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1

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

2

Imaging the megathrust zone and Yakutat/Pacific plate interface in the 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 relationship to slab seismicity, and (2) the interplate coupled zone where the great 1964 earthquake (magnitude 9.3) exhibited the largest amount of rupture. The joint teleseismic migration of two array datasets based on teleseismic 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 (3-5 km) low-velocity layer (shear wave velocity of ~2.0-2.5 km/s) that is ~20-40% slower than underlying oceanic crustal velocities, and is sandwiched between the subducted slab and the overriding North America plate. The observed low-velocity megathrust layer (with P-to-S velocity ratio 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. The subducted crust below the low-velocity channel has gabbroic velocities with a thickness of ~15 km. Both velocities and thickness of the low-velocity channel abruptly increase downdip in central Alaska, which agrees with previously published 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 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, Y.; Abers, G. A.; Li, J.; Christensen, D. H.; Rondenay, S.

2013-12-01

3

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

4

Plate kinematics in the western Pacific derived from geodetic observations  

E-print Network

Tectonophysics: Plate motions­present and recent (3040), 3040 Marine Geology and Geophysics: Plate tectonics (8150, 8155, 8157, 8158); KEYWORDS: GPS, North Bismarck Plate, Australian Plate, Pacific Plate, tectonic spanning the Australian Plate and the western Pacific region to derive new tectonic models of the motions

Tregoning, Paul

5

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

6

Pacific Plate gravity lineaments: Diffuse extension or thermal contraction?  

Microsoft Academic Search

We detect strain very close to zero on the Pacific Plate relative to the Nazca Plate for Anomalies C8–C13. Our observations are in the region of the satellite gravity lineaments, 10°–40°S in the central Pacific. Strain was measured by comparing fracture zone spacing on the Pacific and Nazca Plates in an approach similar to that of Goodwillie and Parsons [1992

Kathleen Dallas Gans; Douglas S. Wilson; Ken C. Macdonald

2003-01-01

7

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

8

Linking the Late Cretaceous to Paleogene Pacific plate and the Atlantic bordering continents using plate circuits and paleomagnetic data  

Microsoft Academic Search

Late Cretaceous to Paleogene paleomagnetic data from the Pacific plate (the Emperor Seamounts) can be compared with data from the Atlantic bordering continents through the use of plate circuit reconstructions. Here we summarize the uncertainties in all data sets and present formal tests. We report agreement between Late Cretaceous Pacific paleomagnetic data and predictions based on the estimates of non-Pacific

Pavel V. Doubrovine; John A. Tarduno

2008-01-01

9

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

NASA Astrophysics Data System (ADS)

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

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

2002-10-01

10

Updated Pacific Plate Paleomagnetic Pole for Chron 32 (72 Ma), Uncertainties in Pacific- Hotspot Rotations, and Updated Pacific-Hotspot Plate Reconstructions  

NASA Astrophysics Data System (ADS)

A fundamental problem of global tectonics and paleomagnetism is determining what part of apparent polar wander is due to plate motion and what part is due to true polar wander. One approach for separating these is available if the hotspots are tracking the motion of the mantle beneath the asthenosphere. To make progress on these questions and assumptions, high-quality paleomagnetic poles for the Pacific plate are needed, as well as estimates of Pacific plate motion relative to the hotspots and the uncertainties in such motion. Here we present results for all three. First, we present an updated Pacific paleomagnetic pole for chron 32 (72 Ma) determined from the skewness of magnetic anomaly 32 (Petronotis et al. 1999). The updated paleomagnetic pole corrects for the spreading-rate dependence of anomalous skewness (Dyment & Arkani-Hamed 1995, Koivisto et al. 2006). We furthermore build on a new method for objectively estimating plate-hotspot rotations and their uncertainties (Andrews et al. 2005) and present an updated reconstruction of the Pacific plate relative to the hotspots at 72 Ma along with the uncertainties in the reconstructions. We combine paleomagnetic and plate reconstructions to determine the total uncertainty of the 72 Ma Pacific plate paleomagnetic pole reconstructed into the Pacific hotspot frame of reference. The results indicate that the pole is distinctively different from the present spin axis, but consistent with our estimate of the coeval paleomagnetic pole for the Indo-Atlantic hotspots. These results therefore indicate that the hypothesis that the Indo-Atlantic hotspots have been fixed relative to the Pacific hotspots cannot be rejected from paleomagnetic data.

Koivisto, E.; Gordon, R. G.

2007-12-01

11

The strength of polyaxial locking interfaces of distal radius plates  

Microsoft Academic Search

BackgroundCurrently available polyaxial locking plates represent the consequent enhancement of fixed-angle, first-generation locking plates. In contrast to fixed-angle locking plates which are sufficiently investigated, the strength of the new polyaxial locking options has not yet been evaluated biomechanically. This study investigates the mechanical strength of single polyaxial interfaces of different volar radius plates.

Konrad L. Hoffmeier; Gunther O. Hofmann; Thomas Mückley

2009-01-01

12

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

13

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

14

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

15

New Reference Models for Pacific Absolute Plate Motion  

NASA Astrophysics Data System (ADS)

Absolute plate motion (APM) models are commonly derived by assuming that age-progressive seamount chains represent the surface expressions of mantle plumes; the chain geometries thus record the relative motion between plumes and plates. Traditionally, plumes have been assigned zero motion (i.e., the fixed hotspot hypothesis), and with this assumption the trails directly reflect plate motion. However, since the early 1970s arguments from sedimentary facies and marine magnetics have been marshaled against the fixity of hotspots, perhaps culminating with more recent and direct inferences of anomalous paleolatitudes for several seamounts in both the Emperor and Louisville chains. These data can broadly be explained by drifting plumes, but paleomagnetic data remain scarce and may allow for some true polar wander; furthermore, several age progressions are incomplete or inconsistent and the present locations of some hotspots are uncertain. Finally, APM models with moving hotspots derive largely from mantle flow modeling whose predictions do not match observations directly. Here, I present new absolute plate motion models for the Pacific plate back to 150 Ma. The first model assumes fixed hotspots and is meant to serve as a reference model representing the classic fixed hotspot hypothesis. It is an updated version of the Wessel and Kroenke [2008] model but now including all available chains, recently published age data and processed using improved modeling techniques. The second model uses the same data but also attempts to honor available data on hotspot mobility. It is intended to be a "work in progress" model that will be updated as additional paleolatitude or age data become available. These models can serve as test beds for tectonic hypothesis and be used to identify seamount chain segments where additional paleomagnetic or age observations would have the most impact.

Wessel, P.

2012-12-01

16

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

17

Paleomagnetic Tests of Pacific Plate Reconstructions and Implications for Motion Between Hotspots  

NASA Astrophysics Data System (ADS)

The plate-motion circuit through the South Pacific and Antarctica is shown to fail paleomagnetic tests of consistency. These failures imply that reconstructions of Pacific basin plates relative to surrounding plates inferred from this circuit are systematically in error and that estimates of motion between hotspots inferred from this circuit are probably too large. Therefore, the motions between hotspots remain poorly known and may be much smaller than previously estimated.

Acton, Gary D.; Gordon, Richard G.

1994-03-01

18

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

19

Geometry and relative motion of the Philippine sea plate and Pacific plate beneath the Kanto-Tokai district, Japan  

Microsoft Academic Search

The recent acquisition of high-density and improved seismic data by the Kanto-Tokai (K-T) Observational Network of the National Research Institute of Earth Science and Disaster Prevention requires the revision of conventional plate configuration models for the K-T district. We propose a new interpretation of the configuration and relative motion of the Philippine Sea (PHS) plate. Pacific (PAC) plate, and Eurasian

Mizuho Ishida

1992-01-01

20

The Kanto Subduction Zone: Seismogenic Layers, Slab Deformations and Volcanism Associated With the two Subducting Philippine Sea Plate and Pacific Plate  

NASA Astrophysics Data System (ADS)

Understanding the details of complex seismicity and tectonic processes in the Kanto subduction zone, which is located at the junction of northeastern Japan arc and Izu-Ogasawara arc, is important in various fields. The most important factor characterizing plate convergence in the Kanto area is that the young, hot and laterally heterogeneous forearc portion of the Philippine Sea plate (PHS) descends into the mantle wedge and collides with the old and cold Pacific plate (PAC). The interaction among overriding, subducting and mutually colliding plates, each having different plate movement, is responsible for complex seismic activity and various subduction modes as have been observed by recent seismic and geodetic networks. Among several noticeable features of seismicity, we focus on the intermediate-depth seismicity of the double Wadati-Benioff seismic zones (WBZ) of the Pacific slab subducting beneath the Izu-Ogasawara arc, and its relation with the overlapping boundary of two slabs, i.e., the contact interface between the two slabs (PHS-PAC interface). Along the upper seismic plane of WBZ, we recognize a remarkable band of intermediate-depth seismicity, which distributes in southeast-northwest direction with a systematic increase of depth northwest from about 90 to 150 km. Focal mechanism solutions of this band are characterized by normal faultings. Associated with this intense seismicity band, we examine the intersection of the bottom of PHS and the upper boundary of PAC (the loci of the deeper limit of PHS-PAC interface), by taking cross-sections of hypocenter distributions. We find the deeper limit of interface also locates southeast-northwest in the depth range between 70 and 100 km and almost parallel with the intense seismicity band with distance 30-40 km apart. To explain reasonably the northwest deepening of the intermediate-depth seismic band, we use the model of dehydration embrittlement of serpentine and temperature structure in the slab proposed by Yamasaki and Seno (2003, JGR, 108). Because PHS-PAC interface deepen northwest, the colder temperature structure of the Pacific slab underneath may remain deeper northwest. As a result the dehydration loci and the corresponding seismogenic layer in the slab may deepen northwest. Further in the overlying asthenospheric mantle the ascending path of aqueous fluid and magma formation point may also be deepened northwest. This inference accords with the location of the volcanic front in western Kanto, which runs northwest above the upper seismic plane of WBZ across isodepth lines with depth range bewteen about 110 and 160 km along the Izu-Ogasawara arc.

Noguchi, S.

2004-12-01

21

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

22

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.

Perton, M.; Levesque, D.; Monchalin, J.-P.; Lord, M. [National Research Council Canada, 75 de Mortagne Blvd, Boucherville, Quebec, J4B 6Y4 (Canada); Smith, J. A.; Rabin, B. H. [Idaho National Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-6188 (United States)

2013-01-25

23

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

24

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

25

New constraints on relative motion between the Pacific Plate and Baja California microplate (Mexico) from GPS measurements  

Microsoft Academic Search

We present a new surface velocity field for Baja California using GPS data to test the rigidity of this microplate, calculate its motion in a global reference frame, determine its relative motion with respect to the North American and the Pacific plates, and compare those results to our estimate for Pacific-North America motion. Determination of Pacific Plate motion is improved

C. Plattner; R. Malservisi; T. H. Dixon; P. Lafemina; G. F. Sella; J. Fletcher; F. Suarez-Vidal

2007-01-01

26

Improved Late Cretaceous and early Cenozoic Paleomagnetic apparent polar wander path for the Pacific plate  

Microsoft Academic Search

Understanding of Pacific plate tectonics and geodynamics is aided by refinement of the plate's apparent polar wander path (APWP). We improved the Late Cretaceous and early Cenozoic APWP by analyzing a large, diverse paleomagnetic data set that combines core sample, seamount magnetic anomaly model, and marine magnetic anomaly skewness data. Our preferred APWP has five mean paleomagnetic poles representing the

Melissa Beaman; William W. Sager; Gary D. Acton; Luca Lanci; Josep Pares

2007-01-01

27

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

28

Changes in Pacific Absolute Plate Motion and Formation of Oceanic Flood Basalt Plateaus  

NASA Astrophysics Data System (ADS)

The origin of the large oceanic flood basalt plateaus that are prominent features of the central western Pacific Basin remains unclear. Major changes in Pacific Absolute Plate Motion (APM) have been identified as occurring at 145, 125, 96, and 47 Ma. Formation of the Shatsky Rise (~145 Ma), the Ontong Java Plateau (122+ Ma), the Southern Hess Rise (95±5 Ma), and the Louisiade Plateau (~48 Ma) appear to coincide with these changes. A smaller, but still prominent change in Pacific APM also occurred at 110 Ma when the Northern Hess Rise formed. Although these concurrent events may simply be chance occurrences, initiation of plate tectonic reorganizations upon arrival of mantle plume heads also was proposed by Ratcliff et al. (1998), who suggested that the mantle plume head delivery of hot material to produce flood basalts also had the potential to trigger reorganizations of plate motions. It should be noted, however, that Pacific Rim subduction zone development also coincides with these APM changes, and that the actual cause and effect of each change in APM has yet to be clearly established. Here we present a modified Pacific APM model that uses several older seamount chains (Musicians, Ratak-Gilbert-Ellice, the Wake trails, and the Liliuokalani trails) to constrain the oldest Pacific plate motion using the hybrid technique of Wessel et al (2006).

Kroenke, L. W.; Wessel, P.

2006-12-01

29

Long-lived Seamount Volcanism in the Western Pacific, and Early Cretaceous Motion of the Pacific Plate  

NASA Astrophysics Data System (ADS)

Most seamounts, islands, and atolls on the present western Pacific Plate were formed by submarine intraplate volcanism, mainly during the Cretaceous. Some seamount chains in the West Pacific Seamount Province, including the Magellan group, define hotspot trails and plate motions. Samples of peralkaline rhyolite pillow lava and radiolarian-bearing pelagic sedimentary rocks were collected by the Japanese submersible Shinkai6500 from Quesada Seamount (western Magellan Seamount group), on the oceanward slope of the Mariana Trench. The Ar-Ar age of the peralkaline rhyolite is 129.3+/-2.6 Ma, about 10 m.y. younger than the radiolarian age of the oldest intercalated tuffaceous claystone (early Berriasian: approximately 140 Ma). The claystone contains fragments of alkali-basalt glass of the shield-building volcanic stage. Because peralkaline rhyolite commonly erupts during the last stage of shield activity, volcanic activity appears to have lasted for approximately 10 m.y. at Quesada Seamount. Slow Early Cretaceous motion of the Pacific Plate permitted the Quesada edifice to remain above the source hotspot for a long time. At Hemler Seamount on the northeastern tip of Quesada Seamount, a Late Cretaceous Ar-Ar age has previously been reported for nephelinite phenocrysts in strongly alkaline basalt, which also records the rejuvenated stage of a long-lived Early Cretaceous seamount volcano. Such seamount trails can be used to calculate the absolute Early Cretaceous motion of the Pacific Plate; in addition to the Quesada to Hemler SW to NE trail, others have been previously reported from Shatsky Rise and western Mid-Pacific Mountain.

Hirano, N.

2002-12-01

30

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

31

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

32

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

33

New constraints on relative motion between the Pacific Plate and Baja California microplate (Mexico) from GPS measurements  

NASA Astrophysics Data System (ADS)

We present a new surface velocity field for Baja California using GPS data to test the rigidity of this microplate, calculate its motion in a global reference frame, determine its relative motion with respect to the North American and the Pacific plates, and compare those results to our estimate for Pacific-North America motion. Determination of Pacific Plate motion is improved by the inclusion of four sites from the South Pacific Sea Level and Climate Monitoring Project. These analyses reveal that Baja California moves as a quasi-rigid block but at a slower rate in the same direction, as the Pacific Plate relative to North America. This is consistent with seismic activity along the western edge of Baja California (the Baja California shear zone), and may reflect resistance to motion of the eastern edge of the Pacific Plate caused by the `big bend' of the San Andreas fault and the Transverse Ranges in southern California.

Plattner, C.; Malservisi, R.; Dixon, T. H.; LaFemina, P.; Sella, G. F.; Fletcher, J.; Suarez-Vidal, F.

2007-09-01

34

Elastostatic bending of a bimaterial plate with a circular interface  

NASA Astrophysics Data System (ADS)

The elastostatic bending of an arbitrarily loaded bimaterial plate with a circular interface is analysed. It is shown that the deflections in the composite solid are directly related to the deflection in the corresponding homogeneous material by integral and differential operators. It is further shown that, by a simple transformation of elastic constants, the Airy stress function induced in the composite by a stretching singularity can be deduced from the deflection induced by a bending singularity. This result is significant for reduction of mathematical labour and for systematic construction of solutions for more complex structures with circular geometry.

Ogbonna, Nkem

2014-09-01

35

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

36

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

37

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 northwestern 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 motion directions, and cannot be responsible for the Hawaiian-Emperor bend (HEB), confirming previous interpretations that the 47 Ma HEB does not primarily reflect an absolute plate motion event.

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

2014-08-01

38

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

39

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

40

Viscous fingering in the Earth's mantle beneath western North American and the Pacific plate  

NASA Astrophysics Data System (ADS)

The recent advent of high resolution seismic tomography provided by the USArray project in western North American and ocean bottom seismometer deployments on the seafloor have shown a critical link between surface geology, volcanic observations and deep mantle structure. A unique pattern of volcanic lineaments have been observed on the south Pacific seafloor which form a group of parallel linear volcanic chains. Recently, similar features have been proposed on continental plates in western North America as a group of Cenozoic volcanic lineaments consisting of the Yellowstone, St George, Colorado Mineral Belt, and Jimenez volcanic trends. In both the North American continent and Pacific ocean case, an array of seismometers were deployed and seismic tomography images reveal a set of regularly spaced, linear, parallel low velocity anomalies that align in the direction of plate motion and correlate with surface volcanism. Here we consider a fluid dynamic model of viscous fingering in the asthenospheric mantle which links deep mantle flow to surface volcanic observations. We present results from physical fluid experiments scaled to mantle dynamics which indicate that Saffman-Taylor instabilities or viscous fingering may form in the asthenosphere beneath moving tectonic plates. Scaling indicates that the wavelength of fingering (l_f) is strongly dependent on asthenospheric channel thickness (B) as l_f = 4B. The presence of a mobile overriding plate acts to align fingers in the direction of plate motion propagating both upstream and downstream. Tomography images indicate that fingering wavelengths may be significantly larger beneath continental plates compared to oceanic plates. Further scaling between laboratory fluid experiments and mantle seismic tomography including comparison of surface volcanic lineaments, tomographic imaging, and lithosphere-asthenosphere thickness will be presented.

Weeraratne, D. S.; Parmentier, E.; Lekic, V.

2012-12-01

41

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

42

The Displacement Rate Across the Pacific Plate due to Horizontal Thermal Contraction  

NASA Astrophysics Data System (ADS)

Horizontal thermal contraction of oceanic lithosphere is expected to impart a relative velocity between various points on the same tectonic plate [Kumar and Gordon, 2009]. The ridge-parallel component of thermal contraction is especially high in young oceanic lithosphere as the contraction rate is inversely proportional to the age of the lithosphere. Here we present a simple kinematic model for the horizontal velocity field due to thermal contraction of a rectangular portion of lithosphere between two fracture zones. We build on this model to make a flat-earth approximation of the relative velocity of different points on the Pacific plate between Baja California and the Heezen fracture zone. Unlike the model of Kumar and Gordon [1999], our model includes the effects of age offsets across fracture zones. Lithosphere near Baja California is found to approach lithosphere near the Heezen fracture zone at a rate of about 3 mm/yr, which is similar in magnitude to the non-closure in the Pacific-North America global plate motion circuit found by DeMets, Gordon, and Argus [2009]. Implications for global plate motion circuits will be discussed.

Gordon, R. G.; Mishra, J. K.

2009-12-01

43

Revised Pacific-Antarctic plate motions and geophysics of the Menard Fracture Zone  

NASA Astrophysics Data System (ADS)

A reconnaissance survey of multibeam bathymetry and magnetic anomaly data of the Menard Fracture Zone allows for significant refinement of plate motion history of the South Pacific over the last 44 million years. The right-stepping Menard Fracture Zone developed at the northern end of the Pacific-Antarctic Ridge within a propagating rift system that generated the Hudson microplate and formed the conjugate Henry and Hudson Troughs as a response to a major plate reorganization ˜45 million years ago. Two splays, originally about 30 to 35 km apart, narrowed gradually to a corridor of 5 to 10 km width, while lineation azimuths experienced an 8° counterclockwise reorientation owing to changes in spreading direction between chrons C13o and C6C (33 to 24 million years ago). We use the improved Pacific-Antarctic plate motions to analyze the development of the southwest end of the Pacific-Antarctic Ridge. Owing to a 45° counterclockwise reorientation between chrons C27 and C20 (61 to 44 million years ago) this section of the ridge became a long transform fault connected to the Macquarie Triple Junction. Following a clockwise change starting around chron C13o (33 million years ago), the transform fault opened. A counterclockwise change starting around chron C10y (28 millions years ago) again led to a long transform fault between chrons C6C and C5y (24 to 10 million years ago). A second period of clockwise reorientation starting around chron C5y (10 million years ago) put the transform fault into extension, forming an array of 15 en echelon transform faults and short linking spreading centers.

Croon, Marcel B.; Cande, Steven C.; Stock, Joann M.

2008-07-01

44

An Evaluation of the Fixed Hotspot Hypothesis for the Pacific Plate  

NASA Astrophysics Data System (ADS)

Using geometry and ages from 12 Pacific seamount chains, we recently constructed two new Pacific absolute plate motion models that extend our self-consistent and high-resolution models back to 145 Ma. The WK08-A model maps the full uncertainty in the age progressions into uncertainties in rotation opening angles, yielding a relatively smooth plate motion model. The WK08-G model relaxes the mapping of age uncertainties in order to better isolate secondary geometry changes seen along many co-registered chains. Both models have been used to assess the viability of the fixed hotspot hypothesis in the Pacific. In constructing these models, we found that only a small group of age samples had to be discarded on the grounds that they were discordant with the dominant trends. We were able to connect plate motions for pre- and post-Emperor age intervals by including the Ratak-Gilbert-Ellice, Liliuokalani and Musicians trails in our analysis. However, as no active hotspot locations exist for the older chains their inclusion adds additional model parameters. Both age and geometry misfits increase with age, reflecting the observed increase in age uncertainties and the broader and less distinct nature of the older trails. Paleomagnetic observations from the Emperor seamount chain have been interpreted to suggest that these seamounts must have formed at latitudes significantly more northerly than the present location of the Hawaii hotspot, implying a drifting mantle plume. At the same time, new estimates of the age of the Hawaii- Emperor bend places bend formation at a time of global plate reorganization. We will present a complete analysis of inter-chain distances between coeval radiometric samples from Pacific chains and compare these distances to the inter-hotspot distances at the present time. Significant departures from the current hotspot separations would be direct and unequivocal evidence of motion between the Pacific hotspot reference frame and the spin axis and as such complement the paleomagnetic analysis. Preliminary results suggest the Emperor segment data may indicate an increase in hotspot separation.

Wessel, P.; Kroenke, L. W.

2008-12-01

45

Cretaceous Pacific plate movement beneath SE China: Evidence from episodic volcanism and related intrusions  

NASA Astrophysics Data System (ADS)

Extensive Late Mesozoic igneous rocks in SE China have been widely considered to be generated under the paleo-Pacific tectonic regime, the plate subduction model, however, remains controversial. This study focuses on the Cretaceous volcanic rocks in northwestern Zhejiang Province. Zircon U-Pb age determination indicates that Cretaceous volcanism in northwestern Zhejiang took place at three episodes of 140-130, 130-127 and 123-118 Ma, in good agreement with the coeval lower volcanic series in southeastern Zhejiang, but lacking the episode at 110-88 Ma corresponding to the upper volcanic series. The Cretaceous volcanic rocks in Zhejiang therefore show an oceanward younging trend. In situ zircon Hf isotope analyses of three episodes of volcanics yield ?Hf(t) values of - 11.2 to - 8.7, -4.8 to - 2.4 and - 4.4 to + 2.2, respectively. The entire sequences display typical isotopic features of magma mixing, implying progressive involvement of juvenile component. Based on systematical researches on the Cretaceous volcanic rocks and a series of granitoid plutons in Zhejiang, it is also identified that the juvenile component involvement gradually occurred from the inland to the coast under an enhanced lithospheric extensional tectonic setting. All the observations in this study indicate the northwestward paleo-Pacific plate subduction with episodic slab rollback which triggered the arc system to retreat towards the Pacific Ocean, rather than the southwestward subduction related to the ridge subduction along the Lower Yangtze River belt.

Liu, Lei; Xu, Xisheng; Xia, Yan

2014-02-01

46

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

47

Pacific absolute plate motion since 145 Ma: An assessment of the fixed hot spot hypothesis  

NASA Astrophysics Data System (ADS)

Using the geometry and ages from 12 Pacific seamount chains, we have determined two new absolute plate motion models that now extend our self-consistent and high-resolution models with covariance estimates back to 145 Ma. The WK08-A model maps the full uncertainty in the age progressions into uncertainties in rotation opening angles, yielding a relatively smooth plate motion model. The WK08-G model relaxes the mapping of age uncertainties in order to better isolate secondary geometry changes seen along many coregistered chains. Both models have been used to assess the viability of the fixed hot spot hypothesis in the Pacific. In determining the models, we found that only a small group of age samples had to be discarded on the grounds that they were discordant with the dominant trends. We were able to connect plate motions for pre- and post-Emperor age intervals by including the Ratak-Gilbert-Ellice and Musicians trails in our analysis. However, as no active hot spot locations exist for the older chains, their inclusion adds additional model parameters. Both age and geometry misfits increase with age, reflecting the observed increase in age uncertainties and the general widening of trails. Secondary (and short-lived) changes in absolute plate motion mapped in WK08-G appear to correlate with the timing and sense of motion of known Pacific Rim tectonic events. Analysis of interchain distances between coeval samples from the Hawaii and Louisville chains suggests possible discrepancies during the older Emperor stage that are compatible with predictions of hot spot drift. We computed a new apparent polar wander path for the Pacific and found a high degree of correspondence with paleomagnetically derived paths, as long as solutions allowing for anomalous skewness were included in the latter. Our polar wander path suggests that there might have been some true polar wander during the Emperor stage, complemented by a smaller amount of hot spot drift than otherwise required. We show that chain geometries and ages, combined with future paleolatitude determinations from additional sites and chains could enable an observation-based description of both hot spot and plate motions without relying on predictions of hot spot drift derived from mantle flow calculations.

Wessel, Paul; Kroenke, Loren W.

2008-06-01

48

Global Plate Reconstructions, Pacific Plate Apparent Polar Wander, and the Origin of the Bend in the Hawaiian-Emperor Chain  

NASA Astrophysics Data System (ADS)

A key tectonic event near 50 Ma B.P. is the formation of the bend in the Hawaiian-Emperor hotspot track. A central question about the formation of the bend is whether it represents a change in plate motion or a change in motion of the Hawaiian hotspot or some combination of the two. In this presentation I will review results of mainly recent work with Rice collaborators and consider the implications for the bend. Koivisto et al. (2011) present an updated test of the fixed-hotspot approximation comparing the observed positions of Indo-Atlantic hotspot tracks with those predicted from Pacific plate hotspot tracks and the global plate motion circuit through Antarctica. This updated study indicates 2 to 5 mm/a motion between hotspots for the past 48 Ma,that is, since the formation of the bend in the Hawaiian-Emperor chain. The confidence limits include zero and thus are consistent with no motion between Pacific hotspots and Indo-Atlantic hotspots for the past 48 Ma. This does not necessarily imply that the hotspots are fixed, as the uncertainties allow for motion up to 8 to 12 mm/a, but does exclude higher rates. When we examine predictions for times preceding 48 Ma B.P. we obtain very different results, however, the apparent rates of inter-hotspot motion increase to about 45-55 ± 20 mm/a. One explanation is that hotspots moved rapidly relative to one another before 48 Ma B.P. and then slowed dramatically at roughly the age of the elbow. An alternative explanation is that as we go further back in time the global plate motion circuit through Antarctica is less reliable. The possibility of motion between East and West Antarctica will be considered. Paleomagnetic data can be used to discriminate between these alternatives. The paleomagnetic results of Petronotis & Gordon [1989], Acton & Gordon [1994], Horner-Johnson & Gordon [2010], Zheng et al. [this meeting], and Boswell et al. [this meeting] will be reviewed and implications discussed.

Gordon, R. G.

2011-12-01

49

Exposed plate interface in the European Alps reveals fabric styles and gradients related to an ancient seismogenic coupling zone  

Microsoft Academic Search

We present observations from a continuous exposure of an ancient plate interface in the depth range of its former seismogenic zone in the central Alps of Europe related to Late Cretaceous-early Tertiary subduction and accretion of the South Penninic lower plate underneath the Adriatic upper plate. The material forming the exposed plate interface zone has experienced flow and fracturing over

Raik Bachmann; Onno Oncken; Johannes Glodny; Wolfgang Seifert; Viktoria Georgieva; Masafumi Sudo

2009-01-01

50

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

51

Early Tertiary rupture of the Pacific plate: 1700 km of dextral offset along the Emperor trough-Line Islands lineament  

NASA Astrophysics Data System (ADS)

Between 67 and ˜40 Ma ago a northwest-southeast-trending fracture system over 8000 km long split the Pacific plate and accumulated at least 1700 km of dextral offset between the east and west portions. This system, here named the Emperor fracture zone (EFZ) system, consisted of several segments, one along the present trace of the Emperor trough and another along the Line Islands, joined by short spreading ridges. The EFZ terminated at its northern end against the Kula-Pacific ridge, and at its southern end in a ridge-transform system, called the Emperor spreading system, which extended to the west, north of Australia. The finite angular velocity vector describing the relative motion between the East and West Pacific plates is ˜0.6°/Ma about a pole at 36°N, 70°W. This vector, added to the known Early Tertiary motion of the Pacific plate with respect to the global hotspot reference frame, accounts in large part for the NNW trend of the Emperor seamount chain relative to the WNW Hawaiian trend, without violation of the integrity of the Antarctic plate. The Meiji-Emperor and Emperor-Hawaiian bends date, respectively, the initiation (˜67 Ma ago) and cessation (˜40 Ma ago) of seafloor spreading on the Emperor spreading system. The postulated Early Tertiary relative motion along the EFZ between the East and West Pacific plates explains (1) the present misalignment of the two sets of magnetic bights of the Pacific, (2) the abrupt truncation of eastern Pacific bathymetric lineaments against the Emperor trough and Line Islands, (3) the contrast in paleolatitude between the eastern and western Pacific as indicated by paleomagnetic and sedimentologic studies, and (4) the anomalous gravity signature of the central Hawaiian ridge that indicates that the ridge loaded thin hot lithosphere.

Farrar, Edward; Dixon, John M.

1981-05-01

52

Geometry and relative motion of the Philippine Sea Plate and Pacific Plate beneath the Kanto-Tokai District, Japan  

NASA Astrophysics Data System (ADS)

The recent acquisition of high-density and improved seismic data by the Kanto-Tokai (K-T) Observational Network of the National Research Institute of Earth Science and Disaster Prevention requires the revision of conventional plate configuration models for the K-T district. We propose a new interpretation of the configuration and relative motion of the Philippine Sea (PHS) plate, Pacific (PAC) plate, and Eurasian (EUR) plate on the basis of the distribution of hypocenters, velocity structure, and focal mechanisms in the K-T district. The new model for the configuration of the PHS and PAC slabs clearly delineates the PHS slab subducting northwestward beneath the K-T district from the Sagami and Suruga troughs and the PAC slab subducting westward beneath the PHS slab from the Japan trench. The thickness of the descending PHS slab is estimated to be 30 ± 5 km. The proposed configuration of the PHS slab is significantly different from those obtained by other researchers, including our own previous study. The new model is fully consistent with global plate motion data. The new model leads to an interpretation of the tectonic processes taking place beneath the K-T district. For the Sagami trough wing of the PHS slab, the northeastern portion of the slab is dipping northwestward in direct contact with the upper surface of the PAC slab; the southwestern portion carrying the Izu Peninsula has been bent upward, because of its buoyancy, producing the observed contorted shape. For the Suruga trough wing, the dip direction of the PHS slab gradually changes from northwestward at the eastern portion to northward at the western portion. The new model also indicates the presence of offset within the PHS slab between the Sagami and Suruga trough wings. This area is characterized by a low level of seismic activity, the absence of a high-velocity structure, and the presence of Quaternary volcanoes. It seems reasonable to speculate that the distribution of Quaternary volcanic edifice construction is controlled by the location of the offset within the PHS slab. In view of this new model, the tectonic processes of large earthquakes which occurred recently in the studied area are also reexamined.

Ishida, Mizuho

1992-01-01

53

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

54

Structure and deformation of the Kermadec forearc in response to subduction of the Pacific oceanic plate  

NASA Astrophysics Data System (ADS)

The Tonga-Kermadec forearc is deforming in response to on-going subduction of the Pacific Plate beneath the Indo-Australian Plate. Previous research has focussed on the structural development of the forearc where large bathymetric features such as the Hikurangi Plateau and Louisville Ridge seamount chain are being subducted. Consequently, knowledge of the `background' forearc in regions of normal plate convergence is limited. We report on an ˜250-km-long multichannel seismic reflection profile that was shot perpendicular to the Tonga-Kermadec trench at ˜28°S to determine the lateral and temporal variations in the structure, stratigraphy and deformation of the Kermadec forearc resulting solely from Pacific Plate subduction. Interpretation of the seismic profile, in conjunction with regional swath bathymetry data, shows that the Pacific Plate exhibits horst and graben structures that accommodate bending-induced extensional stresses, generated as the trenchward dip of the crust increases. Trench infill is also much thicker than expected at 1 km which, we propose, results from increased sediment flux into and along the trench. Pervasive normal faulting of the mid-trench slope most likely accommodates the majority of the observed forearc extension in response to basal subduction erosion, and a structural high is located between the mid- and upper-trench slopes. We interpret this high as representing a dense and most likely structurally robust region of crust lying beneath this region. Sediment of the upper-trench slope documents depositional hiatuses and on-going uplift of the arc. Strong along-arc currents appear to erode the Kermadec volcanic arc and distribute this sediment to the surrounding basins, while currents over the forearc redistribute deposits as sediment waves. Minor uplift of the transitional Kermadec forearc, observed just to the north of the profile, appears to relate to an underlying structural trend as well as subduction of the Louisville Ridge seamount chain 250 km to the north. Relative uplift of the Kermadec arc is observed from changes in the tilt of upper-trench slope deposits and extensional faulting of the basement immediately surrounding the Louisville Ridge.

Funnell, M. J.; Peirce, C.; Stratford, W. R.; Paulatto, M.; Watts, A. B.; Grevemeyer, I.

2014-11-01

55

Tears or thinning? Subduction structures in the Pacific plate beneath the Japanese Islands  

NASA Astrophysics Data System (ADS)

The nature of a subduction zone at depth is affected by the evolution of its tectonic system, and the geometry of the trench line can change over time due to slab roll-back or the arrival of a distinctive feature with the incoming oceanic lithosphere. The configuration of the plate has to accommodate such changes with buckling, thinning or the formation of tears depending on the rate of influx to the trench. Tomographic imaging is commonly used to recognise the presence of such tears through marked reductions in wavespeed anomalies in localised zones. A good example is provided by Pacific plate subduction beneath the Japanese Islands. A horizontal tear in the plate below 300 km depth can be recognised at the southern end of the Izu-Bonin arc associated with the change in slab morphology to the much steeper Mariana arc. Beneath southern Honshu a break in the fast wavespeeds associated with the Pacific plate has been described as a tear based on the evidence of converted phases from the edge of the zone and tensional focal mechanisms for seismic events in the tear zone. In the north, close to the Hokkaido bend in the subduction zone, the reduction in the shear wavespeed anomaly is just as dramatic, but here the characteristics of high frequency guided waves from deep earthquakes indicate continuity of slab material with thinning of the slab. The thinned slab has less wavespeed contrast within the affected cells and so appears in the tomographic images as a weakened anomaly. The various modes of slab deformation represent different ways in which the subducted material accommodates the strains imposed by the evolution of the geometry of the subduction scenario. Not all significant reductions in wavespeed anomalies represent tears and thus it is important that such interpretations be checked against the characteristics of wave propagation through the zone.

Kennett, B. L. N.; Furumura, T.

2010-05-01

56

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

57

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

NASA Astrophysics Data System (ADS)

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

McQuarrie, N.

2004-12-01

58

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

59

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

60

A Maastrichtian palaeomagnetic pole for the Pacific plate from a skewness analysis of marine magnetic anomaly 32  

NASA Astrophysics Data System (ADS)

The asymmetry (skewness) of marine magnetic anomaly 32 (72.1-73.3 Ma) on the Pacific plate has been analysed in order to estimate a new palaeomagnetic pole. Apparent effective remanent inclinations of the seafloor magnetization were calculated from skewness estimates of 108 crossings of anomaly 32 distributed over the entire Pacific plate and spanning a great-circle distance of ~12 000 km. The data were inverted to obtain a palaeomagnetic pole at 72.1 degN, 26.8 degE with a 95 per cent confidence ellipse having a 4.0 deg major semi-axis oriented 98 deg clockwise of north and a 1.8 deg minor semi-axis; the anomalous skewness is 14.2 deg+/-3.7 deg. The possible dependence of anomalous skewness on spreading rate was investigated with two empirical models and found to have a negligible effect on our palaeopole analysis over the range of relevant spreading half-rates, ~25 to ~90 mm yr^-1. The new pole is consistent with the northward motion for the Pacific plate indicated by coeval palaeocolatitude and palaeoequatorial data, but differs significantly from, and lies to the northeast of, coeval seamount poles. We attribute the difference to unmodelled errors in the seamount poles, mainly in the declinations. Comparison with the northward motion inferred from dated volcanoes along the Hawaiian-Emperor seamount chain indicates 13 deg of southward motion of the Hawaiian hotspot since 73 Ma. When the pole is reconstructed with the Pacific plate relative to the Pacific hotspots, it differs by 14 deg-18 deg from the position of the pole relative to the Indo-Atlantic hotspots. This has several possible explanations including bias in one or more of the palaeomagnetic poles, motion between the Pacific and Indo-Atlantic hotspots, and errors in plate reconstructions relative to the hotspots.

Petronotis, Katerina E.; Gordon, Richard G.

1999-10-01

61

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

62

A 65 Ma palaeomagnetic pole for the Pacific plate from the skewness of magnetic anomalies 27r-31.  

NASA Astrophysics Data System (ADS)

The authors use the skewness of seafloor-spreading magnetic anomalies 27r-31 to determine a revised Late Maastrichtian - early Palaeocene palaeomagnetic pole for the Pacific plate. They used numerical experiments to estimate the potential information in magnetic profiles that had not been previously analysed for skeweness information.

Acton, G. D.; Gordon, R. G.

1991-08-01

63

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

64

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

65

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

66

Thermal study of interface between the Orbiter cold plate and typical Shuttle spacecraft payload flight electronics  

NASA Technical Reports Server (NTRS)

Spacelab provides a set of Freon line plumbing and cold plates for experiment equipments which are located in the Shuttle pallet and which need active thermal control. The reported study deals with the thermal problem of attaching a Command and Data Handling module with various electronic boxes whose combined footprints on the baseplate are much larger than the cold plate. A description of two modules and the cold plate assembly in the pallet is presented and a thermal model description is provided. The method employed in modeling heat pipes-honey-comb matrix is based upon an effective conductance between the heat pipe vapor and the walls of the heat pipe. The considered thermal models and a computer program are used to perform steady-state thermal analyses. The temperature gradients in the large module baseplate attached to the small cold plate are predicted as a function of the interface plate thickness.

Hwangbo, H.; Coyle, M. J.

1979-01-01

67

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

68

A new GPS velocity field for the Pacific Plate - Part 2: implications for fault slip rates in western California  

NASA Astrophysics Data System (ADS)

Lower and upper bounds for present deformation rates across faults in central California between the San Andreas Fault and Pacific coast are estimated from a new Global Positioning System (GPS) velocity field for central, western California in light of geodetic evidence presented in a companion paper for slow, but significant deformation within the Pacific Plate between young seafloor in the eastern Pacific and older seafloor elsewhere on the plate. Transects of the GPS velocity field across the San Andreas Fault between Parkfield and San Juan Buatista, where fault slip is dominated by creep and the velocity field thus reveals the off-fault deformation, show that GPS sites in westernmost California move approximately parallel to the fault at an average rate of 3.4 ± 0.4 mm yr-1 relative to the older interior of the Pacific Plate, but only 1.8 ± 0.6 mm yr-1 if the Pacific Plate frame of reference is corrected for deformation within the plate. Modelled interseismic elastic deformation from the weakly coupled creeping segment of the San Andreas Fault is an order-of-magnitude too small to explain the southeastward motions of coastal sites in western California. Similarly, models that maximize residual viscoelastic deformation from the 1857 Fort Tejon and 1906 San Francisco earthquakes mismatch both the rates and directions of GPS site motions in central California relative to the Pacific Plate. Neither thus explains the site motions southwest of the San Andreas fault, indicating that the site motions measure deformation across faults and folds outboard of the San Andreas Fault. The non-zero site velocities thus constitute strong evidence for active folding and faulting outboard from the creeping segment of the San Andreas Fault and suggest limits of 0-2 mm yr-1 for the Rinconada Fault slip rate and 1.8 ± 0.6 to 3.4 ± 0.4 mm yr-1 for the slip rates integrated across near-coastal faults such as the Hosgri, San Gregorio and San Simeon faults.

DeMets, C.; Márquez-Azúa, Bertha; Cabral-Cano, Enrique

2014-12-01

69

Life and Death of the Resurrection Plate: Evidence for an Additional Plate in the NE Pacific in Paleocene-Eocene Time  

NASA Astrophysics Data System (ADS)

We propose an additional plate in the northeastern Pacific Ocean in Paleocene-Eocene time. The Resurrection Plate, named after exposures of the Resurrection Peninsula ophiolite near Seward Alaska, was located northeast of the Kula Plate and north of the Farallon plate. We interpret concurrent near-trench magmatism in southern Alaska and the northwestern US as evidence for two slab windows associated with trench-ridge-trench (TRT) triple junctions that formed the boundaries of the Resurrection Plate. A compilation of geochronology from 100 Ma to the present from Alaska to Oregon displayed in movie form shows the following features. The Sanak-Baranof belt of near trench-intrusions in southern Alaska records a west to east migration of the northern TRT triple junction along a 2100-km-long section of coastline between 61-50 Ma. In Oregon, Washington, and southern Vancouver Island, voluminous basaltic volcanism of the Siletz River Volcanics, Crescent, and Metchosin Formations occurred between ~66-48 Ma. Lack of an age progression indicates this southern triple junction did not migrate significantly. Synchronous near-trench magmatism in southeastern Alaska, on southern Vancouver Island and beneath Puget Sound at ~50 Ma indicates a spreading center was subparallel to the margin of southeastern Alaska and British Columbia and was subducted all at once. We interpret 50 Ma as the approximate time of death of the Resurrection plate. The existence and demise of the Resurrection plate explains: 1) rapid northward terrane transport between 70 and 50 Ma; 2) uplift and magmatism in the Coast Mountains prior to 50 Ma; 3) cessation of magmatism in the Coast Mountains of BC and SE Alaska around 50 Ma; and 4) a major change in Pacific-North America plate motion and birth of the Queen Charlotte transform margin around 50 Ma. Death of the Resurrection plate was a contributing factor in the extensional collapse of the southern Canadian Cordilleran foreland fold and thrust belt after 50 Ma, it may provide an explanation for the puzzling Challis magmatic belt, and it gives a mechanism for either demise of the Kula plate at 50 Ma or near-trench magmatism after 50 Ma in Oregon.

Haeussler, P. J.; Bradley, D. C.; Wells, R.; Rowley, D. B.; Miller, M.; Otteman, A.; Labay, K.

2001-12-01

70

Origin and evolution of marginal basins of the NW Pacific: Diffuse-plate tectonic reconstructions  

E-print Network

Formation of the gigantic linked dextral pull-apart basin system in the NW Pacific is due to NNE- to ENE-ward motion of east Eurasia. This mainly was a response to the Indo-Asia collision which started about 50 Ma ago. The displacement of east Eurasia can be estimated using three aspects: (1) the magnitude of pull-apart of the dextral pull-apart basin system, (2) paleomagnetic data from eastern Eurasia and the region around the Arctic, and (3) the shortening deficits in the Large Tibetan Plateau. All the three aspects indicate that there was a large amount (about 1200 km) of northward motion of the South China block and compatible movements of other blocks in eastern Eurasia during the rifting period of the basin system. Such large motion of the eastern Eurasia region contradicts any traditional rigid plate tectonic reconstruction, but agrees with the more recent concepts of non-rigidity of both continental and oceanic lithosphere over geological times. Based on these estimates, the method developed for resto...

Xu, Junyuan; Ben-Avraham, Zvi; Yu, Ho-Shing

2012-01-01

71

GPS measurements of crustal deformation within the Pacific-Australia plate boundary zone in Irian Jaya, Indonesia  

Microsoft Academic Search

Abstract Global Positioning System (GPS) measurements made in 1991, 1992 and 1993 provide preliminary estimates of slip distribution between the Australian and Pacific plates in Irian Jaya, Indonesia. We interpret the GPS results with constraints from earthquake mechanisms and slip vectors, recent marine surveys, and geology. Three GPS sites in southeastern,Irian Jaya show,motions,that are within,10 mm\\/yr,of the expected,motion,of Australia. A

S. s. o. Puntodewo; R. Mccaffreyb; E. Calaisc; Y. Bockc; J. Raisa; C. Subaryaa

1994-01-01

72

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

73

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

NASA Technical Reports Server (NTRS)

Data obtained by Mark III VLBI measurements of radio signals from permanent and mobile VLBI sites for 5.5 years of observations, starting in October 1982, were used to derive a picture of the earth crust deformation near the North America-Pacific plate boundary. The data, which included the vector positions of the VLBI sites and their rate of change, were used for comparison with a number of lithospheric deformation models based upon the concept that the motions of points near the North America-Pacific plate boundary are a linear combination of North America and Pacific velocities. The best of these models were found to fit 95 percent of the variance in 139 VLBI length and transverse velocity observations. Instantaneous shear deformation associated with plate tectonics is apparently developing in a zone 450 km wide paralleling the San Andreas Fault; some of this deformation will be recovered through elastic rebound, while the rest will be permanently set through plastic processes. Because the VLBI data have not been collected for a significant fraction of the earthquake cycle, they cannot discriminate between elastic and plastic behaviors.

Ward, Steven N.

1988-01-01

74

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

75

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

E-print Network

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

Plattner, Christina

2009-01-01

76

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

77

Mesozoic plate-motion history below the northeast Pacific Ocean from seismic images of the subducted Farallon slab  

PubMed

The high-resolution seismic imaging of subducted oceanic slabs has become a powerful tool for reconstructing palaeogeography. The images can now be interpreted quantitatively by comparison with models of the general circulation of the Earth's mantle. Here we use a three-dimensional spherical computer model of mantle convection to show that seismic images of the subducted Farallon plate provide strong evidence for a Mesozoic period of low-angle subduction under North America. Such a period of low-angle subduction has been invoked independently to explain Rocky Mountain uplift far inland from the plate boundary during the Laramide orogeny. The computer simulations also allow us to locate the largely unknown Kula-Farallon spreading plate boundary, the location of which is important for inferring the trajectories of 'suspect' terrain across the Pacific basin. PMID:10830960

Bunge; Grand

2000-05-18

78

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

79

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

80

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

81

A new fluid-solid interface algorithm for simulating fluid structure problems in FGM plates  

NASA Astrophysics Data System (ADS)

The capability to track material interfaces, especially in fluid structure problems, is among the advantages of meshless methods. In the present paper, the Smoothed Particle Hydrodynamics (SPH) method is used to investigate elastic-plastic deformation of AL and ceramic-metal FGM (Functionally Graded Materials) plates under the impact of water in a fluid-solid interface. Instead of using an accidental repulsive force which is not stable at higher pressures, a new scheme is proposed to improve the interface contact behavior between fluid and solid structure. This treatment not only prevents the interpenetration of fluid and solid particles significantly, but also maintains the gap distance between fluid and solid boundary particles in a reasonable range. A new scheme called corrected smooth particle method (CSPM) is applied to both fluid and solid particles to improve the free surface behavior. In order to have a more realistic free surface behavior in fluid, a technique is used to detect the free surface boundary particles during the solution process. The results indicate that using the proposed interface algorithm together with CSPM correction, one can predict the dynamic behavior of FGM plates under the impact of fluid very promisingly.

Eghtesad, A.; Shafiei, A. R.; Mahzoon, M.

2012-04-01

82

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

83

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

84

Observation of prominent S-to-P converted phases from the deep-subducted Western Pacific slab interfaces and their mineralogical implications  

NASA Astrophysics Data System (ADS)

A prominent S-to-P converted phase is observed between the direct P and S waves in regional seismograms at South Korean stations for the deep-focus earthquakes in the western Pacific subducting slab. The focal depths of the events are ~ 577 km. The amplitudes of the phase reach to ~50 % of amplitude of direct P waves. These anomalous S-to-P converted waves appear to develop on the subducting slab interfaces at a depth of ~300 km beneath stations considering their traveltimes and phase polarization. Development of such large-amplitude slab-converted phase requires a strong seismic contrasts across the slab interface in the upper-mantle. Hydrous gabbro in the oceanic crust may produce a low-velocity layer at the top of slab, yielding high impedance contrasts across the slab interface. The observation suggests that the gabbro-to-eclogite reaction appears to occur along slab interface at the upper mantle. The water contents and slab geometry are constrained by comparing the synthetic seismograms for various cases with observed seismograms. We finally discuss the geodynamic implication for water distribution in the slab, which may be crucial for understanding the volcanic evolution and deep-subduction process in the northeastern Eurasian plate.

He, X.; Hong, T.

2013-12-01

85

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

NASA Astrophysics Data System (ADS)

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

Vaghri, A.; Hearn, E. H.

2011-12-01

86

Spreading-rate-dependent anomalous skewness and the estimate of the chron 32 palaeomagnetic pole for the Pacific plate  

NASA Astrophysics Data System (ADS)

Palaeomagnetic poles can be determined from asymmetry (skewness) of marine magnetic anomalies. Early works applying the skewness method were limited by the discovery of an apparently systematic error known as anomalous skewness (Cande 1976). Anomalous skewness can be thought of as the systematic difference between the observed skewness and the skewness predicted by a simple magnetization model with rectangular 2-D layer 2A prisms of alternating polarity separated by vertical boundaries. In the early works, anomalous skewness could be isolated for anomalies with counterparts across a mid-ocean ridge, but was much harder to estimate for anomalies with subducted counterparts, as is mostly the case in the Pacific plate. Petronotis et al. (1992) presented a solution to this problem by simultaneously estimating anomalous skewness and a best-fitting palaeomagnetic pole from skewness data from a single plate. In their approach, anomalous skewness is assumed to be identical for different crossings of the same plate and any spreading-rate dependence of anomalous skewness is neglected. Nonetheless, anomalous skewness of marine magnetic anomalies is observed to decrease with increasing spreading rate and become negligible above spreading rates of about 50 mm yr-1 (e.g. Roest et al. 1992; Dyment et al. 1994). Dyment &Arkani-Hamed (1995) proposed a model in which the magnetic structure of the oceanic lithosphere is dependent on spreading rate with parameters adjusted to fit the observed spreading- rate dependence of anomalous skewness for some key anomalies. Here we apply their model to determine a new Maastrichtian palaeomagnetic pole for the Pacific plate from skewness estimates of magnetic anomaly 32. Previously Petronotis &Gordon (1999) obtained a palaeopole assuming spreading-rate independent anomalous skewness for the same data used here. They also investigated the possible dependence of anomalous skewness on spreading rate and found it to have negligible effect on their palaeopole. Using the anomalous skewness correction predicted by the model of Dyment &Arkani-Hamed, we find that the data require no additional anomalous skewness, thus providing some validation of their model. Moreover, it appears that the new pole position stays near the original pole position irrespective of what set of spreading rates is used to estimate anomalous skewness. The largest uncertainties in the anomalous-skewness correction are due to uncertainties in spreading rates, which are mainly due to uncertainties in the reversal time scale. The results support the assertion of Petronotis et al. that Pacific plate poles determined from low- palaeolatitude sites are insensitive to anomalous skewness.

Koivisto, E.; Gordon, R.; Dyment, J.; Arkani-Hamed, J.

2006-12-01

87

Orbital replaceable unit-cold plate dry thermal interface concept and test measurements  

NASA Astrophysics Data System (ADS)

A cold plate to an ORU dry thermal interface design that would meet both the joint thermal performance of 5000 W/sq m K and allow easy replacement in space during repeated in-orbit servicing is proposed. The present concept involves a cylindrical arrangement of flexible outer heat pipes which are pneumatically forced onto a central inner heat pipe. A thin coating of a low melting point alloy on the heat pipes provides a detachable continuous thermal path across the joint and allows the performance requirements to be achieved even in the case of failure of the pressure.

Nikanpour, D.; Sill, H. K.; Kreeb, H.

88

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

89

Change of tectono-stratigraphic regime in the Australian plate during the 99 Ma (mid-Cretaceous) and 43 Ma (mid-Eocene) swerves of the Pacific  

NASA Astrophysics Data System (ADS)

The clockwise bend at 99 Ma (mid-Cretaceous) in linear volcanic chains in the tropical Pacific coincides with a change from pre-99 Ma head-on Chilean-type subduction of the Pacific plate beneath eastern Gondwana to 99 43 Ma sinistral oblique Mariana-type subduction and strike-slip breakup by simple sea-floor spreading between Australia and Antarctica and by backarc spreading in the southwest Pacific. The 99 Ma breakup of Australia from Antarctica is documented by a mid-Cretaceous unconformity. This tectono-stratigraphic change founded modern Australia, with a mountain chain along an upper plate margin in the east and lowlands on the lower plate margin in the south. The counterclockwise bend at 43 Ma (mid-Eocene)—the Emperor-Hawaiian bend—coincides with the onset of structure in the Challenger Rift of New Zealand, the Eromanga-Cooper basin of central Australia, and the oil-shale grabens of coastal Queensland.

Veevers, J. J.

2000-01-01

90

Streaking in Cascadia ETS Events and Implications for the Subduction Plate Interface  

NASA Astrophysics Data System (ADS)

The manner in which episodic tremor and slow slip (ETS) propagates across the subduction plate interface provides constraints on its properties and the physical processes involved. We have been examining catalogs of tremor locations to study propagation patterns during ETS. Tremor in the large Cascadia ETS events propagates mainly via three modes: 1) the slow along-strike advance of ETS, 2) rapid tremor reversals (RTRs) that propagate back from the tremor front in an opposite direction to the along-strike advance, but at speeds 10-40 times faster (Houston et al., Nature Geoscience, 2011), and 3) streaks, even faster migrations of tremor parallel to the plate-convergence direction at speeds ~ 70 km/hr (Ghosh et al., G3, 2011). The UW Seismology group has recently deployed an EarthScope-funded seismic experiment, the Array of Arrays, to image tremor more precisely with eight subarrays. A 15-month catalog of high-resolution tremor locations has been generated based on the triangulation of back-projected beams from the subarrays. We detect tremor streaks in this catalog automatically and systematically determine streak propagation properties. Key issues for constraining streak-generation processes include systematic differences between up- and down-dip traveling streaks, how streak properties may depend on depth, and whether streaks accelerate or decelerate during propagation. Stacking automatically-detected streaks can address some of these issues. Two approaches to automatically detecting streaks have been developed and applied to the M6.8 2010 ETS. One method declares a streak when averaged epicenters continue to move in a roughly constant direction for more than 10 km. The second declares a streak if epicenters during a specified time interval, say 20 min, are sufficiently well-correlated with time. The two methods agree well and detect several streaks per day of 15-30 min duration with speeds consistent with those inferred for the 2008 ETS. Although the detection methods have no azimuthal bias, most of the detected streaks align with one direction; furthermore, that direction lies much closer to the plate convergence direction than directly down-dip (the down-dip and plate convergence directions differ significantly along most of Cascadia). Many more streaks are detected in the actual catalog than in randomized versions, in which the times within each hour are permuted. These results lend substantial credence to convergence-parallel streaks as real features of ETS. Streak propagation patterns suggest the plate interface is anisotropic along the slip direction. The ubiquity of streaking parallel to plate convergence implies control by corrugated or smeared structures on the plate interface. This could occur via such structures controlling the orientation of an advancing slip pulse, which could carry streaks along its peak (Rubin, G3, 2011), or more directly via heterogeneous physical properties (such as rheology or permeability) elongated in the convergence direction. In this connection, we note that daily tremor bands in Cascadia ETS are also often oriented parallel to the convergence direction whether the ETS is advancing north or south, even though the direction of ETS advance would be expected to affect the orientation of a slip pulse on a homogeneous interface.

Houston, H.; Ghosh, A.

2011-12-01

91

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

92

A reappraisal of seafloor spreading lineations in the Gulf of California: Implications for the transfer of Baja California to the Pacific plate and estimates of Pacific-North America motion  

Microsoft Academic Search

An analysis of seafloor spreading lineations in the southern Gulf of California demonstrates that divergence of the Baja peninsula from North America since 3.6 Ma has been significantly slower than Pacific-North America (PA-NA) motion estimated solely from closures of global plate circuits. This discrepancy remains unchanged or increases with modifications to the plate circuits and kinematic data used to predict

Charles DeMets

1995-01-01

93

Anatomy of the western Java plate interface from depth-migrated seismic images  

USGS Publications Warehouse

Newly pre-stack depth-migrated seismic images resolve the structural details of the western Java forearc and plate interface. The structural segmentation of the forearc into discrete mechanical domains correlates with distinct deformation styles. Approximately 2/3 of the trench sediment fill is detached and incorporated into frontal prism imbricates, while the floor sequence is underthrust beneath the d??collement. Western Java, however, differs markedly from margins such as Nankai or Barbados, where a uniform, continuous d??collement reflector has been imaged. In our study area, the plate interface reveals a spatially irregular, nonlinear pattern characterized by the morphological relief of subducted seamounts and thicker than average patches of underthrust sediment. The underthrust sediment is associated with a low velocity zone as determined from wide-angle data. Active underplating is not resolved, but likely contributes to the uplift of the large bivergent wedge that constitutes the forearc high. Our profile is located 100 km west of the 2006 Java tsunami earthquake. The heterogeneous d??collement zone regulates the friction behavior of the shallow subduction environment where the earthquake occurred. The alternating pattern of enhanced frictional contact zones associated with oceanic basement relief and weak material patches of underthrust sediment influences seismic coupling and possibly contributed to the heterogeneous slip distribution. Our seismic images resolve a steeply dipping splay fault, which originates at the d??collement and terminates at the sea floor and which potentially contributes to tsunami generation during co-seismic activity. ?? 2009 Elsevier B.V.

Kopp, H.; Hindle, D.; Klaeschen, D.; Oncken, O.; Reichert, C.; Scholl, D.

2009-01-01

94

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

95

True polar wander since 32 Ma B.P.: A paleomagnetic investigation of the skewness of magnetic anomaly 12r on the Pacific plate  

NASA Astrophysics Data System (ADS)

We test the fixed hot spot and fixed spin axis hypotheses through a paleomagnetic investigation of the skewness of crossings of magnetic anomaly 12r (32 Ma B.P.) between the Galapagos and Clarion fracture zones on the Pacific plate. We focus on this region for three reasons. First, numerical experiments show that these crossings, of all those available from the Pacific plate, should contain the most information about the location of the 32 Ma B.P. paleomagnetic pole for the Pacific plate. Second, many of the available crossings are from vector aeromagnetic profiles, which have superior signal-to-noise ratios. Third, the rate of seafloor spreading recorded in these crossings exceeds the threshold (half rate of 50 mm a-1) above which anomalous skewness is negligible. The new pole (83.5°N, 44.6°E) has compact 95% confidence limits (ellipse with major semiaxis length of 3.1° toward 84° clockwise from north and minor semiaxis length of 1.2°) and is not subject to the biases inherent in other methods for estimating Pacific plate paleomagnetic poles. The pole differs significantly by ?5° from the pole predicted if the Pacific hot spots have been fixed with respect to the spin axis, thus demonstrating, for the first time from paleomagnetic data, that Pacific hot spots have moved relative to the spin axis since the formation of the elbow in the Hawaiian-Emperor chain. The pole is consistent, however, with previously published paleomagnetic poles in a reference frame fixed relative to Indo-Atlantic hot spots. Thus, the new results require no motion between Pacific and Indo-Atlantic hot spots since 32 Ma B.P. Instead, superimposed on whatever motion occurs between hot spots, as expected for true polar wander.

Horner-Johnson, Benjamin C.; Gordon, Richard G.

2010-09-01

96

The Interface of Pacific and Other Knowledges in a Supplementary Education Site  

ERIC Educational Resources Information Center

Because identity (language and culture) are central to Pacific knowledge and knowledge construction processes, Pacific students' educational experiences should be viewed through a cultural lens that sees Pacific knowledge and practices as valid and valued. This study explores the relationship between culture and educational outcomes as seen…

Fairbairn-Dunlop, Peggy

2014-01-01

97

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

98

Late cretaceous pelagic sediments, volcanic ASH and biotas from near the Louisville hotspot, Pacific Plate, paleolatitude ???42??S  

USGS Publications Warehouse

Dredging on the deep inner slope of the Tonga Trench, immediately north of the intersection between the Louisville Ridge hotspot chain and the trench, recovered some Late Cretaceous (Maestrichtian) slightly tuffaceous pelagic sediments. They are inferred to have been scraped off a recently subducted Late Cretaceous guyot of the Louisville chain. In the vicinity of the Louisville hotspot (present location 50??26???S, 139??09???W; Late Cretaceous location ???42??S, longitude unknown) Late Cretaceous rich diatom, radiolarian, silicoflagellate, foraminiferal and coccolith biotas, accumulated on the flanks of the guyot and are described in this paper. Rich sponge faunas are not described. ?Inoceramus prisms are present. Volcanic ash is of within-plate alkalic character. Isotope ratios in bulk carbonate ??18O - 2.63 to + 0.85, ??13C + 2.98 to 3.83) are normal for Pacific Maestrichtian sediments. The local CCD may have been shallower than the regional CCD, because of high organic productivity. In some samples Late Cretaceous materials have been mixed with Neogene materials. Mixing may have taken place on the flanks of the guyot during transit across the western Pacific, or on the trench slope during or after subduction and offscraping about 0.5 Ma. ?? 1989.

Ballance, P.F.; Barron, J.A.; Blome, C.D.; Bukry, D.; Cawood, P.A.; Chaproniere, G.C.H.; Frisch, R.; Herzer, R.H.; Nelson, C.S.; Quinterno, P.; Ryan, H.; Scholl, D. W.; Stevenson, A.J.; Tappin, D.G.; Vallier, T.L.

1989-01-01

99

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

100

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

Microsoft Academic Search

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

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

2010-01-01

101

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

102

Decelerating Nazca-South America and Nazca-Pacific Plate motions  

NASA Astrophysics Data System (ADS)

Space geodetic estimates of the rate of Nazca-South America convergence and Nazca-Pacific spreading averaging over several years show that present day rates are significantly slower than the 3 million year average NUVEL-1A model. The implied rates of deceleration are consistent with longer term trends extending back to at least 20 Ma, about the time of initiation of Andes growth, and may reflect consequences of ongoing subduction and construction of the Andes, e.g., increased friction and viscous drag on the subducted slab as the leading edge of South America thickens.

Norabuena, Edmundo O.; Dixon, Timothy H.; Stein, Seth; Harrison, Christopher G. A.

103

Small repeating earthquakes and inter-plate aseismic slip in and around the Kanto district after the 2011 off the Pacific coast of Tohoku earthquake  

NASA Astrophysics Data System (ADS)

The 2011 off the Pacific coast of Tohoku earthquake (Mw9.0) was the largest earthquake in recorded history in Japan. For the stress changes by this earthquake, the seismic activities around the Kanto district including Tokyo metropolitan area have changed significantly. We detect many small repeating earthquakes beneath this area. They may suggest induced interplate aseismic slips at the subducting Philippine Sea (PHS) plate and the subducting Pacific (PAC) plate. The upper boundary of the PAC plate contacts the PHS plate beneath this area, but the northeastern limit of the PHS plate remains poorly understood. In this study, we first estimate the configuration of the subducting PHS plate and PAC plate and the limit of PHS plate beneath the Kanto district by applying receiver function (RF) analysis. Thereafter, we investigate the space-time characteristics of the inter-plate aseismic slips from sequences of small repeating earthquakes beneath the Kanto district after the 2011 Tohoku earthquake. We made many vertical cross-sections of depth-converted RF images to investigate plate configurations. Telemetric seismographic network data covered on the Kanto district 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 a good S/N and epicentral distance between 30 and 90 degrees based on USGS catalogues. As a result, we elucidated the configuration of PHS plate and PAC plate beneath the Kanto district. The PHS plate subducts to the northwest and the direction coincides with plate motion. The northeastern limit of PHS plate is estimated from the change of plate thickness, which gradually decreases to the northeast after contact with the underlying PAC plate beneath the Tokyo metropolitan area. There is little seismic activity from the limit to the thickness of 5 km. Using these plate configurations, we classified small repeating earthquakes and estimated inter-plate aseismic slip at each plate. Although the resultant slip-rates before the 2011 main-shock correspond to the relative plate motion in these areas, they increased in both plates after the event. At the PAC plate, they occur around the coseismic slip area of the largest aftershock and cannot detect within it. Furthermore, the slip areas expanded to the deeper part beyond the northeastern limit of the PHS plate. The slip-rate peaked immediately after the 2011 main-shock and gradually decreases to the velocity of relative plate motion in the next one year or two. The rate of decrease was rapid at the trench-side of the largest aftershock. On the other hand, the slip-rate at the PHS plate increased significantly at relatively deeper part of the west of the largest aftershock. The location with fast slip-rates changes at different times. These slip-rates increases may be caused by localized stress changes with coseismic slips and/or post-seismic deformation.

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

2013-12-01

104

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

PubMed

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

Flesch; Holt; Haines; Shen-Tu

2000-02-01

105

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

106

True Polar Wander and Hotspot Fixity: A Paleomagnetic Investigation of the Skewness of Magnetic Anomaly 12r (32 Ma B.P.) on the Pacific Plate  

NASA Astrophysics Data System (ADS)

Prior studies have shown that Pacific hotspots and Indo-Atlantic hotspots have moved in approximate unison relative to the spin axis since 65 Ma B.P. [Morgan, 1981; Gordon and Cape, 1981; Gordon, 1982] and since 56 Ma B.P. [Petronotis et al., 1994], which is most simply interpreted as true polar wander. In contrast, Pacific hotspots and Indo-Atlantic hotspots give conflicting results for 72 Ma B.P. and for 81 Ma B.P., which may indicate motion between Pacific hotspots and Indo-Atlantic hotspots [Tarduno and Cottrell, 1997; Petronotis et al., 1999; Tarduno et al., 2003]. Thus it is important to estimate Pacific plate apparent polar wander (APW) for more time intervals. From such estimates the APW of Pacific hotspots can be inferred and compared with that of Indo-Atlantic hotspots [e.g., Besse and Courtillot 2002]. Here we present a study of the skewness of anomaly 12r between the Galapagos and Clipperton and between the Clipperton and Clarion fracture zones. We chose this region for several reasons: First, numerical experiments, like those conducted by Acton and Gordon [1991], indicate that magnetic profiles between the Galapagos and Clarion fracture zones should contain the most information about the Pacific plate paleomagnetic pole for chron C12r (32 Ma B.P.). Second, in these two spreading rate corridors, spreading half rates range from 72 to 86 mm/a and therefore have negligible anomalous skewness, given that they exceed ?50 mm/a [Roest et al., 1992; Dyment et al. 1994]. Third, vector aeromagnetic profiles are available for analysis. One of the challenges to interpreting magnetic anomalies in low latitudes where the anomalies strike nearly north-south is the very low amplitude of the signal relative to the noise, the latter of which can be especially intense near the present magnetic equator due to the amplification of diurnal variation by the equatorial electrojet. Previously we showed that vector aeromagnetic profiles record low-latitude Pacific plate magnetic anomalies due to seafloor spreading with much greater clarity than do shipboard profiles in the same region [Horner-Johnson and Gordon, 2003]. The pole that we obtain has compact 95% confidence limits. We reduce the profiles to this pole and show that the appearance of the reduced-to-the-pole profiles is sensitive to the assumed pole position. The new pole shows that Pacific hotspots have moved significantly relative to the spin axis during the formation of the Hawaiian island and seamount chain, and is consistent with Pacific hotspots having moved in approximate unison with Indo-Atlantic hotspots relative to the spin axis since 32 Ma B.P.

Gordon, R. G.; Horner-Johnson, B. C.

2010-12-01

107

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

108

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

109

Diffuse Pacific-North American plate boundary: 1000 km of dextral shear inferred from modeling geodetic data  

USGS Publications Warehouse

Geodetic measurements tell us that the eastern part of the Basin and Range Province expands in an east-west direction relative to stable North America, whereas the western part of the province moves to the northwest. We develop three-dimensional finite element representations of the western United States lithosphere in an effort to understand the global positioning system (GPS) signal. The models are constrained by known bounding-block velocities and topography, and Basin and Range Province deformation is represented by simple plastic (thermal creep) rheology. We show that active Basin and Range spreading by gravity collapse is expected to have a strong southward component that does not match the GPS signal. We can reconcile the gravitational component of displacement with observed velocity vectors if the Pacific plate applies northwest-directed shear stress to the Basin and Range via the Sierra Nevada block. This effect reaches at least 1000 km east of the San Andreas fault in our models. ?? 2011 Geological Society of America.

Parsons, T.; Thatcher, W.

2011-01-01

110

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

111

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  

Microsoft Academic Search

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

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

2009-01-01

112

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

113

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

E-print Network

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

Brothers, Daniel Stephen

2009-01-01

114

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

115

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

NASA Astrophysics Data System (ADS)

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

Spinler, Joshua C.

116

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

117

Tapping of an Enriched Asthenospheric Layer at the Samoan Islands along Fractures Produced by Deformation of the Pacific Plate near the Tonga Trench  

NASA Astrophysics Data System (ADS)

Samoan basalts derive from mantle sources having a strong EMII signature (high 87Sr/86Sr, K, Rb, and Ba). Stratigraphy tied with radiometric dates reveal an increase, maximum, and waning of the influence of the EMII mantle component in the combined history of the shield volcanoes of successively younger islands, Upolu, Tutuila, and Ta\\`{ }u. This fluctuation is superimposed on, and independent of, Hawaiian-like shield-building, waning alkalic, and post-caldera alkalic stages of volcanism. It is inconsistent with any regular arrangement of EMII within the structure of a postulated mantle plume. The islands are surface expressions of longer east-trending submarine volcanic ridges or lineaments. These and several older shield lineaments appear in satellite-derived bathymetry as en echelon, straight or slightly curving volcanic ridges, each 100-500 km long. They formed in eastward succession on the Pacific Plate as it rode to the west past the strongly curving transform corner of the nearby Tonga trench. They trend more to the east than nested sigmoidal ridges of the mid-plate Hawaiian Islands, and are not nested. Another lineament ~500 km long is superimposed obliquely over the older Upolu and Tutuila lineaments, which it capped with locally extensive Quaternary-Historic post-erosional eruptives over a distance of >200 km. It closely parallels the transform portion of the trench, and formed along a narrow fracture that propagated along the crest of the arch in the Pacific plate that was produced by lateral bending of the plate into that part of the trench (1). The EMII influence along this lineament is strongest to the west, and all lavas along it are distinct from those of the older underlying lineaments in the Pb isotopes (2). The simplest interpretation of Samoan volcanism is that enriched components are irregularly concentrated in a layer or layers at the top of the asthenosphere that has been tapped along fractures produced by shear coupling acting on the edge of the Pacific lithospheric plate where it moves close to or bends toward the transform portion of the Tonga Trench. (1) Hawkins, JW, and Natland, JH, 1975. Earth Planet. Sci. Lett., 24: 427-439 (2) Hart, S.R., Staudigel, H., Koppers, A.P., Blusztajn, J., Baker, E.., Workman, R., Jackson, M., Hauri, E., Kurz, M., Sims, K., Fornari, D., Saal, A., and Lyons, S., 2000. Geochem. Geophys. Geosyst., 1: Paper 2000GC00108.

Dieu, J. J.; Hawkins, J. W.; Natland, J. H.

2002-12-01

118

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

119

Pacific plate apparent polar wander between 67 Ma and 44 Ma determined from the analysis of the skewness of both vector and scalar magnetic anomalies due to seafloor spreading  

NASA Astrophysics Data System (ADS)

Pacific plate apparent polar wander between 67 Ma and 44 Ma determined from the analysis of the skewness of both vector and scalar magnetic anomalies due to seafloor spreading The apparent polar wander (APW) path for the Pacific plate is important to the study of Pacific plate motions and their relation to circum-Pacific tectonics. It can be used to discriminate between alternative plate motion circuits, determine the motion of Pacific hotspots relative to the paleomagnetic axis, and test the fixed hotspot hypothesis. The pioneering investigations of Jean Francheteau and his colleagues of Pacific plate APW through the analysis of magnetic anomalies over seamounts helped to demonstrate that the Pacific plate has had substantial northward motion relative to the spin axis since Cretaceous time. We also investigate the APW of the Pacific plate through analysis of magnetic anomalies. Instead of anomalies over seamounts, however, we investigate the skewness (asymmetry) of magnetic anomalies due to seafloor spreading. In prior work, skewness analysis of shipboard magnetic profiles has been used to determine Pacific paleomagnetic poles for chron 25r (57 Ma B.P.; Petronotis et al., 1994), chron 27r to 31n (62 to 69 Ma B.P.; Acton and Gordon, 1991) and chron 32n (72 Ma B.P.; Petronotis and Gordon, 1999). Recently, vector aeromagnetic data from low paleolatitudes, combined with shipboard profiles from low paleolatitudes, were used to determine a paleomagnetic pole with compact confidence limits for anomaly 12r (32 Ma B.P.; Horner-Johnson and Gordon, 2010). Here we use the low-paleolatitude shipboard- and vector aero-magnetic profiles to determine new paleomagnetic poles for the Pacific plate. A new feature of our analysis is a correction for the spreading-rate dependence of anomalous skewness (Koivisto et al. 2011). We estimate anomalous skewness as a function of spreading rate for each anomaly by creating many synthetic profiles using the model of Dyment and Arkani-Hamed (1995) and by experimentally determining the phase shift that causes the resulting synthetic magnetic anomaly to best match a profile produced from a "standard" model for anomalies due to seafloor spreading that assumes simple vertical reversal boundaries (Boswell et al., 2011). Thus, we solve for only two adjustable parameters, the latitude and the longitude of the paleomagnetic pole. We focus on preliminary results from the skewness of crossings of magnetic anomalies 20r (44 Ma B.P.), 24r (55 Ma B.P.) and 30n/31n (67 Ma B.P.) between the Galapagos and Murray fracture zones on the Pacific plate. We choose this region of the Pacific plate because numerical experiments, similar to those conducted by Acton and Gordon (1991), show that these data contribute much more information about the location of paleomagnetic poles than do those from any other region of similar size. Implications for Pacific plate tectonics, motion between hotspots, and true polar wander will be discussed.

Zheng, L.; Gordon, R. G.; Horner-Johnson, B. C.

2011-12-01

120

Size effect on strength of laminate-foam sandwich plates: Finite element analysis with interface fracture  

Microsoft Academic Search

Recent three-point bend tests of size effect on the strength of geometrically scaled sandwich beams of three types – with no notches, and with notches at the upper or lower skin–foam interface, which were previously evaluated using simplified sandwich beam theory and equivalent linear elastic fracture mechanics, are now reanalyzed more accurately by finite elements. Zero-thickness interface elements with a

Ferhun C. Caner; Zden?k P. Bažant

2009-01-01

121

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

122

Large-scale right-slip displacement on the East San Francisco Bay Region fault system, California: Implications for location of late Miocene to Pliocene Pacific plate boundary  

USGS Publications Warehouse

A belt of northwardly younging Neogene and Quaternary volcanic rocks and hydrothermal vein systems, together with a distinctive Cretaceous terrane of the Franciscan Complex (the Permanente terrane), exhibits about 160 to 170 km of cumulative dextral offset across faults of the East San Francisco Bay Region (ESFBR) fault system. The offset hydrothermal veins and volcanic rocks range in age from .01 Ma at the northwest end to about 17.6 Ma at the southeast end. In the fault block between the San Andreas and ESFBR fault systems, where volcanic rocks are scarce, hydrothermal vein system ages clearly indicate that the northward younging thermal overprint affected these rocks beginning about 18 Ma. The age progression of these volcanic rocks and hydrothermal vein systems is consistent with previously proposed models that relate northward propagation of the San Andreas transform to the opening of an asthenospheric window beneath the North American plate margin in the wake of subducting lithosphere. The similarity in the amount of offset of the Permanente terrane across the ESFBR fault system to that derived by restoring continuity in the northward younging age progression of volcanic rocks and hydrothermal veins suggests a model in which 80-110 km of offset are taken up 8 to 6 Ma on a fault aligned with the Bloomfield-Tolay-Franklin-Concord-Sunol-Calaveras faults. An additional 50-70 km of cumulative slip are taken up ??? 6 Ma by the Rogers Creek-Hayward and Concord-Franklin-Sunol-Calaveras faults. An alternative model in which the Permanente terrane is offset about 80 km by pre-Miocene faults does not adequately restore the distribution of 8-12 Ma volcanic rocks and hydrothermal veins to a single northwardly younging age trend. If 80-110 km of slip was taken up by the ESFBR fault system between 8 and 6 Ma, dextral slip rates were 40-55 mm/yr. Such high rates might occur if the ESFBR fault system rather than the San Andreas fault acted as the transform margin at this time. Major transpression across the boundary between the Pacific and North American plates at about 3 to 5 Ma would have resulted in the transfer of significant slip back to the San Francisco Peninsula segment of the San Andreas fault. Since that time, the ESFBR fault system has continued to slip at rates of 11-14 mm/yr. If this interpretation is valid, the ESFBR fault system was the Pacific-North American plate boundary between 8 and 6 Ma, and this boundary has migrated both eastward and westward with time, in response to changing plate margin geometry and plate motions.

McLaughlin, R.J.; Sliter, W.V.; Sorg, D.H.; Russell, P.C.; Sarna-Wojcicki, A. M.

1996-01-01

123

In-situ scanning electron microscopy observations of Li plating and stripping reactions at the lithium phosphorus oxynitride glass electrolyte/Cu interface  

NASA Astrophysics Data System (ADS)

Morphology variations during electrochemical lithium plating-stripping reactions at the lithium phosphorus oxynitride glass electrolyte (LiPON)/copper current collector (Cu) interface are observed in-situ by scanning electron microscopy (SEM). This in-situ SEM observation shows dynamically that the plating reactions at 50 ?A cm-2 distribute initial lithium growth sites sparsely at the LiPON/Cu interface, later, local lithium growth occurs from the pre-plated sites through the Cu film, and finally, most of the precipitated lithium grows to be needle-shape with the height of micron order. This local growth rate attains to be 6.8 mA cm-2, about 100 times higher value than applied one. When those precipitated lithium are stripped at 50 ?A cm-2, core region of each precipitate is mostly stripped but its degree depends on the length of the precipitate. This dependency will arise from the diffusivity of Li. When this stripping current density is increased to 500 ?A cm-2, the coulomb efficiency is further decreased. In-situ SEM observation shows that plated lithium around the interface becomes thin preferentially while that far away from the interface (upper side of plated lithium) remains unchanged. This will isolate most of precipitate lithium from LiPON film electrically, leading to further decreasing of the coulomb efficiency.

Sagane, Fumihiro; Shimokawa, Ryosuke; Sano, Hikaru; Sakaebe, Hikari; Iriyama, Yasutoshi

2013-03-01

124

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. PMID:22885789

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

2013-01-01

125

Nanoscale investigation of the interface situation of plated nickel and thermally formed nickel silicide for silicon solar cell metallization  

NASA Astrophysics Data System (ADS)

In the context of nickel silicide formation from plated nickel layers for solar cell metallization, there are several open questions regarding contact adhesion and electrical properties. Nanoscale characterization by transmission electron microscopy has been employed to support these investigations. Interfacial oxides and silicide phases were investigated on differently prepared samples by different analytical methods associated with transmission electron microscopy analysis. Processing variations included the pre-treatment of samples before nickel plating, the used plating solution and the thermal budget for the nickel-silicon solid-state reaction. It was shown that interface oxides of only few nm thickness on both silicon and nickel silicide are present on the samples, depending on the chosen process sequence, which have been shown to play an important role in adhesion of nickel on silicide in an earlier publication. From sample pretreatment variations, conclusions about the role of an interfacial oxide in silicide formation and its influence on phase formation were drawn. Such an oxide layer hinders silicide formation except for pinhole sites. This reduces the availability of Ni and causes a silicide with low Ni content to form. Without an interfacial oxide a continuous nickel silicide of greater depth, polycrystalline modification and expected phase according to thermal budget is formed. Information about the nature of silicide growth on typical solar cell surfaces could be obtained from silicide phase and geometric observations, which were supported by FIB tomography. The theory of isotropic NiSi growth and orientation dependent NiSi2 growth was derived. By this, a very well performing low-cost metallization for silicon solar cells has been brought an important step closer to industrial introduction.

Mondon, A.; Wang, D.; Zuschlag, A.; Bartsch, J.; Glatthaar, M.; Glunz, S. W.

2014-12-01

126

Evidence for True Polar Wander since mid-Cenozoic time: A Paleomagnetic Investigation of the Skewness of Magnetic Anomaly 12r (32 Ma) Between the Galapagos and Clarion Fracture Zones on the Pacific Plate  

NASA Astrophysics Data System (ADS)

In recent years, some researchers have asserted that there has been no motion of the Pacific hotspots relative to the spin axis since the age (ca. 47 Ma) of the elbow in the Hawaiian-Emperor chain (e.g., Tarduno et al. 2003). In contrast, the apparent polar wander of the Indo-Atlantic hotspots shows distinct motion of the hotspots relative to the spin axis over the same time interval (e.g., Morgan 1981; Besse and Courtillot 2002). If this latter shift is due to true polar wander, one would expect to see a similar shift of Pacific hotspots relative to the spin axis. Here we present critical new data and analyses to test these distinctly different hypotheses. Specifically, we present results of an investigation of the skewness of magnetic anomaly crossings of anomaly 12r between the Galapagos and Clipperton and between the Clipperton and Clarion fracture zones on the Pacific plate. We chose to focus on these adjacent regions for three reasons. First, numerical experiments showed that these crossings, of all those available from the Pacific plate, should contain the most information about the location of the 32 Ma paleomagnetic pole for the Pacific plate. Second, many of the available crossings are from vector aeromagnetic profiles, which have superior signal to noise ratios (Horner-Johnson and Gordon, 2003). Third, the rate of seafloor spreading recorded in these crossings exceeds the threshold (half rate of 50 mm/yr) above which no anomalous skewness occurs. Moreover, for the first time, we combine uncertainties in plate- hotspot rotations (Andrews et al. 2005) with paleomagnetic uncertainties to obtain the total uncertainties of our new paleomagnetic pole reconstructed into the Pacific hotspot frame of reference. The results show significant and unambiguous motion of Pacific hotspots relative to the spin axis since 32 Ma. Moreover, when the 32 Ma Pacific plate paleomagnetic pole is reconstructed into the Pacific hotspot reference frame, it is consistent with the paleomagnetic pole of the Indo-Atlantic hotspots. We conclude that the global set of hotspots have mainly moved in unison relative to the spin axis since 32 Ma, which is most simply interpreted as true polar wander.

Horner-Johnson, B. C.; Gordon, R. G.

2007-12-01

127

Tectonic Structure of the Middle America Pacific Margin and Incoming Cocos Plate From Costa Rica to Guatemala  

NASA Astrophysics Data System (ADS)

A new multibeam bathymetry and magnetic survey with R/V SONNE in summer 2003 has mapped the continental margin and incoming plate of NW Nicaragua, El Salvador and Guatemala, extending existing coverage from offshore Costa Rica and part of Nicaragua to a full coverage map of about 1200 km long by 100 km wide area along the plate boundary. The incoming plate along Nicaragua, El Salvador and Guatemala is of similar age and was formed at superfast spreading rates; however, its morphology changes drastically along strike. The seafloor-spreading inherited morphology is very smooth along Nicaragua, but with ridges up to 800 m high in Guatemala, with a transition across El Salvador. The development and dimensions of the dominant inherited fabric seems to be related to discontinuities at the paleospreading center. A series of troughs oblique to the main fabric may indicate the location of pseudofaults and correspond to areas where the seafloor fabric is most prominent. Bending of the oceanic plate into the trench reactivates the inherited fabric forming a well pervasive faulting system along the oceanic trench slope. The continental slope displays three morphotectonic units that roughly correspond to the upper, middle and lower slope, although the across slope width of each unit is fairly variable. Small canyons and gullies that form at the sudden dip change across the shelf break carve the upper slope. The canyons coalesce and become shallower as the dip decreases downslope. Locally some large canyons continue into the slope toe. The middle slope is a rough terrain variable in width and dip sculptured by pervasive normal faulting and locally by mass wasting processes. The lower slope is formed by en echelon terraces striking similar to the rough terrain of the incoming plate and mimicking the half graben morphology of the underthusting plate. The three morphotectonic slope domains represent differences in tectonic activity, with more stable upper slope, a middle slope dominated by tectonic extension and the thin, highly fractured upper plate of the lower slope riffling over the incoming plate topography. The trench axis is largely empty, with local turbidite ponds at the mouth of a few large canyons transecting the entire slope.

Ranero, C. R.; Weinrebe, W.; Grevemeyer, I.; Phipps Morgan, J.; Vannucchi, P.; von Huene, R.

2003-12-01

128

Mesozoic plate-motion history below the northeast Pacific Ocean from seismic images of the subducted Farallon slab  

Microsoft Academic Search

The high-resolution seismic imaging of subducted oceanic slabs has become a powerful tool for reconstructing palaeogeography. The images can now be interpreted quantitatively by comparison with models of the general circulation of the Earth's mantle. Here we use a three-dimensional spherical computer model of mantle convection to show that seismic images of the subducted Farallon plate provide strong evidence for

Hans-Peter Bunge; Stephen P. Grand

2000-01-01

129

Resistivity of bipolar plate materials at the cathode interface in molten carbonate fuel cells.  

SciTech Connect

Measurements of oxide scale resistivity for prospective bipolar plate materials in the molten carbonate fuel cell (MCFC) are coupled with observations of microstructural/compositional change over time. This work searches for a compromise to the high corrosion rate of Type 316L and the high oxide scale resistance of Type 310S. We tested a group of materials having chromium content ranging from 16 to 31 wt%, including Nitronic 50 and NKK, a Ni-Cr-Fe alloy. Chromium content was found to be the primary determinant of oxide scale composition. In the MCFC cathode compartment, stainless steels generally formed a duplex structure with an inner Cr-rich layer and an outer, Fe-rich layer. The composition of the inner Cr-rich layer was related to the base alloy and had a controlling effect on scale resistivity. Oxide scale resistivity was measured for two electrolyte compositions: Li/K and Li/Na carbonates. Changes in the physical/mechanical properties (spallation/cracking) in the oxide scale of Type 316L provided an understanding of its resistivity fluctuations over time.

Kaun, T. D.

1998-11-18

130

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

131

An unrecognized major collision of the Okhotomorsk Block with East Asia during the Late Cretaceous, constraints on the plate reorganization of the Northwest Pacific  

NASA Astrophysics Data System (ADS)

Interactions at plate boundaries induce stresses that constitute critical controls on the structural evolution of intraplate regions. However, the traditional tectonic model for the East Asian margin during the Mesozoic, invoking successive episodes of paleo-Pacific oceanic subduction, does not provide an adequate context for important Late Cretaceous dynamics across East Asia, including: continental-scale orogenic processes, significant sinistral strike-slip faulting, and several others. The integration of numerous documented field relations requires a new tectonic model, as proposed here. The Okhotomorsk continental block, currently residing below the Okhotsk Sea in Northeast Asia, was located in the interior of the Izanagi Plate before the Late Cretaceous. It moved northwestward with the Izanagi Plate and collided with the South China Block at about 100 Ma. The indentation of the Okhotomorsk Block within East Asia resulted in the formation of a sinistral strike-slip fault system in South China, formation of a dextral strike-slip fault system in North China, and regional northwest-southeast shortening and orogenic uplift in East Asia. Northeast-striking mountain belts over 500 km wide extended from Southeast China to Southwest Japan and South Korea. The peak metamorphism at about 89 Ma of the Sanbagawa high-pressure metamorphic belt in Southwest Japan was probably related to the continental subduction of the Okhotomorsk Block beneath the East Asian margin. Subsequently, the north-northwestward change of motion direction of the Izanagi Plate led to the northward movement of the Okhotomorsk Block along the East Asian margin, forming a significant sinistral continental transform boundary similar to the San Andreas fault system in California. Sanbagawa metamorphic rocks in Southwest Japan were rapidly exhumed through the several-kilometer wide ductile shear zone at the lower crust and upper mantle level. Accretionary complexes successively accumulated along the East Asian margin during the Jurassic-Early Cretaceous were subdivided into narrow and subparallel belts by the upper crustal strike-slip fault system. The departure of the Okhotomorsk Block from the northeast-striking Asian margin resulted in the occurrence of an extensional setting and formation of a wide magmatic belt to the west of the margin. In the Campanian, the block collided with the Siberian margin, in Northeast Asia. At about 77 Ma, a new oceanic subduction occurred to the south of the Okhotomorsk Block, ending its long-distance northward motion. Based on the new tectonic model, the abundant Late Archean to Early Proterozoic detrital zircons in the Cretaceous sandstones in Kamchatka, Southwest Japan, and Taiwan are interpreted to have been sourced from the Okhotomorsk Block basement which possibly formed during the Late Archean and Early Proterozoic. The new model suggests a rapidly northward-moving Okhotomorsk Block at an average speed of 22.5 cm/yr during 89-77 Ma. It is hypothesized that the Okhotomorsk-East Asia collision during 100-89 Ma slowed down the northwestward motion of the Izanagi Plate, while slab pull forces produced from the subducting Izanagi Plate beneath the Siberian margin redirected the plate from northwestward to north-northwestward motion at about 90-89 Ma.

Yang, Yong-Tai

2013-11-01

132

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

133

Late Triassic bimodal igneous rocks in eastern Heilongjiang Province, NE China: Implications for the initiation of subduction of the Paleo-Pacific Plate beneath Eurasia  

NASA Astrophysics Data System (ADS)

This paper reports new zircon LA-ICP-MS and SIMS U-Pb ages and Hf isotope data, and whole-rock major and trace element data for Late Triassic igneous rocks of eastern Heilongjiang Province, NE China. These data provide new insights into the timing of the initiation of subduction of the Paleo-Pacific Plate beneath the Eurasian continent. The zircon U-Pb age data indicate that a suite of Late Triassic (228-202 Ma) igneous rocks is present within the Songnen-Zhangguangcai Range Massif and within the western margin of the Khanka Massif. The Late Triassic igneous rocks within the Songnen-Zhangguangcai Range Massif consist of basalts, basaltic andesites, gabbro-diabases, and rhyolites, whereas coeval igneous rocks in the western margin of the Khanka Massif consist of hornblende gabbros and syenogranitic porphyries. These Late Triassic rocks constitute a geochemically bimodal igneous rock association that contains mafic rocks enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE), and depleted in heavy rare earth elements (HREE) and high field strength elements (HFSE) such as Nb, Ta, Zr, Hf, and Ti. Zircons from these mafic rocks have ?Hf (t) values and TDM1 ages of +2.8 to +9.8 and 477-733 Ma, respectively, suggesting that they formed from a primary magma generated by the partial melting of depleted lithospheric mantle material that had been previously modified by subduction-related fluids. The coeval felsic rocks are characterized by enrichments in LREEs and LILEs, and depletions in HREEs and HFSEs (including Nb, Ta, and Ti), and their zircons have ?Hf (t) values and TDM2 ages of +0.6 to +7.9 and 766 to 1461 Ma, respectively, implying that these rocks were generated during the partial melting of juvenile crustal material. The Late Triassic bimodal igneous rocks in eastern Heilongjiang Province, combined with the regional geologic information, therefore record a post-orogenic extensional environment related to the final late Permian-Early Triassic closure of the Paleo-Asian Ocean. In addition, the presence of Late Triassic bimodal igneous rocks within the eastern margin of the Eurasian continent suggests that the subduction of the Paleo-Pacific Plate beneath the Eurasian continent began after the Late Triassic.

Wang, Feng; Xu, Wen-Liang; Xu, Yi-Gang; Gao, Fu-hong; Ge, Wen-chun

2015-01-01

134

A mega shear zone in the Central Range of Taiwan and it's implication for the Late Mesozoic subduction of the paleo-Pacific plate  

NASA Astrophysics Data System (ADS)

The metamorphic basement "Tananao Complex" exposed in the eastern flank of the Central Range of Taiwan. The ancient Asian continental margin deposited a thick sequence of sandstone, shale, limestone and volcanic rocks that was the protolith of Tananao Complex. In Late Mesozoic Era, the thick sequence of rocks was subjected to several phases of metamorphism and deformation to form the pair metamorphic belts which were the western Tailuko Belt and the eastern Yuli Belt. The Tailuko belt is composed of phyllite, quartzite, quartz-mica schist, meta-conglomerate, gneiss, meta-basite, amphibolite, serpentinite, marble and meta-chert, etc. The Yuli belt is composed of a monotonous assemblage of quartz-mica schist, subordinate meta-basite and serpentinite, etc. It is believed that the boundary of the Tailuko belt and the Yuli belt is a large fault, but the field evidence of the fault has never been found. In this study, meso-scale field investigation of the lithologies and rock fabrics indicate that a mega shear zone, called "The Daguan shear zone", separated the Tailuko belt from the Yuli belt. The Daguan shear zone is a NNE trending and west dipping mega shear zone which is mainly composed of mylonitic dark gray quartz-mica schist and mica schist, intercalated with 1 to 2 centimeters thick of elongated meta-conglomerate band. The shear zone is composed of numerous meso-scale ductile shear zones. Additionally, the shaer zone is characterized by abundant varied quartz veins that have been refolded to lenticular or pod shape and nearly parallel to S2 cleavage. Compaed to the existing geological information of the Central Range, we believe that the Daguan shear zone played a role as the boundary of the subduction zone which the paleo-Pacific Plate subducted into the Eurasian Plate in Late Mesozoic Era.

Yi, D. C.; Lin, C. W.

2012-04-01

135

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

136

Development of sediment drifts approaching an active plate margin under the SW Pacific Deep Western Boundary Current  

NASA Astrophysics Data System (ADS)

The abyssal Pacific Ocean is fed by a 1000 km wide, deep western boundary current (DWBC) that flows northward along the continental margin, east of New Zealand. Between the passive margin of Chatham Rise and the subduction zone of Kermadec Trench, a distance of 1200 km, the DWBC has formed a suite of sediment drifts over a depth range of 2200-5700 m. Airgun and 3.5-kHz profiles record a variety of drift types that reflect regional variations in bathymetry, sediment supply, and the tectonic/volcanic framework. On Chatham Rise the DWBC has deposited a sinuous, linear body along the south flank (3000 m), an extensive apronlike drift on the north flank (2200-4500 m), and a ridgelike drift about the rise base (4500-5200 m). The flow has also deposited a body of sediment over 400 km long within a moat at the base of the nearby Louisville Seamount Chain. Further downcurrent, the 250 km long Rekohu Drift (3600-4190 m) has developed northward to 39°S. South of this latitude, drifts comprise mainly reworked pelagic/hemipelagic material and sediment transported from distant southerly sources. In contrast, drifts north of 39°S have received a major injection of terrigenous sediment from Hikurangi Channel which runs 1400 km from New Zealand, eastward across the Hikurangi Plateau to disgorge on to the abyssal floor at the plateau edge. En route, turbidity current overspill from the channel has moved north under the influence of the shallow DWBC to contribute to a series of small ridge and patch drifts among the numerous seamounts on the plateau at 3500-4200 m. Off Hikurangi Channel mouth, a large fan has accumulated. The DWBC has extended the fan into a drift running over 250 km along the base of Hikurangi Plateau (5150-5770 m) toward Kermadec Trench. Here drift sediment becomes increasingly disrupted by mass wasting associated with the active subduction in this area. The seismic stratigraphy reveals the drifts to rest mainly on a widespread erosional surface that is interpreted to mark the inception of the DWBC in the region with the late Oligocene opening of the Australian-Antarctic seaway. Drift construction commenced during the Miocene but was punctuated in the late Miocene by another period of erosion that coincided with increased bottom water production in Antarctica. Deposition resumed in Plio-Pleistocene times when large quantities of sediment from the rapidly rising landmass of New Zealand were injected into the boundary current. The modern flow continues to affect drift deposition as manifest by an active boundary channel along the foot of Hikurangi Plateau and widespread scour zones and sediment wave fields.

Carter, L.; McCave, I. N.

1994-12-01

137

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  

NASA Technical Reports Server (NTRS)

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 complex distribution of slip, little is known about the activities of these and similar structures in northern Baja California and the southward transition to the oceanic ridge transform-fault system in the Gulf of California. SPOT and LANDSAT Thematic Mapper imagery for northern Baja California was processed to optimize discrimination of lithologic and structural features. This data was used to suggest a preliminary kinematic framework for distribution of relative plate motion between 31 and 33 degrees north, in which continental borderland tectonics play an important role in partitioning of plate motion.

Miller, M. Meghan; Crippen, Robert E.; Dixon, Timothy H.

1991-01-01

138

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

NASA Technical Reports Server (NTRS)

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

Gupta, R. N.

1972-01-01

139

Constraints on the plate interface at the Alaska-Aleutian subduction zone from MCS and OBS data of the ALEUT Project  

NASA Astrophysics Data System (ADS)

In summer 2011, the Alaska Langseth Experiment to Understand the megaThrust (ALEUT) program acquired deep penetration multichannel seismic (MCS) reflection and ocean bottom seismometer (OBS) data along a part of the Aleutian-Alaska subduction zone that exhibits the full spectrum of coupling, from locked to freely slipping. The aim of this program is to characterize variations in the geometry and properties of the plate interface and relate them to downdip and along-strike changes in slip behavior and seismogenesis. Our study encompassed 1) the freely slipping Shumagin Gap; 2) the locked Semidi segment, which last ruptured in 1938, and 3) the locked western Kodiak asperity, the western extent of the 1964 M9.2 rupture. We acquired 3700 km of MCS data with the R/V Langseth along a series of strike and dip profiles that span the entire locked zone on the megathrust, its updip and downdip transitions to stable sliding and bending of the downgoing plate. MCS Data were acquired with a 6600 cu.in. airgun array and two 8-km-long streamers. Refraction data were acquired using the same source and short period OBS spaced at ~15 km along two ~400-km profiles coincident with MCS data across the Shumagin Gap and Semidi segment. Here we present results from MCS and OBS data regarding the plate interface reflectivity, geometry and dimensions as well as the structure and hydration of the downgoing plate. MCS data from all the dip profiles reveal reflections from the interplate interface from the trench, at ~7-8 s twtt or 5.5-6.0 km depth, to 120 km landward of the trench, at 10-12s twtt or 30-40 km depth, with high variation in its reflection response with depth. The downdip transition from the potentially locked region to stable sliding seems to be marked by a change in the plate interface reflection signature itself from a single reflection at shallower depth to a wide zone of reflectivity of up to a few seconds twtt at greater depth. Accretionary prism structure varies along strike but is quite narrow (~ 15-25 km) on all the profiles suggesting an erosive character of the margin before it became an accretionary margin. Above, or seaward of the transition from coupling to stable sliding, the decollement is not characterized by a continuous single reflection but rather consists of several strong reflection sections, especially within the Shumagin gap. Other reflections in the overriding plate appear to delineate one or more large faults are observed 75 km back from the trench and appear to connect to the plate interface within this gap at ~11 s twtt. These faults are associated with a large basin and appear to have accommodated primarily normal motion, although folding of sediments near the fault and complicated fault geometries in the shallow section may indicate that this fault has accommodate other types of motion during its history.Seaward of the trench, MCS data exhibit significant along-strike variations in the structure of the downgoing plate. Pronounced bending faulting, thin sediments (~0.5 km), rougher basement topography and clear Moho reflections are observed in oceanic lithosphere subducting in the weakly coupled Shumagin Gap, while less bending-related deformation and Moho reflectivity and thicker sediment thickness (~1.25 km) is associated with the subducting plate in the Semidi segment. The change in sediment thickness appears to be related to changes in the thickness of sediment being carried into the subduction zone near the plate boundary and in the style of deformation of the accretionary prism. These structural variations between the Shumagin gap and Semidi segment are accompanied by differences in the velocity structure of the downgoing plate based on OBS data. Reduced mantle velocities and altered crustal velocities in the oceanic plate are observed in the Shumagin Gap as it bends and subducts possibly due to hydration. Preliminary analysis suggests more modest decreases in mantle velocities in the Semidi segment, where less bending related faulting is observed. These along-strike variations in the structure of the

Bécel, Anne; Shillington, Donna J.; Nedimovic, Mladen R.; Kuehn, Harold; Webb, Spahr C.

2013-04-01

140

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

141

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.

142

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

143

Plate Tectonics: Plate Interactions  

NSDL National Science Digital Library

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

National Science Teachers Association (NSTA)

2006-11-01

144

Earthquakes, Volcanoes, and Plate Tectonics  

NSDL National Science Digital Library

This page consists of two maps of the world, showing how earthquakes define the boundaries of tectonic plates. Volcanoes are also distributed at plate boundaries (the "Ring of Fire" in the Pacific) and at oceanic ridges. It is part of the U.S. Geological Survey's Cascades Volcano Observatory website, which features written material, images, maps, and links to related topics.

145

Chemical and isotopic diversity in basalts dredged from the East Pacific Rise at 10??S, the fossil Galapagos Rise and the Nazca plate  

USGS Publications Warehouse

We present petrographic, chemical and isotopic data for fresh lava samples dredged from three regions: (1) the fossil Galapagos Rise; (2) an elongate volcano near this extinct spreading center; and (3) the East Pacific Rise at 10??S. The samples from the Galapagos Rise are among the first samples from any fossil spreading center to be analyzed. Alkalic picrites from the elongate seamount and transitional basalts from the East Pacific Rise are both somewhat unusual rock types considering their respective tectonic environments. The dredges from the East Pacific Rise at about 10??S recovered unusual transitional, light rare-earth element (LREE) enriched basalts which show a range of fractionation. On the basis of their chemical and isotopic abundances, it is unlikely that the lavas are related by a single simple process of magmatic differentiation. We suggest that the mantle source region of these basalts was chemically and isotopically heterogeneous. The chemistry of LREE-depleted tholeiitic basalt dredged from near the axis of the extinct Galapagos Rise indicates complex petrogenesis and differentiation. The presence of tholeiitic basalts here indicates that unlike the Guadalupe and Mathematician fossil ridges, the Galapagos Rise has not been the site of voluminous post-abandonment alkalic volcanism. Alkalic basalts of picritic bulk composition dredged from an elongate seamount near the Galapagos Rise do not represent liquid compositions. Instead, we suggest that these alkalic liquids contain added olivine and plagioclase xenocrysts. Although most of the samples analyzed are very fresh, a few have been altered. The latter exhibit characteristic chemical and isotopic effects of seawater alteration. ?? 1982.

Batiza, R.; Oestrike, R.; Futa, K.

1982-01-01

146

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

147

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

148

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

149

Pacific Lamprey  

USGS Multimedia Gallery

Pacific Lamprey mouth suckers adhered to the glass at Bonneville Dam fish viewing window. The native Pacific Lamprey uses the fish ladder at Bonneville Dam.  This species plays a significant role in the foodweb and in Tribal

150

California takes earthquakes very seriously. The state straddles two major tectonic plates and is subject to relatively frequent, often major, potentially devastating quakes.  

E-print Network

California takes earthquakes very seriously. The state straddles two major tectonic plates the Pacific and North American tectonic plates. The Pacific Plate includes a sliver of California and Baja California, as well as Hawaii and most of the Pacific Ocean, while the North American Plate includes

151

Plate TectonicsPlate Tectonics Plate TectonicsPlate Tectonics  

E-print Network

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

Siebel, Wolfgang

152

Movie of the Pacific/Antarctic Ridge  

NSDL National Science Digital Library

This set of movie clips shows ten million years of seafloor spreading at the axis of the Pacific/Antarctic Ridge. The clips show bathymetry and magnetic anomalies from the present day, and from 9.9 million years ago to the present. There is also a flyby down the Pitman Fracture Zone, a remote portion of the Pacific/Antarctic plate boundary in the south Pacific Ocean. Quicktime versions formatted for Macintosh users are also provided.

153

The Nature of Tectonic Plates  

NSDL National Science Digital Library

This lesson provides an overview of the various types of interactions between tectonic plates. The discussion uses the analogy of a cracked egg to describe the tectonic plates composing Earth's crust. Other topics include the concentrated earthquake and volcanic activity associated with plate boundaries, types of interactions at the boundaries, and how plate motions are affecting the Atlantic and Pacific Oceans. The lesson includes an activity in which students will use online references to locate a hypothetical nuclear power plant in a geologically safe area, investigate the history of large earthquakes in South Carolina, provide a likely location for a hypothetical geothermal power plant, and others.

Rhinehart, Ken

154

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

155

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

156

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

157

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

158

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

159

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

160

Is the Pacific splitting in two? 26 January 2008  

E-print Network

to this feat. The world's biggest tectonic plate under the Pacific seems to be tearing apart, forming a new mid the middle of tectonic plates that don't need to be weakened first. Island chains like the Hawaiian://www.newscientist.com/article.ns?id=mg19626333.100 6 December 2007 The day tectonic plates come to rest http

Clouard, Valerie

161

Interface between Education and State Policy: Australia. Asia and the Pacific Programme of Educational Innovation for Development, Education and Polity, No. 2.  

ERIC Educational Resources Information Center

One of seven studies in the "Education and Polity" series, this document looks at alternative futures and the interface of education with four areas: communication; employment and leisure; state policy; and technology. The studies were commissioned during 1984 and were conducted by interdisciplinary teams: two in Australia, two in India, one in…

Hughes, Phillip; And Others

162

Plate Boundaries  

NSDL National Science Digital Library

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

163

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

164

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.

165

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

166

Pacific Fisheries Environmental Laboratory  

NSDL National Science Digital Library

The Pacific Fisheries Environmental Laboratory (PFEL) examines the role of environmental variability on marine ecosystems and commercially important fish stocks. Research areas include comparative fisheries oceanography, physical oceanography, and climate and marine fisheries. This extensive site features both model-derived environmental index products as well as time series data, including sea surface temperature, salinity, isotherm depth, surface winds and pressure maps, and upwelling indices. A live access server also allows users to download and visualize data using a simple graphical user interface. PFEL is also the west coast regional site for the NOAA CoastWatch program, which provides dissemination of oceanographic satellite observation data.

NOAA

167

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

168

Tectonic Plates and Plate Boundaries  

NSDL National Science Digital Library

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

2005-12-17

169

Plate Tectonics  

NSDL National Science Digital Library

The Plate Tectonics SciPack explores the various materials that make up Earth and the processes they undergo to provide a framework for understanding how continents are created and change over time. The focus is on Standards and Benchmarks related to Earth's layers, oceanic and continental plates and the interactions between plates.In addition to comprehensive inquiry-based learning materials tied to Science Education Standards and Benchmarks, the SciPack includes the following additional components:� Pedagogical Implications section addressing common misconceptions, teaching resources and strand maps linking grade band appropriate content to standards. � Access to one-on-one support via e-mail to content "Wizards".� Final Assessment which can be used to certify mastery of the concepts.Learning Outcomes:Plate Tectonics: Layered Earth� Identify that Earth has layers (not necessarily name them), and that the interior is hotter and more dense than the crust.� Identify the crust as mechanically strong, and the underlying mantle as deformable and convecting.Plate Tectonics: Plates� Identify that the outermost layer of Earth is made up of separate plates.� Choose the correct speed of the motion of plates.� Identify the ocean floor as plate, in addition to the continents (to combat the common idea that only continents are plates, floating around on the oceans).� Recognize that oceans and continents can coexist on the same plate.Plate Tectonics: Plate Interactions� Identify the different interactions between plates.� Discuss what happens as a result of those interactions.Plate Tectonics: Consequences of Plate Interactions� 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.Plate Tectonics: Lines of Evidence� Use plate tectonics to explain changes in continents and their positions over geologic time.� Provide evidence for the idea of plates, including the location of earthquakes and volcanoes, continental drift, magnetic orientation of rocks in the ocean floor, etc.

National Science Teachers Association (NSTA)

2007-03-21

170

Revised reconstructions of the Late Cretaceous to recent history of the Pacific basin  

NASA Astrophysics Data System (ADS)

The tectonic evolution of the Pacific basin since the Late Cretaceous involves a number of major plate reorganisations, including multiple fragmentations of the Farallon plate and the formation of the Vancouver, Nazca and Cocos plates, and the incorporation of the Bellingshausen plate into the Antarctic plate. However, many regional plate kinematic models of the northeast and southeast Pacific are based on data derived before the availability of high-resolution satellite altimetry and accurate global positioning system (GPS) navigation, causing inconsistencies in these models. Such inconsistencies arise from differences in previous magnetic anomaly interpretations and fracture zone identifications from satellite-derived gravity anomalies. Discrepancies in published models of the Nazca-Pacific, Vancouver-Pacific and Farallon-Pacific spreading history results have implications for modelling the convergence history along the South American and North American margins within global plate models, influencing the variations in age, location and geometry of plates at subduction zones. We refine reconstructions of the seafloor spreading history of the south (Pacific, Antarctic, and Bellingshausen plates), southeast (Nazca, Farallon and Pacific plates) and northeast (Vancouver, Farallon and Pacific plates) Pacific basin from the Late Cretaceous (83.5 Ma) to present-day, based on a synthesis of marine magnetic anomaly picks and fracture zone identifications from satellite-derived gravity anomalies. We calculate rotations and uncertainties for plate pairs based on Hellinger's (1981) best fitting criteria. We divide the Farallon plate into two segments: the northern segment (Farallon plate) and southern segment (';Pre-Nazca' plate), and reconstruct separate spreading histories for each segment relative to the Pacific plate, and find large differences in our ';Pre-Nazca'-Pacific history compared to published models for this area. We subsequently investigate the difference in the implied convergence history along the South American and North American margins, by embedding our revised regional model in a global plate model, in a context of relevant geological data preserved along the active margins of the Americas. Our global model also incorporates new, well-constrained Eocene-Oligocene kinematics for the West Antarctic Rift System (Granot et al, 2013) which form an important link in the plate circuit between the Pacific and North/South America. Our model considerably refines the evolution of the Pacific basin since the Late Cretaceous, allowing for further insights in global and regional modelling.

Wright, N.; Seton, M.; Williams, S.; Müller, D.

2013-12-01

171

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.; Villaseñor, Antonio; Furlong, Kevin P.

2013-01-01

172

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

173

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

174

Integrating plate coupling and transient slip events along the subduction zone interface in Nankai Trough, SW Japan using GEONET GPS time series  

NASA Astrophysics Data System (ADS)

Large earthquakes (M~=8) have occurred repeatedly along the Nankai trough, Southwest Japan, over the past 1000 years. Recently, time-varying slow earthquakes such as short-/long-term slow slip transients, non- volcanic tremor, low/very-low frequency earthquakes have been observed in the region. To understand the interseismic plate loading process and its relation to large earthquakes and slow transient events, we use recently reanalyzed GEONET GPS data to re-examine the plate loading rate and time variable deformation in space and time.In order to estimate interseismic velocities from the GPS time ser,es, we developed tools to identify earthquake and instrument related offsets. We use QOCA to fit an empirical model to the raw time series, estimate and remove seasonal variations and common mode errors across the network. As a result, we were able to determine the accurate horizontal and vertical interseismic velocities for the entire network using 10 years data (1996-2006), as opposed to the short-time velocity estimates in most previous studies. We inverted for the back slip (or slip deficit rate) along the Nankai trough using 3-D velocity field using a realistic interplate fault geometry. To allow for the nonuniform deformation source, we model interplate coupling beneath Shikoku and Kii Peninsula and Nankai-Suruga trough separately. The results show that strong coupling were found at 10-30 km beneath Shikoku and Kii Peninsula while Tokai region has maximum backslip rate of ~2-3cm/yr at the depth of 5-25 km. There is a good spatial correspondence between the inferred strong coupling region with the past large earthquake rupture zones. We applied the extended Network Inversion Filter [MacGuire and Segall, 2003] to model the spatial and temporal distribution of two major slow slip events: 2000-2004.5 Tokai slow slip event and 2002-2004 Bungo Channel event. The cleaned GPS time series provides much better resolution for transient slip analysis. The inverted slip histories show complex patterns with each event consisting of several subevents. Comparison of the plate coupling pattern and transient slip shows that part of strong coupling area beneath western Bungo Channel overlaps with the aseismic slip locus, indicating at least part of the accumulated slip deficit is released by episodic slow slip events in the region. The transient slip zones is located at the downdip portion of strong coupling region but updip of low frequency earthquakes. Excellent temporal coincidence between the resolved slow slip rate and LFE occurrence were found in both events, supporting the hypothesis that they are closely related and possibly reflect the modulation of slow slip on seismicity.

Liu, Z.; Owen, S.; Dong, D.; Lundgren, P.; Webb, F.; Fielding, E.; Simons, M.; Hetland, E. A.

2008-12-01

175

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

NASA Astrophysics Data System (ADS)

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.

1991-11-01

176

Coseismic Slip Distribution of the 2011 off the Pacific Coast of Tohoku Earthquake Deduced from Land and Seafloor Geodesy  

NASA Astrophysics Data System (ADS)

The 2011 off the Pacific coast of Tohoku Earthquake (M9.0) occurred on 11 March 2011 off the Pacific coast of Tohoku district, northeastern Japan, where the Pacific plate is subducting beneath the overriding continental plate. A number of models of the coseismic slip distribution of this earthquake have been already proposed based on seismological, geodetic, and tsunami data. Here, we present comprehensive coseismic slip distribution model based not only on land GPS data but also on seafloor geodetic observations, which are obtained through recent observation cruises. We combined displacements at seafloor sites that are deduced from two different types of seafloor observations with the displacements at land GPS stations. One is the seafloor crustal deformation observation with GPS/Acoustic ranging (GPS/A). Horizontal displacements associated with the 2011 Tohoku earthquake at 2 GPS/A stations are estimated by comparing the station positions deduced from the observations before and after the earthquake. Another type of the seafloor data is seafloor water pressure that is observed by means of ocean bottom pressure gauge (OBP). We analyzed OBP data observed at 2 cabled and 4 self pop-up stations, and estimated vertical displacements due to the main shock. Displacements at 5 GPS/A stations of Japan Coast Guard [Sato et al., 2011, science] are also included to estimate the coseismic slip distribution of the earthquake. Estimated slip distribution of the 2011 Tohoku Earthquake shows following features. 1) The area of large slip ( > 20 m) is about 100 km x 200 km on the plate interface shallower than 30 km in depth. 2) There is no large slip occurred off southern Iwate prefecture on the plate interface throughout shallow to deep. 3) The latitudinal range of the area of large slip almost corresponds to the one of the area of strong interplate coupling zone off Miyagi prefecture. 4) Significant slip is estimated around the rupture area of 1978 M7.4 Miyagi-oki earthquake (40 ~ 50 km in depth). 5) No large slip is estimated on the shallow plate interface off Fukushima prefecture. These features clarify that the coseismic rupture of the 2011 Tohoku Earthquake is concentrated relatively narrow area off Miyagi prefecture and maximum slip is very large as compared to the empirical scaling law between released moment, fault size, and maximum slip of earthquakes on the subducting plate boundary. The results suggest that most slip occurred on the plate interface where continental crust contacts with the subducting oceanic crust. Off Miyagi prefecture, however, is an exceptional region where coseismic slip also has occurred on the plate interface under the continental mantle. The heterogeneity of the mantle wedge might control this slip heterogeneity in the crust-mantle contact zone. With respect to the shallow plate interface, there is no large slip is estimated off Iwate and Fukushima prefecture. Less accumulated strain due to the weak interplate coupling off Iwate prefecture and strain release due to the slow slip events that are detected by the activity of the small repeating earthquakes (e.g. in 2008) might cause it.

Iinuma, T.; Kido, M.; Osada, Y.; Inazu, D.; Ohzono, M.; Tsushima, H.; Hino, R.; Ohta, Y.; Suzuki, S.; Fujimoto, H.; Miura, S.; Shinohara, M.

2011-12-01

177

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

178

Understanding the structure of subducting plates  

NASA Astrophysics Data System (ADS)

Seismic studies are helping scientists learn more about the structure of subducting oceanic plates. Using an air gun array and 80 ocean bottom seismometers spaced along a 500-kilometer profile, Fujie et al. conducted a seismic reflection and refraction survey at the Kuril trench in the northwestern Pacific margin, where part of the Pacific plate is subducting beneath the Okhotsk plate. They estimated the water content of the subducting plate by measuring the velocity of seismic waves—both P waves and S waves—through the plate. The ratio of seismic wave velocities (Vp/Vs) is an indicator of the lithology, porosity, and presence of fluid in the plate. Their findings showed that the water content in the plate increased toward the trench, along with greater bending and fracturing, suggesting that water enters the plate through the fractures. The authors conclude that the bending and fracturing of the plate as it subducts play an important role in the water cycle in subduction zones. (Geophysical Research Letters, doi:10.1029/2012GL054340, 2013)

Balcerak, Ernie

2013-04-01

179

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

180

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

181

Peen plating  

NASA Technical Reports Server (NTRS)

A process for metal plating which comprises spraying a mixture of metallic powder and small peening particles at high velocity against a surface is described. The velocity must be sufficient to impact and bond metallic powder onto the surface. In the case of metal surfaces, the process has as one of its advantages providing mechanical working (hardening) of the surface simultaneously with the metal plating.

Babecki, A. J. (inventor); Haehner, C. L.

1973-01-01

182

PACIFIC COAST SALMON pacific Coast Salmon  

E-print Network

to spawn and complete their life cycle. Coho salmon and most southern U.S. runs of Chinook salmon tend181 PACIFIC COAST SALMON UNIT 12 pacific Coast Salmon Unit 12 ROBERT G. KOPE NMFS Northwest Fisheries Science Center Seattle Washington INTRODUCTION Pacific salmon support important commercial

183

Non-closure of the geologically instantaneous global plate motion circuit: Implications for plate non-rigidity  

NASA Astrophysics Data System (ADS)

Global plate motion models such as NUVEL-1 provide rigorous tests of the assumption of plate rigidity and appear, at first glance, to strongly validate that assumption. But the complex interactions of the plate circuits in such global models can hide important inconsistencies. Here we make a straighforward comparison of Pacific-North America motion estimated through three non-overlapping sets of data: (1) plate motion data (spreading rates, fault azimuths, and slip vector azimuths) along the Pacific-North America boundary, (2) space geodetic data, and (3) plate motion data along the Pacific-Antarctic-Nubia-North America plate motion circuit. We find that all three estimates are inconsistent with one another and, in particular, the plate circuit results are highly inconsistent with the two directly estimated results, being both of the wrong magnitude and in the wrong direction. The inconsistency is large and described by an angular velocity of non-closure with a magnitude 0.11 ± 0.03 degs/Myr (95% confidence limits). Projected into the Gulf of California, the non-closure is a velocity of 12 ± 3 mm/yr toward 196. If not owing to an unrecognized systematic error, this non-closure is presumably caused by non-rigidity of one or more of the North American, Nubian, Antarctic, and Pacific plates. We consider several hypotheses to explain the inconsistency. We can conceive of no plausible diffuse plate boundary to explain the difference. In particular, deformation in western North America is excludable as the cause of the difference as both direct plate motion data and space geodetic data differ highly significantly from the predictions from the circuit. The bias in rates of seafloor spreading caused by outward displacement of magnetic anomaly reversal boundaries (DeMets and Wilson, 2005) is in the right direction but can account for only ~15% of the inconsistency. Much of the inconsistency may be explainable, however, by horizontal thermal contraction of oceanic lithosphere, especially of the young Pacific plate lithosphere flanking the Pacific-Antarctic Rise and East Pacific Rise. This young lithosphere includes a continuous band connecting Baja California to the Pacific-Antarctic Rise. The expected contraction rate of this young lithosphere is the right order of magnitude to explain the discrepancy. If this hypothesis is correct, simple plate tectonic predictions may need to be corrected by models fully incorporating the horizontal thermal contraction of the lithosphere to obtain the accuracy needed for some plate recontructions and for comparisons with some space geodetic data.

Gordon, R. G.; Royer, J.; Argus, D. F.; Kumar, R. R.

2005-12-01

184

Growth Plate Injuries  

MedlinePLUS

Growth Plate Injuries May 2014 Questions and Answers about Growth Plate Injuries This publication contains general information about ... Classification of Growth Plate Injuries What Is the Growth Plate? The growth plate, also known as the ...

185

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

186

New kinematic models for Pacific-North America motion from 3 Ma to present, I: Evidence for steady motion and biases in the NUVEL-1A model  

Microsoft Academic Search

We use velocities derived from 2-4.5 years of continuous GPS observations at 21 sites on the Pacific and North American plates along with a subset of the NUVEL-1A data to examine the steadiness of Pacific-North America motion since 3.16 Ma, the transfer of Baja California to the Pacific plate, and the magnitude of biases in the NUVEL-1A estimate of Pacific-North

Charles DeMets; Timothy H. Dixon

1999-01-01

187

Tethyan closure, Andean orogeny, and westward drift of the Pacific Basin Laurent Husson a,  

E-print Network

the westward drift of the Pacific basin dominates the observed net westward rotation of Earth's tectonic plates distribution of tectonic plates, and was triggered by the mid-Cenozoic closure of the Tethys Ocean, via reserved. 1. Introduction The tectonic plates that cover the surface of the Earth are, on average, drifting

Husson, Laurent

188

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

189

Beyond Plate Tectonics: “Plate ” Dynamics  

E-print Network

Plate tectonics dogma has resulted in a variety of theories that frequently violate first principles. In this article it is suggested that ridges are in compression, not tension from convection cells, triple junctions cause hot spots (not vice versa), mantle plumes do not cause hot spot tracks, chord push creates pressures well in excess of lithostatic load, the arch effect demonstrates that rifts form both in compression and tension, surging (i.e. the sudden and rapid motion of the plates) occurs episodically, the presence of a basal shear zone a few meters thick during surging, the preferred initiation of subduction zones at the ridge, revision of the Wilson Cycle, the conformance of “old ” school geologists and plate tectonicians, earth-based non bolide impact mass extinctions, the loss of the earth’s magnetic field and its subsequent reappearance, additional application of the least work (or maximum

Richard Moody

190

Paleomagnetic Tests of Global Plate Reconstructions with Fixed and Moving Hotspots  

NASA Astrophysics Data System (ADS)

Three distinct approaches have been used in prior work to estimate the motion of the Pacific basin plates relative to the surrounding continents. The first approach is to use the global plate motion circuit through Antarctica (e.g., the Pacific plate to the Antarctic plate to the African plate to the North American plate). An update to this approach is to incorporate the modest mid-Tertiary motion between East and West Antarctica estimated by Cande et al. (2000). A recently proposed second approach is to take an alternative circuit for the early Tertiary of the Pacific plate to the Australian plate to the East Antarctic plate to the African plate to the North American plate (Steinberger et al. 2004). The third approach is to assume that the hotspots in the Pacific Ocean are fixed relative to those in the Atlantic and Indian Oceans (e.g., Engebretson et al., 1986), which we recently showed indicates motion between East and West Antarctica of 800 ± 500 km near the Ross Sea Embayment. The first approach (global plate motion circuit through Antarctica) indicates very rapid motion between Pacific and Indo-Atlantic hotspots during the early Tertiary (e.g., Raymond et al. 2000). The second approach (global plate motion circuit through Australia) indicates slower, but still substantial, motion between Pacific and Indo-Atlantic hotspots (Steinberger et al. 2004). Because each of the three approaches predicts distinctly different motion between the Pacific plate and the continental plates, they can be tested with paleomagnetic data. The results of such tests indicate that the first approach leads to systematic and significant misfits between Pacific and non-Pacific early Tertiary and Late Cretaceous paleomagnetic poles. The second approach leads to slightly smaller misfits. In contrast, the circuit based on fixed hotspots brings the Pacific and non-Pacific paleomagnetic poles into consistency. Thus the paleomagnetic data decisively favor fixed hotspots over the alternative approaches and suggests that motion between hotspots is substantially less than inferred by Steinberger et al. (2004).

Andrews, D. L.; Gordon, R. G.; Horner-Johnson, B. C.

2004-12-01

191

Plating on some difficult-to-plate metals and alloys  

SciTech Connect

Electrodeposition of coatings on metals such as beryllium, beryllium-copper, Kovar, lead, magnesium, thorium, titanium, tungsten, uranium, zirconium, and their alloys can be problematic. This is due in most cases to a natural oxide surface film that readily reforms after being removed. The procedures we recommend for plating on these metals rely on replacing the oxide film with a displacement coating, or etching to allow mechanical keying between the substrate and plated deposit. The effectiveness of the procedures is demonstrated by interface bond strengths found in ring-shear and conical-head tensile tests.

Dini, J.W.; Johnson, H.R.

1980-02-01

192

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

193

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.

194

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

195

Plate motions: fundamentals  

E-print Network

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

Déverchère, Jacques

196

Simulations of seismic hazard for the Pacific Northwest of the United States from earthquakes associated with the Cascadia subduction zone  

USGS Publications Warehouse

We investigate the impact of different rupture and attenuation models for the Cascadia subduction zone by simulating seismic hazard models for the Pacific Northwest of the U.S. at 2% probability of exceedance in 50 years. We calculate the sensitivity of hazard (probabilistic ground motions) to the source parameters and the attenuation relations for both intraslab and interface earthquakes and present these in the framework of the standard USGS hazard model that includes crustal earthquakes. Our results indicate that allowing the deep intraslab earthquakes to occur anywhere along the subduction zone increases the peak ground acceleration hazard near Portland, Oregon by about 20%. Alternative attenuation relations for deep earthquakes can result in ground motions that differ by a factor of two. The hazard uncertainty for the plate interface and intraslab earthquakes is analyzed through a Monte-Carlo logic tree approach and indicates a seismic hazard exceeding 1 g (0.2 s spectral acceleration) consistent with the U.S. National Seismic Hazard Maps in western Washington, Oregon, and California and an overall coefficient of variation that ranges from 0.1 to 0.4. Sensitivity studies indicate that the paleoseismic chronology and the magnitude of great plate interface earthquakes contribute significantly to the hazard uncertainty estimates for this region. Paleoseismic data indicate that the mean earthquake recurrence interval for great earthquakes is about 500 years and that it has been 300 years since the last great earthquake. We calculate the probability of such a great earthquake along the Cascadia plate interface to be about 14% when considering a time-dependent model and about 10% when considering a time-independent Poisson model during the next 50-year interval.

Petersen, M.D.; Cramer, C.H.; Frankel, A.D.

2002-01-01

197

Plate Tectonics  

NSDL National Science Digital Library

In this activity, presented by the Lane Community College MAPS GIS Program, students will learn the concept of a digital data viewer, and how this resource can help them learn more about plate tectonics. Students will learn terminology associated with both geology and computer aided GIS. The activity is presented as a PDF, and helps the student learn by presenting a series of easy to follow questions. This allows students to learn at their own pace, as it tests their knowledge every step of the way. Visitors will find links to the instructor and student versions of the lesson and links to the web-based GIS utility used in the activity.

2008-12-11

198

Measuring electrical resistivity to interpret tectonic plate coupling  

NASA Astrophysics Data System (ADS)

The coupling of tectonic plates—the degree to which the plates are locked together or free to move—is controlled by factors ranging from temperature and pressure to the shear stress between the plates as well as the shape of the interface between the plates. At subduction margins, GPS observations can be used to identify places where the subducting plates are locked or unlocked. At the Hikurangi margin, a subduction zone that runs north to south off New Zealand's eastern coast, a strong longitudinal gradient in plate coupling is present that is unexplained by any of the familiar factors.

Schultz, Colin

2013-12-01

199

Pacific subduction and Mesozoic mineralization in eastern China  

NASA Astrophysics Data System (ADS)

Northeastern China is well known for the removal of subcontinental lithosphere mantle of the North China craton in the Late Mesozoic and the Cretaceous giant igneous event, while southeastern China is famous for its large scale magmatism and mineralization from the Late Jurassic to the Early Cretaceous. All these can be plausibly interpreted by the interaction between eastern China and the subducting Pacific plate. From Jurassic to Cretaceous, Eastern China was related to the subduction of the Pacific plate under Eurasia in the south, concurrent with oblique subduction of the Izanagi plate in the north (Maruyama et al., 1997; Li and Li, 2007; Sun et al., 2007; Zhou et al., 2000). Cretaceous tectonic evolution of eastern China matches remarkably well with the drifting history of the Pacific plate. The most pronounced phenomena are: (1) eastern China large-scale orogenic lode gold (Au) mineralisation occurred contemporaneously with an abrupt change of ~80 degree in the drifting direction of the subducting Pacific plate, concurrent with the formation of the Ontong Java Plateau (Sun et al., 2007); (2) the subduction of the ridge between the Pacific and Izanagi Plates can plausibly explain the mineralization and rock distribution of the Lower Yangtze River mineralization belt (Ling et al., 2009); (3) southwestward subduction of the Pacific plate and corresponding slab rollback can feasibly interprete the formation of the late Mesozoic (180-125 Ma) magmatism and metallogenic events in SE China. Reference Li, Z. X., and Li, X. H., 2007, Formation of the 1300-km-wide intracontinental orogen and postorogenic magmatic province in Mesozoic South China: A flat-slab subduction model: Geology, v. 35, p. 179-182. Ling, M. X., Wang, F. Y., Ding, X., Hu, Y. H., Zhou, J. B., Zartman, R. E., Yang, X. Y., and Sun, W. D., 2009, Cretaceous ridge subduction along the Lower Yangtze River Belt, eastern China: Economic Geology, v. 104, p. 303-321. Maruyama, S., 1997, Pacific-type orogeny revisited: Miyashiro-type orogeny proposed: Island Arc, v. 6, p. 91-120. Sun, W. D., Ding, X., Hu, Y. H., and Li, X. H., 2007a, The golden transformation of the Cretaceous plate subduction in the west Pacific: Earth and Planetary Science Letters, v. 262, p. 533-542. Zhou, X. M., and Li, W. X., 2000, Origin of Late Mesozoic igneous rocks in Southeastern China: implications for lithosphere subduction and underplating of mafic magmas: Tectonophysics, v. 326, p. 269-287.

Sun, W.; Ling, M.; Liang, H.; Ding, X.; Fan, W.; Yang, X.

2009-12-01

200

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

201

Plate mouse  

PubMed Central

Fracture shaft humerus when surgically fixed is known to go into non-union and one of the main reasons of this is implant failure. The causes of implant failure may lie in the fracture personality, faulty implant material or choice, dubious surgical technique & faulty mechanics of fixation. Implants may break and cut-through but a unique type of implant migration from one surgical compartment to the other or one anatomical part of body to the other has not been hitherto reported. A 45-year-old male, farmer by occupation, was operated for fracture shaft of humerus 15 years back. He presented to us because of pain due to subcutaneous presence of plate in forearm. X-ray of the elbow with forearm showed that the plate used for fixation of humerus had migrated from one body part to another that is from arm to forearm. The patient on deliberation regarding the pros and cons of surgical treatment options, chose not to get his humerus non-union resolved surgically. This was because he could do his activities related to farming reasonably well.

Lal, Hitesh; Sharma, Deepak Kumar; Mittal, Deepak

2012-01-01

202

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

203

High-frequency Pn,Sn phases recorded by ocean bottom seismometers on the Cocos plate  

SciTech Connect

Data from ocean bottom seismometers located on the Cocos plate indicate that high-frequency Pn,Sn phases are generated by earthquakes along the subducting margin of that plate and are propagated across the plate. The Sn phase appears to be severely attenuated as it approaches the ridge crest. Estimates of Pn velocity are lower than previous extimates for western Pacific paths, which may indicate a relationship between Pn,Sn velocity and lithospheric age. High frequencies found in these phases suggest that Q for Pn,Sn propagation across the Cocos plate is similar to that for the western Pacific.

McCreery, C.S.

1981-05-01

204

Origin of the oceanic basalt basement of the Solomon Islands arc and its relationship to the Ontong Java Plateau-insights from Cenozoic plate motion models  

USGS Publications Warehouse

Cenozoic global plate motion models based on a hotspot reference frame may provide a useful framework for analyzing the tectonic evolution of the Solomon Islands convergent margin. A postulated late Miocene collision of the Ontong Java Plateau (OJP) with a NE-facing arc is consistent with the predicted path of the OJP across the Pacific Basin and its Miocene arrival at the trench. Late-stage igneous activity (65-30 Ma) predicted for the OJP as it rode over the Samoan hotspot occurred in correlative stratigraphic sections on Malaita, the supposed accreted flake of OJP in the Solomon Islands arc. Convergence similar to the present velocities between Australia and the Pacific plates was characteristic of the last 43 million years. Prior to 43 Ma Pacific-Australia plate motions were divergent, seemingly at odds with geologic evidence for early Tertiary convergence, particularly in Papua New Guinea. A postulated South Pacific plate may have existed between Australia and the Pacific plate and would have allowed implied northward subduction along the northeastern Australia plate boundary that lasted into the early Eocene. Subsequent reorganization of plate motions in the middle Eocene correlates with middle Eocene marginal basin formation along ridges oblique to the main plate boundary. Cessation of spreading on the Pacific-South Pacific Ridge and its subsequent subduction beneath Asia followed the change in Pacific plate motion at 43 Ma. A trapped remnant of the extinct, NW-trending ridge may still lie beneath the western Philippine Sea. The terminal deformation, metamorphism and ophiolite obduction in the Eocene orogen of the southwest Pacific also correlates with the major change in Pacific plate motion at 43 Ma and the subsequent compression of the dying Eocene arc against outlying continental and oceanic crustal blocks of the Australian plate. The Solomon Islands oceanic basement may represent juxtaposition of oceanic plateaus of the Australian plate beneath overthrust, dismembered ophiolite derived from adjacent marginal basin crust. ?? 1989.

Wells, R.E.

1989-01-01

205

MORVEL: A new estimate for geologically recent plate motions  

NASA Astrophysics Data System (ADS)

MORVEL is a new global set of closure-enforced relative angular velocities for the geologically recent motions of 20 tectonic plates. It is determined from a greatly expanded data set consisting of 1696 seafloor spreading rates, 163 transform fault azimuths, and 56 earthquake slip directions from 29 plate boundaries, and 381 GPS station velocities from the Caribbean, Scotia, and North America plates. The former Africa plate now comprises separate Nubia, Lwandle, and Somalia plates, and the former Australia plate now comprises separate Capricorn, Australia, and Macquarie plates. Seafloor spreading rates, which are estimated over the past 3.16 Ma for slow spreading centers and 0.78 Ma for intermediate and fast spreading centers, are adjusted downward to compensate for the several kilometer outward displacement of magnetic reversal zones, which otherwise biases seafloor spreading rates upward by 0.6-2.6 mm yr-1. MORVEL gives a significantly improved description of recent global plate motions. The largest differences in the motions estimated from MORVEL and NUVEL-1A are along the boundaries of the Nazca plate. The motion of the Caribbean plate along its boundaries with the North and South American plates is nearly twice as fast as predicted by NUVEL-1A and is estimated mainly from GPS measurements at 16 locations in the Caribbean plate interior. The differences between plate velocities that we estimate along 19 plate boundaries using MORVEL and GPS are smaller on average than are the differences between plate motions estimated from NUVEL-1A and GPS, which indicates that MORVEL more accurately describes recent plate motions than does NUVEL-1A. These differences are reduced the most for the boundaries of the Nazca plate and the Arabia-Eurasia and India-Eurasia plate boundaries. MORVEL also reduces by more than half the difference between Pacific-North America motion estimates derived independently from GPS and the NUVEL-1A data.

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

2008-12-01

206

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

207

Plate motion changes, the Hawaiian-Emperor bend, and the apparent success and failure of geodynamic models  

Microsoft Academic Search

Geodynamic models explain present-day plate motions in terms of mantle buoyancy forces arising from subducted lithosphere and lithospheric thickening, or from velocity anomalies mapped by seismic tomography. However, such models do not account for sudden plate tectonic reorganizations, such as the dramatic change in Pacific plate motion implied by the sharp bend in the Hawaiian-Emperor seamount chain about 43 million

Mark A. Richards; Carolina Lithgow-Bertelloni

1996-01-01

208

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

209

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

210

Growth Plate Fractures  

MedlinePLUS

... 2013 by the American Academy of Orthopaedic Surgeons. Growth Plate Fractures Description The bones of children and ... also subject to a unique injury called a growth plate fracture. Growth plates are areas of developing ...

211

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

212

Plate motions and deformations from geologic and geodetic data  

NASA Technical Reports Server (NTRS)

A satellite laser ranging experiment conducted by NASA since 1972 has measured the relative motion between the North America and Pacific plates in California. Based on these measurements, the 896-km distance between San Diego and Quincy, California, is shortening at 62 + or - 9 mm/yr. This geodetic estimate is consistent with the rate of motion between the two plates, calculated from geological data to be 53 + or - 3 mm/yr averaged over the past few million years.

Jordan, T. H.

1986-01-01

213

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

214

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

215

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

216

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

217

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

218

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.

219

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

220

An updated digital model of plate boundaries  

NASA Astrophysics Data System (ADS)

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

Bird, Peter

2003-03-01

221

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

222

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

223

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

224

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

225

North Pacific Regional Summary North Pacific  

E-print Network

of Alaska rockfish pilot sector program; and 7) Bering Sea groundfish (non-pollock) cooperative Sea/Aleutian Islands (BSAI) Groundfish 2. Gulf of Alaska (GOA) Groundfish 3. BSAI King and Tanner subject to overfishing. The North Pacific Region has seven catch share programs (a type of market

226

North Pacific Regional Summary North Pacific  

E-print Network

that includes both an IFQ and a fishing cooperative; 6) Central Gulf of Alaska rockfish pilot sector program to overfishing. The North Pacific Region has seven catch share programs (a type of market-based management), more than any other region.1 These are the: 1) Western Alaska community development quota (CDQ) program; 2

227

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

228

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

229

Volume III, Chapter 3 Pacific Lamprey  

E-print Network

Volume III, Chapter 3 Pacific Lamprey #12;TABLE OF CONTENTS 3.0 Pacific Lamprey (Lampetra................................................................................................................. 3-14 #12;PACIFIC LAMPREY III, 3-1 May 2004 3.0 Pacific Lamprey (Lampetra tridentata) The anadromous and parasitic Pacific lamprey (Lampetra tridentata) is a native inhabitant of the Pacific Northwest. Pacific

230

Changjiang (Yangtze) Pacific Ocean  

E-print Network

Bohai Sea Yellow Sea East China Sea Pacific Ocean Han River SOUTH KOREA NORTH KOREA Yalu River TAIWAN REPUBLIC of CHINA Sea of Japan Huizhou Bay Seahan Bay Liaodong Bay JAPAN Bay Kyunggi Shangdong Peninsula

231

Gravity fields of eight north Pacific seamounts: implications for density  

E-print Network

values ( 100K compensation) for the three western Pacific seamounts (BI, SE, VV) are higher than expected. This suggests that the f1rst five are compensated and that the last three are not. Ribe and Watts [ 1982] divided the Pacific plate into eight... seamounts formed at or near the r1dge crest due to the young age of the crust at the t1me the seamounts began forming. 102 Watts and Ribe [1984] studied flexure of the lithosphere around the Mage11an Seamounts, which are northwest of the three western...

Freitag, Helen Clare

2012-06-07

232

Partitioning of Oblique Plate Convergence at the Sumatran Plate Boundary  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

233

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.

234

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

235

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.

236

Late Cretaceous and Paleogene tectonic evolution of the North Pacific Ocean  

NASA Astrophysics Data System (ADS)

The Late Cretaceous history of the northern Pacific Ocean has not been adequately deciphered, largely because a major plate reorganization occurred during the Cretaceous magnetic quiet interval. Using primary data to reconstruct plate motions from fracture zone trends and Late Cretaceous seafloor spreading magnetic anomalies allows formulation of a reasonable sequence of events that accounts for all the geologic features of that region, especially the Emperor and Chinook troughs. The primary event in our reconstruction is the subduction of the old northwest Pacific triple junction. New relative plate motions imposed by formation of convergent boundaries along both the northern Pacific and Farallon plates caused the Farallon plate to crack. This subdivision occurred 82 m.y. ago and resulted in the formation of the Kula and Chinook plates. The Chinook plate was bounded on the north by the Chinook-Kula ridge, the western arm of the Great Magnetic Bight, on the west by the southern Emperor trough, a slowly spreading rift valley, on the south by the Mendocino transform, and on the east by the Chinook-Farallon ridge. The northern Emperor trough formed the initial western boundary of the Kula plate. From 82 m.y. ago to 50 m.y. ago this configuration was stable: the Chinook plate expanded, the Chinook-Kula ridge migrated north, and the Kula plate was subducted. With the subduction of this ridge, the Chinook plate adhered to the Pacific plate and the Pacific-Farallon ridge became the north-south-trending feature reflected by anomalies 22 and younger. This reconstruction obviates the awkward Late Cretaceous shifting of triple junctions found in other proposed histories and provides reasonable explanations for the several structural features of the region. To achieve closure of vector triangles representing the relative Late Cretaceous plate motions some extension must occur, presumably across the eastern Mendocino fracture zone, between the northern and southern portions of the Farallon plate. These two plates apparently were independent units between 105 and 50 m.y. ago; the initiation and cessation of rapid North Farallon-North American convergence 82 and 50 m.y. ago may have determined the nature and duration of the Laramide orogeny.

Rea, David K.; Dixon, John M.

1983-10-01

237

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.

1984-01-01

238

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

239

Angular shear plate  

Microsoft Academic Search

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

Mitchell C. Ruda; Alan W. Greynolds; Tilman W. Stuhlinger

2009-01-01

240

Rotatable shear plate interferometer  

DOEpatents

A rotatable shear plate interferometer comprises a transparent shear plate mounted obliquely in a tubular supporting member at 45.degree. with respect to its horizontal center axis. This tubular supporting member is supported rotatably around its center axis and a collimated laser beam is made incident on the shear plate along this center axis such that defocus in different directions can be easily measured.

Duffus, Richard C. (Livermore, CA)

1988-01-01

241

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.

242

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

243

Pacific Symposium on Biocomputing '99, World Scientific, New Jersey; Pacific Symposium on Biocomputing '00, World Scientific, New Jersey; Pacific Symposium on Biocomputing '01, World Scientific, New Jersey  

SciTech Connect

The Pacific Symposium on Biocomputing is an international, multidisciplinary conference covering current research in the theory and application of computational methods in problems of biological significance. Researchers from the United States, the Asian Pacific nations and around the world gather each year at PSB to exchange research results and discuss open issues in all aspects of computational biology. PSB provides a forum for work on databases, algorithms, interfaces, visualization, modeling and other computational methods, as applied to biological problems. The data-rich areas of molecular biology are emphasized.

Altman, R.B.; Dunker, A.K.; Hunter, L.; Klein, T.E.; Lauderdale, K.

2003-04-28

244

Adjustable orifice plate seal  

SciTech Connect

This patent describes an orifice fitting of the type having a body with a flow passage for connecting into a pipeline, an orifice plate seal seat located in a slot in the flow passage, a plate carrier which carries an orifice plate having a orifice for the passage of fluid, and gear means in the body for moving the plate carrier from an inactive position out of the flow passage to an active position in the slot in engagement with the seat and with the orifice plate in the flow passage, an improved mans for sealing the orifice plate against the seat. It comprises the plate carrier having a mounting hole therethrough which has an axis, the orifice plate locating in the mounting hole with the orifice concentric with the axis; an annular seal member located on a downstream side of the plate carrier and encircling the mounting hole, the seal member having a downstream face for engaging the seat; a retaining ring located in the mounting hole, sandwiching the orifice plate between the retaining ring and the seal member; mounting means for mounting the retaining ring to the plate carrier so that the retaining ring may protrude in an upstream direction from the plate carrier by an amount that may be adjusted to fit the axial width of the slot; and wherein the mounting means comprises: a set of threads on the perimeter of the retaining ring which engages the threads in the mounting hole, so that rotating the retaining ring relative to the plate carrier will provide a selected protrusion of the retaining ring from the plate carrier; and set screws located in threaded apertures spaced around the retaining ring and extending through the retaining ring into engagement with the orifice plate, so that rotating the set screws in one direction in the threaded.

Foster, J.H.; Beson, J.

1992-03-10

245

An improved plating process  

NASA Technical Reports Server (NTRS)

An alternative to the immersion process for the electrodeposition of chromium from aqueous solutions on the inside diameter (ID) of long tubes is described. The Vessel Plating Process eliminates the need for deep processing tanks, large volumes of solutions, and associated safety and environmental concerns. Vessel Plating allows the process to be monitored and controlled by computer thus increasing reliability, flexibility and quality. Elimination of the trivalent chromium accumulation normally associated with ID plating is intrinsic to the Vessel Plating Process. The construction and operation of a prototype Vessel Plating Facility with emphasis on materials of construction, engineered and operational safety and a unique system for rinse water recovery are described.

Askew, John C.

1994-01-01

246

Angular shear plate  

SciTech Connect

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

247

Multicolor printing plate joining  

NASA Technical Reports Server (NTRS)

An upper plate having ink flow channels and a lower plate having a multicolored pattern are joined. The joining is accomplished without clogging any ink flow paths. A pattern having different colored parts and apertures is formed in a lower plate. Ink flow channels each having respective ink input ports are formed in an upper plate. The ink flow channels are coated with solder mask and the bottom of the upper plate is then coated with solder. The upper and lower plates are pressed together at from 2 to 5 psi and heated to a temperature of from 295 F to 750 F or enough to melt the solder. After the plates have cooled and the pressure is released, the solder mask is removed from the interior passageways by means of a liquid solvent.

Waters, W. J. (inventor)

1984-01-01

248

Fifty Million Years of Fixed Hotspots: A New Self-Consistent Global Set of Plate Rotations  

NASA Astrophysics Data System (ADS)

We have developed new methods for appropriately estimating the uncertainties in plate rotations relative to hotspots. Using these new methods and the latest available relative plate rotations, and also incorporating uncertainties in relative plate motions, we showed that there is no significant motion between Pacific hotspots and Indo-Atlantic hotspots for the past ca. 50 Myr. Here we take the next step and seek a sequence of rotations based on simultaneous inversion of hotspot track data in the Pacific, Atlantic, and Indian Oceans. The resulting set of reconstructions are thus optimal estimates for global plate motion relative to the hotspots for the past 50 Myr. Evidence for significant changes in plate motion, including changes in pole of rotation and in rates of rotation, will be presented. Implications for true polar wander will be discussed.

Kumar, R. R.; Andrews, D. L.; Gordon, R. G.

2004-12-01

249

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

250

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.

251

Mapping The Pacific Coast  

NSDL National Science Digital Library

Maps of the Pacific Coast from the earliest period of European exploration continue to interest cartographers, geographers, and antiquarians. The maps in the Quivira Collection date from 1540 to 1802 and include early depictions of California as an island, Russian cartographic interpretations of the Pacific Coast, and overland maps across the continent westward to the ocean. All told, this online collection includes forty-five maps, books, and illustrations organized into six thematic galleries. Visitors can start by listening to an audio introduction, and then look around through the thematic galleries, which include such intriguing headings as " In the Wake of Captain James Cook" and "Secret Russian Explorations in the Pacific". Of course, visitors must click their way into the "California as an Island" section, if not just for a taste of six examples of what is perhaps one of the best-known cartographic mistakes in the world.

252

PACIFIC EARTHQUAKE ENGINEERING RESEARCH CENTER  

E-print Network

PACIFIC EARTHQUAKE ENGINEERING RESEARCH CENTER PEER Testbed Study on a Laboratory Building, Berkeley PEER Report 2005/12 Pacific Earthquake Engineering Research Center College of Engineering to "exercise" the PEER performance-based earthquake engineering methodology. All projects involved

Adolphs, Ralph

253

Geologically current motion of 56 plates relative to the no-net-rotation reference frame  

NASA Astrophysics Data System (ADS)

NNR-MORVEL56, which is a set of angular velocities of 56 plates relative to the unique reference frame in which there is no net rotation of the lithosphere, is determined. The relative angular velocities of 25 plates constitute the MORVEL set of geologically current relative plate angular velocities; the relative angular velocities of the other 31 plates are adapted from Bird (2003). NNR-MORVEL, a set of angular velocities of the 25 MORVEL plates relative to the no-net rotation reference frame, is also determined. Incorporating the 31 plates from Bird (2003), which constitute 2.8% of Earth's surface, changes the angular velocities of the MORVEL plates in the no-net-rotation frame only insignificantly, but provides a more complete description of globally distributed deformation and strain rate. NNR-MORVEL56 differs significantly from, and improves upon, NNR-NUVEL1A, our prior set of angular velocities of the plates relative to the no-net-rotation reference frame, partly due to differences in angular velocity at two essential links of the MORVEL plate circuit, Antarctica-Pacific and Nubia-Antarctica, and partly due to differences in the angular velocities of the Philippine Sea, Nazca, and Cocos plates relative to the Pacific plate. For example, the NNR-MORVEL56 Pacific angular velocity differs from the NNR-NUVEL1A angular velocity by a vector of length 0.039 ± 0.011° a-1 (95% confidence limits), resulting in a root-mean-square difference in velocity of 2.8 mm a-1. All 56 plates in NNR-MORVEL56 move significantly relative to the no-net-rotation reference frame with rotation rates ranging from 0.107° a-1 to 51.569° a-1.

Argus, Donald F.; Gordon, Richard G.; DeMets, Charles

2011-11-01

254

Tsunami Strike! Pacific Edition  

NSDL National Science Digital Library

Tsunami Strike! Pacific Edition is a scenario-based learning experience for kids from middle school through high school (approximate ages 13-17). The scenario tells the story of four main characters at different locations in the Pacific basin who are each impacted by a major tsunami that originates in Alaska’s Aleutian Islands. Over the course of the story, learners not only view the unfolding events and how each of the characters responds, but also observe how warning scientists analyze and communicate the tsunami threat. Fourteen short lessons provide interactive instruction focused on the science, safety, and history of tsunamis.

COMET

2011-08-23

255

Changes in Plate Motion During Quaternary and Neogene Time (Invited)  

NASA Astrophysics Data System (ADS)

We review some of the evidence for significant changes in plate motion during the past 25 Ma. We will review plate motions estimated over the past 0.78 to 3.2 Ma in the MORVEL set of relative plate angular velocities [DeMets, Gordon, and Argus, 2009], which are derived mainly from spreading rates from marine magnetic anomalies and from the azimuths of well-surveyed transform faults. We will also review plate relative angular velocities estimated from geodetic data while focusing on the GEODVEL set of relative plate angular velocities [Argus et al. 2009], which is determined from a combination of GPS, VLBI, SLR, and DORIS data. We will compare these two data sets to search for recent statistically significant changes in plate motion and, in some cases, discuss possible causes of these changes. We will also review Neogene changes in plate motion with a focus on the change in plate motion in the Indian and Pacific Oceans at about 6 to 8 Ma ago [e.g., Cande et al. 1995; DeMets, Gordon, and Royer 2005; Merkouriev and DeMets, 2006], which includes the onset of lithospheric folding in the equatorial Indian Ocean.

Gordon, R. G.; Demets, C.; Argus, D.; Royer, J.

2009-12-01

256

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

257

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

258

Plates and FEM  

NASA Astrophysics Data System (ADS)

The word plate is a collective term for systems in which transfer of forces occurs in two directions; walls, deep beams, floors and bridge slabs are all plates. We distinguish two main categories, plates that are loaded in their plane, and plates loaded perpendicularly to their plane. For both categories we give an approach with differential equations, such that a basic understanding is provided and for certain characteristic cases an exact solution can be determined. We follow the displacement method, working with differential equations. In plates that are loaded in their plane, the plane stress state is called the membrane state. All stress components are parallel to the mid- plane of the plate. In special cases we can simply determine the stresses.

Blaauwendraad, J.

259

Deep earthquakes in the southwest Pacific: A tectonic interpretation  

SciTech Connect

This paper examines the spatial distribution deep earthquakes in the Tonga-Fiji-New Hebrides region of the southwest Pacific. Our interpretation emphasizes the complex Cenozoic tectonics of the Pacific/Indo-Australian plate boundary as a primary control on the distribution and deformation of subducted lithosphere. Most deep earthquakes in the interarc region are associated with the contorted Pacific plate lithosphere subducted at the Tonga Trench. However, anomalous groups of deep earthquakes located west of the Tonga zone are unrelated to the present plate configuration. Tectonic reconstructions of the region to 8 m.y. B.P. provide circumstantial evidence that (1) the anomalous events west of the Tonga zone occur in two pieces of detached lithosphere, subducted at the Vitiaz and proto-New Hebrides trenches during the late Miocene, (2) the flattening of the inclined seismic zone in northernmost Tonga is related to the rapid opening of the Lau Basin since 4 m.y. B.P., and (3) the sharp westward curvature of the Tonga seismic zone in this area coincides with a preexisting bend in the late Miocene Vitiaz arc. The sharpness of its present curvature appears to be secondary effect of shear flow in the lower mantle and compression between detached (Vitiaz) and attached (Tonga) lithosphere. Thus much of the contortion of the subducted lithosphere beneath Tonga-Fiji may be produced by local tectonic interactions, rather than collision of the slab with an impenetrable boundary in the midmantle. copyright American Geophysical Union 1987

Hamburger, M.W.; Isacks, B.L.

1987-12-10

260

Understanding Plate Motions  

NSDL National Science Digital Library

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

2007-12-12

261

Plating methods, a survey  

NASA Technical Reports Server (NTRS)

Results are presented of a comprehensive search of the literature available, much of which has been generated by the research centers of NASA and its contractors, on plating and coating methods and techniques. Methods covered included: (1) electroplating from aqueous solutions; (2) electroplating from nonaqueous solutions; (3) electroplating from fused-salt baths; (4) electroforming; (5) electroless plating, immersion plating, and mirroring; (6) electroplating from gaseous plasmas; and (7) anodized films and conversion coatings.

Berkowitz, J. B.; Emerson, N. H.

1972-01-01

262

Pacific Northwest National Laboratory  

E-print Network

, this approach works against the student's natural learning patterns. The Pacific Northwest National Laboratory concepts and then builds up to more complex problems. Frequent checks on learning, exercises, and optional the information to everyday experiences. · "Heads Up" interaction elements--pointing out important concepts

263

The Pacific Rim.  

ERIC Educational Resources Information Center

The articles in this special edition were compiled to provide information to Canadian social studies teachers about Pacific Rim countries. Section 1, entitled "The Big Picture and Future Interests," contains: (1) "Social Studies for the 21st Century" (J. Tucker); (2) "Culture and Communication: A Perspective on Asian Studies for Tomorrow's…

Thomas, Paul F., Ed.

1988-01-01

264

Pacific Southwest Research Station  

E-print Network

Pacific Southwest Research Station General Technical Report PSW-GTR-245 (English) August 2013 should either contact the USDA SNAP Hotline Number at (800) 221-5689, which is also in Spanish or call the State Information/Hotline Numbers. All Other Inquiries For any other information not pertaining to civil

Standiford, Richard B.

265

Pacific Southwest Research Station  

E-print Network

Pacific Southwest Research Station General Technical Report PSW-GTR-241 February 2014 United States, persons should either contact the USDA SNAP Hotline Number at (800) 221-5689, which is also in Spanish or call the State Information/Hotline Numbers. All Other Inquiries For any other information

Standiford, Richard B.

266

The Pacific is Viable  

Microsoft Academic Search

ll is quiet in the Pacific. The past year has seen no coups or new insurrections. Nauru voted out those who led it from riches to rags and now struggles to save something from the wreckage. But for the 30th successive year, there has been no growth. With aid running at more than $1.5 billion a year to soften the

Helen Hughes

267

eastern Pacific marine molluscs  

Microsoft Academic Search

SUMMARY Several recent studies have proposed the use of higher taxa as a proxy for species-level biodiversity patterns. Here this premise is evaluated by using a large database of benthic marine molluscs from the eastern Pacific. In this assemblage, diversity patterns at the genus and family level are significantly correlated with those at the species level. However, the choice of

268

Global Dynamic Numerical Simulations of Plate Tectonic Reorganizations  

NASA Astrophysics Data System (ADS)

We use a new numerical approach for global geodynamics to investigate the origin of present global plate motion and to identify the causes of the last two global tectonic reorganizations occurred about 50 and 100 million years ago (Ma) [1]. While the 50 Ma event is the most well-known global plate-mantle event, expressed by the bend in the Hawaiian-Emperor volcanic chain, a prominent plate reorganization at about 100 Ma, although presently little studied, is clearly indicated by a major bend in the fracture zones in the Indian Ocean and by a change in Pacific plate motion [2]. Our workflow involves turning plate reconstructions into surface meshes that are subsequently employed as initial conditions for global Boundary Element numerical models. The tectonic setting that anticipates the reorganizations is processed with the software GPlates, combining the 3D mesh of the paleo-plate morphology and the reconstruction of paleo-subducted slabs, elaborated from tectonic history [3]. All our models involve the entire planetary system, are fully dynamic, have free surface, are characterized by a spectacular computational speed due to the simultaneous use of the multi-pole algorithm and the Boundary Element formulation and are limited only by the use of sharp material property variations [4]. We employ this new tool to unravel the causes of plate tectonic reorganizations, producing and comparing global plate motion with the reconstructed ones. References: [1] Torsvik, T., Müller, R.D., Van der Voo, R., Steinberger, B., and Gaina, C., 2008, Global Plate Motion Frames: Toward a unified model: Reviews in Geophysics, VOL. 46, RG3004, 44 PP., 2008 [2] Wessel, P. and Kroenke, L.W. Pacific absolute plate motion since 145 Ma: An assessment of the fixed hot spot hypothesis. Journal of Geophysical Research, Vol 113, B06101, 2008 [3] L. Quevedo, G. Morra, R. D. Mueller. Parallel Fast Multipole Boundary Element Method for Crustal Dynamics, Proceeding 9th World Congress and 4th Asian Pacific Congress on Computational Mechanics, July 2010, iopscience.iop.org/1757-899X/10/1/012012. [4] G. Morra, P. Chatelain, P. Tackley and P. Koumoutzakos, 2007, Large scale three-dimensional boundary element simulation of subduction, in Proceeding International Conference on Computational Science - Part III, LNCS 4489, pp. 1122-1129. Interaction between two subducting slabs.

Morra, G.; Quevedo, L.; Butterworth, N.; Matthews, K. J.; Müller, D.

2010-12-01

269

Author's personal copy Plate tectonic reconstructions with continuously closing plates$  

E-print Network

Author's personal copy Plate tectonic reconstructions with continuously closing plates$ Michael May 2011 Keywords: Geodynamics Plate tectonics a b s t r a c t We present a new algorithm for modeling margins and plates, traditional global plate tectonic reconstructions have become inadequate

Bower, Dan J.

270

Prediction of Emperor-Hawaii seamount locations from a revised model of global plate motion and mantle flow  

Microsoft Academic Search

The bend in the Hawaiian-Emperor seamount chain is a prominent feature usually attributed to a change in Pacific plate motion ~47Myr ago. However, global plate motion reconstructions fail to predict the bend. Here we show how the geometry of the Hawaiian-Emperor chain and other hotspot tracks can be explained when we combine global plate motions with intraplate deformation and movement

Bernhard Steinberger; Rupert Sutherland; Richard J. O'Connell

2004-01-01

271

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.

272

The Moving Plates  

NSDL National Science Digital Library

This lesson focuses on relative versus absolute velocity. Students can use a program (must be connected to the internet) to calculate the different types of velocities for different points along plate boundaries. A very brief description of the earth's plates is given, with links to additional information and images. Includes discussion questions.

273

Mapping Plate Boundaries  

NSDL National Science Digital Library

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

Johnson, Rurik

2009-11-12

274

How Do Plates Move?  

NSDL National Science Digital Library

The representation shows the circulation of convection cells in the mantle related to plate movement. A static cross-sectional diagram and accompanying text illustrates the how material heated by the core rises and then sinks when it eventually cools down and attributes this cycle of heating and cooling to tectonic plate movement.

275

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). PMID:16045807

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

2005-01-01

276

Plating To Reinforce Welded Joints  

NASA Technical Reports Server (NTRS)

Electrodeposition used to strengthen welded joints gouged, nicked, or suffered other mechanical damage. Plating cell, typically of acrylic plastic such as poly (Methylmetacrylate), is assembled around part to be plated. Areas not to be plated are masked with plater's tape. Weld area is plated in standard nickel-plating process.

Otousa, J. E.

1982-01-01

277

Plate Tectonics Prof. Thomas Herring  

E-print Network

1 Plate Tectonics Prof. Thomas Herring MIT 05/14/02 Lexington HS Plate tectonics 2 Contact/14/02 Lexington HS Plate tectonics 3 Overview · Development of the Plate tectonic theory · Geological Data ­ Sea-floor spreading ­ Fault types from earthquakes ­ Transform faults ­ Today's measurements of plate tectonics 05

Herring, Thomas

278

Intro to Plate Tectonic Theory  

NSDL National Science Digital Library

This website from PBS provides information about the plate tectonics, the theory that the Earth's outer layer is made up of plates, which have moved throughout time. The four types of plate boundaries are described and illustrated with animations. The first page of plate tectonics also provides a plate tectonics activity and information about related people and discoveries.

2008-05-28

279

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.

280

Thermophoresis of Graphene Plates  

NASA Astrophysics Data System (ADS)

Thermophoresis of graphene plates in an air medium is discussed within the framework of a molecular-kinetic approach. Its rate is found to be independent of the plate area and the aspect ratio of a rectangular graphene. It does depend on the plate orientation in space, which is controlled by the principle of least resistance. The dependence is expressed via a geometrical parameter ?, whose limiting values within the variation interval are found to be 0.46 and 0.65. A solution of the Euler problem on the Brownian rotation of a plate around its center of mass as a result of collisions of molecules in the temperature gradient field allowed us to obtain for the graphene plates a statistical average of ? =0.5. This value turned out to be the same as the one for spherical nanoparticles, for which rotations are irrelevant.

Bubenchikov, A. M.; Bubenchikov, M. A.; Potekaev, A. I.; Maslov, A. S.; Ovcharenko, V. V.; Usenko, O. V.

2014-11-01

281

Young tracks of hotspots and current plate velocities  

NASA Astrophysics Data System (ADS)

Plate motions relative to the hotspots over the past 4 to 7 Myr are investigated with a goal of determining the shortest time interval over which reliable volcanic propagation rates and segment trends can be estimated. The rate and trend uncertainties are objectively determined from the dispersion of volcano age and of volcano location and are used to test the mutual consistency of the trends and rates. Ten hotspot data sets are constructed from overlapping time intervals with various durations and starting times. Our preferred hotspot data set, HS3, consists of two volcanic propagation rates and eleven segment trends from four plates. It averages plate motion over the past ~5.8 Myr, which is almost twice the length of time (3.2 Myr) over which the NUVEL-1A global set of relative plate angular velocities is estimated. HS3-NUVEL1A, our preferred set of angular velocities of 15 plates relative to the hotspots, was constructed from the HS3 data set while constraining the relative plate angular velocities to consistency with NUVEL-1A. No hotspots are in significant relative motion, but the 95 per cent confidence limit on motion is typically +/-20 to +/-40 km Myr-1 and ranges up to +/-145 km Myr-1. The uncertainties of the new angular velocities of plates relative to the hotspots are smaller than those of previously published HS2-NUVEL1 (Gripp & Gordon 1990), while being averaged over a shorter and much more uniform time interval. Nine of the fourteen HS2-NUVEL1 angular velocities lie outside the 95 per cent confidence region of the corresponding HS3-NUVEL1A angular velocity, while all fourteen of the HS3-NUVEL1A angular velocities lie inside the 95 per cent confidence region of the corresponding HS2-NUVEL1 angular velocity. The HS2-NUVEL1 Pacific Plate angular velocity lies inside the 95 per cent confidence region of the HS3-NUVEL1A Pacific Plate angular velocity, but the 0 to 3 Ma Pacific Plate angular velocity of Wessel & Kroenke (1997) lies far outside the confidence region. We show that the change in trend of the Hawaiian hotspot over the past 2 to 3 Myr has no counterpart on other chains and therefore provides no basis for inferring a change in Pacific Plate motion relative to global hotspots. The current angular velocity of the Pacific Plate can be shown to differ from the average over the past 47 Myr in rate but not in orientation, with the current rotation being about 50 per cent faster (1.06 +/- 0.10 deg Myr-1) than the average (0.70 deg Myr-1) since the 47-Myr-old bend in the Hawaiian-Emperor chain.

Gripp, Alice E.; Gordon, Richard G.

2002-08-01

282

PLATE TECTONICS USING GIS Understanding plate tectonics using real  

E-print Network

PLATE TECTONICS USING GIS Understanding plate tectonics using real global data sets pertaining OF THE UPSTATE, SC An afternoon field trip to observe the evidences for plate tectonic history, and to witness

283

The surface and through crack problems in layered orthotropic plates  

NASA Technical Reports Server (NTRS)

An analytical method is developed for a relatively accurate calculation of Stress Intensity Factors in a laminated orthotropic plate containing a through or part-through crack. The laminated plate is assumed to be under bending or membrane loading and the mode 1 problem is considered. First three transverse shear deformation plate theories (Mindlin's displacement based first-order theory, Reissner's stress-based first-order theory, and a simple-higher order theory due to Reddy) are reviewed and examined for homogeneous, laminated and heterogeneous orthotropic plates. Based on a general linear laminated plate theory, a method by which the stress intensity factors can be obtained in orthotropic laminated and heterogeneous plates with a through crack is developed. Examples are given for both symmetrically and unsymmetrically laminated plates and the effects of various material properties on the stress intensity factors are studied. In order to implement the line-spring model which is used later to study the surface crack problem, the corresponding plane elasticity problem of a two-bonded orthotropic plated containing a crack perpendicular to the interface is also considered. Three different crack profiles: an internal crack, an edge crack, and a crack terminating at the interface are considered. The effect of the different material combinations, geometries, and material orthotropy on the stress intensity factors and on the power of stress singularity for a crack terminating at the interface is fully examined. The Line Spring model of Rice and Levy is used for the part-through crack problem. The surface crack is assumed to lie in one of the two-layered laminated orthotropic plates due to the limitation of the available plane strain results. All problems considered are of the mixed boundary value type and are reduced to Cauchy type of singular integral equations which are then solved numerically.

Erdogan, Fazil; Wu, Binghua

1991-01-01

284

GEODVEL: Plate Motions From Space Geodesy  

NASA Astrophysics Data System (ADS)

We determine the relative angular velocities among eleven major plates using four space geodetic techniques. The data input consist of site motions estimated from 24 years of VLBI, 24 years of SLR, 14 years of GPS, and 12 years of DORIS data. We assign sites to plates on the basis of geology. We let sites move independently of plates if they are suspected of moving significantly due to isostatic adjustment to unloading of the late Pleistocene ice sheets. GEODVEL differs substantially from REVEL [Sella et al. 2002]. The 95% confidence limits in the GEODVEL angular velocities exclude REVEL for 19 of 21 plate pairs. The median angular velocity difference is 0.026 deg/Myr, which is 2.9 mm/yr. We will show that this difference is due partly to differences in the means by which the velocity of Earth's center is determined. (Sella et al. 2002 adopt ITRF19997; ITRF2000 differs from ITRF1997 by 2 mm/yr; we estimate the Earth center velocity to be near ITRF2000.) The relative angular velocities of seven plates are tightly constrained: North America, Eurasia, South America, Nubia, Pacific, Australia, and Antarctica. The three-dimensional standard error ellipsoids have principal semiaxes between 0.005 deg/Myr and 0.014 deg/Myr long; the one-dimensional 95% confidence limits are 0.6 to 1.8 mm/yr. We will compare GEODVEL against an updated set of angular velocities determined from seafloor spreading rates and transform azimuths.

Argus, D. F.; Gordon, R. G.; Ma, C.; Eanes, R. J.; Heflin, M. B.; Owen, S. E.; Willis, P.

2006-12-01

285

NNR-MORVEL56: No-net-rotation model of geologically current plate motions  

NASA Astrophysics Data System (ADS)

We determine NNR-MORVEL56, a set of estimates of the velocities of 56 plates relative to the reference frame yielding no net rotation of the plates. We furthermore determine the full 168 by 168 covariance matrix describing uncertainties in the 56 velocities. 25 plate velocities are from geologically current plate motion model MORVEL [DeMets et al. 2010]; 31 plate velocities are from Bird [2003]. We calculate the 31 plate velocities relative to the MORVEL plates in the same manner by which Bird [2003] calculated them relative to NUVEL-1A. Because the 31 plates from Bird [2003] comprise just 2.8% of Earth’s surface, NNR-MORVEL56, they contribute insignificantly to the no-net-rotation frame; The estimates of the 31 plates from Bird [2003] relative to the 25 plates in MORVEL are nevertheless useful. The velocity of the Pacific plate differs between NNR-MORVEL56 and hotspot model HS3B-MORVEL [Zheng et al., abstract in GP session] on plate motion and reference frames] by a highly significant 0.34 °/Myr, which is up to 38 mm/y on Earth’s surface. This difference is 23 per cent smaller than our prior estimate of the difference from NNR-NUVEL1A [Argus and Gordon 2001] and HS3-NUVEL1A [Gripp and Gordon 2002].

Argus, D.; Gordon, R. G.; Demets, C.; Zheng, L.

2010-12-01

286

Oregon offers something for everyone who loves the outdoors --especially geologists. Oregon is a land filled with wonder and intrigue. Over the state's long history, plate tectonic and volcanic activity  

E-print Network

. Oregon is a land filled with wonder and intrigue. Over the state's long history, plate tectonic tectonic plate under- neath the Pacific Ocean produced the Coast Range over millions of years. Hot fluids coming off the diving plate, beginning about 35 million years ago, resulted in the volcanic eruptions

Tullos, Desiree

287

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

NASA Astrophysics Data System (ADS)

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

Eagles, Graeme; Scott, Benjamin G. C.

2014-12-01

288

Pacific Tsunami Museum  

NSDL National Science Digital Library

The Pacific Tsunami Museum is dedicated to promoting public education about tsunamis for citizens of Hawaii and the Pacific Region, as well as preserving the social and cultural history of Hawaii. Materials available at the museum's site include a listing of exhibits, a link to a webcam overlooking Hilo Bay, and event announcements. There is also a listing of programs sponsored by the museum, including class visits, a tsunami observer program and evacuation notification team, and a walking tour of historical tsunami sites. The students' page features games and puzzles, a frequently-asked-questions feature, links to related websites, and an online collection of tsunami warning signs. Other materials include a collection of tsunami-related art, interviews with survivors, and an archive of photographs.

289

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.

290

Earthquakes and plate tectonics.  

USGS Publications Warehouse

Earthquakes occur at the following three kinds of plate boundary: ocean ridges where the plates are pulled apart, margins where the plates scrape past one another, and margins where one plate is thrust under the other. Thus, we can predict the general regions on the earth's surface where we can expect large earthquakes in the future. We know that each year about 140 earthquakes of magnitude 6 or greater will occur within this area which is 10% of the earth's surface. But on a worldwide basis we cannot say with much accuracy when these events will occur. The reason is that the processes in plate tectonics have been going on for millions of years. Averaged over this interval, plate motions amount to several mm per year. But at any instant in geologic time, for example the year 1982, we do not know, exactly where we are in the worldwide cycle of strain build-up and strain release. Only by monitoring the stress and strain in small areas, for instance, the San Andreas fault, in great detail can we hope to predict when renewed activity in that part of the plate tectonics arena is likely to take place. -from Author

Spall, H.

1982-01-01

291

Plate Tectonics Jigsaw  

NSDL National Science Digital Library

This activity is a slight variation on an original activity, Discovering Plate Boundaries, developed by Dale Sawyer at Rice University. I made different maps, including more detail in all of the datasets, and used a different map projection, but otherwise the general progression of the activity is the same. More information about jigsaw activities in general can be found in the Jigsaws module. The activity occurs in several sections, which can be completed in one or multiple classes. In the first section, students are divided into "specialist" groups, and each group is given a global map with a single dataset: global seismicity, volcanoes, topography, age of the seafloor, and free-air gravity. Each student is also given a map of plate boundaries. Their task in the specialist group is to become familiar with their dataset and develop categories of plate boundaries based only on their dataset. Each group then presents their results to the class. In the second section, students reorganize into groups with 1-2 of each type of specialist per group. Each new group is given a plate, and they combine their different datasets on that one plate and look for patterns. Again, each plate group presents to the class. The common patterns and connections between the different datasets quickly become apparent, and the final section of the activity involves a short lecture from the instructor about types of plate boundaries and why the common features are generated at those plate boundaries. A follow-up section or class involves using a problem-solving approach to explain the areas that don't "fit" into the typical boundary types - intra-plate volcanism, earthquakes in the Eastern California Shear Zone, etc.

Egger, Anne

292

Identification of the North American plate in east Siberia by means of GPS  

NASA Astrophysics Data System (ADS)

Since 1995, the Russia/US collaborative Project RUSEG provided GPS observations over the vast landmass of east Asia including the Arctic region. Project participants are: RDAAC/GSRAS (G. Steblov) on the Russian side; Columbia U. (M. Kogan and C. Scholz), MIT (R. King), and U. of California - Berkeley (R. Burgmann) on the US side. The authors of this talk analyzed convergence of Eurasian, North American, and Pacific plates in east Asia using the GPS solution LDO_030112. It is based on observations collected in 1996-2002 at about 50 stations in east Siberia, the Urals, Kamchatka, and Sakhalin, combined with 74 global IGS stations and 6 stations in the Pacific plate. The 3-plate reference frame is defined independently of geologic plate models. Comparison of velocities in east Asia relative to Eurasia and to North America allows us to conclude that east Siberia to the east of the Cherskiy Range belongs to the North American plate. This was hypothesized since the onset of the plate tectonic concept but it was never proved geodetically. The plate geometry in east Asia compatible with GPS velocities is the simplest possible: the interaction of three major plates. The existence of microplates in this region is not evidenced by GPS. A distributed non-platelike deformation is characteristic of China. Plate-related GPS velocities in stable interiors of Eurasian, North American, and Pacific plates are remarkably uniform and small, 0.6-0.7 mm/yr indicating average strain rates on the order of 1e-10.

Kogan, M.; Steblov, G.; Scholz, C.

2003-04-01

293

Farallon Plate remnants  

NSDL National Science Digital Library

The Rockies are fifteen hundred kilometers, or one thousand miles, to the east. The cause must be the tectonic plate that built these mountains. Its name is Farallon. Farallon started off normally enough. It plunged beneath the North American Plate at a forty-five degree angle. This process sprouted volcanoes to form the Sierra Nevada in what is now California. Next, mantle motions pulled North America westward over Farallon, and the plate scraped along the bottom of the continent - for fifteen hundred kilometers. As North America continued its westward trek, Farallon settled to the bottom of the mantle.

Stuart Snodgrass

2002-03-14

294

Plate Tectonics at Work  

NSDL National Science Digital Library

This is a brief description of the results of plate movement according to the Theory of Plate Tectonics. It explains how divergence at the mid-ocean ridges accounts for the discoveries of Harry Hess. The site also refers to the invention of the magnetometer and the discovery of the young age of the ocean floor basalt. It concludes that these are the kinds of discoveries and thinking that ultimately led to the development of the theory of plate tectonics and that in just a few decades, have greatly changed our view of and notions about our planet and the sciences that attempt to explain its existence and development.

295

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.

296

Po Anisotropy in Old Pacific Lithosphere  

NASA Astrophysics Data System (ADS)

Po is the high frequency, scattered P phase guided within the oceanic lithosphere, sometimes known as Pn. During the PLATE experiment (Pacific Lithosphere Anisotropy and Thickness Experiment), in which two subarrays of ocean bottom seismometers were deployed on old seafloor (~150-160 Ma) in the northwestern Pacific south of the Shatsky Rise, we recorded 5 to 6 Po phases per day generated by earthquakes in western Pacific subduction zones. Each subarray was deployed on an arm of a magnetic bight, where the magnetic anomalies form a 90° bend that was created at a ridge-ridge-ridge triple junction. Spreading rates on both limbs were fast, about 70 mm/yr halfrate. Our goal is to decipher the pattern of anisotropy as a function of depth in the oceanic lithosphere and asthenosphere, taking advantage of the right angle bend in seafloor spreading direction to more clearly reveal the transition between fossil anisotropy in the lithosphere and dynamically maintained anisotropy in the asthenosphere. Po and So anisotropy as a function of frequency will provide some of the needed constraints on lithospheric anisotropy. Using more than 600 Po phases from earthquakes listed in PDE catalogs during the one year deployment, we find that the velocity on each limb as measured by the onsets of the phases in the 10 to 15 Hz band varies from 8.6 km/s in the fast direction perpendicular to the magnetic anomalies to about 7.9 km/s parallel to the anomalies. This large anisotropy is consistent with seismic refraction measurements and the idea that anisotropy in the shallow lithosphere is strongest at fast spreading rates.

Forsyth, D. W.; Weeraratne, D. S.; Rau, C. J.; Rowe, Z.

2011-12-01

297

Tsunami deposits in Holocene bay mud in southern Kanto region, Pacific coast of central Japan  

Microsoft Academic Search

Tsunami have probably deposited sand sheets that are intercalated in Holocene bay-floor mud exposed on the Boso and Miura Peninsulas, facing the convergent boundary of the Pacific, Philippine Sea, and Eurasian Plates. We have identified seven sand sheets at four drowned valleys, and correlated these by 137 radiocarbon dates of shells and wood. The sheets consist of poorly sorted muddy

O. Fujiwara; F Masuda; T Sakai; T Irizuki; K Fuse

2000-01-01

298

Equatorial Pacific Sediment Deposition during the Early to Middle Miocene: Carbon Cycling and Proxies for Productivity  

E-print Network

by plate tectonics, as expected. In contrast, CaCO?, accumulation was low in the divergence region, and coincides with a dissolution event known from other site studies in the equatorial Pacific. The pattern of uranium deposition resembles CaCO? and Corg...

Piela, Christine Marie

2012-02-14

299

Seismological evidence of mantle flow driving plate motions at a palaeo-spreading centre  

NASA Astrophysics Data System (ADS)

A long-standing question about the dynamics of mid-ocean spreading centres is whether mantle upwelling is passive or active. During passive upwelling, the motion of the overlying plate would be expected to drive mantle flow. In contrast, during active upwelling, decompression melting of the mantle beneath the spreading axis would result in a low-density melt that creates local buoyancy, forcing mantle convection and driving plate motion. Seismic images of older parts of the Pacific Plate reveal dipping reflectors in the lower crust that could be shear zones created by active mantle flow, but there is little seismological evidence to indicate that mantle flow drags the plate. Here we use active-source seismic data to image the Pacific Plate that was created at a palaeo-spreading centre in the northwest Pacific Ocean. We identify very high P-wave velocities of 8.5-8.6 km s-1 and strong seismic anisotropy of 8.5-9.8% in the uppermost mantle, immediately below the lower-crustal dipping reflectors. We suggest that such strong seismic anisotropy, caused by the alignment of olivine crystals in response to mantle flow, could have been generated if mantle flow was much faster than plate motion. We conclude that both the lower-crustal dipping reflectors and the anisotropy were formed by a drag force at the Moho caused by rapid mantle flow, providing direct evidence for active mantle flow at a spreading centre.

Kodaira, Shuichi; Fujie, Gou; Yamashita, Mikiya; Sato, Takeshi; Takahashi, Tsutomu; Takahashi, Narumi

2014-05-01

300

Quarter Wave Plate Program  

NSDL National Science Digital Library

The Quarter Wave Plate program displays the effect of a quarter wave plate on an incident electromagnetic wave. The default electromagnetic wave is plane polarized but this polarization can be changed by specifying the components of the waveâs Jones vector using the input fields. The slider can be used to rotate the quarter wave plate to change its orientation. Quarter Wave Plate is an Open Source Physics program written for the teaching of optics. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the optics_quarterwave.jar file will run the program if Java is installed. Other optics programs are also available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Optics.

Simov, Kiril; Christian, Wolfgang

2008-05-20

301

Half Wave Plate Program  

NSDL National Science Digital Library

The Half Wave Plate program displays the effect of a half wave plate on an incident electromagnetic wave. The default electromagnetic wave is plane polarized but this polarization can be changed by specifying the components of the waveâs Jones vector using the input fields. The slider can be used to rotate the half wave plate to change its orientation. Half Wave Plate is an Open Source Physics program written for the teaching of optics. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the optics_halfwave.jar file will run the program if Java is installed. Other optics programs are also available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Optics.

Simov, Kiril; Christian, Wolfgang

2008-05-20

302

Violin plate modes.  

PubMed

As the first step toward developing a generic model for the acoustically radiating vibrational modes of the violin and related instruments, the modes of both freely supported and edge-constrained top and back plates have been investigated as functions of shape, arching height, elastic anisotropy, the f-holes and associated island area, thickness graduations, and the additional boundary constraints of the ribs, soundpost, and bass-bar present in the assembled instrument. Comsol shell structure finite element software has been used as a quasi-experimental tool, with physical and geometric properties varied smoothly, often over several orders of magnitude, allowing the development of the plate modes to be followed continuously from those of an initially square plate to those of doubly-arched, guitar-shaped, orthotropic plates and their dependence on all the above factors. PMID:25618046

Gough, Colin

2015-01-01

303

Feynman's wobbling plate  

NASA Astrophysics Data System (ADS)

In the book Surely You Are Joking, Mr. Feynman! Richard Feynman tells a story of a Cornell cafeteria plate being tossed into the air. As the plate spun, it wobbled. Feynman noticed a relation between the two motions. He solved the motion of the plate by using the Lagrangian approach. This solution didn't satisfy him. He wanted to understand the motion of the plate by analyzing the motion of its individual particles and the forces acting on them. He was successful, but he didn't tell us how he did it. We provide an elementary explanation for the two-to-one ratio of wobble to spin frequencies, based on an analysis of the motion of the particles and the forces acting on them. We also demonstrate the power of numerical simulation and computer animation to provide insight into a physical phenomenon and guidance on how to do the analysis.

Tuleja, Slavomir; Gazovic, Boris; Tomori, Alexander; Hanc, Jozef

2007-03-01

304

Tectonic Plate Movement.  

ERIC Educational Resources Information Center

Presents an activity that employs movement to enable students to understand concepts related to plate tectonics. Argues that movement brings topics to life in a concrete way and helps children retain knowledge. (DDR)

Landalf, Helen

1998-01-01

305

Flat plate solar oven  

SciTech Connect

The construction of an Indian Rs. 186 (US $20.33) flat-plate solar oven is described. Detailed drawings are provided and relevant information on cooking times and temperature for different foods is given.

Parikh, M.

1981-01-01

306

Plate Tectonics Learning Module  

NSDL National Science Digital Library

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

Haberlin, Rita

307

The effects of emitter-tied field plates on lateral PNP ionizing radiation response  

SciTech Connect

Radiation response comparisons of lateral PNP bipolar technologies reveal that device hardening may be achieved by extending the emitter contact over the active base. The emitter-tied field plate suppresses recombination of carriers with interface traps.

Barnaby, H.J.; Schrimpf, R.D.; Cirba, C.R. [Vanderbilt Univ., Nashville, TN (United States); Pease, R.L. [RLP Research, Inc., Albuquerque, NM (United States); Fleetwood, D.M. [Sandia National Labs., Albuquerque, NM (United States); Kosier, S.L. [VTC Inc., Bloomington, MN (United States)

1998-03-01

308

Plate Tectonics: An Introduction  

NSDL National Science Digital Library

In the early 1900s, most geologists thought that Earth's appearance, including the arrangement of the continents, had changed little since its formation. This video segment describes the impact the theory of plate tectonics has had on our understanding of Earth's geological history, and provides a brief overview of what is currently known about the Earth's tectonic plates and their motions. The segment is two minutes twenty-one seconds in length. A background essay and list of discussion questions are also provided.

309

Fractal multifiber microchannel plates  

NASA Technical Reports Server (NTRS)

The construction and performance of microchannel plates (MCPs) made using fractal tiling mehtods are reviewed. MCPs with 40 mm active areas having near-perfect channel ordering were produced. These plates demonstrated electrical performance characteristics equivalent to conventionally constructed MCPs. These apparently are the first MCPs which have a sufficiently high degree of order to permit single channel addressability. Potential applications for these devices and the prospects for further development are discussed.

Cook, Lee M.; Feller, W. B.; Kenter, Almus T.; Chappell, Jon H.

1992-01-01

310

The San Andreas fault experiment. [gross tectonic plates relative velocity  

NASA Technical Reports Server (NTRS)

A plan was developed during 1971 to determine gross tectonic plate motions along the San Andreas Fault System in California. Knowledge of the gross motion along the total fault system is an essential component in the construction of realistic deformation models of fault regions. Such mathematical models will be used in the future for studies which will eventually lead to prediction of major earthquakes. The main purpose of the experiment described is the determination of the relative velocity of the North American and the Pacific Plates. This motion being so extremely small, cannot be measured directly but can be deduced from distance measurements between points on opposite sites of the plate boundary taken over a number of years.

Smith, D. E.; Vonbun, F. O.

1973-01-01

311

The East Asian Sea: A vanished Cenozoic ocean between the Pacific and Indian oceans revealed by subducted slab constraints  

NASA Astrophysics Data System (ADS)

We have mapped an extensive 2500 km by 7500 km swath of sub-horizontal slabs at 600 to 1200 km depths that we call the 'East Asian Sea'. The northern margin of the East Asian Sea slabs begin at Taiwan and Japan, and extend south to SE Australia near New Zealand, underlying the Philippine Sea, the Caroline Sea, New Guinea, and northern to eastern Australia. When restored with other mapped slabs under Asia-Oceania, the mapped slabs reveal a vanished ocean that existed between the Pacific and Indian oceans in the Cenozoic. The subduction of the Asian Sea fills a crucial gap in plate tectonic reconstructions of East Asia by accounting for a significant proportion of fast Pacific and Indo-Australian convergence towards Eurasia since 43 Ma, during which time the Pacific moved ~3000 km WNW and Australia moved ~2500 km northward in a near-orthogonal direction relative to a mantle reference. In addition, the Australian plate expanded up to 2000 km at its northern and eastern margins. Slabs were primarily mapped from the MITP08 global P-wave mantle tomographic model (Li et al., 2008) and compared to other global P- and S-wave global tomography. Reconstructed slab lengths were assessed by quantitative flexural slip unfolding of mid-slab surfaces to a spherical Earth surface model. Seismic tomographic volumes were also calculated for selected serial cross-sections. We present a plate tectonic reconstruction with the slab constraints, with the implication that the East Asian Sea was progressively overrun and subducted beneath the Philippine Sea, the Caroline Sea and the expanding Melanesian arcs. Reconstructions to earlier periods indicate the East Asian Sea was originally Pacific or proto-Pacific mantle lithosphere, and was fragmented from the Pacific plate during the major ~45 Ma Eocene motion change. This implies that the East Asian Sea was initially the upper plate of the Mariana and Tonga-Kermadec Western Pacific subduction zones.

Wu, Jonny; Lu, Renqi; Suppe, John; Kanda, Ravi V. S.

2014-05-01

312

The Pacific Region.  

PubMed

Population education in the Pacific region is summarized in terms of awareness and commitment, curriculum and instructional materials development, integration into the school curricula, training programs, and evaluation research. Several population education issues of current concern relate to the increase in chronic diseases such as diabetes and hypertension that are associated with life styles and diet, and the rising incidence of AIDS and teenage pregnancy. In the Pacific region, many countries have advanced population programs and policies, while some still do not even have a population policy. The issue of balancing population and resources is a topic that has not been sufficiently addressed in resource-poor countries. There is wide variance in awareness and commitment to population education in the Pacific region. Commitment and continuous support are crucial to population education projects. Lack of support is sometimes due to changing government personnel and lack of awareness of policy makers. Population education is not the same as family planning or sex education, and traditionally is spread through seminars and workshops by part time project personnel unconnected to the entire educational apparatus. Presently, only 8 population projects are functioning in the region, with 2-3 in the planning stages. Materials development in the Pacific region has been devoted to the secondary school level, yet awareness is increasing that sexuality, family health, and the environment should be introduced at the primary level. A popular strategy is to integrate population issues into the existing curriculum, such as in Fiji, the Marshall Islands, and Kiribati, which also have teacher training curriculum. In most countries sex education is still a controversial topic, and materials are developed by teacher committees working after school rather in a curriculum development unit. AIDS has pushed this topic into the public sector. A chart is provided for each country and curriculum with population education and the level of schooling for formal and informal education. Training programs tend to be orientation workshops, materials development workshops, or teacher training workshops. Evaluation research in population education has been weak, due to an emphasis on program implementation, curriculum development, and limited resources and expertise. PMID:12286393

Tagica, K

1993-03-01

313

Pacific Northwest National Laboratory  

NSDL National Science Digital Library

The Pacific Northwest National Laboratory, one of nine US Department of Energy multi-program national laboratories, conducts research concerning environmental science and technology. This huge site holds information on research in atmospheric science and climate change, analytic and physical chemistry, computational science and engineering, environmental remediation, statistics, thermal and energy systems, and so much more. Many of the individual research pages contain downloadable publications. Section headings for the site include Energy, Environment, Health and Safety, Information Technology, National Security, and Nuclear Technology, among others. Also included here is the Environmental Molecular Sciences Laboratory, a facility that conducts "fundamental research on the physical, chemical, and biological processes that underpin critical environmental issues."

314

Animation of the Tectonic Evolution of the Southwest Pacific  

NASA Astrophysics Data System (ADS)

The marginal and back arc basins of the southwestern Pacific cover a region from almost the equator south to 40°S and from 150°E to 175°W. Included in this region is the well-studied Tasman Sea which ranges in age from Late Cretaceous to Early Eocene with its distinct abandoned spreading center clearly showing in the satellite-derived gravity data. The Coral Sea, also with a distinct abandoned seafloor spreading center is dated as Paleocene to Early Eocene. Opening of these two marginal basins set the stage for the development of the Fiji Basins/Lau Basin complex of back-arc basins. 'Eua, a volcanic arc island on the Tonga Arc, is dated from at least Middle Eocene. It rode outward as the southwestern Pacific back-arc and marginal basins opened behind it and indicates that subduction was on-going through most of the Cenozoic. While subduction zones make closure of plate circuits difficult, a reasonable plate tectonic scenerio for the southwestern Pacific will be presented in a global context. The impact of large igneous provinces [LIPs], such as the Ontong Java, as well as possible hotspot tracks on the southwestern Pacific will be considered. Prior to the opening of the Eocene and younger, southwestern Pacific back-arc basins, the west-dipping subduction zone that existed beneath the Lord Howe Rise - Three Kings Rise region was roughly sub-parallel to the magnetic isochrons found in the Central Pacific from anomalies C30 [~66 Ma] to C7 [~25 Ma]. These magnetic lineations between the major Galapagos and Resolution fracture zones disappear after C7 and only conclusively reappear after C4 [~7 Ma] with a different trend that is now roughly subparallel to the present day orientation of the Tonga-Kermadec trench. It is possible that the opening of the southwestern marginal basins and the reorientation of the westward-dipping subduction zone had a profound effect on the spreading direction of the East Pacific Rise.

Lawver, L. A.; Gahagan, L. M.

2002-12-01

315

Global strike-slip faults: Bounds from plate tectonics  

NASA Astrophysics Data System (ADS)

According to the tenets of plate tectonics, a transform fault is a strike-slip fault along which neither convergence nor divergence occurs. Analysis of global plate motion data indicates that the only true transform faults are the strike-slip faults that offset segments of mid-ocean ridges. Thus, many of Earth's major strike-slip fault systems are not true transform faults as they accommodate large components of oblique convergence or oblique divergence. This is particularly true for several important ocean-continent systems such as the San Andreas, the strike-slip systems bounding the northern and southern Caribbean plate, the Alpine fault system of New Zealand, the Anatolian fault system, and the Azores-Gibraltar-Alboran sea system. These strike-slip systems are commonly sites of large scale mountain building and basin formation. Here we examine the far-field constraints on the motions of the plates bounding several of these strike-slip systems using both conventional plate motion circuits and results from global positioning system and other space geodetic data. We pay particular attention to the San Andreas fault system in central and northern California, where the San Andreas system is part of the boundary between the Sierran microplate and the Pacific plate. Most of the fault system accommodates obliquely convergent motion, giving rise to the California Coast Range, but in the northern San Francisco Bay Area it is obliquely divergent, producing San Pablo Bay and a gap in the Coast Range that permits the Sierran watershed to drain to the Pacific through the Golden Gate.

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

2006-12-01

316

Scintillating plate calorimeter mechanical design  

Microsoft Academic Search

Progress on designs for compensating scintillator plate calorimeters will be presented. One design includes a lead composite absorber, fiber readout, and radiation hardened scintillator plates, and the second design has depleted uranium absorbers, wave length shifter plate readout, and scintillator plates. The lead absorber is cast with slots to accept the scintillator in the first design, while the depleted uranium

A. Buehring; N. Hill; T. Kirk; J. Nasiatka; E. Petereit; L. Price; J. Proudfoot; H. Spinka; D. Underwood; M. Burke; D. Hackworth; T. Hordubay; D. Marshik; D. Scherbarth; R. Swensrud

1990-01-01

317

An Introduction to Plate Tectonics  

NSDL National Science Digital Library

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

318

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

319

Caribbean plate interactions  

SciTech Connect

Vector analysis of plate motions, derived from studies of Atlantic magnetic lineations and fracture zone trends, indicates the following relative movements between the Caribbean, North American, and South American Plates. (1) During Early Jurassic to Early Cretaceous, the North American Plate moved 1900 km westward and 900 km northward relative to the South American Plate. A broad zone including the Caribbean region, i.e., the zone between the North and South America Plates, was a site of left-lateral shear and north-south extension. (2) During Early Cretaceous to Late Cretaceous, the North American Mate moved an additional 1200 km westward relative to South America across this zone. (3) During Late Cretaceous to the end of the Eocene, the North American Plate moved 200 km westward and 400 km northward relative to the South American Plate. (4) From the end of the Eocene to near the end of the Miocene, North America converged on South America some 200 km and moved 100 km eastward relative to it. Through the Mesozoic and earliest Tertiary history of the Caribbean, the region was a shear zone within which left-lateral displacement exceeded 3000 km and north-south extension exceeded 1300 km. In regard to time, 80% of the history of the Caribbean region is one of north-south extension and left-lateral shear. In terms of space, 97% of the shear is left-lateral and the ratio of divergence versus convergence is 7 to 1. Thus, characterizing the Caribbean region, and the Atlantic to its east, as a zone of north-south extension and left-lateral shear, is a fair generalization.

Ball, M. (Geological Survey, Denver, CO (United States))

1993-02-01

320

Musical Plates: A Study of Plate Tectonics  

NSDL National Science Digital Library

In this project, students use Real-Time earthquake and volcano data from the Internet to explore the relationship between earthquakes, plate tectonics, and volcanoes. There is a teachers guide that explains how to use real time data, and in the same section, there is a section for curriculum standards, Supplement and enrichment activities, and assessment suggestions. Included on this webpage are four core activities, and three enrichment activities, including an activity where the student writes a letter to the president. There is also a link to reference materials that might also interest you and your students.

2007-01-01

321

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

Microsoft Academic Search

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

Vladimir Kostoglodov

1988-01-01

322

Development and implementation of adaptive critic based optimal neurocontroller on a cantilever plate  

Microsoft Academic Search

An adaptive critic-based optimal neurocontroller was developed and applied to a non-linear cantilevered plate system to improve its vibrational characteristics. The smart structural system which incorporates a two dimensional aluminum plate mounted with PZT actuators and PVDF sensors is interfaced to a PC with a DAS 1600 data acquisition card. The neural network plant model was acquired from a previous

Abhishek Gupta; S. N. Balakrishnan; Levent Acar

1999-01-01

323

Hypervelocity Impact on Interfaces: A Molecular-Dynamics Simulations Study  

NASA Astrophysics Data System (ADS)

Silicon/silicon nitride interfaces are found in micro electronics and solar cells. In either application the mechanical integrity of the interface is of great importance. Molecular-dynamics simulations are performed to study the failure of interface materials under the influence of hypervelocity impact. Silicon nitride plates impacting on silicon/silicon nitride interface targets of different thicknesses result in structural phase transformation and delamination at the interface. Detailed analyses of atomic velocities, bond lengths, and bond angles are used to qualitatively examine the respective failure mechanisms.

Bachlechner, Martina E.; Owens, Eli T.; Leonard, Robert H.; Cockburn, Bronwyn C.

2008-03-01

324

Delamination characterization of composite plates with holes/inclusions under general in-plane loading  

E-print Network

/epoxy plates under tensile loads l5) . The FEM model The quasi ? 3D isoparametric element Representative model showing Guassian points in mesh 1' or the evalu- ation of stresses along the interfaces and free edge FEM model used to evaluate strain energy... to uniaxial tension . . . . . . . . . . . . . 35 Interlaminar stresses through the thickness at the free edge for a plate with a through hole subjected to uniaxial tension . . . . . . . . . 36 Maximum interlaminar stresses through the thickness for a, plate...

Bense, Ronald

2012-06-07

325

A plate tectonic model of the Palaeozoic tectonic history of New South Wales  

Microsoft Academic Search

An updated* tectonic model for the Palaeozoic tectonic history of New South Wales, based on actualistic models of plate tectonics, has resulted from tectonic analyses and syntheses during the compilation of the Tectonic Map of New South Wales.Most emphasis is given to marginal seas, which characterize Pacific marginal mobile zones. Marginal seas form in the regime of lithospheric tension under

Erwin Scheibner

1973-01-01

326

Late Cretaceous to Paleogene plate motion, mantle flow and polar wander constrained by paleomagnetic data  

NASA Astrophysics Data System (ADS)

A wide range of investigations including plate circuit analyses, comparisons of the age progression of coeval hotspots on the Pacific plate and geodynamic modeling are consistent with paleomagnetic results that indicate motion of hotspots in Earth's mantle during Late Cretaceous to Paleogene times, with important changes in the rate of motion near 50 Ma. In the Pacific, the change has been hypothesized to reflect plume dynamics and hotspot-ridge capture; in the Cretaceous the two long-lived Pacific hotspots with well-defined age progressive tracks (Hawaii and Louisville) were near ridges that subsequently waned. In the case of the Hawaiian hotspot, the ridge in question appears to have become extinct close to the time of the bend in the hotspot track. Testing whether a deeper component of Pacific mantle flow also changed near 50 Ma requires a higher resolution investigation of reference frames for absolute plate motion. Here we use select paleomagnetic data prior to and after 50 Ma to test prior inferences about absolute plate motion changes and polar wander, and use these analyses to parse components of mantle flow.

Tarduno, J. A.; Bono, R.

2011-12-01

327

Survey of ion plating sources. [conferences  

NASA Technical Reports Server (NTRS)

Based on the type of evaporation source, gaseous media and mode of transport, the following is discussed: resistance, electron beam, sputtering, reactive and ion beam evaporation. Ionization efficiencies and ion energies in the glow discharge determine the percentage of atoms which are ionized under typical ion plating conditions. The plating flux consists of a small number of energetic ions and a large number of energetic neutrals. The energy distribution ranges from thermal energies up to a maximum energy of the discharge. The various reaction mechanisms which contribute to the exceptionally strong adherence - formation of a graded sustrate/coating interface are not fully understood, however the controlling factors are evaluated. The influence of process variables on the nucleation and growth characteristics are illustrated in terms of morphological changes which affect the mechanical and tribological properties of the coating.

Spalvins, T.

1979-01-01

328

About the REL Pacific Region  

ERIC Educational Resources Information Center

REL Pacific is one of ten Regional Educational Laboratories established and funded by the U.S. Department of Education's Institute of Education Sciences. Their region encompasses approximately 4.9 million square miles and serves seven Pacific island entities, including American Samoa; the Commonwealth of the Northern Mariana Islands; the…

Regional Educational Laboratory Pacific, 2014

2014-01-01

329

Regional Summary Pacific Management Context  

E-print Network

Regional Summary Pacific Management Context The Pacific Region includes California, Oregon surplus of healthier stocks is often restricted to protect weaker stocks with which they co to potential interactions with marine mammals, turtles, and seabirds. 3 In contrast to Inter-American Tropical

330

Origin and subsidence of Guyots in Mid-Pacific Mountains  

NASA Astrophysics Data System (ADS)

Morphologic and magnetic data suggest that the Mid-Pacific Mountains formed during Early Cretaceous time as a broad ENE trending double chain of midplate island seamounts over a mantle hot spot as the Pacific plate moved westward and slightly southward. Dredge, drill core, and reflection seismic data indicate that coral-rudistid reefs grew on the subsiding seamounts and evolved to atolls and banks, largely burying the volcanic foundations. Magnetic data indicate that by late Aptian time, about 110 Ma, the seamounts were located at about 20°-25°S, which we suggest was near the fringes of the latitudinal zone of vigorous reef growth, where upward growth rates could just keep up with subsidence. A broad uplift probably related to the widespread regional emplacement of Aptian volcanics as oceanic plateaus, seamounts, and deep-water flows and sills raised the Mid-Pacific Mountain reefs out of the water, and both reflection seismic and isotopic data suggest that a karstic topography developed on many of the emergent reefs. As subsidence recommenced, the reefs could hot grow upward apace with subsidence. Renewed volcanism in Late Cretaceous time in the easternmost Mid-Pacific Mountains maintained islands for a while, as at Horizon Guyot, but probably without large reefs. Elsewhere, pelagic conditions have prevailed as the guyots sank to their present-day depths. These depths are systematically related to the inferred age of the volcanic foundations, being greatest on the youngest volcanoes.

Winterer, Edward L.; Metzler, Christopher V.

1984-11-01

331

Tectonic Plates, Earthquakes, and Volcanoes  

NSDL National Science Digital Library

According to theory of plate tectonics, Earth is an active planet -- its surface is composed of many individual plates that move and interact, constantly changing and reshaping Earth's outer layer. Volcanoes and earthquakes both result from the movement of tectonic plates. This interactive feature shows the relationship between earthquakes and volcanoes and the boundaries of tectonic plates. By clicking on a map, viewers can superimpose the locations of plate boundaries, volcanoes and earthquakes.

332

Tomography and Dynamics of Western-Pacific Subduction Zones  

NASA Astrophysics Data System (ADS)

We review the significant recent results of multiscale seismic tomography of the Western-Pacific subduction zones and discuss their implications for seismotectonics, magmatism, and subduction dynamics, with an emphasis on the Japan Islands. Many important new findings are obtained due to technical advances in tomography, such as the handling of complex-shaped velocity discontinuities, the use of various later phases, the joint inversion of local and teleseismic data, tomographic imaging outside a seismic network, and P-wave anisotropy tomography. Prominent low-velocity (low-V) and high-attenuation (low-Q) zones are revealed in the crust and uppermost mantle beneath active arc and back-arc volcanoes and they extend to the deeper portion of the mantle wedge, indicating that the low-V/low-Q zones form the sources of arc magmatism and volcanism, and the arc magmatic system is related to deep processes such as convective circulation in the mantle wedge and dehydration reactions in the subducting slab. Seismic anisotropy seems to exist in all portions of the Northeast Japan subduction zone, including the upper and lower crust, the mantle wedge and the subducting Pacific slab. Multilayer anisotropies with different orientations may have caused the apparently weak shear-wave splitting observed so far, whereas recent results show a greater effect of crustal anisotropy than previously thought. Deep subduction of the Philippine Sea slab and deep dehydration of the Pacific slab are revealed beneath Southwest Japan. Significant structural heterogeneities are imaged in the source areas of large earthquakes in the crust, subducting slab and interplate megathrust zone, which may reflect fluids and/or magma originating from slab dehydration that affected the rupture nucleation of large earthquakes. These results suggest that large earthquakes do not strike anywhere, but in only anomalous areas that may be detected with geophysical methods. The occurrence of deep earthquakes under the Japan Sea and the East Asia margin may be related to a metastable olivine wedge in the subducting Pacific slab. The Pacific slab becomes stagnant in the mantle transition zone under East Asia, and a big mantle wedge (BMW) has formed above the stagnant slab. Convective circulations and fluid and magmatic processes in the BMW may have caused intraplate volcanism (e.g., Changbai and Wudalianchi), reactivation of the North China craton, large earthquakes, and other active tectonics in East Asia. Deep subduction and dehydration of continental plates (such as the Eurasian plate, Indian plate and Burma microplate) are also found, which have caused intraplate magmatism (e.g., Tengchong) and geothermal anomalies above the subducted continental plates. Under Kamchatka, the subducting Pacific slab shortens toward the north and terminates near the Aleutian-Kamchatka junction. The slab loss was induced by friction with the surrounding asthenosphere, as the Pacific plate rotated clockwise 30 Ma ago, and then it was enlarged by the slab-edge pinch-off by the asthenospheric flow. The stagnant slab finally collapses down to the bottom of the mantle, which may trigger upwelling of hot mantle materials from the lower mantle to the shallow mantle. Suggestions are also made for future directions of the seismological research of subduction zones.

Zhao, D.

2012-01-01

333

Updated test of fixity of the Iceland hotspot relative to Pacific hotspots  

NASA Astrophysics Data System (ADS)

Hotspot fixity has long been challenged on the basis of plate-circuit reconstructions. If the motion of one plate over its hotspots is known, and if these hotspots are assumed to be fixed with respect to those under the second plate, reconstructions of the past positions of the two plates can be used to compare the predicted positions of hotspots under the second plate with its known trace. If the plates are rigid, if all ancient plate boundaries in the global plate circuit have been recognized and incorporated, and if hotspots are fixed relative to one another, the predicted track should coincide with the known trace (within uncertainties). Inconsistencies, on the other hand, give an estimate of the relative motion between hotspots. Here we present updated predictions for the track of the Iceland hotspot assuming it to be fixed relative to a Pacific hotspot reference frame. We build on a new method for objectively estimating plate-hotspot rotations and their uncertainties (Andrews et al., 2006). Besides the uncertainties in plate-hotspot rotations, uncertainties in relative plate motions are accumulated through the plate circuit to obtain the final uncertainty in the predicted positions. Predictions are made for ages of 11 Ma (chron 5), 20 Ma (chron 6), 33 Ma (chron 13), 39 Ma (chron 18), 48 Ma (chron 21), 56 Ma (chron 25) and 68 Ma (chron 31). The current position of the Iceland hotspot is taken to be at 64°N, 344°E. The observed and predicted Iceland hotspot tracks are not significantly different over the past 48 Myr. The 68 Ma reconstructed point, however, lies ~1100 km from the oldest lavas on the West Coast of Greenland dated as about 65 Ma (Larsen et al., 1992). If this misfit occurred entirely between 68 Ma and 48 Ma, it gives an early Tertiary rate of motion between the Iceland and Pacific hotspots of about 55 ± 15 mm yr-1. Thus, we show that the Iceland hotspot has had no significant motion relative to a Pacific hotspot frame since 48 Ma. Prior to 48 Ma, however, the apparent inter-hotspot drift rates increase to about 55 ± 15 mm yr-1. A possible cause for the pre-48 Ma apparent motion is a systematic error in the global plate circuits used to make the predictions. Potential candidate for the error is pre-48 Ma motion across Antarctica.

Koivisto, E.; Andrews, D. L.; Gordon, R. G.

2008-12-01

334

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

NASA Technical Reports Server (NTRS)

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

Gordon, R. G.

1998-01-01

335

Bipolar battery plate  

NASA Technical Reports Server (NTRS)

A liquid-impermeable plate (10) having through-plate conductivity with essentially zero resistance comprises an insulator sheet (12) having a series of spaced perforations (14) each of which contains a metal element (16) sealingly received into the perforation (14). A low-cost plate can readily be manufactured by punching a thermoplastic sheet (40) such as polypropylene with a punching tool (52), filling the apertures with led spheres (63) having a diameter smaller than the holes (50) but larger than the thickness of the sheet, sweeping excess spheres (62) off the sheet with a doctor blade (60) and then pressing a heated platen (74) onto the sheet to swage the spheres into a cylindrical shape and melt the surrounding resin to form a liquid-impermeable collar (4) sealing the metal into the sheet.

Rowlette, John J. (Inventor)

1987-01-01

336

Discovering Plate Boundaries  

NSDL National Science Digital Library

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

2007-12-12

337

Plate Tectonics and Volcanism  

NSDL National Science Digital Library

This is a lesson where learners explore plate movement and the relationship between plate tectonics and volcanoes. The lesson models scientific inquiry using the 5E instructional model and includes teacher notes, prerequisite concepts, common misconceptions, student journal and reading. This is lesson five in the Astro-Venture Geology Training Unit that was developed to increase students' awareness of and interest in astrobiology and the many career opportunities that utilize science, math and technology skills. The lessons are designed for educators to use with the Astro-Venture multimedia modules.

338

Azimuthal anisotropy layering in the Pacific upper mantle  

NASA Astrophysics Data System (ADS)

As the mechanically strong outer layer of the Earth, the lithosphere is a fundamental component in plate tectonics. Resolving the internal structure of the lithosphere and underlying asthenosphere, as well as the coupling between the two, is critical for our understanding of the formation, stabilization and subsequent deformation of continents and oceans. One key aspect of the problem, identified as one of the Grand Challenges of modern seismology, is the thickness of lithosphere, or the depth of the lithosphere-asthenosphere-boundary (LAB). Seismic detection of the LAB, however, remains 'elusive', possibly due to the smooth character of the seismic velocity gradient across the boundary. In continents recent surface wave studies have proven azimuthal anisotropy a powerful tool in revealing the internal structure of the continental lithosphere and its boundary with the asthenosphere (e.g. Yuan and Romanowicz, 2010). Here we expand our regional waveform inversion to the much greater size Pacific region, focusing on the 3D anisotropic structure of the oceanic upper mantle. Specifically, we look for the anisotropy stratification signal beneath the ocean basins, and correlate it with simultaneously inverted isotropic shear velocities to infer the structure of the Pacific oceanic lithosphere and asthenosphere, and the LAB topography throughout the region. Our results show a strong age progressive pattern in isotropic shear velocity, radial anisotropy and azimuthal anisotropy. Two domains of azimuthal anisotropy are observed in the upper 250 km, each possessing a distinct fast axis direction of anisotropy. An anisotropic LAB is drawn in the Pacific, which maps the rapid depth variation of fast axis directions toward the current absolute plate direction. At slightly shallower depth, an isotropic shear velocity horizon is robustly defined throughout the ocean basin, based on maximum negative velocity gradients with respect to depth. We argue that the offset between the two horizons reflects differences in the thermal and chemical properties of the Pacific oceanic lithosphere.

Yuan, H.; French, S. W.; Romanowicz, B. A.

2013-12-01

339

Gravity models of two-level collision of lithospheric plates in northeastern Asia  

NASA Astrophysics Data System (ADS)

Structural forms of emplacement of crustal and mantle rigid sheets in collision zones of lithospheric plates in northeastern Asia are analyzed using formalized gravity models reflecting the rheological properties of geological media. Splitting of the lithosphere of moving plates into crustal and mantle constituents is the main feature of collision zones, which is repeated in the structural units irrespective of their location, rank, and age. Formal signs of crustal sheet thrusting over convergent plate boundaries and subduction of the lithospheric mantle beneath these boundaries have been revealed. The deep boundaries and thickness of lithospheric plates and asthenospheric lenses have been traced. A similarity in the deep structure of collision zones of second-order marginal-sea buffer plates differing in age is displayed at the boundaries with the Eurasian, North American, and Pacific plates of the first order. Collision of oceanic crustal segments with the Mesozoic continental margin in the Sikhote-Alin is characterized, as well as collision of the oceanic lithosphere with the Kamchatka composite island arc. A spatiotemporal series of deep-seated Middle Mesozoic, Late Mesosoic, and Cenozoic collision tectonic units having similar structure is displayed in the transitional zone from the Asian continent to the Pacific plate.

Petrishchevsky, A. M.

2013-11-01

340

Plate Kinematics in Northeast Asia Constrained by GPS  

NASA Astrophysics Data System (ADS)

GPS observations in Siberia combined with global observations, collected in 1995-2003, allow us to improve constraints on the geometry and relative motion of the Eurasian (EUR), North American (NAM), and Pacific (PAC) plates [1]. In contrast to our earlier work and to other published studies, we estimate simultaneously both the relative plate rotation vectors (RV) and the translation rate of the reference frame (RF) which is treated as a free parameter. With this approach, we get identical values of RV regardless of which RF is used. Our estimate of RV for the EUR-NAM pair and the estimate based on the ITRF2000 catalog differ significantly because of the non-uniform sampling of EUR in ITRF2000, with most stations clustered in Europe. There are small (<1 mm/yr) but systematic plate-residual velocities within stable EUR, westward in Siberia and eastward in Europe, which, if real, indicate a small relative motion of these formerly independent plates. By comparing velocities relative to EUR and to NAM, we conclude that east Siberia to the east of the Cherskiy Range belongs to the North American plate. This fact was assumed in the literature for three decades but not proven because of uncertainties with the plate boundary arising from the ambiguous seismicity. Smaller plates in east Asia, such as Amurian and Okhotsk, are not required by the GPS velocities in our analysis. [1] Steblov, G.M., M.G. Kogan, R.W. King, C.H. Scholz, R. Bürgmann, and D.I. Frolov, Imprint of the North American Plate in Siberia revealed by GPS, Geophys. Res. Lett., 30(18), 1924, doi:10.1029/2003GL017805, 2003.

Kogan, M. G.; Steblov, G. M.; King, R. W.; Herring, T. A.; Scholz, C. H.; Bürgmann, R.; Frolov, D. I.; Levin, V. Y.

2004-05-01

341

Volcanism and vertical tectonics in the Pacific Basin related to global Cretaceous transgressions  

NASA Astrophysics Data System (ADS)

The dominance of volcanic processes and the importance of vertical tectonics in the geological evolution of the Pacific Basin has been recognised since the time of Charles Darwin. Data gathered on several legs of the Deep Sea Drilling Project (DSDP) and numerous marine expeditions in the past decade have confirmed Menard's postulate that the Pacific Basin was the scene of volcanism on an enormous scale in Mesozoic time. Widespread mid-plate volcanism between ˜110 and 70 m.y. B.P. characterised the area bounded by the Line Islands, the Mid-Pacific Mountains and the Nauru Basin-Marshall Islands. Heating of the Pacific lithospheric plate during this period of volcanism resulted in regional uplift and the bathymetric evolution of the area diverged significantly from a "normal" Parsons-Sclater subsidence curve. The Farallon plate, now almost entirely subducted, was also the scene of mid-plate volcanism that produced such features as the Nicoya Plateau now found as an allochthonous ophiolitic terrain landward of the middle America trench. Large, benthonic, reef-associated foraminifera comprising a pseudorbitoid fauna, hitherto considered to be largely restricted to Central America, have now been additionally recorded from DSDP Sites 165, 315 and 316 in the Line Islands, Site 462 in the Nauru Basin, and in New Guinea. The distribution of this fauna, of Campanian/Maastrichtian age, is interpreted as indicating "stepping stone" connections (aseismic ridges, plateaus and seamounts) between the Caribbean, Farallon, and Pacific plates 70-80 m.y. B.P. Similarities between the geology of the Nauru Basin and the Caribbean Ocean crust reinforce the interpretation of the latter as a former part of the Farallon plate. Estimates of the sea-level and continental freeboard change caused by the thermally induced uplift of the Pacific and Farallon plates, as well as substantial areas in the Atlantic and Indian Ocean Basins, indicate that such shallowing of the sea floor could have been the major factor in causing global Cretaceous transgressions.

Schlanger, Seymour O.; Jenkyns, Hugh C.; Premoli-Silva, Isabella

1981-02-01

342

Nuclear reactor alignment plate configuration  

DOEpatents

An alignment plate that is attached to a core barrel of a pressurized water reactor and fits within slots within a top plate of a lower core shroud and upper core plate to maintain lateral alignment of the reactor internals. The alignment plate is connected to the core barrel through two vertically-spaced dowel pins that extend from the outside surface of the core barrel through a reinforcement pad and into corresponding holes in the alignment plate. Additionally, threaded fasteners are inserted around the perimeter of the reinforcement pad and into the alignment plate to further secure the alignment plate to the core barrel. A fillet weld also is deposited around the perimeter of the reinforcement pad. To accomodate thermal growth between the alignment plate and the core barrel, a gap is left above, below and at both sides of one of the dowel pins in the alignment plate holes through with the dowel pins pass.

Altman, David A; Forsyth, David R; Smith, Richard E; Singleton, Norman R

2014-01-28

343

Amphibious seismic survey images plate interface at 1960 Chile Earthquake  

Microsoft Academic Search

The southern central Chilean margin at the site of the largest historically recorded earthquake in the Valdivia region, in 1960 (Mw = 9.5), is part of the 5000-km-long active subduction system whose geodynamic evolution is controversially debated and poorly understood. Covering the area between 36° and 40°S, the oceanic crust is segmented by prominent fracture zones. The offshore forearc and

C. Krawcyzk

2003-01-01

344

Canadian Pacific Railway Collection  

NSDL National Science Digital Library

The Canadian Pacific Railway collection provides access to over 1500 images documenting the company's activities all around British Columbia from the 1880s to the 1950s. The pictures portray railway stations both urban and rural, along with images of workers, buildings, hotels, ships, and yards that were part of the railroad's vast empire. Visitors can click on the Collection area to get started and the search function is another good way to focus in on items of interest. Within the History tab is an elegant and well-developed essay on the company, complete with illustrative images while the Photographers section provides great insight into who exactly took these pictures. And, of course, casual users may just wish to click on the Gallery to get a sampling of the works that make up this archive.

2005-01-01

345

Microstructure and properties of magnesium AZ31B–aluminum 7075 explosively welded composite plate  

Microsoft Academic Search

A composite plate of Mg alloy (AZ31B) and an Al alloy (7075) was fabricated by explosive welding. The microstructure and properties of the bonding interface after explosive cladding were investigated. The results show that the bonding interface had a wavy appearance with solidified melts in a regularly spaced pattern of discrete regions. Adiabatic shear bands and twin structure were found

Y. B. Yan; Z. W. Zhang; W. Shen; J. H. Wang; L. K. Zhang; B. A. Chin

2010-01-01

346

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

NASA Astrophysics Data System (ADS)

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

Gordon, R. G.; Royer, J.

2005-12-01

347

Stainless steel bipolar plates  

Microsoft Academic Search

In this research, a specific surface modification technology was developed for stainless steel bipolar plates to obtain a corrosion-resistant oxide film. The surface roughness was measured, and an electron spectroscopy analysis (ESCA) was conducted to verify the chemical composition of the surface layer. From the binding energy of the ESCA spectrum, the amounts of chemical shift were used to identify

Shuo-Jen Lee; Jian-Jang Lai; Ching-Han Huang

2005-01-01

348

The Arctic plate boundary  

Microsoft Academic Search

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

Øyvind Engen; Olav Eldholm; Hilmar Bungum

2003-01-01

349

Bipolar battery plate  

SciTech Connect

A method is described of forming a bipolar plate for a battery comprising the steps of: disposing metal pellets in each aperture of a perforated thermoplastic sheet to form an assembly; heating and pressing the assembly to seal the pellets into the apertures with first and second surfaces exposed in the opposite faces of the sheet.

Rowlette, J.J.

1987-04-21

350

INL HIP Plate Fabrication  

SciTech Connect

This document outlines the process used to bond monolithic fuel plates by Hot Isostatic Pressing (HIP). This method was developed at Idaho National Laboratory (INL) for the Reduced Enrichment for Research and Test Reactors (RERTR) program. These foils have been used in a number of irradiation experiments in support of the United States Global Threat Reduction Initiative (GTRI) program.

B. H. Park; C. R. Clark; J. F. Jue

2010-02-01

351

The Plate Tectonics Project  

Microsoft Academic Search

The Plate Tectonics Project is a multiday, inquiry-based unit that facilitates students as self-motivated learners. Reliable Web sites are offered to assist with lessons, and a summative rubric is used to facilitate the holistic nature of the project. After each topic (parts of the Earth, continental drift, etc.) is covered, the students will generate a portion of the summative assessment

Annamae J. Hein

2011-01-01

352

Earthquakes and Plates  

NSDL National Science Digital Library

The representation depicts global distribution of earthquakes. A world map shows the location of large earthquakes that occurred from 1975-1995. A slider at the bottom left of the map allows the user to change the map to reveal the location of major plates or to select both views layered on top of one another.

353

Plate Tectonics Quiz  

NSDL National Science Digital Library

This quiz for younger students asks them 10 questions about plate motions, rock types in continental and oceanic crust, crustal formation and mountain building, the supercontinent Pangea, and the theory of continental drift. A link to a page on continental drift provides information to answer the questions.

354

Stainless steel bipolar plates  

NASA Astrophysics Data System (ADS)

In this research, a specific surface modification technology was developed for stainless steel bipolar plates to obtain a corrosion-resistant oxide film. The surface roughness was measured, and an electron spectroscopy analysis (ESCA) was conducted to verify the chemical composition of the surface layer. From the binding energy of the ESCA spectrum, the amounts of chemical shift were used to identify the major chemical compositions. The thickness of the oxide film was analyzed by auger electron spectroscopy (AES). From the results of the ESCA and AES analyses, the effects of the surface modification on the integrity of the surface were evaluated. Uniform corrosion and localized corrosion tests were also conducted to investigate any improvement on the corrosion characteristics. A single cell was assembled for cell performance tests. The surface of the treated plates was bright and smooth. The ESCA and AES analyses showed that the treated plates had a much higher chrome content. The metallurgical structure was dense with substantially less defects. The chemical and electrochemical properties were more stable. The corrosion rates of the treated plates were also much improved, resulting in better electric conductivity, stable cell performance as well as longer cell life.

Lee, Shuo-Jen; Lai, Jian-Jang; Huang, Ching-Han

355

The Plate Tectonics Project  

ERIC Educational Resources Information Center

The Plate Tectonics Project is a multiday, inquiry-based unit that facilitates students as self-motivated learners. Reliable Web sites are offered to assist with lessons, and a summative rubric is used to facilitate the holistic nature of the project. After each topic (parts of the Earth, continental drift, etc.) is covered, the students will…

Hein, Annamae J.

2011-01-01

356

Earth: Plates on the Move  

NSDL National Science Digital Library

In this activity, students explore how the movement of tectonic plates forms mountains, volcanoes, oceans, and earthquakes. It first describes the plates and the various types of interaction at plate boundaries. An interactive map of the world shows the relationship between plate boundaries and earthquakes, allowing the student to click on selected place to explore a volcano, mountain, hotspot or earthquake. They then zoom in the see how the plates are moving, play an animation about the plate interaction, and read a story about the event. In addition, a set of links lead to more detailed information.

357

The Fight Over Pacific Salmon  

NSDL National Science Digital Library

This week's In The News focuses on the recently heightened, ongoing US-Canada controversy over fishing rights. Since the expiration of the Pacific Salmon Treaty in 1994, the United States and Canada have been unable to agree on salmon catch quotas in the north Pacific. With the opening of the fishing season on July 1, 1998, newspapers reported tension at the docks and rumors of protests in British Colombia. The twelve resources listed offer background information on Pacific Salmon and the salmon fisheries controversy, and include several US and Canadian perspectives.

Payne, Laura X.

1998-01-01

358

Current plate motions relative to the hotspots consistent with the MORVEL global set of plate relative angular velocities  

NASA Astrophysics Data System (ADS)

Estimates of plate motions relative to the hotspots are useful in investigations of plate driving forces, motion between hotspots, and in estimating the net-rotation of the lithosphere. HS3B-MORVEL is a new set of angular velocities of the plates relative to the hotspots. In HS3B-MORVEL, relative plate angular velocities are constrained to be consistent with those of MORVEL, which is a new closure-enforced global set of angular velocities. MORVEL describes the geologically current motions of 25 plates, 18 of which are determined solely from marine geophysical data, which typically average motion over hundreds of thousands to millions of years [DeMets, Gordon, and Argus 2010]. Seven other plates are tied in partly or entirely through geodetic data. The HS3B data set builds on the HS3 data set, which includes two volcanic propagation rates and eleven segment trends and is determined from the age and location of volcanoes from four plates [Gripp and Gordon, 2002]. In HS3B we adjust the volcanic propagation rates from HS3 for a 10% bias in K/Ar age dates. In HS3B-MORVEL, the angular velocity relative to the hotspots of eight plates—Eurasia, Nubia, Somalia, Lwandle, Antarctica, Sundaland, Amur, and Yangtze—all differ insignificantly from zero. The motion of the other 17 plates differ significantly from zero (p<0.05). The net rotation of the lithosphere is ?0.1°/Myr lower than found for HS3-NUVEL1A. We construct two further sets of absolute plate angular velocities. The first set of angular velocities, T57-MORVEL, is determined from the data set of Morgan and Phipps Morgan [2006], which consists of 57 trends of widely distributed hotspot tracks. All angular velocities in T57-MORVEL lie outside the 95% confidence limits of the corresponding HS3B-MORVEL angular velocity. We consider two hypotheses to explain this discrepancy: (1) Pacific hotspots move relative to non-Pacfic hotspots at ?5-15 mm/yr, or (2) anachronism—some T57 trends may average plate motion over tens of millions of years, while the HS3B data average over only the past ?6 Myr. The second set of angular velocities, SKS-MORVEL, uses the shear-wave splitting data set of Kreemer [2009] to constrain the direction of plate motion. All angular velocities in SKS-MORVEL lie within the 95% confidence limits of the corresponding HS3B-MORVEL angular velocity. Thus, the alternative "absolute" frames of reference from the orientation of shear-wave splitting and from hotspot tracks are mutually consistent.

Zheng, Lin; Gordon, Richard G.; Kreemer, Corné; Demets, Charles; Argus, Donald F.

2010-05-01

359

Plate tectonics and crustal deformation around the Japanese Islands  

NASA Technical Reports Server (NTRS)

We analyze over a century of geodetic data to study crustal deformation and plate motion around the Japanese Islands, using the block-fault model for crustal deformation developed by Matsu'ura et al. (1986). We model the area including the Japanese Islands with 19 crustal blocks and 104 faults based on the distribution of active faults and seismicity. Geodetic data are used to obtain block motions and average slip rates of faults. This geodetic model predicts that the Pacific plate moves N deg 69 +/- 2 deg W at about 80 +/- 3 mm/yr relative to the Eurasian plate which is much lower than that predicted in geologic models. Substantial aseismic slip occurs on the subduction boundaries. The block containing the Izu Peninsula may be separated from the rigid part of the Philippine Sea plate. The faults on the coast of Japan Sea and the western part of the Median Tectonic Line have slip rates exceeding 4 mm/yr, while the Fossa Magna does not play an important role in the tectonics of the central Japan. The geodetic model requires the division of northeastern Japan, contrary to the hypothesis that northeastern Japan is a part of the North American plate. Owing to rapid convergence, the seismic risk in the Nankai trough may be larger than that of the Tokai gap.

Hashimoto, Manabu; Jackson, David D.

1993-01-01

360

Tectonic Plates, Earthquakes, and Volcanoes  

NSDL National Science Digital Library

The representation shows earthquake and volcanic activity corresponds to plate boundaries. This interactive topographical map with the ocean water removed shows the boundaries of major plates and the locations of major volcanic eruptions and earthquakes worldwide.

361

The Pacific Northwest GPS Velocity Field (Invited)  

NASA Astrophysics Data System (ADS)

Surface velocities derived from GPS observations have allowed high resolution views of the active deformation and rotation of the Cascadia forearc and backarc as well as elastic strain accumulation arising from subduction fault locking. We present an update of the Pacific Northwest GPS velocity field presented earlier by McCaffrey et al. (Geophys. Jour. Int., 2007) and Payne et al. (Geology, 2008). The new velocity field includes more recent survey-mode and continuous observations as well as an expanded area, extending from the Oregon and Washington coasts on the west to Yellowstone on the east. It combines new Scripps Orbit and Permanent Array Center (SOPAC) daily solutions for 1994-2010 for the Basin and Range Geodetic (BARGN), Eastern Basin and Range - Yellowstone (EBRY), Pacific Northwest Geodetic Array (PANGA), Plate Boundary Observatory (PBO), and Western Canada Deformation Array (WCDA) networks (http://sopac.ucsd.edu/processing/gamit) with our solutions using data from surveys conducted by Idaho National Laboratory, Massachusetts Institute of Technology, National Geodetic Survey, Geologic Survey of Canada, Rensselaer Polytechnic Institute, US Geological Survey, University of Washington, and others, 1991-2010. The new field reveals that the large-scale clockwise rotation seen in western Washington and Oregon also extends southward into southern Idaho and the Snake River Plain as well as into the northern Basin and Range of Nevada. The axes of rotation generally fall near the Oregon-Washington-Idaho border and the Idaho Batholith. Continued densification of the network around the Snake River Plain is permitting a better view of its relationship to nearby Basin and Range extension. We will present interpretations of the active tectonics of the region based on this new field.

McCaffrey, R.; King, R. W.; Payne, S. J.

2010-12-01

362

Astronomical Society of the Pacific  

NSDL National Science Digital Library

The Astronomical Society of the Pacific is an international nonprofit scientific and educational organization founded in 1889 that works to increase understanding and appreciation of astronomy. The Astronomical Society of the Pacific is the largest general astronomy society in the world. The society provides many kinds of educational materials which can be ordered online from this site. The site includes links to many other astronomy-related sites.

2003-10-10

363

75 FR 13731 - National Marine Fisheries Service, Pacific Fishery Management Council (Pacific Council); April 9...  

Federal Register 2010, 2011, 2012, 2013, 2014

...Pacific Fishery Management Council (Pacific...Pacific Fishery Management Council, 7700...Report D. Marine Protected Areas 1. Update on...Marine Sanctuary Management Plan Review E...Service Report 4. Methodology Review...

2010-03-23

364

http://www.clivar.org/organization/pacific/pacific_SPICE.php Alexandre Ganachaud, Christophe Maes,  

E-print Network

http://www.clivar.org/organization/pacific/pacific_SPICE.php Alexandre Ganachaud, Christophe Maes, and SPICE participants Progress from Southwest PacIfic Ocean Circulation and Climate Experiment: SPICE #12

365

Glacial isostasy and plate motion  

Microsoft Academic Search

The influence of glacial-isostatic adjustment (GIA) on the motion of tectonic plates is usually neglected. Employing a recently developed numerical approach, we examine the effect of glacial loading on the motion of the Earth’s tectonic plates where we consider an elastic lithosphere of laterally variable strength and the plates losely connected by low viscous zones. The aim of this paper

Volker Klemann; Zdenek Martinec; Erik R. Ivins

2008-01-01

366

Microchannel plate streak camera  

DOEpatents

An improved streak camera in which a microchannel plate electron multiplier is used in place of or in combination with the photocathode used in prior streak cameras. The improved streak camera is far more sensitive to photons (uv to gamma-rays) than the conventional x-ray streak camera which uses a photocathode. The improved streak camera offers gamma-ray detection with high temporal resolution. It also offers low-energy x-ray detection without attenuation inside the cathode. Using the microchannel plate in the improved camera has resulted in a time resolution of about 150 ps, and has provided a sensitivity sufficient for 1000 keV x-rays.

Wang, C.L.

1984-09-28

367

Microchannel plate streak camera  

DOEpatents

An improved streak camera in which a microchannel plate electron multiplier is used in place of or in combination with the photocathode used in prior streak cameras. The improved streak camera is far more sensitive to photons (UV to gamma-rays) than the conventional x-ray streak camera which uses a photocathode. The improved streak camera offers gamma-ray detection with high temporal resolution. It also offers low-energy x-ray detection without attenuation inside the cathode. Using the microchannel plate in the improved camera has resulted in a time resolution of about 150 ps, and has provided a sensitivity sufficient for 1000 KeV x-rays.

Wang, Ching L. (Livermore, CA)

1989-01-01

368

Microchannel plate streak camera  

DOEpatents

An improved streak camera in which a microchannel plate electron multiplier is used in place of or in combination with the photocathode used in prior streak cameras is disclosed. The improved streak camera is far more sensitive to photons (UV to gamma-rays) than the conventional x-ray streak camera which uses a photocathode. The improved streak camera offers gamma-ray detection with high temporal resolution. It also offers low-energy x-ray detection without attenuation inside the cathode. Using the microchannel plate in the improved camera has resulted in a time resolution of about 150 ps, and has provided a sensitivity sufficient for 1,000 KeV x-rays. 3 figs.

Wang, C.L.

1989-03-21

369

Bipolar battery plate  

NASA Technical Reports Server (NTRS)

A liquid-impermeable plate (10) having throughplate conductivity with essentially zero resistance comprises an insulator sheet (12) having a series of spaced perforations (14) each of which contains a metal element (16) sealingly received into the perforation (14). A low-cost plate can readily be manufactured by punching a thermoplastic sheet (40) such as polypropylene with a punching tool (52), filling the apertures with lead spheres (63) having a diameter smaller than the holes (50) but larger than the thickness of the sheet, sweeping excess spheres (62) off the sheet with a doctor blade (60) and then pressing a heated platen (74) onto the sheet to swage the spheres into a cylindrical shape and melt the surrounding resin to form a liquid-impermeable collar (4) sealing the metal into the sheet.

Rowlette, John J. (Inventor)

1985-01-01

370

North American plate dynamics  

NASA Technical Reports Server (NTRS)

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

Richardson, Randall M.; Reding, Lynn M.

1991-01-01

371

Spreading behaviour of the Pacific-Farallon ridge system since 83 Ma  

NASA Astrophysics Data System (ADS)

We present improved rotations, complete with uncertainties, for the Pacific-Farallon Ridge (PFR) between geomagnetic chrons 34y (83 Ma) and 10y (28.28 Ma). Despite substantial shortening since ˜55 Ma, this ridge system and its remnants (e.g. the East Pacific Rise) have produced as much as 45 per cent of all oceanic lithosphere created since the Late Cretaceous, but reconstructions face the twin challenges of extensive subduction of Farallon crust-which precludes reconstruction by fitting conjugate magnetic anomaly and fracture zone (FZ) traces-and asymmetric spreading behaviour for at least the past 51 Myr. We have calculated best-fit `half'-angle stage rotations between nine geomagnetic chron boundaries (34y, 33y, 29o, 24.3o, 20o, 18.2o, 17.1y, 13y and 10y) using combined anomaly and FZ data from both the northern and southern Pacific Plate. For rotations younger than chron 24.3o, estimates for spreading asymmetry, derived using anomaly picks from yet-to-be subducted Farallon/Nazca crust in the south Pacific, allow full stage rotations to be calculated. Between 50 and 83 Ma, where no direct constraints on spreading asymmetry are possible, a `best-fit' full stage rotation was calculated based on the net Nazca:Pacific spreading asymmetry (Pacific spreading fraction fPAC = 0.44) over the past 50 Myr, with conservative lower and upper bounds, based on variability in the degree of spreading asymmetry over periods of <15 Myr, assuming fPACs of 0.5 and 0.36, respectively. Synthetic flowlines generated from our new stage rotation produce a better match to Pacific FZ trends than previously published rotations. With the exception of the chron 18o-20o rotation, the six stage poles for rotations between chrons 33y and 13y (74-33 Ma) all cluster tightly at 60-75°E, 60-68°N, consistent with the relatively constant trend of the major Pacific FZs. This stability spans at least one episode of Farallon Plate fragmentation caused by subduction of PFR segments beneath the Americas, at 55-48 Ma, which appears to have greatly accelerated divergence on the surviving ridge without significantly affecting the location of the instantaneous rotation pole. Together with quasi-periodic 15-20 Myr variations in the degree of spreading asymmetry that also appear to correlate with changes in spreading rate, this indicates that forces other than slab pull may be a factor in determining Pacific-Farallon Plate motions.

Rowan, Christopher J.; Rowley, David B.

2014-06-01

372

Plated wire memory subsystem  

NASA Technical Reports Server (NTRS)

The work performed entailed the design, development, construction and testing of a 4000 word by 18 bit random access, NDRO plated wire memory for use in conjunction with a spacecraft imput/output unit and central processing unit. The primary design parameters, in order of importance, were high reliability, low power, volume and weight. A single memory unit, referred to as a qualification model, was delivered.

Reynolds, L.; Tweed, H.

1972-01-01

373

Plate Tectonics: The Mechanism  

NSDL National Science Digital Library

This text explains how detailed mapping of the ocean floor led scientists like Howard Hess and R. Deitz to revive the Holmes convection theory. Hess and Deitz modified the theory considerably and called their new theory Sea-floor Spreading. Among the seafloor features that supported the sea-floor spreading hypothesis were: mid-oceanic ridges, deep sea trenches, island arcs, geomagnetic patterns, and fault patterns. These features are treated in detail and related to the current Theory of Plate Tectonics.

374

Martian plate tectonics  

NASA Astrophysics Data System (ADS)

The northern lowlands of Mars have been produced by plate tectonics. Preexisting old thick highland crust was subducted, while seafloor spreading produced thin lowland crust during late Noachian and Early Hesperian time. In the preferred reconstruction, a breakup margin extended north of Cimmeria Terra between Daedalia Planum and Isidis Planitia where the highland-lowland transition is relatively simple. South dipping subduction occured beneath Arabia Terra and east dipping subduction beneath Tharsis Montes and Tempe Terra. Lineations associated with Gordii Dorsum are attributed to ridge-parallel structures, while Phelegra Montes and Scandia Colles are interpreted as transfer-parallel structures or ridge-fault-fault triple junction tracks. Other than for these few features, there is little topographic roughness in the lowlands. Seafloor spreading, if it occurred, must have been relatively rapid. Quantitative estimates of spreading rate are obtained by considering the physics of seafloor spreading in the lower (approx. 0.4 g) gravity of Mars, the absence of vertical scarps from age differences across fracture zones, and the smooth axial topography. Crustal thickness at a given potential temperature in the mantle source region scales inversely with gravity. Thus, the velocity of the rough-smooth transition for axial topography also scales inversely with gravity. Plate reorganizations where young crust becomes difficult to subduct are another constraint on spreading age. Plate tectonics, if it occurred, dominated the thermal and stress history of the planet. A geochemical implication is that the lower gravity of Mars allows deeper hydrothermal circulation through cracks and hence more hydration of oceanic crust so that more water is easily subducted than on the Earth. Age and structural relationships from photogeology as well as median wavelength gravity anomalies across the now dead breakup and subduction margins are the data most likely to test and modify hypotheses about Mars plate tectonics.

Sleep, N. H.

1994-03-01

375

Plate motion and deformation  

SciTech Connect

Our goal is to understand the motions of the plates, the deformation along their boundaries and within their interiors, and the processes that control these tectonic phenomena. In the broadest terms, we must strive to understand the relationships of regional and local deformation to flow in the upper mantle and the rheological, thermal and density structure of the lithosphere. The essential data sets which we require to reach our goal consist of maps of current strain rates at the earth's surface and the distribution of integrated deformation through time as recorded in the geologic record. Our success will depend on the effective synthesis of crustal kinematics with a variety of other geological and geophysical data, within a quantitative theoretical framework describing processes in the earth's interior. Only in this way can we relate the snapshot of current motions and earth structure provided by geodetic and geophysical data with long-term processes operating on the time scales relevant to most geological processes. The wide-spread use of space-based techniques, coupled with traditional geological and geophysical data, promises a revolution in our understanding of the kinematics and dynamics of plate motions over a broad range of spatial and temporal scales and in a variety of geologic settings. The space-based techniques that best address problems in plate motion and deformation are precise space-geodetic positioning -- on land and on the seafloor -- and satellite acquisition of detailed altimetric and remote sensing data in oceanic and continental areas. The overall science objectives for the NASA Solid Earth Science plan for the 1990's, are to Understand the motion and deformation of the lithosphere within and across plate boundaries'', and to understand the dynamics of the mantle, the structure and evolution of the lithosphere, and the landforms that result from local and regional deformation. 57 refs., 7 figs., 2 tabs.

Minster, B.; Prescott, W.; Royden, L.

1991-02-01

376

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  

USGS Publications Warehouse

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 of the contact zone with the overlying Philippine Sea slab is located close to and parallel to this obliquely oriented seismic belt, suggesting that the deepening of the seismic belt there is caused by the contact with the overlying slab. The contact with this cold slab hinders the heating of the Pacific slab crust by hot mantle wedge, which would cause delay of eclogite-forming phase transformations and hence deepening of the seismic belt there. The depth limit of the subducting low-velocity crust also deepens toward the north, supporting this idea. Copyright 2007 by the American Geophysical Union.

Hasegawa, A.; Nakajima, J.; Kita, S.; Okada, T.; Matsuzawa, T.; Kirby, S.H.

2007-01-01

377

Discovering Plate Boundaries  

NSDL National Science Digital Library

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

Dale Sawyer

1997-09-15

378

Advances in sputtered and ion plated solid film lubrication  

NASA Technical Reports Server (NTRS)

The glow discharge or ion assisted vacuum deposition techniques, primarily sputtering and ion plating, have rapidly emerged and offer great potential to deposit solid lubricants. The increased energizing of these deposition processes lead to improved adherence and coherence, favorable morphological growth, higher density, and reduced residual stresses in the film. These techniques are of invaluable importance where high precision machines tribo-components require very thin, uniform lubricating films (0.2 m), which do not interface with component tolerances. The performance of sputtered MoS2 films and ion plated Au and Pb films are described in terms of film thickness, coefficient of friction, and wear lives.

Spalvins, T.

1985-01-01

379

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

NASA Astrophysics Data System (ADS)

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

García-Casco, A.

2012-04-01

380

New kinematic models for Pacific-North America motion from 3 Ma to present, I: Evidence for steady motion and biases in the NUVEL-1A Model  

NASA Astrophysics Data System (ADS)

We use velocities derived from 2-4.5 years of continuous GPS observations at 21 sites on the Pacific and North American plates along with a subset of the NUVEL-1A data to examine the steadiness of Pacific-North America motion since 3.16 Ma, the transfer of Baja California to the Pacific plate, and the magnitude of biases in the NUVEL-1A estimate of Pacific-North America motion. We find that Pacific-North America motion has remained steady since 3.16 Ma, but at rates significantly faster than predicted by NUVEL-1A. In the vicinity of Baja California, our GPS-derived model and recent seafloor spreading rates in the southern Gulf of California both indicate that the NUVEL-1A model underestimates Pacific-North America rates by 4±2 mm yr-1. Steady Pacific-North America motion since 3.16 Myr and increasing seafloor spreading rates since 3.58 Myr in the Gulf of California imply that Pacific-North America motion was partitioned between seafloor spreading in the Gulf of California and decelerating slip along faults in or offshore from the Baja peninsula.

DeMets, Charles; Dixon, Timothy H.

381

Symmetries in laminated composite plates  

NASA Technical Reports Server (NTRS)

The different types of symmetry exhibited by laminated anisotropic fibrous composite plates are identified and contrasted with the symmetries of isotropic and homogeneous orthotropic plates. The effects of variations in the fiber orientation and the stacking sequence of the layers on the symmetries exhibited by composite plates are discussed. Both the linear and geometrically nonlinear responses of the plates are considered. A simple procedure is presented for exploiting the symmetries in the finite element analysis. Examples are given of square, skew and polygonal plates where use of symmetry concepts can significantly reduce the scope and cost of analysis.

Noor, A. K.

1976-01-01

382

Pacific Hagfish, Eptatretus stouti, and Black Hagfish, E. deani: The Oregon Fishery and Port Sampling Observations, 1988-92  

E-print Network

, horny teeth on each side of the tongue-like dental plate, and one longer median tooth situated dorsally to three distinct sizes ofeggs, but they usually carried only one group of eggs over 5 mm in length. Mature Pacific hagfishfemales averaged 28 eggs over 5 mm in length, and black hag fishfemales averaged 14 eggs

383

Low-volume intraplate volcanism in the Early/Middle Jurassic Pacific basin documented by accreted sequences in Costa Rica  

NASA Astrophysics Data System (ADS)

Countless seamounts occur on Earth that can provide important constraints on intraplate volcanism and plate tectonics in the oceans, yet their nature and origin remain poorly known due to difficulties in investigating the deep ocean. We present here new lithostratigraphic, age and geochemical data from Lower/Middle Jurassic and Lower Cretaceous sequences in the Santa Rosa accretionary complex, Costa Rica, which offer a valuable opportunity to study a small-sized seamount from a subducted plate segment of the Pacific basin. The seamount is characterized by very unusual lithostratigraphic sequences with sills of potassic alkaline basalt emplaced within thick beds of radiolarite, basaltic breccia and hyaloclastite. An integration of new geochemical, biochronological and geochronological data with lithostratigraphic observations suggests that the seamount formed ~175 Ma ago on thick oceanic crust away from subduction zones and mid-ocean ridges. This seamount traveled ~65 Ma in the Pacific before accretion. It resembles lithologically and compositionally "petit-spot" volcanoes found off Japan, which form in response to plate flexure near subduction zones. Also, the composition of the sills and lava flows in the accreted seamount closely resembles that of potassic alkaline basalts produced by lithosphere cracking along the Line Islands chain. We hypothesize based on these observations, petrological constraints and formation of the accreted seamount coeval with the early stages of development of the Pacific plate that the seamount formed by extraction of small volumes of melt from the base of the lithosphere in response to propagating fractures at the scale of the Pacific basin.

Buchs, David M.; Pilet, SéBastien; Cosca, Michael; Flores, Kennet E.; Bandini, Alexandre N.; Baumgartner, Peter O.

2013-05-01

384

Fuel cell end plate structure  

DOEpatents

The end plates (16) of a fuel cell stack (12) are formed of a thin membrane. Pressure plates (20) exert compressive load through insulation layers (22, 26) to the membrane. Electrical contact between the end plates (16) and electrodes (50, 58) is maintained without deleterious making and breaking of electrical contacts during thermal transients. The thin end plate (16) under compressive load will not distort with a temperature difference across its thickness. Pressure plate (20) experiences a low thermal transient because it is insulated from the cell. The impact on the end plate of any slight deflection created in the pressure plate by temperature difference is minimized by the resilient pressure pad, in the form of insulation, therebetween.

Guthrie, Robin J. (East Hartford, CT); Katz, Murray (Newington, CT); Schroll, Craig R. (Glastonbury, CT)

1991-04-23

385

Equatorial Pacific magnetic anomalies identified from vector aeromagnetic data  

NASA Astrophysics Data System (ADS)

It has long been challenging to identify magnetic anomalies due to seafloor spreading in the equatorial Pacific. Here we show that Project Magnet vector aeromagnetic profiles from the equatorial Pacific record magnetic anomalies due to seafloor spreading much more clearly than do shipboard total intensity profiles. The anomalies are reliably recorded at wavelengths between ~20 and ~150 km in the vertical and east components, which have high coherence, differ in phase by ~90°, and resemble synthetic magnetic anomaly profiles. From an analysis of a single near-equatorial vector aeromagnetic profile we infer that the magnetic lineations strike ~8°-10° counter-clockwise of north and that magnetic anomaly 7 is located ~400 km further east than previously estimated. The newly estimated location of anomaly 6 is consistent with a tentative estimate by Wilson from a low-amplitude shipboard magnetic profile. Because the skewness of profiles over the seafloor formed near the paleoequator changes rapidly with paleolatitude and paleostrike, a skewness analysis of these data may provide useful bounds on the location of Pacific Plate paleomagnetic poles, and indicate that this seafloor has had little, if any, northward motion relative to the spin axis since it formed.

Horner-Johnson, Benjamin C.; Gordon, Richard G.

2003-11-01

386

20. 'Portals and Gusset Plates for 3 180'61/2' c. ...  

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

20. 'Portals and Gusset Plates for 3 - 180'-6-1/2' c. to c. End Pins Single Track Through Spans, 10th, 11th, & 13th Crossings of Sacramento River, Southern Pacific Co. Sacramento Division, The Phoenix Bridge Co., C.O's. 839, 840 & 841, Drawing #12, Engineer C. Scheidl, Draftsman B. Heald, Scale 1-1/2' = 1'0', April 16th, 1901.' - Southern Pacific Railroad Shasta Route, Bridge No. 310.58, Milepost 310.58, Sims, Shasta County, CA

387

Writing and Visualization for Teaching Plate Tectonics  

NASA Astrophysics Data System (ADS)

The Theory of Plate Tectonics is probably the most important paradigm for understanding the workings of our planet. As such it is an integral part in any Introductory Geology course. Whereas geology majors usually easily embrace the Theory of Plate Tectonics, the enthusiasm for the coherence and elegance of this theory appears to be much more subdued among the majority of non-science majors. While visual and electronic media certainly support the teaching of the theory, pretty pictures and animations are not sufficient for many non-science majors to grasp the concepts of interacting lithospheric plates. It is well known that students do better in learning scientific concepts if they create their own understanding through research and inquiry-based learning, by working in the field, manipulating real earth-science data, and through writing. Writing assignments give instructors the opportunity to assess their students' learning and to clarify misconceptions yet they also have to be willing to teach students how to craft a science paper. Most electronic media and textbook-added CD-ROMs are not useful for making the structure of a science paper transparent. I found many of the necessary ingredients for effectively teaching plate tectonics in the interactive CD-ROM, "Our Dynamic Planet", developed by Wm. Prothero together with G. Kelly (University of California at Santa Barbara). It allows students to select and manipulate real earth-science data of plate-tectonically active regions, and provides an electronic interface that lets students create graphical representations of their collected data. A downloadable Teacher's Manual provides suggestions on teaching students to write a scientific argument, rooted in sound pedagogy. Originally designed for a large oceanography class, the material was modified for use in a small introductory geology class for non-science majors. Various assignments were given to instruct students in writing a scientific argument based on their own collected data and observations. The main goals are for students o To see the relationship between data and the development of a scientific theory o To understand the elements of scientific discourse o To learn how to derive conclusions from interpretations and observations o To back interpretations with observations o To be able to write a scientific argument o To understand the Theory of Plate Tectonics, and o To gain a better understanding about how science works The results of several surveys will be presented that confirm that most of the expected outcomes continue to be met.

Thomas, S. F.

2004-12-01

388

Motion of Pacific mantle plumes  

Microsoft Academic Search

The Hawaiian--Emperor hotspot chain, and its distinctive bend at 47 Ma, have figured prominently in the development of ideas on the nature of mantle plumes, plate motion, and frames of reference. However, paleomagnetic data from Ocean Drilling Program (ODP) Leg 197, together with results from plate circuit and geodynamic modeling studies, indicate southward motion of the Hawaiian hotspot during formation

R. D. Cottrell; J. A. Tarduno; P. V. Doubrovine

2007-01-01

389

Variations in oceanic plate bending along the Mariana trench  

NASA Astrophysics Data System (ADS)

We quantify along-trench variations in plate flexural bending along the Mariana trench in the western Pacific Ocean. A 3-D interpreted flexural deformation surface of the subducting Pacific Plate was obtained by removing from the observed bathymetry the effects of sediment loading, isostatically-compensated topography based on gravity modeling, age-related lithospheric thermal subsidence, and residual short-wavelength features. We analyzed flexural bending of 75 across-trench profile sections and calculated five best-fitting tectonic and plate parameters that control the flexural bending. Results of analysis revealed significant along-trench variations: the trench relief varies from 0.9 to 5.7 km, trench-axis vertical loading (-V0) from -0.73×1012 to 3.17×1012 N/m, and axial bending moment (-M0) from 0.1×1017 to 2.7×1017 N. The effective elastic plate thickness seaward of the outer-rise region (TeM) ranges from 45 to 52 km, while that trench-ward of the outer-rise (Tem) ranges from 19 to 40 km. This corresponds to a reduction in Te of 21-61%. The transition from TeM to Tem occurs at a breaking distance of 60-125 km from the trench axis, which is near the outer-rise and corresponds to the onset of observed pervasive normal faults. The Challenger Deep area is associated with the greatest trench relief and axial vertical loading, while areas with seamounts at the trench axis are often associated with more subtle trench relief, smaller axial vertical loading, and greater topographic bulge at the outer-rise.

Zhang, Fan; Lin, Jian; Zhan, Wenhuan

2014-09-01

390

Spot brazing of aluminum to copper with a cover plate  

NASA Astrophysics Data System (ADS)

It is difficult to join dissimilar metals when an intermetallic compound is formed at the joining interface. Spot brazing can be accomplished in a short time by resistance heating. Therefore, it is said that the formation of a intermetallic compound can be prevented. In this study, aluminum and copper were joined by spot brazing with a cover plate. The cover plate was used to supply heat to base metals and prevent heat dissipation from the base metals. The ability to braze Al and Cu was investigated by observation and analysis. Pure aluminum (A1050) plate and oxygen-free copper (C1020) plate were used as base metals. Cu-Ni-Sn-P brazing filler was used as the brazing filler metal. SPCC was employed as cover plate. Brazing was done with a micro spot welder under an argon gas atmosphere. Brazing ability was estimated by tensile shear strength and cross sectional microstructure observation. Al and Cu can be joined by spot brazing with Cu-Ni-Sn-P brazing filler and cover plate.

Hayashi, Junya; Miyazawa, Yasuyuki

2014-08-01

391

Northern east Pacific rise: Magnetic anomaly and bathymetric framework  

SciTech Connect

The oceanic crust in the eastern Pacific between 7/sup 0/N and 30/sup 0/N and east of 127/sup 0/W contains a fairly complete history of the spreading centers associated with the East Pacific Rise since 25 m.y. B.P. (late Oligocene). In this paper, we have summarized the seafloor spreading magnetic-anomaly data and the bathymetric data that reflect the record of this technique history. The well-defined magnetic lineations north of the Clarion fracture zone, in the mouth of the Gulf of California, and on the east flank of the East Pacific Rise (EPR) are carefully examined and used to provide a guide for interpreting the spreading pattern between the Clarion and Clipperton fracture zones, southward of the Rivera fracture zone over the Mathematician Ridge, and over the entire EPR east of the Mathematician Ridge between the Rivera and Siqueiros fracture zones. The bathymetric data provide a trace of the fracture zone pattern in each of the above mentioned areas. The fracture zone bathymetry and the seafloor spreading magnetc lineations on the EPR south of the Rivera fracture zone have a distinctive fanning pattern caused by close poles of rotation and plate boundary reorganizations. All these data provide a good record of the plate reorganizations in the middle Miocene at magnetic anomaly 5A time (12.5 to 11 m.y. B.P.), in the late Miocene at a magnetic anomaly 3'--4 time (6.5 m.y. B.P.), and in the Pliocene at magnetic anomaly 2'--3 time (3.5 m.y.B.P.). Several abandoned spreading centers, including the Mathematician Ridge, were left behind as a result of these reorganizations. The Mathematician Ridge is shown to be a set of ridges and trough whose origin is related to the tectonics activity associated with each of the above mentioned reorganizations since anomaly 5A.

Klitgord, K.D.; Mammerickx, J.

1982-08-10

392

The longevity of the South Pacific isotopic and thermal anomaly  

USGS Publications Warehouse

The South Pacific is anomalous in terms of the Sr, Nd, and Pb isotope ratios of its hot spot basalts, a thermally enhanced lithosphere, and possibly a hotter mantle. We have studied the Sr, Nd, and Pb isotope characteristics of 12 Cretaceous seamounts in the Magellans, Marshall and Wake seamount groups (western Pacific Ocean) that originated in this South Pacific Isotopic and Thermal Anomaly (SOPITA). The range and values of isotope ratios of the Cretaceous seamount data are similar to those of the island chains of Samoa, Tahiti, Marquesas and Cook/Austral in the SOPITA. These define two major mantle components suggesting that isotopically extreme lavas have been produced at SOPITA for at least 120 Ma. Shallow bathymetry, and weakened lithosphere beneath some of the seamounts studied suggests that at least some of the thermal effects prevailed during the Cretaceous as well. These data, in the context of published data, suggest: 1. (1)|SOPITA is a long-lived feature, and enhanced heat transfer into the lithosphere and isotopically anomalous mantle appear to be an intrinsic characteristic of the anomaly. 2. (2)|The less pronounced depth anomaly during northwesterly plate motion suggests that some of the expressions of SOPITA may be controlled by the direction of plate motion. Motion parallel to the alignment of SOPITA hot spots focusses the heat (and chemical input into the lithosphere) on a smaller cross section than oblique motion. 3. (3)|The lithosphere in the eastern and central SOPITA appears to have lost its original depleted mantle characteristics, probably due to enhanced plume/lithosphere interaction, and it is dominated by isotopic compositions derived from plume materials. 4. (4)|We speculate (following D.L. Anderson) that the origin of the SOPITA, and possibly the DUPAL anomaly is largely due to focussed subduction through long periods of the geological history of the earth, creating a heterogeneous distribution of recycled components in the lower mantle. ?? 1991.

Staudigel, H.; Park, K.-H.; Pringle, M.; Rubenstone, J.L.; Smith, W.H.F.; Zindler, A.

1991-01-01

393

The cartilage-bone interface.  

PubMed

In the knee joint, the purpose of the cartilage-bone interface<