles acquired across the North Pacific oceanic crust formed at intermediate spreading rates. Basement topography is rougher and no clear dipping events have been imaged suggesting that the spreading rate may be an important factor that controls the strength and abundance of such dipping reflectors and the lateral change in the Moho reflection characters. Lower crustal dipping reflections (LCDR) have been only imaged at very few places across the Pacific oceanic crust: (Eittreim et al., 1988, Reston et al. 1999, Ranero et al., 1997, Hallenborg et al., 2003). These LCDR have been interpreted as being either formed near the spreading center during accretion or off-axis post-accretion structures. Interpretations proposed included lithologic banding from passive accretion, shear structures from active mantle upwelling, off-axis magmatism, or enhanced reflectivity of latent structures by crustal aging (e.g., hydrothermal circulation, etc). Another alternative that we propose is that the dipping reflectors are shear zones that form in the lower crustal mush zone due to active upwelling that contain frozen melts segregated into the shear zones during deformation. Characteristics of the wide-angle reflection data are also different between the two lines. Lateral variations in the Moho reflections and crustal refractions are clearly observed and will be discussed with respect to the structures imaged on the coincident reflection images. The transition between fast to intermediate spreading rates occurs near a triple junction that separated the Pacific, Kula and Farallon plates that ceased spreading in the Late Eocene. MCS profiles across and around the fossil triple junction reveal deep reflections into the crust and below the Moho down to 15-km depth. These reflections could possibly be caused by gabbroic melts that froze in the mantle lithosphere when the triple junction was abandoned.

Becel, A.; Shillington, D. J.; Nedimovic, M. R.; Kuehn, H.; Webb, S. C.; Holtzman, B. K.

2012-12-01

88

Plate Tectonics  

NSDL National Science Digital Library

In this activity students use data from underwater earthquakes to outline the location of plate boundaries. Data from the Northeast Pacific, eastern Equatorial Pacific, and North Atlantic are examined in more detail. Background information on plate tectonics is provided.

2002-01-01

89

Crustal structure and configuration of the subducting Philippine Sea plate beneath the Pacific coast industrial zone in Japan inferred from receiver function analysis  

NASA Astrophysics Data System (ADS)

We apply receiver function (RF) analyses to estimate the crustal structure and configuration of the subducting Philippine Sea (PHS) plate beneath the Pacific coast industrial zone stretching from Tokyo to Fukuoka in Japan. Destructive earthquakes often occurred at the plate interface of the PHS plate, and seismic activities increase after the 2011 Tohoku earthquake (Mw9.0) around the Tokyo metropolitan area. Investigation on the crustal structure is the key to understanding the stress concentration and strain accumulation process, and information on configuration of the subducting plate is important to mitigate future earthquake disasters. In this study, we searched for the best-correlated velocity structure model between an observed receiver function at each station and synthetic ones by using a grid search method. Synthetic RFs were calculated from many assumed one-dimensional velocity structures that consist of four layers with positive velocity steps. Observed receiver functions were stacked without considering back azimuth or epicentral distance. We further constructed the vertical cross-sections of depth-converted RF images transformed the lapse time of time series to depth by using the estimated structure models. Telemetric seismographic network data covered on the Japanese Islands including the Metropolitan Seismic Observation network, which constructed under the Special Project for Earthquake Disaster Mitigation in the Tokyo Metropolitan area and maintained by Special Project for Reducing Vulnerability for Urban Mega Earthquake Disasters, are used. We selected events with magnitudes greater or equal to 5.0 and epicentral distance between 30 and 90 degrees based on USGS catalogues. As a result, we clarify spatial distributions of the crustal S-wave velocities. Estimated average one-dimensional S-wave velocity structure is approximately equal to the JMA2011 structural model although the velocity from the ground surface to 5 km in depth is slow. In particular, the Kanto plain and Boso peninsula are covered in thick sediment layers. The velocity perturbations in the crust are consistent with existing tomography models. There are low-velocity zones in the upper crust to the crust-mantle boundary corresponding to volcanoes. In contrast, non-volcanic mountain foothills are relatively high-velocity zones. We also elucidated the configuration of PHS plate to a depth of about 60 km. The PHS plate subducts to the northwest and the direction coincides with plate motion. The northeastern margin of PHS plate is estimated from the plate thickness, which gradually decreases to the northeast after contact with the underlying Pacific plate beneath the Tokyo metropolitan area. Asperities of some large earthquakes seem to be corresponded to the high-velocity area in the PHS slab. On the other hand, non-volcanic low-frequency earthquakes located in the plate interface are characterized by relatively low-velocity areas. They may indicate the serpentinized mantle wedge which reflects dehydration of the subducting oceanic crust.

Igarashi, T.; Iidaka, T.; Sakai, S.; Hirata, N.

2012-12-01

90

On gravity from SST, geoid from SEASAT, and plate age and fracture zones in the Pacific  

NASA Technical Reports Server (NTRS)

Data from an additional 50 satellite-to-satellite tracking (SST) passes were combined with earlier measurements of the high degree and order (n, m, 12) gravity in the central Pacific. A composite map was produced which shows good agreement with conventional GEM models. Data from the SEASAT altimeter was reduced and found to agree well with both the SST and the GEM fields. The maps are dominated especially in the east, by a pattern of roughly east-west anomalies with a transverse wavelength of about 2000 km. Further comparison with regional bathymetric data shows a remarkably close correlation with plate age. Each anomaly band is framed by those major fracture zones having large offsets. The regular spacing of these fractures seems to account for the fabric in the gravity fields. Other anomalies are accounted for by hot spots. The source of part of these anomalies is in the lithosphere itself. The possible plume size and ascent velocity necessary to supply deep mantle material to the upper mantel without complete thermal equilibration is considered.

Marsh, B. D.; Marsh, J. G.; Williamson, R. G.

1983-01-01

91

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

92

The August and October, 2008 earthquake swarms on the Explorer/Pacific plate boundary  

NASA Astrophysics Data System (ADS)

In August and October of 2008, earthquake swarms occurred on the Explorer/Pacific plate boundary. The August swarm lasted for approximately 4 days. Seventy-five earthquakes were reported by the Canadian National Seismograph Nework (CNSN), with the largest having a magnitude of 5.9. The U.S. Navy's Sound Surveillance System (SOSUS) hydrophones reported 148 earthquakes. Over 250 earthquakes were recorded on the Central Oregon Locked Zone Array (COLZA), a temporary array of 15 ocean bottom seismometers (OBS) and hydrophones. The October swarm lasted about 2 days with only one reported CNSN magnitude 4.4 earthquake. This event was also observed with the COLZA network. SOSUS reported 119 earthquakes over the course of two days. In this poster, we use the COLZA T-phase data to better understand the tectonic significance of these swarms. T-phases are generated by earthquakes and converted to acoustic energy at the seafloor. We used the ANSS magnitudes to calibrate an empirical magnitude scale for maximum amplitudes handpicked from the COLZA T-phase observations. This enabled us to lower the magnitude threshold to 2.8. A b-value of 0.78 was obtained for the August swarm suggesting that it may be a tectonic event rather then a magmatic one. Focal mechanisms reported by the Harvard CMT catalog for 3 of the largest events also support strike-slip motion. The reported SOSUS hypocenter locations indicate a linear NE/SW trend west of and parallel to the Explorer Ridge while the ANSS locations are very scattered but suggest a northwest/southeast trend in line with but east of the Dellwood-Revere transform fault. To obtain better-constrained locations, we plan to relocate the events and COLZA T-phase data using cross-correlation techniques developed to locate seismic tremor. We expect the COLZA data will allow us to determine whether activity was primarily focused along the Explorer Ridge axis, along the Dellwood-Revere transform, or within the plate. This investigation could provide us with new insight into the evolution and possible fragmentation of the Explorer Plate.

Czoski, P. A.; Trehu, A. M.; Williams, M. C.; Dziak, R. P.; Embley, R. W.

2011-12-01

93

Fragmentation on a grand scale: A slab fragment dislodged from the descending Pacific plate slab wedged Beneath Tokyo  

Microsoft Academic Search

The Eurasian-Philippine Sea-Pacific plate triple junction located 250 km southeast of Tokyo not only produces megathrust subduction earthquakes along the Sagami trough (including the 1703 M=8.3 Genroku and 1923 M=7.9 Kanto shocks) but is also associated with enigmatic M~6-7 earthquakes directly beneath Tokyo (such as the 1855 M~7.1 Ansei-Edo earthquake and 2006 M=6.0 Chiba shocks). In the past, the Tokyo

R. S. Stein; S. Toda; S. B. Bozkurt; S. H. Kirby; J. Nakajima; A. Hasegawa

2007-01-01

94

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

NASA Technical Reports Server (NTRS)

Marine magnetic profiles from the Gulf of Californa are studied in order to revise the estimate of Pacific-North America motion. It is found that since 3 Ma spreading has averaged 48 mm/yr, consistent with a new global plate motion model derived without any data. The present data suggest that strike-slip motion on faults west of the San Andreas is less than previously thought, reducing the San Andreas discrepancy with geodetic, seismological, and other geologic observations.

Demets, Charles; Gordon, Richard G.; Stein, Seth; Argus, Donald F.

1987-01-01

95

Distribution of the Pacific/North America motion in the Queen Charlotte Islands-S. Alaska plate boundary zone  

NASA Astrophysics Data System (ADS)

We present GPS data that constrain the distribution of the relative Pacific/North America motion across the Queen Charlotte Islands-Alaska Panhandle margin (NW North America). Velocities from a network of 22 campaign and permanent sites indicate that the Pacific/North America transpressive motion is mostly accommodated along the locked Queen Charlotte-Fairweather Fault. A significant portion (6-7 mm/yr) of the relative plate motion is taken up by distributed dextral shear across a ~200 km wide region of the margin. Two models have been proposed to describe how the Pacific/North America convergence is accommodated off the Queen Charlotte Islands: Internal shortening vs. underthrusting of the Pacific plate. Although the GPS data cannot discriminate between the models, they provide strong constraints on the convergence distribution. The significant non-transient motion of GPS sites along the central British Columbia-southern Alaska margin has implications for seismic hazard and tectonic evolution models of the Canadian Cordillera.

Mazzotti, Stéphane; Hyndman, Roy D.; Flück, Paul; Smith, Alex J.; Schmidt, Michael

2003-07-01

96

Microstructure and Phase Constitution Near the Interface of Explosively Welded Aluminum/Copper Plates  

NASA Astrophysics Data System (ADS)

The microstructure changes and the phase constitution within the layers close to the bonding interface strongly influence the properties of bimetallic strips. In this work, the layers near the interface of explosively welded aluminum and copper plates were investigated by means of microscopic observations, mostly with the use of transmission electron microscopy (TEM) equipped with energy dispersive spectrometry (EDX). The study was focused on the identification of the intermetallic phases, the possible interdiffusion between the copper and the aluminum, and the changes in the dislocation structure of the parent plates. In macro-/mesoscale, the interfaces were outlined by a characteristic sharp transition indicating that there was no mechanical mixing between the welded metals in the solid state. In micro-/nanoscale, the layers adhering to the interface show typical deformed microstructure features, i.e., structure refinement, elongated dislocation cells, slip bands, and microtwins (in copper plate). The internal microstructure of the intermetallic inclusion is composed mostly of dendrites. The electron diffractions and TEM/EDX chemical composition measurements revealed three crystalline equilibrium phases of the ?-Al4Cu9, ?-AlCu, and ?-Al2Cu type (the last one was dominant). However, most of the observed phases of the general Cu m Al n type (also crystalline) do not appear in the equilibrium Al-Cu phase diagram. Inside the intermetallic inclusions, no significant regularity in the phase distribution with respect to the parent sheets was observed. Therefore, it was concluded that the processes occurring in the melt determined their local chemical composition.

Paul, Henryk; Lity?ska-Dobrzy?ska, Lidia; Pra?mowski, Mariusz

2013-08-01

97

Metamorphic soles and flip flops: rheology of the plate interface during early subduction stages  

NASA Astrophysics Data System (ADS)

Metamorphic soles underlie most extensive ophiolites worldwide (i.e., ~several 100 km long, non metamorphosed obducted pieces of oceanic lithosphere). These metamorphic soles (MS) are tectonic slices dragged along and welded to the ophiolite and generally comprise m to ~500 m thick (strongly deformed and thus partly thinned) high-T granulite to amphibolite facies mafic protoliths, together with subordinate metaradiolarites. There is wide recognition that these HT MS formed during subduction initiation (ie., < 1-2 My after inception) at the expense of the upper part of the oceanic crust, atop the incipiently underthrusting lower plate. This sole observation implies a spectacular yet unaccounted for jump of the lower contact of the ophiolite thrust during early subduction stages, from above to below the MS. Besides, the review of recent P-T determinations constraining the formation of high-T MS evidences a fairly narrow range between 1±0.2 GPa, 700-850°C. This is, consistently, significantly warmer than the later subduction regime, during which (a) lower T amphibolite to greenschist facies units from the top of the oceanic crust, yet with comparatively greater amounts of metasediments, become accreted below the high-T MS, (b) later, non metamorphosed and/or HP-LT units derived from uppermost crustal material are underthrust beneath the metamorphic sole s.l., as in W. Turkey or Oman. This contribution tentatively explains how metamorphic soles get attached to the upper plate ophiolite by a simple conceptual model of the plate interface rheology during early subduction stages. This model draws on the existence of a major flip, in terms of mechanical behaviour, as the plate interface progressively cools: (1) rheological data suggest that the mechanical resistance of the upper plate mantle is initially greater than that of the lower plate (variably hydrothermalized) oceanic crust; (2) as the system cools, and even more so once the upper plate mantle gets incipiently serpentinized (i.e., at ~700-750°C), the effective resistance of both lithologies/domains will progressively converge. I propose that this particular P-T window corresponds to the transient, optimal period during which similar effective rheology on both sides maximizes interplate mechanical coupling: deformation gets distributed over a larger band (on the 500 m to km scale), which allows the high-T MS to be transfered from the downgoing plate to the upper plate. (3) at decreasing, lower T, the lower plate oceanic crust becomes stronger than the upper plate mantle (this crust also gets efficiently eclogitized at depths and thus rarely returned with respect to subduction duration). The plate interface becomes highly localized again and later underthrusting and tectonic slicing at the toe of the upper plate detaches progressively shallower parts of the incoming material. Flip flops are firmly tied to the ophiolite by then... This interpretation of the plate interface rheology during progressive cooling is consistent with reports of low-temperature obduction-related deformation (i.e., 700-900°C) at the base of the ophiolite mantle itself. It may also provide constraints on the long-term mechanical properties of both basalt and peridotite.

Agard, Philippe

2014-05-01

98

Influence of cumulative convergence on lithospheric thrust fault development and topography along the Australian-Pacific plate boundary south of New Zealand  

Microsoft Academic Search

The development of faulting and topography resulting from initial convergence within oceanic lithosphere is largely unknown. We explore relationships among convergence, structural development, and topography along ?1500 km of the submarine Australian-Pacific plate boundary south of New Zealand, the Macquarie Ridge Complex (MRC). Due to the variable orientation of the boundary and close proximity of the Australian-Pacific poles of rotation,

T. A. Meckel; P. Mann; Sharon Mosher; Millard F. Coffin

2005-01-01

99

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

NASA Astrophysics Data System (ADS)

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

Biasi, Glenn P.

2009-01-01

100

Direct evidence for upper mantle structure in the NW Pacific Plate: Microstructural analysis of a petit-spot peridotite xenolith  

NASA Astrophysics Data System (ADS)

Petit-spots, the late Miocene alkali basaltic volcanoes on the Early Cretaceous NW Pacific Plate, originate at the base of the lithosphere. The petit-spot volcanic rocks enclose fragments of tholeiitic basalt, dolerite, gabbro, and mantle peridotite, providing a unique window into the entire section of subducting oceanic lithosphere. We provide here the first direct observations on the deep structure of the Pacific lithosphere using microstructural analyses of a petit-spot peridotite xenolith. The xenolith is a lherzolite that consists mainly of coarse- and medium-grained olivine, orthopyroxene, and clinopyroxene, as well as fine-grained aggregates of spinel and orthopyroxene that probably represent replaced pyrope-rich garnet. A strong deformational fabric is marked by a parallel alignment of millimeter-sized elongate minerals and their crystallographic preferred orientation. The olivine displays a [010] fiber pattern with a girdle of [100] axes and a maximum of [010] perpendicular to the foliation, a pattern which is consistent with a transpressional deformation in high temperature conditions at the base of oceanic lithosphere. Our microstructural observations and seismic data indicate that the lower part of the NW Pacific lithosphere possess an early stage structure of mantle flow at the asthenosphere. This interpretation is compatible with a conventional model in which oceanic lithosphere is thickened during cooling and plate convection. A discrepancy between the weak anisotropy in the petit-spot peridotite and the strong azimuthal anisotropy from the seismic data in the NW Pacific plate implies the existence of a highly anisotropic component in the deep oceanic lithosphere.

Harigane, Yumiko; Mizukami, Tomoyuki; Morishita, Tomoaki; Michibayashi, Katsuyoshi; Abe, Natsue; Hirano, Naoto

2011-02-01

101

Deep low-frequency earthquakes in tremor localize to the plate interface in multiple subduction zones  

USGS Publications Warehouse

Deep tremor under Shikoku, Japan, consists primarily, and perhaps entirely, of swarms of low-frequency earthquakes (LFEs) that occur as shear slip on the plate interface. Although tremor is observed at other plate boundaries, the lack of cataloged low-frequency earthquakes has precluded a similar conclusion about tremor in those locales. We use a network autocorrelation approach to detect and locate LFEs within tremor recorded at three subduction zones characterized by different thermal structures and levels of interplate seismicity: southwest Japan, northern Cascadia, and Costa Rica. In each case we find that LFEs are the primary constituent of tremor and that they locate on the deep continuation of the plate boundary. This suggests that tremor in these regions shares a common mechanism and that temperature is not the primary control on such activity. Copyright 2009 by the American Geophysical Union.

Brown, J. R.; Beroza, G. C.; Ide, S.; Ohta, K.; Shelly, D. R.; Schwartz, S. Y.; Rabbel, W.; Thorwart, M.; Kao, H.

2009-01-01

102

Chemistry of Springs Across the Mariana Forearc Shows Progressive Devolatilization of the Subducting Pacific Plate  

NASA Astrophysics Data System (ADS)

Upwelling pore water fresher than seawater has been sampled from serpentinite mud volcanoes on six cruises to the Mariana forearc in 1987-2003: ODP Legs 125 and 195, Alvin and Shinkai-6500 diving cruises in 1987 and 1996, and two cruises in 1997 and 2003 using piston and gravity coring and the ROV Jason. Low-chlorinity water has been sampled at ten sites on nine serpentinite mud volcanoes from 13o47'N to 19o33'N, ranging from 50-90 km from the trench axis, corresponding to depths to the top of the subducting slab of ~15 to 29 km below the seafloor. Another six seamounts failed to yield freshened water, probably because we failed to hit the right spots. We achieved this success rate using high-resolution bathymetric and sonar maps generated on the same cruises. The freshened waters show systematic variations in composition across the forearc. Near the trench, at 50-56 km distance, springs have high Ca (47-75 mmol/kg) and Sr (310-920 umol/kg) and low alkalinity (3 meq/kg). Farther from the trench, at 70-90 km, springs have high carbonate alkalinity (35-56 meq/kg) and near-zero Ca and Sr, apparently because carbonate dissolution has joined dehydration as a major process at the top of the subducting plate. Sulfate, Na/Cl, K, Rb, Cs, and B all increase regularly with distance from the trench, from values less than in seawater to greater, in response to increasing temperature at depth. All of the waters have high pH and are heavily depleted in Mg, Si, and F relative to seawater. Springs with high carbonate alkalinity also have high CH4, which feeds microbial communities in the shallow subsurface that reduce sulfate to bisulfide at pH 12.5. Chlorinity ranges from 235-538 mmol/kg but does not vary systematically with distance from the trench, because of either variable supply at the source or variable uptake of H2O by serpentinization along the flow path. Volatile elements and compounds including H2O and CO2 thus are progressively leached from the sediment and altered oceanic crust at the top of the subducting Pacific Plate, probably in response to increasing temperature over a range of 100-250oC. Based on leaching of K, the 150oC isotherm is crossed approximately beneath Big Blue Seamount at a depth of ~22 km below the seafloor, 70 km behind the trench. The systematic and sharp chemical gradients across the forearc imply that the aqueous solutions carrying these volatiles rise vertically from their source region at the top of the subducting plate rather than traveling long distances along the decollement before ascending.

Mottl, M. J.; Wheat, C. G.; Fryer, P.; Gharib, J.; Hulme, S.

2003-12-01

103

Lateral structural change of the subducting Pacific plate beneath Japan inferred from high-frequency body wave analysis  

NASA Astrophysics Data System (ADS)

We studied the detailed lateral structure of the subducting Pacific plate near Honshu by analyzing waveforms from deep earthquakes recorded at fore-arc Hi-net dense high-gain network and F-net broadband stations in Japan. Such waveforms explain the low-frequency precursors followed by high-frequency energies due to the multiple scattering and diffractions of seismic waves in the stochastic waveguide of the Pacific slab (Furumura and Kennett, 2005). However, recent analysis shows that for some particular source-receiver paths, the waveforms exhibit loss of high frequency energy in P-coda, loss of low-frequency precursor and presence of P-to-P or P-to-S converted phases in P-coda for deep earthquakes occurring in the subeducting Pacific plate. Such complexities in the observed waveforms indicate sudden lateral change in the wave guiding properties of the subducting slab, such as expected to be caused by the thinning or tearing the slab in deeper part. To explain the observations, we employ two-dimensional finite-difference method (FDM) simulations of complete high-frequency P-SV wave propagation taking thinning of the Pacific slab into account. We expect that the observed guided wave energy must decouple from waveguide where the slab is deformed or thin. Low frequency energy leaks out of the slab and travels to the receivers along paths in the low velocity and low-Q mantle surrounding the slab, while high frequency signal of shorter wavelength can travel through thin plate. The results of this study, along with the evidence for weak velocity anomaly as inferred from seismic tomography (Obayashi et al., 2009) and observations of slab tear in the Pacific plate (Kennett and Furumura, 2010), we expect a local velocity anomaly or thinning in the oceanic lithosphere along the junction between Izu-Bonin and Honshu arc. It is necessary to examine these effects further with a 3D FDM simulation for different slab geometries and source depths.

Padhy, S.; Furumura, T.; Maeda, T.

2011-12-01

104

Fluid Pressure in the Shallow Plate Interface at the Nankai Trough Subduction Zone  

NASA Astrophysics Data System (ADS)

The factors controlling the occurrence, magnitude, and other characteristics of great earthquakes is a fundamental outstanding question in fault physics. Pore fluid pressure is perhaps the most critical yet poorly known parameter governing the strength and seismogenic character of plate boundary faults, but unfortunately cannot be directly inferred through available geophysical sensing methods. Moreover, true in situ fluid pressure has proven difficult to measure even in boreholes. At the Nankai Trough, several hundred meters of sediment are subducted beneath the frontal portion of the accretionary prism. The up-dip portion of the plate interface is therefore hosted in these fine-grained marine sedimentary rocks. ODP Leg 190 and 196 showed that these rapidly-loaded underthrust sediments are significantly overpressured near the deformation front. Here, we attempt to quantitatively infer porosity, pore pressure, and effective normal stress at the plate interface at depths currently inaccessible to drilling. Using seismic reflection interval velocity calibrated at the boreholes to porosity, we quantitatively infer pore pressure to ˜ 20 km down-dip of the deformation front, to a plate interface depth of ˜ 6 km. We have developed a Nankai-specific velocity-porosity transform using ODP cores and logs. We use this function to derive a porosity profile for each of two down-dip seismic sections extracted from a 3-D dataset from the Cape Muroto region. We then calculate pore fluid pressure and effective vertical (fault-normal) stress for the underthrust sediment section using a compaction disequilibrium approach and core-based consolidation test data. Because the pore fluid pressure at the fault interface is likely controlled by that of the top of the underthrust section, this calculation represents a quantitative profile of effective stress and pore pressure at the plate interface. Results show that seismic velocity and porosity increase systematically downdip in the underthrust section, but the increase is suppressed relative to that expected from normally consolidating sediments. The computed pore pressure increases landward from an overpressure ratio (? * = hydrostatic pressure divided by the lithostatic overburden) of ˜ 0.6 at the deformation front to ˜ 0.77 where sediments have been subducted 15 km. The results of this preliminary analysis suggest that a 3-dimensional mapping of predicted effective normal stress in the seismic data volume is possible.

Tobin, H. J.; Saffer, D.

2003-12-01

105

Investigation on the Interface Morphologies of Explosive Welding of Inconel 625 to Steel A516 Plates  

NASA Astrophysics Data System (ADS)

The purpose of this study is to produce composite plates by explosive cladding process. This is a process in which the controlled energy of explosives is used to create a metallic bond between two similar or dissimilar materials. The welding conditions were tailored through parallel geometry route with different operational parameters. In this investigation, a two-pronged study was adopted to establish the conditions required for producing successful solid state welding: (a) Analytical calculations to determine the weldability domain or welding window; (b) Metallurgical investigations of explosive welding experiments carried out under different explosive ratios to produce both wavy and straight interfaces. The analytical calculations confirm the experimental results. Optical microscopy studies show that a transition from a smooth to wavy interface occurs with an increase in explosive ratio. SEM studies show that the interface was outlined by characteristic sharp transition between two materials.

Mousavi, S. A. A. Akbari; Zareie, H. R.

2011-01-01

106

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

107

Changes in electrical resistivity track changes in plate coupling of the Hikurangi subduction interface, New Zealand (Invited)  

NASA Astrophysics Data System (ADS)

Inter-plate coupling on the Hikurangi subduction margin along the east coast of New Zealand's North Island changes from north to south from almost uncoupled to locked. Magnetotelluric (MT) data from the northern part of the Hikurangi margin show a dipping conductor is present above the subduction interface and is interpreted to mark a layer of fluid and/or clay rich sediments within the subduction interface shear zone. Results from a MT profile in the southern part of the Hikurangi subduction margin, where the plates are locked, show the conductivity structure is markedly different than in the north. Here, no conductor is observed along the plate interface. The difference in plate-coupling and resistivity structure between the northern and southern parts of the Hikurangi margin suggest that the presence of fluid and/or clay rich sediments plays an important role in controlling the frictional processes at the interface and thus the inter-seismic coupling.

Heise, W.; Caldwell, G.; Hill, G.; Bertrand, E. A.; Bennie, S.; Ogawa, Y.

2013-12-01

108

Constraints on Pacific Plate Kinematics and Dynamics with Global Positioning System Measurements  

Microsoft Academic Search

Global positioning system (GPS) receivers are capable of generating precise geodetic data that can yield important constraints on both plate kinematics and dynamics. Geodetic measurements can determine plate motion rates over time scales for which little data are currently available. High-quality geodetic data may also allow the investigation of plate driving forces because changes in the intraplate stress field can

T. H. Dixon; M. P. Golombek; C. L. Thornton

1985-01-01

109

Pelagic and benthic ecology of the lower interface of the Eastern Tropical Pacific oxygen minimum zone  

NASA Astrophysics Data System (ADS)

The distributions of pelagic and benthic fauna were examined in relation to the lower boundary of the oxygen minimum zone (OMZ) on and near Volcano 7, a seamount that penetrates this feature in the Eastern Tropical Pacific. Although the broad, pronounced OMZ in this region is an effective barrier for most zooplankton, zooplankton abundances, zooplankton feeding rates, and ambient suspended particulate organic carbon (POC) peaked sharply in the lower OMZ (about 740-800 m), in association with the minimum oxygen concentration and the increasing oxygen levels just below it. Zooplankton in the lower OMZ were also larger in size, and the pelagic community included some very abundant, possibly opportunistic, species. Elevated POC and scatter in the light transmission data suggested the existence of a thin, particle-rich, and carbon-rich pelagic layer at the base of the OMZ. Gut contents of planktonic detrifvores implied opportunistic ingestion of bacterial aggregates, possibly from this layer. Benthic megafaunal abundances on the seamount, which extended up to 730 m, peaked at about 800 m. There was a consistent vertical progression in the depth of first occurrence of different megafaunal taxa in this depth range, similar to intertidal zonation. Although the vertical gradients of temperature, salinity, and oxygen were gradual at the lower OMZ interface (in contrast to the upper OMZ interface at the thermocline), temporal variability in oxygen levels due to internal wave-induced vertical excursions of the OMZ may produce the distinct zonation in the benthic fauna. The characteristics of the lower OMZ interface result from biological interactions with the chemical and organic matter gradients of the OMZ. Most zooplankton are probably excluded physiologically from pronounced OMZs. The zooplankton abundance peak at the lower interface of the OMZ occurs where oxygen becomes sufficiently high to permit the zooplankton to utilize the high concentrations of organic particles that have descended through the OMZ relatively unaltered because of low metazoan abundance. A similar scenario applies to megabenthic distributions. Plankton layers and a potential short food chain (bacteria to zooplankton) at OMZ interfaces suggest intense utilization and modification of organic material, localized within a thin midwater depth zone. This could be a potentially significant filter for organic material sinking to the deep-sea floor.

Wishner, Karen F.; Ashjian, Carin J.; Gelfman, Celia; Gowing, Marcia M.; Kann, Lisa; Levin, Lisa A.; Mullineaux, Lauren S.; Saltzman, Jennifer

1995-01-01

110

New observations on mid-plate volcanism and the tectonic history of the Pacific plate, Tahiti to Easter microplate  

Microsoft Academic Search

We describe the geology and tectonics of a continuous swathe of seafloor between Tahiti and the western edge of the Easter microplate imaged by GLORIA and Sea Beam on two separate cruise transits in 1987 and 1988. The data reveal that mid-plate volcanism is common in this region, even on deep seafloor hundreds of kilometres from major lines of seamounts

R. C. Searle; J. Francheteau; B. Cornaglia

1995-01-01

111

Effects of the Yakutat terrane collision with North America on the neighboring Pacific plate  

NASA Astrophysics Data System (ADS)

High-resolution bathymetry data show a 30 km N-S trending ridge within the deep-sea Surveyor Fan between the mouths of the Yakutat Sea Valley and Bering Trough in the Gulf of Alaska. The ridge originates in the north, perpendicular to and at the base of the continental slope, coincident with the Transition Fault, the strike-slip boundary between the Yakutat terrane (YAK) and the Pacific plate (PAC). The ridge exhibits greatest relief adjacent to the Transition Fault, and becomes less distinct farther from the shelf edge. Seismic reflection data reveal a sharp basement high beneath the ridge (1.1 sec of relief above "normal" basement in two-way travel time) as well as multiple similarly oriented strike-slip fault segments. The ridge, basement high, and faults are aligned and co-located with an intraplate earthquake swarm on the PAC, which includes four events > 6.5 Mw that occurred from 1987-1992. The swarm is defined by right-lateral strike-slip events, and is collectively called the Gulf of Alaska Shear Zone (GASZ). Based on the extent of historic seismicity, the GASZ extends at least 230 km into the PAC, seemingly ending at the Kodiak-Bowie Seamount Chain. Farther southwest, between the Kodiak-Bowie and Patton-Murray Seamount Chains, there is a large regional bathymetric low with an axis centered along the Aja Fracture Zone, perpendicular to the GASZ and Aleutian Trench. Basement and overlying sediment in the low are irregularly, but pervasively faulted. The GASZ and faulted bathymetric low could represent PAC deformation due to PAC-YAK coupling whereby YAK resistance to subduction is expressed as deformation in the thinner (weaker) PAC crust. The YAK is an allochthonous, basaltic terrane coupled to the PAC that began subducting at a low angle beneath North America (NA) ~25-40 Ma. Due to its 15-25 km thickness, the YAK is resistant to subduction compared to the normal oceanic crust of the PAC. As a result the plates developed differential motion along the Transition Fault and have different, convergent, vectors for motion relative to NA. Although a tear on the scale of the GASZ in normal oceanic crust is unusual, preexisting zones of weakness, such as the Aja Fracture Zone and bending faults at the flexural bulge, may have proven to be a kinematically favorable localization for strain. These results expand on a previous tectonic model wherein the differing YAK and PAC vectors caused the northern PAC to behave as two tectonic blocks, separated by the GASZ. In this model, the eastern block of the PAC exhibits a counter-clockwise rotation that accounts for motion along the Transition Fault and GASZ. We will analyze seismic reflection, bathymetric, magnetic, and gravity data in order to further investigate this intraplate deformation and the cause of strain localization in both areas. New bathymetric and 2D seismic reflection data will allow us to confirm whether the GASZ previously extended beyond the Kodiak-Bowie Seamount Chain and the current zone of active seismicity, as well as to characterize the GASZ at opposite ends.

Reece, R.; Gulick, S. P.; Christeson, G. L.; Barth, G. A.; van Avendonk, H.

2011-12-01

112

The Juan Fernandez microplate north of the Pacific-Nazca-Antarctic plate junction at 35 deg S  

NASA Astrophysics Data System (ADS)

Evidence for the existence of the Juan Fernandez microplate, just north of the junction between the East Pacific Rise and the Chile Fracture Zone, is adduced from the results of the Pascua 3 expedition. The 'SEABEAM' bathymetric system allows the plate fabric to be revealed along each swath. An analysis of faults, scarps, and submarine volcanoes is conducted for the entire Pascua 3 data set, and the results obtained furnish strong constraints for the kinematic model and geometry of the Juan Fernandez microplate proposed by Anderson-Fontana et al. (1986).

Francheteau, J.; Yelles-Chaouche, A.; Craig, H.

1987-12-01

113

Localized double-array stacking analysis of PcP: D??? and ULVZ structure beneath the Cocos plate, Mexico, central Pacific, and north Pacific  

USGS Publications Warehouse

A large, high quality P-wave data set comprising short-period and broadband signals sampling four separate regions in the lowermost mantle beneath the Cocos plate, Mexico, the central Pacific, and the north Pacific is analyzed using regional one-dimensional double-array stacking and modelling with reflectivity synthetics. A data-screening criterion retains only events with stable PcP energy in the final data stacks used for modelling and interpretation. This significantly improves the signal stacks relative to including unscreened observations, allows confident alignment on the PcP arrival and allows tight bounds to be placed on P-wave velocity structure above the core-mantle boundary (CMB). The PcP reflections under the Cocos plate are well modelled without any ultra-low velocity zone from 5 to 20??N. At latitudes from 15 to 20??N, we find evidence for two P-wave velocity discontinuities in the D??? region. The first is ???182 km above the CMB with a ??ln Vp of +1.5%, near the same depth as a weaker discontinuity (<+0.5%) observed from 5 to 15??N in prior work. The other reflector is ???454 km above the CMB, with a ??ln Vp of +0.4%; this appears to be a shallower continuation of the joint P- and S-wave discontinuity previously detected south of 15?? N, which is presumed to be the perovskite to post-perovskite phase transition. The data stacks for paths bottoming below Mexico have PcP images that are well matched with the simple IASP91 structure, contradicting previous inferences of ULVZ presence in this region. These particular data are not very sensitive to any D??? discontinuities, and simply bound them to be Pacific confirm the presence of a ???15-km thick ultra-low velocity zone (ULVZ) just above the CMB, with ??ln Vp and ??ln Vs of around -3 to -4% and -4 to -8%, respectively. The ULVZ models predict previous S-wave data stacks well. The data for this region indicate laterally varying Vp discontinuities in D???, with one subregion having a ??ln Vp of 0.5% 140 km above the CMB. Beneath the north Pacific, the PcP arrivals are compatible with only weak ULVZ (??ln Vp ??? 0 to -3%), and there is a weak D??? reflector with ??ln Vp = 0.5%, near 314 km above the CMB. These results indicate localized occurrence of detectable ULVZ structures rather than ubiquitous ULVZ structure and emphasize the distinctiveness between the large low shear velocity province under the central Pacific and circum-Pacific regions. ?? 2008 Elsevier B.V.

Hutko, A. R.; Lay, T.; Revenaugh, J.

2009-01-01

114

Into the Future: Continuing Evolution of the Pacific-Juan de Fuca-North America Plate System  

NASA Astrophysics Data System (ADS)

The death of a series of spreading ridge segments adjacent to California and Mexico starting about 28.5 Ma led to the piecewise destruction of a subduction regime and the opening of slab windows beneath the continent. The formation, growth, and healing of these slab windows has been a transient process marked at the surface by overprinted pulses of volcanism in the former forearc triggered by asthenospheric upwelling behind subducting slab edges. In the subsurface, where windows opened beneath thin forearc lithosphere, the shallow asthenosphere promoted a plastic mode of mechanical behavior in the lithosphere characterized by fault-block deformation. This plastic mode of deformation resulted mainly from (1) asthenosphere in direct contact with the lower crust instead of stronger lithospheric mantle; and (2) lower crust shifting from brittle to ductile behavior as a result of conductive heating. Our finite-rotation model built from quantitative reconstruction of Farallon-North America slab windows and their magmatic signatures allows us to investigate past and future fault-block kinematics of the North America continental margin. While the shallow asthenosphere thermally weakened coastal California and promoted plastic deformation in the lower crust, the actual fragmentation of the upper crust into fault blocks occurred in concert with retrograde motion of a partially subducted Monterey plate fragment following its capture by the Pacific plate ca. 19 Ma. This abrupt change from convergent to transtensional deformation initiated the pulling apart and clockwise pivoting of the adjacent western Transverse Ranges and California Borderlands region. A similar reversal in plate motion occurred adjacent to coastal Mexico following capture of a Magdalena plate fragment by the Pacific plate ca. 12.5 Ma. In this case, the transtensional strain that initiated Baja California pulling away from the Mexican continental margin was localized along already thermally weakened Comondu volcanic arc crust. In California, running our kinematic model into the future suggests that the current locus of strike-slip motion may shift to the east side of the Sierra Nevada Mountains, starting about 2 My from now as a result of convergence between the Sierra Nevada and Peninsular Range batholiths. Alternatively, the locus of fault slip may remain on the San Andreas fault, requiring new fragments to be broken from the southern Sierra Nevada and Mojave blocks, to make room for the Peninsular Range to slip past on their west side. Or perhaps, eastern parts of the Peninsular Range may transfer back to the North America plate, with the Whittier-Elsinore fault accommodating most of the relative plate motion.

McCrory, P. A.; Wilson, D. S.; Stanley, R. G.

2007-12-01

115

Tide gauge records of uplift along the northern Pacific-North American plate boundary, 1937 to 2001  

NASA Astrophysics Data System (ADS)

Vertical crustal motions at 15 sites along the northern Pacific-North America plate boundary are determined using relative sea level changes from tide gauge records. Our analysis is based on monthly mean sea levels, from which barometric pressure and seasonal effects are removed. The records are corrected for common-mode oceanographic variations. These records are statistically examined for non-linear behavior related to glacial isostatic, tectonic and postseismic effects. To estimate land uplift rates, the local effect of global sea level rise is removed from the relative sea level rates. Slow rates of vertical motion are observed along the southern strike-slip plate boundary. The extremely rapid uplift of the northern strike-slip boundary can be attributed entirely to viscoelastic postglacial rebound associated with tidewater-glacier retreat in Glacier Bay and regional post-Little Ice Age deglaciation. Isostatic modeling indicates a mantle viscosity of ˜2 × 1019-5 × 1019 Pa s, similar to that found elsewhere along the Pacific-North America plate margin. At Yakutat, near the transition of plate motion from strike-slip to subduction, complex non-linear behavior is evident, with a significant change in uplift rate following the 1979 St. Elias earthquake. Non-linear uplift rates are predominant within the 1964 Great Alaskan earthquake near-field. Rapid uplift at Kodiak during a 3.5 year period starting mid-1964 totaled 47 ± 8 cm. Anchorage, Seward and Seldovia exhibited oscillatory uplift in the period immediately following the earthquake until mid-1972. Since mid-1972, uplift rates have increased steadily at Anchorage, Seward, Cordova, and Valdez. During this period Nikiski and Kodiak show decreasing uplift rates.

Larsen, Christopher F.; Echelmeyer, Keith A.; Freymueller, Jeffrey T.; Motyka, Roman J.

2003-04-01

116

Long-term coupling along the subduction plate interface: insights from exhumed rocks and models  

NASA Astrophysics Data System (ADS)

Fragments of subducted oceanic lithosphere returned along the plate interface convey crucial information regarding the thermal and rheological conditions of convergent plate boundaries. Combining evidence from exhumed rocks worldwide and the results of recently published thermo-mechanical models, we herein investigate how long-term mechanical coupling takes place along deep portions of the plate interface (40-80 km depth), for which there is no counterflow (unlike in accretionary prisms) and no other known mechanisms to return eclogites than interplate friction or buoyancy. Geological evidence indicates that, unlike subduction, exhumation is highly discontinuous. Besides, eclogites worldwide are found in essentially two types of tectonic setting, either as large scale (>km) slices with coherent PT estimates (W. Alps) or as isolated fragments (frequently m-hm) in a serpentinite- or sedimentary-rich matrix showing contrasting equilibration depths (with hints of punctuated exhumation and even reburial in some localities; Franciscan, Cuba, Sistan). This latter type tends to show warmer equilibration paths (although minor lawsonite-eclogite blocks can be found), whereas the larger tectonic slices from the former type remain systematically cold. Serpentinites are crucial for both in permitting decoupling and acting as a buoy, and fluid budget is important too in enhancing floatability and allowing large slices to survive. Numerical models implementing free migration of fluids in the subduction zone also show that the plate interface is strongly localized in the absence of fluids: mechanical decoupling efficiently occurs along the sediment veneer and/or at the top of the highly hydrothermalized crust. Whenever fluids are released in greater amounts (depending on initial fluid content and/or thermal structure), deformation becomes much more distributed and affects both the mantle wedge and the top of the downgoing lithosphere (hydrated crust and mantle top), thereby increasing mechanical coupling between the two plates. Based on natural data and numerical modelling we thus propose that rheological contrast chiefly controls mechanical decoupling (and early exhumation). On a steady-state basis the subduction interface is apparently efficiently decoupled. In this context, we hypothesize that the liberation of fluid through pulses (or a somewhat increased amount of fluids) is required to locally modify mechanical coupling and induce the slicing of large pieces of oceanic material along the subduction interface (type 1). By contrast, an extreme hydration of the subduction interface and mantle wedge will result in the formation of serpentinite melanges and extensive material mixing (e.g., cold plumes, mafic pods and localized melting; type 2). This latter situation may be promoted by young/fast/wet subduction, such as subduction initiation and/or subduction of young lithosphere or subduction of a particularly hydrated lithosphere section (e.g., at the ridge and/or prior to entering the trench). By contrast cold, slow subduction (type 1) will result in irregular hydration and localized coupling able to detach large slices.

Agard, P.; Angiboust, S.; Guillot, S.; Garcia-Casco, A.

2012-04-01

117

Episodic Mesozoic thickening and reworking of the North China Archean lower crust correlated to the fast-spreading Pacific plate  

NASA Astrophysics Data System (ADS)

A central target in Earth sciences is to understand the processes controlling the stabilization and destruction of Archean continents. The North China craton (NCC) has in part lost its dense crustal root after the Mesozoic, and thus it is a key region to test models of crust-mantle differentiation and subsequent evolution of the continental crust. However, the timing and mechanisms responsible for its crustal thickening and reworking have been long debated. Here we report the Early Cretaceous Yinan (eastern NCC) adakitic granites, for which major/trace elemental models demonstrate that they are complementary to the analogy of the documented eclogitic relicts within the NCC. Based on their Late Archean inherited zircons, depleted mantle Nd model ages of ˜2.8 Ga, large negative ?Nd(t) values (-36.7 to -25.3) and strongly radiogenic initial 87Sr/86Sr ratios (0.7178-0.7264), we suggest that the Yinan adakitic granites were potentially formed by the dehydration melting of a thickened Archean mica-bearing mafic lower crust during the Early Cretaceous (ca. 124 Ma), corresponding to a major period (117-132 Ma) of the NCC Mesozoic intrusive magmatism. Combined previous results, it is shown that the thickening and reworking of the North China Archean lower crust occurred largely as two short-lived episodes at 155-180 Ma and 117-132 Ma, rather than a gradual, secular event. These correlated temporally with the superfast-spreading Pacific plate during the Mesozoic. The synchroneity of these events suggests rapid plate motion of the Pacific plate driving the episodic NCC crustal thickening and reworking, resulting in dense eclogitic residues that became gravitationally unstable. The onset of lithospheric delamination occurred when upwelling asthenosphere heated the base of lower crust to form coeval felsic magmas with or without involvement of juvenile mantle material. Collectively, the circum-Pacific massive crustal production could be attributed to the unusually rapid motion of Pacific at 155-180 Ma and 117-132 Ma.

Zhang, Jun-Bo; Ling, Wen-Li; Liu, Yong-Sheng; Duan, Rui-Chun; Gao, Shan; Wu, Yuan-Bao; Yang, Hong-Mei; Qiu, Xiao-Fei; Zhang, Yong-Qing

2014-02-01

118

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

NASA Technical Reports Server (NTRS)

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

Fitch, T. J.

1971-01-01

119

Modeling thermal and stress behavior of the fuel-clad interface in monolithic fuel mini-plates  

SciTech Connect

A fuel development and qualification program is in process with the objective of qualifying very high density monolithic low enriched uranium–molybdenum fuel for high-performance research reactors. The monolithic fuel foil creates differences in the mechanical and structural characteristics of the fuel plate because of the planar interface created by the fuel foil and cladding. An initial finite element analysis model has been developed to investigate worst-case scenarios for the basic monolithic fuel plate structure using typical mini-plate irradiation conditions in the Advanced Test Reactor. Initial analysis shows that the stress normal to the fuel–clad interface dominates during irradiation and that the presence of small, rounded delaminations at the interface is not of great concern. However, larger and/or fuel–clad delaminations with sharp corners can create areas of concern, as maximum principal cladding stress, strain, displacement, and peak fuel temperature are all significantly increased. Furthermore, stresses resulting from temperature gradients that cause the plate to bow or buckle in an unconstrained fuel plate configuration is greatly enhanced in a constrained fuel plate configuration. The sensitivities of the model and input parameters are discussed, along with some overlap of initial experimental observations using as-fabricated plate characterization and post-irradiation examination.

Gregory K. Miller; Douglas E. Burkes; Daniel M. Wachs

2010-08-01

120

Finite Element Modeling of Laminated Composite Plates with Locally Delaminated Interface Subjected to Impact Loading  

PubMed Central

This paper investigates the effects of localized interface progressive delamination on the behavior of two-layer laminated composite plates when subjected to low velocity impact loading for various fiber orientations. By means of finite element approach, the laminae stiffnesses are constructed independently from their interface, where a well-defined virtually zero-thickness interface element is discreetly adopted for delamination simulation. The present model has the advantage of simulating a localized interfacial condition at arbitrary locations, for various degeneration areas and intensities, under the influence of numerous boundary conditions since the interfacial description is expressed discretely. In comparison, the model shows good agreement with existing results from the literature when modeled in a perfectly bonded state. It is found that as the local delamination area increases, so does the magnitude of the maximum displacement history. Also, as top and bottom fiber orientations deviation increases, both central deflection and energy absorption increase although the relative maximum displacement correspondingly decreases when in contrast to the laminates perfectly bonded state.

Abo Sabah, Saddam Hussein; Kueh, Ahmad Beng Hong

2014-01-01

121

Finite element modeling of laminated composite plates with locally delaminated interface subjected to impact loading.  

PubMed

This paper investigates the effects of localized interface progressive delamination on the behavior of two-layer laminated composite plates when subjected to low velocity impact loading for various fiber orientations. By means of finite element approach, the laminae stiffnesses are constructed independently from their interface, where a well-defined virtually zero-thickness interface element is discreetly adopted for delamination simulation. The present model has the advantage of simulating a localized interfacial condition at arbitrary locations, for various degeneration areas and intensities, under the influence of numerous boundary conditions since the interfacial description is expressed discretely. In comparison, the model shows good agreement with existing results from the literature when modeled in a perfectly bonded state. It is found that as the local delamination area increases, so does the magnitude of the maximum displacement history. Also, as top and bottom fiber orientations deviation increases, both central deflection and energy absorption increase although the relative maximum displacement correspondingly decreases when in contrast to the laminates perfectly bonded state. PMID:24696668

Abo Sabah, Saddam Hussein; Kueh, Ahmad Beng Hong

2014-01-01

122

Analysis of Genes Isolated from Plated Hemocytes of the Pacific Oyster, Crassostreas gigas  

Microsoft Academic Search

A complementary deoxyribonucleic acid library was constructed from hemocytes of Crassostrea gigas that had been plated on poly-lysine plates for 24 h. From this library, 2,198 expressed sequence tags (ESTs) of greater than\\u000a or equal to 100 bp were generated and analyzed. A large number of genes that potentially could be involved in the physiology\\u000a of the oyster hemocyte were uncovered. They

Steven Roberts; Giles Goetz; Samuel White; Frederick Goetz

2009-01-01

123

Newly imaged shape of the deep seismic zone within the subducting Pacific plate beneath the Hokkaido corner, Japan-Kurile arc-arc junction  

Microsoft Academic Search

The geometry of the deep seismic zone associated with the subducting Pacific plate beneath the North American plate in the Hokkaido corner, Japan-Kurile arc-arc junction has been investigated based on the hypocenters accurately relocated by a dense local seismographic network with three-dimensional P and S wave velocity structures. The model suggests that the lateral changes in the dip of the

Kei Katsumata; Naoto Wada; Minoru Kasahara

2003-01-01

124

Geodetic constraints on areal changes in the Pacific-North America plate boundary zone: What controls Basin and Range extension?  

NASA Astrophysics Data System (ADS)

Using ˜1500 geodetic velocities we model the present-day spatial patterns of areal changes inside the Pacific-North America plate boundary zone. From this model we show that between the central Gulf of California and the Queen Charlotte Islands there is no significant net change in surface area. This zero net areal-change result allows us to relate regions of areal growth to areas of equivalent contraction elsewhere within the plate boundary zone. We find that areal growth of the Basin and Range province (BRP) and its eastern margin (˜5.2 ± 0.1 × 103 m2/yr) is balanced by areal reduction near northwestern California between 38°N and 42°N. The San Andreas fault system south of 38°N and the plate boundary zone north of ˜42°N (including the Juan de Fuca and Gorda Ridge systems) each have no significant net areal change. Our results suggest a kinematic relationship between extension in the BRP and contraction near the northern California Coast Ranges and Klamath Mountains. From these observations we propose that, although BRP extension may be caused by internal forces, the southernmost Cascadia subduction zone provides a “window of escape” that acts as a stress guide to BRP extension as well as northwestward Sierra Nevada motion. Such a dynamic model is consistent with independent findings that (1) the least principal horizontal stress orientations in the BRP are toward northern California, (2) extension directions in the BRP have changed orientation to track the northward migration of the Mendocino triple junction, and (3) the southernmost Cascadia subduction zone is a relatively weak plate boundary.

Kreemer, Corné; Hammond, William C.

2007-10-01

125

Faunal breaks and species composition of Indo-Pacific corals: the role of plate tectonics, environment and habitat distribution  

PubMed Central

Species richness gradients are ubiquitous in nature, but the mechanisms that generate and maintain these patterns at macroecological scales remain unresolved. We use a new approach that focuses on overlapping geographical ranges of species to reveal that Indo-Pacific corals are assembled within 11 distinct faunal provinces. Province limits are characterized by co-occurrence of multiple species range boundaries. Unexpectedly, these faunal breaks are poorly predicted by contemporary environmental conditions and the present-day distribution of habitat. Instead, faunal breaks show striking concordance with geological features (tectonic plates and mantle plume tracks). The depth range over which a species occurs, its larval development rate and genus age are important determinants of the likelihood that species will straddle faunal breaks. Our findings indicate that historical processes, habitat heterogeneity and species colonization ability account for more of the present-day biogeographical patterns of corals than explanations based on the contemporary distribution of reefs or environmental conditions.

Keith, S. A.; Baird, A. H.; Hughes, T. P.; Madin, J. S.; Connolly, S. R.

2013-01-01

126

Faunal breaks and species composition of Indo-Pacific corals: the role of plate tectonics, environment and habitat distribution.  

PubMed

Species richness gradients are ubiquitous in nature, but the mechanisms that generate and maintain these patterns at macroecological scales remain unresolved. We use a new approach that focuses on overlapping geographical ranges of species to reveal that Indo-Pacific corals are assembled within 11 distinct faunal provinces. Province limits are characterized by co-occurrence of multiple species range boundaries. Unexpectedly, these faunal breaks are poorly predicted by contemporary environmental conditions and the present-day distribution of habitat. Instead, faunal breaks show striking concordance with geological features (tectonic plates and mantle plume tracks). The depth range over which a species occurs, its larval development rate and genus age are important determinants of the likelihood that species will straddle faunal breaks. Our findings indicate that historical processes, habitat heterogeneity and species colonization ability account for more of the present-day biogeographical patterns of corals than explanations based on the contemporary distribution of reefs or environmental conditions. PMID:23698011

Keith, S A; Baird, A H; Hughes, T P; Madin, J S; Connolly, S R

2013-07-22

127

Evidence from GPS measurements for contemporary interplate coupling on the southern Hikurangi subduction thrust and for partitioning of strain in the upper plate  

Microsoft Academic Search

The spatial extent and strength of contemporary coupling between the Pacific and Australian plates on the Hikurangi subduction interface beneath the Wellington region of New Zealand are not well known. Consequently, the potential for the plate interface to produce great thrust earthquakes, or to load the major Wellington and Wairarapa faults in the overlying plate, is also unknown. To address

Desmond Darby; John Beavan

2001-01-01

128

Rheology of the plate interface — Dissolution precipitation creep in high pressure metamorphic rocks  

NASA Astrophysics Data System (ADS)

Subduction zone models invoke deformation to be concentrated along the plate interface, in a region of particularly low temperature. Geophysical observations do not provide constraints on temperature, stress and deformation patterns with desired resolution. In contrast, the record of high pressure metamorphic rocks exhumed from subduction zones provides details on P-T-history, deformation mechanisms, and stress state, albeit not readily correlated with the former dynamic situation on larger scale. Here we review available information on dissolution precipitation creep (DPC) in high pressure metamorphic rocks, which - if representative for subduction zones in general - can pose constraints on conditions, rheology, and flow patterns along the plate interface. The key observations and conclusions are that: (1) Deformation is typically highly inhomogeneous and localized into shear zones; (2) stresses are generally too low to drive crystal plastic deformation; (3) microfabrics suggest dissolution precipitation creep to be the predominant deformation mechanism; (4) an aqueous fluid at quasi-lithostatic pressure is available throughout, allowing for tensile fracturing and crack healing or sealing; (5) low stress combined with high strain rates required for localized deformation at typical subduction rates implies low viscosity; and (6) contribution of shear heating to the thermal budget of subduction zones should be moderate. The dominant deformation mechanism DPC is reviewed in some detail, including experimental and theoretical approaches. Various examples of DPC in high pressure metamorphic rocks are illustrated, emphasizing the role of interphase boundaries as sites of dissolution. Rheology governed by DPC is proposed to control interplate coupling and development of a subduction channel with return flow, being a likely candidate for rapid exhumation of high pressure metamorphic rocks.

Wassmann, Sara; Stöckhert, Bernhard

2013-11-01

129

Unlocking the Secrets of Slow Slip on the Plate Interface Using Cascadia LFEs  

NASA Astrophysics Data System (ADS)

Low-frequency earthquakes (LFEs) have been associated with tectonic tremor and slow slip on the deep extension of subduction zones (Japan, Cascadia, Alaska, Costa Rica) and major strike-slip faults (SAF). These tiny earthquakes are thought to represent small amounts of slip on the fault interface in places with very high pore fluid pressures and low effective stresses. Tectonic tremor has been shown to often consist of a superposition of many LFEs occurring at nearly the same time. Using data from the 2-year Array of Arrays (AofA) and 6-year CAFE experiments in northern Cascadia, we employ a matched-filter autocorrelation method to find new LFE families. Similar to the method of Brown et al. (GRL, 2008), ours makes use of efficient coding to minimize the significant computational time required. To date, we have identified and located 8 LFE families, all of which are very near the plate interface. By analyzing a 6-year history of individual LFE families, we find several new patterns that vary with downdip distance on the plate interface. The two end-member LFE families (LFE1 - farthest updip, and LFE4 - farthest downdip) illustrate the greatest differences in behavior. The recurrence interval of LFE activity increases updip. LFE1 is only active during major ETS episodes every 12-15 months, while LFE4 repeats every 2 weeks. This observation mirrors that already reported for tremor swarms in Cascadia (Wech et al., 2011, Nature GeoSci.), further supporting the idea that tremor and LFEs are closely linked. In addition, we observe that the duration of the initial burst of activity is longer for updip LFE families than for downdip ones. LFE1 exhibits an initial burst of frenzied activity that lasts ~4 hours, which we interpret to be the passage of the slow-slip rupture front. In contrast, LFE4 has initial bursts that last at most 1 hour (see Creager et al., this session). The different duration of bursts, combined with the different recurrence intervals, suggests that locations farther updip are capable of accumulating and releasing larger amounts of slip than locations farther downdip. This observation may provide insight into how frictional properties vary over the subduction interface. During each of the past 5 ETS episodes, LFE1 was active over a 5-day period following the initial burst. During these 5 days, most of the activity was concentrated in roughly 5 residual bursts (of duration <1hr) that occurred at exponentially increasing recurrence intervals. After 5 days, the residual bursts ceased and no activity was detected until the next ETS episode. In addition, nearly all of the residual bursts occurred during times of favorable tidal shear stress, suggesting that these later bursts occurred in an environment with very low stress such that small tidal fluctuations activate or inhibit slip. In contrast, the initial bursts occurred independently of the tidal stress. For the last 2 ETS episodes, the residual bursts correspond to rapid tremor reversals (RTRs) imaged by the AofA (see Thomas et al., this session). This observation may indicate that RTRs could be modulated and perhaps even triggered by favorable tidal stressing in the extremely low stress region behind the initial slip front. This idea is consistent with the proposal by Houston et al. (2011, Nature GeoSci.) that RTRs are associated with a slip-weakened plate interface.

Sweet, J. R.; Creager, K. C.; Thomas, T.; Vidale, J. E.; Houston, H.

2012-12-01

130

Petrological insights into intermediate-depths of a subduction plate interface  

NASA Astrophysics Data System (ADS)

Understanding processes acting along the subduction interface is crucial to assess lithospheric scale coupling between tectonic plates, exhumation of deep-seated rocks and mechanisms causing intermediate-depth seismicity. Yet, despite a wealth of geophysical studies aimed at better characterizing the subduction interface, we still lack critical petrological data constraining such processes as intermediate-seismicity within oceanic subduction zones. This contribution reviews recent findings from two major localities showing deeply subducted ophiolitic remnants (Zermatt-Saas, Monviso), which crop out in the classic, well-preserved fossil subduction setting of the Western Alps. We herein show that both ophiolite remnants represent large, relatively continuous fragments of oceanic lithosphere (i.e., several km-thick tectonic slices across tens of km) exhumed from ~80 km depths and thereby provide important constraints on interplate coupling mechanisms. In both fragments (but even more so in the Zermatt-Saas one) pervasive hydrothermal processes and seafloor alteration, promoting fluid incorporation in both mafic and associated ultramafic rocks, was essential, together with the presence of km-thick serpentinite soles, to decrease the density of the tectonic slices and prevent them from an irreversible sinking into the mantle. The Monviso case sudy provides further insights into the subduction plate interface at ~80 km depths. The Lago Superiore Unit, in particular, is made of a 50-500 m thick eclogitized mafic crust (associated with minor calcschist lenses) overlying a 100-400 m thick metagabbroic body and a km-thick serpentinite sole, and is cut by two 10 to 100m thick eclogite-facies shear zones, respectively located at the boundary between basalts and gabbros, and between gabbros and serpentinites (the Lower Shear Zone: LSZ). The LSZ gives precious information on both seismicity and fluid flow: (1) Eclogite breccias, reported here for the first time, mark the locus of an ancient fault zone associated with intraslab, intermediate-depth earthquakes at ~80 km depth. They correspond to m-sized blocks made of 1-10 cm large fragments of eclogite mylonite later embedded in serpentinite in the eclogite facies LSZ. We suggest that seismic brecciation (possibly at magnitudes Mw ~4) occurred in the middle part of the oceanic crust, accompanied by the input of externally-derived fluids. (2) Prominent fluid-rock interactions, as attested by ubiquitous metasomatic rinds, affected the fragments of mylonitic basaltic eclogites and calcschists dragged and dismembered within serpentinite during eclogite-facies deformation. Detailed petrological and geochemical investigations point to a massive, pulse-like, fluid-mediated element transfer essentially originating from serpentinite. Antigorite breakdown, occurring ca. 15 km deeper than the maximum depth reached by these eclogites, is regarded as the likely source of this highly focused fluid/rock interaction and element transfer. Such a pulse-like, subduction-parallel fluid migration pathway within the downgoing oceanic lithosphere may have been promoted by transient slip behaviour along the LSZ under eclogite-facies conditions. These petrological data are finally tied to bi-phase numerical models in which fluid migration is driven by fluid concentrations in the rocks, non-lithostatic pressure gradients and deformation, and that allow for mantle wedge hydration and mechanical weakening of the plate interface. We suggest that the detachment of such oceanic tectonic slices is largely promoted by fluid circulation along the subduction interface, as well as by subducting a strong and originally discontinuous mafic crust.

Angiboust, Samuel; Agard, Philippe

2013-04-01

131

The Hawaiian-Emperor Bend: A Record of Pronounced Change in Pacific Absolute Plate Motion  

Microsoft Academic Search

Following the development of the hot spot hypothesis (Morgan, 1971) there was almost unanimous agreement that the Hawaiian-Emperor Bend (HEB) was the archetypal example of a large change in absolute plate motion (APM) recorded by hot spot volcanism. Lately, however this conviction has come under renewed scrutiny. Norton (1995) analyzed the geological evidence for contemporaneous tectonic activity and found none,

P. Wessel; L. W. Kroenke; Y. Harada; A. Sterling

2002-01-01

132

Distribution and migration of aftershocks of the 2010 Mw 7.4 Ogasawara Islands intraplate normal-faulting earthquake related to a fracture zone in the Pacific plate  

NASA Astrophysics Data System (ADS)

describe the aftershocks of a Mw 7.4 intraplate normal-faulting earthquake that occurred 150 km east Ogasawara (Bonin) Islands, Japan, on 21 December 2010. It occurred beneath the outer trench slope of the Izu-Ogasawara trench, where the Pacific plate subducts beneath the Philippine Sea plate. Aftershock observations using ocean bottom seismographs (OBSs) began soon after the earthquake and multichannel seismic reflection surveys were conducted across the aftershock area. Aftershocks were distributed in a NW-SE belt 140 km long, oblique to the N-S trench axis. They formed three subparallel lineations along a fracture zone in the Pacific plate. The OBS observations combined with data from stations on Chichi-jima and Haha-jima Islands revealed a migration of the aftershock activity. The first hour, which likely outlines the main shock rupture, was limited to an 80 km long area in the central part of the subsequent aftershock area. The first hour activity occurred mainly around, and appears to have been influenced by, nearby large seamounts and oceanic plateau, such as the Ogasawara Plateau and the Uyeda Ridge. Over the following days, the aftershocks expanded beyond or into these seamounts and plateau. The aftershock distribution and migration suggest that crustal heterogeneities related to a fracture zone and large seamounts and oceanic plateau in the incoming Pacific plate affected the rupture of the main shock. Such preexisting structures may influence intraplate normal-faulting earthquakes in other regions of plate flexure prior to subduction.

Obana, Koichiro; Takahashi, Tsutomu; No, Tetsuo; Kaiho, Yuka; Kodaira, Shuichi; Yamashita, Mikiya; Sato, Takeshi; Nakamura, Takeshi

2014-04-01

133

Evolution of the Walker Lane: An Incipient Transform Fault and Future Pacific-North America Plate Boundary  

NASA Astrophysics Data System (ADS)

Since ~30 Ma, western North America has been evolving from an Andean type margin to a dextral transform. Transform growth has been marked by arc retreat, orogenic collapse, and inland steps of the San Andreas fault system (SAF). In the western Great Basin (WGB), a system of dextral faults, known as the Walker Lane (WL) in the north and eastern California shear zone (ECSZ) in the south, currently accommodates ~20% of the Pacific - North America dextral motion. In contrast to the continuous 1100-km-long SAF, discontinuous ~10-250-km-long dextral faults comprise the WL-ECSZ. Displacement across the WL-ECSZ decreases N-ward from ?60 km in south to E-central California, to ~25 km in NW Nevada, to zero in NE California. Geodetic strain rates are ~10 mm/yr across the WL-ECSZ in the WGB but decrease to <2.5 mm/yr at the NW terminus in NE California. The evolution of the WL-ECSZ is closely linked to events along the SAF. The early Miocene elimination of microplates along the southern California coast, S-ward steps in the Rivera triple junction at 19-16 Ma and 13 Ma, and an increase in plate motions ~12 Ma induced the first major episode of deformation in the WL-ECSZ, which began ~13 Ma along the N60°W-trending Las Vegas shear zone (LVSZ). The LVSZ shear zone paralleled plate motions, formed inboard of where the SAF initially organized into a through-going structure, and accommodated ~60 km of right slip ~13 to 6 Ma. In the late Miocene, the southern part of the transform shifted (~13-6 Ma) east to the Gulf of California (GC), the Big Bend of the SAF developed, and plate motions changed from ~N60°W to N37°W (11-6 Ma). Coincidentally (~11-6 Ma), dextral shear shifted west in the WL-ECSZ from the LVSZ to a NNW belt in the WGB. Dextral shear was favored in the WGB as it paralleled the new plate motion, aligned with the GC, and avoided the Big Bend bottleneck. By ~4 Ma, dextral shear had propagated to the northern WL (NW Nevada - NE California) in concert with the N-ward migration of the Mendocino triple junction (MTJ). The northern WL is the least developed part of the WL-ECSZ, with right slip decreasing from ~25 km to zero to the NW. Here, en echelon left-stepping dextral faults are analogous to Riedel shears developed above a through-going shear zone at depth. Coeval extension and dextral shear have induced slight counterclockwise rotations, which may ultimately rotate Riedel shears toward the main shear zone at depth, facilitate hard linkage between Riedel shears, and produce a through-going strike-slip fault. The WL-ECSZ now terminates near the south end of the Cascade arc near the latitude of the MTJ, suggesting that the SAF and WL-ECSZ are migrating N-ward at similar rates. With continued N-ward migration, the MTJ will collide with the NW-propagating WL off southern Oregon in ~8 Ma. The plate boundary will then likely jump inland to the WL-ECSZ. The current setting is one stage in the progressive dismembering of an Andean type margin through lateral growth and inland stepping of a transform fault. This process is fragmenting the continental margin and transferring slices of North America to the Pacific plate. Evolving transform faults may therefore be important in generating far-traveled exotic terranes.

Faulds, J. E.; Henry, C. D.

2009-12-01

134

Plate Coupling, Block Rotation and Crustal Deformation in the Pacific Northwest  

NASA Astrophysics Data System (ADS)

GPS measurements in the northwestern US and adjacent parts of Canada describe the relative motions of crustal blocks, the interseismic friction on faults, and the permanent deformation associated with convergence between the Juan de Fuca and North American plates. To estimate angular velocities of the oceanic Juan de Fuca and Explorer plates and several continental crustal blocks, we invert the GPS velocities with seafloor spreading rates, earthquake slip vector azimuths, fault slip azimuths and rates. We also determine the distribution of frictional properties on the block-bounding faults. The Cascadia megathrust is locked offshore, except in southern Oregon, where significant locking extends inland. Most of Oregon and southwest Washington rotate clockwise relative to North America at rates of 0.4 to 1.0°/Myr. No shear or extension along the Cascades volcanic arc is occurring at the mm/yr level during the past decade. The agreement of spin rates derived from GPS velocities with those estimated from paleomagnetic declination anomalies suggests that the rotations have been steady for several millions of years. Rotations in the PNW do not result in net westward flux of crustal material. Rotation of Oregon and western Washington indicates that the rate of permanent shortening, the type that causes upper plate earthquakes, across the Puget Sound region is 4.4±0.3 mm/yr.

McCaffrey, R.; Qamar, A. I.; King, R. W.; Wells, R.

2006-12-01

135

Three-Dimensional Variations in Tectonic Stress Along a Complex Plate Boundary: Australia-Pacific Plate Interaction in Central New Zealand  

NASA Astrophysics Data System (ADS)

In recent years, a number of regional seismological studies have determined the present-day principal tectonic stress directions at points along the Australia-Pacific plate boundary in central New Zealand. To date, however, there has not been a broader-scale study of tectonic stress that capitalises on high-quality seismological data recorded by the GeoNet monitoring system. In this study, we have computed tectonic stress parameters throughout central New Zealand (latitudes 38-43°S) using a data set of almost 3500 earthquake focal mechanisms recorded by GeoNet between January 2004 and February 2011. Each earthquake has been relocated using the nationwide 3D seismic velocity model of Eberhart-Phillips et al. (2010, SRL) and the NonLinLoc algorithm of Lomax et al. (2000, Advances in Seismic Event Location). The estimated uncertainties in each hypocenter are propagated into the focal mechanism calculations, and thereby into the stress parameter estimates using Bayesian algorithms (Arnold & Townend, 2007, GJI; Walsh et al., 2009, GJI). In most regional or broader-scale studies of tectonic stress it is common to compute the azimuth of maximum horizontal compressive stress, SHmax. Here we describe a method of representing the stresses acting on dipping structures, notably the Hikurangi subduction thrust beneath the North Island, and on arbitrarily oriented cross-sections.

Townend, J.; Sherburn, S.; Arnold, R.

2011-12-01

136

Evaluation of a new approach for modelling the screw-bone interface in a locking plate fixation: a corroboration study.  

PubMed

Computational modelling of the screw-bone interface in fracture fixation constructs is challenging. While incorporating screw threads would be a more realistic representation of the physics, this approach can be computationally expensive. Several studies have instead suppressed the threads and modelled the screw shaft with fixed conditions assumed at the screw-bone interface. This study assessed the sensitivity of the computational results to modelling approaches at the screw-bone interface. A new approach for modelling this interface was proposed, and it was tested on two locking screw designs in a diaphyseal bridge plating configuration. Computational models of locked plating and far cortical locking constructs were generated and compared to in vitro models described in prior literature to corroborate the outcomes. The new approach led to closer agreement between the computational and the experimental stiffness data, while the fixed approach led to overestimation of the stiffness predictions. Using the new approach, the pattern of load distribution and the magnitude of the axial forces, experienced by each screw, were compared between the locked plating and far cortical locking constructs. The computational models suggested that under more severe loading conditions, far cortical locking screws might be under higher risk of screw pull-out than the locking screws. The proposed approach for modelling the screw-bone interface can be applied to any fixation involved application of screws. PMID:23636756

Moazen, Mehran; Mak, Jonathan H; Jones, Alison C; Jin, Zhongmin; Wilcox, Ruth K; Tsiridis, Eleftherios

2013-07-01

137

Two-dimensional model calculations of earthquake cycle on a fluid-infiltrated plate interface at a subduction zone: Focal depth dependence on pore pressure conditions  

Microsoft Academic Search

We execute 2D model calculations of earthquake cycle at a subduction zone to compare two types of pore pressure models on a plate interface: hydrostatic pressure model and excess pressure model. In addition, we discuss the pore pressure fluctuations due to pore dilatation and compaction on the fluid-infiltrated plate interface. The calculation results suggest: (1) The hydrostatic pressure model tends

Yuta Mitsui; Kazuro Hirahara

2007-01-01

138

Rheological contrast between serpentines and olivine and weakening of a subducting plate interface  

NASA Astrophysics Data System (ADS)

Recent seismic observations have suggested that water released by dehydration reactions within a subducting slab is transported through the base of the overlying mantle, thereby causing serpentinization. The degrees of viscous coupling between the serpentinite layer and the overlying mantle wedge might influence the style of mantle convection and the thermal state of a subduction zone (Wada et al., 2008). Serpentine minerals (lizardite, chrysotile, and antigorite) are hydrous phyllosilicates (13 wt% H2O). In subduction zone environments, lizardite and chrysotile seem to form at temperatures below 300-400°C, whereas antigorite is stable at higher temperatures of 300 to 600°C. Previous deformation experiments have revealed that the low- and high-temperature serpentine species display intracrystalline plastic flow in the mantle wedge (e.g., Hilairet et al., 2007; Hirauchi et al., 2010). In particular, Hilairet et al. (2007) indicated that the strength of antigorite is an order of magnitude lower than that of olivine at geological time scales: however, the rheological contrast between lizardite/chrysotile and antigorite under the mantle wedge conditions is not directly constrained. We therefore conducted two-layer shear deformation experiments on serpentines and olivine under P-T conditions (P = 1 GPa, T = 250, 300°C) that correspond to the forearc mantle wedge in subduction zones. The experimental results show that strain rates in lizardite/chrysotile are approximately an order of magnitude higher than those in olivine, whereas strain rates in antigorite is only 1 to 2 times higher than those in olivine. The contrasts in strain rates between lizardite/chrysotile and antigorite is represented by a factor of 5 to 6. Based on the results of our experiments, we suggest that the rheology of lizardite/chrysotile can only explain strong decoupling on the subducting plate interface. Our experiments also show that antigorite is not significantly weaker than olivine in the dislocation-accommodated creep regime, as compared to Hilairet et al. (2007), resulting in weak decoupling at the plate interface. Therefore, we suggest that the degrees of viscous coupling in subduction zones are strongly controlled by the serpentine species stable in the base of the mantle wedge, depending on various parameters (e.g., cool vs. warm subduction zones, change with depth).

Hirauchi, K.; Katayama, I.

2010-12-01

139

Earth's Decelerating Tectonic Plates  

Microsoft Academic Search

Space geodetic and oceanic magnetic anomaly constraints on tectonic plate motions are employed to determine a new global map of present-day rates of change of plate velocities. This map shows that Earth's largest plate, the Pacific, is presently decelerating along with several other plates in the Pacific and Indo-Atlantic hemispheres. These plate decelerations contribute to an overall, globally averaged slowdown

A M Forte; R Moucha; D B Rowley; S Quere; J X Mitrovica; N A Simmons; S P Grand

2008-01-01

140

Deformation across the Pacific-North America plate boundary near San Francisco, California  

USGS Publications Warehouse

We have detected a narrow zone of compression between the Coast Ranges and the Great Valley, and we have estimated slip rates for the San Andreas, Rodgers Creek, and Green Valley faults just north of San Francisco. These results are based on an analysis of campaign and continuous Global Positioning System (GPS) data collected between 1992 and 2000 in central California. The zone of compression between the Coast Ranges and the Great Valley is 25 km wide. The observations clearly show 3.8??1.5 mm yr-1 of shortening over this narrow zone. The strike slip components are best fit by a model with 20.8??1.9 mm yr-1 slip on the San Andreas fault, 10.3??2.6 mm yr-1 on the Rodgers Creek fault, and 8.1??2.1 mm yr-1 on the Green Valley fault. The Pacific-Sierra Nevada-Great Valley motion totals 39.2??3.8 mm yr-1 across a zone that is 120 km wide (at the latitude of San Francisco). Standard deviations are one ??. The geodetic results suggest a higher than geologic rate for the Green Valley fault. The geodetic results also suggest an inconsistency between geologic estimates of the San Andreas rate and seismologic estimates of the depth of locking on the San Andreas fault. The only convergence observed is in the narrow zone along the border between the Great Valley and the Coast Ranges.

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

2001-01-01

141

Unraveling The Complex Interaction Between The Southern Caribbean, Northwest South America And The Pacific Plates During The Cenozoic  

NASA Astrophysics Data System (ADS)

We have studied the prominent Sierra Nevada de Santa Marta Massif (the highest peak in the world whose local base is at sea level, ~5.75km) in Northern Colombia and we are interested in quantifying the thermal and tectonic history of the Northernmost Andes during the Cenozoic in order to understand the complex interaction between the Caribbean, the South American and the Pacific plates. In order to do so, apatite fission track data (by the LA-ICP-MS method) has been used, collected along several traverses and a single vertical profile within the massif. Our results show that the easternmost part of Sierra Nevada de Santa Marta exhumed at elevated rates (?0.2 Km/My) during 65-58 Ma in response to the collision of the Caribbean Plateau with north-western South America. A second pulse of exhumation (?0.32 Km/My) during 50-40 Ma was probably driven by the underthrusting of the Caribbean Plate beneath northern South America. More southern portions of the Sierra Nevada de Santa Marta (the Sierra Nevada Province) exhumed rapidly during 26-29 Ma (~0.7 Km/My), whereas farther north, the northwestermost corner of the Sierra Nevada de Santa Marta (the Santa Marta Province) exhumed at elevated rates during 30-25 Ma and 25-16 Ma. Our thermochronological data show that the highest exhumation rates within the Sierra Nevada de Santa Marta progressed towards the northwest via the propagation of NW-verging thrusts. The late Oligocene-Miocene exhumation was mainly a consequence of compression originating at the Pacific margin of South America that also gave rise to uplift and exhumation in other regions of Eastern Colombia (e.g. in the Santander Massif). Major continental faults such as the left-lateral Santa Marta-Bucaramanga Fault have played an important role transferring the deformation, Exhumation of the Sierra Nevada de Santa Marta Massif is not recorded after ~16 Ma, which is unexpected, given the high elevation and high erosive power of the climate, implying that rock and surface uplift that gave rise to the current topography was probably very recent and there has been insufficient time to expose the fossil apatite partial annealing zone.

Villagomez, D.; Spikings, R.

2013-05-01

142

A computer-interfaced photometer and systematic spacing of duplicates to control within-plate enzyme-immunoassay variation.  

PubMed

A Multiskan photometer for reading microtiter plate enzyme immunoassays was linked with a time sharing computer to facilitate control of assay variation and analysis of results. The interface that converted photometer output to RS-232-C format required changes to divide the output into segments short enough for input to the computer. To measure within-plate variation and investigate how the method of allocating sample duplicates to plate wells may affect the estimation of sample variance, uniformity tests were conducted with 47 plates. Coefficients of variation (CV) among wells within-plates ranged from 4.6 to 20.7% and in two-thirds of the plates exceeded 10%. Duplicates allocated to adjacent wells (method 1) gave consistently higher CV for sample means than duplicates allocated to opposite plate quadrants (method 2). In general, the CV by method 2 was about 30% smaller than that by method 1. Analysis of variance confirmed the effectiveness of the quadrant pattern of duplicate allocation as a method of controlling variation that arises from well position effects. PMID:6348166

Stemshorn, B W; Buckley, D J; St Amour, G; Lin, C S; Duncan, J R

1983-07-29

143

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

NASA Astrophysics Data System (ADS)

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

Biasi, G. P.

2006-12-01

144

Thermochemical Analysis of Phases Formed at the Interface of a Mg alloy-Ni-plated Steel Joint during Laser Brazing  

NASA Astrophysics Data System (ADS)

The thermodynamic stability of precipitated phases at the steel-Ni-Mg alloy interface during laser brazing of Ni-plated steel to AZ31B magnesium sheet using AZ92 magnesium alloy filler wire has been evaluated using FactSage thermochemical software. Assuming local chemical equilibrium at the interface, the chemical activity-temperature-composition relationships of intermetallic compounds that might form in the steel-Ni interlayer-AZ92 magnesium alloy system in the temperature range of 873 K to 1373 K (600 °C to 1100 °C) were estimated using the Equilib module of FactSage. The results provided better understanding of the phases that might form at the interface of the dissimilar metal joints during the laser brazing process. The addition of a Ni interlayer between the steel and the Mg brazing alloy was predicted to result in the formation of the AlNi, Mg2Ni, and Al3Ni2 intermetallic compounds at the interface, depending on the local maximum temperature. This was confirmed experimentally by laser brazing of Ni electro-plated steel to AZ31B-H24 magnesium alloy using AZ92 magnesium alloy filler wire. As predicted, the formation of just AlNi and Mg2Ni from a monotectic and eutectic reaction, respectively, was observed near the interface.

Nasiri, Ali M.; Chartrand, Patrice; Weckman, David C.; Zhou, Norman Y.

2013-04-01

145

Stress Drops of Earthquakes on the Subducting Pacific Plate in the South-East off Hokkaido, Japan  

NASA Astrophysics Data System (ADS)

Large earthquakes have been occurring repeatedly in the South-East of Hokkaido, Japan, where the Pacific Plate subducts beneath the Okhotsk Plate in the north-west direction. For example, the 2003 Tokachi-oki earthquake (Mw8.3 determined by USGS) took place in the region on September 26, 2003. Yamanaka and Kikuchi (2003) analyzed the slip distribution of the earthquake and concluded that the 2003 earthquake had ruptured the deeper half of the fault plane of the 1952 Tokachi-oki earthquake. Miyazaki et al. (2004) reported that a notable afterslip was observed at adjacent areas to the coseismic rupture zone of the 2003 earthquake, which suggests that there would be significant heterogeneities of strength, stress and frictional properties on the surface of the Pacific Plate in the region. In addition, some previous studies suggest that the region with a large slip in large earthquakes permanently have large difference of strength and the dynamic frictional stress level and that it would be able to predict the spatial pattern of slip in the next large earthquake by analyzing the stress drop of small earthquakes (e.g. Allmann and Shearer, 2007 and Yamada et al., 2010). We estimated stress drops of 150 earthquakes (4.2 ? M ? 5.0), using S-coda waves, or the waveforms from 4.00 to 9.11 seconds after the S wave arrivals, of Hi-net data. The 150 earthquakes were the ones that occurred from June, 2002 to December, 2010 in south-east of Hokkaido, Japan, from 40.5N to 43.5N and from 141.0E to 146.5E. First we selected waveforms of the closest earthquakes with magnitudes between 3.0 and 3.2 to individual 150 earthquakes as empirical Green's functions. We then calculated source spectral ratios of the 150 pairs of interested earthquakes and EGFs by deconvolving the individual S-coda waves. We finally estimated corner frequencies of earthquakes from the spectral ratios by assuming the omega-squared model of Boatwright (1978) and calculated stress drops of the earthquakes by using the model of Madariaga (1976). The estimated values of stress drop range from 1 to 10 MPa with a little number of outliers(Fig.(a)). Fig.(b) shows the spatial distribution of stress drops in south-east off Hokkaido, Japan. We found that earthquakes occurred around 42N 145E had larger stress drops. We are going to analyze smaller earthquakes and investigate the spatial pattern of the stress drop in the future. Fig. (a) Estimated values of stress drop with respect to seismic moments of earthquakes. (b) Spatial distribution of stress drops.

Saito, Y.; Yamada, T.

2013-12-01

146

Exhumation and Coupling at the Plate Interface: Large Tectonic Slices V. Melange Formation? Key Contexts and Possible Controlling Parameters  

NASA Astrophysics Data System (ADS)

Fragments of subducted oceanic lithosphere returned along the plate interface convey crucial information regarding the thermal and rheological conditions of convergent plate boundaries. Geological evidence indicate that, unlike subduction, exhumation is non-steady (Agard et al., Earth Sci. Rev. 2009). We herein focus on deep processes along the plate interface (40-80 km depth), for which there is no counterflow (unlike in accretionary prisms) and no other known mechanisms to return eclogites than interplate friction or buoyancy. These eclogites are of two major types: large scale (>km) slices with coherent PT estimates (W. Alps) versus isolated fragments (frequently m-hm) in a serpentinite- or sedimentary-rich matrix showing contrasting equilibration depths (with hints of punctuated exhumation and even reburial; Franciscan, Cuba, Sistan; e.g., Garcia-Casco et al., Geol. Acta 2006). This latter type tends to show warmer equilibration paths, whereas the larger tectonic slices from the former type remain systematically cold. Serpentinites are crucial for both in permitting decoupling and acting as a buoy, and fluid budget is important too in enhancing floatability and allowing large slices to survive (Angiboust and Agard, Lithos 2010). Numerical models implementing free migration of fluids in the subduction zone also show that the plate interface is strongly localized in the absence of fluids: mechanical decoupling efficiently occurs along the sediment veneer and/or at the top of the highly hydrothermalized crust. Whenever fluids are released in greater amounts (depending on initial fluid content and/or thermal structure), deformation becomes much more distributed and affects both the mantle wedge and the top of the downgoing lithosphere (crust and hydrated mantle top), thereby increasing mechanical coupling between the two plates. Based on natural data and numerical modelling we herein propose that rheological contrast chiefly controls mechanical decoupling. On a steady-state basis the subduction interface is apparently efficiently decoupled. In this context, we hypothetize that the liberation of fluid through pulses (or a somewhat increased amount of fluids) is required to locally modify mechanical coupling and induce the slicing of large pieces of oceanic material along the subduction interface (type 1). By contrast, an extreme hydration of the subduction interface and mantle wedge will result in the formation of serpentinite melanges and extensive material mixing (e.g., cold plumes, mafic pods and localized melting; type 2). This latter situation may be promoted by young/fast/wet subduction, such as subduction initiation and/or subduction of young lithosphere or subduction of a particularly hydrated lithosphere section (e.g., at the ridge and/or prior to entering the trench), whereas cold, slow subduction (type 1) will result in irregular hydration and localized coupling able to detach large slices.

Agard, P.; Angiboust, S.; Guillot, S.; Garcia-Casco, A.

2011-12-01

147

Pore pressure evolution at the plate interface along the Cascadia subduction zone from the trench to the ETS transition zone  

Microsoft Academic Search

Pore fluid pressures in subduction zones are a primary control on fault strength and slip dynamics. Numerous studies document elevated pore pressures in the outer wedge along several margins. Seismic observations and the occurrence of non-volcanic tremor provide additional evidence for the presence of near-lithostatic pore pressures at the plate interface far down-dip from the trench (~35 km depth). Here

R. M. Skarbek; A. W. Rempel; D. A. Schmidt

2010-01-01

148

Neotectonic Studies of Northern Baja California, Mexico, with Landsat Thematic Mapper and Spot Panchromatic Imagery: Partitioning of Dextral and Extensional Strain at the Pacific-North America Plate Boundary.  

National Technical Information Service (NTIS)

Numerous studies of active faulting in southern California indicate that the San Jacinto, Elsinore, and adjacent faults west of the San Andreas fault accommodate a significant proportion of Pacific-North America relative plate motion. Because of the compl...

M. M. Miller R. E. Crippen T. H. Dixon

1991-01-01

149

Complex Faulting in the Pacific-North America Transform Offshore Southern California And Implications on Plate Boundary Tectonics and Tsunamigenesis  

NASA Astrophysics Data System (ADS)

Complexity in the tectonic model for Pacific-North America transform motion in the offshore southern California region is demonstrated by earthquakes near San Clemente Island and Fortymile Bank. Observed focal mechanisms show movements opposite to those predicted by the plate tectonic theory for right-slip on NW- trending transform faults and observed in other parts of the California Continental Borderland. Also, there is evidence suggesting that moderate earthquakes in the Inner Borderland have greater magnitudes based on long-period seismic waves than the nominal Richter local magnitudes reported in earthquake catalogs. With better data showing the geologic structure of the area now available, we can try to derive a more complete understanding of this complex tectonic behavior and resulting consequences for local tsunamigenesis. The "backwards" earthquakes suggest the occurrence of plate boundary deformation and/or microplate tectonics with the western side of a block containing Fortymile Bank moving instantaneously faster to the northwest than the adjacent block to the west. Such motions may be consistent with clockwise rotation of blocks in the continental borderland due to the regional dextral shear couple as proposed by Crouch (1978) and Luyendyk and others (1980) based upon paleomagnetic and other geologic data. Alternatively, as initially observed for the 1986 Offshore Oceanside earthquake (MS=5.8) by Hauksson and Jones (1988), the anomalous focal mechanism may be due to an inaccurate model of crustal seismic velocity structure for the offshore region. Use of a refined velocity model may show these anomalous earthquakes to have oblique-reverse mechanisms like the 1986 mainshock. Furthermore, more recent seismicity, located with greater accuracy due to expansion of the Southern California Seismograph Network (SCSN), has apparent NE alignments suggestive of significant active secondary fault structure located off the major NW-trending right-slip faults. Such faulting was also inferred to be significant during the clockwise vertical-axis block rotations of the western Transverse Ranges. Interaction between faults within conjugate systems may enhance vertical movements including subsidence at basins where blocks diverge and uplift where blocks converge, thereby producing local tsunamis during large earthquakes. It was not until recently that local earthquake sources were identified offshore Southern California as potentially damaging tsunami sources. Erroneous magnitude estimate of offshore earthquakes can have serious implications for tsunamigenesis and tsunami warning. A half magnitude error can make the difference between a non-tsunamigenic and a tsunamigenic event especially when a marginal event is considered. Better magnitude estimates using long-period seismographs may be necessary for more accurate identification of potentially tsunamigenic local earthquakes.

Legg, M. R.; Barberopoulou, A.

2007-12-01

150

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

NASA Astrophysics Data System (ADS)

Five studies along the Pacific-North America (PA-NA) plate boundary offer new insights into continental margin processes, the development of the PA-NA tectonic margin and regional earthquake hazards. This research is based on the collection and analysis of several new marine geophysical and geological datasets. Two studies used seismic CHIRP surveys and sediment coring in Fallen Leaf Lake (FLL) and Lake Tahoe to constrain tectonic and geomorphic processes in the lakes, but also the slip-rate and earthquake history along the West Tahoe-Dollar Point Fault. CHIRP profiles image vertically offset and folded strata that record deformation associated with the most recent event (MRE). Radiocarbon dating of organic material extracted from piston cores constrain the age of the MRE to be between 4.1--4.5 k.y. B.P. Offset of Tioga aged glacial deposits yield a slip rate of 0.4--0.8 mm/yr. An ancillary study in FLL determined that submerged, in situ pine trees that date to between 900-1250 AD are related to a medieval megadrought in the Lake Tahoe Basin. The timing and severity of this event match medieval megadroughts observed in the western United States and in Europe. CHIRP profiles acquired in the Salton Sea, California provide new insights into the processes that control pull-apart basin development and earthquake hazards along the southernmost San Andreas Fault. Differential subsidence (>10 mm/yr) in the southern sea suggests the existence of northwest-dipping basin-bounding faults near the southern shoreline. In contrast to previous models, the rapid subsidence and fault architecture observed in the southern part of the sea are consistent with experimental models for pull-apart basins. Geophysical surveys imaged more than 15 ˜N15°E oriented faults, some of which have produced up to 10 events in the last 2-3 kyr. Potentially 2 of the last 5 events on the southern San Andreas Fault (SAF) were synchronous with rupture on offshore faults, but it appears that ruptures on three offshore faults are synchronous with Colorado River diversions into the basin. The final study was used coincident wide-angle seismic refraction and multichannel seismic reflection surveys that spanned the width of the of the southern Baja California (BC) Peninsula. The data provide insight into the spatial and temporal evolution of the BC microplate capture by the Pacific Plate. Seismic reflection profiles constrain the upper crustal structure and deformation history along fault zone on the western Baja margin and in the Gulf of California. Stratal divergence in two transtensional basins along the Magdalena Shelf records the onset of extension across the Tosco-Abreojos and Santa Margarita faults. We define an upper bound of 12 Ma on the age of the pre-rift sediments and an age of ˜8 Ma for the onset of extension. Tomographic imaging reveals a very heterogeneous upper crust and a narrow, high velocity zone that extends ˜40 km east of the paleotrench and is interpreted to be remnant oceanic crust.

Brothers, Daniel Stephen

151

Intraplate shearing and basin deformation in the Pacific Plate as a result of the Yakutat Block collision with North America  

NASA Astrophysics Data System (ADS)

The Yakutat Block (YAK), an allochthonous terrane coupled to the Pacific Plate (PAC), collided with the North American plate ~10Ma and began subducting at the Aleutian Trench. Due to its thickness, the YAK is resistant to subduction compared to the PAC. As a result, the YAK is undergoing flat-slab subduction and now has developed its own vector relative to the PAC. High-resolution bathymetry data shows a 30km N-S trending ridge within the Surveyor Fan between the mouths of the Yakutat Sea Valley and Bering Trough. The ridge originates in the north at the base of the continental slope, which is coincident with the Transition Fault, the strike-slip boundary between the YAK and the PAC. The ridge exhibits greatest relief adjacent to the Transition Fault, and becomes less distinct farther from the shelf edge. As the highest relief feature in this part of the basin, the ridge has completely redefined sediment distribution patterns within the Surveyor Fan. Seismic reflection data reveal a sharp basement high beneath the ridge (1.1 sec of relief above “normal” basement in two-way travel time) as well as multiple strike-slip fault systems that are also N-S oriented. The ridge, basement high, and faults are aligned and co-located with an intraplate earthquake swarm on the PAC, which includes four events > 6.5 Mw that occurred from 1987-1992. This earthquake swarm is defined by mostly right-lateral strike-slip events, and is known as the Gulf of Alaska Shear Zone (GASZ). Based on the extent of seismicity, the GASZ extends 230km into the PAC. Tearing of oceanic crust on this scale is rare. A recent wide-angle seismic study shows the YAK to be a 20-25km thick mafic body while the 30 Myr old Pacific crust in the northern Gulf of Alaska is of normal thickness. Intraplate deformation occurring within the PAC could be the result of PAC-YAK coupling whereby YAK resistance to subduction is expressed as deformation in the thinner (weaker) PAC crust. Although a large tear in normal oceanic crust is unusual, preexisting zones of weakness within the PAC crust that are proximal to and under stress from the YAK may have proven to be a kinematically favorable localization for strain. These results support a recently proposed tectonic model wherein the differing YAK and PAC vectors caused the northern PAC to split into two different blocks, separated by the GASZ. In this model, the eastern block of the PAC would exhibit a counter-clockwise rotation that accounts for motion along the Transition Fault and GASZ. We will analyze this intraplate deformation zone using seismic imaging, bathymetry, and magnetic data in order to examine the cause of the strain localization and its southern termination, the influence of this shear zone on the sedimentary history, and relationship with the PAC-YAK interplate deformation along the Transition Fault.

Reece, R.; Gulick, S. P.; Christeson, G. L.; Worthington, L. L.

2009-12-01

152

Aftershocks of the 2010 Mw 7.4 Bonin Islands normal-faulting earthquake: Implication for deformation of the Pacific Plate  

NASA Astrophysics Data System (ADS)

A Mw 7.4 normal-faulting earthquake occurred 150 km east of Chichi-jima Island, Bonin Islands, Japan on December 21, 2010 (UTC). This is an earthquake occurred within the Pacific plate beneath the outer trench-slope region along the Izu-Ogasawara (Bonin) trench, where the Pacific plate subducts beneath the Philippine Sea plate. According to Japan Meteorological Agency (JMA), the associated tsunami was observed over a wide area along the Pacific coast of Japan. Normal faulting earthquakes in outer trench-slope region are a result of the bending of the incoming/subducting oceanic plates. The bending-related normal faults cutting the oceanic plate are likely associated with hydration of the oceanic plate prior to subduction [e.g., Ranero et al., 2003]. The normal faulting earthquakes can be a key to understand deformation and resulting hydration of the oceanic plate. That is also important for consideration of tsunami generation in shallow outer trench-slope region. Aftershock observation of the 2010 Bonin Islands earthquake were conducted by R/V Kairei of Japan Agency for Marine-Earth Science and Technology (JAMSTEC) using ocean bottom seismographs (OBSs). First OBS was deployed in the source area on December 25, 2010 and retrieved on January 7, 2011. Other 4 OBSs were deployed on January 6 and 7 and retrieved on March 11 and 12, 2011. Overall aftershocks distributed in a 130 km long area extended in a NW-SE direction although Izu-Bonin trench extends N-S direction in this area. Most of the aftershocks were located at depths shallower than 30 km, corresponding to the oceanic crust and the uppermost mantle of the Pacific plate. The aftershocks show a complicated distribution. In the central part of the aftershock area, aftershocks formed three subparallel lines with roughly 15 km intervals oriented NW-SE direction. In the southeastern part of the aftershock area away from the trench, the aftershocks distributed along ESE-WNW direction. We estimated aftershock distribution before the OBS deployment using three seismic stations on Chichi-jima and Haha-jima Islands operated by JMA and National Research Institute for Earth Science and Disaster Prevention (NIED), Japan. We used a matched filter technique [e.g., Shelly et al., 2007] with the aftershocks determined by the OBSs as templates. The aftershocks immediately after the mainshock occurred only in a 80 km long area near the central part of the aftershock area. The aftershock area expanded over hours or days in an ESE direction away from the trench. Faults oriented from NW-SE to E-W directions have been identified around the aftershock area including a region far away from the trench [e.g., Okamura, et al., 1992]. The aftershock distribution and its expansion suggest that the mainshock occurred beneath the outer trench-slope near the trench. Then, the aftershock activity expanded along the pre-existing faults within the Pacific plate. Consideration of both normal faults formed near the trench and pre-existing fractures formed far away from the trench is required to understand the deformation and hydration of the oceanic plate prior to the subduction.

Obana, K.; Takahashi, T.; No, T.; Kaiho, Y.; Kodaira, S.; Yamashita, M.; Sato, T.; Noguchi, N.; Nakamura, T.

2011-12-01

153

Plate motion  

SciTech Connect

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

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

1991-01-01

154

Investigation of interface properties and weldability of aluminum and copper plates by explosive welding method  

Microsoft Academic Search

In this study, weldability of aluminum sheet to copper sheet by explosive welding and the effect of explosive ratio on the joint interface have been investigated experimentally. Experimental results show that aluminium can be bonded to copper sheet by using explosive welding. The joint interface was transformed from linear to wavy appearance by increasing explosive ratio with respect to upper

Behcet Gulenc

2008-01-01

155

Project NEPTUNE: an innovative, powered, fibre-optic cabled deep ocean observatory spanning the Juan de Fuca plate, NE Pacific  

NASA Astrophysics Data System (ADS)

NEPTUNE is an innovative facility, a deep-water cabled observatory, that will transform marine science. MARS and VENUS are deep and shallow-water test bed facilities for NEPTUNE located in Monterey Canyon, California and in southern British Columbia, respectively; both were funded in 2002. NEPTUNE will be a network of over 30 subsea observatories covering the 200,000 sq. km Juan de Fuca tectonic plate, Northeast Pacific. It will draw power via two shore stations and receive and exchange data with scientists through 3000 km of submarine fiber-optic cables. Each observatory, and cabled extensions, will host and power many scientific instruments on the surrounding seafloor, in seafloor boreholes and buoyed through the water column. Remotely operated and autonomous vehicles will reside at depth, recharge at observatories, and respond to distant labs. Continuous near-real-time multidisciplinary measurement series will extend over 30 years. Free from the limitations of battery life, ship schedules/ accommodations, bad weather and delayed access to data, scientists will monitor remotely their deep-sea experiments in real time on the Internet, and routinely command instruments to respond to storms, plankton blooms, earthquakes, eruptions, slope slides and other events. Scientists will be able to pose entirely new sets of questions and experiments to understand complex, interacting Earth System processes such as the structure and seismic behavior of the ocean crust; dynamics of hot and cold fluids and gas hydrates in the upper ocean crust and overlying sediments; ocean climate change and its effect on the ocean biota at all depths; and the barely known deep-sea ecosystem dynamics and biodiversity. NEPTUNE is a US/Canada (70/30) partnership to design, test, build and operate the network on behalf of a wide scientific community. The total cost of the project is estimated at about U.S. 250 million from concept to operation. Over U.S. 50 million has already been funded for design, development, and the test beds. NEPTUNE will be among the first of many such cabled ocean observatories. Much is to be gained by being among the scientific and industrial pioneers. The multidisciplinary data archive will be an amazing, expanding resource for scientists and students. The public will share in the research discoveries of one of the last unexplored places on earth through an extensive education/outreach program.

Barnes, C.; Delaney, J.

2003-04-01

156

Images for the base of the Pacific lithospheric plate beneath Wellington, New Zealand, from 500 kg dynamite shots recorded on a 100 km-long, 1000 seismometer array  

NASA Astrophysics Data System (ADS)

Seismic P and S-wave reflections are recorded from a west-dipping horizon at depth of 105 km beneath Wellington, New Zealand. From the depth and dip of this horizon we interpret this horizon to be the bottom of the subducting Pacific plate. In May 2011 the Seismic Array on Hikurangi margin Experiment (SAHKE) recorded reflections on a ~100 km-long high-resolution seismic line across the lower North Island of New Zealand. The main goal of this experiment was to provide a detailed image of the west dipping subducted Pacific plate beneath the Wellington city region. The seismic line had ~1000 seismographs spaced between 50-100 m apart and the 500 kg shots were in 50 m-deep, drill holes. An exceptionally high-resolution image for the top of the subducting Pacific Plate at a depth of 20-25 km beneath the Wellington region is seen. In addition, on most of the shots are a pair of 10-14 Hz reflections between 27 and 29 s two-way-travel-time (twtt) at zero offset. The quality of this reflection pair varies from shot to shot. When converted to depth and ray-traced the best solution for these deep events is a west-dipping ( ~ 15 degrees) horizon at a depth of about 105 km. This is consistent with the dip of the upper surface of the plate beneath Wellington, and therefore we argue that the deep (~105 km) reflector is the base of the Pacific plate. On two of the shots another pair 5-8 Hz reflections can also be seen between 47 and 52 s, and the move-out of these events is consistent with them being S-wave reflections from the same 105 km deep, west-dipping, boundary for a Vp/Vs ~ 1.74. Both the P-and S-wave reflections occur in pairs of twtt-thickness of 2 and 5 s, respectively and appear to define a ~ 6-8 km thick channel at the base of the plate if the Vp/Vs ratio~ 5/2 or 2.5. Such a high value of Vp/Vs is consistent with the channel containing fluids or partial melt of an unknown percent. Although we can't rule out the double reflections in both P and S as being multiples, this seems unlikely as multiples are not seen any where else in the shot gathers. Thus the lithosphere-asthenosphere boundary (LAB), at least in this setting, appears to be a sharp boundary, less than 10 km thick. As the top of the subduction zone is 20-25 km deep beneath our profile, the total thickness of the plate beneath Wellington is about 80 km. This is consistent with the thickness of old oceanic plates measured elsewhere with passive seismic methods.

Stern, T. A.; Henrys, S. A.; Sato, H.; Okaya, D. A.

2012-12-01

157

Investigation on the Interface Morphologies of Explosive Welding of Inconel 625 to Steel A516 Plates  

Microsoft Academic Search

The purpose of this study is to produce composite plates by explosive cladding process. This is a process in which the controlled energy of explosives is used to create a metallic bond between two similar or dissimilar materials. The welding conditions were tailored through parallel geometry route with different operational parameters. In this investigation, a two-pronged study was adopted to

S. A. A. Akbari Mousavi; H. R. Zareie

2011-01-01

158

Life and death of the resurrection plate: Evidence for its existence and subduction in the northeastern Pacific in Paleocene-Eocene time  

USGS Publications Warehouse

Onshore evidence suggests that a plate is missing from published reconstructions of the northeastern Pacific Ooean in Paleocene- Eocene time. The Resurrection plate, named for the Resurrection Peninsula ophiolite near Seward, Alaska, was located east of the Kula plate and north of the Farallon plate. We interpret coeval near-trench magmatism in southern Alaska and the Cascadia margin as evidence for two slab windows associated with trench-ridge-trench (TRT) triple junctions, which formed the western and southern boundaries of the Resurrection plate. In Alaska, the Sanak-Baranof belt of near-trench intrusions records a west-to-east migration, from 61 to 50 Ma, of the northern TRT triple junction along a 2100-km-long section of coastline. In Oregon, Washington, and southern Vancouver Island, voluminous basaltic volcanism of the Siletz River Volcanics, Crescent Formation, and Metchosin Volcanics occurred between ca. 66 and 48 Ma. Lack of a clear age progression of magmatism along the Cascadia margin suggests that this southern triple junction did not migrate significantly. Synchronous near-trench magmatism from southeastern Alaska to Puget Sound at ca. 50 Ma documents the middle Eocene subduction of a spreading center, the crest of which was subparallel to the margin. We interpret this ca. 50 Ma event as recording the subduction-zone consumption of the last of the Resurrection plate. The existence and subsequent subduction of the Resurrection plate explains (1) northward terrane transport along the southeastern Alaska-British Columbia margin between 70 and 50 Ma, synchronous with an eastward-migrating triple junction in southern Alaska; (2) rapid uplift and voluminous magmatism in the Coast Mountains of British Columbia prior to 50 Ma related to subduction of buoyant, young oceanic crust of the Resurrection plate; (3) cessation of Coast Mountains magmatism at ca. 50 Ma due to cessation of subduction, (4) primitive mafic magmatism in the Coast Mountains and Cascade Range just after 50 Ma, related to slab-window magmatism, (5) birth of the Queen Charlotte transform margin at ca. 50 Ma, (6) extensional exhumation of high-grade metamorphic terranes and development of core complexes in British Columbia, Idaho, and Washington, and extensional collapse of the Cordilleran foreland fold-and-thrust belt in Alberta, Montana, and Idaho after 50 Ma related to initiation of the transform margin, (7) enigmatic 53-45 Ma magmatism associated with extension from Montana to the Yukon Territory as related to slab breakup and the formation of a slab window, (8) right-lateral margin-parallel strike-slip faulting in southern and western Alaska during Late Cretaceous and Paleocene time, which cannot be explained by Farallon convergence vectors, and (9) simultaneous changes in Pacific-Farallon and Pacific-Kula plate motions concurrent with demise of the Kula-Resurrection Ridge.

Haeussler, P. J.; Bradley, D. C.; Wells, R. E.; Miller, M. L.

2003-01-01

159

Primary mandibular reconstruction: analysis of 64 cases and evaluation of interface radiation dosimetry on bridging plates.  

PubMed

The combination of a myocutaneous flap or free cutaneous tissue transfer with a three-dimensional bendable reconstruction plate either of stainless steel or titanium has provided very satisfactory results in primary restoration of mandibular defects following surgical resections in irradiated patients or in those who require postoperative radiotherapy. Sixty-four cases have been treated and evaluated prospectively using this technique. Fifty-three of the patients had the soft-tissue defect restored with a myocutaneous flap, 8 had a free cutaneous tissue flap, 2 were reconstructed with tongue flaps, and 1 closed primarily. The stainless steel plate of the A.O. type was used in 53 cases and the titanium plate system and hollow screws in the other 11 cases. A success rate of 78.9% was found with a median follow-up of 384 days. Thirty of the 64 cases had preoperative irradiation and 15 were treated postoperatively. A plate failure rate of 23% was encountered in those treated with preoperative irradiation and in 20% with those having postoperative irradiation. Forty-nine of the 64 patients or 76.5% experienced no perioperative complications. Five or 7.8% of the complications were minor. Ten patients or 15.6% experienced a major complication with one death due to a myocardial infarct. A radiation dosimetric model was employed using both stainless steel and titanium. The results from this study showed that, when using a parallel pair of beams, an excess dose of irradiation for the lowest energy cobalt-60 is 13%, for 6 mV it is 15%, and for 18 mV it is 20%. The excess tissue dose, both for stainless steel and titanium plates, extends for about 0.2 mm for cobalt-60, 1.1 mm at 6 mV, and for 25 mm at 18 mV. Patients with plates, therefore, can be treated safely with postoperative irradiation using either cobalt-60 or 6-mV energy. PMID:2041453

Gullane, P J

1991-06-01

160

Primary mandibular reconstruction: analysis of 64 cases and evaluation of interface radiation dosimetry on bridging plates  

Microsoft Academic Search

The combination of a myocutaneous flap or free cutaneous tissue transfer with a three-dimensional bendable reconstruction plate either of stainless steel or titanium has provided very satisfactory results in primary restoration of mandibular defects following surgical resections in irradiated patients or in those who require postoperative radiotherapy. Sixty-four cases have been treated and evaluated prospectively using this technique. Fifty-three of

Patrick J. Gullane

1991-01-01

161

Did the 2010 Chile earthquake change the locking degree at neighboring plate interface segments of the Andean subduction zone?  

NASA Astrophysics Data System (ADS)

A widely held view is that lateral extents and magnitudes of great earthquakes are fundamentally controlled by the stress build-up along the plate interface as inferred from the degree of locking. Therefore, inferring the distribution of locking and its along-strike variations has become an essential tool for seismic and tsunami hazard assessment. Recent studies have explored the main parameters affecting the spatial distribution of locking degree, but the time evolution of locking has not yet been clearly documented. Here we used time-series of continuous GPS at adjacent segments (> 500 km distance) to the rupture zone of the 2010 Chile (Mw=8.8) earthquake to explore the differences in locking degree before (2008-2010) and after (2010-2013) this event. Results suggest that the interseismic velocity (landward displacements) increased both in the northern (27°S-32°S) and southern (41°S-45°S) unruptured segments. The variations of displacements can be explained by an increase and homogenization of the locking degree at areas that were creeping before the 2010 earthquake. The estimated increase of locking degrees have peaks of about 20% and 100% for the northern and southern regions respectively. The b-value, which parameterizes the frequency-magnitude distribution of seismicity, decreased after the 2010 earthquake in the northern segment (in the southern segment there is not enough seismicity for estimating b-value) from 1.2 to 0.7 indicating a tendency for asperities to be brought closer to failure due to increase of shear stresses on the plate interface. By means of a 3D thermo-mechanical subduction model we are able to simulate the dynamic response of the system and study the stress variations before and after the earthquake, supporting the rearrangment of shear stresses at adjacent segments. Our results suggest that locking degree can evolve over a short timescale due to the change of the stress regime induced by great earthquakes. We propose that the seismic cycle along a margin is a self-organized system in the sense of a lateral connected evolution of build-up and release of stress at different seismotectonic segments. Importantly, the 2010 earthquake may have increased the seismic potential of the northern and southern neighboring plate interface segments, which broke last in 1922 and 1960, respectively.

Moreno, Marcos; Báez, Juan Carlos; Bedford, Jonathan; Quinteros, Javier; Tassara, Andres; Melnick, Daniel; Oncken, Onno; Vigny, Christophe; Bartsch, Mitja; Bevis, Michael; Soto, Hugo; Barrientos, Sergio; Ortega, Ismael; Valderas, Maria

2014-05-01

162

A serial sample loading system: interfacing multiwell plates with microfluidic devices.  

PubMed

There is an increasing demand for novel high-throughput screening (HTS) technologies in the pharmaceutical and biotechnological industries. The robotic sample-handling techniques currently used in these industries, although fast, are still limited to operating in multiwell plates with the sample volumes per reaction in the microliter regime. Digital microfluidics offers an alternative for reduction in sample volume consumption for HTS but lacks a reliable technique for transporting a large number of samples to the microfluidic device. In this report, we develop a technique for serial delivery of sample arrays to a microfluidic device from multiwell plates, through a single sample inlet. Under this approach, a serial array of sample plugs, separated by an immiscible carrier fluid, is loaded into a capillary and delivered to a microfluidic device. Similar approaches have been attempted in the past, however, either with a slower sample loading device such as a syringe pump or vacuum-based sample loading with limited driving pressure. We demonstrated the application of our positive-pressure-based serial sample loading (SSL) system to load a series of sample plugs into a capillary. The adaptability of the SSL system to generate sample plugs with a variety of volumes in a predictable manner was also demonstrated. PMID:22885789

Rane, Tushar D; Zec, Helena C; Wang, Tza-Huei

2012-10-01

163

A Serial Sample Loading System: Interfacing Multi-well plates with Microfluidic Devices  

PubMed Central

There is an increasing demand for novel high-throughput screening (HTS) technologies in the pharmaceutical and biotechnological industries. The robotic sample handling techniques currently used in these industries, although fast, are still limited to operating in multi-well plates with the sample volumes per reaction in the microliter regime. Digital microfluidics offers an alternative for reduction in sample volume consumption for HTS but lacks a reliable technique for transporting large number of samples to the microfluidic device. In this report, we develop a technique for serial delivery of sample arrays to a microfluidic device from multi-well plates, through a single sample inlet. Under this approach, a serial array of sample plugs, separated by an immiscible carrier fluid, is loaded into a capillary and delivered to a microfluidic device. Similar approaches have been attempted in the past, however, either with a slower sample loading device like syringe pump or vacuum based sample loading with limited driving pressure. We demonstrated the application of our positive pressure based ‘Serial Sample Loading’ (SSL) system to load a series of sample plugs into a capillary. The adaptability of the SSL system to generate sample plugs with a variety of volumes in a predictable manner was also demonstrated.

Rane, Tushar D.; Zec, Helena; Wang, Jeff Tza-Huei

2013-01-01

164

Geochronology and origin of the Pratt-Welker Seamount Chain, Gulf of Alaska: A new pole of rotation for the Pacific Plate  

NASA Astrophysics Data System (ADS)

40K-40Ar and fission-track dating of four seamounts near the southeast end of the Pratt-Welker seamount chain in the Gulf of Alaska, in conjunction with previously published K-Ar and fission-track ages near the northwest end of the chain, documents the complex origin of this seamount chain. Transitional basalts from the adjacent guyots Hodgkins, Davidson, and Denson are dated as 14.3 to 18.2 m.y. These ages, only slightly younger than the ages of the underlying crust, indicate formation of these three seamounts at or very near a spreading center. In contrast, alkalic series lavas (alkali olivine basalts and trachytes) from Kodiak, Giacomini, Dickins, and Hodgkins fit a systematic linear age progression: 23.9±0.6 m.y., 20.9±0.4 m.y., 4.0±0.2 m.y., and 2.8±0.2 m.y., respectively. Hodgkins has apparently experienced two generically different episodes of volcanism, separated by about 12 m.y. The age progression among dated alkali basalts is consistent with the hot spot hypothesis and suggests that for the last 24 m.y. the Pacific plate has moved northwest at 4.4±0.4 cm/yr with respect to the Pratt-Welker hot spot. This volcanic propagation rate, together with the rates from other parallel Neogene Pacific chains, allows an improved estimate of the pole and rate of rotation of the Pacific plate relative to hot spots: 70°N, 95°W, and 0.88°±0.10°/m.y. We conclude that no significant motion of the Pratt-Welker hot spot with respect to other Pacific hot spots has yet been detected. However, the Pratt-Welker age data may alternatively be explained by either the longitudinal roll or propagating crack hypothesis. New K-Ar ages from Horton guyot, in the Cobb seamount chain, indicate alkalic volcanism 20.7± .0 m.y. ago, consistent with a predicted age of 20 m.y. based on the hot spot hypothesis. Guyot depths from Horton and the dated Pratt-Welker seamounts are consistent with the K-Ar ages and normal subsidence of oceanic crust.

Turner, D. L.; Jarrard, R. D.; Forbes, R. B.

1980-11-01

165

Earthquakes along the Ryukyu-Kyushu Arc: Strain segmentation, lateral compression, and the thermomechanical state of the plate interface  

NASA Astrophysics Data System (ADS)

We systematically determined the focal depths and mechanisms of 49 large to moderate-sized earthquakes (mb?5.4) that occurred along the Ryukyu-Kyushu arc since 1963 by inverting the waveforms and amplitudes of P and SH wave trains at teleseismic distances. The results are sufficiently precise to delineate seismogenic structures near the plate interface in detail, revealing features not predicted by plate kinematics. In contrast to previous studies of this arc and those along other subduction zones, shallow seismicity along the plate interface is systematic, showing two distinct layers of activities. The second layer of seismicity is delineated by a few earthquakes that occurred at depths between 50 and 65 km, some 10-20 km directly beneath the seismogenic portion of the interplate thrust zone. These earthquakes indicate lateral compressional strain within the subducted slab as their P axes are subparallel to the local strike of the arc, not perpendicular to the arc as one would expect from the direction of plate convergence. The occurrence of these events cannot be accounted for by membrane stress due to the geometry of the subducted slab. To our knowledge, similar earthquakes occurred only beneath the northern Indoburman ranges and along the Banda arc where subducted slabs, as part of the Indian plate, are being dragged northward with their northern edges bumping into east-west trending collision zones nearby. By drawing an analogy between the tectonic settings of these three regions, we interpret events beneath the plate interface along the Ryukyu-Kyushu arc as a consequence of ongoing collision between the Philippine Sea plate and Eurasia near Taiwan. The interplate thrust zone is largely aseismic down to a depth of approximately 30 km. A large number of earthquakes showing low-angle thrust faulting commence at this depth and are accompanied by two events that show antithetic thrust faulting at a slightly shallower depth of 20-25 km. These observations suggest that the strength of the plate interface increases significantly below the depth of proximately 25±5 km. Based upon available heat flow measurements between the trench axis and the volcanic arc, we estimated the temperature field and magnitude of shear traction along the interplate thrust zone, the deepest interplate earthquakes (˜40-50 km) correspond to temperatures of approximately 730-980°C, comparable to the limiting temperature of intraplate mantle earthquakes (˜800°C) and that of intermediate- and deep-focus earthquakes at Wadati-Benioff zones (potential temperature ˜900°K). Therefore, the cessation of seismicity in general is probably controlled by similar temperature conditions regardless of the tectonic settings of source regions. The magnitude of shear traction along the seismogenic portion (˜40-50 km depth) of the interplate thrust zone seems to be of the order of 100 MPa which, in turn, implies a low average coefficient of friction of only 0.10±0.05, considerably less than those observed for laboratory specimens. The inception of intermediate-focus earthquakes within the subducted slab is at a depth of about 100 km. Whereas shallow earthquakes show no apparent variations along the entire arc, intermediate-depth earthquakes indicate downdip extension along the northern end of the arc near Kyushu but abruptly change to downdip compression along the rest of the arc. All available evidence indicates that this is a spatial pattern unrelated to earthquake cycles. At the moment, tectonic interpretation of such a distinct strain segmentation along the arc is enigmatic. Without the presence of clear discontinuities in the age of the subducted slab, the sudden switch in the strain field of the slab is difficult to explain by the continuously varying rate of subduction along the arc. In any case, this pattern of strain segmentation requires the presence of a major accommodation structure, such as a tear fault, in the subducted slab near the Tokara channel. Appendix is available with entire article on microfiche. Order from American Geophysical Union,

Kao, Honn; Chen, Wang-Ping

1991-12-01

166

Distribution and mechanism of Neogene to present-day vertical axis rotations, Pacific-Australian Plate Boundary Zone, South Island, New Zealand  

NASA Astrophysics Data System (ADS)

Remarkably little knowledge exists about mechanisms of vertical axis rotation in continental crust. Steeply dipping basement rocks in South Island, New Zealand, provide an opportunity to map the distribution of rotations across the Pacific-Australian plate boundary zone, and to delineate boundaries of rotated blocks in unusual detail. We synthesize new structural data with new and existing paleomagnetic data, with geodetic data, and with patterns of Neogene-Quaternary faulting in the strike-slip Marlborough fault system. For the past 20 m.y., vertical axis rotations have been hinged about two crustal-scale boundaries near the east coast. The NE hinge accommodated ˜50° of early-middle Miocene clockwise rotation, which caused deformation of the eastern ends of the Alpine-Wairau and Clarence strike-slip faults. The SW hinge has accommodated a further 30°-50° of finite clockwise rotation since ˜4 Ma and deflects active fault traces. The locus of rotation has shifted southwestward astride a subduction margin that is lengthening in that direction. Rotating rocks are pinned to the south against a locked collision zone where the continental Chatham Rise impinges against the margin. Slip on inland strike-slip faults is transformed seaward across a zone of fault termination into rigid body rotation of a large continental block that has been thrust eastward over the downgoing subducted slab of the Pacific plate. The rotation mechanism is a "migrating hinge," which resembles a flexed telephone book. Strike-slip faults are translated through a brecciated hinge region that does not coincide with a fixed material line in the rock.

Little, Timothy A.; Roberts, Andrew P.

1997-01-01

167

Unbending and horizontal fracture of the subducting Pacific plate, as evidenced by the 1993 Kushiro-oki and the 1981 and 1987 intermediate-depth earthquakes in Hokkaido  

NASA Astrophysics Data System (ADS)

A large number of aftershocks of the 1993 Kushiro-oki earthquake ( MJMA = 7.8), 1987 Hidaka earthquake ( MJMA = 7.0), and 1981 Western Hidaka earthquake ( MJMA = 7.1) have been observed by the seismic network of Hokkaido University. These three earthquakes are the largest events that have occurred in the depth range from 100 km to 200 km under the Pacific side of Hokkaido for 109 years. They migrated from west to east in the last 12 years. Their focal mechanism solutions represent typical down-dip extension in the lower zone of the double seismic zone in the descending Pacific plate. We investigated aftershock distributions of the three intermediate-depth earthquakes to study physical properties of the descending slab. Aftershocks of the Kushiro-oki earthquake spread horizontally over an area of 50 km × 40 km. A vertical cross-section of this aftershock distribution shows that it extends from the lower seismic zone almost to the upper seismic zone. It shows a slightly concave shape of about 35 km in length. Aftershocks of the Hidaka and Western Hidaka earthquakes also extend horizontally over areas of 10 km × 10 km and 8 km × 12 km, respectively. These main shocks occurred in the lower seismic zone. The horizontal aftershock distributions of all three large earthquakes indicate that the horizontal nodal planes of the focal mechanisms, rather than the vertical nodal planes, are the fault planes. Such a characteristic suggests that the descending lithosphere under Hokkaido has been unbent macroscopically over the last 12 years. Unbending and the long horizontal faults of the intermediate-depth earthquakes may be caused by mantle flow in the asthenosphere beneath the Pacific plate. We suggest that the descending slab of about 100 km thickness constitutes two layers: a seismic, brittle upper layer and an aseismic, ductile lower layer. Small ruptures may tend to occur easily along both boundary surfaces of the upper layer under the action of forces, especially unbending, and form the double seismic zone.

Suzuki, Sadaomi; Kasahara, Minoru

1996-01-01

168

Geophysical evidence of trench-breaching slip along megathrust plate interface in the Japan Trench  

NASA Astrophysics Data System (ADS)

Repeated bathymetry and seismic surveys along a profile in the central part of the rupture of the 2011 Tohoku-oki earthquake show that a co-seismic fault reaches the trench axis, forming a deformed sediment mass seaward of the frontal prism above a graben, probably due to large trench-ward movement of the hanging wall block. If the seismic structures we observed in the trench axis represent a structural proxy showing trench-breaching slip, it can be possible by using seismic data, to map an area where co-seismic slip reaches the trench axis. In order to test this hypothesis, we have started a high-resolution seismic imaging project along the entire Japan Trench axis, and the survey has been completed from 38 N to 40 N by the summer of 2013. Based on preliminary results from the survey, we found along the trench axis continuation of key structures which consist of a small-scale fold-and-thrust zone at the trench axis and seismically transparent zone at the landward, except 39.5 N to 40 N where extremely thin incoming sediments are observed due to rough geometry of the top of the igneous crust. Those structures are interpreted to be formed by overprinting "basal friction-driven thrust fault" and "gravity-driven normal fault" that alternatively occurred during an earthquake cycle with slip to the trench. Although we believe that the high-resolution seismic data have a potential to define the spatial distribution of slips to the trench, those data do not yield any information about temporal variations of the slip. In order to examine the temporal variation of slip to the trench, we will therefore integrate the seismic images with geological studies, such as piston-coring. Furthermore, in order to know even longer records of earthquake slips and evidences of seismic fault motions (i.e., high velocity slip) along megathrust interface at the trench axis, we proposed a new ocean drilling project, called JTRACK, which consists of along-and-across trench axis drilling transect in the Japan Trench.

Kodaira, Shuichi; Nakamura, Yasuyuki; Miura, Seiichi; Fujiwara, Toshiya; Kanamatsu, Toshiya; Ikehara, Ken

2014-05-01

169

Compilation of Surface Creep on California Faults and Comparison of WGCEP 2007 Deformation Model to Pacific-North American Plate Motion  

USGS Publications Warehouse

This Appendix contains 3 sections that 1) documents published observations of surface creep on California faults, 2) constructs line integrals across the WG-07 deformation model to compare to the Pacific ? North America plate motion, and 3) constructs strain tensors of volumes across the WG-07 deformation model to compare to the Pacific ? North America plate motion. Observation of creep on faults is a critical part of our earthquake rupture model because if a fault is observed to creep the moment released as earthquakes is reduced from what would be inferred directly from the fault?s slip rate. There is considerable debate about how representative creep measured at the surface during a short time period is of the whole fault surface through the entire seismic cycle (e.g. Hudnut and Clark, 1989). Observationally, it is clear that the amount of creep varies spatially and temporally on a fault. However, from a practical point of view a single creep rate is associated with a fault section and the reduction in seismic moment generated by the fault is accommodated in seismic hazard models by reducing the surface area that generates earthquakes or by reducing the slip rate that is converted into seismic energy. WG-07 decided to follow the practice of past Working Groups and the National Seismic Hazard Map and used creep rate (where it was judged to be interseismic, see Table P1) to reduce the area of the fault surface that generates seismic events. In addition to following past practice, this decision allowed the Working Group to use a reduction of slip rate as a separate factor to accommodate aftershocks, post seismic slip, possible aseismic permanent deformation along fault zones and other processes that are inferred to affect the entire surface area of a fault, and thus are better modeled as a reduction in slip rate. C-zones are also handled by a reduction in slip rate, because they are inferred to include regions of widely distributed shear that is not completely expressed as earthquakes large enough to model. Because the ratio of the rate of creep relative to the total slip rate is often used to infer the average depth of creep, the ?depth? of creep can be calculated and used to reduce the surface area of a fault that generates earthquakes in our model. This reduction of surface area of rupture is described by an ?aseismicity factor,? assigned to each creeping fault in Appendix A. An aseismicity factor of less than 1 is only assigned to faults that are inferred to creep during the entire interseismic period. A single aseismicity factor was chosen for each section of the fault that creeps by expert opinion from the observations documented here. Uncertainties were not determined for the aseismicity factor, and thus it represents an unmodeled (and difficult to model) source of error. This Appendix simply provides the documentation of known creep, the type and precision of its measurement, and attempts to characterize the creep as interseismic, afterslip, transient or triggered. Parts 2 and 3 of this Appendix compare the WG-07 deformation model and the seismic source model it generates to the strain generated by the Pacific - North American plate motion. The concept is that plate motion generates essentially all of the elastic strain in the vicinity of the plate boundary that can be released as earthquakes. Adding up the slip rates on faults and all others sources of deformation (such as C-zones and distributed ?background? seismicity) should approximately yield the plate motion. This addition is usually accomplished by one of four approaches: 1) line integrals that sum deformation along discrete paths through the deforming zone between the two plates, 2) seismic moment tensors that add up seismic moment of a representative set of earthquakes generated by a crustal volume spanning the plate boundary, 3) strain tensors generated by adding up the strain associated with all of the faults in a crustal volume spanning the plate

Wisely, Beth A.; Schmidt, David A.; Weldon, Ray J., II

2008-01-01

170

Relationship between compressional-wave velocity and porosity of sediments along subduction plate interface  

NASA Astrophysics Data System (ADS)

Evolution of physical properties of sediments along subduction interface has effects on wedge strength, wedge geometry, dewatering and dehydration processes, and seismic behavior. Sediments have initially more than 70% of porosity prior to subduction. Through underthrusting and accretion, porosity of sediments decreases by compaction and cementation to be lithified sediments. The purpose of this study is to understand evolution of physical properties from a state before subduction to a state within a wedge using a relationship between compressional-wave velocity and porosity. In this study, we obtained new data for sediments from a reference site in IODP NanTroSEIZE, Expedition 333. In addition to that, we have complied velocity-porosity relationships for the samples and also for previous studies from NanTroSEIZE (off Kumano) (Hashimoto et al., 2010, 2011), ODP Leg 190 (off Shikoku) (Hoffman and Tobin, 2004) and ODP Leg 170 (off Costa Rica) (Gettemy and Tobin, 2003). Velocity measurement procedure in this study to obtain new data is as following: Two pumps were used to control pore fluid pressure and confining pressure. The pore pressure of 1000kPa was kept under drained conditions. Confining (effective) pressure was increased stepwise in the measurements. Velocity measurements were conducted under isotropic pressure conditions. Confining pressure was pressurized in tens seconds and kept for more than 8 hours for next step to obtain equilibrium conditions between effective pressure and sediments strain. Lead zirconate titanate (PZT) shear wave transducers (500kHz) were used in a source-receiver pair to measure wave speed. Porosity and P-wave velocity ranges about 27 - 75% and 1.4 - 2.2 km/s in this study, respectively. In the comparison in Vp-porosity relationships between sedimetns from reference sites and others, sediments were classified into two, simply compacted sediments (reference site and slope sediments) and wedge sediments. Different trends in Vp-porosity relationships were observed for the classified sediments. For compacted sediments, Vp-porosity relationships are along the global empirical relationships (Erickson and Jarrard 1988) and almost within the area between normal and highly compaction curves. On the other hand, some of Vp-porosity relationships for wedge sediments represent trends with higher velocity at a porosity. Such trend was observed for wedge sediments from Site C0001 and C0004. Those higher Vp trend in Vp-porosity relationship for wedge sediments can be explained by shear strain of sediments and/or cementation. Even though the velocity measurements was conducted under hydrostatic condition, we examined the void ratio-porosity curve as a kind of compaction curve. On the basis of the curves, break points were observed at the pressure which corresponds to the effective pressure assuming the hydrostatic pore fluid pressure. The result suggests that the sediments were under condition of normal compaction. Some of void ratio-porosity curve represent a evidence of weak cement which can correspond with anomaly in porosity-depth curve in the shallow portion of the reference sites.

Yamaguchi, M.; Hashimoto, Y.

2012-12-01

171

SEISMICITY AND VOLCANISM IN THE PACIFIC NORTHWEST: EVIDENCE FOR THE SEGMENTATION OF THE JUAN DE FUCA PLATE.  

USGS Publications Warehouse

The distributions of earthquakes and late Cenozoic and Quaternary volcanism in Washington and northern Oregon change markedly across two northeast-striking lines, one near Mount Rainier and one near Mount Hood. On the basis of these observations and a comparison with the Nazoa subduction zone, we propose that the Juan de Fuca subduction zone is divided into two segments. Landward of the coastal thrust zone, we suggest the Juan de Fuca plate dips more steeply beneath the southern segment than beneath the northern segment. Refs.

Weaver, Craig, S.; Michaelson, Caryl, A.

1985-01-01

172

Earth's Decelerating Tectonic Plates  

SciTech Connect

Space geodetic and oceanic magnetic anomaly constraints on tectonic plate motions are employed to determine a new global map of present-day rates of change of plate velocities. This map shows that Earth's largest plate, the Pacific, is presently decelerating along with several other plates in the Pacific and Indo-Atlantic hemispheres. These plate decelerations contribute to an overall, globally averaged slowdown in tectonic plate speeds. The map of plate decelerations provides new and unique constraints on the dynamics of time-dependent convection in Earth's mantle. We employ a recently developed convection model constrained by seismic, geodynamic and mineral physics data to show that time-dependent changes in mantle buoyancy forces can explain the deceleration of the major plates in the Pacific and Indo-Atlantic hemispheres.

Forte, A M; Moucha, R; Rowley, D B; Quere, S; Mitrovica, J X; Simmons, N A; Grand, S P

2008-08-22

173

Structure of Pacific-plate upper mantle from active-source seismic measurements of the NoMelt experiment  

NASA Astrophysics Data System (ADS)

We present results from the active-source seismic component of the NoMelt experiment, conducted in 2011 on ~70 Ma Pacific lithosphere between the Clarion and Clipperton fracture zones. This experiment is motivated by the apparent mismatch between laboratory predictions of lithospheric properties and available field observations. The overall goal of the experiment is to determine the detailed structure of mature, "normal" oceanic lithosphere. The experiment design consists of a 600x400 km array of broad-band (BB) and short-period (SP) ocean bottom seismometers (OBS) and magnetotelluric (MT) instruments. The BB OBS array will measure anisotropic velocity and anelasticity structure based on surface waves and map the base of the lithosphere based on receiver functions. The MT instruments will reveal the presence of any existing melt. The BB OBS and MT arrays are currently still on the seafloor. Observations from the SP OBS array, presented here, constrain the velocity structure of the uppermost mantle to a depth of ~30 km below the Moho based on seismic refraction arrivals (Pn) sourced from an airgun array firing shots at 500-m intervals. We present results from the primary active-source line, which extends 600 km along the center of the segment in the flow-line direction and was instrumented with 31 SP OBS spaced 20 km apart. The instruments record Pn arrivals to distances as great as 500 km. The apparent velocity of Pn arrivals is ~8.5 km/s over most of the transect, but apparent velocities as high as 9.0 km/s are observed for Pn propagating westward over the western end of the transect. The unusually high horizontal phase velocity of westward propagating Pn is not due to seafloor structure, which deepens by ~100 m from east to west along the length of the transect, and it does not appear to be due to crustal structure. The high apparent velocity may indicate dipping structure within the uppermost mantle beneath a portion of the transect. Sub-Moho structure is also indicated by wide-angle reflections that approach the Pn branch near 185 km and 400 km range. A very preliminary analysis of the data suggest that these wide-angle reflections arise from discontinuities at ~12 and ~30 km below the Moho. We expect that a complete analysis of this dataset will reveal uppermost lithospheric structure in unprecedented detail.

Lizarralde, D.; Gaherty, J. B.; Collins, J. A.; Hirth, G.; Evans, R. L.

2012-12-01

174

The Biggest Plates on Earth: Plate Tectonics  

NSDL National Science Digital Library

In this lesson, students investigate the movement of Earth's tectonic plates, the results of these movements, and how magnetic anomalies present at spreading centers document the motion of the crust. As a result of this activity, students will be able to describe the motion of tectonic plates, differentiate between three types of plate boundaries, infer what type of boundary exists between two tectonic plates, and understand how magnetic anomalies provide a record of geologic history and crustal motion around spreading centers. As an example, they will also describe plate boundaries and tectonic activity in the vicinity of the Juan de Fuca plate adjacent to the Pacific Northwest coast of North America.

175

Observations of seafloor fluid venting along the transform margin between the North American and Pacific plates in the Gulf of California  

NASA Astrophysics Data System (ADS)

Detailed surveys of the seafloor morphology at nine representative sections of the North American - Pacific Plate boundary on the floor of the Gulf of California were conducted by the Monterey Bay Aquarium Research Institute (MBARI) during a two ship expedition in March and April 2012. One of the objectives of this program was to better understand the distribution and impact of seafloor fluid venting along an active transform fault. At issue is whether the fault itself forms an active fluid flow conduit. An autonomous underwater vehicle (AUV) provided detailed bathymetry of the seafloor, and a remotely operated vehicle (ROV) allowed ground-truth observations and sampling of the surveyed area. The AUV surveys provide high-resolution multibeam bathymetry with a vertical precision of 0.15 m, horizontal resolution of 1.0 and 2-10 kHz CHIRP seismic reflection profiles. The nine surveys captured the morphology of a highly active fault zone in unprecedented detail. Among the features highlighted by these surveys are areas of distinctive seafloor textures. This distinctive morphology commonly occurs on the surface of elevated features that are up to 10 m higher than the surrounding seafloor and is characterized by considerable fine scale surface topography observed in both the AUV and ROV surveys. The surface topography is made up of broken and irregular blocks of methane-derived carbonates, separated by seafloor craters and open cracks that are 1 to 2 m deep and up to 10 m across. Individual patches of this distinctive morphology which are commonly ~100 m across occur within two of the nine survey areas. The presence of active chemosynthetic biological communities in open karst-like cracks show many of these sites are areas of active fluid seepage. In some places methane bubble venting was observed. Seepage was only observed where truncated strata exposed permeable layers adjacent to the fault rather than directly along the fault trace.

Lundsten, E. M.; Anderson, K.; Paull, C. K.; Caress, D. W.; Thomas, H.; Gwiazda, R.; Herguera, J.; McGann, M. L.; Edwards, B. D.; Hinojosa, A.; Mejia Mercado, B.; Sanchez, A.; Conlin, D.; Thompson, D.

2012-12-01

176

Structural and Tectonic Map Along the Pacific-North America Plate Boundary in Northern Gulf of California, Sonora Desert and Valle de Mexicali, Mexico, from Seismic Reflection Evidence  

NASA Astrophysics Data System (ADS)

Between 1978 and 1983, Petróleos Mexicanos (PEMEX) carried on an intense exploration program in the northern Gulf of California, the Sonora Desert and the southern part of the Mexicali Valley. This program was supported by a seismic reflection field operation. The collected seismic data was 2D, with travel time of 6 s recording, in 48 channels, and the source energy was: dynamite, vibroseis and air guns. Since 2007 to present time, the existing seismic data has been re-processing and ire-interpreting as part of a collaboration project between the PEMEX's Subdirección de Exploración (PEMEX) and CICESE. The study area is located along a large portion of the Pacific-North America plate boundary in the northern Gulf of California and the Southern part of the Salton Trough tectonic province (Mexicali Valley). We present the result of the processes reflection seismic lines. Many of the previous reported known faults were identify along with the first time described located within the study region. We identified regions with different degree of tectonic activity. In structural map it can see the location of many of these known active faults and their associated seismic activity, as well as other structures with no associated seismicity. Where some faults are mist placed they were deleted or relocated based on new information. We included historical seismicity for the region. We present six reflection lines that cross the aftershocks zone of the El Mayor-Cucapah earthquake of April 4, 2010 (Mw7.2). The epicenter of this earthquake and most of the aftershocks are located in a region where pervious to this earthquake no major earthquakes are been reported. A major result of this study is to demonstrate that there are many buried faults that increase the seismic hazard.

Gonzalez-Escobar, M.; Suarez-Vidal, F.; Mendoza-Borunda, R.; Martin Barajas, A.; Pacheco-Romero, M.; Arregui-Estrada, S.; Gallardo-Mata, C.; Sanchez-Garcia, C.; Chanes-Martinez, J.

2012-12-01

177

Plate Motions  

NSDL National Science Digital Library

To prepare for this exercise students read the Chapter on plate tectonics in their text book. In class, they are given a color isochron map of the sea floor. They are given 4 tasks: Answer basic questions about the timing and rate of opening of the N. and S. Atlantic; Determine what has happened to the oceanic crust that is created on the eastern side of the East Pacific Rise; Determine what type of plate boundary existed on the western edge of the N. America plate before the San Andreas Fault and when this transition occurred; and Reconstruct the motion of the plates over the last 40 Ma assuming that the surface area of the Earth has not changed.

Nunn, Jeffrey

178

The nitrite-oxygen interface at the top of the oxygen minimum zone in the eastern tropical North Pacific  

NASA Astrophysics Data System (ADS)

Observations of continuous chemical profiles through the top of the oxygen minimum zone off the Pacific coast of Mexico show a secondary fluorescence peak associated with a layer of near-zero oxygen and nitrite concentrations and large curvatures in the profiles. The layer is about 4 m thick and the oxygen and nitrite fluxes into the layer are estimated tobe within a factor of 2 of 1.5 mg-at. m -2d -1. The fluorescence peak is probably due to microorganisms that obtain energy for growth from the oxidation of nitrite. The integrated carbon production rate required to maintain the peak is estimated at 1 mg-at. m -2d -1. Nitrification is most likely the dominant process in the layer and the nitrifying bacteria could produce the fluorescence. Alternatively, the fluorescence might be from photosynthetic bacteria that oxidize nitrite in a manner similar to the photosynthetic oxidation of sulfur compounds, or from bioluminescence.

Anderson, James Jay

1982-10-01

179

New Insights into Strain Accumulation and Release in the Central and Northern Walker Lane, Pacific-North American Plate Boundary, California and Nevada, USA  

NASA Astrophysics Data System (ADS)

The Walker Lane is a 100 km-wide distributed zone of complex transtensional faulting that flanks the eastern margin of the Sierra Nevada. Up to 25% of the total Pacific-North American relative right-lateral plate boundary deformation is accommodated east of the Sierra Nevada, primarily in the Walker Lane. The results of three studies in the Central and Northern Walker Lane offer new insights into how constantly accumulating plate boundary shear strain is released on faults in the Walker Lane and regional earthquake hazards. This research is based on the collection and analysis of new of geologic and geodetic datasets. Two studies are located in the Central Walker Lane, where plate boundary deformation is accommodated on northwest trending right-lateral faults, east-northeast trending left-lateral faults, and north trending normal faults. In this region, a prominent set of left-stepping, en-echelon, normal fault-bounded basins between Walker Lake and Lake Tahoe fill a gap in Walker Lane strike slip faults. Determining how these basins accommodate shear strain is a primary goal of this research. Paleoseismic and neotectonic observations from the Wassuk Range fault zone in the Walker Lake basin record evidence for at least 3 Holocene surface rupturing earthquakes and Holocene/late Pleistocene vertical slip rates between 0.4-0.7 mm/yr on the normal fault, but record no evidence of right-lateral slip along the rangefront fault. A complementary study presents new GPS velocity data that measures present-day deformation across the Central Walker Lane and infers fault slip and block rotation rates using an elastic block model. The model results show a clear partitioning between distinct zones of strain accommodation characterized by (1) right-lateral translation of blocks on northwest trending faults, (2) left-lateral slip and clockwise block rotations between east and northeast trending faults, and (3) right-lateral oblique normal slip with minor clockwise block rotations on north trending faults. Block model results show that a component of right-lateral slip in the normal-fault bounded basins is required to adequately fit the GPS data. New GPS data from the Northern Walker Lane constrains present-day slip rates on the Mohawk Valley, Grizzly Valley, and Honey Lake fault zones. Block model results predict right-lateral slip rates of 2.2 +/- 0.2 mm/yr for the Mohawk Valley fault and 1.1 +/- 0.4 mm/yr for the Honey Lake fault. The GPS data do not require slip on the Grizzly Valley fault, although right-lateral slip rates up to 1.2 mm/yr are allowed without increasing the block model misfit. The present-day distribution of slip between the Honey Lake and Mohawk Valley faults is opposite that predicted by latest Quaternary and Holocene geologic slip rate estimates. A temporally variable Wallace-type strain release model that includes 104-year timescale variations in fault slip rate could reconcile both datasets.

Bormann, Jayne M.

180

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

NASA Astrophysics Data System (ADS)

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 Oligocene. Over a period of less than 15Ma, this boundary changed from mid-ocean ridge spreading to simple translation, the record of which is recorded in the fabric and fracture zones of the oceanic lithosphere. Application of available well-constrained plate motions imply that substantial deformation of the oceanic lithosphere must have occurred after fracture zone formation to create the arcuate structure of these fracture zones today. Plate reconstructions of this plate boundary system from the Oligocene through the Early-Mid Miocene are used here to isolate the timing of transitions in plate motion from divergence to translational motion. These reconstructions identify rapid rotations in plate motions after approximately 25Ma. By 20Ma, the majority of crust created along this plate boundary was already in place, and the Australian Plate was translating northwards relative to the Pacific towards New Zealand, where a corner of Australian Plate is ultimately subducted. The timing of this transition in plate motions implies that the onset of subduction at the Puysegur Trench may have been as early as approximately 20Ma. These reconstructions also identify the shape of fracture zones either side of the relic mid-ocean ridge through the time of their formation. Comparison of these restored fracture zones with their present-day appearance delineates a broad zone of deformation extending ~150km into the plate interior from the Macquarie Ridge Complex, the modern plate boundary structure. This area of deformation coincides with a broad distribution of seismicity in the Australian Plate on both inter- and intra-plate structures, including two great (M8+) earthquakes over the past twenty years, one of which occurred over 130km from the plate boundary. The persistence of this deformation through time indicates a link with the evolution of the plate boundary from divergence to translation and subduction, and may be a result of stress build-up within the Australian Plate as a consequence of the impingement of the subducting plate on the thickened lithosphere of southern New Zealand. Such a collision may act as a resisting force to subduction, and if it continues, further deformation internal to the Macquarie Block may lead to a southward migration of the Australia:Pacific subduction interface and the capturing of this section of lithosphere onto the Pacific Plate.

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

2007-12-01

181

Tectonic Plate Coupling and Elastic Thickness Using a Viscoelastic Model of Crustal Deformation in Southern North Island, New Zealand  

Microsoft Academic Search

The crustal deformation in the Wellington region of North Island, New Zealand has been studied by inverting GPS-derived crustal velocities using a steady-state viscoelastic model of oblique plate convergence. The deformation is driven by pseudo-backslip on the locked Pacific-Australia plate interface. Finite element techniques are used to calculate effective Green functions for the slip elements and slip velocities are determined

S. C. Cohen; D. J. Darby

2001-01-01

182

Dynamic instability of a thin circular plate with friction interface and its application to disc brake squeal  

Microsoft Academic Search

The mathematical formulation for determining the dynamic instability due to transverse doublet modes in the self-excited vibration of a thin annular plate is presented in this paper. An analytical approach is developed to obtain the stability results from the eigenvalue problem of a stationary disc with a finite contact area. The approach uses the eigenfunctions of transverse doublet modes in

Jaeyoung Kang; Charles M. Krousgrill; Farshid Sadeghi

2008-01-01

183

Very low frequency earthquakes related to small asperities on the plate boundary interface at the locked to aseismic transition  

Microsoft Academic Search

Very low frequency (VLF) seismic signals observed in southwestern Japan are evidently radiated from shear slips on the upper surface of the subducting Philippine Sea Plate. We used grid moment tensor inversion and centroid moment tensor inversion to calculate 242 moment tensor solutions with moment magnitudes between 3.1 and 3.8 from continuous seismograms recorded over a 5 year period by

Yoshihiro Ito; Kazushige Obara; Takanori Matsuzawa; Takuto Maeda

2009-01-01

184

Suloy, Pacific Ocean  

NASA Technical Reports Server (NTRS)

A demarcation line identifies a convergence in the Pacific Ocean (1.5N, 133.0W) where two open ocean currents have interfaced. This interface phenomena was first observed in the White Sea by Soviet cosmonauts who coined the term `Suloy' to describe the event. At the actual interface, there is usually a slight upwelling as the currents clash, causing a shadow effect that can be observed and an audible hissing sound as the currents meet head on.

1992-01-01

185

Long-term Spatial and Temporal Variations in Seismic Activity Along the Juan de Fuca Plate System (Northeast Pacific Ocean) Recorded on Military Hydrophone Arrays  

Microsoft Academic Search

Since August 1991 U.S. Navy hydrophones have been used by NOAA\\/OSU to monitor seismicity from seafloor spreading centers in the northeast Pacific Ocean. Over the last decade, more than 10,000 earthquakes have been located using the Tertiary (T-) wave of these seafloor events recorded by this hydro-acoustic monitoring system. Before a reliable analysis of the long-term behavior of northeast Pacific

J. H. Haxel; R. P. Dziak; D. R. Bohnenstiehl; M. J. Fowler

2004-01-01

186

Dynamic instability of a thin circular plate with friction interface and its application to disc brake squeal  

NASA Astrophysics Data System (ADS)

The mathematical formulation for determining the dynamic instability due to transverse doublet modes in the self-excited vibration of a thin annular plate is presented in this paper. An analytical approach is developed to obtain the stability results from the eigenvalue problem of a stationary disc with a finite contact area. The approach uses the eigenfunctions of transverse doublet modes in classical plate theory and establishes the formulation of modal instability due to the modal-interaction of a doublet mode pair. The one-doublet mode model of a disc and a discrete model equivalent to the one-doublet mode model are proposed for providing a more fundamental understanding of the onset of squeal. The analytical models are validated through a comparison of results from a modal expansion model obtained from finite element component models. Throughout the analytical investigation, the pad arc length is found to be a critical design parameter in controlling squeal propensity.

Kang, Jaeyoung; Krousgrill, Charles M.; Sadeghi, Farshid

2008-09-01

187

A variety of slip behaviors along plate interface and interplay among them before and after the 2011 Mw9.0 Tohoku-Oki earthquake (Invited)  

NASA Astrophysics Data System (ADS)

Prior to the 11 March 2011 Mw 9.0 Tohoku earthquake in Japan, two distinct sequences of foreshock migrations along the trench axis toward the mainshock epicenter were identified by an earthquake catalog created using a waveform correlation technique [Kato et al., 2012, Science]. In addition, the time history of quasi-static slip along the plate interface extracted from small repeating earthquakes shows that transient slip coincided with the two sequences of earthquake migrations. The transient slip first started to build up from mid- to late February. After the Mw 7.3 foreshock, the amount of transient slip increased abruptly to the north of the Mw 7.3 epicenter, though it slightly slowed down logarithmically with time, a phenomenon commonly observed in afterslip. In contrast, slip in the earthquake migration zone (to the south of the Mw 7.3 epicenter) increased almost linearly during the final phase. Geodetic measurements also detected transient deformation after the Mw 7.3 foreshock [Ohta et al., 2012, GRL]. These results provide strong evidence for the propagation of slow-slip events toward the Mw 9.0 epicenter. The slow-slip events may have caused stress loading onto the prospective hypocenter of the Mw 9.0 mainshock and prompted the initiation of unstable dynamic rupture. Similar stress loading by transient slip onto prospective hypocenter was identified by earthquake migrations prior to the 2008 Mw 6.8 interplate (Ibaraki-Oki) earthquake, and by geodetic measurement before the 2004 Mw 7.0 earthquake offshore of eastern Hokkaido [Murakami et al., 2006, GRL]. Stress loading by slow slip transients plays a crucial role to prompt initiation of dynamic rupture, provided that large-sized potential earthquake-nucleation patch is close to failure. After the Tohoku-Oki mainshock rupture, any subsequent seismicity along the plate interface in the foreshock area was abruptly terminated, and has remained very low ever since [Kato and Igarashi, 2012, GRL]. This observation indicates that the accumulated stress along the plate interface was almost entirely released from the foreshock area. On-fault aftershocks including small repeating earthquakes have been concentrated at edges of the large slip-zone. It is thus likely that the stress increase generated by abrupt mainshock slip termination triggered the post-seismic transient afterslip event. It is of crucial importance to advance our understanding of interplay between dynamic and quasi-static slip.

Kato, A.; Obara, K.

2013-12-01

188

Multiple H-bonds directed self-assembly of an amphiphilic and plate-like codendrimer with janus faces at water-air interface.  

PubMed

An amphiphilic diblock codendrimer composed of a third generation poly(methallyl dichloride) end-capped by eight hydroxyl groups (PMDC(OH)(8)) and a second generation poly(urethane amide) end-capped by four alkyl groups (PUA(C16)(4)) were found to self-assemble into highly oriented ribbons at the water-air interface. Further investigation on the ribbon formation shows that the ribbons are hierarchically self-organized by the janus and plate-like shape of g3-PMDC(OH)(8)-b-g2-PUA(C16)(4). Sextuple H-bonds existing at different positions of the molecular plate are the main driving force for the one-dimensional growth of the ribbon. The recognition of these H-bonds leads to a highly ordered stacking of the codendrimers, and the crystallization of the alkyl chains results in a primary ribbon with a ca. 7.6 +/- 0.5 nm width. The primary ribbons prefer to organize into secondary ribbons with an average width of 53 +/- 6.0 nm. The manner of recognition and assembly is similar to the organization of a kind of toy building block with janus faces, which provides a new strategy to the design of well-defined nanomaterials. PMID:19361164

Yang, Miao; Wang, Wei; Lieberwirth, Ingo; Wegner, Gerhard

2009-05-01

189

The imaging plate system interfaced to the large-volume press at beamline X17B1 of the national synchrotron light source  

NASA Astrophysics Data System (ADS)

A double imaging plate is interfaced to the Large Volume High Pressure Device (LVHPD) SAM-85 for the collection of in situ X ray powder diffraction data suitable for Rietveld analysis. The two-dimensional detector, combined with the uniform pressure and temperature environments of the LVHPD and the wide energy range available from a new Laue-Bragg monochromator at X17B1, results in high-quality diffraction data suitable for Rietveld refinements. A disk-type heater is used to minimize extrinsic diffraction peaks from the surrounding materials. Diffraction effects resulting from the boron-epoxy pressure transmitting medium are removed by subtraction. To demonstrate the quality of data obtained from the imaging-plate system, the cation distributions over the available sites in the crystal structures of NiAl2O4-spinel and (Ni,Mg)2SiO4-olivine have been refined from data collected at high pressures and temperatures. In both cases cation ordering is observed to increase with pressure.

Chen, J.; Parise, J. B.; Li, R.; Weidner, D. J.; Vaughan, M.

190

Fault kinematics in northern Central America and coupling along the subduction interface of the Cocos Plate, from GPS data in Chiapas (Mexico), Guatemala and El Salvador  

NASA Astrophysics Data System (ADS)

New GPS measurements in Chiapas (Mexico), Guatemala and El Salvador are used to constrain the fault kinematics in the North America (NA), Caribbean (CA) and Cocos (CO) plates triple junction area. The regional GPS velocity field is first analysed in terms of strain partitioning across the major volcano-tectonic structures, using elastic half-space modelling, then inverted through a block model. We show the dominant role of the Motagua Fault with respect to the Polochic Fault in the accommodation of the present-day deformation associated with the NA and CA relative motion. The NA/CA motion decreases from 18-22 mm yr-1 in eastern Guatemala to 14-20 mm yr-1 in central Guatemala (assuming a uniform locking depth of 14-28 km), down to a few millimetres per year in western Guatemala. As a consequence, the western tip of the CA Plate deforms internally, with ?9 mm yr-1 of east-west extension (?5 mm yr-1 across the Guatemala city graben alone). Up to 15 mm yr-1 of dextral motion can be accommodated across the volcanic arc in El Salvador and southeastern Guatemala. The arc seems to mark the northern boundary of an independent forearc sliver (AR), pinned to the NA plate. The inversion of the velocity field shows that a four-block (NA, CA, CO and AR) model, that combines relative block rotations with elastic deformation at the block boundaries, can account for most of the GPS observations and constrain the overall kinematics of the active structures. This regional modelling also evidences lateral variations of coupling at the CO subduction interface, with a fairly high-coupling (?0.6) offshore Chiapas and low-coupling (?0.25) offshore Guatemala and El Salvador.

Franco, A.; Lasserre, C.; Lyon-Caen, H.; Kostoglodov, V.; Molina, E.; Guzman-Speziale, M.; Monterosso, D.; Robles, V.; Figueroa, C.; Amaya, W.; Barrier, E.; Chiquin, L.; Moran, S.; Flores, O.; Romero, J.; Santiago, J. A.; Manea, M.; Manea, V. C.

2012-06-01

191

Pre-Cretaceous Tectonic Evolution of the Pacific Plate and Extension of the Geomagnetic Polarity Reversal Time Scale with Implications for the Origin of the Jurassic 'Quiet Zone'.  

National Technical Information Service (NTIS)

Linear magnetic anomalies resulting from seafloor spreading were map ped in the vicinity of the magnetic bright in the western Pacific Ocean. New aeromagnetic data allowed the magnetic bright to be more accurately mapped from M21 to M28 and enabled the id...

D. R. Bracey D. W. Handschumacher T. W. Hilde W. W. Sager

1987-01-01

192

Unbending and horizontal fracture of the subducting Pacific plate, as evidenced by the 1993 Kushiro-oki and the 1981 and 1987 intermediate-depth earthquakes in Hokkaido  

Microsoft Academic Search

A large number of aftershocks of the 1993 Kushiro-oki earthquake (MJMA = 7.8), 1987 Hidaka earthquake (MJMA = 7.0), and 1981 Western Hidaka earthquake (MJMA = 7.1) have been observed by the seismic network of Hokkaido University. These three earthquakes are the largest events that have occurred in the depth range from 100 km to 200 km under the Pacific

Sadaomi Suzuki; Minoru Kasahara

1996-01-01

193

Investigations on the micro-scale surface interactions at the tool and workpiece interface in micro-manufacturing of bipolar plates for proton exchange membrane fuel cells  

NASA Astrophysics Data System (ADS)

Micro-forming studies have been more attractive in recent years because of miniaturization trend. One of the promising metal forming processes, micro-stamping, provides durability, strength, surface finish, and low cost for metal products. Hence, it is considered a prominent method for fabricating bipolar plates (BPP) with micro-channel arrays on large metallic surfaces to be used in Proton Exchange Membrane Fuel Cells (PEMFC). Major concerns in micro-stamping of high volume BPPs are surface interactions between micro-stamping dies and blank metal plates, and tribological changes. These concerns play a critical role in determining the surface quality, channel formation, and dimensional precision of bipolar plates. The surface quality of BPP is highly dependent on the micro-stamping die surface, and process conditions due to large ratios of surface area to volume (size effect) that cause an increased level of friction and wear issues at the contact interface. Due to the high volume and fast production rates, BPP surface characteristics such as surface roughness, hardness, and stiffness may change because of repeated interactions between tool (micro-forming die) and workpiece (sheet blank of interest). Since the surface characteristics of BPPs have a strong effect on corrosion and contact resistance of bipolar plates, and consequently overall fuel cell performance, evolution of surface characteristics at the tool and workpiece should be monitored, controlled, and kept in acceptable ranges throughout the long production cycles to maintain the surface quality. Compared to macro-forming operations, tribological changes in micro-forming process are bigger challenges due to their dominance and criticality. Therefore, tribological size effect should be considered for better understanding of tribological changes in micro-scale. The integrity of process simulation to the experiments, on the other hand, is essential. This study describes an approach that aims to investigate the surface topography changes during long-run micro-stamping of BPPs, and establish relationships between surface roughness--corrosion resistance and surface roughness-contact resistance characteristics of BPPs. Formability levels of formed BPPs and repeatability characteristics of the process were investigated. In addition, blank thickness changes, von-Mises stress, plastic strain levels and distributions of micro-stamping process were determined via finite element analysis (FEA). Test results revealed that the surface roughness change for the stamping dies and BPPs was unsteady (no trend) due to the continuous change of surface topography (i.e. asperity deformation). Sub-micron range local plastic deformations on stamping dies led to surface topography changes on BPP in long-run manufacturing case. As surface defects trigger corrosion, the correlation between surface roughness and corrosion resistance of BPPs was found to be direct. Increasing number of surface irregularities (asperities) lowered contact surface area that resulted in increased contact resistance. ZrN coated BPPs, on the other hand, did not change surface roughness, however; it improved the protection of BPPs against corrosion significantly. In addition, ZrN coating increased the conductivity of BPPs and reduced the contact resistance between BPP and gas diffusion layer (GDL), at certain extent. As dimensional stability and repeatability was confirmed in forming of both uncoated and coated BPPs during the long run manufacturing, different formability levels were achieved for coated and uncoated samples. Lower channel height values were obtained for coated plates because of the different surface hardness of uncoated and coated plates. In tribological size effect part of study, micro stamping experiments using three different dies with distinct channel height values at different stamping force levels were performed. It was concluded that decrease in forming die dimensions led to increase in coefficient of friction as previously reported by other researchers as one of the consequences of tribolog

Peker, Mevlut Fatih

194

Anomalous deepening of a belt of intraslab earthquakes in the Pacific slab crust under Kanto, central Japan: Possible anomalous thermal shielding, dehydration reactions, and seismicity caused by shallower cold slab material  

Microsoft Academic Search

A belt of intraslab seismicity in the Pacific slab crust parallel to iso-depth contours of the plate interface has been found beneath Hokkaido and Tohoku. Hypocenter relocations have shown that this seismic belt does not run parallel to but obliquely to the iso-depth contours beneath Kanto, deepening toward the north from ~100 km to ~140 km depth. The depth limit

Akira Hasegawa; Junichi Nakajima; Saeko Kita; Tomomi Okada; Toru Matsuzawa; Stephen H. Kirby

2007-01-01

195

Anomalous deepening of a belt of intraslab earthquakes in the Pacific slab crust under Kanto, central Japan: Possible anomalous thermal shielding, dehydration reactions, and seismicity caused by shallower cold slab material  

Microsoft Academic Search

A belt of intraslab seismicity in the Pacific slab crust parallel to iso-depth contours of the plate interface has been found beneath Hokkaido and Tohoku. Hypocenter relocations have shown that this seismic belt does not run parallel to but obliquely to the iso-depth contours beneath Kanto, deepening toward the north from ?100 km to ?140 km depth. The depth limit

Akira Hasegawa; Junichi Nakajima; Saeko Kita; Tomomi Okada; Toru Matsuzawa; Stephen H. Kirby

2007-01-01

196

Monitoring of slip at the transition zone on the plate interface estimated from non-volcanic deep low-frequency tremors in southwestern Japan  

NASA Astrophysics Data System (ADS)

In southwestern Japan, non-volcanic deep low-frequency (DLF) tremors (e.g., Obara, 2002) and short-term slow slip events (S-SSEs; e.g., Obara et al., 2004) occur in temporal and spatial coincidence with the active stages of DLF tremors (Obara et al., 2004). Based on this feature, Hiramatsu et al. (2008) proposed a method to monitor slip at the transition zone between the locked and aseismic slip zones on the plate interface using DLF tremors. In this study, we applied the method as the same way of previous studies (Hiramatsu et al., 2008; Hirose et al., 2010) and estimated the long-term average slip rate at the transition zone from DLF tremors in southwestern Japan. We also estimated the slip distributions of S-SSEs from DLF tremors using the modified envelope correlation method (ECM) tremor catalog (Maeda and Obara, 2009) and the hourly centroid tremor catalog (Obara et al., 2010) along with the ECM tremor catalog (Obara, 2002) in southwestern Japan. The modified ECM applied both the differential travel time and the spatial distribution of mean square amplitudes to estimate a tremor's spatial location and radiation energy. The hourly centroid tremor catalog is constructed using a clustering process to estimate centroid locations, revealing clear depth-dependent behavior of the tremor activity. The cumulative seismic moment from 2001 to 2009 increases at a constant rate, indicating a constant moment release rate in the long-term average. We estimated slip rate at the transition zone using the formula ? {M0} = ? S_? {U}, where ? {M0} is the moment release rate, ? the rigidity, S the fault area that is related to the slip of S-SSEs in each region, and ? {U} the slip rate. We obtained the slip rates of 4.1 ± 0.5 cm/yr, 3.7 ± 0.6 cm/yr, and 2.6 ± 0.2 cm/yr in the western Shikoku, northern Kii peninsula, and Tokai regions, respectively, at the transition zone through the analyzed period. The slip deficit rate at the transition zone in each region is 2.6cm/yr, 2.6cm/yr, and 1.5cm/yr, respectively (Kobayashi and Hashimoto, 2007; Tabei et al., 2007; Suito and Ozawa, 2009). The convergence rate of the Philippine Sea plate in each region is estimated to be 6.3-6.8 cm/yr, 5.0-6.5 cm/yr, and 3.0-4.0 cm/yr (Miyazaki and Heki, 2001; Hori et al., 2004). The estimated slips at the transition zone therefore compensate the difference between the convergence rate at the trench and the slip deficit rate at the transition zone of the subducting Philippine Sea plate. For the slip distributions of the S-SSEs, we assumed sub-faults with uniform slip on the plate interface and estimated the slip from the cumulative seismic moment in each sub-fault. As the result, the slip distribution of most S-SSEs correlates roughly with the slip distribution estimated from the inversion of tilt meter records (Hirose and Obara, 2010), indicating that this procedure is useful to determine the slip distribution of S-SSEs quickly and easily.

Ishida, R.; Hiramatsu, Y.; Obara, K.; Matsuzawa, T.

2011-12-01

197

Along-strike Changes in Plate-bending Seismicity in the Mariana Islands: Implications for Strength of Interplate Coupling and Hydration of the Subducting Pacific Slab  

Microsoft Academic Search

The occurrence of plate-bending earthquakes not only indicates the degree of coupling experienced along the shallow thrust of a subduction zone, but also the potential depth extent of slab hydration due to water circulation along faults prior to subduction. Using a combination of hypocentroidal decomposition relative relocation and teleseismic P & SH waveform inversion techniques, we refine the locations of

E. L. Emry; D. A. Wiens; P. Shore

2010-01-01

198

How Plates Move  

NSDL National Science Digital Library

This information on the two major types of plate interaction and the resulting features discusses the Mid Atlantic Ridge and the mid-ocean ridges in connection with divergence and ocean trenches and connects the Pacific Ring of Fire to the concept of subduction. Volcanic activity as a result of subduction is also covered. The site also features links to goals, objectives, and materials for a hands-on lesson on how plates move.

199

Imaging the Structure of the Pacific-North American Plate Boundary using Airborne Laser Swath Mapping (ALSM) Data and Wavelet Analysis  

NASA Astrophysics Data System (ADS)

Since the 1906 San Francisco earthquake, geologists have noted that the topography of active fault zones is significantly modified by repeated fault ruptures over geologic time. Here, we present an analysis of fault zone topography generated by high-resolution Airborne Laser Swath Mapping (ALSM) data collected by the National Center for Airborne Laser Mapping (NCALM). The digital elevation models (DEMs) generated from the ALSM data reveal the location, orientation, and curvature of scarps associated with active, plate-boundary faults. In particular, we have examined topographic data from the B4 and Northern California data sets, as well as data from faults within the Eastern California Shear Zone. We used a wavelet-based convolution scheme, based on topographic forms modified from the profile scarp-diffusion model of Hanks et al. (1984), extended to encompass along-strike features. We applied this filtering methodology to digital topography along fault zones to estimate the best-fitting height, orientation, morphologic age, and associated Signal-to-Noise Ratio (SNR) of scarps found within these datasets. These results will be available to the community via a GIS web portal so that other workers can mine these data to understand patterns of fault-zone structure observed along the plate-bounding fault zones. To evaluate the utility of this methodology for identifying and characterizing fault scarps within the topographic swaths, we present sample results from the Calaveras fault, part of the San Andreas fault system in northern California. We found that along this fault, the filtering algorithm correctly identifies scarps characterized by ground surveys, previous analysis of aerial photography, and/or field mapping. However, some mapped fault traces with low SNR values because of their subtle morphologic expression are not identified by the algorithm. Similarly, some fluvial scarps that trend in a similar orientation to the overall fault zone are erroneously identified as fault scarps by the algorithm. Future work includes further refinement and field verification of the method, and eventual application to all on-land faults for which ALSM data are available within the western U.S. plate margin.

Sanquini, A.; Cheung, K.; Gudmundsdottir, M. H.; Moon, S.; Lin, N.; Shelef, E.; Hilley, G. E.; Prentice, C. S.

2011-12-01

200

Cenozoic deep-water sedimentary basin formation at the Australia-Pacific plate boundary, southern New Caledonia Trough and Taranaki Basin, New Zealand  

NASA Astrophysics Data System (ADS)

Investigation of four petroleum exploration wells and seismic-reflection interpretation reveal >2 km of tectonic subsidence related to Cretaceous rift structures, and 2-3km of Cenozoic subsidence with little faulting of the upper crust. Comparisons to thermal cooling models require stretching factors that are incompatible with the continental foundations of the basin. In addition, up to 50 % of the subsidence signal occurred in the Mid-Cenozoic, hundreds of kilometres from potential contemporary plate boundaries. Thus, upper crustal faulting, thermal relaxation or flexure cannot explain the 300-500 km wide and 2000 km long sedimentary basin system. We suggest that not all deep-water basins are the evolved products of processes that form shallow-water sedimentary basins, but instead they may be influenced by different processes such as convection in the asthenospheric mantle, instabilities in the mantle lithosphere and/or detachment fault zones that inevitably lead to deeper water.

Baur, J. R.; Sutherland, R.; Stern, T. A.

2010-12-01

201

Influence of elastomeric seal plate surface chemistry on interface integrity in biofouling-prone systems: Evaluation of a hydrophobic "easy-release" silicone-epoxy coating for maintaining water seal integrity of a sliding neoprene/steel interface  

NASA Astrophysics Data System (ADS)

The scientific hypothesis of this work is that modulation of the properties of hard materials to exhibit abrasion-reducing and low-energy surfaces will extend the functional lifetimes of elastomeric seals pressed against them in abrasive underwater systems. The initial motivation of this work was to correct a problem noted in the leaking of seals at major hydropower generating facilities subject to fouling by abrasive zebra mussel shells and extensive corrosion. Similar biofouling-influenced problems can develop at seals in medical devices and appliances from regulators in anesthetic machines and SCUBA diving oxygen supply units to autoclave door seals, injection syringe gaskets, medical pumps, drug delivery components, and feeding devices, as well as in food handling equipment like pasteurizers and transfer lines. Maritime and many other heavy industrial seal interfaces could also benefit from this coating system. Little prior work has been done to elucidate the relationship of seal plate surface properties to the friction and wear of elastomeric seals during sliding contacts of these articulating materials, or to examine the secondary influence of mineralized debris within the contacting interfaces. This investigation utilized the seal materials relevant to the hydropower application---neoprene elastomer against carbon steel---with and without the application of a silicone-epoxy coating (WearlonRTM 2020.98) selected for its wear-resistance, hydrophobicity, and "easy-release" capabilities against biological fouling debris present in actual field use. Analytical techniques applied to these materials before and after wear-producing processes included comprehensive Contact Angle measurements for Critical Surface Tension (CA-CST) determination, Scanning Electron Microscopic inspections, together with Energy Dispersive X-ray Spectroscopy (SEM-EDS) and X-Ray Fluorescence (XRF) measurements for determination of surface texture and inorganic composition, Multiple Attenuated Internal Reflection (MAIR-IR) and Microscopic Infrared Spectroscopy for organic surface compositional details, light microscopy for wear area quantification, and profilometry for surface roughness estimation and wear depth quantification. Pin-on-disc dynamic Coefficient of Friction (CoF) measurements provided data relevant to forecasts of seal integrity in dry, wet and biofouling-influenced sliding contact. Actual wear of neoprene seal material against uncoated and coated steel surfaces, wet and dry, was monitored after both rotary and linear cyclic wear testing, demonstrating significant reductions in elastomer wear areas and depths (and resultant volumes) when the coating was present. Coating the steel eliminated a 270% increase in neoprene surface area wear and an 11-fold increase in seal abrasive volume loss associated with underwater rusting in rotary experiments. Linear testing results confirm coating efficacy by reducing wear area in both loading regimes by about half. No coating delamination was observed, apparently due to a differential distribution of silicone and epoxy ingredients at the air-exposed vs. steel-bonded interfaces demonstrated by IR and EDS methods. Frictional testing revealed higher Coefficients of Friction (CoF) associated with the low-speed sliding of Neoprene over coated rather than uncoated steel surfaces in a wet environment, indicating better potential seal adhesion between the hydrophobic elastomer and coating than between the elastomer and intrinsically hydrophilic uncoated steel. When zebra mussel biofouling debris was present in the articulating joints, CoF was reduced as a result of a water channel path produced between the articulating surfaces by the retained biological matter. Easier release of the biofouling from the low-CST coated surfaces restored the seal integrity more rapidly with further water rinsing. Rapid sliding diminished these biofouling-related differences, but revealed a significant advantage in reducing the CoF of the elastomer-on-coating couples to less than 50% of the elastomer-on-steel coupl

Andolina, Vincent L.

202

Tectonic evolution of the Pacific Ocean since 74 ma  

NASA Astrophysics Data System (ADS)

A recent re-evaluation of the Late Mesozoic and Cenozoic sea-floor spreading data in the eastern Pacific has allowed us to make a new interpretation of the timing and sequence of the tectonic events which produced the present configuration of the plates (Whitman and Harrison, 1981; Whitman, 1981). Rotation parameters specifying the relative motion between all pairs of plates in the ocean basin have been calculated from the best fit of oceanic magnetic anomalies, with additional input from bathymetry and crustal ages of the Deep Sea Drilling Project sites. The rotation parameters for the relative motion between the Pacific and Antarctic plates are taken from Weissel et al. (1977) and the continental rotation parameters are from Barron et al. (1981). Plate motions have been determined back to 74 Ma. This time marks the initiation of spreading at the Pacific-Antarctic Ridge which caused the separation of the Campbell Plateau from Antarctica (Barron et al., 1981). Thus, this time is the earliest fix on the position of the Pacific plate relative to the continents surrounding the Pacific Ocean basin using sea-floor spreading. Since it is not possible to derive quantitative information about the relative motion between two plates separated by a trench, all rotations for the oceanic plates of the Pacific basin have been calculated relative to the Pacific plate and then relative to North America through the plate circuit: Pacific-Antarctica-Africa-North America Since we also know the relative position of North America with respect to the other continents, we can show the relative position of the Pacific plate and the other oceanic plates with respect to all of the continental plates surrounding the Pacific Ocean basin.

Whitman, J. M.; Harrison, C. G. A.; Brass, G. W.

1983-12-01

203

Recent plate motions and crustal deformation  

SciTech Connect

Reports by U.S. workers on geodetic measurements of recent plate motions or crustal deformation published in 1987-1990 are reviewed. The review begins with global plate motions, proceeds through plate boundaries in California, Alaska, and the Pacific Northwest, and finishes with volcanic phenomena, monument stability and longevity, and GPS relative position measurements. 184 refs.

Lisowski, M. (USAF, Geophysics Laboratory, Hanscom AFB, MA (United States))

1991-01-01

204

Channel plate for DNA sequencing  

DOEpatents

This invention is a channel plate that facilitates data compaction in DNA sequencing. The channel plate has a length, a width and a thickness, and further has a plurality of channels that are parallel. Each channel has a depth partially through the thickness of the channel plate. Additionally an interface edge permits electrical communication across an interface through a buffer to a deposition membrane surface. 15 figs.

Douthart, R.J.; Crowell, S.L.

1998-01-13

205

Channel plate for DNA sequencing  

DOEpatents

This invention is a channel plate that facilitates data compaction in DNA sequencing. The channel plate has a length, a width and a thickness, and further has a plurality of channels that are parallel. Each channel has a depth partially through the thickness of the channel plate. Additionally an interface edge permits electrical communication across an interface through a buffer to a deposition membrane surface.

Douthart, Richard J. (Richland, WA); Crowell, Shannon L. (Eltopia, WA)

1998-01-01

206

The Indosinian collision-extension event between the South China Block and the Palaeo-Pacific plate: Evidence from Indosinian alkaline granitic rocks in Dashuang, eastern Zhejiang, South China  

NASA Astrophysics Data System (ADS)

This study reports on the first comprehensive analysis of the geology, petrology and origin of the Dashuang pluton in Jinhua, eastern Zhejiang, South China, which is predominantly composed of quartz monzonite and subordinate quartz syenite that includes variable amounts of aegirine-augite. The quartz monzonite has a porphyritic texture defined by K-feldspar phenocrysts, whereas the quartz syenite shows considerable variation in grain size and is categorised into fine- and coarse-grained types. Zircons from the quartz monzonite and fine-grained quartz syenite yield LA-MC-ICP-MS (laser ablation-multi-collector-inductively coupled plasma-mass spectrometry) U-Pb ages of 231.60 ± 0.86 Ma and 231.7 ± 1.1 Ma, respectively, indicating crystallisation in the Middle Triassic. The chemistry of the quartz monzonite indicates a calc-alkaline to alkaline evolutionary trend, which may reflect partial melting of upper mantle contaminated by Proterozoic basement rocks, subjected to fractional crystallisation during ascent. Both the fine- and coarse-grained quartz syenites are alkaline and have high rare earth element (REE) concentrations, especially light rare earth elements (LREE), and are relatively enriched in large ion lithosphere elements (LILE). The Al2O3 and NaO2 contents of the quartz syenite increase proportionally with SiO2, owing to greater amounts of aegirine-augite and feldspar. The fine-grained quartz syenite has the lowest initial 87Sr/86Sr ratio and lowest Nd model age, and the highest ?Nd value compared with the quartz monzonite. The quartz syenite compositions are best explained by fractional crystallisation of an enriched mantle-derived alkaline magma. Slight chemical variations result from source heterogeneities, as well as the spatially variable degrees of melting, assimilation, and other factors. Our new age and geochemical data for the alkaline rocks in eastern Zhejiang, considered together with collisional granites from South Korea, support a history of collision and extension between the Palaeo-Pacific plate and the South China Block during the Indosinian. We use these data to refine the geodynamic model for Indosinian multi-plate convergence in South China.

Mao, Jianren; Ye, Haimin; Liu, Kai; Li, Zilong; Takahashi, Yutaka; Zhao, Xilin; Kee, Weon-Seo

2013-07-01

207

Extension rate determination through the analysis of high-resolution LiDAR dataset and cosmogenic dating of the Fish Lake Valley fault zone: Implications for Pacific-North America plate boundary deformation  

NASA Astrophysics Data System (ADS)

The oblique normal-dextral Fish Lake valley fault (FLVF) accommodates much of the Pacific-North America plate boundary deformation in the northern part of the eastern California shear zone (ECSZ). New geologic slip rates from FLVF, near the California/Nevada border, provide constraints on the kinematic relationships among the major faults in this complex part of the Pacific-North America plate boundary. Analysis of light detection and ranging (LiDAR) data (1 m horizontal resolution and a decimeter vertical accuracy), coupled with cosmogenic nuclide 10Be geochronology, provides new insights into the late Pleistocene extension rate of this fault system. Right-lateral shear accommodates most of the deformation on the NW-striking FLVF, but fault segments that strike approximately N exhibit predominantly normal slip. This extension is manifest by east- to southeast- and west- to northwest- dipping normal fault scarps cutting late Pleistocene alluvial fans. LiDAR data are crucial to the recognition and analysis of these fault strands, allowing for a comprehensive study of all normal fault scarps that would be otherwise nearly impossible. The high vertical resolution of the LiDAR-derived digital elevation models, plus the ease of analysis using geographic information systems (GIS) software allow for the precise measurement of cumulative scarp heights across numerous scarps. Using these measurements and cosmogenic 10Be dates of the faulted alluvial fans we present the extension rates on the FLVF at four different locations, from south to north: Furnace Creek, Wildhorse Creek, Perry Aiken Creek, and Indian Creek. The vertical component of oblique slip (measured in ArcGIS 9.2 using LiDAR-derived DEMs) along the FLVF at Furnace Creek = 25 ± 1.3 m, Wildhorse Creek = 42 ± 2.1 m, Perry Aiken Creek = 85 ± 4.3 m, and Indian Creek = 75 ± 3.8 m. Previous work by Frankel et al. (2007, GRL) reported cosmogenic nuclide 10Be ages from the offset Furance Creek and Indian Creek alluvial fans of ~94 ka and ~71 ka, respectively. New cosmogenic 10Be dates from the offset alluvial deposits at Wildhorse Creek and Perry Aiken Creek yield ages of ~121 ka and ~71 ka, respectively. Combining displacement from LiDAR data and 10Be geochronology yields a vertical component of slip ranging from 0.3 mm/yr at Furnace Creek and Wildhorse Creek, to the south, to 1.2 mm/yr at Perry Aiken Creek, and 1.1 mm/yr at Indian Creek, to the north. These slip rates are generally in agreement with previous estimates based on alluvial fan morphology, soil development, and theodolite surveys. Assuming a 60° dip for the fault planes, we calculate late Pleistocene extension rates for the FLVF of 0.2, 0.2, 0.7 and 0.6 mm/yr, at the four sites, from south to north. Comparison of these rates with geodetic measurements of ~1 mm/yr of extension across the ECSZ north of the Garlock fault indicate that as much as half of the current rate of east-west extension in this part of western North America is accommodated along the FLVF. Our data also imply an increase in late Pleistocene extension rates from south to north, which is opposite the trend of the dextral slip rate along the FLVF. This discrepancy can be explained by an extensional transition zone in northern Fish Lake Valley that transfers slip between FLVF and the Walker Lane Belt to the north and east, and by westward transfer of slip onto the Saline Valley-Hunter Mountain-Panamint Valley fault system to the south and west. Determining the extension rates of the faults parallel or sub-parallel to the FLVF at the same latitude, such as the White Mountain and Sierra Nevada frontal faults, will further improve our understanding of how slip is accommodated and transferred from the ECSZ into the Walker Lane Belt along this important segment of the Pacific-North America plate boundary.

Ganev, P. N.; Dolan, J. F.; Frankel, K. L.; Finkel, R. C.

2009-04-01

208

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

209

Tectonics of the Easter plate  

NASA Technical Reports Server (NTRS)

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

Engeln, J. F.; Stein, S.

1984-01-01

210

Global Plate Velocities from the Global Positioning System  

NASA Technical Reports Server (NTRS)

We have analyzed 204 days of Global Positioning System (GPS) data from the global GPS network spanning January 1991 through March 1996. On the basis of these GPS coordinate solutions, we have estimated velocities for 38 sites, mostly located on the interiors of the Africa, Antarctica, Australia, Eurasia, Nazca, North America, Pacific, and South America plates. The uncertainties of the horizontal velocity components range from 1.2 to 5.0 mm/yr. With the exception of sites on the Pacific and Nazca plates, the GPS velocities agree with absolute plate model predictions within 95% confidence. For most of the sites in North America, Antarctica, and Eurasia, the agreement is better than 2 mm/yr. We find no persuasive evidence for significant vertical motions (less than 3 standard deviations), except at four sites. Three of these four were sites constrained to geodetic reference frame velocities. The GPS velocities were then used to estimate angular velocities for eight tectonic plates. Absolute angular velocities derived from the GPS data agree with the no net rotation (NNR) NUVEL-1A model within 95% confidence except for the Pacific plate. Our pole of rotation for the Pacific plate lies 11.5 deg west of the NNR NUVEL-1A pole, with an angular speed 10% faster. Our relative angular velocities agree with NUVEL-1A except for some involving the Pacific plate. While our Pacific-North America angular velocity differs significantly from NUVEL-1A, our model and NUVEL-1A predict very small differences in relative motion along the Pacific-North America plate boundary itself. Our Pacific-Australia and Pacific- Eurasia angular velocities are significantly faster than NUVEL-1A, predicting more rapid convergence at these two plate boundaries. Along the East Pacific Pise, our Pacific-Nazca angular velocity agrees in both rate and azimuth with NUVFL-1A.

Larson, Kristine M.; Freymueller, Jeffrey T.; Philipsen, Steven

1997-01-01

211

Kinematics to dynamics in the New Zealand plate-boundary zone  

NASA Astrophysics Data System (ADS)

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

Lamb, Simon

2014-05-01

212

Relationship between outer forearc subsidence and plate boundary kinematics along the Northeast Japan convergent margin  

NASA Astrophysics Data System (ADS)

Tectonic erosion along convergent plate boundaries, whereby removal of upper plate material along the subduction zone interface drives kilometer-scale outer forearc subsidence, has been purported to explain the evolution of nearly half the world's subduction margins, including part of the history of northeast Japan. Here, we evaluate the role of plate boundary dynamics in driving forearc subsidence in northeastern Japan. A synthesis of newly updated analyses of outer forearc subsidence, the timing and kinematics of upper plate deformation, and the history of plate convergence along the Japan trench demonstrate that the onset of rapid fore-arc tectonic subsidence is contemporaneous with upper plate extension during the opening of the Sea of Japan and with an acceleration in convergence rate at the trench. In Plio-Quaternary time, relative uplift of the outer forearc is contemporaneous with contraction across the arc and a decrease in plate convergence rate. The coincidence of these changes across the forearc, arc, backarc system appears to require an explanation at the scale of the entire plate boundary. Similar observations along other western Pacific margins suggest that correlations between forearc subsidence and major changes in plate kinematics are the rule, rather than the exception. We suggest that a significant component of forearc subsidence at the northeast Japan margin is not the consequence of basal tectonic erosion, but instead reflects dynamic changes in plate boundary geometry driven by temporal variations in plate kinematics. If correct, this model requires a reconsideration of the mass balance and crustal recycling of continental crust at nonaccretionary margins.

Regalla, Christine; Fisher, Donald M.; Kirby, Eric; Furlong, Kevin P.

2013-12-01

213

Plate Tectonics  

NSDL National Science Digital Library

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

Rohlfing, Mrs.

2011-02-03

214

Intermittent plate tectonics?  

PubMed

Although it is commonly assumed that subduction has operated continuously on Earth without interruption, subduction zones are routinely terminated by ocean closure and supercontinent assembly. Under certain circumstances, this could lead to a dramatic loss of subduction, globally. Closure of a Pacific-type basin, for example, would eliminate most subduction, unless this loss were compensated for by comparable subduction initiation elsewhere. Given the evidence for Pacific-type closure in Earth's past, the absence of a direct mechanism for termination/initiation compensation, and recent data supporting a minimum in subduction flux in the Mesoproterozoic, we hypothesize that dramatic reductions or temporary cessations of subduction have occurred in Earth's history. Such deviations in the continuity of plate tectonics have important consequences for Earth's thermal and continental evolution. PMID:18174440

Silver, Paul G; Behn, Mark D

2008-01-01

215

Assembly of plate-like nanoparticles in immiscible polymer blends--effect of the presence of a preferred liquid-liquid interface.  

PubMed

The assembly of lamellar (clay) nanoparticles in a blend of polystyrene (PS) and poly(methyl methacrylate) (PMMA) with drop-matrix morphology is studied combining viscoelastic measurements and morphological analyses. A reference system based on pure PS is used to highlight the effect on the assembly process of the presence of liquid interfaces where the particles are inclined to gather. The filler content is varied in a wide range to cover all the possible structures, from isolated flocs up to space-spanning networks. The goal is to elucidate whether the particles govern the blend morphology or the structural evolutions of the fluids dictate the space arrangement of the filler. The PMMA drops anchor the lamellae frustrating their peculiar mobility in the polymer melt. On the other hand, the clay radically affects the blend morphology, inducing irregularly-shaped drops and drop clustering phenomena even in case of partial coverage of the drop surface. Above the critical filler content for the saturation of the polymer-polymer interface, a space-spanning particle network eventually builds up. Despite the embedding of the PMMA drops, such a superstructure exhibits the same features of those forming in homogeneous mediums, enabling the use of approaches conceived for systems with single-phase matrix. Compared to the latter, the percolation and fractal models reveal subtle and yet meaningful differences in terms of stress-bearing mechanisms and structure of the building blocks which constitute the network. PMID:24718850

Filippone, Giovanni; Causa, Andrea; Salzano de Luna, Martina; Sanguigno, Luigi; Acierno, Domenico

2014-05-14

216

Ridge forces, absolute plate motions, and the intraplate stress field  

Microsoft Academic Search

The study calculates torque poles for a variety of possible forces acting on the plates, including ridge push, slab pull, and collisional resistance. These poles are compared to the directions of the absolute plate motions. A strong correlation is found between ridge torque poles and the azimuth of absolute plate motions for the North American, South American, Pacific, Cocos, and

Randall M. Richardson

1992-01-01

217

Plate Tectonics  

NSDL National Science Digital Library

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

Smoothstone; Company, Houghton M.

218

Plate Tectonics  

NSDL National Science Digital Library

Create a poster all about Plate Tectonics! Directions: Make a poster about Plate Tectonics. (20 points) Include at least (1) large picture (15 points) on your poster complete with labels of every part (10 points). (15 points) Include at least three (3) facts about Plate Tectonics. (5 points ...

Walls, Mrs.

2011-01-30

219

Evolution of hierarchical hexagonal stacked plates of CuS from liquid-liquid interface and its photocatalytic application for oxidative degradation of different dyes under indoor lighting.  

PubMed

Blue solution of copper(II) acetylacetonate complex, [Cu(acac)(2)] in dichloromethane (DCM) and an aqueous alkaline solution of thioacetamide (TAA) constitute a biphasic system. The system in a screw cap test tube under a modified hydrothermal (MHT) reaction condition produces a greenish black solid at the liquid-liquid interface. It has been characterized that the solid mass is an assembly of hexagonal copper sulfide (CuS) nanoplates representing a hierarchical structure. The as-synthesized CuS nanoplates are well characterized by several physical techniques. An ethanolic dispersion of CuS presents a high band gap energy (2.2 eV) which assists visible light photocatalytic mineralization of different dye molecules. Thus a cleanup measure of dye contaminated water body even under indoor light comes true. PMID:20704231

Basu, Mrinmoyee; Sinha, Arun Kumar; Pradhan, Mukul; Sarkar, Sougata; Negishi, Yuichi; Pal, Tarasankar

2010-08-15

220

Geologic structure and processes of the eastern Pacific margin: California and Costa Rica  

Microsoft Academic Search

The margin of the eastern Pacific has been sculpted during Tertiary geologic times by convergent and transcurrent plate motion along both continental and oceanic plate boundaries. Interpretations of central California geology predict margin development by Early Tertiary plate convergence, the transition to a transform plate boundary, and subsequent modification of that boundary. Deep penetration seismic reflection transects (EDGE profiles) provide

Kirk Duncan McIntosh

1992-01-01

221

A plate-tectonic model for the Mesozoic and Early Cenozoic history of the Caribbean plate  

Microsoft Academic Search

We present a model in which the Caribbean plate is an intra-American feature formed along the Caribbean spreading center as opposed to the current model that considers the Caribbean plate as a far-travelled crustal segment that formed in the Pacific region. Paleomagnetic data, which cover an age range from Jurassic through Paleocene, indicate the ophiolite complexes in Costa Rica and

Martin Meschede; Wolfgang Frisch

1998-01-01

222

Tectonic Plates and Plate Boundaries  

NSDL National Science Digital Library

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

Foundation, Wgbh E.

2005-12-17

223

Kinematics to dynamics in the New Zealand plate-boundary zone  

NASA Astrophysics Data System (ADS)

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

Lamb, S. H.

2013-12-01

224

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

USGS Publications Warehouse

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

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

2013-01-01

225

Present-day kinematics of the Rivera plate and implications for tectonics in southwestern Mexico  

NASA Technical Reports Server (NTRS)

A model for the present-day motion of the Rivera plate relative to the North America, Cocos, and Pacific plates is derived using new data from the Pacific-Rivera rise and Rivera transform fault, together with new estimates of Pacific-Rivera motions. The results are combined with the closure-consistent NUVEL-1 global plate motion model of DeMets et al. (1990) to examine present-day deformation in southwestern Mexico. The analysis addresses several questions raised in previous studies of the Rivera plate. Namely, do plate motion data from the northern East Pacific rise require a distinct Rivera plate? Do plate kinematic data require the subduction of the Rivera plate along the seismically quiescent Acapulco trench? If so, what does the predicted subduction rate imply about the earthquake recurrence interval in the Jalisco region of southwestern Mexico?

Demets, Charles; Stein, Seth

1990-01-01

226

Evolution of mantle structure beneath the northwest Pacific: Evidence from seismic tomography and paleogeographic reconstructions  

Microsoft Academic Search

Plate motions and subducting slab morphology are intricately connected, and through the integration of seismicity, tomographic images, and relative plate motions, the evolution of mantle structure can be interpreted. Tomographic images of P wave, shear wave speed, and bulk sound speed perturbations of the northwest Pacific region have been interpreted to define the extent and geometry of the subducting Pacific

Meghan S. Miller; Brian L. N. Kennett

2006-01-01

227

No-net-rotation model of current plate velocities incorporating plate motion model NUVEL-1  

NASA Technical Reports Server (NTRS)

NNR-NUVEL1 is presented which is a model of plate velocities relative to the unique reference frame defined by requiring no-net-rotation of the lithosphere while constraining relative plate velocities to equal those in global plate motion model NUVEL-1 (DeMets et al., 1990). In NNR-NUVEL1, the Pacific plate rotates in a right-handed sense relative to the no-net-rotation reference frame at 0.67 deg/m.y. about 63 deg S, 107 deg E. At Hawaii the Pacific plate moves relative to the no-net-rotation reference frame at 70 mm/yr, which is 25 mm/yr slower than the Pacific plate moves relative to the hotspots. Differences between NNR-NUVEL1 and HS2-NUVEL1 are described. The no-net-rotation reference frame differs significantly from the hotspot reference frame. If the difference between reference frames is caused by motion of the hotspots relative to a mean-mantle reference frame, then hotspots beneath the Pacific plate move with coherent motion towards the east-southeast. Alternatively, the difference between reference frames can show that the uniform drag, no-net-torque reference frame, which is kinematically equivalent to the no-net-rotation reference frame, is based on a dynamically incorrect premise.

Argus, Donald F.; Gordon, Richard G.

1991-01-01

228

A model for the motion of the Philippine Sea plate consistent with NUVEL-1 and geological data  

Microsoft Academic Search

We investigate angular velocity vectors of the Philippine Sea (PH) plate relative to the adjacent major plates, Eurasia (EU) and Pacific (PA), and the smaller Caroline (CR) plate. Earthquake slip vector data along the Philippine Sea plate are inverted, subject to the constraint that EU-PA motion equals that predicted by the global relative plate model NUVEL-1. The resulting solution fails

Tetsuzo Seno; Seth Stein; Alice E. Gripp

1993-01-01

229

Mantle heterogeneity and off axis volcanism on young Pacific lithosphere  

Microsoft Academic Search

Plate tectonics and mantle plumes explain most volcanism on earth, but there are numerous actively forming linear volcanic chains in the middle of tectonic plates that are not explained by these theories. Using the multidisciplinary geophysical dataset of the MELT and GLIMPSE experiments, we show that associated with 3 volcanic chains west of the East Pacific Rise there are low

Nicholas Harmon; Donald W. Forsyth; Dayanthie S. Weeraratne; Yingjie Yang; Spahr C. Webb

230

6. BUILDER'S PLATE ON WEST TRUSS: 'MOSELEY IRON BUILDING WORKS, ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

6. BUILDER'S PLATE ON WEST TRUSS: 'MOSELEY IRON BUILDING WORKS, BOSTON 1888, PATENTED 1881 TO T.W.E. MOSELEY' - Upper Pacific Mills Bridge, Moved to Merrimack College, North Andover, MA, Lawrence, Essex County, MA

231

Plate Tectonics  

NSDL National Science Digital Library

In this lesson, students are introduced to the theory of plate tectonics and explore how the theory was developed and supported by evidence. Through class discussion, videos, and activities, students seek connections between tectonic activity and geologic features and investigate how the theory of plate tectonics evolved.

2006-01-01

232

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

233

Errors in plate rotations as described by covariance matrices and their combination in reconstructions  

NASA Technical Reports Server (NTRS)

The use of covariance matrices to describe the errors in plate rotations and to combine the contributions of individual plate pairs for plate reconstructions is discussed. Particular attention is given to finite rotations and the combination of covariance matrices for a circuit of successive plate pair rotations. Examples of errors in plate reconstructions in which the position of the Pacific plate relative to North America is reconstructed are presented.

Jurdy, Donna M.; Stefanick, Michael

1987-01-01

234

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

235

Asia-Pacific POPIN highlights: Pacific POPIN.  

PubMed

The Pacific Population Information Network (Pacific POPIN) is currently established in Fiji, Kiribati, Papua New Guinea, Samoa, Solomon Islands, Tonga, Tuvalu, and Vanuatu with the support of the University of the South Pacific and the South Pacific Commission (SPC). The University of the South Pacific has helped coordinate the network and to build national and subregional collections. Various titles are deposited at the national level with identified national government departments and at the subregional level with the Pacific Collection of the University Library. Second and third copies are sent to the National Library of Papua New Guinea and the SPC Library. The SPC, on the other hand, has researched population issues in order to meet the information demands of various South Pacific island countries and territories, and to provide technical assistance to them in population and related areas. Demographer at the SPC explains the role and functions of the SPC Demography/Population Program in light of the situation in the South Pacific and the program and the changing approaches to population issues which are being experienced. Pacific POPIN involvement and preparations for the 1994 International Conference on Population and Development are discussed, as well as SPC staff movement and the profile of the Pacific POPIN coordinator. PMID:12319034

Fong, E R

1993-09-01

236

Plate-induced Miocene extension in southern California  

SciTech Connect

Miocene crustal extension in southern California can be explained by the interaction of tectonic plates in relative motion. The Pacific, Juan de Fuca, and Farallon (Guadalupe) plates are represented by flat elastic plates surrounded by an infinite elastic plate, the eastern part of which represents the North America plate. Forcing is by assigned subduction pull, and tractions at all plate boundaries satisfy a viscous constitutive law. Plate bottoms are stress-free. In the first part of the solution plate velocities and boundary tractions are found from static equilibrium. Then principal horizontal stresses and strains in plate interiors caused by tractions and subduction pull are found by a boundary element procedure. Using plate boundary geometry from Stock and Hodges for early- and mid-Miocene times, it is found that the portion of the North America plate margin between the Mendocino and Rivera triple junctions has maximum extensional strain directed westward. This result is generally consistent with directions associated with metamorphic core complex formation in southern California. The model is also consistent with extensional strain and rotation sense of crustal blocks in the vicinity of Los Angeles, as inferred by Luyendyk and others from paleomagnetic data. In the model the greatest extensional strain of the North America plate occurs near the Pacific-North America transform, in the area above the absent Farallon slab. Extension direction varies from northwest to southwest according to plate geometry, subduction pull (Juan de Fuca and Guadalupe), and plate boundary tractions.

Stuart, W.D. (Geological Survey, Pasadena, CA (United States) Univ. of California, Santa Barbara, CA (United States))

1992-01-01

237

Femoral plating.  

PubMed

We have demonstrated that we are able to meet both trauma and orthopedic goals with immediate plate fixation of femoral fractures in patients with blunt polytrauma. Our femoral fracture mortality rate is less than our predicted institutional mortality rate of patients with comparative injury severity scores. Ipsilateral femoral neck and shaft fractures are easily repaired with femoral plating. Infections, even in open fractures and systemically unstable patients, are rare. Implant failures have been infrequent and are easily reconstructed with intramedullary nails. Knee motion has been restored reliably. Stainless steel DCP plate fixation requires primary bone grafting. Achieving union and subsequent knee rehabilitation often requires that patients remain on crutches for up to 6 months. Our experience with titanium LCDCP plates is preliminary, but we are seeing a significant amount of callus formation and, perhaps, earlier union and bearing weight. PMID:8090475

Riemer, B L; Foglesong, M E; Miranda, M A

1994-10-01

238

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

239

High-frequency seismic radiation during Maule earthquake (Chile, 27/02/2010, Mw 8.8) inferred by backprojection of P waves: evidence of activation of two distinct zones at the downdip part of the plate interface  

NASA Astrophysics Data System (ADS)

We back-project the seismic radiation released by Maule earthquake (Chile, 27/02/2010, Mw 8.8) in three frequency bands: 0.4-3 Hz, 1-4 Hz, 2-8 Hz. We measure the coherence of the seismic traces at 557 stations of US array by semblance. Travel times are estimated starting from a 1D global velocity model (ak135) corrected by two terms: a static correction and a dynamic correction. Static corrections are the mean time corrections to the 1D velocity model, and dynamic corrections are finer time shifts depending on the source-receiver path. Both terms are extracted from the time shifts between different receivers of P-phases of 23 high-magnitude calibration aftershocks, most of which have high precision locations based on the temporary deployment following the Maule earthquake (IMAD). The dynamic corrections are extended over a fine source grid by kriging interpolation. This procedure makes the backprojection results independent of the main shock catalog hypocentre and allows coherent imaging to higher frequencies. During the first 20 seconds of the rupture process, the source is stable nearby the nucleation point, which is close to epicentre proposed by Vigny et al (Science, 2011) based on high rate GPS motion. Afterwards, it moves bilaterally, with the northern front moving with an average velocity of ˜3 km/s. Most of the energy is emitted from the northern patch of the bi-lateral rupture (˜70%), with sporadic emissions from the southern patch. The maximum of stacked energy is located about 150 km north-eastwards from the epicenter and a relative maximum appears south of Arauco peninsula. In the dip direction, energy is mostly emitted from the down-dip edge of the co-seismic area, roughly matching the aftershock distribution. Specifically, we find that coherent radiation is emitted from two distinct belts nearly parallel to the trench. The position of these belts is in good agreement with the location of the aftershocks, which also are arranged in two disconnected zones of the subduction interface at different depths, the deeper of which is characterised by a large number of repeating event clusters (Rietbrock, Jenkins et al., this session). Thus, our backprojection analysis in combination with the aftershock distribution demonstrates the existence of a peculiar doubled downdip transition from seismogenic behaviour to stable sliding. We suspect fluids released from the downgoing plate to be the cause of the transitions in frictional behaviour because of (1) the co-location of high Vp/Vs ratios with the deep interface seismicity, (2) systematic decrease of depth of onset of deeper seismicity with younging incoming plate age, (3) patchy occurrence along-strike of deeper seismicity.

Palo, M.; Tilmann, F. J.; Krueger, F.; Ehlert, L.; Lange, D.; Rietbrock, A.; Jenkins, J.; Hicks, S. P.

2013-12-01

240

Subducting characteristic of the Pacific slab beneath northeast China  

NASA Astrophysics Data System (ADS)

The volcanoes locating in northeast China are very active. Some researchers consider that the origin of volcanoes is closely related to the subducting western Pacific plate and the upwelling asthenosphere. The thickness and the existing range of the subducted plate are not clear as far although the seismic tomography results obviously show that the Pacific plate exists below the volcano region. Therefore, in this study, we adopted the method combining the teleseismic tomography with travel time forward modeling to further study the velocity structure beneath northeast China, especially the precise model of subducted Pacific plate. Our results show that (1) the average thickness and velocity perturbation of slab is 85 km and 1%, respectively, and the slab has not been thickened compared with the previous result of the Japan Sea; (2) the Pacific plate subducted into the mantle transition zone with a shallow dip angle, and changed horizontally when it touched the bottom of mantle transition zone, and extended westward to Longitude 127°E and then stops over there; (3) the horizontal slab locates right below the volcano region. These above features help people understand the origin of intraplate volcanoes and the geodynamical process better. (a) Tomographic result along 43°N. Red and blue colors represent the high and low velocity anomalies, respectively, and the scale is shown at the right-bottom; The profile line is shown in (b); The black triangles represent the volcanoes locating near the profile; The black solid and dashed lines show the depths of upper and lower boundaries of Pacific plate, respectively. The red dots represent the deep earthquakes around the profile. (b) Location of profile AA' along 43°N. Black triangles denote volcanoes; White squares represent the stations; Blue contours denote the depth of upper boundary of Pacific plate; Black and red dots represent the deep epicenters.

Jiang, G.; Zhang, G.; Xu, Y.

2012-12-01

241

The Plate Boundary Observatory: Data Management Progress and Highlights  

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 880 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser

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

2007-01-01

242

Musical Plates  

NSDL National Science Digital Library

This on-line project is part of the Center for Improved Engineering and Science Education (CIESE) program. As they complete this series of lessons, students will use real-time data to solve a problem, study the correlation between earthquakes and tectonic plates, and determine whether or not there is a relationship between volcanoes and plate boundaries. Musical Plates has four Core Activities that will teach students how to access and interpret real-time earthquake and volcano data and to how use the information to solve a real-world problem. Each of the core activities is designed to be used in a 45-minute class period. This unit also has three enrichment lessons and a final project lesson that can also be used for assessment.

2007-12-12

243

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

244

The Plate Boundary Observatory: Operational Status and Data Plans  

Microsoft Academic Search

The Plate Boundary Observatory (PBO), part of the larger 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. The science goals of PBO require that plate boundary deformation be adequately characterized over the wide range of spatial and

G. Anderson; K. Feaux; M. Jackson; W. Prescott

2004-01-01

245

A Forecaster's Overview of the Northwest Pacific  

NSDL National Science Digital Library

This module provides an introduction to the northwest Pacific for weather forecasters. It touches on major aspects of the geography, oceanography, and climatology. Geography looks at plate tectonics, topography, and human population. Oceanography examines ocean currents, coastal tidal ranges, and sea ice distribution. Climatology briefly discusses jets streams, distribution of synoptic features, storm tracks of tropical and extratropical cyclones, the fronts, and sensible weather associated with the Northeast and Southwest Monsoons.

Byrd, Greg

2012-01-11

246

Preliminary determination of Pacific-North America relative motion in the southern Gulf of California using the Global Positioning System  

NASA Technical Reports Server (NTRS)

GPS data from experiments conducted in 1985 and 1989 in the southern Gulf of California, Mexico, allow a determination of relative motion between the Pacific and North American plates. The data indicate motion by Cabo San Lucas on the Pacific plate relative to North America at a rate of 47 + or - 7 mm/yr and azimuth of 57 + or - 6 deg west of north, equivalent within uncertainties to the NUVEL-1 global plate motion model.

Dixon, T. H.; Gonzalez, G.; Lichten, S. M.; Tralli, D. M.; Ness, G. E.

1991-01-01

247

Preliminary determination of Pacific-North America relative motion in the southern Gulf of California using the Global Positioning System  

NASA Astrophysics Data System (ADS)

GPS data from experiments conducted in 1985 and 1989 in the southern Gulf of California, Mexico, allow a determination of relative motion between the Pacific and North American plates. The data indicate motion by Cabo San Lucas on the Pacific plate relative to North America at a rate of 47 + or - 7 mm/yr and azimuth of 57 + or - 6 deg west of north, equivalent within uncertainties to the NUVEL-1 global plate motion model.

Dixon, T. H.; Gonzalez, G.; Lichten, S. M.; Tralli, D. M.; Ness, G. E.

1991-05-01

248

Creation of the Cocos and Nazca plates by fission of the Farallon plate  

NASA Astrophysics Data System (ADS)

Throughout the Early Tertiary the area of the Farallon oceanic plate was episodically diminished by detachment of large and small northern regions, which became independently moving plates and microplates. The nature and history of Farallon plate fragmentation has been inferred mainly from structural patterns on the western, Pacific-plate flank of the East Pacific Rise, because the fragmented eastern flank has been subducted. The final episode of plate fragmentation occurred at the beginning of the Miocene, when the Cocos plate was split off, leaving the much reduced Farallon plate to be renamed the Nazca plate, and initiating Cocos-Nazca spreading. Some Oligocene Farallon plate with rifted margins that are a direct record of this plate-splitting event has survived in the eastern tropical Pacific, most extensively off northern Peru and Ecuador. Small remnants of the conjugate northern rifted margin are exposed off Costa Rica, and perhaps south of Panama. Marine geophysical profiles (bathymetric, magnetic and seismic reflection) and multibeam sonar swaths across these rifted oceanic margins, combined with surveys of 30-20 Ma crust on the western rise-flank, indicate that (i) Localized lithospheric rupture to create a new plate boundary was preceded by plate stretching and fracturing in a belt several hundred km wide. Fissural volcanism along some of these fractures built volcanic ridges (e.g., Alvarado and Sarmiento Ridges) that are 1-2 km high and parallel to "absolute" Farallon plate motion; they closely resemble fissural ridges described from the young western flank of the present Pacific-Nazca rise. (ii) For 1-2 m.y. prior to final rupture of the Farallon plate, perhaps coinciding with the period of lithospheric stretching, the entire plate changed direction to a more easterly ("Nazca-like") course; after the split the northern (Cocos) part reverted to a northeasterly absolute motion. (iii) The plate-splitting fracture that became the site of initial Cocos-Nazca spreading was a linear feature that, at least through the 680 km of ruptured Oligocene lithosphere known to have avoided subduction, did not follow any pre-existing feature on the Farallon plate, e.g., a "fracture zone" trail of a transform fault. (iv) The margins of surviving parts of the plate-splitting fracture have narrow shoulders raised by uplift of unloaded footwalls, and partially buried by fissural volcanism. (v) Cocos-Nazca spreading began at 23 Ma; reports of older Cocos-Nazca crust in the eastern Panama Basin were based on misidentified magnetic anomalies. There is increased evidence that the driving force for the 23 Ma fission of the Farallon plate was the divergence of slab-pull stresses at the Middle America and South America subduction zones. The timing and location of the split may have been influenced by (i) the increasingly divergent northeast slab pull at the Middle America subduction zone, which lengthened and reoriented because of motion between the North America and Caribbean plates; (ii) the slightly earlier detachment of a northern part of the plate that had been entering the California subduction zone, contributing a less divergent plate-driving stress; and (iii) weakening of older parts of the plate by the Galapagos hotspot, which had come to underlie the equatorial region, midway between the risecrest and the two subduction zones, by the Late Oligocene.

Lonsdale, Peter

2005-08-01

249

Seismic Hazard of American Samoa and Neighboring South Pacific Islands: Data, Methods, Parameters, and Results.  

National Technical Information Service (NTIS)

American Samoa and the neighboring islands of the South Pacific lie near active tectonic-plate boundaries that host many large earthquakes which can result in strong earthquake shaking and tsunamis. To mitigate earthquake risks from future ground shaking,...

C. S. Mueller D. E. McNamara K. S. Rukstales M. Walling M. D. Petersen N. Luco S. C. Harmsen

2012-01-01

250

Geodynamics of the Eastern Pacific Region, Caribbean and Scotia Arcs. Volume 9  

SciTech Connect

This book analyze the geodynamic phenomena related to the interaction of the eastern Pacific with the Americas between Canada and the Antarctic peninsula. Studies include the Cordilleran arcs and Juan de Fuca plate.

Cabre, R.

1983-01-01

251

Mid-Cretaceous Evolution of the Pacific-Phoenix-Farallon Triple Junction  

Microsoft Academic Search

Growth of the Pacific plate occurred rapidly during the mid-Cretaceous, however, the absence of magnetic lineations during the Cretaceous quiet zone (KQZ) obscures the details of specific tectonic events. A bight in magnetic anomaly 34 ( ~35S 145W, ~2000 km south of Tahiti) indicates the passage of a triple junction joining the Pacific, Phoenix, and Farallon plates at 83.5 Ma.

R. F. Viso; R. L. Larson; R. A. Pockalny

2001-01-01

252

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

253

Tsunamis and Earthquakes (Local Tsunamis in the Pacific Northwest)  

NSDL National Science Digital Library

On the Pacific Northwest an oceanic tectonic plate (Juan de Fuca) is being pulled and driven (subducted) beneath the North American continental plate. Earthquakes generated along that fault may produce local tsunamis. Local tsunamis are those generated by earthquakes near the coast. This site provides links to external webpages describing the physics behind a tsunami. Resources featured in the links include glossary of terms and photo galleries.

254

Morphology of the distorted subducted Pacific slab beneath the Hokkaido corner, Japan  

Microsoft Academic Search

The intersection of the Japan and Kurile arcs is expressed as a cuspate feature at the trench, a bend in the Japanese islands, and a complex lithospheric structure and is known as the Hokkaido corner. The Pacific plate is subducting beneath the two arcs in the northwest Pacific at different velocities, which has resulted in an arc–arc collision and distortion

M. S. Miller; B. L. N. Kennett; A. Gorbatov

2006-01-01

255

Seismic anisotropy of the Pacific slab and mantle wedge beneath the Japanese islands  

Microsoft Academic Search

The mantle beneath the Japanese islands is complex because of subduction of the Pacific and Philippine Sea plates and the deformation associated with it. Detection of seismic anisotropy should be useful for understanding the processes occurring in such mantle. Here we resolve seismic anisotropy of the mantle wedge from that of the underlying subducted Pacific slab using a large number

Yoko Tono; Yoshio Fukao; Takashi Kunugi; Seiji Tsuboi

2009-01-01

256

Morphology of the distorted subducted Pacific slab beneath the Hokkaido corner, Japan  

Microsoft Academic Search

The intersection of the Japan and Kurile arcs is expressed as a cuspate feature at the trench, a bend in the Japanese islands, and a complex lithospheric structure and is known as the Hokkaido corner. The Pacific plate is subducting beneath the two arcs in the northwest Pacific at different velocities, which has resulted in an arc arc collision and

M. S. Miller; B. L. N. Kennett; A. Gorbatov

2006-01-01

257

South Pacific Traverse RP-7-SU-71 Pago Pago to Callao to Seattle.  

National Technical Information Service (NTIS)

Profiles of bathymetry, free-air and Bouguer anomalies, and magnetic anomalies across the Tonga Trench and Melanesian region, South Pacific at 30 degrees S, Peru-Chile trench and the Nasca and Pacific plates are presented and discussed. Approximately 13,2...

W. H. Lucas

1972-01-01

258

Short-lived and discontinuous intraplate volcanism in the South Pacific: Hot spots or extensional volcanism?  

Microsoft Academic Search

South Pacific intraplate volcanoes have been active since the Early Cretaceous. Their HIMU-EMI-EMII mantle sources can be traced back into the West Pacific Seamount Province (WPSP) using plate tectonic reconstructions, implying that these distinctive components are enduring features within the Earth's mantle for, at least, the last 120 Myr. These correlations are eminent on the scale of the WPSP and

Anthony A. P. Koppers; Hubert Staudigel; Malcolm S. Pringle; Jan R. Wijbrans

2003-01-01

259

Stochastic modelling of a large subduction interface earthquake in Wellington, New Zealand  

NASA Astrophysics Data System (ADS)

The Wellington region, home of New Zealand's capital city, is cut by a number of major right-lateral strike slip faults, and is underlain by the currently locked west-dipping subduction interface between the down going Pacific Plate, and the over-riding Australian Plate. A potential cause of significant earthquake loss in the Wellington region is a large magnitude (perhaps 8+) "subduction earthquake" on the Australia-Pacific plate interface, which lies ~23 km beneath Wellington City. "It's Our Fault" is a project involving a comprehensive study of Wellington's earthquake risk. Its objective is to position Wellington city to become more resilient, through an encompassing study of the likelihood of large earthquakes, and the effects and impacts of these earthquakes on humans and the built environment. As part of the "It's Our Fault" project, we are working on estimating ground motions from potential large plate boundary earthquakes. We present the latest results on ground motion simulations in terms of response spectra and acceleration time histories. First we characterise the potential interface rupture area based on previous geodetically-derived estimates interface of slip deficit. Then, we entertain a suitable range of source parameters, including various rupture areas, moment magnitudes, stress drops, slip distributions and rupture propagation directions. Our comprehensive study also includes simulations from historical large world subduction events translated into the New Zealand subduction context, such as the 2003 M8.3 Tokachi-Oki Japan earthquake and the M8.8 2010 Chili earthquake. To model synthetic seismograms and the corresponding response spectra we employed the EXSIM code developed by Atkinson et al. (2009), with a regional attenuation model based on the 3D attenuation model for the lower North-Island which has been developed by Eberhart-Phillips et al. (2005). The resulting rupture scenarios all produce long duration shaking, and peak ground accelerations that, typically range between 0.2-0.7 g in Wellington city. Many of these scenarios also produce long period motions that are currently not captured by the current NZ design spectra.

Francois-Holden, C.; Zhao, J.

2012-12-01

260

A Simple Model for the Vertical Crustal Movement Associated with the Earthquake Cycle Along the Pacific Coast of Northeast Japan  

NASA Astrophysics Data System (ADS)

Before the 2011 M9.0 Tohoku-oki earthquake, rapid subsidence more than 5mm/yr has been observed along the Pacific coast of the Tohoku area by leveling, tide gauges, and GPS (Kato, 1979, Kato and Tsumura, 1979, El-Fiky and Kato, 1999). On the other hand, Stage 5e (~125 ka) marine terraces are widely recognized along the same area, implying the area is uplifting in a long-term. Ikeda (1999) hypothesized that these deformation signals reflect accumulation of elastic strain at the plate interface and there is a possibility of a giant earthquake causing a coastal uplift. However, the coastal area subsided as large as 1m during the 2011 main shock. Though we observe significant postseismic uplift, it is not certain if the preseismic as well as coseismic subsidence will be recovered. We construct a simple model of earthquake deformation cycle to interpret the vertical movement along the Pacific coast of northeast Japan. The model consists of a 40 km thick elastic lithosphere overlying a Maxwell viscoelastic asthenospher with a viscosity of 10^19 Pa s. Plate boundary is modeled as two rectangular faults located in the lithosphere and connected each other. As for the kinematic conditions of these faults, we represent the temporal evolution of fault slip as a sum of the steady term and the perturbation term following Savage and Prescott (1978). The first steady term corresponds to the long-term plate subduction, which contributes to long-term geomorphic evolution such as the marine terraces (Hashimoto et al., 2004). The second perturbation term represent earthquake cycle effects. We evaluate this effect under assumptions that earthquake occurrence is perfectly periodic, plate interface is fully coupled during interseismic periods, and the slip deficit is fully released by earthquakes. If the earthquake recurrence interval is shorter than the relaxation time of the structure, interseismic movement is in the opposite direction to the coseismic ones and changes almost linearly in time. On the other hand, if the earthquake recurrence is much longer than the relaxation time, we see significant temporal variation in the interseismic movement. If the shallow portion of the plate interface is locked over a long period, the coastal area has a postseismic uplift and then significant subsidence follows until the next earthquake. If the deeper portion of the plate interface is locked for a long time, we expect a significant coastal uplift in the interseismic period, which is inconsistent with the observation. The observed vertical movement can be reproduced only if the shallow portion has been locked for a long time and the deeper portion had earthquake much more frequently. Such a spatially heterogeneous behavior in earthquake recurrence is responsible for the enigmatic vertical movement along the northeast Japan. The result also indicates a high possibility of strain accumulation in the shallow portion of the plate interface when we observe a significant subsidence just above the deeper end of the locked zone.

Sagiya, T.

2013-12-01

261

Geomorphology and structural segmentation of the crest of the southern (Pacific-Antarctic) East Pacific Rise  

Microsoft Academic Search

Geomorphology of the boundary between Pacific and Antarctic plates was mapped with a Sea Beam multibeam echosounder and a SeaMARC II bathymetric side scan sonar, from the southern end of Juan Fernandez microplate at 35 deg S to Heezen transform at 56 deg S. There are six spreading center systems separated by two large, left-stepping nontransform offsets (at 36.5 deg

Peter Lonsdale

1994-01-01

262

Azimuthal anisotropy of the Pacific region  

NASA Astrophysics Data System (ADS)

Azimuthal anisotropy is the dependence of local seismic properties on the azimuth of propagation. We present the azimuthally anisotropic component of a 3D SV velocity model for the Pacific Ocean, derived from the waveform modeling of over 56,000 multi-mode Rayleigh waves followed by a simultaneous inversion for isotropic and azimuthally anisotropic vsv structure. The isotropic vsv model is discussed in a previous paper (A. Maggi, E. Debayle, K. Priestley, G. Barruol, Multi-mode surface waveform tomography of the Pacific Ocean: a close look at the lithospheric cooling signature, Geophys. J. Int. 166 (3) (2006). doi:10.1111/j.1365-246x.2006.03037.x). The azimuthal anisotropy we find is consistent with the lattice preferred orientation model (LPO): the hypothesis of anisotropy generation in the Earth's mantle by preferential alignment of anisotropic crystals in response to the shear strains induced by mantle flow. At lithospheric depths we find good agreement between fast azimuthal anisotropy orientations and ridge spreading directions recorded by sea-floor magnetic anomalies. At asthenospheric depths we find a strong correlation between fast azimuthal anisotropy orientations and the directions of current plate motions. We observe perturbations in the pattern of seismic anisotropy close to Pacific hot-spots that are consistent with the predictions of numerical models of LPO generation in plume-disturbed plate motion-driven mantle flow. These observations suggest that perturbations in the patterns of azimuthal anisotropy may provide indirect evidence for plume-like upwelling in the mantle.

Maggi, Alessia; Debayle, Eric; Priestley, Keith; Barruol, Guilhem

2006-10-01

263

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

NSDL National Science Digital Library

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

Egger, Anne

2003-03-18

264

Tectonic Plates and Plate Boundaries (WMS)  

NSDL National Science Digital Library

The earths crust is constantly in motion. Sections of the crust, called plates, push against each other due to forces from the molten interior of the earth. The areas where these plates collide often have increased volcanic and earthquake activity. These images show the locations of the plates and their boundaries in the earths crust. Convergent boundaries are areas where two plates are pushing against each other and one plate may be subducting under another. Divergent boundaries have two plates pulling away from each other and indicate regions where new land could be created. Transform boundaries are places where two plates are sliding against each other in opposite directions, and diffuse boundaries are places where two plates have the same relative motion. Numerous small microplates have been omitted from the plate image. These images have been derived from images made available by the United States Geological Surveys Earthquake Hazards Program.

Sokolowsky, Eric; Mitchell, Horace

2004-06-14

265

Geologic maps of Pacific basin and rim  

SciTech Connect

A major component of the Circum-Pacific Map Project is to compile five regional geologic maps at a scale of 1:10 million and a final map of the Pacific Ocean basin at a scale of 1:17 million. The Geologic Map of the Northeast Quadrant was published in 1983, and the Geologic Map of the Southeast Quadrant in 1985. The Geologic Maps of the Northwest Quadrant, the Southwest Quadrant, and the Antarctic Region are expected to reach publication during 1986. The Geologic Map of the Pacific Basin, with energy and mineral resources, is scheduled for publication in 1989. Each geologic map is a synthesis of a large amount of information. The land areas portray rock types by patterns and ages by colors; major faults are shown if they form the boundaries for map units. The oceanic areas include bathymetric contours, 13 sea-floor sediment types, all Deep Sea Drilling Program (DSDP) sites, selected DSDP columns, and selected sites of pre-Quaternary bedrock or sediment recovery. A correlation diagram on each map shows stratigraphic columns for the five regional maps, map units, geologic ages, and a time scale. An inset map shows presently active tectonic plates. The principal information sources for each sheet are given in a reference list, and each map is accompanied by explanatory notes. This map series represents the first integrated set of geologic maps of the entire Pacific Ocean basin and rim, including the Antarctic continent- altogether more than half the surface area of planet Earth.

Craddock, C.

1986-07-01

266

Pacific Languages at the University of the South Pacific.  

ERIC Educational Resources Information Center

Examines the use of Pacific languages in the teaching of the University of the South Pacific (USP). In introducing Pacific languages, the USP is responding to language planning in the various countries that operate the university. The challenge has been to integrate Pacific languages into university structures by creating both individual units…

Lynch, John; Mugler, France

2002-01-01

267

Global Plate Driving Forces at 50Ma  

NASA Astrophysics Data System (ADS)

We apply a novel workflow utilising the BEM-Earth geodynamic software to analyse the global coupled plate-mantle dynamics at 50 Ma. A subduction history model based on kinematic data going as far back as 80 Ma was developed using the GPlates software. Advection of the plates into the mantle takes into account the absolute plate motions and lithospheric thickness derived from its age to produce an estimated density heterogeneity initial model condition in the upper mantle. The resulting global model consists of regions of a mantle viscosity and density structure that is post-processed to ensure smooth non-overlapping 3D surfaces. BEM-Earth is then free to evolve the model toward the 50 Ma solution. The evolution of the model is driven by self-consistent buoyancy driven mantle dynamics. We use the model velocity output to quantify changes in forces driving the plates before and after 50 Ma. We analyse the rapid change in plate motion of India, Africa and plates in the Pacific Ocean basin by considering slab-pull, ridge-push and mantle drag/suction forces that naturally result from such top-down driven mantle flow. We compare the results with plate kinematic reconstructions and other geological observations.

Butterworth, N. P.; Quevedo, L. E.; Müller, R. D.

2011-12-01

268

Three-dimensional dynamic models of subducting plate-overriding plate-upper mantle interaction  

NASA Astrophysics Data System (ADS)

We present fully dynamic generic three-dimensional laboratory models of progressive subduction with an overriding plate and a weak subduction zone interface. Overriding plate thickness (TOP) is varied systematically (in the range 0-2.5 cm scaling to 0-125 km) to investigate its effect on subduction kinematics and overriding plate deformation. The general pattern of subduction is the same for all models with slab draping on the 670 km discontinuity, comparable slab dip angles, trench retreat, trenchward subducting plate motion, and a concave trench curvature. The narrow slab models only show overriding plate extension. Subduction partitioning (vSP? / (vSP? + vT?)) increases with increasing TOP, where trenchward subducting plate motion (vSP?) increases at the expense of trench retreat (vT?). This results from an increase in trench suction force with increasing TOP, which retards trench retreat. An increase in TOP also corresponds to a decrease in overriding plate extension and curvature because a thicker overriding plate provides more resistance to deform. Overriding plate extension is maximum at a scaled distance of ~200-400 km from the trench, not at the trench, suggesting that basal shear tractions resulting from mantle flow below the overriding plate primarily drive extension rather than deviatoric tensional normal stresses at the subduction zone interface. The force that drives overriding plate extension is 5%-11% of the slab negative buoyancy force. The models show a positive correlation between vT? and overriding plate extension rate, in agreement with observations. The results suggest that slab rollback and associated toroidal mantle flow drive overriding plate extension and backarc basin formation.

Meyer, C.; Schellart, W. P.

2013-02-01

269

Linguistic Diversity in the Pacific.  

ERIC Educational Resources Information Center

Reviews Peter Muhlhausler's book "Linguistic Ecology: Language Change and Linguistic Imperialism in the Pacific Region." Discusses the linguistic diversity of the Pacific, the linguistic impact of colonialism in the Pacific, and the role of linguists in the evolving linguistic situation in the Pacific. (Author/VWL)

Crowley, Terry

1999-01-01

270

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

271

Plate Tectonics: Consequences of Plate Interactions  

NSDL National Science Digital Library

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

National Science Teachers Association (NSTA)

2006-11-01

272

Upgrading user interfaces to computational chemistry codes  

SciTech Connect

Researchers at Pacific Northwest Laboratory are attempting to improve the user interface to a number of computational chemistry codes. We used TAE+ to implement a new graphical user interface to one of these codes. From this task we learned that TAE+, in its current form, is not sufficient to satisfy our long term goals. We have several suggestions for improvements which will make TAE+ usable for this type of task. 4 refs., 4 figs.

Adams, K.

1990-06-01

273

Caribbean plate tectonics  

NSDL National Science Digital Library

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

Sting; Commons, Wikimedia

274

The Plate Boundary Observatory: Data Management Progress and Highlights  

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, PBO will install 891 continuous GPS stations, up to 174 borehole strainmeter stations, and five laser strainmeters,

G. Anderson; K. Hodgkinson; M. Jackson; J. Wright

2005-01-01

275

The Plate Boundary Observatory: Data Management Progress and Highlights  

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,

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

2006-01-01

276

Modeling the mechanisms for the 100 Ma plate reorganisation  

NASA Astrophysics Data System (ADS)

Several global plate tectonic reorganizations have been identified throughout Earth history at 300, 250, 220, 150, and 50 Ma and are often associated with major environmental change and phases of natural resource formation. The ultimate cause of such events is ascribed to either a plate driving mechanism with the mantle playing a passive role or to major mantle overturns driving plate tectonic episodicity. A significant yet often over-looked plate reorganization event occurred at the Albian/Cenomanian boundary. This ~100 Ma event is marked by a major bend in the fracture zones in the Indian Ocean from 310° to 360°, a change in Pacific plate motion, as evidenced by the bend of the Mid-Pacific Mountains, Marcus Wake/Marshall Gilbert and Line Islands, and a period of peak ophiolite emplacement along the eastern margin of the Pacific rim. Coincident with the event is a regime change along the eastern Gondwana margin, from long-lived subduction to transtension, as well subsidence followed by rapid uplift in the sedimentary basins of central-eastern Australia (e.g. Eromanga and Surat basins). In order to analyze the possible mechanisms that may have triggered the ~100 Ma plate reorganization, we present preliminary results of combined regional and global geodynamic models performed with a recently developed, Multipole-accelerated Boundary Element Code (FMM-BEM) for solving the momentum equation in a spherical Earth. We generalize the problem to regional subduction initiation and expiration models around the Pacific and explicitly model the termination of subduction along the eastern Gondwana margin. We test the possibility that the termination of this subduction system triggered the larger plate reorganization at ~100 Ma. Our models will embed deep events; as slab avalanches and a general set of deep density and viscosity profiles. Finally, we assess the possible scenarios and mechanisms that may explain the ultimate causes of plate reorganization events.

McKeon, R. L.; Morra, G.; Müller, D.; Seton, M.

2009-12-01

277

Subduction Drive of Plate Tectonics  

NASA Astrophysics Data System (ADS)

Don Anderson emphasizes that plate tectonics is self-organizing and is driven by subduction, which rights the density inversion generated as oceanic lithosphere forms by cooling of asthenosphere from the top. The following synthesis owes much to many discussions with him. Hinge rollback is the key to kinematics, and, like the rest of actual plate behavior, is incompatible with bottom-up convection drive. Subduction hinges (which are under, not in front of, thin leading parts of arcs and overriding plates) roll back into subducting plates. The Pacific shrinks because bounding hinges roll back into it. Colliding arcs, increasing arc curvatures, back-arc spreading, and advance of small arcs into large plates also require rollback. Forearcs of overriding plates commonly bear basins which preclude shortening of thin plate fronts throughout periods recorded by basin strata (100 Ma for Cretaceous and Paleogene California). This requires subequal rates of advance and rollback, and control of both by subduction. Convergence rate is equal to rates of rollback and advance in many systems but is greater in others. Plate-related circulation probably is closed above 650 km. Despite the popularity of concepts of plumes from, and subduction into, lower mantle, there is no convincing evidence for, and much evidence against, penetration of the 650 in either direction. That barrier not only has a crossing-inhibiting negative Clapeyron slope but also is a compositional boundary between fractionated (not "primitive"), sluggish lower mantle and fertile, mobile upper mantle. Slabs sink more steeply than they dip. Slabs older than about 60 Ma when their subduction began sink to, and lie down on and depress, the 650-km discontinuity, and are overpassed, whereas younger slabs become neutrally buoyant in mid-upper mantle, into which they are mixed as they too are overpassed. Broadside-sinking old slabs push all upper mantle, from base of oceanic lithosphere down to the 650, back under shrinking oceans, forcing rapid Pacific spreading. Slabs suck forward overriding arcs and continental lithosphere, plus most subjacent mantle above the transition zone. Changes in sizes of oceans result primarily from transfer of oceanic lithosphere, so backarcs and expanding oceans spread only slowly. Lithosphere parked in, or displaced from, the transition zone, or mixed into mid-upper mantle, is ultimately recycled, and regional variations in age of that submerged lithosphere may account for some regional contrasts in MORB. Plate motions make no kinematic sense in either the "hotspot" reference frame (HS; the notion of fixed plumes is easily disproved) or the no-net-rotation frame (NNR) In both, for example, many hinges roll forward, impossible with gravity drive. Subduction-drive predictions are fulfilled, and paleomagnetic data are satisfied (as they are not in HS and NNR), in the alternative framework of propulsionless Antarctica fixed relative to sluggish lower mantle. Passive ridges migrate away from Antarctica on all sides, and migration of these and other ridges permits tapping fresh asthenosphere. (HS and NNR tend to fix ridges). Ridge migration and spreading rates accord with subduction drive. All trenches roll back when allowance is made for back-arc spreading and intracontinental deformation. Africa rotates slowly toward subduction systems in the NE, instead of moving rapidly E as in HS and NNR. Stable NW Eurasia is nearly stationary, instead of also moving rapidly, and S and E Eurasian deformation relates to subduction and rollback. The Americas move Pacificward at almost the full spreading rates of passive ridges behind them. Lithosphere has a slow net westward drift. Reference: W.B. Hamilton, An alternative Earth, GSA Today, in press.

Hamilton, W. B.

2003-12-01

278

Pacific Tsunami Museum  

NSDL National Science Digital Library

This website assists the Pacific Tsunami Museum in its goal "to promote public tsunami education for residents of Hawaii and the Pacific Region." Visitors can learn about the causes of tsunamis, its characteristics, the wrap-around effect, and much more. Teachers and students can discover the museum's education and science programs. Everyone will enjoy the live video stream of Hilo Bay and the abundant tsunami pictures. Interested users can also find out how to become involved with the museum.

279

Interface dermatitis.  

PubMed

Interface dermatitis includes diseases in which the primary pathology involves the dermo-epidermal junction. The salient histological findings include basal cell vacuolization, apoptotic keratinocytes (colloid or Civatte bodies), and obscuring of the dermo-epidermal junction by inflammatory cells. Secondary changes of the epidermis and papillary dermis along with type, distribution and density of inflammatory cells are used for the differential diagnoses of the various diseases that exhibit interface changes. Lupus erythematosus, dermatomyositis, lichen planus, graft versus host disease, erythema multiforme, fixed drug eruptions, lichen striatus, and pityriasis lichenoides are considered major interface diseases. Several other diseases (inflammatory, infective, and neoplastic) may show interface changes. PMID:23619439

Joshi, Rajiv

2013-01-01

280

Pressurized bellows flat contact heat exchanger interface  

NASA Technical Reports Server (NTRS)

Disclosed is an interdigitated plate-type heat exchanger interface. The interface includes a modular interconnect to thermally connect a pair or pairs of plate-type heat exchangers to a second single or multiple plate-type heat exchanger. The modular interconnect comprises a series of parallel, plate-type heat exchangers arranged in pairs to form a slot therebetween. The plate-type heat exchangers of the second heat exchanger insert into the slots of the modular interconnect. Bellows are provided between the pairs of fins of the modular interconnect so that when the bellows are pressurized, they drive the plate-type heat exchangers of the modular interconnect toward one another, thus closing upon the second heat exchanger plates. Each end of the bellows has a part thereof a thin, membrane diaphragm which readily conforms to the contours of the heat exchanger plates of the modular interconnect when the bellows is pressurized. This ensures an even distribution of pressure on the heat exchangers of the modular interconnect thus creating substantially planar contact between the two heat exchangers. The effect of the interface of the present invention is to provide a dry connection between two heat exchangers whereby the rate of heat transfer can be varied by varying the pressure within the bellows.

Voss, Fred E. (inventor); Howell, Harold R. (inventor); Winkler, Roger V. (inventor)

1990-01-01

281

The age and origin of the Pacific islands: a geological overview.  

PubMed

The Pacific Ocean evolved from the Panthalassic Ocean that was first formed ca 750 Ma with the rifting apart of Rodinia. By 160 Ma, the first ocean floor ascribed to the current Pacific plate was produced to the west of a spreading centre in the central Pacific, ultimately growing to become the largest oceanic plate on the Earth. The current Nazca, Cocos and Juan de Fuca (Gorda) plates were initially one plate, produced to the east of the original spreading centre before becoming split into three. The islands of the Pacific have originated as: linear chains of volcanic islands on the above plates either by mantle plume or propagating fracture origin, atolls, uplifted coralline reefs, fragments of continental crust, obducted portions of adjoining lithospheric plates and islands resulting from subduction along convergent plate margins. Out of the 11 linear volcanic chains identified, each is briefly described and its history summarized. The geology of 10 exemplar archipelagos (Japan, Izu-Bonin, Palau, Solomons, Fiji, New Caledonia, New Zealand, Society, Galápagos and Hawaii) is then discussed in detail. PMID:18768382

Neall, Vincent E; Trewick, Steven A

2008-10-27

282

Diffraction phenomena inside thick Fresnel zone plates  

Microsoft Academic Search

The parabolic wave equation method is used to describe the complex wave field inside the body of a thick zone plate used to focus X ray radiation. Two analytical approaches are applied: (1) Diffraction of a plane wave incident onto a separate interface between opaque and open zones is considered. We construct an approximate analytical solution to the classical problem

Yuri V. Kopylov; Alexei V. Popov; Alexander V. Vinogradov

1996-01-01

283

Diffusion brazing nickel-plated stainless steel  

NASA Technical Reports Server (NTRS)

To bond parts, sandwich assembly is made up of aluminum core, aluminum face sheet with brazing alloy interface, and nickel plated stainless steel part. Sandwich is placed between bottom and top glide sheet that is placed in stainless steel retort where assembly is bonded at 580 C.

Beuyukian, C. S.; Mitchell, M. J.

1976-01-01

284

The 5 September 2012 Nicoya, Costa Rica Mw 7.6 earthquake rupture process from joint inversion of high-rate GPS, strong-motion, and teleseismic P wave data and its relationship to adjacent plate boundary interface properties  

NASA Astrophysics Data System (ADS)

On 5 September 2012, a large thrust earthquake (Mw 7.6) ruptured a densely instrumented seismic gap on the shallow-dipping plate boundary beneath the Nicoya Peninsula, Costa Rica. Ground motion recordings directly above the rupture zone provide a unique opportunity to study the detailed source process of a large shallow megathrust earthquake using very nearby land observations. Hypocenter relocation using local seismic network data indicates that the event initiated with small emergent seismic waves from a hypocenter ~10 km offshore, 13 km deep on the megathrust. A joint finite-fault inversion using high-rate GPS, strong-motion ground velocity recordings, GPS static offsets, and teleseismic P waves reveals that the primary slip zone (slip > 1 m) is located beneath the peninsula. The rupture propagated downdip from the hypocenter with a rupture velocity of ~3.0 km/s. The primary slip zone extends ~70 km along strike and ~30 km along dip, with an average slip of ~2 m. The associated static stress drop is ~3 MPa. The seismic moment is 3.5 × 1020 Nm, giving Mw = 7.6. The coseismic large-slip patch directly overlaps an onshore interseismic locked region indicated by geodetic observations and extends downdip to the intersection with the upper plate Moho. At deeper depths, below the upper plate Moho, seismic tremor and low-frequency earthquakes have been observed. Most tremor locates in adjacent areas of the megathrust that have little coseismic slip; a region of prior slow slip deformation to the southeast also has no significant coseismic slip or aftershocks. An offshore locked patch indicated by geodetic observations does not appear to have experienced coseismic slip, and aftershocks do not overlap this region, allowing the potential for a comparable size rupture offshore in the future.

Yue, Han; Lay, Thorne; Schwartz, Susan Y.; Rivera, Luis; Protti, Marino; Dixon, Timothy H.; Owen, Susan; Newman, Andrew V.

2013-10-01

285

Global plate velocities from the Global Positioning System  

Microsoft Academic Search

We have analyzed 204 days of Global Positioning System (GPS) data from the global GPS network spanning January 1991 through March 1996. On the basis of these GPS coordinate solutions, we have estimated velocities for 38 sites, mostly located on the interiors of the Africa, Antarctica, Australia, Eurasia, Nazca, North America, Pacific, and South America plates. The uncertainties of the

Kristine M. Larson; Jeffrey T. Freymueller; Steven Philipsen

1997-01-01

286

Seismicity and plate tectonics in south central Alaska  

NASA Technical Reports Server (NTRS)

Hypocenter distribution shows that the Benioff zone associated with the Aleutian arc terminates in interior Alaska some 75 km north of the Denali fault. There appears to be a break in the subducting Pacific plate in the Yentna River-Prince William Sound area which separates two seismically independent blocks, similar to the segmented structure reported for the central Aleutian arc.

Van Wormer, J. D.; Davies, J.; Gedney, L.

1974-01-01

287

Plate Tectonics: The Hawaiian Archipelago  

NSDL National Science Digital Library

Since the Hawaiian Islands were all created by volcanic activity, it is somewhat surprising that only the island of Hawaii now possesses any active volcanoes. Why did the volcanoes that built the other islands stop erupting and why are those on the big island still active? This video segment, adapted from a NOVA television broadcast, shows how plumes of hot material rise from the Earth's interior to create 'hot spots' in the crust which are the locations of volcanic activity. Movement of the Pacific Plate causes volcanic islands to continually form, migrate away from the hot spot, and become extinct, forming chains of islands like the Hawaiian Islands. The segment is four minutes thirty-seven seconds in length.

288

Plate Tectonics: The Hawaiian Archipelago  

NSDL National Science Digital Library

Since the Hawaiian Islands were all created by volcanic activity, it is somewhat surprising that only the island of Hawaii now possesses any active volcanoes. Why did the volcanoes that built the other islands stop erupting and why are those on the big island still active? This video segment, adapted from a NOVA television broadcast, shows how plumes of hot material rise from the Earth's interior to create 'hot spots' in the crust which are the locations of volcanic activity. Movement of the Pacific Plate causes volcanic islands to continually form, migrate away from the hot spot, and become extinct, forming chains of islands like the Hawaiian Islands. The segment is four minutes thirty-seven seconds in length.

2011-07-12

289

The History of the Pacific Superplume  

NASA Astrophysics Data System (ADS)

To understand the birth place and episodic activity of the Pacific superplume, we reconstructed the paleogeograhy of continents and oceanic plates from 1.0 Ga supercontinent Rodinia until now by adopting the most confident available data set to determine paleopositions of oceanic plateaus, seamounts, and oceanic arc, in addition to major continents, by using plate trajectory for the last 150Ma and for the farther back to 1.0Ga, by the paleomagnetic constraints tied with geologic connections. Our main focus is the frequency change of ancient activity of plume rocks that are now preserved in the accretionary complex around the circum-Pacific orogenic belts. Several conclusions are led through our reconstruction. (1) Cretaceous oceanic plateaus which present widespread in western Pacific (e.g., Manihiki Plateau, Shatsky Rise, Hess Rise, Mid-Pacific Mountain, Nauru Basin) are traced back and concentrated to the present active region of the Pacific superplume. This suggests that those were once formed a huge composite volcanoes as large as 4000 km x 2400 km across during the Cretaceous by superplume activity. These are equivalent to Australia or Tharsis bulge volcanic complex on Mars. The estimated thickness of oceanic crust ca. 30-40 km suggests that major parts may have been above sea-level during the Cretaceous time. The Cretaceous global warming may be related to this hyper-active superplume event which have carried mantle CO2 to the surface of 3.2 x 1021 g, assuming 0.3 wt% x 350 million km3 (magma volume) x 3.07 g/cm3 during 150-75 Ma. This CO2 output amount occupies as much as 37 wt% among the total output from mantle estimated by using erupted basaltic volume estimated by Larson (1991, Geology, 549-550) and present output rate of CO2. The similar episodic activity of Pacific superplume seems to have occurred at 750-700 Ma, 550-500Ma, 300-250Ma by considering the frequency of occurrences of greenstones in the accretionary complexes of the world. (2) Rodinia rifted and separated at 750Ma on the similar latitude to present active region of the Pacific superplume. This suggests that Pacific superplume may be born at 750Ma to break-up supercontinent Rodinia to support the original idea by Maruyama (1994, J. Geol. Soc. Japan, 100, 24-49) as African superplume may be born at 250-200 Ma to break-up Pangea. (3) At 1000Ma, the Grenvillian orogens cemented amalgamated collisional continents to form the supercontinent Rodinia. This suggests that the large amounts of oceanic slab must have subducted along the Grenvillian sutures and might have caused the birth of Pacific superplume.

Suzuki, N.; Utsunomiya, A.; Maruyama, S.

2001-12-01

290

Sputtering and ion plating  

NASA Technical Reports Server (NTRS)

The proceedings of a conference on sputtering and ion plating are presented. Subjects discussed are: (1) concepts and applications of ion plating, (2) sputtering for deposition of solid film lubricants, (3) commercial ion plating equipment, (4) industrial potential for ion plating and sputtering, and (5) fundamentals of RF and DC sputtering.

1972-01-01

291

Plate Tectonics Animation  

NSDL National Science Digital Library

Plate tectonics describes the behavior of Earth's outer shell, with pieces (plates) bumping and grinding and jostling each other about. Explore these maps and animations to get a jump start on understanding plate tectonic processes, history, and how motion of the plates affects our planet today.

2002-01-01

292

Pre-seismic crustal deformation caused by an underthrusting oceanic plate, in eastern Hokkaido, Japan  

Microsoft Academic Search

Eastern Hokkaido is being considered as one of the prime candidates for a future great earthquake in Japan. Geodetic work and seismological data suggest that the continental plate is being compressed and dragged down into the asthenosphere by the underthrusting Pacific plate. A quantitative examination of this idea was carried out by an application of the finite-element method to a

Kunihiko Shimazaki

1974-01-01

293

A geometric technique for relocating hotspots and refining absolute plate motions  

Microsoft Academic Search

An age-independent, geometric relationship is presented that links hotspots to the seamounts which they produce, and so permits the use of undated seamounts to refine the motion of tectonic plates. This technique has the potential to rigorously assess hotspot fixity and to locate extinct hotspots. The present application of this method points to a recent change in Pacific plate motion,

Paul Wessel; Loren Kroenke

1997-01-01

294

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

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 880 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser

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

2007-01-01

295

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

Microsoft Academic Search

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

S. C. Eriksson; S. E. Olds

2009-01-01

296

17. Photocopy of drawing (original 8 x 101/2 inch plate ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

17. Photocopy of drawing (original 8 x 10-1/2 inch plate located in: USDA Forest Service, North Pacific Region, recreation handbook, date unknown). COMMUNITY BLDG., PLATE A-9 (enlarged from a 4x5 negative) - Austin Pass Warming Hut, Washington Highway 542, Glacier, Whatcom County, WA

297

Estimation of current plate motions in Papua New Guinea from Global Positioning System observations  

Microsoft Academic Search

Plate tectonic motions have been estimated in Papua New Guinea from a 20 station network of Global Positioning System sites that has been observed over five campaigns from 1990 to 1996. The present velocities of the sites are consistent with geological models in which the South Bismarck, Woodlark, and Solomon Sea Plates form the principal tectonic elements between the Pacific

Paul Tregoning; Kurt Lambeck; Art Stolz; Peter Morgan; Simon C. McClusky; Peter van der Beek; Herbert McQueen; Russell J. Jackson; Rodney P. Little; Alex Laing; Brian Murphy

1998-01-01

298

Deck view, west approach; former Western Pacific (now Union Pacific) ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Deck view, west approach; former Western Pacific (now Union Pacific) Railroad at left; wind turbine generators atop hill in background; view to northeast; 90mm lens - Carroll Overhead Bridge, Altamont Pass Road, Livermore, Alameda County, CA

299

Plate tectonics and the Gulf of California region  

SciTech Connect

The geology and tectonism of California have been influenced greatly by the collision and interaction between the Pacific plate and the North American plate. The forces generated by this interaction caused substantial horizontal movement along the San Andreas fault system and created the Gulf of California rift zone. This article summarizes the unique features of the gulf, describes the theory of plate tectonics, explains how tectonism may have affected the geologic evolution and physiography of the gulf, and illustrates the process by which the Colorado River became linked to the gulf.

Schmidt, N.

1990-11-01

300

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

301

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

302

Asia-Pacific.com!  

NSDL National Science Digital Library

Asia-Pacific.com!, an invaluable resource for users interested in business and economics in Asia and the Pacific Rim, offers an informative assortment of resources, news, and data. The site links to respected media sources throughout the region including Singapore Business Times, Jakarta Post, and The Australian, as well as in-depth journal articles, and book reviews, tables of contents, and purchasing information. Data analysis includes links to economic sources, company annual reports, and trade reports. Users are also invited to send their questions and queries to Asia-Pacific.com!'s panel of experts, who include George T. Haley, Associate Professor/ Director of Marketing and International Business Programs at the University of New Haven, Usha C.V. Haley, Associate Professor of Strategy and International Business at the New Jersey Institute of Technology, and Tan Chin Tiong, Professor and Provost of the new Singapore Management University.

303

Eastern Pacific Ocean Conference  

NASA Astrophysics Data System (ADS)

The promotion of interaction among investigators of all oceanographic disciplines studying the eastern Pacific Ocean was the goal of the 1990 Eastern Pacific Ocean Conference (EPOC), held October 17-19 on the snow-covered slopes of Mt. Hood, Oreg. Thirty oceanographers representing all disciplines attended.Dick Barber, Duke University Marine Lab, Beaufort, N.C., chaired a session on the eastern equatorial Pacific Ocean, emphasizing issues related to biological activity. Steve Ramp of the Naval Postgraduate School in Montery, Calif., chaired a session on recent results from northern and central California experiments. On October 19, following an early morning earthquake, a business meeting and discussions regarding a collaboration in future experiments were held.

304

MACMA: a Virtual Lab for Plate Tectonics  

NASA Astrophysics Data System (ADS)

MACMA (Multi-Agent Convective MAntle) is a tool developed to simulate evolutive plate tectonics and mantle convection in a 2-D cylindrical geometry (Combes et al., 2012). The model relies mainly on a force balance to compute the velocity of each plate, and on empirical rules to determine how plate boundaries move and evolve. It includes first-order features of plate tectonics: (a) all plates on Earth do not have the same size, (b) subduction zones are asymmetric, (c) plates driven by subducting slabs and upper plates do not exhibit the same velocities, and (d) plate boundaries are mobile, can collide, merge and disappear, and new plate boundaries can be created. The MACMA interface was designed to be user-friendly and a simple use of the simulator can be achieved without any prerequisite knowledge in fluid dynamics, mantle rheology, nor in numerical methods. As a preliminary study, the simulator was used by a few students from bachelor's degree to master's degree levels. An initial configuration for plate tectonics has to be created before starting a simulation: the number and types of plate boundaries (ridge, subduction, passive margins) has to be defined and seafloor ages must be given. A simple but interesting exercise consists in letting students build such an initial configuration: they must analyze a map of tectonic plates, choose a 2-D section and examine carefully a map of seafloor ages. Students mentioned that the exercise made them realize that the 3-D spherical structure of plate tectonics does not translate directly in a simple 2-D section, as opposed to what is usually shown in books. Physical parameters: e.g. mantle viscosity, number of layers to consider in the mantle (upper and lower mantle, possible asthenosphere), initial time and mantle temperature, have to be chosen, and students can use this virtual lab to see how different scenarios emerge when parameters are varied. Very importantly, the direct visualization of the mobility of plate boundaries is a feature that clearly seems interesting to students. They are used to see dynamic representations of continental drift, but this does not include the dynamics of the oceanic lithosphere and the corresponding fluctuations in seafloor age distribution. The 2-D geometry of the simulator is a simplification that actually brings a clearer view of plate boundary creations, migrations, and collisions, together with global plate tectonics reorganization events.

Grigne, C.; Combes, M.; Tisseau, C.

2013-12-01

305

Tectonic stress state in NE Japan as part of the Okhotsk plate  

NASA Astrophysics Data System (ADS)

An existing geodetic flow velocity model, obtained by using an internal free network adjustment technique, is used to derive estimates for various strain rates parameters in NE Japan. The greatest shortening rates of the principal strains, trending ˜E-W, are located in regions where much steady, internal, frame-invariant plastic flow deformation is observed to be taking place. The internal geodetic adjustment technique yielded the internal deformation in the Tohoku arc; most of the intraplate deformations, including the much folding deformations observed in the inner zone, are produced from within. An interseismic transient elastic loading at a strongly coupled/locked Japan trench would not be needed. The observed ongoing extensive ductile folding deformation in the inner zone of Tohoku may mean that the geodetic strain rates, causing shortening at ˜2-3 cm/yr, probably reflect the more correct level of the deformation, which is steady/permanent, in NE Japan as compared with seismic/faulting data, which indicate ˜0.5 cm/yr shortening. The calculated principal strain rates are used to make an interpretation for the origin of the deviatoric principal stresses within the greater regional plate tectonic framework. The tectonic stress state in NE Japan, as part of the Okhotsk plate, could mostly be influenced by the Okhotsk plate, which is extruding southward to lessen the significant accumulated contractional deformation in NE Asia in the Verkhoyansk-Cherskii mountains. The principal strain rates are ˜N-S extensional essentially everywhere in NE Japan, as a result of the southerly extrusion, except in its southernmost leading edge, in the Uetsu/Fossa Magna province, where the Japan Alps rampart rises in front of the extrusion. Here an ˜E-W compressional stress state prevails. A second ˜E-W contractional zone is found in north-central Tohoku, extending from the Sanriku province in the outer zone to the inner zone in the Japan Sea side, being more prevalent in the latter zone. The calculated rotation rates from the geodetic flow model are clockwise (CW) in both of the ˜E-W contractional regions. NE Japan, extruding southward, faces buttresses in (1) the Oga-Ojika Line (OOL), and/or a crustal weakness zone between the northern and the southern halves of Tohoku approx. at ˜38.5°N latitude, and, especially, (2) the Japanese Alps rampart; these obstacles cause the northern and southernmost Tohoku to veer to its right and rotate CW, thereby setting up the ˜E-W-trending compressional deformation in their respective inner zones. Between the OOL (or the 38.5°N boundary) and the Kanto Tectonic Line (KTL), the sense of the differential rotations is counterclockwise (CCW), towards the ocean to the SE. The northern Tohoku (north of the OOL) and the southernmost Tohoku (south of the KTL) cannot rotate CCW towards the ocean because of the Izu block's collision in the south and the relatively strong coupling along the subduction interface beneath the Japan trench in the north off-Sanriku. The relatively stronger long-term coupling between the northern Tohoku and the Pacific plate at the Sanriku coast, with respect to that in off-Fukushima, is due to a flatter subduction of the Pacific slab there, increasing the plates' interface contact area; the flattening of the subduction dip angle was caused by CCW rotation and shifting of the northern Tohoku along the dextral Honjo-Matsushima Line, roughly corresponding to the OOL, towards the Pacific and overriding of the subduction zone during the formation of the Japan Sea.

Altis, Sungat

2001-09-01

306

Multimodal Interfaces  

Microsoft Academic Search

In this paper, we present an overview of research in our laboratories on Multimodal Human Computer Interfaces. The goal for such interfaces is to free human computer interaction from the limitations and acceptance barriers due to rigid operating commands and keyboards as the only\\/main I\\/O-device. Instead we move to involve all available human communication modalities. These human modalities include Speech,

Alex Waibel; Minh Tue Vo; Paul Duchnowski; Stefan Manke

1996-01-01

307

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

308

Microstructural modifications in an explosively welded Ti\\/Ti clad material: I. Bonding interface  

Microsoft Academic Search

Microstructural modifications of the bonding interface in an explosively welded Ti\\/Ti clad material using the preset angle\\u000a standoff configuration with various flyer plate speeds have been studied. Explosive welding was completed at flyer plate speed\\u000a over 420 m\\/s. The wavelength and amplitude of the wavy interface increased with increasing flyer plate speed up to 1060 m\\/s.\\u000a The planar interface was

M. Nishida; A. Chiba; K. Imamura; H. Minato; J. Shudo

1993-01-01

309

Stop motion microphotography of laser driven plates  

SciTech Connect

Laser driven plates have been used for several years for high velocity shock wave and impact studies. Recent questions about the integrity and ablation rates of these plates coupled with an improved capability for microscopic stop motion photography led to this study. For these experiments, the plates were aluminum, coated on the ends of optical fibers. A high power laser pulse in the fiber ionizes the aluminum at the fiber/coating interface. The plasma thus created accelerates the remaining aluminum to high velocities, several kilometers per second. We defined {open_quotes}thick{close_quotes} or {open_quotes}thin{close_quotes} coatings as those where a flying plate (flyer) was launched vs. the material being completely ionized. Here we were specifically interested in the thick/thin boundary to develop data for the numerical models attempting to predict flyer behavior.

Frank, A.M. [Lawrence Livermore National Lab., CA (United States); Trott, W.M. [Sandia National Labs., Albuquerque, NM (United States)

1994-09-01

310

Nazca Plate Program of the International Decade of Ocean Exploration - Oceanographer Cruise-RP-2-OC-73.  

National Technical Information Service (NTIS)

Oceanographer, a NOAA ship, sailed to the southeast Pacific in spring, 1973 as part of the International Decade of Ocean Exploration Nazca Plate Program. Measurements of the gravity and magnetic field were made, seismic refraction and reflection operation...

B. H. Erickson

1974-01-01

311

Fiji in the South Pacific.  

ERIC Educational Resources Information Center

This text introduces Fiji and other island nations located in the Pacific, the world's largest ocean. Cut off from the world by vast expanses of water, these people developed a unique culture. Contents include: Teacher Overview, Geography of the South Pacific Islands, History of the South Pacific, Fiji, Traditional Village Life, Yaquna Ceremony,…

Scott, Rosalind; Semaan, Leslie

312

Australia in the Pacific.  

ERIC Educational Resources Information Center

Discusses Australia's growth since European settlement and its development into a major world trader in industrial and high technology raw materials. Examines the country's expanding relations with New Zealand and other Pacific states which is the outgrowth of the realization that all will gain from greater international cooperation. (GEA)

Kennedy, Kerry; Welch, Ian

1988-01-01

313

The North Pacific Megatrend  

Microsoft Academic Search

Megatrends are trans-basin features comprised of fracture zones and seamount\\/island chains. They appear to be hot lines rather than isolated hot spots. The North Pacific Megatrend begins in Japan, crosses the trench in the form of the Geisha Guyots, skirts along the northern Mapmaker Seamounts, encompasses the Hawaiian chain, and passes through the Clipperton and Clarion fracture zones to the

N. Christian Smoot; Dong R. Choi

2003-01-01

314

Pacific basin energy  

SciTech Connect

Testimony is presented concerning pending legislation which provides for the assessment and development of the potential for renewable energy sources in the U.S. insular areas, including the trust territories. Options for self-sufficiency throughout the Pacific basin are considered in light of rapidly escalating fuel costs.

Not Available

1980-01-01

315

Plastic in the Pacific  

NSDL National Science Digital Library

Imagine every person on earth had 100 pounds of plastic. That's how much new plastic will be manufactured this year. In this video from QUEST produced by KQED, learn how much of that will end up in the ocean in a massive area dubbed the Pacific Garbage Patch.

Kqed

2012-08-08

316

A review of the tectonic evolution of the Northern Pacific and adjacent Cordilleran Orogen  

NASA Astrophysics Data System (ADS)

Numerous plate kinematic models for the North Pacific realm have been developed since the advent of plate tectonics in the early seventies (e.g Atwater (1970), Mammerickx and Sharman (1988)). Although published kinematic models are consistent with the broad scale features of the North Pacific, the link between plate motions and the evolution of the North American Cordillera remains poorly understood. Part of the problem lies in conflicting interpretations of geological versus paleomagnetic data sets, with the result being a lack of consensus regarding: the paleolocation of key geological units; the paleogeography of terrane formation and amalgamation; the motion, boundaries and even existence of oceanic plates; and the character (e.g. trend of subduction) and position of plate boundaries within the northern Pacific basin. Remnants of the Farallon and Kula plates, and some short-lived microplates, demonstrate the complicated tectonic evolution of the oceanic realm west of the North American margin (e.g. Rea and Dixon (1983); McCrory and Wilson (2013); Shephard et al. (2013)). The creation and destruction of major tectonic plates and microplates has presumably left a record in the Cordilleran orogen of western North America. However, working backward from the geological relationships to plate reconstructions remains difficult. Here we investigate the relationship between the plate motions of the Pacific Ocean and the terrane movements in the North American Cordillera by revising the marine magnetic and gravity anomalies of the northern Pacific. In particular, we reevaluate plate boundaries at times of major changes in plate geometry of the Pacific, Kula, Chinook and Farallon plates from C34n onward. Our focus is also on the plate geometries of the Resurrection, Eshamy and Siletz-Crescent plates during the time between anomaly C26 and C12, and the links between plate interactions and on-shore tectonic events recorded in the geological record of Vancouver Island, including the accretion of the Pacific Rim and Crescent terranes to Wrangellia between C25 and C18. References: Atwater, T. (1970). Implications of plate tectonics for the Cenozoic tectonic evolution of western North America. Geological Society of America Bulletin, 81, 3513-3536. McCrory, P. a., & Wilson, D. S. (2013). A kinematic model for the formation of the Siletz-Crescent forearc terrane by capture of coherent fragments of the Farallon and Resurrection plates. Tectonics, 32, 1-19. doi:10.1002/tect.20045 Rea, D. K., & Dixon, J. M. (1983). Late Cretaceous and Paleogene tectonic evolution of the North Pacific Ocean. Earth and Planetary Science Letters, 65, 145-166. Shephard, G. E., Müller, R. D., & Seton, M. (2013). The tectonic evolution of the Arctic since Pangea breakup: Integrating constraints from surface geology and geophysics with mantle structure. Earth-Science Reviews, 124, 148-183. doi:10.1016/j.earscirev.2013.05.012 Mammerickx, J., & Sharman, G. F. (1988). Tectonic evolution of the North Pacific during the Cretaceous quiet period. Journal of Geophysical Research, 93(B4), 3009-3024. doi:10.1029/JB093iB04p03009

Jakob, Johannes; Gaina, Carmen; Johnston, Stephen T.

2014-05-01

317

Observe animations of processes that occur along plate boundaries  

NSDL National Science Digital Library

Here are three animations that reveal how tectonic plates move relative to each other at three types of plate boundaries--transform, convergent, and divergent boundaries. Key features such as the asthenosphere are labeled in the animations. In addition, each animation is equipped with movie control buttons that allow students to play, pause, and move forward and backward through each clip. The animation of a transform boundary shows the North American and Pacific plates sliding past one another, while an oceanic plate subducts under a continental plate producing volcanic activity in the convergent boundary animation. Two coordinated movie clips are used to demonstrate what occurs at a divergent boundary from different viewpoints. Copyright 2005 Eisenhower National Clearinghouse

Education, Terc. C.; Littell, Mcdougal

2003-01-01

318

The Cretaceous iron belt of northern Chile: role of oceanic plates, a superplume event, and a major shear zone  

Microsoft Academic Search

The Cretaceous constitutes a turning point in the tectonic, magmatic, and metallogenic history of Chile. The geological evidence indicates that a major change occurred in late Neocomian time when superplume emplacement (Mid-Pacific Superplume) and plate reorganization processes took place in the Pacific. The superplume event resulted in a major ridge-push force resulting in increased coupling between the subducting and overriding

Roberto Oyarzun; Jorge Oyarzán; Jean Jacques Ménard; Javier Lillo

2002-01-01

319

Slab-plume interaction beneath the Pacific Northwest  

Microsoft Academic Search

The Pacific Northwest has undergone complex plate reorganization and intense tectono-volcanic activity to the east during the Cenozoic (last 65 Ma). Here we show new high-resolution tomographic images obtained using shear and compressional data from the ongoing USArray deployment that demonstrate first that there is a continuous, whole-mantle plume beneath the Yellowstone Snake River Plain (YSRP) and second, that the

Mathias Obrebski; Richard M. Allen; Mei Xue; Shu-Huei Hung

2010-01-01

320

Hyperbolic Interfaces  

NASA Astrophysics Data System (ADS)

Fluid interfaces, such as soap films, liquid droplets, or lipid membranes, are known to give rise to several special geometries, whose complexity and beauty continue to fascinate us, as observers of the natural world, and challenge us as scientists. Here I show that a special class of surfaces of constant negative Gaussian curvature can be obtained in fluid interfaces equipped with an orientational ordered phase. These arise in various soft and biological materials, such as nematic liquid crystals, cytoskeletal assemblies, or hexatic colloidal suspensions. The purely hyperbolic morphology originates from the competition between surface tension, that reduces the area of the interface at the expense of increasing its Gaussian curvature, and the orientational elasticity of the ordered phase, that in turn suffers for the distortion induced by the underlying curvature.

Giomi, Luca

2012-09-01

321

Beyond Interface  

NSDL National Science Digital Library

Beyond Interface is an exhibition of digital art, created in conjunction with the Museums and the Web 1998 conference held in April. The conference and the Website are coordinated by Archives & Museums Informatics. Beyond Interface is curated by Steve Dietz, who explains, "This online exhibition presents a simple proposition. There is art that is created to 'be' on the Net. After that, it gets more complex very quickly. Beyond Interface explores some of the complicating issues but does not attempt a comprehensive investigation." Users can follow links to the works of 24 net artists, writings on the philosophies of net art, and the complete conference proceedings of Museums and the Web 1998, which include the Best of the Web Award for 1998.

322

My Plate Food Guide  

MedlinePLUS

... you won't get the best nutrition. 1. Vegetables The vegetable portion of MyPlate is shown in green. It's ... the largest sections on the plate. That's because vegetables provide many of the vitamins and minerals we ...

323

Plate Tectonics: Further Evidence  

NSDL National Science Digital Library

The representation depicts the spreading of the sea floor along the mid-ocean ridges. The resource generally describes the theory of plate tectonics, including the movement of plates with regard to one another.

324

External Resource: Plate Tectonics  

NSDL National Science Digital Library

This Windows to the Universe interactive webpage connects students to the study and understanding of plate tectonics, the main force that shapes our planets surface. Topics: plate tectonics, lithosphere, subduction zones, faults, ridges.

1900-01-01

325

The PLATES Project  

NSDL National Science Digital Library

This is the web page for PLATES, a program of research into plate tectonic and geologic reconstructions at the University of Texas at Austin Institute for Geophysics. The page contains links to a brief overview of plate tectonics and plate reconstructions using the PLATES Project's global plate reconstruction model, in addition to movies in the format of powerpoint animations which can be downloaded for later use. Models are shown on the evolution of the earth's oceans and the movement of the earth's tectonic plates from the Late Precambrian through the present day, reconstructing (i.e. "predicting") geological environments through geologic history. Maps of the following can be accessed: late Neo-Proterozoic, Silurian, early Jurassic, early Cretaceous, Cretaceous-Tertiary Boundary, and Oligocene. Movies are available on the following subjects: global plate motion, Jurassic to present day, opening of the Indian Ocean, and tectonic evolution of the Arctic region.

326

Metallic glass as a temperature sensor during ion plating  

NASA Technical Reports Server (NTRS)

The temperature of the interface and/or a superficial layer of a substrate during ion plating was investigated using a metallic glass of the composition Fe67Co18B14Si1 as the substrate and as the temperature sensor. Transmission electron microscopy and diffraction studies determined the microstructure of the ion-plated gold film and the substrate. Results indicate that crystallization occurs not only in the film, but also in the substrate. The grain size of crystals formed during ion plating was 6 to 60 nm in the gold film and 8 to 100 nm in the substrate at a depth of 10 to 15 micrometers from the ion-plated interface. The temperature rise of the substrate during ion plating was approximately 500 C. Discontinuous changes in metallurgical microstructure, and physical, chemical, and mechanical properties during the amorphous to crystalline transition in metallic glasses make metallic glasses extremely useful materials for temperature sensor applications in coating processes.

Miyoshi, K.; Spalvins, T.; Buckley, D. H.

1985-01-01

327

Geology: Plate Tectonics  

NSDL National Science Digital Library

This site is the Plate Tectonics portion of the Geology site from the University of California, Berkeley, Museum of Paleontology. This exhibit has a section devoted to the explanation of the history of plate tectonics and a section that focuses on the mechanisms driving plate tectonics. The mechanisms section discusses convection, mid-oceanic ridges, geomagnetic anomalies, deep sea trenches, and island arcs. The site also contains links to numerous animations illustrating historical plate positions and movements.

328

Laser induced copper plating  

Microsoft Academic Search

Argon laser induced plating of copper spots and lines from copper sulfate solutions on glass and phenolic resin paper has been investigated. The substrates had to be precoated with an evaporated copper film. The highest plating rates have been obtained with a small film thickness of 25 nm. Spots with a thickness up to 30 ?m were plated.

A. K. Al-Sufi; H. J. Eichler; J. Salk; H. J. Riedel

1983-01-01

329

Optimal truss plates  

Microsoft Academic Search

Sandwich plates comprised of truss cores faced with either planar trusses or solid sheets are optimally designed for minimum weight subject to prescribed combinations of bending and transverse shear loads. Motivated by recent advances in manufacturing possibilities, attention is focussed on plates with truss elements and faces made from a single material. The optimized plates are compared with similarly optimized

Nathan Wicks; John W Hutchinson

2001-01-01

330

Plate Tectonic Theory  

NSDL National Science Digital Library

This is the web site for a Plate Tectonics Theory class at The University of Nevada, Reno. The home page/syllabus contains links to several of the topics covered in the course. The topics with web based lecture materials are earthquake seismology, structure of the Earth, composition of the Earth, lithospheric deformation, the plate tectonics paradigm, and the driving mechanisms of plate tectonics.

Louie, John

331

Earthquakes and Plate Tectonics  

NSDL National Science Digital Library

This article describes the theory of plate tectonics and its relation to earthquakes and seismic zones. Materials include an overview of plate tectonics, a description of Earth's crustal plates and their motions, and descriptions of the four types of seismic zones.

332

Friction measurement on free standing plates using atomic force microscopy.  

PubMed

A method is introduced to measure friction on small, free standing objects, specifically microfabricated silicon plates, based on atomic force microscopy (AFM). An AFM tip is brought into contact with the plate resting on a substrate. The substrate is displaced laterally and, provided the AFM tip does not slide over the plate, the twisting of the AFM cantilever is used to measure the friction of the underlying plate-substrate interface. The method can measure nano-Newton to micro-Newton forces (both friction and applied load) and provides a means to measure friction of macroscopic structures at low load. PMID:23387654

Tang, X S; Loke, Y C; Lu, P; Sinha, Sujeet K; O'Shea, S J

2013-01-01

333

Plate Motion and Crustal Deformation Estimated with Geodetic Data from the Global Positioning System  

NASA Technical Reports Server (NTRS)

We use geodetic data taken over four years with the Global Positioning System (GPS) to estimate: (1) motion between six major plates and (2) motion relative to these plates of ten sites in plate boundary zones. The degree of consistency between geodetic velocities and rigid plates requires the (one-dimensional) standard errors in horizontal velocities to be approx. 2 mm/yr. Each of the 15 angular velocities describing motion between plate pairs that we estimate with GPS differs insignificantly from the corresponding angular velocity in global plate motion model NUVEL-1A, which averages motion over the past 3 m.y. The motion of the Pacific plate relative to both the Eurasian and North American plates is observed to be faster than predicted by NUVEL-1A, supporting the inference from Very Long B ase- line Interferometry (VLBI) that motion of the Pacific plate has speed up over the past few m.y. The Eurasia-North America pole of rotation is estimated to be north of NUVEL-1A, consistent with the independent hypothesis that the pole has recently migrated northward across northeast Asia to near the Lena River delta. Victoria, which lies above the main thrust at the Cascadia subduction zone, moves relative to the interior of the overriding plate at 30% of the velocity of the subducting plate, reinforcing the conclusion that the thrust there is locked beneath the continental shelf and slope.

Argus, Donald F.; Heflin, Michael B.

1995-01-01

334

Palaeotectonic implications of increased late Eocene-early Oligocene volcanism from South Pacific DSDP sites  

USGS Publications Warehouse

Late Eocene-early Oligocene (42-35 Myr) sediments cored at two DSDP sites in the south-west Pacific contain evidence of a pronounced increase in local volcanic activity, particularly in close association with the Eocene-Oligocene boundary. This pulse of volcanism is coeval with that in New Zealand and resulted from the development of an Indo- Australian / Pacific Plate boundary through the region during the late Eocene. The late Eocene / earliest Oligocene was marked by widespread volcanism and tectonism throughout the Pacific and elsewhere, and by one of the most important episodes of Cenozoic climatic cooling. ?? 1985 Nature Publishing Group.

Kennett, J. P.; Von Der Borch, C.; Baker, P. A.; Barton, C. E.; Boersma, A.; Cauler, J. P.; Dudley, Jr. , W. C.; Gardner, J. V.; Jenkins, D. G.; Lohman, W. H.; Martini, E.; Merrill, R. B.; Morin, R.; Nelson, C. S.; Robert, C.; Srinivasan, M. S.; Stein, R.; Takeuchi, A.; Murphy, M. G.

1985-01-01

335

Progress in Pacific islands.  

PubMed

The article announces the formation of family planning associations on the Tonga, Tahiti, Gilbert and Ellice Island groups. The administrative structures of the Associations are briefly described and organizational methods and directions to involve all islands of a particular groups are reported. All of the territories are within the area served by the South Pacific Commission which has set up a family planning seminar for the areas involved. PMID:12305000

1970-02-01

336

Marquesas Islands, Pacific Ocean  

NASA Technical Reports Server (NTRS)

As with most small island groups around the world, the Marquesas Island group 9.0S, 140.0W) is usually concealed by heavy cloud cover throughout the day making them very difficult to photograph in their entirety. Located in the south central Pacific Ocean, just north of the Tuamotu Archipelago, the islands partially seen in this view are: Nuku Hiva, Ua Huka and Ua Pu.

1993-01-01

337

Pacific Marine Environmental Laboratory  

NSDL National Science Digital Library

Located in Seattle, Washington, PMEL carries out interdisciplinary scientific investigations in oceanography and atmospheric science. Current programs focus on open ocean observations in support of long-term monitoring and forecasting. A comprehensive site focusing on NOAA research in the Pacific Ocean. Site includes an abundant amount of information, data, publications, and links to additional resources. Features interactive data sets, maps, 3-D visualizations, and video.

338

The Central Pacific Megatrend  

Microsoft Academic Search

The WNW-ESE-trending Central Pacific Megatrend is a transbasinal feature comprising several types of geornorphic features—ridges, linear seamount chains, and fractures. First appearing on the satellite altimetry data set, an updated bathymetry effort is presented to verify the existence of such a feature. The route is traced from the Banda Sea in the Indonesian region to South America, a distance of

N. Christian Smoot; Bruce A. Leybourne

2001-01-01

339

North Pacific Bloom  

NASA Technical Reports Server (NTRS)

Many images are made of relatively bright phytoplankton blooms. However, not all such blooms reflect more light than they absorb. SeaWiFS collected this image of a patch in the north Pacific that had been darkened because the photosynthetic pigments of the phytoplankton living there had absorbed more of the incoming solar radiation than the relatively phytoplankton-poor surrounding waters. The Hawaiian islands can be seen through the clouds about 1000 kilometers to the southwest of the patch.

2002-01-01

340

Angular shear plate  

DOEpatents

One or more disc-shaped angular shear plates each include a region thereon having a thickness that varies with a nonlinear function. For the case of two such shear plates, they are positioned in a facing relationship and rotated relative to each other. Light passing through the variable thickness regions in the angular plates is refracted. By properly timing the relative rotation of the plates and by the use of an appropriate polynomial function for the thickness of the shear plate, light passing therethrough can be focused at variable positions.

Ruda, Mitchell C. (Tucson, AZ); Greynolds, Alan W. (Tucson, AZ); Stuhlinger, Tilman W. (Tucson, AZ)

2009-07-14

341

11. GIRDER PARTIAL ELEVATION AND SECTIONS, 80 FOOT THROUGH PLATE ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

11. GIRDER PARTIAL ELEVATION AND SECTIONS, 80 FOOT THROUGH PLATE GIRDER SPAN. (Also includes a Marking Diagram and a schedule of parts.) American Bridge Company, Ambridge Plant No. 5, sheet no. 1, dated April 7, 1928, order no. F5073. For U.S. Steel Products Company, Pacific Coast Depot, order no. SF578. For Southern Pacific Company, order no. 8873-P-28746. Scale 1/4 inch to one foot. - Napa River Railroad Bridge, Spanning Napa River, east of Soscol Avenue, Napa, Napa County, CA

342

Slippage on Rock Interfaces with Spatially Variable Friction.  

National Technical Information Service (NTIS)

Frictional slippage on material interfaces is pervasive in mechanical problems of all types, but it can be particularly important in geomechanics where slippage occurs at all scales from microcracks to great faults that bound the Earth's tectonic plates. ...

W. A. Olsson

1983-01-01

343

76 FR 38370 - Western Pacific Fisheries; Approval of a Marine Conservation Plan for Pacific Insular Areas...  

Federal Register 2010, 2011, 2012, 2013

...Pacific Insular Areas; Western Pacific Sustainable Fisheries Fund AGENCY: National Marine...INFORMATION CONTACT: Jarad Makaiau, Sustainable Fisheries, NMFS Pacific Islands Regional...be deposited into the Western Pacific Sustainable Fisheries Fund (Fund) for use by...

2011-06-30

344

78 FR 48861 - Western Pacific Fisheries; Approval of a Marine Conservation Plan for Pacific Insular Areas...  

Federal Register 2010, 2011, 2012, 2013

...Pacific Insular Areas; Western Pacific Sustainable Fisheries Fund AGENCY: National Marine...INFORMATION CONTACT: Jarad Makaiau, Sustainable Fisheries, NMFS Pacific Islands Regional...be deposited into the Western Pacific Sustainable Fisheries Fund (Fund) for use by...

2013-08-12

345

Mantle Heterogeneity and Off Axis Volcanism on Young Pacific Lithosphere  

NASA Astrophysics Data System (ADS)

Plate tectonics and mantle plumes explain most volcanism on earth, but there are numerous actively forming linear volcanic chains in the middle of tectonic plates that are not explained by these theories. Using the multidisciplinary geophysical dataset of the MELT and GLIMPSE experiments, we show that associated with 3 volcanic chains west of the East Pacific Rise there are low seismic velocities and densities in the asthenosphere that extend to the East Pacific Rise spreading center. Analogous to the Hawaiian swell, the low-density anomalies produce swells beneath the volcanoes on young seafloor. The associated gravity anomalies are part of a set of gravity lineaments that have been previously interpreted as being due to thermo-elastic cracking of the lithosphere or small-scale convection. The correlation between the surface volcanism and subsurface density and velocity anomalies and their extension to the spreading center suggest that pre-existing, buoyant or fertile asthenospheric mantle heterogeneities are stretched in the direction of plate motion by shear between the plate and the underlying mantle. These heterogeneities seed small-scale convection, producing upwelling and pressure release melting, forming volcanic chains that extend nearly to the ridge axis.

Harmon, N.; Forsyth, D. W.; Weeraratne, D. S.; Webb, S. C.; Yang, Y.

2011-12-01

346

Mantle heterogeneity and off axis volcanism on young Pacific lithosphere  

NASA Astrophysics Data System (ADS)

Plate tectonics and mantle plumes explain most volcanism on earth, but there are numerous actively forming linear volcanic chains in the middle of tectonic plates that are not explained by these theories. Using the multidisciplinary geophysical dataset of the MELT and GLIMPSE experiments, we show that associated with 3 volcanic chains west of the East Pacific Rise there are low seismic velocities and densities in the asthenosphere that extend to the East Pacific Rise spreading center. Analogous to the Hawaiian swell, the low-density anomalies produce swells beneath the volcanoes on young seafloor. The associated gravity anomalies are part of a set of gravity lineaments that have been previously interpreted as being due to thermo-elastic cracking of the lithosphere or small-scale convection. The correlation between the surface volcanism and subsurface density and velocity anomalies and their extension to the spreading center suggest that pre-existing, buoyant or fertile asthenospheric mantle heterogeneities are stretched in the direction of plate motion by shear between the plate and the underlying mantle. These heterogeneities seed small-scale convection, producing upwelling and pressure release melting, forming volcanic chains that extend nearly to the ridge axis.

Harmon, Nicholas; Forsyth, Donald W.; Weeraratne, Dayanthie S.; Yang, Yingjie; Webb, Spahr C.

2011-11-01

347

Tsunami source of the 2011 off the Pacific coast of Tohoku Earthquake  

NASA Astrophysics Data System (ADS)

Tsunami waveform inversion for the 11 March, 2011, off the Pacific coast of Tohoku Earthquake (M 9.0) indicates that the source of the largest tsunami was located near the axis of the Japan trench. Ocean-bottom pressure, and GPS wave, gauges recorded two-step tsunami waveforms: a gradual increase of sea level (˜2 m) followed by an impulsive tsunami wave (3 to 5 m). The slip distribution estimated from 33 coastal tide gauges, offshore GPS wave gauges and bottom-pressure gauges show that the large slip, more than 40 m, was located along the trench axis. This offshore slip, similar but much larger than the 1896 Sanriku "tsunami earthquake," is responsible for the recorded large impulsive peak. Large slip on the plate interface at southern Sanriku-oki (˜30 m) and Miyagi-oki (˜17 m) around the epicenter, a similar location with larger slip than the previously proposed fault model of the 869 Jogan earthquake, is responsible for the initial water-level rise and, presumably, the large tsunami inundation in Sendai plain. The interplate slip is ˜10 m in Fukushima-oki, and less than 3 m in the Ibaraki-oki region. The total seismic moment is estimated as $3.8 × 1022 N m (Mw = 9.0).

Fujii, Y.; Satake, K.; Sakai, S.; Shinohara, M.; Kanazawa, T.

2011-07-01

348

Significant Variations in the Strength of the Lithosphere-Asthenosphere Boundary Across the California Plate Boundary  

NASA Astrophysics Data System (ADS)

To investigate changes in the properties of the lithosphere-asthenosphere transition across a major plate boundary we use Sp common conversion point (CCP) stacked receiver functions to calculate the depth and strength of mantle interfaces beneath a region encompassing most of California, including the boundary between the Pacific and North American Plates, Great Valley, Sierra Nevada, Eastern California Shear Zone and Walker Lane. Using broadband data from permanent stations (including the Southern and Northern California Seismic Networks), the EarthScope Transportable Array, and numerous temporary deployments, we calculated approximately 108,000 individual Sp receiver functions and stacked them in three dimensions using a common conversion point approach. A clear Sp phase consistent with a velocity decrease exists throughout our study region and its depth ranges from 45 to 120 km. The depth of this phase falls within the transition from high velocity lithosphere to slower asthenosphere seen in surface wave tomography and we interpret this phase to be the seismological lithosphere-asthenosphere boundary (LAB). Generally, the depth of the LAB phase varies gradually, with a few exceptions where rapid lateral variations can occur over distances of 25-50 kilometers. For example, in Southern California we observe thinner lithosphere ( ~50 km) beneath the Inner Borderlands, which abruptly transitions to thicker lithosphere beneath the Outer Borderlands (~90 km) and the Western Transverse Range (~85 km), as seen in Lekic et al. (2011). Thinner than average lithosphere (~55 km) is also observed beneath the southern edge of the Great Valley, located in the vicinity of the Isabella Anomaly, and beneath portions of Walker Lane. The most striking feature of the Sp CCP stack is a change in LAB amplitude across the plate boundary. Average phase amplitude beneath crustal blocks translating with motions similar to the Pacific Plate are at least 40% smaller than phase amplitudes for those blocks whose motion more closely aligns with North America. The boundary between the two sets of blocks is often, but not always, co-located with the plate boundary defined by the San Andreas Fault. Where the LAB phase is strong, on the eastern side of the plate boundary, a large and rapid drop in shear velocity is implied, while on the western side of the boundary, the weaker phase indicates a smaller and/or more gradual drop in shear velocity. Comparison to shear-wave splitting and surface wave tomography indicates that the systematic changes in LAB amplitude across the plate boundary are not readily explained by lateral changes in mantle azimuthal anisotropy and surface wave tomography suggests that the variation in LAB amplitude is related to differences in lithospheric mantle velocities (Lin et al. 2011, 2012). In addition, the laterally abrupt nature of the change in LAB amplitude is consistent with an origin in the higher viscosities of the lithosphere. This interpretation implies that some boundaries between crustal blocks observed at the surface persist to the base of the lithosphere.

Ford, H. A.; Fischer, K. M.; Lekic, V.

2012-12-01

349

Mid-Cretaceous tectonic evolution of the Pacific-Phoenix-Farallon triple junction  

Microsoft Academic Search

This dissertation involves interpretation of geophysical data and physical models of plume-ridge fluid dynamics to comment on a major plate boundary reorganization that involved the triple junction joining the Pacific, Phoenix, and Farallon plates during Cretaceous time. The tectonic system examined herein involves a major ridge-ridge-ridge triple junction that was repositioned by hundreds of kilometers contemporaneously with the eruption of

Richard Viso

2005-01-01

350

Plate motions: Simpler than they look  

NASA Astrophysics Data System (ADS)

Plate motions shape Earth's surface through time. These kinematics are of paramount importance to make inferences on sea-level change, mantle/lithosphere interactions and dynamic topography among others. Over the last few decades much effort has gone into plate motion reconstructions at finer temporal resolution from ocean-floor finite-rotations. However, measurements feature substantial noise arising mainly from the challenge of identifying precisely magnetic lineations of the ocean-floor, as well as from uncertainties in geomagnetic reversal timescales. It is therefore standard practise to smooth reconstructions typically by averaging over 2 to 5 Myr-long intervals. But this comes at the price of i) downgrading the native resolution of costly measurements and ii) having to choose one among many smoothing methods that do not yield a unique result. At the native resolution of reconstructions, however, the scenario arising is puzzling, as plate motions vary erratically and significantly over short periods of less than 1 Myr. This equally undermines our ability to make geodynamic inferences, because the rates at which forces need to be built upon plates to explain these kinematics far exceed the most optimistic estimates based, for instance, on the temporal evolution of lithospheric slabs into Earth's mantle. Here we focus on the longest and most temporally-resolved records of ocean-floor spreading ever produced, across mid-oceanic ridges in the Atlantic, Indian and South Pacific Oceans. We show that the largest kinematic changes across these ridges relate to data-noise, and are of apparent nature. We overcome this limitation employing a trans-dimensional hierarchical Bayesian framework, which drastically reduces noise without loss of temporal resolution. Changes in the temporal trends of plate motions occur on timescales no shorter than a few million years, yielding simpler kinematic patterns and more plausible dynamics. This has important implications for the figure of contemporary plate motions observed from space geodesy, which must have remained stable for longer than ever thought.

Sambridge, M.; Iaffaldano, G.; Bodin, T.

2012-12-01

351

Present-day plate motions. [ocean bottom movements  

NASA Technical Reports Server (NTRS)

An instantaneous plate-motion model, Relative Motion 2 (RM2), is obtained by inverting a data set comprising 110 spreading rates, 78 transform fault azimuths, and 142 earthquake slip vectors. RM2 is compared with angular velocity vectors which best fit the data along individual plate boundaries and, while the model performs close to optimally in most regions, attention is directed to those regions which are not suitably described by the model. Reasons for the discrepancies between RM2 and observations for the India-Antarctica plate boundary, the Pacific-India plate boundary, and the east-west trending transform fault azimuths observed in the French-American Mid-Ocean Undersea Study area are discussed.

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

1978-01-01

352

Pole of rotating analysis of present-day Juan de Fuca plate motion  

NASA Technical Reports Server (NTRS)

Convergence rates between the Juan de Fuca and North American plates are calculated by means of their relative, present-day pole of rotation. A method of calculating the propagation of errors in addition to the instantaneous poles of rotation is also formulated and applied to determine the Euler pole for Pacific-Juan de Fuca. This pole is vectorially added to previously published poles for North America-Pacific and 'hot spot'-Pacific to obtain North America-Juan de Fuca and 'hot spot'-Juan de Fuca, respectively. The errors associated with these resultant poles are determined by propagating the errors of the two summed angular velocity vectors. Under the assumption that hot spots are fixed with respect to a mantle reference frame, the average absolute velocity of the Juan de Puca plate is computed at approximately 15 mm/yr, thereby making it the slowest-moving of the oceanic plates.

Nishimura, C.; Wilson, D. S.; Hey, R. N.

1984-01-01

353

A great earthquake rupture across a rapidly evolving three-plate boundary.  

PubMed

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. PMID:19359581

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

2009-04-10

354

Hypervelocity plate acceleration  

SciTech Connect

Shock tubes have been used to accelerate 1.5-mm-thick stainless steel plates to high velocity while retaining their integrity. The fast shock tubes are 5.1-cm-diameter, 15.2-cm-long cylinders of PBX-9501 explosive containing a 1.1-cm-diameter cylindrical core of low-density polystyrene foam. The plates have been placed directly in contact with one face of the explosive system. Plane-wave detonation was initiated on the opposite face. A Mach disk was formed in the imploding styrofoam core, which provided the impulse required to accelerate the metal plate to high velocity. Parametric studies were made on this system to find the effect of varying plate metal, plate thickness, foam properties, and addition of a barrel. A maximum plate velocity of 9.0 km/s has been observed. 6 refs., 17 figs.

Marsh, S.P.; Tan, T.H.

1991-01-01

355

Late Pliocene equatorial Pacific  

Microsoft Academic Search

Late Pliocene foraminiferal Mg\\/Ca and ?18O records from Ocean Drilling Program Hole 806B in the western equatorial Pacific (WEP) reveal warm pool climate evolution during the onset of Northern Hemisphere glaciation, 3.1–2.3 Myr B.P. Mg\\/Ca data indicate an average late Pliocene sea surface temperature (SST) of 27.8°C, a small long-term cooling of 0.3°C between 3.1 and 2.3 Ma, and a

Martín Medina-Elizalde; David W. Lea

2010-01-01

356

Late Pliocene equatorial Pacific  

Microsoft Academic Search

Late Pliocene foraminiferal Mg\\/Ca and delta18O records from Ocean Drilling Program Hole 806B in the western equatorial Pacific (WEP) reveal warm pool climate evolution during the onset of Northern Hemisphere glaciation, 3.1-2.3 Myr B.P. Mg\\/Ca data indicate an average late Pliocene sea surface temperature (SST) of 27.8°C, a small long-term cooling of 0.3°C between 3.1 and 2.3 Ma, and a

Martín Medina-Elizalde; David W. Lea

2010-01-01

357

Ceramic burner plate  

SciTech Connect

This invention relates to a ceramic burner plate using a fiber composite ceramic of low thermal conductivity having gas passages, and provides a burner plate, wherein the burner plate contains a lithium component and such components as nickel, manganese, cobalt, titanium, copper, iron, chromium, and vanadium, to assist in the combustion of gas, and has a surface construction having triangular projections, hexagonal projections or rhombic projections, to ensure increased heat radiation.

Mihara, T.; Kusuda, T.; Noma, K.; Taki, H.

1985-03-12

358

Zone plate interferometer  

NASA Technical Reports Server (NTRS)

A developed form of the Fresner zone-plate interferometer is described. Three basic configurations are distinguished, associated with the real and virtual first order foci of a zone plate. Related versions and higher order variants are also educed. Compensated phase zone plates used in this application are found to produce uniform amplitude wavefronts. The properties of the interferometer in this form are discussed and an example given of its high-quality performance.

Smartt, R. N.

1974-01-01

359

Understanding Plate Motions  

NSDL National Science Digital Library

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

360

Plate Motion Calculator  

NSDL National Science Digital Library

This program calculates tectonic plate motion at any location on Earth using one or more plate motion models. The possible plate motion models are GSRM v1.2 (2004), CGPS (2004), HS3-NUVEL1A, REVEL 2000, APKIM2000.0, HS2-NUVEL1A, NUVEL 1A, NUVEL 1, and two models for ITRF2000. Plates or frames are selected from dropdown lists or can be entered by the user. Position coordinates can be entered in geographic coordinates (decimal degrees, or degrees/minutes/seconds) or in WGS84 cartesian XYZ, as either a single point or multiple points.

Estey, Lou

361

Plates on the Move  

NSDL National Science Digital Library

This fun Web article is part of OLogy, where kids can collect virtual trading cards and create projects with them. Here, they learn about the Earth's outer shell and its constant movement. It begins with an overview that explains tectonic plates. There is an animation that shows recent earthquakes and their relationship to plate boundaries. Students can click to explore 12 individual volcanoes, mountains, hotspots, and earthquakes. For each of the geological formations or events, they will see a map that shows how the plates are moving, an animation about plate interaction, stats, and a story about that particular formation or event.

362

Diabetes in Asian and Pacific Islander Americans  

MedlinePLUS

... in Asian and Pacific Islander Americans Diabetes in Asian and Pacific Islander Americans 4 Steps to Manage ... want to learn more about controlling the disease. Asian Americans/Pacific Islanders and Diabetes (from the Office ...

363

Pacific Educational Research Journal, 1996.  

ERIC Educational Resources Information Center

This first issue of the new "Pacific Educational Research Journal" offers articles covering diverse subjects and using diverse research methods. The new journal represents a rejuvenation of a previous publication to address educational issues specific to the Pacific region. Ethnic groups specifically addressed include Hawaiians, second-generation…

Berg, Kathleen F., Ed.; Lai, Morris K., Ed.

1996-01-01

364

Pacific summary report. [Contains glossary  

Microsoft Academic Search

Lease Sale 80, held on October 17, 1984, was the second areawide lease sale in the Pacific Region. Two future sales for the Pacific Outer Continental Shelf are proposed for 1987. There have been numerous oil and gas discoveries during the past 5 years as industry focuses its exploration efforts on the previously overlooked Miocene Monterey zone. The southern Santa

R. W. Rudolph; P. M. Nikituk

1985-01-01

365

Microstructural modifications in an explosively welded Ti/Ti clad material: I. Bonding interface  

NASA Astrophysics Data System (ADS)

Microstructural modifications of the bonding interface in an explosively welded Ti/Ti clad material using the preset angle standoff configuration with various flyer plate speeds have been studied. Explosive welding was completed at flyer plate speed over 420 m/s. The wavelength and amplitude of the wavy interface increased with increasing flyer plate speed up to 1060 m/s. The planar interface was obtained at flyer plate speed of 1150 m/s. The trace of melting was observed at the bonding interface in the present experimental conditions. It is concluded that the melting layer is responsible for the bonding of explosively welded Ti/Ti clad materials. An anomaly hardening zone was formed at the bonding interface in the clad material welded at flyer plate speed of 1150 m/s. The origin of the observed anomalous hardening has also been discussed.

Nishida, M.; Chiba, A.; Imamura, K.; Minato, H.; Shudo, J.

1993-03-01

366

Did the Cocos-Nazca Spreading Center Form at a Transform Fault During Farallon Plate Break-Up?  

NASA Astrophysics Data System (ADS)

The break-up of the Farallon plate was the most important event during the Early Miocene plate tectonic reorganization of the East Pacific. The opening of a new oceanic spreading center perpendicular to the existing Pacific spreading is unique and probably had far-reaching consequences for the active continental margins of Central- and South America. Most of the original fissure where the Farallon plate split into the Cocos plate and the Nazca plate has already been subducted beneath Central- and South America together with much of the oceanic crust that was formed during the early phase of Cocos-Nazca spreading. This makes a full reconstruction of plate kinematics in the area back to the time of the opening poorly constrained and leaves many questions open about the mechanisms involved and the subduction zones affected by this event. The remains of the fissure in the Cocos- and Nazca plates have been identified offshore Costa Rica and Peru, resp., where they have been investigated with geophysical methods in recent years. The 600 km long still existing segment of the fissure in the Nazca plate has recently been almost completely mapped with swath bathymetry. If the origin of the Farallon break-up was a transform fault then this structure must also be present on the Pacific plate in the area conjugate to the Farallon remains offshore Costa Rica and Ecuador. However, very few ship data were available from this area in the Central Pacific so far and at the scale of satellite altimetry no such structures were detectable. During a R/V Sonne cruise the area in question was investigated with magnetics, gravity, and swath bathymetry to fill a major gap in the framework of East Pacific plate tectonic development and to test the transform fault hypothesis. The magnetic measurements were carried out with a gradiometer and a three-component vectormagnetometer to identify the almost north-south striking seafloor spreading anomalies at low geomagnetic latitude.

Barckhausen, U.; Ranero, C. R.; Weinrebe, W.

2004-12-01

367

Fracture of composite plates containing periodic buffer strips  

NASA Technical Reports Server (NTRS)

Fracture of a composite plate which consists of perfectly bonded parallel load carrying laminates and buffer strips is considered. Fatigue cracks appear and spread in main laminates or in buffer strips or in both perpendicular to the interfaces. The external load is applied to the plate parallel to the strips and away from the crack region. The problem is solved for fully imbedded cracks and for broken laminates or strips. Corresponding stress intensity factors are calculated.

Erdogan, F.; Bakioglu, M.

1974-01-01

368

Seismological evidence for thermally-controlled dehydration reactions in the oceanic crust of the Pacific slab  

Microsoft Academic Search

When the oceanic plate subducts at the trench, the hydrated oceanic crust carries water into the earth in the form of hydrous minerals. Hydrous minerals in the oceanic crust become unstable with increasing pressure and temperature, and dehydration reactions occur accompanied by the release of water to the surroundings. Tsuji et al. (2008) estimated detailed seismic-velocity structure around the Pacific

J. Nakajima; Y. Tsuji; A. Hasegawa

2008-01-01

369

Relative motions of hotspots in the Pacific, Atlantic and Indian Oceans since late Cretaceous time  

Microsoft Academic Search

The history of the motion of the Pacific plate over the Hawaiian hotspot defined by the ages of volcanic rocks along the Hawaiian-Emperor chain is used here to calculate relative positions of hotspots (presumed to be fixed) beneath Iceland, Tristan de Cunha, Reunion, Kerguelen, and St. Paul's Island. The positions are found to lie from several hundred to more than

Peter Molnar; Joann Stock

1987-01-01

370

Geochemical zoning of volcanic chains associated with Pacific hotspots  

NASA Astrophysics Data System (ADS)

Recent Hawaiian volcanism is manifest as two geographically and geochemically distinct groups of volcanoes, the Loa trend in the south and the Kea trend in the north. The differences between the Loa and Kea lavas are attributed to spatial variations in the geochemical structure of the underlying Hawaiian mantle plume. In turn, the Hawaiian plume structure is thought to reflect heterogeneities in its mantle source. Here we compile geochemical data from the Hawaiian and two other volcanic ocean island chains--the Samoan and Marquesas--that formed above mantle plumes upwelling beneath the Pacific plate. We find that the volcanoes at both Samoa and the Marquesas show geographic and geochemical trends similar to those observed at Hawaii. Specifically, two subparallel arrays of volcanoes exist at both locations. In each case, the southern trend of volcanoes has higher radiogenic lead isotope ratios, 208Pb*/206Pb*, and lower neodymium isotope ratios, ?Nd, than those of the corresponding northern trend. We suggest that geochemical zoning may be a common feature of mantle plumes beneath the Pacific plate. Furthermore, we find that the pattern repeats between island chains, with the highest 208Pb*/206Pb* and the lowest ?Ndfound at Samoa in the south and the lowest 208Pb*/206Pb* and the highest ?Nd observed at Hawaii in the north. We infer that isotopically enriched material is preferentially distributed in the lower mantle of the Southern Hemisphere, within the Pacific low seismic velocity zone.

Huang, Shichun; Hall, Paul S.; Jackson, Matthew G.

2011-12-01

371

Plates and their motions  

NASA Technical Reports Server (NTRS)

Work on plate motions published in 1983-1986 and in early 1987 is reviewed. Models for these motions, including global ones for driving forces and local ones for subduction history and back-arc spreading, are addressed. The problem of reference frames, both hotspot and paleomagnetic, is discussed. The assessment of errors in plate motion studies is reviewed.

Jurdy, Donna M.

1987-01-01

372

Magnitogorsk Armor Plate.  

National Technical Information Service (NTIS)

This is a sketch of how the metallurgists at the Magnitogorsk (Magnitka) steel factory in the Soviet Union fulfilled the Soviet Union's need for armor plate during World War II. Since no mills for rolling armor plate existed in Magnitka before the war, en...

Y. Petrov

1968-01-01

373

Polygonal Fresnel zone plates  

Microsoft Academic Search

The performance of Fresnel zone plates having a polygonal boundary between zones has been studied. The contribution of the complex amplitude of each zone is calculated analytically and numerically solved. The case of a continuous phase plate is considered as the limit case in performance for each polygonal shape. This performance is compared with respect to the circular case. Also

Javier Alda; Francisco Javier González

2009-01-01

374

Blue Willow Story Plates  

ERIC Educational Resources Information Center

In the December 1997 issue of "SchoolArts" is a lesson titled "Blue Willow Story Plates" by Susan Striker. In this article, the author shares how she used this lesson with her middle-school students many times over the years. Here, she describes a Blue Willow plate painting project that her students made.

Fontes, Kris

2009-01-01

375

Internet Geography: Plate Tectonics  

NSDL National Science Digital Library

This site is part of GeoNet Internet Geography, a resource for pre-collegiate British geography students and their instructors. This page focuses on the structure of the Earth and the theory of plate tectonics, including continental drift, plate boundaries, the Ring of Fire, and mountains.

376

Embodied User Interfaces: Towards Invisible User Interfaces  

Microsoft Academic Search

There have been several recent examples of user interface techniques in which the user uses a computational device by physically manipulating the device. This paper proposes that these form an interesting new paradigm for user interface design, Embodied User Interfaces. This paper presents and defines this paradigm, and places it in the evolution of user interface paradigms leading towards the

Kenneth P. Fishkin; Thomas P. Moran; Beverly L. Harrison

1998-01-01

377

Fashion Plate Collection  

NSDL National Science Digital Library

There are fashion plates, and then there are the exquisite fashion plates that constitute the University of Washington Libraries digitized collection. The plates were first collected by long-time home economics professor Blanche Payne, who taught at the University from 1927 to 1966. The plates come from leading French, American, and British fashion journals of the 19th and early 20th century and they document many stylistic periods, such as the Empire, Romantic, Victorian, and Edwardian. Visitors will want to start by reading an essay on the collection, and then they should feel welcome to browse the collection of over 400 plates at their leisure, or to browse the collection by subject. One fascinating aspect of the site is an extended excerpt from the 1913 book "Dame fashion" which comments on the history and transformation of various fashions during the 19th century.

378

Biomechanics of bone-fracture fixation by stiffness-graded plates in comparison with stainless-steel plates  

PubMed Central

Background In the internal fixation of fractured bone by means of bone-plates fastened to the bone on its tensile surface, an on-going concern has been the excessive stress-shielding of the bone by the excessively-stiff stainless-steel plate. The compressive stress-shielding at the fracture-interface immediately after fracture-fixation delays callus formation and bone healing. Likewise, the tensile stress-shielding of the layer of the bone underneath the plate can cause osteoporosis and decrease in tensile strength of this layer. Method In order to address this problem, we propose to use stiffness-graded plates. Accordingly, we have computed (by finite-element analysis) the stress distribution in the fractured bone fixed by composite plates, whose stiffness is graded both longitudinally and transversely. Results It can be seen that the stiffness-graded composite-plates cause less stress-shielding (as an example: at 50% of the healing stage, stress at the fracture interface is compressive in nature i.e. 0.002 GPa for stainless steel plate whereas stiffness graded plates provides tensile stress of 0.002 GPa. This means that stiffness graded plate is allowing the 50% healed bone to participate in loadings). Stiffness-graded plates are more flexible, and hence permit more bending of the fractured bone. This results in higher compressive stresses induced at the fractured faces accelerate bone-healing. On the other hand, away from the fracture interface the reduced stiffness and elastic modulus of the plate causes the neutral axis of the composite structure to be lowered into the bone resulting in the higher tensile stress in the bone-layer underneath the plate, wherein is conducive to the bone preserving its tensile strength. Conclusion Stiffness graded plates (with in-built variable stiffness) are deemed to offer less stress-shielding to the bone, providing higher compressive stress at the fractured interface (to induce accelerated healing) as well as higher tensile stress in the intact portion of the bone (to prevent bone remodeling and osteoporosis).

Ganesh, VK; Ramakrishna, K; Ghista, Dhanjoo N

2005-01-01

379

Roving the Pacific: Pacific Manuscripts Bureau Microfilming in the Pacific Islands.  

ERIC Educational Resources Information Center

Provides an overview of microfilming by the Pacific Manuscripts Bureau (PMB), a non-profit organization established in 1968 to identify and preserve archives, manuscripts, and rare printed documents relating to the South Pacific Islands. Describes a 1997 PMB microfilming expedition to Papua New Guinea and the Solomon Islands. (PEN)

Maidment, Ewan