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1

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

NASA Astrophysics Data System (ADS)

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

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

2002-12-01

2

Episodic North America and Pacific Plate motions  

NASA Astrophysics Data System (ADS)

The North America plate motion for the period 20-0 m.y. is modeled by two absolute angular velocity vectors, with a change occurring at about 9 m.y. The model incorporates new geologic constraints based on (1) the recognition of a discontinuity in North America plate motion at 9 m.y., (2) a reexamination of the Iceland and Yellowstone hotspot traces, (3) improved delineation of the present North America - Pacific relative motion, and (4) a revised history of Pacific absolute motion. The two-stage model is consistent with several features of the late Cenozoic geologic history of North America, including geological observations relating to tectonism along a large portion of both the eastern and western boundaries of North America. This plate model, combined with a previously established Pacific plate model, makes specific predictions concerning the 15-0 m.y. history of the North America-Pacific plate boundary which compare favorably with the known history. These models together resolve most of the discrepancies previously encountered between absolute and relative motion models of the two plates. The implications of the North America plate model are the greatest for those events related to the 9 m.y. change in its motion. Among the geologic consequences of this change are rifting in the western United States, intense compressional deformation along the northern Caribbean plate boundary, a hiatus in Aleutian arc volcanic activity, and a change in the orientation of the Lesser Antilles arc. This picture reinforces the notion that the major plates behave rigidly and transmit stresses over great distances. The predictive power of the model may help in interpreting the history of the North America plate boundary in those areas where clear observations are lacking. An extra force needs to be applied to a plate to cause a change in plate motion. By treating the plate as a rigid spherical shell overlying a uniformly viscous fluid, we derive a simple class of forces sufficient to cause a given change in plate motion. Such force balance considerations indicate that an additional force applied in the northwest Pacific region, toward the northeast, would result in the observed change in North America plate motion. This force is surprisingly similar to that which apparently caused a large change in Pacific plate motion about 5 m.y. later. We propose that a common mantle process is responsible for both changes and is related to the ability of the northwest Pacific subducted lithosphere to enter into the lower mantle.

Pollitz, Fred F.

1988-08-01

3

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

NASA Astrophysics Data System (ADS)

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

Ohmi, Shiro; Hori, Sadaki

2000-04-01

4

Deformations of the northwestern Pacific plate  

NASA Astrophysics Data System (ADS)

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

Patrikeev, V. N.

2013-09-01

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

GPS determination of current Pacific North American plate motion  

Microsoft Academic Search

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

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

1999-01-01

7

Upper mantle low anisotropy channels below the Pacific Plate  

NASA Astrophysics Data System (ADS)

A new 3D anisotropic model has been obtained at a global scale by using a massive dataset of seismic surface waves. Though seismic heterogeneities are usually interpreted in terms of heterogeneous temperature field, a large part of lateral variations are also induced by seismic anisotropy of upper mantle minerals. New insight into convection processes can be gained by taking seismic anisotropy into account in the inversion procedure. The model is best resolved in the Pacific Plate, the largest and the most active tectonic plate. Superimposed on the large-scale radial (? parameter) and azimuthal anisotropy (of VSV velocity) within and below the lithosphere, correlated with present or past Pacific Plate motions, are smaller-scale (<1000 km) lateral variations of anisotropy not predicted by plate tectonics. Channels of low anisotropy down to a depth of 200 km (hereafter referred to as LAC) are observed and are the best resolved anomalies: one east-west channel between Easter Island and the Tonga-Kermadec subduction zones (observed on both radial and azimuthal anisotropies) and a second one (only observed on azimuthal anisotropy) extending from the south-west Pacific up to south-east Hawaii, and passing through the Polynesia hotspot group for plate older than about 40 Ma. These features provide strong constraints on the decoupling between the plate and asthenosphere. They are presumably related to cracking within the Pacific Plate and/or to secondary convection below the rigid lithosphere, predicted by numerical and analog experiments. The existence and location of these LACs might be related to the current active volcanoes and hotspots (possibly plumes) in the Central Pacific. LACs, which are dividing the Pacific Plate into smaller units, might indicate a future reorganization of plates with ridge migrations in the Pacific Ocean.

Montagner, J.-P.

2002-09-01

8

Is Baja California part of the Pacific Plate?  

Microsoft Academic Search

Coupling GPS observations with numerical modeling we can answer this important question and evaluate the effect of a non-complete coupling on the kinematics of the Western hemisphere. Until 12 Ma the western coast of Baja California (BC) was the location of the subduction of the Pacific plate (PA) underneath the North American plate (NA). It is a common assumption that

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

2005-01-01

9

ConcepTest: Pacific Plate Motion  

NSDL National Science Digital Library

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

10

Probing the Pacific’s oldest MORB glass: mantle chemistry and melting conditions during the birth of the Pacific Plate  

Microsoft Academic Search

Major element chemistry of basalt from the southern East Pacific Rise (EPR) is different from that of the EPR at the time of the formation of the Pacific Plate at 170 Ma. Glass recovered from Jurassic age (170 Ma) Pacific ocean crust [Bartolini and Larson, Geology 29 (2001) 735–738] at Ocean Drilling Program Hole 801C records higher Fe8 (10.77 wt%)

Martin Fisk; Katherine A Kelley

2002-01-01

11

Swimming Across the Pacific: A Swimming Interface for Virtual Reality  

Microsoft Academic Search

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

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

12

Guadalupe Island, Mexico as a new constraint for Pacific plate motion  

NASA Astrophysics Data System (ADS)

We use GPS data collected on Isla de Guadalupe and in northern Baja California, Mexico, to estimate site velocities relative to Pacific plate motion. The velocities of all three geodetic monuments on Guadalupe fit a rigid Pacific plate model with residuals of 1 mm/yr. Using the Guadalupe data and data from five IGS stations on the Pacific plate (CHAT, KOKB, KWJ1, MKEA, and THTI) we estimate an angular velocity for this plate that is consistent with other recently-published estimates. Our results indicate that Isla de Guadalupe lies on the Pacific plate, and that GPS data collection on the island usefully constrains Pacific plate motion and rigidity.

Gonzalez-Garcia, J. J.; Prawirodirdjo, L.; Bock, Y.; Agnew, D.

2003-08-01

13

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

14

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

Microsoft Academic Search

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

Tom Parsons

15

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

16

Paleogene tropical Pacific: Clues to circulation, productivity, and plate motion  

NASA Astrophysics Data System (ADS)

Stratigraphic data from 63 Deep Sea Drilling Project and Ocean Drilling Program (ODP) sites that sample the lower Neogene and Paleogene sediments of the tropical Pacific have been compiled and put on the biostratigraphic and paleomagnetic timescale refined by ODP Leg 199 scientists. Sediment accumulation rates have been calculated for ten intervals ranging in age from 10 to 56 Ma and have been plotted for the midpoint of each interval at the associated paleoposition for each site used. A fixed hot spot model was used for reconstruction of the Pacific lithospheric plate. All such reconstructed intervals show the development of a tongue of high accumulation rates associated with the oceanographic divergence at the geographic equator. The development of this equatorial band is weakest between 46 and 56 Ma, the time of the peak warmth in Paleogene climate. Possible motion of the Hawaiian hot spot or true polar wander between 46 and 56 Ma appears to have had little effect on the plate rotation estimate of the position of the equator. In addition to temporal changes in the calcite compensation depth and in productivity, the biggest change in the patterns of sediment accumulation rates in the eastern tropical Pacific was the development of a relatively strong divergence between 6° and 10°N, near the region of divergence between the modern North Equatorial Current and the North Equatorial Counter Current. Changes in the equatorial circulation appear to be associated in time with the opening and closing of oceanic gateways, particularly the complex closing of the Caribbean-Pacific gateway.

Moore, T. C.; Backman, Jan; Raffi, Isabella; Nigrini, Catherine; Sanfilippo, Annika; PäLike, Heiko; Lyle, Mitchell

2004-09-01

17

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

18

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

19

Geologic constraints on the Cenozoic Antarctica-Australia-Pacific relative plate motion circuit  

Microsoft Academic Search

In a revised interpretation of the sea-floor spreading pattern in the southwest Pacific Ocean, Stock and Molnar predicted that the modern Australia-Pacific plate boundary through New Zealand formed about 35 Ma and has accommodated about 800 km of relative motion. Geologic constraints onshore in New Zealand, however, suggest that the modern plate boundary formed about 23 Ma and has accommodated

Peter J. J. Kamp; Paul G. Fitzgerald

1987-01-01

20

Propagation of Flexural Waves At the Interface Between Floating Plates  

Microsoft Academic Search

We present a theoretical study of wave propagation in two adjoining ?oating plates of difierent ?exural rigidity, such as fast-ice sheets that abut across a pressure ridge, etc. Analytical formulas for the transmission and re?ection coe-cients for various conditions at the interface are obtained using the Wiener-Hopf technique for the case of semi- inflnite elastic plates joined by a straight

Hyuck Chung; Colin Fox

2002-01-01

21

The golden transformation of the Cretaceous plate subduction in the west Pacific  

Microsoft Academic Search

Long-term couplings between the subducting and overlying plates are very important to understanding plate tectonics, in particular intraplate evolutions. Geological records of this coupling however, are usually not well preserved. Here we show a good example in eastern China where Cretaceous tectonic evolution matches remarkably well with the drifting history of the Pacific plate. The most pronounced phenomenon is that

Weidong Sun; Xing Ding; Yan-Hua Hu; Xian-Hua Li

2007-01-01

22

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

NASA Astrophysics Data System (ADS)

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 pole positions from synthetic apparent polar wander paths. This congruency points to the veracity of the plate circuits and the accuracy of the paleomagnetic estimates. In contrast to the agreement seen for the Late Cretaceous, small discrepancies are observed in the comparisons of the Pacific Paleogene data and predictions from synthetic apparent polar wander paths. Such a disparity in a younger time interval is unexpected, given the agreement of the Late Cretaceous data. The possibility that minor, temporally variable nondipole field components contribute to the discrepancy cannot be completely discounted. However, an alternative and more straightforward explanation is suggested by further comparisons of the mean non-Pacific paleomagnetic data and the highest-quality poles that contribute to the means. In particular, we note that (1) the Pacific Paleogene data are in full agreement with coeval poles from North America meeting strict reliability criteria and (2) the non-Pacific Paleogene poles of synthetic apparent polar wander paths are dominated by results from the North Atlantic Igneous Province (NAIP), but taken as a whole, the NAIP data fail a paleomagnetic reversal test. Hence, minor discrepancies between Paleocene paleomagnetic data from the Pacific and Atlantic hemispheres may point to limitations of the latter, which incorporate a relatively large number of older, lower-quality data. These findings call for renewed data collections utilizing comprehensive rock magnetic and paleomagnetic (demagnetization) procedures to improve resolution of Paleocene non-Pacific data. The uncertainties of the Pacific paleolatitude data and the non-Pacific reference poles are larger than the differences related to the use of the two alternative plate circuits (through East to West Antarctica and through Australia to the Lord Howe Rise) that link the Atlantic and Pacific hemispheres. While no preference can thus be given to either plate circuit, their overall consistency with paleomagnetic data suggests that they can be used to investigate long-term motion of the Pacific plate since Late Cretaceous times.

Doubrovine, Pavel V.; Tarduno, John A.

2008-07-01

23

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

24

Two Small Crustal Plates in the South Pacific near Easter Island.  

National Technical Information Service (NTIS)

Limited marine and earthquake seismic data suggest that two small crustal plates may now exist in the South Pacific centered at 24 degrees and 34 degrees S. These small plates may have existed for only the last 3 m.y., and may reflect a continuing instabi...

E. M. Herron

1972-01-01

25

High Attenuation Zone Beneath the Subducting Pacific Plate?  

NASA Astrophysics Data System (ADS)

Interesting systematic change in waveform observed in seismic networks on Japan islands from events in Java - Tonga subduction zones (the epicentral distances are from 40-80 degrees). Some waveforms sampling eastern region (oceanward) of Japan subduction zones from Tohoku to Izu have been broadened and the amplitude has been decayed. These characteristics can be due to anelasticity in the propagating media. We estimated anelasticity using two kinds of differential attenuation (? t*) method; S-S0 method and S-P method. The methods are based on forward modeling of waveform by using absorption band model. A reference signal is modified synthetically with changing parameter Q to find best fit with observed signal. The S-S0 method determines differential attenuation of S-wave to a reference S0-wave. The S-P method determines differential attenuation of S-wave to P-wave. In the modeling, we used normalized amplitude. Therefore, we only take account of dispersion but amplitude decay. Two types of waveform data set were recorded by tiltmeters installed at stations of the High Sensitivity Seismograph Network of Japan (Hi-net), and broad band seismograph network (F-net). The both networks are operated by National Research Institute for Earth Science and Disaster Prevention (NIED). The tiltmeters can be used as broadband seismometers with horizontal components and have dense spatial distribution. The broad band seismograph network is sparser than that of tiltmeters, but each station has three components including vertical component. Using data from five events, a high attenuation region is detected in the upper mantle beneath subducting Pacific plate in Japan subduction zones from Tohoku to Izu. If we assume that all the absorption occurred only in the upper mantle (400 km thick), the estimate value of Qs is 40-60. The spatial distribution of the high attenuation zone is correspondent to that of a low velocity zone suggested by Obayashi et al. [2005]. The origin of the high attenuation and low velocity zone will be discussed in the future work.

Shito, A.; Kawakatsu, H.; Obara, K.

2005-12-01

26

Apparent Polar Wander of the Pacific Plate and Pacific Hotspots: Implications for True Polar Wander and Hotspot Fixity  

NASA Astrophysics Data System (ADS)

Whether the apparent polar wander (APW) path of the Indo-Atlantic hotspots is a record of true polar wander could be tested from a detailed APW path of the Pacific plate, the motion of which can be estimated relative to the hotpots independently of reconstructions in the Atlantic and Indian Ocean basins. Such an APW path has previously been lacking because of the difficulty in obtaining fully oriented paleomagnetic samples from oceanic plates. We present an APW path for the Pacific plate and for the hotspots of the Pacific basin. Our Pacific plate APW path from 125 Ma to the present is based mainly on the analysis of the skewness of marine magnetic anomalies due to seafloor spreading and is determined with better accuracy and resolution from 32 Ma to 81 Ma than is the APW path of any continent. Our path is defined by eleven paleomagnetic poles from non-overlapping age windows. Nine of these poles, those with ages from 32 Ma to 81 Ma, are determined from skewness analysis of 1563 crossings of marine magnetic anomalies due to seafloor spreading. They reveal the APW of the Pacific plate over this time interval with an accuracy and age-resolution far superior to other data sets. The skewness-only portion of the path indicates northward motion of the Pacific plate with 3 main swings in declination, clockwise from 81 Ma to 68 Ma, counterclockwise from 68 Ma to 40 Ma, and clockwise from 40 Ma to the present. The older two poles are from combinations of data types. There is no significant motion of the pole from 125 Ma to 88 Ma, but there is a sudden large counterclockwise shift of the pole in the brief interval from 88 to 81 Ma. This large and rapid shift of the pole is strongly supported by paleocolatitude data from azimuthally unoriented vertical cores of igneous rock obtained by deep sea drilling. In a reference frame attached to the Pacific hotspots, the spin axis lay near 80°N, 160°E during mid-Cenozoic time (32-40 Ma), near 80°N, 210°E during early Cenozoic time (55-68 Ma), and near 75°N, 170°E during Campanian and early Maastrichtian time (73-81 Ma). Thus, there was modest motion of the spin axis from 81 Ma to 32 Ma (or younger) with larger swings before and after. The most recent shift, sometime during the past 32 Myr, has been about 10° in arc length. A bigger shift of about 20° arc length occurred from 88 to 81 Ma, near the end of the Cretaceous normal polarity superchron. The largest difference between Pacific hotspot APW and Atlantic hotspot APW occurs for 73 to 81 Ma. The poles available from this time interval for the continents are highly scattered and some are likely biased. Overall there is good agreement between the two sets of curves, with the Indo-Atlantic hotspot APW path resembling a smoothed version of the Pacific hotspot APW path. The substantial overlap of confidence regions for the 125 Ma poles indicates no significant net motion between Pacific hotspots and Indo-Atlantic hotspots for the past 125 Ma. Within uncertainties, however, such motion could be as much as 9 mm/yr for the combined effect of the two paleomagnetically observable degrees of freedom. These results indicate that motion between Pacific and Indo-Atlantic hotspots is small enough that the hotspot reference frame is useful for estimating true polar wander.

Gordon, R. G.; Horner-Johnson, B. C.; Petronotis, K. E.; Acton, G. D.

2004-05-01

27

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

NASA Astrophysics Data System (ADS)

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

Meckel, Timothy Ashworth

28

Ontong Java Plateau and late Neogene changes in Pacific plate motion  

NASA Astrophysics Data System (ADS)

Aided by a new geometrical technique called hot spotting, we recently proposed a new model for the absolute motion of the Pacific plate. This model, called WK97, assumed the Hawaiian hotspot is under Loihi and that there was a change in plate motion at 3-6 Ma. The model located the Louisville hotspot close to the Hollister Ridge, a shallow volcanic ridge associated with a geoid high, seismicity, and recent volcanism. Most of the tectonic implications of WK97, however, were not addressed. Furthermore, although several recent studies suggest that the geochemistry of Hollister lavas may indicate a mixture between Louisville melt material and Pacific-Antarctic Ridge mid-ocean ridge basalt, these studies strongly disagree with WK97 and consider it seriously flawed. Here we discuss numerous tectonic predictions of WK97 and present a large amount of observational evidence in support of it. We find that a late Neogene collision between the Ontong Java Plateau and the northern margin of the Australia plate appears to have altered the motion of the Pacific plate, as inferred from hotspot volcanism, by forcing it to rotate counter-clockwise. This rotation, about a low-latitude pole, appears to have induced right-lateral shear stress along the entire Pacific plate divergent boundary, which resulted in the formation of extensional transform faults, microplates, and propagating ridges. This change in motion also appears to have triggered concomitant circum-Pacific tectonism, including trench migration and back arc rifting. The WK97 suggests that long-lived, plume-fed volcanism on the Pacific plate appears very limited, perhaps only to five to six hotspots: Hawaii, Louisville, Cobb, Caroline, and perhaps Marquesas and Bowie; the geometry of these chains are consistent with our model. Despite some evidence for volcanic age progressions, most other Pacific Neogene hotspots are most likely "crack spots", i.e., sites of extensional volcanism at preexisting zones of weakness reactivated by plate stresses. Indeed, several volcanic ridges, such as Hollister Ridge near the Louisville hotspot, appear to have formed in response to stresses following the change in absolute plate motion. WK97 also obviates the need for simultaneous, different directions of mantle flow in the south central Pacific. Transpression at the San Andreas and Alpine strike-slip faults and Aleutian Arc explosivity since 6 Ma also appear to be consequences of the changes in Pacific plate motion. Furthermore, both the WK97 model and observed relative plate motions suggest that adjoining plates have changed their absolute motions as well and that large changes in absolute plate motion do not necessarily imply large changes in relative plate motion. Our findings support slab pull as the dominant plate tectonic driving force, highlight the rheological difference between strong oceanic lithosphere and weak continental crust, and suggest that WK97 presently provides a unifying, albeit preliminary, framework for relating both intraplate and circum-Pacific tectonism and volcanism in the late Neogene.

Wessel, Paul; Kroenke, Loren W.

2000-12-01

29

Depth of the decoupling plate interface and thermal structure under arcs  

Microsoft Academic Search

Subduction proceeds as thrust movements at the boundary between the subducting plate and the rigid overlying plate. At depth below this mechanically decoupling plate interface, the subducting plate couples with the overlying mantle, and flow is induced in the mantle wedge. This induced flow is the main factor that controls thermal structure under arcs. Depth of this decoupling to coupling

Yoshitsuga Furukawa

1993-01-01

30

Holocene Pacific North American plate interaction in southern Alaska: Implications for the Yakataga seismic gap  

Microsoft Academic Search

The St. Elias, Alaska, earthquake (magnitude 7.1 Ms) on February 28, 1979, occurred along the complex Pacific North American plate boundary between Yakutat Bay and Prince William Sound, rupturing only a fraction of the seismic gap identified in that region. To aid in evaluating the potential for, and likely site of, a future earthquake occurring in the remainder of the

John C. Lahr; George Plafker

1980-01-01

31

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

Microsoft Academic Search

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

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

1987-01-01

32

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

Microsoft Academic Search

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

J. K. Hillier; A. B. Watts

2004-01-01

33

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

Microsoft Academic Search

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

J. M. Fletcher; B. W. Eakins

2001-01-01

34

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

NASA Astrophysics Data System (ADS)

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

Eberhart-Phillips, Donna; Reyners, Martin

2012-08-01

35

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

USGS Publications Warehouse

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

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

2007-01-01

36

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

37

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

38

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

NASA Astrophysics Data System (ADS)

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

Stock, J. M.

2011-12-01

39

Nonlinear free vibration analysis of piezoelastic laminated plates with interface damage  

Microsoft Academic Search

This paper presents a nonlinear model for piezoelastic laminated plates with damage effect of the intra-layers and inter-laminar\\u000a interfaces. Discontinuity of displacement and electric potential on the interfaces are depicted by three shape functions.\\u000a By using the Hamilton variation principle, the three-dimensional nonlinear dynamic equations of piezoelastic laminated plates\\u000a with damage effect are derived. Then, by using the Galerkin method,

Yi-ming Fu; Sheng Li; Ye-jie Jiang

2009-01-01

40

Nazca absolute plate motion and Pacific basin inter-hotspot motion  

NASA Astrophysics Data System (ADS)

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

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

2003-04-01

41

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

2013-09-01

42

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

43

Holocene Pacific North American plate interaction in southern Alaska: Implications for the Yakataga seismic gap  

NASA Astrophysics Data System (ADS)

The St. Elias, Alaska, earthquake (magnitude 7.1 Ms) on February 28, 1979, occurred along the complex Pacific North American plate boundary between Yakutat Bay and Prince William Sound, rupturing only a fraction of the seismic gap identified in that region. To aid in evaluating the potential for, and likely site of, a future earthquake occurring in the remainder of the gap, we have formulated a kinematic model of neotectonic deformation in southern Alaska from available geologic and seismic data. In this model the part of the North American plate bordering on the Gulf of Alaska is divided into three subblocks, which are partially coupled to the Pacific plate. On the basis of the model, the gap-filling rupture or ruptures would most likely be along the north-dipping thrust faults of the Pamplona zone between Icy Bay and the eastern end of the Aleutian Trench. If the accumulated strain of 3.8 m postulated for this region were released suddenly in one event involving the remainder of the gap, the result would be an earthquake as large as magnitude 8.

Lahr, John C.; Plafker, George

1980-10-01

44

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

USGS Publications Warehouse

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

Geist, E. L.

1996-01-01

45

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

46

The recent history of the Galapagos triple junction preserved on the Pacific plate  

NASA Astrophysics Data System (ADS)

At the Galapagos triple junction, the Cocos and Nazca plates are broken by a succession of transient rifts north and south of the Cocos-Nazca (C-N) Rift. Modeling has suggested that each rift initiated at the East Pacific Rise (EPR), its location controlled by the distance of the C-N Rift tip from the EPR. Evidence on the Pacific plate confirms that each transient rift formed a true RRR triple junction with the EPR and clarifies the history of the region. At ˜1.5 Ma the triple junctions began jumping rapidly toward the C-N Rift suggesting that the C-N Rift tip moved closer to the EPR. Pacific abyssal hills became broad and shallow indicating enhanced magma supply to the region. At ˜1.4 Ma, the Galapagos microplate developed when extension became fixed on the southern transient rift to form the South scarp of the future Dietz rift basin. Lavas flooded the area and a Galapagos-Nazca magmatic spreading center initiated at the EPR. We suggest that a hotspot was approaching the southern triple junction from the west. The hotspot crossed to the Nazca plate ˜1.25 Ma. Dietz seamount formed within the young spreading center, dikes intruded Dietz rift basin, and eruptions built volcanic ridges. Since ˜0.8 Ma magmatic spreading has jumped northward twice, most recently to Dietz volcanic ridge. Amagmatic extension to the east has formed the large North scarp of Dietz rift basin. Northward jumping of the southern triple junction has maintained the microplate boundary close to the proposed hotspot.

Smith, Deborah K.; Schouten, Hans; Montési, Laurent; Zhu, Wenlu

2013-06-01

47

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

48

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

49

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

50

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

51

Rapid tremor reversals in Cascadia generated by a weakened plate interface  

NASA Astrophysics Data System (ADS)

Slow slip along the plate interface at subduction zones can generate weak seismic tremor in a quasi-periodic process called episodic tremor and slip. This process differs in character from regular earthquake rupture and can release stresses that build up on the deep plate interface. Here we analyse the spatial and temporal evolution of the five largest episodic tremor and slip events between 2004 and 2009 in northern Washington on the Cascadia subduction zone. We find that the events are similar, but not identical because they initiate in different locations and propagate along the plate interface at different average speeds of 7 to 12km per day. Our analysis reveals that tremor can migrate rapidly back, away from the region where tremor and slip are advancing, through parts of the plate interface that have just ruptured in the past three days. These rapid tremor reversals propagate backwards for tens of kilometres at speeds that are 20 to 40 times faster than the relatively slow, steady advance of episodic tremor and slip. Our observations suggest that once the plate interface is weakened by the initial advance of episodic tremor and slip, it allows stresses to induce slip more easily or fluid pressure waves to migrate back more rapidly, generating rapid tremor reversals.

Houston, Heidi; Delbridge, Brent G.; Wech, Aaron G.; Creager, Kenneth C.

2011-06-01

52

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

PubMed

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

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

2006-06-29

53

Slow earthquakes associated with fault healing on a serpentinized plate interface.  

PubMed

Slow earthquakes that occur at subduction zones are distinct from regular earthquakes in terms of their slip behavior. We consider this difference to relate to localized hydration reactions at the plate interface that influence the frictional properties. The results of laboratory friction experiments indicate that simulated serpentine faults are characterized by a low healing rate and large slip-weakening distance compared with unaltered dry fault patches. These results are consistent with the slip mechanism of slow earthquakes, indicating that a locally serpentinized plate interface could trigger slow earthquakes, assisted by pore pressure build-up, whereas unaltered dry patches that remain strongly coupled are potential sites of regular earthquakes. PMID:23648808

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

2013-01-01

54

Slow earthquakes associated with fault healing on a serpentinized plate interface  

PubMed Central

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

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

2013-01-01

55

Paleomagnetic data and pelagic sediment facies and the motion of the Pacific plate relative to the spin axis since the late Cretaceous  

Microsoft Academic Search

In order to study the motion of the Pacific plate with respect to the spin axis during the Cenozoic and Upper Cretaceous we combined an analysis of the distribution of pelagic sediments on the sea floor with paleomagnetic data collected on the Pacific plate. The facies distribution of sediments is used to determine the time when an equatorial crossing took

Gerardo Suárez; Peter Molnar

1980-01-01

56

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

Microsoft Academic Search

Data obtained by Mark III VLBI measurements of radio signals from permanent and mobile VLBI sites for 5.5 years of observations, starting in October 1982, were used to derive a picture of the earth crust deformation near the North America-Pacific plate boundary. The data, which included the vector positions of the VLBI sites and their rate of change, were used

Steven N. Ward

1988-01-01

57

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

58

Deep-Sea Drilling for Landlubber Geologists --- The Southwest Pacific, an Accordion Plate Tectonics Analog for the Cordilleran Geosyncline  

Microsoft Academic Search

The Deep Sea Drilling Project offers the geologist who is not trained in marine geology an unparalleled opportunity to study deep-sea sediments and volcanic rocks in their environment of formation and an opportunity to evaluate concepts of plate tectonics theory. Results of deep-sea drilling in the southwest Pacific are useful in interpreting the early history of the Cordilleran geosyncline as

Michael Churkin Jr.

1974-01-01

59

Mantle Flow Beneath the Juan de Fuca and East Pacific Rise Spreading Centers and Adjacent Plates  

NASA Astrophysics Data System (ADS)

Observations of seismic anisotropy are a principal means of inferring the direction of mantle flow beneath tectonic plates. Azimuthal anisotropy of mantle head waves (Pn) observed in mid-plate settings, for example, has been used to infer that beneath oceanic crust the mantle flow that is frozen in is parallel to the paleospreading direction. While the agreement between historical measurements of azimuthal anisotropy and paleospreading direction is good, the combined uncertainties in experimental results (many of which date back 30 to 50 years) and in inferring the paleospreading direction are often 10-15°. In contrast to historical results from mid-plate settings, recent studies of Pn anisotropy beneath the East Pacific Rise (EPR) and the Mid-Atlantic Ridge reveal that the fast-direction of seismic anisotropy - and by inference the direction of mantle flow - is skewed with respect to the current spreading direction. This result indicates that sub-ridge mantle flow is not an entirely passive response to plate spreading. Here we use data from recent active-source seismic experiments to investigate azimuthal anisotropy of Pn arrivals in two near-ridge settings. These modern experiments, which use dense arrays of ocean-bottom seismometers (OBSs) and well-navigated seismic shooting lines, can constrain azimuthal anisotropy to within ±1°. One data set is from the multi-scale Endeavour seismic tomography experiment (ETOMO) that took place in September 2009. Seismic data were collected using 68 four-component OBSs at 64 sites and the 6600 in3 airgun array of the R/V Marcus G. Langseth. The study includes 5567 shots covering 90 km along-axis and 50 km across. The second data set is from the UNDERSHOOT experiment, which was conducted at the EPR between the Siqueiros and Clipperton transforms, a section of ridge that is sub-divided by the 9°03'N overlapping spreading center (OSC). Seismic data were collected using a combination of four-component OBSs and single-component hydrophones at 57 sites and the 8500 in3 airgun array of the R/V Maurice Ewing. The study includes ~5000 shots covering 200 km along-axis and 100 km across. For each data set we document evidence for mantle anisotropy using Pn arrivals that propagate beneath the axis of spreading and for paths that sample solely the Pacific, Juan de Fuca and Cocos plates. We also present results for subsets of the data that are grouped geographically. For the EPR we select data subsets that sample three regions, one each north and south of the 9°03'N OSC and one centered on the OSC. For these subsets, the azimuth of anisotropy is effectively identical to that reported previously for the entire data set (~10° anticlockwise of the spreading direction). We thus conclude that the orientation of seismic anisotropy does not vary with local plate boundary geometry, e.g. the trend of ridge segments which differ to either side of the OSC or the presence of the OSC itself. Instead, the anisotropy is a regional-scale signal related to the azimuth of mantle divergence. Our results will further test the hypothesis that beneath spreading centers the axes of mantle upwelling and asthenospheric flow are skewed with respect to the plate spreading direction.

Toomey, D. R.; Hooft, E. E.; Wilcock, W. S.

2010-12-01

60

A laboratory use image plate camera for surface and interface structure analysis  

Microsoft Academic Search

We designed a new X-ray camera with an image plate (IP) detector so as to study surface and interface structures. It is made up of two goniometers with coaxial setup and a curved IP cassette that traverses up and down. The axis of rotation is vertical and perpendicular to the incident beam. The sample is mounted on one of the

Sae Shibata; Shuichi Doi; Isao Takahashi

2001-01-01

61

Interseismic locking of the plate interface in the northern Cascadia subduction zone, inferred from inversion of GPS data  

Microsoft Academic Search

We inverted GPS velocities from 20 continuous and 53 campaign sites in the northern Cascadia subduction zone using a Bayesian inverse method to estimate the locking state of the plate interface. The results are consistent with previous estimates based on thermal arguments and forward modeling. They suggest that the completely locked segment of the plate interface is offshore and that

Shoichi Yoshioka; Kelin Wang; Stephane Mazzotti

2005-01-01

62

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

USGS Publications Warehouse

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

Gromme, S.; Vine, F. J.

1972-01-01

63

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

NASA Astrophysics Data System (ADS)

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

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

2001-12-01

64

The northern edge of Pacific plate position near Kamchatka-Aleutian junction  

NASA Astrophysics Data System (ADS)

Two geochemical transects were carried out through Kamchatka: one previously studied SE-NW across the arc and one SW-NE trending along the Sredinny Range (SR) back arc zone. These data with Ar-Ar dating constrain magma source in space and time and allows us to relate these to tectonic position setting of the region at a given time. The cross arc transect from Gamchen volcano in Eastern Volcanic Front (EVF) through Central Kamchatka Depression (CKD) to Ichinsky volcano in SR based on Quaternary rocks showed continuous geochemical zonation from arc front to back arc of present subduction zone, including strong and gradual increase in LILE, LREE and HFSE in whole rocks. The transect along the SR from the Achtang lava field to Tekletunup volcano (the back arc zone) comprises two age groups of volcanic rocks each with uniform in geochemical features. Late Miocene-Pliocene rocks (3-6 Ma) represent voluminous plateau lavas of depleted basalts with low HFSE and HREE. Fluid-mobile elements are enriched and enrichment patterns are in fact similar to the typical arc front lavas. The younger group of Quaternary rocks (<1 Ma) is represented by monogenetic cones and stratovolcanoes that combine the typical LILE/HFSE-enrichment of a subduction setting with enrichment in all incompatible elements. In Eocene-Miocene times SR represented the active volcanic front of the Proto-Kamchatka subduction zone. In later times Kamchatka arc system has been modified by the accretion of the Kronotsky terranes. The time of accretion and the SE-outward 200 km shift of the subduction zone to the presently active EVF has been estimated from 40 to 2 Ma. Our data can help to better constrain the timing of this event by arguing that the systematic change in SR rock geochemistry with time is the result of this arc shift and has been facilitated by a massive slab roll-back event. In this scenario the SR plateau lavas represent the volcanic front until as recently as 3 Ma. The younger Quaternary rocks at SR are the present back arc lavas of the recent subduction zone. Both, the systematic geochemical zonation from contemporary arc front to back arc and the uniformity of geochemistry of young volcanic rocks along the SR show that the volcanism of the region is explained by the only one mechanism - subduction of the Pacific Plate below Kamchatka. A trend is documented from fluid-dominated melting in the EVF, through the upwelling of a strongly fluid-fluxed mantle below the CKD to melting of a fluid-enriched mantle aided by strong upwelling and decompression in the SR back arc zone. Magmatism has continued to be active in SR up to the Holocene even though seismic data today do not show a signal for a downgoing plate below this region. But the absence of the seismicity does not mean the absence of plate because at temperatures higher than 600-700°C seismicity is lost. We argue that the northern edge of the Pacific Plate is represented by a wide (150 km) boundary as a set of transform faults which can be projected on Kamchatka surface from the morphology of the downgoing oceanic plate. Also this edge is marked by the termination of Holocene volcanoes on surface along of SR. The absence of the young volcanism to the north of the on-land projection of the Alpha fault marks the plate boundary at depth.

Gordeychik, Boris; Churikova, Tatiana; Volynets, Anna; Wörner, Gerhard; Layer, Paul

2010-05-01

65

Plate Tectonics  

NSDL National Science Digital Library

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

2002-01-01

66

Absolute plate motions in a reference frame defined by moving hot spots in the Pacific, Atlantic, and Indian oceans  

NASA Astrophysics Data System (ADS)

We defined a new global moving hot spot reference frame (GMHRF), using a comprehensive set of radiometric dates from arguably the best-studied hot spot tracks, refined plate circuit reconstructions, a new plate polygon model, and an iterative approach for estimating hot spot motions from numerical models of whole mantle convection and advection of plume conduits in the mantle flow that ensures their consistency with surface plate motions. Our results show that with the appropriate choice of a chain of relative motion linking the Pacific plate to the plates of the Indo-Atlantic hemisphere, the observed geometries and ages of the Pacific and Indo-Atlantic hot spot tracks were accurately reproduced by a combination of absolute plate motion and hot spot drift back to the Late Cretaceous (˜80 Ma). Similarly good fits were observed for Indo-Atlantic tracks for earlier time (to ˜130 Ma). In contrast, attempts to define a fixed hot spot frame resulted in unacceptable misfits for the Late Cretaceous to Paleogene (80-50 Ma), highlighting the significance of relative motion between the Pacific and Indo-Atlantic hot spots during this period. A comparison of absolute reconstructions using the GMHRF and the most recent global paleomagnetic frame reveals substantial amounts of true polar wander at rates varying between ˜0.1°/Ma and 1°/Ma. Two intriguing, nearly equal and antipodal rotations of the Earth relative to its spin axis are suggested for the 90-60 Ma and 60-40 Ma intervals (˜9° at a 0.3-0.5°/Ma rate); these predictions have yet to be tested by geodynamic models.

Doubrovine, Pavel V.; Steinberger, Bernhard; Torsvik, Trond H.

2012-09-01

67

Dose Variation at Bone\\/Titanium Interfaces Using Titanium Hollow Screw Osseointegrating Reconstruction Plates  

Microsoft Academic Search

Purpose: To evaluate dose variations at bone\\/titanium interfaces in an experimental model designed to simulate postoperative radiotherapy in patients with mandibular reconstructions using a titanium hollow-screw osseointegrating reconstruction plate (THORP) system.Materials and Methods: The model consisted of a 25 × 25 × 10 mm3 block of fresh bovine femoral diaphysis, to the surface of which a segment of THORP system

Abdelkarim S Allal; Michel Richter; Mariateresa Russo; Michel Rouzaud; John M Kurtz

1998-01-01

68

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

69

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

NASA Astrophysics Data System (ADS)

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.

1988-07-01

70

Pacific Plate Apparent Polar Wander and Latitudinal Shift of the Hawaiian Hotspot: A Brief Review and Future Prospects  

NASA Astrophysics Data System (ADS)

Except for young volcanic islands, the Pacific plate is largely lacking outcrop amenable to traditional paleomagnetic analysis. As a result, a wide variety of alternative methods have been developed for estimating pole positions including analysis of the magnetic anomalies over seamounts ("seamount poles"), shape analysis of magnetic anomalies due to seafloor spreading ("skewness poles"), analysis of the amplitudes of magnetic anomalies due to seafloor spreading, analysis of azimuthally unoriented piston cores and deep-sea drilling cores in both sedimentary and igneous rocks, and analysis of equatorial sediment facies. In the 1970s, studies of seamount poles, of skewness, and of equatorial sediment facies all provided strong evidence for northward motion of the Pacific plate, in general agreement with the northward motion of the Pacific plate predicted if it is assumed that the hotspots are fixed relative to the spin axis. Beginning in about 1980, however, strong evidence was obtained that the northward motion of the Pacific plate relative to the spin axis was less than its northward motion relative to the Hawaiian and other hotspots, implying a southward drift of the Hawaiian hotspot. Results from DSDP Leg 55 first demonstrated southward motion of the Hawaiian hotspot [Kono 1980, Jackson, Koizumi et al. 1980]. Morgan [1981] showed that paleomagnetic poles and hotspot tracks from the Indian and Atlantic Oceans (and bordering continents) predicted this southward motion if the Pacific hotspots are fixed relative to those in the Indo-Atlantic, while both move together relative to the spin axis. This coherent motion of global hotspots can be interpreted as the result of true polar wander. Gordon & Cape [1981] and Gordon [1982] analyzed equatorial sediment facies, published piston core paleomagnetic data, and skewness data. They showed that the data were mutually consistent and indicated southward motion of the Hawaiian hotspot relative to the spin axis consistent with Morgan's predictions. Since then, the apparent polar wander of the Pacific plate has been elaborated in considerably greater detail. Here I concentrate on the results from skewness. Because the ages of the magnetic anomalies analyzed are unambiguous and automatically known to the nearest polarity chron, the ages of skewness poles are precisely known. The geometry of spreading on the Pacific plate during Cenozoic and Late Cretaceous time enables the estimation of poles with very compact confidence regions. Poles have been determined for many different anomalies and give a detailed, but far from complete, view of Pacific plate apparent polar wander since 83 Ma. In contrast, results from igneous rocks obtained by deep sea drilling are far sparser, less accurate, and give only paleolatitudes and not unique poles. The data are nevertheless useful, especially for time intervals lacking magnetic reversals (i.e., the Cretaceous Normal Polarity Superchron) and to provide an independent test of the results from skewness and other approaches. These independent tests reveal a high level of consistency with skewness results, strongly supporting the usefulness and reliability of skewness analysis.

Gordon, R. G.

2005-05-01

71

Absolute movement of Pacific Ocean plate based on paleoclimatic and paleomagnetic data and trajectory of hot spots during last 120 million years  

NASA Astrophysics Data System (ADS)

Climatic zonality in the open ocean influences the nature of sediment accumulation. Analysis of materials from deep water drilling in the northwest Pacific and published information on the time when parts of the Pacific plate passed the equator were used to determine the positions of equatorial high productivity zones in the past. According to these data, 100 million years ago the central Pacific plate was 36 deg further south than at present. The mean rate of latitude drift of the plate has been 4 centimeters per year. Paleomagnetic poles indicate movement of the Pacific plate to the north by more than 5000 km over the past 120 million years. The most reliable paleomagnetic poles were selected by comparing paleomagnetic and paleoclimatic data, obtaining a trajectory of apparent migration of the paleomagnetic poles. A map is presented of movements of the North Pole relative to the Pacific plate, based on hot spot trajectories. The data obtained from these three independent sources unambiguously indicate movement of the Pacific plate over the past 120 million years by approximately 9000 km toward the northwest.

Kononov, M. V.

1985-03-01

72

Load Sharing Mechanism Across Graft-Bone Interface in Static Cervical Locking Plate Fixation  

PubMed Central

Objective This study is a retrospective clinical study over more than 4 years of follow up to understand the mechanism of load sharing across the graft-bone interface in the static locking plate (SLP) fixation compared with non-locking plate (NLP). Methods Orion locking plates and Top non-locking plates were used for SLP fixation in 29 patients and NLP fixation in 24 patients, respectively. Successful interbody fusion was estimated by dynamic X-ray films. The checking parameters were as follows : screw angle (SA) between upper and lower screw, anterior and posterior height of fusion segment between upper and lower endplate (AH & PH), and upper and lower distance from vertebral endplate to the end of plate (UD & LD). Each follow-up value of AH and PH were compared to initial values. Contributions of upper and lower collapse to whole segment collapse were estimated. Results Successful intervertebral bone fusion rate was 100% in the SLP group and 92% in the NLP group. The follow-up mean value of SA in SLP group was not significantly changed compared with initial value, but follow-up mean value of SA in NLP group decreased more than those in SLP group (p=0.0067). Statistical analysis did not show a significant difference in the change in AH and PH between SLP and NLP groups (p>0.05). Follow-up AH of NLP group showed more collapse than PH of same group (p=0.04). The upper portion of the vertebral body collapsed more than the lower portion in the SLP fixation (p=0.00058). Conclusion The fused segments with SLP had successful bone fusion without change in initial screw angle, which was not observed in NLP fixation. It suggests that there was enough load sharing across bone-graft interface in SLP fixation.

Han, In Ho; Kuh, Sung Uk; Chin, Dong Kyu; Jin, Byung Ho; Cho, Yong Eun

2009-01-01

73

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

74

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

NASA Astrophysics Data System (ADS)

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.

Bunge, Hans-Peter; Grand, Stephen P.

2000-05-01

75

Pacification.  

National Technical Information Service (NTIS)

Pacification is the military, political, economic, and social process of establishing or reestablishing local government responsive to and involving the participation of the people. As a program implemented jointly with the U.S. military effort in South V...

T. D. Tho

1980-01-01

76

Slab break-off related to the Pacific-Izanagi ridge and the 50 Ma plate reorganization  

NASA Astrophysics Data System (ADS)

A hemisphere-wide plate reorganization occurred approximately 50 million years ago, causing a plethora of tectonic events in the Pacific, Indian and Atlantic oceans. The ultimate driver of this reorganization, either a plate tectonic/top-down or a mantle flow/bottom-up mechanism, remains unresolved. Top-down mechanisms often invoke a dramatic change in slab pull due to the arrival of a mid ocean ridge or aseismic ridge at a subduction zone. Bottom-up mechanisms require sudden lateral or vertical changes in mantle flow. We use a combination of surface geology, plate reconstructions, forward geodynamic models and seismic tomography to investigate the effect a slab break-off event related to the intersection of the Pacific-Izanagi ridge and the East Asian subduction zone on the 50 Ma plate reorganization. The intersection of an active mid ocean ridge with a subduction zone commonly results in the formation of a slab window. Surface manifestations of an underlying slab window are observed in the geology of southern and central Japan including: the cessation of a major accretion phase in the late Cretaceous; elevated geothermal gradients and heat flux around 55 Ma; and the emplacement of the Okitsu Melange due to underlying hot, buoyant material at 55 Ma. The cessation of granitic plutonism in Korea suggests that subduction along the margin terminated at around 60-50 Ma before restarting again ~42 Ma. We independently reconstructed the now subducted ocean floor in Panthalassa based on the magnetic lineations preserved in the ocean floor in the western Pacific and following a simple, symmetrical spreading regime with inferred intermediate spreading rates. Our plate reconstructions result in the progressively southward arrival of the Pacific-Izanagi ridge parallel to the East Asian margin between 60-50 Ma, consistent with the geological observations listed above. In addition, we carry out a series of forward geodynamic models with imposed surface plate velocities, lithospheric age and assimilated subducted slabs. Our models result in slab break-off along the East Asian margin coincident with the 50 Ma plate reorganization. We compare the present-day mantle temperature field predicted by our models to seismic tomography images over East Asia. These images reveal a break in the continuity of slab material in the mid-mantle, compatible with the slab break-off observed in both the geological record and geodynamic models. Our results suggest that the 50 Ma hemisphere-wide plate reorganization could have been triggered by a plate-driven mechanism rather than by a change in mantle flow alone. We suggest that the major change in direction of Pacific mantle flow may have been a consequence of a cessation of the long-lasting subduction along the East Asian subduction zone around 50 Ma.

Whittaker, J. M.; Seton, M.; Flament, N.; Gurnis, M.; Talsma, A. S.; Müller, R. D.

2011-12-01

77

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

78

Inception of the eastern California shear zone and evolution of the Pacific-North American plate boundary: From kinematics to geodynamics  

Microsoft Academic Search

The San Andreas Fault (SAF) is the transform boundary between the Pacific and the North American plates, yet up to 25% of the relative plate motion is now accommodated by the eastern California shear zone (ECSZ). Here we investigate the inception of the ECSZ and its geodynamic interactions with the SAF using a 3-D viscoelastoplastic finite element model. For a

Mian Liu; Hui Wang; Qingsong Li

2010-01-01

79

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

NASA Astrophysics Data System (ADS)

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

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

2003-12-01

80

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.

81

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

82

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

NASA Astrophysics Data System (ADS)

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

Symons, C. M.; Mosher, S.

2006-12-01

83

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

84

Illuminating the plate interface structure beneath Cook Strait, New Zealand, with receiver functions  

NASA Astrophysics Data System (ADS)

Using teleseismic receiver functions derived from broadband seismic arrays on the north end of the South Island and south end of the North Island of New Zealand, we image seismic impedance discontinuities in the upper mantle beneath Cook Strait using common conversion point (CCP) and Kirchhoff migration methods. Our primary findings are observations of discontinuities associated with the top of the subducting Pacific Plate. Our results suggest that contrary to recent suggestions, the plate is continuous under the northern South Island through the region of seismicity deeper than 50 km. West of Cook Strait, the slab dips steeply to the northwest. We find evidence for a low-velocity layer at the top of the slab, near which much of the seismicity is concentrated. We see hints of two crustal discontinuities, consistent with observations from previous studies. We also see substantial and continuous energy on the transverse receiver function stacks above the mantle wedge extending to the northwestern edge of our stacks, which may indicate seismic anisotropy above 50 km depth.

Boyd, Oliver S.; Savage, Martha K.; Sheehan, Anne F.; Jones, Craig H.

2007-06-01

85

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

NASA Astrophysics Data System (ADS)

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 décollement. Western Java, however, differs markedly from margins such as Nankai or Barbados, where a uniform, continuous décollement 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 décollement 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 décollement and terminates at the sea floor and which potentially contributes to tsunami generation during co-seismic activity.

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

2009-11-01

86

The Magellan seamount trail: implications for Cretaceous hotspot volcanism and absolute Pacific plate motion  

Microsoft Academic Search

The Magellan Seamount Trail (MST) delineates a northwest trending chain of four Cretaceous guyots in the West Pacific Seamount Province (WPSP). Seamount morphology, 40Ar\\/39Ar geochronology and Sr–Nd–Pb geochemistry of the MST provides evidence for a hotspot origin between the Samoa, Rarotonga and Society hotspots of the South Pacific Isotopic and Thermal Anomaly (SOPITA). The MST yields an excellent linear age

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

1998-01-01

87

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

88

Tectostratigraphic evidence for Late Paleozoic Pacific plate collision and post-Upper Jurassic transpression in northeastern Chihuahua, Mexico  

SciTech Connect

The rocks of Mina Plomosas, Chihuahua include a structurally complex association of Ordovician to Permian and Upper Jurassic strata. The structural deformation has historically been considered as two-fold including late Paleozoic compression associated with the collision of North and Afro-South America followed by loosely defined Laramide influences. These interpretations, however, are inconsistent with respect to timing, direction and style of deformation and the tectostratigraphic development of northeastern Mexico. Paleozoic strata which are folded, overturned and thrusted to the southwest are in opposition to the predicted, and elsewhere observed, northwestward compression. More likely, deformation is the result of late Paleozoic, northeastward directed Pacific plate collision causing underthrusting of the Paleozoic strata. Typical Laramide deformations are also in question. Upper Jurassic La Casita-equivalent rocks are twisted into distally thrusted, arcuate, en echelon, omega-folded anticlines which rotate into the trend of the suspected continuation of the oblique strike-slip San Marcos Fault. Such structures are diagnostic of transpressive mobile belts. The implications of late Paleozoic Pacific plate interactions and post-middle Paleozoic transpressive tectonics are that northern Mexico was located to the northwest during the Paleozoic and was repositioned following deposition of Upper Jurassic strata.

Montgomery, H.A.

1985-01-01

89

Relationship between tectonic evolution of North China craton and Pacific plate subduction slab evolution since ~47 Ma  

NASA Astrophysics Data System (ADS)

The Pacific plate movement happened some obviously changes at ~47 Ma. If we only consider the Pacific plate subduction just since this time, we can find that the subduction slab can reach eastern North China after ~20My (at ~27 Ma), and the slab may be destructed completely when it reach this position (An et al., 2009, G-cubed, doi:10.1029/2009GC002562). In the 20-My-movement processes, the evolution of the cold slab can be divided into several stages with the slab is heated and destructed. In different evolution stages, the slab also can result in different effects on the overlying asthenosphere and lithosphere. The slab evolution showed some temporal consistence with the tectonic activities in the eastern North China, and also with the Japan Sea opening; Furthermore, the possible effects acted on the overlying lithosphere by the slab in different stages can interpret the tectonic events happened in eastern North China since the early Paleogene (An et al., 2011, Earth Science Frontiers, 18(3)(in Chinese with English abstract), http://www.earthsciencefrontiers.net.cn/CN/abstract/abstract4277.shtml). For example, regional lithosphere seems to be thickening, Tangshan-Xingtai faults became active but the activities of the Taihangshan Piedmont faults decreased.

An, M.

2011-12-01

90

Sr-Nd-Pb Isotopic Signatures of High-Ti Basalts From the Pacific Rivera Plate, Western Margin of Mexico.  

NASA Astrophysics Data System (ADS)

Knowledge of the chemical and isotopic composition of ocean floor basalts is crucial for petrogenetic modeling of continental arc magmas. However, for Mexico few information is available, which was primarily that obtained from the DSDP perforations front of Acapulco and in the mouth of the Gulf of California. In this contribution we present new geochemical and geochronological analyses of Mid Ocean Ridge basalts, dredged at a depth of approx 2.800 m, offshore Manzanillo. The sampled area lies at the southeastern edge of the Rivera Plate close to its poorly defined boundary with the Cocos Plate and the Middle America Trench. Hand sized pillow fragments are glass-free and characterized by a fresh interior zone with porphyritic texture and a slightly more altered outer rim. Four tholeiitic samples were analyzed. Two generations of olivine phenocrysts were observed. Large grains without chrome spinel and smaller grains with chrome spinel and other inclusions. Both occur together with microphenocrysts of uninverted (monoclinic) pidgeonite and plagioclase (An60-80) in the fresh interior zone whereas the outer rim zone shows more alterated olivines, smectite, and secondary carbonates in vesicles. SiO2 contents are between 48.6 and 50.5 wt.% and TiO2 is substantially elevated with 2.5 to 3.9 wt.%. On the other hand, MgO is heterogeneous at relatively low levels (3.2 to 6.2 wt.%; Mg # 32-45). 87Sr/86Sr and epsilon Nd values are quite homogeneous with MORB-like ratios of 0.7025 and +11.8, respectively. Pb isotopic ratios, on the other hand, are somewhat lower than typical Pacific MORB values but lie well in the depleted mantle field. Within error, consistently young 39Ar/40Ar ages of 1.3 +/- 0.3 Ma and 1.4 +/- 0.7 Ma were obtained from the interior zone and the outer rim. More than 99% of the Ar was of atmospheric origin, which was responsible for the relatively large errors. Our high-Ti basalts are best interpreted as resulting from a propagating rift magmatism, probably as a consequence of subduction related stress in the Pacific in front of the North American Plate. This observation is also supported by magnetic anomalies and the relief of the ocean floor in the East Pacific Rise -- Pacific Cocos Segment.

Schaaf, P.; Bandy, W. L.; Mortera, C.; Canet, C.

2008-12-01

91

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

Microsoft Academic Search

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

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

2006-01-01

92

Upper Plate Deformation is Dominated by Varying Interface Coupling in the Chilean Subduction Context  

Microsoft Academic Search

It has been almost two decades now that GPS has been used to measure plate tectonics and quantify plate deformation. In South America, the debate rapidly focused on the motion of the Nazca plate relative to the South America plate. Space geodesy allows to compare plate motions averaged over a few years to plate motion averaged over several million of

C. Vigny; A. Socquet; R. Madariaga; J. Ruegg; J. Campos; S. Barrientos

2008-01-01

93

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

94

Eocene propagating rifts in the southwest Pacific and their conjugate features on the Nazca plate  

Microsoft Academic Search

We have mapped a 1200 km long NW-SE trending lineament in Seasat and Geosat radar altimeter data crossing a remote portion of the Southwest Pacific Basin. This lineament runs obliquely both to the fracture zones (FZs) and magnetic lineations between the Austral and Agassiz FZs. By examining shipboard magnetics, gravity, and bathymetric profiles in this region and in the conjugate

Steven C. Cande; William F. Haxby

1991-01-01

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

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

2013-05-22

97

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

NASA Astrophysics Data System (ADS)

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

Mosher, Sharon; Massell Symons, Christina

2008-02-01

98

Holocene subsidence at the transition between strike-slip and subduction on the Pacific-Australian plate boundary, Marlborough Sounds, New Zealand  

Microsoft Academic Search

This paper provides the first solid evidence in support of a century-old hypothesis that the mountainous Marlborough Sounds region in central New Zealand is subsiding. More recent hypotheses suggest that this may be a result of southward migration of a slab of subducted Pacific Plate causing flexural downwarping of the overlying crust in the vicinity of the transition between subduction

Bruce W. Hayward; Hugh R. Grenfell; Ashwaq T. Sabaa; Jon Kay; Rhiannon Daymond-King; Ursula Cochran

2010-01-01

99

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

NASA Astrophysics Data System (ADS)

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

Hirauchi, K.; Katayama, I.

2010-12-01

100

Sub-crustal earthquakes within the Australia-Pacific plate boundary zone beneath the Southern Alps, New Zealand  

NASA Astrophysics Data System (ADS)

Sub-crustal earthquakes have been observed sporadically for ˜40 years in the central South Island of New Zealand. We report on 20 events recorded between December 2008 and February 2012 near the Alpine Fault in the continental collision zone between the Australian and Pacific plates. A subset of 18 events at depths of 47-74 km occurs south of Mt. Cook and together with recently reported tremor locations indicates along-strike variations in deformation behaviour along the plate boundary. The sub-crustal earthquakes south of Mt. Cook increase in depth, frequency and size southwards towards the Puysegur subduction zone. Focal mechanisms could be determined for 14 earthquakes and exhibit predominantly strike-slip and reverse faulting solutions. Stress inversion analysis of the focal mechanisms yields a stress field favouring oblique-reverse faulting. We interpret the geographic and vertical distributions of these sub-crustal events in relation to a previously proposed tectonic model of a remnant passive margin that formed south of New Zealand in the Eocene and was overridden when dextral strike-slip motion initiated on the Alpine Fault. We infer that sub-crustal earthquakes occur along the leading edge of this structure, which is attached to the continental Australian crust.

Boese, C. M.; Stern, T. A.; Townend, J.; Bourguignon, S.; Sheehan, A.; Smith, E. G. C.

2013-08-01

101

Structural geomorphology of the eltanin fault system and adjacent transform faults of the Pacific-Antarctic plate boundary  

NASA Astrophysics Data System (ADS)

Seabeam and SeaMARC II swath-mapping surveys, with ancillary magnetic and gravity profiling, describe the fast-slipping (84 86 mm year-1) 380 km-long Heezen transform (56° S) and the 145 km-long Raitt transform (54° S), together with the youngest parts of their rise-flank fracture zones. Archived seismicity, satellite altimetry, and older geophysical traverses extend these descriptions, constrain the structural interpretations, and allow preliminary interpretations of the adjacent Tharp, Hollister, and Udintsev transforms. At Heezen transform, Pacific-Antarctic plate motion is partitioned between the principal strike-slip fault zone in a deep transform valley and a marginal zone of rifting 30 40 km north of the transform axis, where a zone of secondary Riedel shearing evolved into a belt of crustal extension following a Pliocene change in relative plate motion. Crustal extension and lithospheric rupture along this belt has opened rift valleys, allowed the eruption of high volcanic ridges, and suppressed uplift of a transverse ridge along the north side of the transform valley. The south side has a high transverse ridge that is probably a flexural response to the mass deficiency of the valley; it subsides and vanishes along the eastern part of the valley, which has been infilled with recent volcanism. At the eastern risecrest intersection is another uplift of old lithosphere, an intersection high raised by transfer of heat from a curved and transform-parallel overshot ridge that prolongs the axial ridge of the East Pacific Rise (EPR). Tharp transform appears to be a mirror-image of Heezen transform, but with less evidence of volcanism at the marginal rifting site. Raitt transform responded differently to the Pliocene change in plate motion: a single strike-slip zone was replaced with an en echelon pair of newly oriented faults, connected by a 10 km-long mid-Raitt spreading axis which has accreted rough, obliquely lineated crust. Transverse ridges have been raised along both sides of the transform, probably in response to the mass deficiency of the strip of mid-Raitt crust and to heating at the mid-Raitt axis. The intersections of Raitt transform with the EPR crest lack long overshot ridges, but periodically have tall, narrow intersection highs probably raised mainly by intrusion across the transform into old lithosphere. Udintsev transform adjusted to the change in slip direction by segmenting like Raitt transform, but the mid-Udintsev spreading axis grew within a widened transtensional transform valley bordered on both sides by high transverse ridges. Volcanism at the intersections with the rifted crest of the Pacific-Antarctic Ridge does not infill and close off the transform valley, so the Udintsev transverse ridges extend past the intersections to become part of the rise-flank fracture zones. At faster separating parts of the Pacific-Antarctic boundary, and on most of the rest of the EPR, fracture zone structure is mainly inherited from the variable arrangement of volcanic ridges and tectonic uplifts at the risecrest intersections, rather than from structures formed at the transform valley.

Lonsdale, P.

1994-04-01

102

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

103

Mapping Crustal Thickness Variation and Relative Plate-Hotspot Motion for the Pacific Ocean using Satellite Gravity Inversion  

NASA Astrophysics Data System (ADS)

We determine crustal thickness for the Pacific Ocean, between 80oN to 80oS and 140oE to 295oE, using a gravity inversion method which incorporates a lithosphere thermal gravity anomaly correction (Greenhalgh & Kusznir, 2007; Chappell & Kusznir, 2008). Superposition of illuminated satellite gravity anomaly data onto crustal thickness maps from gravity inversion provides improved determination of sea-floor spreading trajectories, hot spot tracks and their inter-relationship. Data used in the gravity inversion are bathymetry, free-air gravity anomaly and sediment thickness from Sandwell and Smith (2008), Smith and Sandwell (2009) and Laske and Masters (1997) respectively. The gravity inversion method, which is carried out in the 3D spectral domain and predicts Moho depth, incorporates a lithosphere thermal gravity anomaly correction. Lithosphere thermal model re-equilibration (cooling) times, used to calculate the lithosphere thermal gravity anomaly correction, are conditioned by ocean isochron information (Mueller et al. 2008), and continental margin breakup ages. The lithosphere thinning distribution, used to define the initial thermal model temperature perturbation, may be defined using ocean isochron information or derived from the gravity inversion using no a priori isochron information. The resulting maps of crustal thickness with superimposed illuminated satellite gravity data show plate boundaries, micro-plates, micro-continents, oceanic plateaus and volcanic seamounts trails. The physical significance of the mapped parameter (i.e. crustal thickness) combined with its high resolution and broad scale allows observational links to be made between plate and hot-spot motion both present and past. Crustal thickness variation predicted by gravity inversion also shows intriguing relationships with tectonic fabric and roughness within oceanic lithosphere indicated by illuminated satellite free-air gravity data.

Sinclair, A.; Kusznir, N. J.; Alvey, A.

2011-12-01

104

Propagation behaviors of thickness-twist modes in an inhomogeneous piezoelectric plate with two imperfectly bonded interfaces.  

PubMed

The thickness-twist modes in an inhomogeneous piezoelectric plate with two imperfectly bonded interfaces are analyzed, and an exact solution is obtained according to the spring-type relation from the equations of the linear theory of piezoelectricity. The frequency shift, the displacement and the stress components are all obtained and plotted. Both theoretical analysis and numerical examples show that the effect of mechanical imperfection is more evident than that of the electrical imperfection on the thickness-twist modes. Results show that the displacement and the stress components all change obviously due to the imperfectly bonded interfaces. The relationship between the frequency shift ?? and the non-dimensional number ? that is related to the imperfect interfaces is linear, which can be used to provide the foundation for a new experimental procedure for measuring the level of the interface bonding. PMID:21752416

Jin, Feng; Li, Peng

2011-06-21

105

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

106

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

107

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

Microsoft Academic Search

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

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

2010-01-01

108

Intermediate depth earthquakes beneath Nelson, New Zealand, and the southwestern termination of the subducted Pacific plate  

NASA Astrophysics Data System (ADS)

There has been debate on how convergence of mantle lithosphere is accommodated during continental collision in the central South Island of New Zealand-whether by intracontinental subduction or continuous deformation of mantle lithosphere. Intermediate depth earthquakes are sparse beneath the central South Island, and abundant seismicity 130-230 km deep within the Hikurangi subduction zone to the northeast ends abruptly beneath the Nelson region of the northern South Island. This termination of seismicity has previously been interpreted as marking the southwestern edge of the subducted slab. Here we investigate the stress and strain regime at this termination of activity, and find that it is very similar to that within the subducted plate both updip and along strike towards the northeast. Our results are consistent with subduction continuing further southwest, albeit largely aseismically, as suggested by shallow earthquakes in the northeastern South Island.

Reyners, Martin; Robertson, Elizabeth de J.

2004-02-01

109

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

110

Focal mechanism of a shock at the northwestern boundary of the pacific plate: Extensional feature of the oceanic lithosphere and compressional feature of the continental lithosphere  

Microsoft Academic Search

First motions of P-wave and S-wave polarization angles for a shallow shock that occurred on July 25, 1965, at about 70 km oceanward from the Kuril trench indicate a double couple dip-slip source with a horizontal tension axis in the direction perpendicular to the trench. This suggests that the Pacific plate in this region is being extended in this direction.

Kunihiko Shimazaki

1972-01-01

111

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

112

Constraints on Late Cretaceous and Cenozoic Extension in the Ross Sea from the Southwest Pacific Plate Circuit  

NASA Astrophysics Data System (ADS)

Magnetic anomalies and fracture zone trends north of the Ross Sea associated with Australia-Antarctic, Pacific-Antarctic and Lord Howe Rise-Antarctic sea floor spreading place strong constraints on Late Cretaceous and Cenozoic motion between East and West Antarctica. There appear to be two episodes of extension in the Western Ross Sea in this time period. The younger episode, starting about 45 Ma and ending around 25 Ma, is well constrained by differences in spreading rates on the Southeast Indian Ridge (SEIR) on either side of the Balleny FZ and by magnetic anomalies straddling the Adare Trough (Cande et al., 2000). These data document about 150 km of ENE-WSW directed extension across the Adare Basin just north of the Ross Sea. An earlier (80 to 55 Ma) episode of extension is not well constrained in large part because the spreading rate between Australia and East Antarctica was very slow and identifications of magnetic anomalies older than anomaly 24 on the SEIR are problematical. However, there are useful constraints imposed by fitting magnetic anomalies and fracture zone traces from north of the Iselin Bank, from southwest of the Campbell Plateau and from the South Tasman Sea. These features form a network of tectonic constraints that have to be fit by any proposed model of East - West Antarctic motion. A reconstruction of the conjugate splays of the Emerald FZ shows that the Iselin Trough, a fossil rift structure northeast of the Iselin Bank, formed by a local ccw rotation of 12 degrees about 72.6° S, 183° E of the Iselin Bank between anomalies 27 and 24, thus constraining East-West Antarctic extension in this period to the corridor west of the Iselin Bank. These features also enable us to test the plate circuit formed by closing the Campbell Plateau and Challenger Plateau to its pre-rift (50 Ma) configuration and closing the Tasman Sea, SEIR and Pacific-Antarctic ridge. Rotations for the SEIR which treat the older Australia-Antarctic magnetic anomalies as isochrons (Tikku and Cande, 1999) are not appropriate for this test since they produce a large overlap of the South Tasman Rise and Tasmania with Northern Victoria Land. The SEIR rotations of Royer and Rollett (1997), which do not fit the Australia-Antarctic anomalies very well, produce a reasonable closure of the Iselin Bank with Northern Victoria Land and predict about 100 km of additional (pre-55 Ma) extension in the northern Ross Sea.

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

2004-12-01

113

When oceans meet: a teleost shows secondary intergradation at an Indian-Pacific interface  

PubMed Central

The Indo-West Pacific is characterized by extraordinary marine species diversity. The evolutionary mechanisms responsible for generating this diversity remain puzzling, but are often linked to Pleistocene sea level fluctuations. The impact of these sea level changes on the population genetic architecture of the estuarine fish Lates calcarifer are investigated via a natural experiment in a region of the Indo-West Pacific known to have undergone considerable change during the Pleistocene. L. calcarifer, a coastline-restricted catadromous teleost, provides an excellent model for studying the effects of sea level change as its habitat requirements potentially make it sensitive to the region's physical history. Evidence was found for a large phylogenetic break (4% mtDNA control region; 0.47% ATPase 6 and 8) either side of the Torres Strait, which separates the Western Pacifc and Indian Oceans, although some mixing of the clades was evident. This suggests clinal secondary introgression of the clades via contemporary gene flow. Further, populations on Australia's east coast appear to have passed through a bottleneck. This was linked to the historical drying of the Great Barrier Reef coastal lagoon, which resulted in a significant loss of habitat and forced retreat into isolated refugia. These results suggest that historical eustatic changes have left a significant imprint on the molecular diversity within marine species as well as among those in the Indo-West Pacifc.

Chenoweth, S. F.; Hughes, J. M.; Keenan, C. P.; Lavery, S.

1998-01-01

114

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

115

Swimming Across the Pacific: A Virtual Swimming Interface Proposal for SIGGRAPH 2004 Emerging Technology  

Microsoft Academic Search

As a locomotion interface for virtual reality, swimming afloat in water, is an unfamiliar and intriguing paradigm. We propose to bring our virtual swimming apparatus to SIG- GRAPH 2004 Emerging Technology. In our exhibit, we will showcase the swimming apparatus and the virtual ocean en- vironment. The swimming participant will be suspended in the apparatus, an 8ft cubic frame mounted

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

116

Constraints on Pacific Plate Paleo-equator from Detailed Skewness Analysis of Magnetic Isochrons 32-25 near the Molokai, Clarion and Clipperton Fracture Zones  

NASA Astrophysics Data System (ADS)

Plate tectonics study based on total field marine magnetic anomalies measured by proton precession magnetometers has always been challenging in the equatorial area due to the relatively smaller amplitude of the anomaly and larger diurnal variations of the magnetic field resulting from the varying current of the ionosphere including the effect of the electrojet. Previous investigation of the magnetic anomalies in the equatorial Pacific has been used to study the paleomagnetic pole of the Pacific plate. However, the skewness of the magnetic data was low in coherence and accuracy, and the anomaly pattern is unable to be determined between the Clipperton fracture zone and the modern equator. Here we corrected a set of shipboard magnetic profiles using Comprehensive Model : Phase 4 ( CM4 ) which is designed to estimate the Near- Earth magnetic field by sources in the Earth's core, ionosphere and magnetosphere. We use the CM4 model to remove the diurnal variation of the ionosphere magnetic field which reduces the long-wavelength component of noise in magnetic data. In this study we deskewed more than 40 ship magnetic data sets in the central Pacific, including the Nathaniel B Palmer cruise NBP0207, by comparing the data profile with zero- skewness synthetics. The magnetic profiles are then mapped on a satellite gravity map along with their skewness values. Theoretical models show that for a ridge trending 170 degrees from north, a sudden ~90 degree change in skewness occurs when the magnetized crust moves across the paleo-equator. On the map we were able to identify that the skewness generally decreases systematically as the latitude increases. Despite the noisy data, we located positions where the ridge crossed the paleo-equator at the time of creation of the individual magnetic isochrons. The track of the paleo-equator moves southward relative to the Pacific plate during chron 32-25 time. The track of the paleo-equatorial crossing also has implications for constraints on the paleomagnetic pole.

Meng, L.; Stock, J.

2008-12-01

117

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

National Technical Information Service (NTIS)

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 corro...

T. D. Kaun

1998-01-01

118

Block kinematics of the Pacific-North America plate boundary in the southwestern United States from inversion of GPS, seismological, and geologic data  

NASA Astrophysics Data System (ADS)

The active deformation of the southwestern United States (30°-41°N) is represented by a finite number of rotating, elastic-plastic spherical caps. GPS-derived horizontal velocities, geologic fault slip rates, transform fault azimuths, and earthquake-derived fault slip vector azimuths are inverted for block angular velocities, creep on block-bounding faults, permanent strain rates within the blocks, and the rotations of 11 published GPS velocity fields into to a common North American reference frame. GPS velocities are considered to be a combination of rigid block rotations, recoverable elastic strain rates resulting from friction on block-bounding faults, and nonrecoverable strain rates resulting from slip on faults within the blocks. The resulting Pacific-North America angular velocity is similar to some published estimates and satisfies transform azimuths and one spreading rate in the Gulf of California, earthquake slip vectors in the Gulf of California and Alaska, and GPS velocities along coastal California and within the Pacific Basin. Published fault slip rates are satisfied except in the southern Mojave Desert where the motion of the Mohave block relative to North America is faster than can be explained by mapped faults. The largest blocks, the Sierra Nevada-Great Valley and the eastern Basin and Range, show permanent strain rates, after removing elastic strain, of only a few nanostrain per year, demonstrating approximately rigid behavior. Observed horizontal strain rates correlate strongly with predicted strain rates from known faults suggesting that the short-term strains evident in GPS velocities are largely elastic. In only about 20% of the region is distributed deformation needed to match the data, indicating that a plate tectonic style description of the deformation of the western United States is plausible. Most blocks rotate about vertical axes at approximately the same rate as the Pacific (relative to North America), suggesting that locally, spin rates are communicated from block to block, arguing against both floating block and ball-bearing mechanisms of block rotation. The similarities of the blocks' spin rates to that of the Pacific suggests that the Pacific strongly influences their motions through edge tractions. However, it is shown that the blocks cannot rotate about the Pacific-North America pole without spinning counter to the sense of Pacific-North America shear. Unlike some other broad plate boundaries, in the western United States, vertical axis rotations take up very little of the slip rate budget across the region.

McCaffrey, Robert

2005-07-01

119

Orbital Replaceable Unit (ORU)/cold plate thermal interface study. Volume 1: Executive Summary  

NASA Astrophysics Data System (ADS)

A pressurized dry heat pipe connector concept and low melting point alloy interface material were compared for thermal control of high power orbit replaceable payloads. The use of the pressurized contact concept for improving the efficiency of a dry thermal interface has considerable advantages over other methods of mechanical clamping, particularly where large contact areas are required for the transfer of high heat fluxes. Moderate values for the joint conductance, up to 1000 W/sq m K are attainable. A cylindrical or conically shaped contact surface where connector heat pipes are pressed together in a radial direction can transfer high heat fluxes in relatively small sized thermal connectors. It also enables passive back-up concepts such as the low melting point alloy interface material to be integrated in the connector design. Tests show it is possible to achieve values of 7000 W/sq m K with the proposed thermal interface concept.

Nikanpour, D.

1987-04-01

120

A Revised Cretaceous-Cenozoic Apparent Polar Wander Path for the Pacific Plate and its Tectonic Implications  

Microsoft Academic Search

We have revised calculated pole positions of the Pacific apparent polar wander path (APWP) for the Cretaceous and Cenozoic. Previous poles on the Pacific APWP have been constrained primarily by seamount magnetic anomaly inversions and skewness of seafloor spreading magnetic anomalies, both with shortcomings related to interpretation of magnetic anomalies. We compiled a diverse data set consisting of paleocolatitudes determined

W. W. Sager; M. A. Beaman

2005-01-01

121

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

NASA Astrophysics Data System (ADS)

The occurrence of plate-bending earthquakes not only indicates the degree of coupling experienced along the shallow thrust of a subduction zone, but also the potential depth extent of slab hydration due to water circulation along faults prior to subduction. Using a combination of hypocentroidal decomposition relative relocation and teleseismic P & SH waveform inversion techniques, we refine the locations of earthquakes occurring seaward of the Marianas trench during 1976-2010 in order to determine the depth to which extension occurs in the subducting slab. A total of 205 CMT earthquakes in the Pacific plate or within a region 80 km west of the trench were located. Of those, 40 events ranging from Mw 4.9-7.4 were found to be intraplate trench and outer rise earthquakes. Six of these earthquakes were compressional and occurred only in the region south of Guam. The remainder of the events were extensional and are located throughout the entire length of the subduction zone. In the central part of the margin, east of the Celestial Serpentinite Seamount, extensional events occur directly beneath bathymetrically determined horst and graben structures in the incoming plate. The largest of these earthquakes was a Mw 7.4 event occurring during 1990 in a section of the trench where seamounts on the Pacific seafloor are being subducted. Preliminary results from inversion of teleseismic P waveforms for several of the plate bending events in this area give depths of 10-20 km. As expected, the weakly coupled Mariana subduction zone exhibits predominantly extensional earthquakes in the trench and outer rise along most of the margin. However, the southernmost section may be more strongly coupled, as evidenced by the 1993 Mw 7.7 Guam earthquake - thought by some to have occurred along the shallow thrust zone. Accurate depths obtained through waveform modeling will help us to determine whether the compressional earthquakes in the Pacific slab south of Guam are simply bending events located below the neutral plane or whether the entire incoming plate is under compression due to increased coupling within the southern part of the Marianas seismogenic zone. In addition, we observed a difference in the frequency of CMT earthquakes between the more seismic southern half and the generally quieter northern half of the subduction zone. Extensional faulting continues to a depth of at least 20 km in the subducting slab east of Celestial Serpentinite Seamount and provides a significant pathway for fluid circulation and hydration of the slab. Results from an upcoming ocean-bottom seismometer (OBS) experiment will allow us to better define the degree of hydration in the subducting slab and the depth range of plate-bending earthquakes.

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

2010-12-01

122

Kinematic framework of the Cocos-Pacific Plate Boundary from 13°N to the Orozco TRANSFORM FAULT: RESULTS FROM AN EXTENSIVE MAGNETIC AND SEAMARC II SURVEY  

NASA Astrophysics Data System (ADS)

During the summer of 1987, magnetic anomaly data were collected by surface ship as part of an extensive SeaMARC II investigation of the East Pacific Rise (EPR) from 13°N to the Orozco transform. The survey extended to either side of the rise axis onto seafloor at least 1.8 million years (m.y.) in age, enabling the recent evolution of the structural and kinematic framework of the plate boundary to be studied in detail. North of 13°50'N there has been a major perturbation in the evolution of the plate boundary. Swaths of lineaments that trend oblique to EPR-parallel topography form a north pointing, V-shaped discordant zone on the Pacific and Cocos plates that is broadly symmetric about the EPR axis. On the Pacific plate a zone of discordant morphology 130 km long and between 6 and 14 km wide with a structural grain that is highly oblique to the present-day spreading direction is observed on seafloor 0.9-1.8 m.y. in age. A similar but more subtle feature of the same age is also present on the Cocos plate. These zones of discordant lineaments can be correlated with changes in the magnetic lineation pattern. On the Pacific plate the disturbed zone lies between anomalies J and 2, creating greater than normal distance between the anomalies. On the Cocos plate the disturbed zone is characterized by a distinct, high-amplitude, northwestward trending magnetic anomaly. The observed structural grain and the changes in the magnetic anomaly patterns associated with the disturbed zones are very similar to those observed at propagating ridges. Based on the magnetic anomalies, a propagation rate of 10.8 cm/yr in a N10°W direction is estimated for the past 1.8 m.y. A detailed examination of the structures developed within the disturbed zone on the Pacifc plate indicates that the rift propagation in this area can best be explained by the model of Wilson (1990) which involves cyclic rift failure with inward curvature of both rift tips. Plate adjustment to the propagation event is ongoing. There is a pronounced change in the morphology of the rise axis with distance from the propagation event. Close to and for ˜100 km behind the propagator tip, the EPR crest is not well developed and is characterized by a series of low (relief of 100-200 m) ridges and troughs with a poorly defined neovolcanic zone. Further away (>100 km) from the propagator tip the rise crest is a single, linear, horst-shaped ridge with a well-developed narrow axial graben at the axis of the ridge. Regional morphologic and magnetic data suggest that this cycle of rift propagation may have begun approximately 2.5 million years before present (m.y.B.P.) near the eastern ridge-transform intersection of the paleo-O'Gorman transform and is continuing today at the Orozco transform.

Madsen, John A.; Fornari, Daniel J.; Edwards, Margo H.; Gallo, David G.; Perfit, Michael R.

1992-05-01

123

Geological Observation of the Young Petit-Spot Volcanoes on the Early Cretaceous Pacific Plate using SHINKAI 6500  

NASA Astrophysics Data System (ADS)

Young volcanoes are newly discovered on the cool, thick, and old Pacific Plate approximately 600 km ESE off the northern Japan Trench, during KR04-08 cruise using R/V Kairei (JAMSTEC) in 2004. The site was predicted lava eruption based on previous study for young alkali-basalt lavas (5.95 Ma) on the Japan Trench oceanward slope (the Kaiko knolls lava field). We named the Petit-Spot for such small and young volcanoes. Four SHINKAI 6500 submersible dives (dive #877 to #880) were performed in the Petit-Spot knolls and the Kaiko Knolls lava field during May 2005. Dives were initially targeted in the hopes of finding outcrops of lava flow, sampling rocks, observation of eruptive styles, and discussion of the stratigraphy of the monogenic Petit-Spot volcanoes. Three dives were conducted at the Petit-Spot lava field. One young knoll, named the Yukawa Knoll, discovered by the dredges (D-07, 08) during KR04-08 cruise was selected for dive #877. Two other knolls for dives #878 and #879 show the similar features of bathymetry and acoustic reflectivity to the Yukawa Knoll. In contrast, one site of knoll and fault wall for dive #880 situate in the Kaiko Knolls lava field, the Japan Trench oceanward slope. Dives were planned to ascending the slope from the foot of knoll with continuously observation of lavas and volcaniclastic sequences, and sampling along the slope. The basin or flat floor at the beginning of the dive was fully covered in soft pelagic sediment. We found oblong shaped pillow lavas and the pillow robes outcrops along the slope. However, outcrops are exhibited in limited area around the summit of knoll. Lavas commonly include peperites. Rock fragments sampled appear to be volcanic breccias containing clasts of lava enclosed in sedimentary rock; manganese coating on these breccias is thin, suggesting they were deposited recently. Based on above observation, we assumed that knolls in the Petit-Spot lava field show feeder dike or cryptdome like stratigraphy with some lava flows, in-situ and redeposited hyaloclastites, and water-chilled bumps. That is, basaltic lavas mainly inject into pelagic sediment layer. Furthermore, lavas show very high vesicularity in spite of high water pressure about 6000m deep, suggesting high volatile composition. Brecciated lava clasts containing peridotitic xenolith. These features may indicate that the Petit-Spot volcanoes also have aspect as a kind of abyssal diatreme induced in the oceanic lithosphere.

Machida, S.; Hirano, N.; Ingle, S.; Ishii, T.; Abe, N.

2005-12-01

124

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

125

Contributions to the Geochemistry of Nazca Plate Sediments, Southeast Pacific. 1. Geochemical Investigations of Sediments Across the Nazca Plate at 12S.  

National Technical Information Service (NTIS)

The mineralogy, chemical compositions and metal accumulation rates of near-surface sediments have been investigated across the Nazca lithospheric plate at approximately 12 degrees S. Analyses have been made of the top and bottom intervals of eighteen free...

G. M. McMurtry

1975-01-01

126

Computer simulation of the interface between two liquid crystalline phases in rod–plate binary mixtures  

Microsoft Academic Search

Metropolis Monte Carlo NVT computer simulations of 50:50 mixtures of L\\/D=5 hard spherocylinders (NHSC=510) and L\\/D=0.12 hard cut spheres (NCS=510) have been performed. At the start of the simulation, the system is taken as a totally demixed state of pure rods and pure plates. For a packing fraction of 44% the system is found to be a fully mixed isotropic

Amparo Galindo; George Jackson; Demetri J. Photinos

2000-01-01

127

A three-dimensional eigenfunction expansion approach for singular stress field near an adhesively-bonded scarf joint interface in a rigidly-encased plate  

Microsoft Academic Search

A three-dimensional eigenfunction expansion approach for determination of the singular stress field in the vicinity of an adhesively-bonded scarf joint interface in a plate, with its top and bottom surfaces being encased, fully or partially, between infinitely rigid blocks is presented. The plate is subjected to extension\\/bending (mode I) and in-plane shear\\/twisting (mode II) far-field loading. Both the adhesive layer

Sou-Hsiung Jack Chiu; Reaz A. Chaudhuri

2011-01-01

128

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

129

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

PubMed

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

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

2012-08-10

130

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  

NASA Astrophysics Data System (ADS)

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.

1996-02-01

131

Cascadia tremor located near plate interface constrained by S minus P wave times.  

PubMed

Nonvolcanic tremor is difficult to locate because it does not produce impulsive phases identifiable across a seismic network. An alternative approach to identifying specific phases is to measure the lag between the S and P waves. We cross-correlate vertical and horizontal seismograms to reveal signals common to both, but with the horizontal delayed with respect to the vertical. This lagged correlation represents the time interval between vertical compressional waves and horizontal shear waves. Measurements of this interval, combined with location techniques, resolve the depth of tremor sources within +/-2 kilometers. For recent Cascadia tremor, the sources locate near or on the subducting slab interface. Strong correlations and steady S-P time differences imply that tremor consists of radiation from repeating sources. PMID:19179527

La Rocca, Mario; Creager, Kenneth C; Galluzzo, Danilo; Malone, Steve; Vidale, John E; Sweet, Justin R; Wech, Aaron G

2009-01-30

132

Detection of very-low-frequency earthquakes coincident with episodic tremors and slow slip events in the transition zone of the subducting plate interface  

Microsoft Academic Search

Non-volcanic deep low-frequency tremors and slow slip events occur simultaneously in the transition zone from the locked to the aseismic slip along the Nankai subduction zone in southwest Japan. To understand the stress relaxation process in the transition zone of the deep portion of the subducting plate interface, it is important to identify all seismic and geodetic phenomena. A large

Y. Ito; K. Obara

2006-01-01

133

Electric field forced vibration of a periodic piezocomposite plate with laminated structure and reflection and transmission of a plane wave at the fluid-composite interface  

Microsoft Academic Search

We address the problems of the vibration of a periodic piezocomposite plate (2-2 composite) under external electric fields and the reflection and transmission of a plane wave incident on the fluid-composite interface based on an analytical method developed recently, which takes into account explicitly the heterogeneous nature of the piezocomposites. It is shown that due to the finite thickness of

Q. M. Zhang; Xuecang Geng

1995-01-01

134

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

135

Palaeomagnetic palaeolatitudes of the Ontong Java Plateau from 120 to 55 Ma: implications for the apparent polar wander path of the Pacific Plate  

NASA Astrophysics Data System (ADS)

We present palaeomagnetic inclinations from Late Cretaceous-Early Tertiary deep-water carbonates obtained during ODP Leg 192 drilling at the Ontong Java Plateau (OJP) for the following periods: magnetochrons C33n (73.6-79.1 Ma), C32 (71.1-73.6 Ma), C27r-C31n (61.3-68.7 Ma) and C25-C26 (55.9-60.9 Ma). Compaction-induced inclination shallowing is considered to be negligible for the OJP sediments examined here because: (i) their palaeomagnetic inclinations are in excellent accord with those recently obtained from underlying OJP basement rocks, (ii) the studied sediments have anisotropy of anhysteretic remanent magnetization fabrics that appear poorly correlated with individual characteristic remanent magnetization inclinations and (iii) in the few cases where we observe a significant difference between our new OJP sedimentary palaeomagnetic data and data from other parts of the Pacific Plate, obtained mainly from seamount magnetization studies and skewness analyses, the sedimentary inclinations are not systematically lower, and therefore, cannot be explained in terms of inclination shallowing. Combining our new data with existing OJP palaeomagnetic data we obtain an internally consistent data set that we interpret to indicate northward motion of the plateau from its formation at ~120 Ma until 55 Ma. At 120 Ma the central plateau was located at 24° +/- 4°S. Approximately 45 Myr later (~76 Ma) the plateau is located near 21°S. Our data, therefore, indicate that the OJP was either stationary or exhibited a slow northward latitudinal drift during this interval. In contrast, from ~76 Ma until 68 Ma the plateau moved rapidly through approximately 10° of latitude to ~10°S. These intervals of slow and rapid motion track similar motions previously proposed for the entire Pacific Plate during the Cretaceous but extends the interval of slow motion into the Late Cretaceous. From 68 Ma until 56 Ma the plateau was again almost latitudinally stationary before moving slowly northward. More direct palaeomagnetic data are necessary to better define Pacific Plate motions during this time interval.

Hall, Stuart; Riisager, Peter

2007-05-01

136

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

NASA Astrophysics Data System (ADS)

Pore fluid pressures in subduction zones are a primary control on fault strength and slip dynamics. Numerous studies document elevated pore pressures in the outer wedge along several margins. Seismic observations and the occurrence of non-volcanic tremor provide additional evidence for the presence of near-lithostatic pore pressures at the plate interface far down-dip from the trench (~35 km depth). Here we use numerical models in one and two dimensions to evaluate the pore pressure and compaction state of sediments on the subducting Juan de Fuca plate in Cascadia from the trench to the ETS zone. 2-D models allow pressure to diffuse vertically and also laterally normal to strike of the megathrust; 1-D models simulate only vertical diffusion. Model parameters are chosen with reference to two strike-normal profiles: one through central Oregon and one through the Olympic Peninsula of Washington. We examine temporal variations in sediment input to the trench and consider implications for fault strength and permeability as well as the down-dip extent to which compactive dewatering can be considered a significant fluid source. In 1-D, we use a general and fully nonlinear model of sediment compaction derived without making any assumptions regarding stress-strain or porosity-permeability relations and allowing finite strains. In contrast, most previous models of fluid flow in subduction zones have used linear models of diffusion that rely on assumptions of constant sediment permeability and infinitesimal strains for their formulation. Our nonlinear finite-strain model remains valid at greater depths, where stresses and strains are large. Boundary conditions in 1-D are constrained by pore pressure estimates along the megathrust fault that are based on seismic velocities (e.g. Tobin and Saffer, 2010) and data from consolidation tests conducted on sediments gathered during ODP Leg 204 (Tan, 2001). Initial conditions rely on input sediment thickness; while sediment thickness at the trench in Cascadia is fairly well constrained (~1-3 km) by seismic studies, it is less clear how much of the section is frontally accreted and how much is subducted with the downgoing plate. Along the Washington profile, Batt et al. (2001) estimated that 80-100% of the incoming sediment is frontally accreted, based on comparisons between accretionary flux at the trench and erosional flux in the Olympic Mountains. We assume that similar values hold for the Oregon profile as well. Values of permeability along the plate interface are extracted from 1-D models and used to parameterize 2-D models. 2-D modeling is motivated by the need to examine time dependency of sediment influx, as well as the influence of splay faults within the accretionary wedge. Preliminary results indicate that fluid flux resulting from sediment compaction is complete well up-dip of the ETS zone, where the magnitude of fluid flux associated with mineral dehydration reactions becomes more significant. Ongoing work is centered on incorporating the effects of dehydration fluid sources within our models of pore pressure evolution and examining the implications of our results on the dynamics of slow slip events.

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

2010-12-01

137

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

NASA Astrophysics Data System (ADS)

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

Little, Timothy A.; Roberts, Andrew P.

1997-01-01

138

<interface  

Microsoft Academic Search

This essay interrogates the colonial modernity of Anglo-Australian lesbian hegemony through an experimental text which plays with the aesthetics of cyberspace. Mobilizing the hypertext mark up language (HTML) form of the Internet, it spatializes the creative, the erotic, and the political that landscape the vicissitudes of everyday life for a lesbian of Southeast Asian background living in Australia, “interface” performs

Audrey Yue

1999-01-01

139

Discussion of “Break-up spots: Could the Pacific open as a consequence of plate kinematics?” by Clouard and Gerbault  

NASA Astrophysics Data System (ADS)

Available isotopic age dates from the Foundation, Austral, Cook, Tokelau, and Gilbert island-seamount chains, combined with kinematic plate-hotspot modelling, indicate that the five chains originated from three distinct melting anomalies (or “hotspots”) well before the onset of postulated intraplate oblique extension. The kinematic pattern produces the observed range of dates due to overlap of the resulting traces. The oblique extension mechanism may have enhanced volcanism, but it cannot be the sole explanation.

Pilger, Rex H.

2008-10-01

140

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

141

Earth's Decelerating Tectonic Plates  

SciTech Connect

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

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

2008-08-22

142

Adaptive lagrange finite element methods for high precision vibrations and piezoelectric acoustic wave computations in SMT structures and plates with nano interfaces  

Microsoft Academic Search

This paper discusses the validity of (adaptive) Lagrange generalized plain finite element method (FEM) and plate element method\\u000a for accurate analysis of acoustic waves in multi-layered piezoelectric structures with tiny interfaces between metal electrodes\\u000a and surface mounted piezoelectric substrates. We have come to conclusion that the quantitative relationships between the acoustic\\u000a and electric fields in a piezoelectric structure can be

Zhang Wu; Hong Tao

2002-01-01

143

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

144

Geochemistry of primitive lavas of the Central Kamchatka Depression: Magma generation at the edge of the Pacific Plate  

NASA Astrophysics Data System (ADS)

New and published major and trace element and isotope (O, Sr, Nd) compositions of the Late Quaternary rocks from the Central Kamchatka Depression (CKD) are used to demonstrate systematic changes in magma genesis along the northern segment of the Kamchatka Arc, above and north of the subducting Pacific slab edge. We envision a number of possible petrologic scenarios for magma generation beneath the CKD and formulate quantitative mass-balance models which lead to three major conclusions departing significantly from previous interpretations of the CKD rocks. First, this study demonstrates that eclogite melts contribute to the composition of virtually all CKD lavas and could be the major agent transferring material from the subducted slab to the mantle wedge, including fluid-mobile elements (e.g., K, Ba). Second, thermal state of the mantle wedge beneath the CKD has primary control on the major composition of primitive magmas, favoring production of low temperature andesitic and dacitic mantle melts toward the slab edge. Third, hydrous slab-fluids might not be required to generate CKD magmatism. Instead, strong enrichment in LILE, high ?18O and 87Sr/86Sr, in some CKD magmas could originate from assimilation of hydrothermally-altered mafic lithosphere. Several concurring factors could facilitate partial melting of the subducting slab beneath the all CKD volcanoes and favor variable modification of the eclogite melts during interaction with the mantle wedge. Large input from slab melting makes CKD magmatism unique in Kamchatka and may contribute to the CKD volcanoes being the most productive arc volcanoes on Earth.

Portnyagin, Maxim; Bindeman, Ilya; Hoernle, Kaj; Hauff, Folkmar

145

The Biggest Plates on Earth: Plate Tectonics  

NSDL National Science Digital Library

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

146

Paleomagnetism of the Paleocene Ghost Rocks, Kodiak Islands, Alaska: Implications for Paleocene Pacific-Basin/North America Plate Configurations  

NASA Astrophysics Data System (ADS)

Paleocene volcanic and sedimentary rocks of the Ghost Rocks, part of the Chugach accretionary complex, may provide important constraints for possible paleogeographic models of plate configurations along the NW margin of North America. The Ghost Rocks, along with other Late Cretaceous to E. Eocene units of southern Alaska, contain anomalous near-trench igneous rocks which decrease in age from NW to SE along this margin and record relative motion of a trench-ridge-trench triple junction with respect to the margin. Thick sections of similar-aged volcanic rocks also exist in coastal Washington and Oregon. Two models have been proposed to explain these anomalous volcanic rocks. Moore et al. (1983) ascribes the progression of ages of the TRT rocks to migration of the Chugach terrane past a Kula-Farallon-NA boundary located off of present- day Oregon. Haeussler et al. (2003) call for the existence of two TRT triple junctions, one located off the present-day Oregon margin, the other of which migrated from NW (Sanak) to SE (Baranof) between Paleocene and Eocene time, which requires an intervening oceanic plate (the Resurrection Plate). Our work has included extensive sampling of both volcanic and sedimentary units of the Ghost Rocks, and detailed structural studies. The geological work indicates that much of the Ghost Rocks, particularly the large section containing volcanics at Alitak Bay, is composed of intact blocks bordered by fault zones, with steep upright to locally overturned bedding. The paleomagnetic results have revealed that the majority of the sedimentary rocks have poorly-behaved magnetizations carried by authigenic sulphide minerals. The majority of the igneous rocks (primarily beautiful exposures of basaltic-andesite pillows) have well-defined magnetizations with unblocking temperatures ranging from 450 to 550 C. The sites from Alitak Bay were corrected for vertical-axis rotations by rotating site-specific bedding strikes to agree with an average regional strike of 250 degrees. Incremental rotations applied to the site-mean directions (a paleomagnetic rotation test) indicate that best clustering occurs at the optimal rotation; thus the Alitak rocks were magnetized prior to rotation. Because the resulting rotation-corrected structure at Alitak Bay is monoclinal, all versions of paleomagnetic fold tests on the Alitak Bay rocks are inconclusive. Volcanics from Kiliuda Bay, using data from Plumley et al 1983 and this study, also have well-defined magnetizations. A regional fold test using the combined rotation-corrected Alitak Bay results and the results from Kiliuda Bay indicates best clustering occurs at 100% untilting, resulting in a combined site mean of D = 162, I = 60, k = 19, a95 = 6, N = 30. While a pre-tilting, and pre-rotation, remagnetization cannot be entirely ruled out, our new data suggest these rocks likely retain their original magnetization. Based on this we conclude that the Ghost Rocks were likely magnetized at a latitude of 41° ±7 N. These data thus support migration of at least a portion of the Chugach terrane, and its TRT-related rocks, from a position off shore present-day Oregon, since Paleocene time.

Housen, B. A.; Roeske, S. M.; Gallen, S.; O'Connell, K.

2008-12-01

147

Seismicity of the Prince William Sound Region and its relation to plate structure and the 1964 Great Alaska Earthquake  

NASA Astrophysics Data System (ADS)

We have relocated more than 11,000 earthquakes within the Prince William Sound region of southcentral Alaska where oblique subduction of the Pacific plate and Yakutat blocks beneath North America occurs at a dip angle of 3°. Subduction of the Yakutat block creates a major asperity at the subduction interface, which slipped during the 1964 Great Alaska earthquake. Comparison of relocated seismicity and stress orientations obtained from first-motion information suggests that rheological changes within the upper plate serve to concentrate seismicity. The migration of fluid from the lower plate(s), especially in the region south of the contact fault zone where underthrust sedimentary rocks lying on top of the subducted Pacific plate are pinched out by the subduction process, may also serve to concentrate seismicity. Slivers of oceanic material caught within the upper plate during past episodes of subduction could be responsible for several regions of unusually clustered seismicity (e.g., Tazlina Glacier, Knight Island regions) that appear to extend from the upper plate across the plate interface into the lower plate(s). Seismicity trends also parallel long-wavelength Bouguer gravity anomalies, suggesting an underlying relationship to density variations in the upper and lower plate(s).

Doser, Diane I.; de la Peña, Alejandro; Veilleux, Annette M.

148

Plate Motions  

NSDL National Science Digital Library

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

Nunn, Jeffrey

149

Metallurgical reactions at the interface of Sn\\/Pb solder and electroless copper-plated AlN substrate  

Microsoft Academic Search

Intermetallic formation between electroless-plated copper and Sn\\/Pb solder is investigated. An interlayer is formed between copper and solder, and segregation of Pb-rich and Sn-rich phases are observed. X-ray diffraction and EDX analysis results suggest that the major intermetallic formed in the interlayer is Cu6Sn5. For the as-plated sample, the adhesion strength of Cu to the AIN substrate after 150°C aging

Bi-Shiou Chiou; Jiann-Haur Chang; Jenq-Gong Duh

1995-01-01

150

Widespread remagnetizations associated with sedimentary greigite (Fe3S4): Implications for Neogene tectonic rotations within the Australia-Pacific plate boundary zone, New Zealand  

NASA Astrophysics Data System (ADS)

Greigite (Fe3S4) can grow at any time during diagenesis when dissolved iron and sulfide are available in sedimentary pore waters. Greigite can produce syn-depositional paleomagnetic signals that are useful for paleomagnetic studies, but it can also produce late remagnetizations that make paleomagnetic interpretations much more complicated. Determining the timing of remanence acquisition is therefore a key aspect of paleomagnetic studies of the spatially and stratigraphically widespread sedimentary sequences in which greigite is the dominant remanence carrier. We demonstrate from paleomagnetic results, which are constrained rigorously by field tests, that late diagenetic greigite growth has remagnetized up to 65% of sampled localities on the Hikurangi margin, East Coast, New Zealand. This means that the magnetizations that record large, clockwise vertical axis tectonic rotations (50-80°) of the Hikurangi margin are often considerably younger than the age of the host sediments, with remagnetizations clustered at 5-8 Ma. The remagnetizations require much greater rotation rates (8-14°/Ma) than were inferred before the remagnetizations were recognized and that are also much greater than the present geodetically observed rate (3-4°/Ma). This requires a change in tectonic regime, with slower rotation rates since development of the North Island shear belt at 1-2 Ma. Our results are consistent with long- and short-term deformation on the Hikurangi margin being driven by realignment of the subducting Pacific plate, with collision of the Hikurangi Plateau in the late Miocene potentially being key to both initiation of tectonic rotations and widespread remagnetization of Neogene sediments. The remagnetizations are inferred to have been caused by migration of gas hydrates through the sediments in association with collision of the Hikurangi Plateau.

Rowan, C.; Roberts, A. P.

2011-12-01

151

Decarbonation of the Subducting Pacific Plate Triggered by the Lawsonite-to-Epidote Transition Beneath the Mariana Forearc Serpentinite Mud Volcanoes  

NASA Astrophysics Data System (ADS)

A band of serpentinite mud volcanoes in the outer half of the Mariana forearc provides a unique view into conditions, processes, and fluxes in the shallowest part of a subduction zone, to depths of ~25 km. These large mud volcanoes, up to 2 km high and 50 km across, are abundant along a 600-km swath from 13°47'N to 19°33'N and from 50 to 90 km behind the trench. They form when water generated by dehydration of the subducting Pacific Plate ascends into the overlying mantle of the Philippine Plate and converts it to serpentinite. This low-density rock then rises buoyantly along fractures and extrudes at the seafloor, usually as a point source, producing a mud volcano with a central conduit that is narrow relative to the diameter of the volcano. This conduit feeds flows of unconsolidated sedimentary serpentinite that comprise the bulk of the seamount and contain variably serpentinized clasts of harzburgite ranging in size from silt to boulders. The upwelling serpentinite brings up fragments of subducted ocean crust metamorphosed in the blueschist facies. Also rising up are the aqueous fluids generated during, and responsible for, this metamorphism and serpentinization, that exit the seafloor as springs on the summits of the mud volcanoes. Because depleted harzburgite is much simpler chemically and mineralogically than most igneous rocks, these upwelling pore waters retain a clear chemical signal of their deep metamorphic origin in spite of their long ascent. The ascending fluids are all fresher than seawater because of slab dehydration. Their chemistry varies abruptly with distance: near the trench, at 48-54 km, they have pH 10.7, much higher Ca and Sr than seawater and much lower alkalinity, sulfate, Na/Cl, K, Rb, and B. Farther from the trench, at 70 to 90 km, the waters have pH 12.5 and show the opposite trends relative to seawater for all of these species. Sulfate, Na/Cl, K, Rb, Cs, and B all increase regularly with distance from the trench, leached from the subducting sediment and altered basalt in response to increasing temperature at depth from ~100- 350°C. The pH, alkalinity, and methane content of the springs increase abruptly with distance because carbonate dissolution joins dehydration as a major process at the top of the subducting plate. Because serpentinization during ascent generates both high pH and H2, the resulting dissolved carbonate is reduced to methane such that carbonate alkalinity is replaced by hydroxyl alkalinity: 4H2 + CO3= = CH4 + H2O + 2OH-. This reaction accounts for the much higher pH of the distal springs and the fact that most of the ascending C is as methane rather than dissolved carbonate. The abrupt transition occurs ~70 km from the trench, where metabasites recovered from the serpentinite mud indicate the transition from lawsonite-blueschist to epidote-blueschist facies also occurs. Thermodynamic modeling indicates that this transition triggers decarbonation of the subducting slab, as replacement of lawsonite by epidote drastically depletes the solution in Ca and shifts the equilibrium toward massive dissolution of subducted carbonate. Fluxes of sulfate, C, Na, K, Rb, Cs, B, Ca, and Sr in the forearc springs represent only a few percent of the amounts subducted, consistent with continued supply at greater depth.

Mottl, M. J.; McCollom, T. M.; Wheat, C. G.; Fryer, P.

2008-12-01

152

Issues related to composite plating and environmental exposure effects on composite-concrete interface in external strengthening  

Microsoft Academic Search

The effect of short-term environmental exposure on the response of in situ formed externally composite strengthened concrete is investigated. Measured response from static loading is described in terms of environmental degradation of composite and composite-concrete interface. Results indicate that degradation occurs primarily at the level of the resin in contact with the concrete, and that due care should be taken

V. M. Karbhari; L. Zhao

1997-01-01

153

Multimode migration of scattered and converted waves for the structure of the Hikurangi slab interface, New Zealand  

Microsoft Academic Search

Reflectivity imaging of local earthquake seismograms has revealed the structure of the Hikurangi subduction interface at the location of two strong earthquakes that occurred in 1990. The earthquakes originated within the continental plate of the North Island of New Zealand and below in the subducting Pacific slab. We used seismograms from 500 well-located events in two earthquake sequences recorded by

John N. Louie; Sergio Chávez-Pérez; Stuart Henrys; Stephen Bannister

2002-01-01

154

The Fairway-Aotea Basin and the New Caledonia Trough, witnesses of the Pacific-Australian plate boundary evolution : from mid-Cretaceous cessation of subduction to Eocene subduction renewal  

NASA Astrophysics Data System (ADS)

The geodynamical history of the SW Pacific is controlled since the Mesozoic by the evolution of peri-Pacific subduction zones, in a trench retreat by slab roll-back process, which successively occurred along the Eastern Gondwana margin. In this context, most basins which formed after 45 Ma reached a stage of seafloor spreading, have recorded the inversions of the earth's magnetic field and present typical oceanic crust morphologies. By contrast, the New Caledonia and Fairway basins, which are narrower and present thick sedimentary covers have a less known and more controversial origin. Based on a regional geological synthesis and on interpretation of multichannel seismic reflection and refraction data, combined with drill hole data off New Zealand and a compilation of regional potential data, we distinguish 2 phases of the evolution of the Fairway-Aotea Basin (FAB) and the New Caledonia Trough (NCT), which reflect the evolution of the Gondwana-Pacific plate boundary: Phase 1: Mid Cretaceous formation of the FAB in a continental intra- or back- arc position of the Pacific-Gondwana subduction system. The formation of this shallow basin reflects the onset of continental breakup of the Eastern Gondwana margin during Cenomanian which was most probably caused by a dynamic change of the subduction zone through a « verticalization » of the slab. This event may be the result of the 99 Ma kinematic plate reorganization which probably led to subduction cessation along the Gondwana-Pacific plate boundary. A tectonic escape mechanism, in relation with the locking of the subduction zone by the Hikurangi Plateau, could also be responsible of the trench retreat leading to backarc extension. Phase 2: Regional Eocene-Oligocene uplift followed by rapid subsidence (3-4 km) of the system « Lord Howe Rise - FAB - Norfolk Ridge ». The structural style of this deformation leads us to suggest that detachment of the lower crust is the cause of subsidence. We therefore propose a model in which the system, initially shallow during Cretaceous (phase 1), would have greatly subsided during Eocene-Oligocene, giving birth to the NCT, as the renewal of the Australia-Pacific convergent plate boundary took place. This renewal of convergence at 45 Ma would have driven the lithosphere of the system to thicken (uplift), leading to a root instability and to its detachment in the mantle (subsidence). Superposed on these two main phases, some local effects, controlled by the geometry of the plate boundary, also appear. Particularly, latest late Eocene local deformation of the Northern NCB is documented, synchronously with the New Caledonian obduction. This asymmetrical deformation which lasted less than a few million years led to the uplift of the Fairway Ridge and the subsidence of the Eastern margin of the basin along NC’s western coast (10 km vertical amplitude). We suggest that as the oceanic crust of the South Loyalty Basin was being obducted onto the Norfolk Ridge at 37 Ma, the NCB subsided under the effect of the overloading and underthrusted to accommodate the compressional deformation as a foreland flexural basin.

Collot, J.; Geli, L. B.; Lafoy, Y.; Sutherland, R.; Herzer, R. H.; Roest, W. R.

2009-12-01

155

Spatial Distribution of Pore Pressure and Effective Stress at the Western Nankai Trough Plate Interface Based on 3D Seismic Reflection Data  

NASA Astrophysics Data System (ADS)

Pore fluid pressure modulates stress on faults and is a key parameter governing faulting mechanics, including seismic and tsunamigenic slip on subduction zone megathrusts, yet has been notoriously difficult to measure directly. However, seismic velocity can serve as a proxy for porosity, which in turn can be used to estimate pore pressure and vertical effective stress in clastic sediments undergoing consolidation. 3D pre-stack depth migration (PSDM) provides the best available measure of interval velocity from seismic reflection data. We use PSDM velocity extracted along a surface immediately beneath the decollement in a an 8 x 25 km portion of a 3D survey of the accretionary wedge at the Nankai Trough subduction zone off Shikoku Island, Japan. Using a transform locally calibrated by ODP boreholes, we first compute porosity at the base of the plate boundary decollement and the adjacent underlying sediments from the PSDM velocity to 20 km down-dip. We next calculate pore fluid pressure and effective vertical (fault-normal) stress for the top of the underthrust sediment section using a compaction disequilibrium approach and porosity data from drilling. Because the pore fluid pressure at the fault interface is likely controlled by that of the top of the underthrust sediment section, this calculation results in a quantitative profile of effective stress and pore pressure at the plate interface. Analysis of the uncertainties in the successive transforms suggests that the derived pressure and stress have a precision of approximately ± 10%. Results show that the fault and immediately adjacent footwall are nearly undrained as sediments subduct, and that the fault slips under a resolved shear stress of no more than ~ 5 MPa, or only about half the value expected if excess pore pressure played no role. Spatial heterogeneity in effective stress within the survey volume implies areas of relatively high and low strength.

Tobin, H.; Saffer, D.; Costa-Pisani, P.; Kramer, G.; Moore, G.

2006-12-01

156

Geologically current plate motions  

NASA Astrophysics Data System (ADS)

We describe best-fitting angular velocities and MORVEL, a new closure-enforced set of angular velocities for the geologically current motions of 25 tectonic plates that collectively occupy 97 per cent of Earth's surface. Seafloor spreading rates and fault azimuths are used to determine the motions of 19 plates bordered by mid-ocean ridges, including all the major plates. Six smaller plates with little or no connection to the mid-ocean ridges are linked to MORVEL with GPS station velocities and azimuthal data. By design, almost no kinematic information is exchanged between the geologically determined and geodetically constrained subsets of the global circuit-MORVEL thus averages motion over geological intervals for all the major plates. Plate geometry changes relative to NUVEL-1A include the incorporation of Nubia, Lwandle and Somalia plates for the former Africa plate, Capricorn, Australia and Macquarie plates for the former Australia plate, and Sur and South America plates for the former South America plate. MORVEL also includes Amur, Philippine Sea, Sundaland and Yangtze plates, making it more useful than NUVEL-1A for studies of deformation in Asia and the western Pacific. Seafloor spreading rates are estimated over the past 0.78 Myr for intermediate and fast spreading centres and since 3.16 Ma for slow and ultraslow spreading centres. Rates are adjusted downward by 0.6-2.6mmyr-1 to compensate for the several kilometre width of magnetic reversal zones. Nearly all the NUVEL-1A angular velocities differ significantly from the MORVEL angular velocities. The many new data, revised plate geometries, and correction for outward displacement thus significantly modify our knowledge of geologically current plate motions. MORVEL indicates significantly slower 0.78-Myr-average motion across the Nazca-Antarctic and Nazca-Pacific boundaries than does NUVEL-1A, consistent with a progressive slowdown in the eastward component of Nazca plate motion since 3.16 Ma. It also indicates that motions across the Caribbean-North America and Caribbean-South America plate boundaries are twice as fast as given by NUVEL-1A. Summed, least-squares differences between angular velocities estimated from GPS and those for MORVEL, NUVEL-1 and NUVEL-1A are, respectively, 260 per cent larger for NUVEL-1 and 50 per cent larger for NUVEL-1A than for MORVEL, suggesting that MORVEL more accurately describes historically current plate motions. Significant differences between geological and GPS estimates of Nazca plate motion and Arabia-Eurasia and India-Eurasia motion are reduced but not eliminated when using MORVEL instead of NUVEL-1A, possibly indicating that changes have occurred in those plate motions since 3.16 Ma. The MORVEL and GPS estimates of Pacific-North America plate motion in western North America differ by only 2.6 +/- 1.7mmyr-1, ~25 per cent smaller than for NUVEL-1A. The remaining difference for this plate pair, assuming there are no unrecognized systematic errors and no measurable change in Pacific-North America motion over the past 1-3 Myr, indicates deformation of one or more plates in the global circuit. Tests for closure of six three-plate circuits indicate that two, Pacific-Cocos-Nazca and Sur-Nubia-Antarctic, fail closure, with respective linear velocities of non-closure of 14 +/- 5 and 3 +/- 1mmyr-1 (95 per cent confidence limits) at their triple junctions. We conclude that the rigid plate approximation continues to be tremendously useful, but-absent any unrecognized systematic errors-the plates deform measurably, possibly by thermal contraction and wide plate boundaries with deformation rates near or beneath the level of noise in plate kinematic data.

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

2010-04-01

157

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

Microsoft Academic Search

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

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

2008-01-01

158

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

159

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

NASA Astrophysics Data System (ADS)

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

Fucugauchi, J. U.

2008-05-01

160

Magmatic switch-on and switch-off along the South China continental margin since the Permian: Transition from an Andean-type to a Western Pacific-type plate boundary  

NASA Astrophysics Data System (ADS)

Detrital zircon provenance data for the Tananao schist in eastern Taiwan is consistent with its protolith being deposited on the South China continental margin at around, or soon after, 150 Ma, rather than being of an exotic origin and much older as previously suggested. The absence of ca. 200 Ma zircons agrees with the presence of a magmatic gap in the region after the orogenic and magmatic front migrated to central South China, due to a flat-slab subduction. The characteristic lack of input from interior South China (i.e., the lack of 1100-750 Ma and 470-420 Ma populations), and the immature nature of some of the schist units, suggest that they were sourced from the nearby coastal regions. On the other hand, they exhibit a dominant 190-150 Ma magmatic zircon population, suggesting the presence of abundant magmatic rocks of that age along the coastal regions. This, along with our newly discovered ca. 180 Ma I-type granites from eastern Zhejiang and other ca. 190-180 Ma magmatic rocks recently reported from the coastal regions, led us to propose that a new continental arc was initiated after ca. 190 Ma along the coastal region after a magmatic gap due to flat-slab subduction. This newly initiated arc likely persisted until ca. 90 Ma, and is represented by the I-type granitic rocks in eastern Taiwan. Slab roll-back likely caused the arc system to retreat towards the Pacific Ocean after 90 Ma, and ca. 60-17 Ma bimodal magmatism adjacent to the South China Sea signifies continental margin extension in the lead-up to, and during, the opening of the South China Sea. We thus argue that the continental margin of East Asia was transformed from an Andean-type plate margin at 280-90 Ma, to the present-day Western Pacific-type plate margin soon after 90 Ma.

Li, Zheng-Xiang; Li, Xian-Hua; Chung, Sun-Lin; Lo, Ching-Hua; Xu, Xisheng; Li, Wu-Xian

2012-04-01

161

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

162

Cooling history of the Pacific lithosphere  

Microsoft Academic Search

Plate tectonics is expressed most simply in oceanic plates where a thermal boundary layer or blithosphereQ forms and thickens as the plate cools during its journey away from mid-ocean ridges. Numerous studies based dominantly on surface observables have established that the oceanic lithosphere, particularly across the Pacific, does not cool continuously as it ages. Based on a seismic model of

Michael H. Ritzwoller; Nikolai M. Shapiro; Shi-Jie Zhong

2004-01-01

163

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

164

Seismicity near the slip maximum of the 1960 Mw 9.5 Valdivia earthquake (Chile): Plate interface lock and reactivation of the subducted Valdivia Fracture Zone  

NASA Astrophysics Data System (ADS)

Understanding the processes behind subduction-related hazards is an important responsibility and major challenge for the Earth sciences. Few areas demonstrate this as clearly as south-central Chile, where some of the largest earthquakes in human history have occurred. We present the first observation of local seismicity in the Villarrica region (39°-40°S), based on a temporary local network of 55 stations installed from the Chilean coast into the Argentinian back-arc for one year. While consistent with the Chilean national catalog (SSN), our results allow us to observe smaller magnitudes with a completeness of about 2.0 and image the geometry of the Wadati-Benioff Zone from the Chile Trench down to 200 km. Offshore, a gap in interplate seismicity is observed in the region of the 1960 Valdivia earthquake slip. Above the interface, two offshore seismicity clusters possibly indicate ongoing stress relaxation. In the subducting Nazca Plate, we find a prominent seismicity cluster along the extrapolated trace of the oceanic Valdivia Fracture Zone (VFZ). The seismicity cluster is observed between 70 and 130 km depth and comprises mainly strike-slip events. It indicates weakening and reactivation of the major VFZ by dehydration of oceanic crust and mantle. Interpreting the subducted VFZ section as a localized reservoir of potential fluid release offers an explanation for the Villarrica volcanic complex that is located above the reactivated VFZ and shows the highest volcanic activity in South America. Crustal seismicity is observed near Puyehue volcano, which recently started to erupt (June 2011).

Dzierma, Yvonne; Thorwart, Martin; Rabbel, Wolfgang; Siegmund, Claudia; Comte, Diana; Bataille, Klaus; Iglesia, Paula; Prezzi, Claudia

2012-06-01

165

Plate Tectonics: Plates  

NSDL National Science Digital Library

This Science Object is the second of five Science Objects in the Plate Tectonics SciPack. It provides a conceptual understanding of what plates are and how they move, contributing to a constantly changing surface. The Earth's continents and ocean basins are made up of plates consisting of the crust and the upper part of the mantle. One plate can consist of both continental and oceanic crust. These plates move very slowly (an inch or so per year) on the hot, deformable layer of the mantle beneath them. The outward transfer of Earth's internal heat drives convection circulation in the mantle. This convection, together with gravitational pull on the plates themselves, causes the plates to move. Learning Outcomes:� 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.

National Science Teachers Association (NSTA)

2006-11-01

166

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.

167

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

NASA Astrophysics Data System (ADS)

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

Andolina, Vincent L.

168

Crustal Recycling by Surface Processes Along the Pacific-North America Plate Boundary: From the Colorado Plateau to the Salton Trough and Gulf of California  

NASA Astrophysics Data System (ADS)

Delivery of sediment from the Colorado Plateau to basins in the Salton Trough and northern Gulf of California exerts an incompletely understood control on structure, magmatism, rheology, and rift evolution. This study examines the volumetric rate at which crust of the continent interior is moved as sediment and converted into new crust in deep sedimentary basins along the active oblique-divergent plate boundary. The modern Colorado River was integrated by a series of lake spillover events that propagated from Lake Mead to the Salton Trough between 6.0 and 5.3 Ma (Spencer et al., 2001, 2008; House et al., 2005; Dorsey et al., 2007). Thus all transfer of sediment from the Colorado Plateau to the Salton Trough and northern Gulf post-dates 5.3 Ma. The volume of Colorado River sediment in subsurface basins of the Salton Trough and northern Gulf of California is estimated using published geophysical and borehole data, and two end-member crustal models. In the first model, pre-existing granitic crust has been fully ruptured by oblique rifting, and new crust is being formed by input of sediment from above mixed with mafic intrusions from below (Fuis et al., 1984). In the second model, the middle and lower crust consists of thinned granitic rock that has undergone large-scale crustal flow (Gonzalez et al., 2005). Using the two crustal models for basin depth, and measured basin areas, the total volume of Colorado River sediment in subsurface basins is bracketed between 198,000 and 291,000 km3. The volume of rock eroded from the Colorado Plateau can be approximated by multiplying the pre-dam sediment discharge (1.2-1.5 x 108 t/yr; Meade and Parker, 1985) by the total lifetime of sediment output (5.3 m.y.) and converting mass to volume by bracketing average sediment density between 2300 and 2500 kg/m3. This yields an equivalent sediment volume of 200,000-270,000 km3 that would have been delivered to the plate boundary at early-1900's discharge rates. Thus, despite current uncertainties, the volume of sediment stored in sedimentary basins along the Gulf-Trough corridor is comparable to the volume of rock that likely was eroded from the Colorado Plateau in the past 5-6 m.y. Using the equivalent rock volume, age, and along-strike extent of these basins, the rate of crustal addition by sediment input is roughly 75-110 km3 per km strike length along the plate boundary per m.y. This is similar to rates of crustal growth by magmatic accretion at subduction-related island arcs and slow mid-ocean spreading centers. Miocene tectonic collapse of the Cordilleran orogen, followed by intensification of monsoonal flow to the Colorado Plateau at ca. 6 Ma, resulted in delayed re-routing of the Colorado River and subsequent rapid funneling of sediment into lowland basins along the plate boundary (Chapin, 2008). This catchment-to-basin conveyer belt operates at scales and volumetric rates comparable to igneous processes of crustal formation and recycling. Similar catchment systems may be expected to form in other settings where potential energy resulting from collapse of an orogenic highland combines with climate forcing related to induced changes in ocean circulation to erode and transfer crust from a stable continental interior to an active plate boundary.

Dorsey, R. J.

2009-12-01

169

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

170

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

171

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

172

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.

173

Evaluation of soft tissue reactions at the interface of titanium limited contact dynamic compression plate implants with different surface treatments: an experimental sheep study.  

PubMed

Five types of limited contact dynamic compression plates (LC-DCPs) of pure titanium with different surface treatments and an electropolished stainless steel LC-DCP were tested. The surface roughness parameters and chemical surface conditions were determined and checked for probable surface contamination. After an implantation period of 3 months on long bones of sheep, the soft tissue adjacent to the plates was evaluated histomorphometrically. The difference in roughness parameters was statistically significant for most surface conditions. A correlation was found between the surface roughness of the implants and the thickness of the adjacent soft tissue layer. The thinnest soft tissue reaction layer with a good adhesion to the implant surface was observed for the titanium anodized plates with coarse surface. Smooth implants, in particular the electropolished stainless steel plates, induced statistically significant thicker soft tissue layers. Profilometer roughness measurements combined with scanning electron microscopy techniques were useful methods to characterize the surface morphology. PMID:8730964

Ungersböck, A; Pohler, O E; Perren, S M

1996-04-01

174

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

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

175

Interface Board Connector.  

National Technical Information Service (NTIS)

This patent application discloses an interface board connector that includes a plurality of individual conductive partition element seats. Each partition element seat includes four spring fingers that extend into apertures in a dielectric base plate of th...

D. H. Steinbrecher

2011-01-01

176

Slip partitioning along major convergent plate boundaries  

Microsoft Academic Search

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

Guang Yu; Steven G. Wesnousky; Göran Ekström

1993-01-01

177

Seismic Anisotropy beneath Pacific Ocean Lithosphere Subducted at Kamchatka  

Microsoft Academic Search

We present new measurements of source-side shear-wave splitting from the Kamchatka portion of the Pacific plate subduction zone. The study region includes the abrupt lateral termination of subducted Pacific lithosphere at the Bering fault, termed the slab edge. Source-side splitting results from shear-waves emanating from slab earthquakes crossing an anisotropic upper-mantle region lying strictly beneath the subducting Pacific plate. Observations

R. M. Russo; J. M. Lees

2005-01-01

178

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

179

Influence of the glass-fiber/matrix interface quality on the monoaxial and biaxial mechanical behavior of composite plates and tubes  

NASA Astrophysics Data System (ADS)

The behavior of composite samples differing in interface quality was investigated under the following types of loading: monoaxial tension with monitoring of acoustic emission spectra; interlaminar shear; crack initiation and crack growth in mode I; viscoelasticity in bending; and biaxial monotonic tension and cylic loading with increasing amplitude and dynamic fatigue. In general, the results demonstrate a strong influence of the fiber/matrix interface on the mechanical behavior of the composites.

Krawczak, Patricia; Pabiot, Jose

180

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

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

181

An Analysis of the Relaxation of Laminar Boundary Layer on a Flat Plate after Passage of an Interface with Application to Expansion-Tube Flows.  

National Technical Information Service (NTIS)

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 ...

R. N. Gupta

1972-01-01

182

High-resolution animated tectonic reconstruction of the South Pacific and West Antarctic Margin  

Microsoft Academic Search

An animated reconstruction shows South Pacific plate kinematics between 90 and 45 Ma, using the satellite-derived gravity anomaly field, interpolated isochrons and plate rotation parameters from both published and new work on marine geophysical data. The Great South Basin and Bounty Trough, New Zealand, are shown as the earliest Pacific–Antarctic plate boundary that opened before 83 Ma. The earliest true

Graeme Eagles; Karsten Gohl; Robert D. Larter

2004-01-01

183

Plate tectonics conserves angular momentum  

NASA Astrophysics Data System (ADS)

A new combined understanding of plate tectonics, Earth internal structure, and the role of impulse in deformation of the Earth's crust is presented. Plate accelerations and decelerations have been revealed by iterative filtering of the quaternion history for the Euler poles that define absolute plate motion history for the past 68 million years, and provide an unprecedented precision for plate angular rotation variations with time at 2-million year intervals. Stage poles represent the angular rotation of a plate's motion between adjacent Euler poles, and from which the maximum velocity vector for a plate can be determined. The consistent maximum velocity variations, in turn, yield consistent estimates of plate accelerations and decelerations. The fact that the Pacific plate was shown to accelerate and decelerate, implied that conservation of plate tectonic angular momentum must be globally conserved, and that is confirmed by the results shown here (total angular momentum ~1.4 E+27 kgm2s-1). Accordingly, if a plate decelerates, other plates must increase their angular momentums to compensate. In addition, the azimuth of the maximum velocity vectors yields clues as to why the "bend" in the Emperor-Hawaiian seamount trend occurred near 46 Myr. This report summarizes processing results for 12 of the 14 major tectonic plates of the Earth (except for the Juan de Fuca and Philippine plates). Plate accelerations support the contention that plate tectonics is a product of torques that most likely are sustained by the sinking of positive density anomalies due to phase changes in subducted gabbroic lithosphere at depth in the upper lower mantle (above 1200 km depth). The tectonic plates are pulled along by the sinking of these positive mass anomalies, rather than moving at near constant velocity on the crests of convection cells driven by rising heat. These results imply that spreading centers are primarily passive reactive features, and fracture zones (and wedge-shaped sites of seafloor spreading) are adjustment zones that accommodate strains in the lithosphere. Further, the interlocked pattern of the Australian and Pacific plates the past 42 Million years (with their absolute plate motions near 90° to each other) is taken as strong evidence that large thermally driven "roller" convection cells previously inferred as the driving mechanism in earlier interpretations of continental drift and plate tectonics, have not been active in the Earth's mantle the past 42 Million years, if ever. This report also presents estimates of the changes in location and magnitude of the Earth's axis of total plate tectonic angular momentum for the past 62 million years.

Bowin, C.

2009-03-01

184

Study Program for Encapsulation Materials Interface for Flat-Plate Solar Array (FSA) Project. Final Report, March 23, 1977-January 31, 1984.  

National Technical Information Service (NTIS)

The early validation of a 20 year service integrity for the bonded interface in solar cell modules is an important requirement in the Low Cost Solar Array (LSA) project. The sixth and final phase of the program, as reported in this document, generates and...

D. H. Kaelble C. L. Leung

1984-01-01

185

Plate motion controls on back-arc spreading  

NASA Astrophysics Data System (ADS)

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

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

1986-05-01

186

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

187

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

188

Plating on stainless steel alloys  

SciTech Connect

Quantitative adhesion data are presented for a variety of electroplated stainless steel type alloys. Results show that excellent adhesion can be obtained by using a Wood's nickel strike or a sulfamate nickel strike prior to final plating. Specimens plated after Wood's nickel striking failed in the deposit rather than at the interface between the substrate and the coating. Flyer plate quantitative tests showed that use of anodic treatment in sulfuric acid prior to Wood's nickel striking even further improved adhesion. In contrast activation of stainless steels by immersion or cathodic treatment in hydrochloric acid resulted in very reduced bond strengths with failure always occurring at the interface between the coating and substrate.

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

1981-09-11

189

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

Microsoft Academic Search

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

G. P. Hayes; K. P. Furlong

2007-01-01

190

Real Plates and Dubious Microplates  

NASA Astrophysics Data System (ADS)

From the onset of plate tectonics, the existence of most of the plates was never put in doubt, although the boundaries of some plates, like Africa, were later revised. There are however, two microplates in northeast Asia, the Amurian and Okhotsk, whose existence and the sense of rotation was revised several times. The rms value of plate-residual GPS velocities is 0.5-0.9 mm/a for sets of stations representing the motion of the following plates: Antarctic, Australian, Eurasian, North American, Nubian, Pacific, and South American. This value can be regarded as an upper bound on deviation of real plates from infinite stiffness. The rms value of plate-residual GPS velocities is 1.2-1.8 mm/a for the Indian, Nazca, and Somalian plates. Higher rms values for India and Nazca are attributed to the noisier data. The higher rms value for Somalia appears to arise from the distributed deformation to the east of the East African Rift; whether this statement is true can only be decided from observations of denser network in the future. From the analysis of plate-residual GPS velocities, the Canadian Arctic and northeastern Siberia belong to the North American plate. The detailed GPS survey on Sakhalin Island shows that the Sea of Okhotsk region also belongs to the North American plate while the region to the west of it belongs to the Eurasian plate. These results provide a constraint on the geometry of the North American plate and put in doubt the existence of smaller plates in northeast Asia.

Kogan, M. G.; Steblov, G. M.

2008-12-01

191

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.

192

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

193

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

Microsoft Academic Search

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

Charles Demets; Seth Stein

1990-01-01

194

The Pacific lithosphere-asthenosphere boundary: Seismic imaging and anisotropic constraints from SS waveforms  

NASA Astrophysics Data System (ADS)

The lithosphere-asthenosphere boundary (LAB) separating the rigid lid from the underlying weaker, convecting asthenosphere is a fundamental interface in mantle dynamics and plate tectonics. However, the exact depth and defining mechanism of the LAB interface remain poorly understood. The ocean plates are ideal for testing hypotheses regarding the nature of a plate since they make up 70% of Earth's surface area and have a relatively simple geological history. Seismically imaging the oceanic LAB at high resolution has proved challenging. Yet, several studies have recently increased resolution with provocative results. We summarize recent imaging of discontinuity structure beneath much of the Pacific using receiver functions from ocean floor borehole seismometers and land stations located at ocean-continent margins, SS precursors, and waveform modeling of multiple phases including multiple bounce S waves, ScS reverberations, and surface waves. Overall, there is much agreement among these different approaches about the reported depth of a negative discontinuity that occurs near the expected depth of the LAB. Some of the apparent discrepancies in depth are explained by the variation in sensitivity of seismic waves that sample structure at different wavelengths. Yet, when the results are considered together, no single age-depth relationship is illuminated. There are also puzzling discrepancies in where the discontinuity is detected, which again suggests greater complexity. Here we test the possibility that discrepant detection of a strong sharp discontinuity is caused by anisotropic structure. We stack SS waveforms with bounce points in the central Pacific into azimuthal bins. We use two methods, one that inverts for discontinuity structure based on subtle variations in the character of the SS waveform, and another that considers SS at higher frequency. We find azimuthal variation in the amplitude of the waveform, including a polarity reversal. We suggest that anisotropy is an important factor in imaging and constraining discontinuity structure of the oceanic plate, and must be carefully considered to constrain the age-depth dependence and defining mechanism of the oceanic lithosphere.

Rychert, Catherine A.; Schmerr, Nicholas; Harmon, Nicholas

2012-09-01

195

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.

196

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

197

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

198

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

199

Vibroacoustical behaviour of multilayered heterogeneous plates with elastic support and interface condition: Application to the case of the double-deck French high- speed train  

NASA Astrophysics Data System (ADS)

Mass Transit has to meet specifications of increasing difficulty which put in the forefront areas which were before considered as secondary. In particular, passengers acoustic comfort has become a major criterion, reflecting the requirements for quality transportation. The present work has its origin in this specific context and more specially in the intention of FAIVELEY TRANSPORT, a Railway equipment supplier, to improve the acoustic behaviour of its products. The aim of this study is the comprehension of the physical phenomena of the noise transmission through the doors of the transport vehicles, from outside to inside. The Railway access doors are the main application of this work. The considered frequency range is low frequencies below 500 Hz. The final objective is to notably reduce the transmitted noise in order to improve the passengers' acoustic comfort inside the transport vehicles. To do this, we developed a model based on an analytical integro-modal approach, associated with a Rayleigh-Ritz approximation. The original aspect of this work is to develop a model of a vibrating structure which take into account its multilayered and heterogeneous aspects and its complex boundary and interface conditions (linear and punctual elastic stiffness). This model is the basis of a specific software for preliminary design studies (VANTAIL) which is able to indicate, with a parametric study, the contribution of each different part of the doors to the global vibroacoustic behaviour. An experimental study on an industrial structure (the access door of the double deck French high speed train) permits us to validate the developed software, to define its limits and to validate the proposed vibroacoustic treatments.

Chabaud, Thierry Rene

1998-10-01

200

Economics Planning of Super Tall Buildings in Asia Pacific Cities  

Microsoft Academic Search

SUMMARY The purpose of this paper is to study the economics planning of super tall office buildings in Asia Pacific cities. This study is based on the case study of the Asia Pacific's 10 tallest buildings which are distributed over six major cities. All are landmark buildings with similar functions. From the analysis of the collected data, the floor plate

Paul H K HO

201

Plate subrotations  

NASA Astrophysics Data System (ADS)

The kinematics of plates is defined by Euler pole and angular velocity. However, during their journey, plates may be affected by additional simultaneous rotations (i.e., subrotations) while they are rotating about their Euler poles. The kinematic description of this particular plate motion requires a different analytical approach: two angular velocities and two poles are necessary to completely describe plate displacements. If a subrotation occurs, none of the points on a plate moves along circles of the Euler pole but, instead, follows cycloid trajectories because of the combination of the two simultaneous rotations. Regardless of the forces that move the lithosphere, every time a plate experiences a subrotation, an additional force (or resisting) force could act on the plate, generating the two-rotation motion. In the hot spot reference frame, we applied this model to the North America plate, investigating its past motion for a time interval ?t = 43 Ma up to the present and comparing results with those obtained by Gordon and Jurdy (1986). This application shows how the different positions of the North America plate over most of the Cenozoic can be reconstructed by two-rotation plate kinematics.

Cuffaro, Marco; Caputo, Michele; Doglioni, Carlo

2008-08-01

202

Plate tectonics conserves angular momentum  

NASA Astrophysics Data System (ADS)

A new combined understanding of plate tectonics, Earth internal structure, and the role of impulse in deformation of the Earth's crust is presented. Plate accelerations and decelerations have been revealed by iterative filtering of the quaternion history for the Euler poles that define absolute plate motion history for the past 68 million years, and provide an unprecedented precision for plate angular rotation variations with time at 2-million year intervals. Stage poles represent the angular rotation of a plate's motion between adjacent Euler poles, and from which the maximum velocity vector for a plate can be determined. The consistent maximum velocity variations, in turn, yield consistent estimates of plate accelerations and decelerations. The fact that the Pacific plate was shown to accelerate and decelerate, implied that conservation of plate tectonic angular momentum must be globally conserved, and that is confirmed by the results shown here (total angular momentum ~1.4+27 kg m2 s-1). Accordingly, if a plate decelerates, other plates must increase their angular momentums to compensate. In addition, the azimuth of the maximum velocity vectors yields clues as to why the "bend" in the Emperor-Hawaiian seamount trend occurred near 46 Myr. This report summarizes processing results for 12 of the 14 major tectonic plates of the Earth (except for the Juan de Fuca and Philippine plates). Plate accelerations support the contention that plate tectonics is a product of torques that most likely are sustained by the sinking of positive density anomalies revealed by geoid anomalies of the degree 4-10 packet of the Earth's spherical harmonic coefficients. These linear positive geoid anomalies underlie plate subduction zones and are presumed due to phase changes in subducted gabbroic lithosphere at depth in the upper lower mantle (above 1200 km depth). The tectonic plates are pulled along by the sinking of these positive mass anomalies, rather than moving at near constant velocity on the crests of convection cells driven by rising heat. The magnitude of these sinking mass anomalies is inferred also to be sufficient to overcome basal plate and transform fault frictions. These results imply that spreading centers are primarily passive reactive features, and fracture zones (and wedge-shaped sites of seafloor spreading) are adjustment zones that accommodate strains in the lithosphere. Further, the interlocked pattern of the Australian and Pacific plates the past 42 Million years (with their absolute plate motions near 90° to each other) is taken as strong evidence that large thermally driven "roller" convection cells previously inferred as the driving mechanism in earlier interpretations of continental drift and plate tectonics, have not been active in the Earth's mantle the past 42 Million years, if ever. This report also presents estimates of the changes in location and magnitude of the Earth's axis of total plate tectonic angular momentum for the past 62 million years.

Bowin, C.

2010-03-01

203

An expression of Philippine Sea plate rotation: the Parece Vela and Shikoku Basins  

Microsoft Academic Search

The Philippine Sea plate, located between the Pacific, Eurasian and Australian plates, is the world's largest marginal basin plate. The motion of the Philippine Sea plate through time is poorly understood as it is almost entirely surrounded by subduction zones and hence, previous studies have relied on palaeomagnetic analysis to constrain its rotation. We present a comprehensive analysis of geophysical

Maria Sdrolias; Walter R. Roest; R. Dietmar Mqllera

204

Plate Tectonics  

NSDL National Science Digital Library

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

Heaton, Timothy

205

SAMI Automated Plug Plate Configuration  

NASA Astrophysics Data System (ADS)

The Sydney-AAO Multi-object Integral field spectrograph (SAMI) is a prototype wide-field system at the Anglo-Australian Telescope (AAT) which uses a plug-plate to mount its 13×61-core imaging fibre bundles (hexabundles) in the optical path at the telescope's prime focus. In this paper we describe the process of determining the positions of the plug-plate holes, where plates contain three or more stacked observation configurations. The process, which up until now has involved several separate processes and has required significant manual configuration and checking, is now being automated to increase efficiency and reduce error. This is carried out by means of a thin Java controller layer which drives the configuration cycle. This layer controls the user interface and the C++ algorithm layer where the plate configuration and optimisation is carried out. Additionally, through the Aladin display package, it provides visualisation and facilitates user verification of the resulting plates.

Lorente, N. P. F.; Farrell, T.; Goodwin, M.

2013-10-01

206

The Plate Boundary Observatory: Community Focused Web Services  

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

207

Plate Tectonics, The Cause of Earthquakes  

NSDL National Science Digital Library

This page provides an overview of the role of plate tectonics in the generation of earthquakes. It provides a map of plate locations and figures that illustrate fault types and tectonic environments (extensional, transform, and compressional). Examples of surface features in the Pacific Northwest, Nevada, Indonesia, the San Andreas Fault, the Red Sea, the Zagoros Mountains in Iran, and on the planet Venus are provided.

Louie, John

208

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

209

Plate Tectonics  

NSDL National Science Digital Library

Plate tectonic activity is being observed presently on a historic timescale, especially in the form of volcanic eruptions and earthquakes, but, as with many large-scale Earth science phenomena, it is hard to ...

210

Safeguards training at Pacific Northwest Laboratory  

Microsoft Academic Search

In recent years considerable attention has been given to upgrading security education programs at facilities across the country. At Pacific Northwest Laboratory (PNL), a Laboratory-wide Safeguard Awareness Training Program has been established in order to raise the cognizance of the entire staff with regard to safeguards issues and concerns. This aggressive safeguards program involves a strong interface of physical security

Dickman

1988-01-01

211

Tectonic map of the Circum-Pacific region, Pacific basin sheet  

USGS Publications Warehouse

Circum-Pacific Map Project: The Circum-Pacific Map Project was a cooperative international effort designed to show the relationship of known energy and mineral resources to the major geologic features of the Pacific basin and surrounding continental areas. Available geologic, mineral, and energy-resource data are being complemented by new, project-developed data sets such as magnetic lineations, seafloor mineral deposits, and seafloor sediment. Earth scientists representing some 180 organizations from more than 40 Pacific-region countries are involved in this work. Six overlapping equal-area regional maps at a scale of 1:10,000,000 form the cartographic base for the project: the four Circum-Pacific Quadrants (Northwest, Southwest, Southeast, and Northeast), and the Antarctic and Arctic Sheets. There is also a Pacific Basin Sheet at a scale of 1:17,000,000. The Base Map Series and the Geographic Series (published from 1977 to 1990), the Plate-Tectonic Series (published in 1981 and 1982), the Geodynamic Series (published in 1984 and 1985), and the Geologic Series (published from 1984 to 1989) all include six map sheets. Other thematic map series in preparation include Mineral-Resources, Energy-Resources and Tectonic Maps. Altogether, more than 50 map sheets are planned. The maps were prepared cooperatively by the Circum-Pacific Council for Energy and Mineral Resources and the U.S. Geological Survey and are available from the Branch of Distribution, U. S. Geological Survey, Box 25286, Federal Center, Denver, Colorado 80225, U.S.A. The Circum-Pacific Map Project is organized under six panels of geoscientists representing national earth-science organizations, universities, and natural-resource companies. The six panels correspond to the basic map areas. Current panel chairmen are Tomoyuki Moritani (Northwest Quadrant), R. Wally Johnson (Southwest Quadrant), Ian W.D. Dalziel (Antarctic Region), vacant. (Southeast Quadrant), Kenneth J. Drummond (Northeast Quadrant), and George W. Moore (Arctic Region). Project coordination and final cartography was being carried out through the cooperation of the Office of the Chief Geologist of the U.S. Geological Survey, under the direction of General Chairman, George Gryc of Menlo Park, California. Project headquarters were located at 345 Middlefield Road, MS 952, Menlo Park, California 94025, U.S.A. The framework for the Circum-Pacific Map Project was developed in 1973 by a specially convened group of 12 North American geoscientists meeting in California. The project was officially launched at the First Circum-Pacific Conference on Energy and Mineral Resources, which met in Honolulu, Hawaii, in August 1974. Sponsors of the conference were the AAPG, Pacific Science Association (PSA), and the Coordinating Committee for Offshore Prospecting for Mineral Resources in Offshore Asian Areas (CCOP). The Circum-Pacific Map Project operates as an activity of the Circum-Pacific Council for Energy and Mineral Resources, a nonprofit organization that promotes cooperation among Circum-Pacific countries in the study of energy and mineral resources of the Pacific basin. Founded by Michel T. Halbouty in 1972, the Council also sponsors conferences, topical symposia, workshops and the Earth Science Series books. Tectonic Map Series: The tectonic maps distinguish areas of oceanic and continental crust. Symbols in red mark active plate boundaries, and colored patterns show tectonic units (volcanic or magmatic arcs, arc-trench gaps, and interarc basins) associated with active plate margins. Well-documented inactive plate boundaries are shown by symbols in black. The tectonic development of oceanic crust is shown by episodes of seafloor spreading. These correlate with the rift and drift sequences at passive continental margins and episodes of tectonic activity at active plate margins. The recognized episodes of seafloor spreading seem to reflect major changes in plate kinematics. Oceanic plateaus and other prominences of greater than normal oceanic crustal thickness such as hotspot traces are also shown. Colored a

Scheibner, E.; Moore, G.W.; Drummond, K.J.; Dalziel, Corvalan, Q.J.; Moritani, T.; Teraoka, Y.; Sato, T.; Craddock, C.

2013-01-01

212

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

213

Aqueous Solutions and their Interfaces  

SciTech Connect

Preface of the special issue of the Journal of Physical Chemistry in conjunction with the international workshop "Aqueous Solutions and their Interfaces". The topics include the structure of liquid water, the analysis of X-ray and neutron scattering experimental data, the vibrational spectroscopy of liquid water, the structure and spectroscopy of aqueous interfaces and the development of theoretical approaches to model the structure and spectra of liquid water and interfaces. This work was supported by the US Department of Energy's Office of Basic Energy Sciences, Chemical Sciences program. Pacific Northwest National Laboratory is operated by Battelle for DOE.

Xantheas, Sotiris S.; Voth, Gregory A.

2009-04-02

214

Plate tectonics and the Gulf of California region  

Microsoft Academic Search

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

N. Schmidt

1990-01-01

215

Evolution of subducted slab morphology in the Western Pacific based on seismic tomography and paleogeographic reconstructions  

NASA Astrophysics Data System (ADS)

Plate motions and subducting slab morphology are intricately connected. Through the integration of seismicity, tomographic images, and relative plate motions the evolution of mantle structure can be interpreted. Tomographic images of P-wave, shear wave-speed, and bulk sound speed perturbations of the Northwest Pacific region have been interpreted to define the extent and geometry of the subducting Pacific plate in the upper mantle. The morphology of the subducted Pacific plate along the Kurile-Japan-Izu-Bonin-Mariana arc system was found to vary both in geometry and dip along the entire length of the margin. To understand these differences and evolution to the current slab morphology a tectonic reconstruction for the Western Pacific was created, which describes the geologic history of the past 20 million years. The paleogeographic reconstruction illustrates the collision of the Japan and Kurile arcs, the opening of the Kurile Basin and Sea of Japan, change in motion of the Izu-Bonin arc, developing curvature of the Mariana arc, disparity in Pacific plate velocities along the convergent margin, and variation in rates of trench retreat along different segments of the arc system. The new plate motion model and interpretations of the physical properties of the mantle imaged with the P-wave and joint tomography are tools to assess the spatial and temporal evolution of the Pacific plate morphology from the mid-Miocene to the present and provide limitations in plausible plate motions for the region.

Miller, M. S.

2007-12-01

216

Sharp Lithosphere-asthenosphere Boundaries of Oceanic Plates  

Microsoft Academic Search

P- and S-receiver function (RF) analysis of borehole broadband ocean bottom seismic data (Kumar et al., 2008, this meeting) and the high-resolution RF image of the subducting Pacific plate beneath the northeast Japan (Kawakatsu, 2008, this meeting) both show the presence of sharp lithosphere-asthenosphere boundaries (LABs) of oceanic plates which appear to show dependence on the plate age. The apparent

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

2008-01-01

217

Vibration Analysis of Plates by MLS-Element Method  

Microsoft Academic Search

This paper presents a novel numerical method, the moving least square element (MLS-element) method for the free vibration analysis of plates based on the Mindlin shear deformable plate theory. In the MLS-element method, a plate can be first divided into multiple elements which are connected through selected nodal points on the interfaces of the elements. An element can be of

L. Zhou; Y. Xiang

2010-01-01

218

Volcanism in response to plate flexure.  

PubMed

Volcanism on Earth is known to occur in three tectonic settings: divergent plate boundaries (such as mid-ocean ridges), convergent plate boundaries (such as island arcs), and hot spots. We report volcanism on the 135 million-year-old Pacific Plate not belonging to any of these categories. Small alkalic volcanoes form from small percent melts and originate in the asthenosphere, as implied by their trace element geochemistry and noble gas isotopic compositions. We propose that these small volcanoes erupt along lithospheric fractures in response to plate flexure during subduction. Minor extents of asthenospheric melting and the volcanoes' tectonic alignment and age progression in the direction opposite to that of plate motion provide evidence for the presence of a small percent melt in the asthenosphere. PMID:16873612

Hirano, Naoto; Takahashi, Eiichi; Yamamoto, Junji; Abe, Natsue; Ingle, Stephanie P; Kaneoka, Ichiro; Hirata, Takafumi; Kimura, Jun-Ichi; Ishii, Teruaki; Ogawa, Yujiro; Machida, Shiki; Suyehiro, Kiyoshi

2006-07-27

219

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

220

Environmental materials and interfaces  

SciTech Connect

A workshop that explored materials and interfaces research needs relevant to national environmental concerns was conducted at Pacific Northwest Laboratory. The purposes of the workshop were to refine the scientific research directions being planned for the Materials and Interface Program in the Molecular Science Research Center (MSRC) and further define the research and user equipment to the included as part of the proposed Environmental and Molecular Science Laboratory (EMSL). Three plenary information sessions served to outline the background, objectives, and status of the MSRC and EMSL initiatives; selected specific areas with environmentally related materials; and the status of capabilities and facilities planned for the EMSL. Attention was directed to four areas where materials and interface science can have a significant impact on prevention and remediation of environmental problems: in situ detection and characterization of hazardous wastes (sensors), minimization of hazardous waste (separation membranes, ion exchange materials, catalysts), waste containment (encapsulation and barrier materials), and fundamental understanding of contaminant transport mechanisms. During all other sessions, the participants were divided into three working groups for detailed discussion and the preparation of a written report. The working groups focused on the areas of interface structure and chemistry, materials and interface stability, and materials synthesis. These recommendations and suggestions for needed research will be useful for other researchers in proposing projects and for suggesting collaborative work with MSRC researchers. 1 fig.

Not Available

1991-11-01

221

Plate coupling in the northern South Island and southernmost North Island, New Zealand, as illuminated by earthquake focal mechanisms  

Microsoft Academic Search

Subduction of the Pacific plate in the northern South Island and southernmost North Island of New Zealand is transitional, insofar as the crustal thickness of the Pacific plate increases significantly along strike in the northern South Island. Focal mechanisms of 145 events shallower than 100 km in this region have been determined using both first motion polarity data and amplitudes

Martin Reyners; Russell Robinson; Peter McGinty

1997-01-01

222

A Forecaster's Overview of the Northwest Pacific  

NSDL National Science Digital Library

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

Byrd, Greg

2012-01-11

223

Low Seismic Anisotropy Channels below the Pacific Ocean and Geodynamic implications  

NASA Astrophysics Data System (ADS)

A new 3D anisotropic model has been obtained at a global scale by using a massive dataset of seismic surface waves. Though seismic heterogeneities are usually interpreted in terms of heterogeneous temperature field, a large part of lateral variations are also induced by seismic anisotropy of upper mantle minerals. New insight on convection processes can be gained by taking seismic anisotropy into account in the inversion procedure. The model is best resolved in the Pacific Plate, the largest and the most active tectonic plate. Superimposed on the large scale radial anisotropy within and below the lithosphere, correlated with present or past Pacific plate motions, are smaller scale (<1000km) lateral variations of radial and azimuthal anisotropy not predicted by plate tectonics. Channels of low anisotropy (hereafter referred as LAC) are observed and are the best resolved anomalies: One east-west channel between easter Island and the Tonga- Kermadec subduction zones and a second one extending from the south-west Pacific up to Hawaii, and passing through the Polynesia hotspot group of Polynesia for plate older than about 40 MA. These features are presumably related to secondary convection below the rigid lithosphere, predicted by numerical and tank experiments. The existence and location of these LACs are related to the current active plumes in Central Pacific. LACs, which are dividing the Pacific Plate into smaller units, associated with plumes might indicate a future reorganization of plates with ridge migrations in the Pacific Ocean.

MONTAGNER, J.

2001-12-01

224

Bone plate  

US Patent & Trademark Office Database

A bone plate assembly and method of use comprising a head; a shaft; an upper surface; a lower surface having a fixed plane intended to be adjacent to the patient's bone when the plate is in use; a first hole positioned in the head wherein the first hole passes through the upper and lower surfaces and is configured to fix a shaft of a first bone anchor along a first axis; a second hole positioned on the anterior portion of the upper surface of the head wherein the second hole passes through the upper and lower surfaces and is configured to fix a shaft of a second bone anchor along a second axis; and a third hole positioned in the posterior side of the head wherein the third hole passes through the upper and lower surfaces and is configured to fix a shaft of a third bone anchor along a third axis, wherein the first axis, the second axis and the third axis do not intersect in the bone when the plate is in use.

Gehlert; Rick J. (Albuquerque, NM)

2012-09-18

225

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

226

Tectonic Plates and Plate Boundaries  

NSDL National Science Digital Library

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

2011-05-09

227

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.

228

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

National Technical Information Service (NTIS)

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

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

2012-01-01

229

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

230

Photovoltaic-Array/Power-Conditioner Interface.  

National Technical Information Service (NTIS)

Two years' of effort to improve terrestrial flat-plate photovoltaic (PV) system efficiency through increased understanding of the array/power conditioner interface is reported. The flat-plate PV array is a highly variable source of dc electrical energy du...

H. M. Branz G. W. Hart C. H. Cox

1982-01-01

231

Major Australian-Antarctic plate reorganization at Hawaiian-Emperor bend time.  

PubMed

A marked bend in the Hawaiian-Emperor seamount chain supposedly resulted from a recent major reorganization of the plate-mantle system there 50 million years ago. Although alternative mantle-driven and plate-shifting hypotheses have been proposed, no contemporaneous circum-Pacific plate events have been identified. We report reconstructions for Australia and Antarctica that reveal a major plate reorganization between 50 and 53 million years ago. Revised Pacific Ocean sea-floor reconstructions suggest that subduction of the Pacific-Izanagi spreading ridge and subsequent Marianas/Tonga-Kermadec subduction initiation may have been the ultimate causes of these events. Thus, these plate reconstructions solve long-standing continental fit problems and improve constraints on the motion between East and West Antarctica and global plate circuit closure. PMID:17916729

Whittaker, J M; Müller, R D; Leitchenkov, G; Stagg, H; Sdrolias, M; Gaina, C; Goncharov, A

2007-10-01

232

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

Microsoft Academic Search

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

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

2006-01-01

233

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

National Technical Information Service (NTIS)

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

W. H. Lucas

1972-01-01

234

3-D simulation of temporal change in tectonic deformation pattern and evolution of the plate boundary around the Kanto Region of Japan due to the collision of the Izu-Bonin Arc  

Microsoft Academic Search

The Kanto region of Japan is in a highly complex tectonic setting with four plates interacting with each other: beneath Kanto, situated on the Eurasian and North American plates, the Philippine sea plate subducts and the Pacific plate further descends beneath the North American and Philippine sea plates, forming the unique trench-trench-trench triple junction on the earth. In addition, the

A. Hashima; T. Sato; T. Ito; T. Miyauchi; H. Furuya; N. Tsumura; K. Kameo; S. Yamamoto

2010-01-01

235

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

236

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

237

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

Microsoft Academic Search

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

Peter Lonsdale

1994-01-01

238

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

NASA Astrophysics Data System (ADS)

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

Meyer, C.; Schellart, W. P.

2013-02-01

239

Elevation of Ridges and Evolution of the Central Eastern Pacific  

Microsoft Academic Search

An empirical relationship between ridge elevation and age of the oceanic crust is presented for the Pacific, Atlantic, and Indian oceans. This relationship is accounted for by the thermal contraction of a cooling lithosphere as it moves away from a center of spreading, and thus is compatible with plate theory. Hence, it is possible to use topographic profiles to predict

John G. Sclater; Roger N. Anderson; M. Lee Bell

1971-01-01

240

Intermittent Plate Tectonics  

Microsoft Academic Search

Intermittent Plate Tectonics A basic premise of Earth Science is that plate tectonics has been continuously operating since it began early in Earth's history. Yet, plate-tectonic theory itself, specifically the collisional phase of the Wilson Cycle, constitutes a process that is capable of stopping all plate motion. The plausibility of a plate-tectonic hiatus is most easily illustrated by considering the

P. G. Silver; M. D. Behn

2006-01-01

241

Petrology and plate tectonics  

Microsoft Academic Search

Petrology played an important role in the formulation of plate tectonics and early plate tectonic interpretations of the geologic past. In the last few years widespread interest in plate tectonics and progress in plate tectonic interpretations have begun to give petrology various feedback effects.In the period 1971–1974 there were two symposiums intended particularly to connect petrology with plate tectonics [Wyllie,

Akiho Miyashiro

1975-01-01

242

Azimuthal anisotropy of the Pacific region  

NASA Astrophysics Data System (ADS)

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

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

2006-10-01

243

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

Microsoft Academic Search

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

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

2009-01-01

244

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

245

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

246

Seismicity Associated with a Stranded Plate Fragment Above the Juan de Fuca Slab in the Vicinity of the Mendocino Triple Junction  

NASA Astrophysics Data System (ADS)

Our new model of the subducted Juan de Fuca (JdF) plate beneath western North America, combined with the spatial resolution of double-differenced earthquake relocations, offers new insights regarding subsurface seismic sources in the complex tectonic setting near the Mendocino triple junction. Relocated seismicity resolves a double seismic zone within the slab beneath northwestern California that strongly constrains the location of the plate interface and delineates a cluster of seismicity ~10 km above the interface that includes the April 1992 M7.1 Cape Mendocino earthquake near its eastern edge. This cluster does not just represent aftershocks to the M7.1 event, but has persisted through time. About half of the earthquakes within the cluster occurred within the year following the April 1992 event. However, the remaining earthquakes either occurred within the 17 years preceding April 1992 or the 17 years following April 1993. The seismogenic structure forms a triangular shape approximately 80-km long in a north-south direction and up to 50-km long in a west-east direction. The structure is up to 8-km thick, and its surface dips gently landward from depths of ~6 to 14 km. Interpretation of the M7.1 event as occurring above the subduction interface requires a more complex slab geometry than previously envisioned. Specifically, the slab just east of the trench dips about 15° and then flattens to a dip of just a few degrees from ~15-25 km before it steepens again to about 25° from ~25-45 km, which is the maximum depth it can be imaged by hypocenters. The seismicity cluster is situated above the slab where it flexes concave upward in the transition from its initial moderate dip to a flat dip. Flat slab segments are observed elsewhere around the Pacific Rim where the subducting plate is relatively buoyant owing to young or thick oceanic crust, consistent with this JdF segment which is ~8-5 Ma where it enters the trench. These data provide compelling evidence that a significant fault with no surface expression exists in the forearc above the plate interface. We speculate that the seismicity cluster represents a detached fragment of oceanic plate that did not subduct and has been stranded within the accretionary prism, similar perhaps to the fragment of former Farallon plate found in the King Range not far to the south. Similar subsurface tectonic elements within the Cascadia forearc, such as remnants of the Resurrection plate, may also have the potential to generate damaging earthquakes-complicating our efforts to characterize earthquake hazards within the Cascadia subduction system.

McCrory, P. A.; Waldhauser, F.; Oppenheimer, D. H.; Blair, J. L.

2011-12-01

247

Pseudomorphic Interfaces.  

National Technical Information Service (NTIS)

The objectives of this work were to develop the epitaxial growth of ZnSe on epitaxially grown GaAs, fully characterize this interface electrically, and fabricate a depletion mode field effect transistor which incorporates this interface in the device stru...

J. A. Cooper L. A. Kolodziejski M. R. Melloch R. F. Pierret R. L. Gunshor

1988-01-01

248

Data Access and Web Services at the EarthScope Plate Boundary Observatory  

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

249

Modeling the mechanisms for the 100 Ma plate reorganisation  

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

250

Marginal deformation of crustal plates as key to crustal motion, crustal spirals, and the driving force  

SciTech Connect

Present plate tectonic models concentrate on compressive- and extensive-type plate margins, often incorporating shear margins as a subtype of compressive margins. However, if a single moving plate is considered, it becomes apparent that the leading edge is a compressive margin, the trailing edge is an extensive margin, and the lateral edges are shear margins. Conversely, if a plate's margin can be recognized by identifying areas of subduction (compression), rifting (extension), and strike slip and buckle folding (shearing), then not only can a plate be identified but its motion can also be inferred. The Pacific plate provides an excellent example. It is bounded by subduction trenches along its west-northwest margin, extension rifts along its east-southeast margin, and shear and buckle-fold complexes along its south-southwest and north-northeast margins. A west-northwest motion is inferred. As other major plates are examined, two striking features are revealed. A west-northwest to northwest motion is consistently identified, and the plates line up end to end forming a northwest-spiraling segmented band encircling the globe. The lateral margins of this band form the well-known Tethyan shear system. The plates comprising this band are of varying sizes and composition, and the extent of deformation along a plate margin is directly related to plate size. The Pacific and Eurasian plates dominate in size and marginal deformation. The tail of this north-spiraling ribbon of crustal plates is deformed in the Southern Hemisphere, most notably in the area of the African, Indian, and Australian plates. Each southern plate has a strong north component of motion as well as a counterclockwise spiraling action. The plates appear to have rotated in response to drag along the southern margin of the Pacific and Eurasian plates.

Wood, B.G.M.

1986-07-01

251

Pacific Languages at the University of the South Pacific.  

ERIC Educational Resources Information Center

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

Lynch, John; Mugler, France

2002-01-01

252

Pacific Languages at the University of the South Pacific.  

ERIC Educational Resources Information Center

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

Lynch, John; Mugler, France

2002-01-01

253

Diffraction phenomena inside thick Fresnel zone plates  

Microsoft Academic Search

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

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

1996-01-01

254

Static strength tests of steel plate strengthened concrete beams  

Microsoft Academic Search

The behaviour of damaged concrete beams strengthened by externally bonded steel plates is experimentally investigated. The\\u000a study includes an investigation of the mode of failure, including flexural failure and the interface separation of the steel\\u000a plate. Simply supported beams under monotonically increasing loads are considered exclusively. A total of five plain concrete\\u000a beams externally reinforced with bonded steel plates were

S. A. Hamoush; S. H. Ahmad

1990-01-01

255

Interface Energies.  

National Technical Information Service (NTIS)

A practical scheme for the calculation of interface energies has been developed. It combines the theory of generalized Wannier functions, the generalized recursion method for calculating local densities of states and electronic density, and the local dens...

C. C. Pei W. Kohn

1977-01-01

256

Television Interfaces  

Microsoft Academic Search

This article considers television interfaces, the screens of menus and metadata that must be engaged, as part of emergent television viewing practices. Found on devices and services such as TiVo, Hulu, YouTube, and Apple's iTunes suite, television interfaces are productive spaces that reframe the programming we watch, introduce new metadata-based aesthetics, alter the rhythms of the time we spend with

Daniel Chamberlain

2010-01-01

257

Comparison and Establishment of Three Absolute Plate Motion Models  

NASA Astrophysics Data System (ADS)

Three absolute models of plate motion: PRF - ITRF2000 derived from assumption that the Pacific ridge was fixed, HS2 - ITRF2000 based on the hotspot data, and NNR - ITRF2000 are presented in this paper. It is suggested that the PRF - ITRF2000 is probably an appropriate absolute reference frame.

Jin, Shuang-Gen; Zhu, Wen-Yao

2002-01-01

258

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

259

An oceanic flood basalt province within the Caribbean plate  

Microsoft Academic Search

The thick oceanic crust of the Caribbean plate appears to be the tectonized remnant of an eastern Pacific oceanic plateau that has been inserted between North and South America. The emplacement of the plateau into its present position has resulted in the obduction and exposure of its margins, providing an opportunity to study the age relations, internal structure and compositional

C. W. Sinton; R. A. Duncan; M. Storey; J. Lewis; J. J. Estrada

1998-01-01

260

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

261

CALUTRON FACE PLATE  

Microsoft Academic Search

The construction of a removable cover plate for a calutron tank is ; described. The plate is fabricated of a rectangular frame member to which is ; welded a bowed or dished plate of thin steel, reinforced with transverse ; stiffening ribs. When the tank is placed between the poles of a magnet, the ; plate may be pivoted away

Brobeck

1959-01-01

262

Stiffened plates in bending  

Microsoft Academic Search

A semianalytical method developed by the author for the analysis of bare plates has been extended to the static analysis of stiffened plates. Both concentric and eccentric stiffeners have been considered. Deposition of the stiffener eccentric to the plate gives rise to axial and bending displacements in the middle plane of the plate. Three coupled differential equations are resulted due

M. Mukhopadhyay

1994-01-01

263

Pacific Journal of Mathematics  

NSDL National Science Digital Library

The electronic issues of the Pacific Journal of Mathematics is available as of October, 2000. Articles on Stekloff eigenvalues, Cantor systems, and Bertini Theorems are among those featured. Articles may be viewed in .pdf, hyperdvi, dvi, or .ps format.

2005-11-02

264

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

PubMed

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

Neall, Vincent E; Trewick, Steven A

2008-10-27

265

Imprint of the North American plate in Siberia revealed by GPS  

Microsoft Academic Search

GPS observations in east Siberia combined with global observations, collected 1995-2002, place constraints on the geometry and motions of the Eurasian, North American, and Pacific plates in east Asia. By comparing velocities relative to Eurasia and to North America, we conclude that east Siberia to the east of the Cherskiy Range belongs to the North American plate, hypothesized for three

G. M. Steblov; M. G. Kogan; R. W. King; C. H. Scholz; R. Bürgmann; D. I. Frolov

2003-01-01

266

Imprint of the North American plate in Siberia revealed by GPS  

Microsoft Academic Search

GPS observations in east Siberia combined with global observations, collected 1995–2002, place constraints on the geometry and motions of the Eurasian, North American, and Pacific plates in east Asia. By comparing velocities relative to Eurasia and to North America, we conclude that east Siberia to the east of the Cherskiy Range belongs to the North American plate, hypothesized for three

G. M. Steblov; M. G. Kogan; R. W. King; C. H. Scholz; R. Bürgmann; D. I. Frolov

2003-01-01

267

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

268

14. Date Plate, 'C.O. #836, Dwg. #12A, Full Size. For ...  

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

14. Date Plate, 'C.O. #836, Dwg. #12A, Full Size. For Portal Strut with Date Plate `DP' see dwg. #12' - Southern Pacific Railroad Shasta Route, Bridge No. 301.85, Milepost 301.85, Pollard Flat, Shasta County, CA

269

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

270

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

271

High Attenuation Zone Beneath the Subducting Pacific Plate?  

Microsoft Academic Search

Interesting systematic change in waveform observed in seismic networks on Japan islands from events in Java - Tonga subduction zones (the epicentral distances are from 40-80 degrees). Some waveforms sampling eastern region (oceanward) of Japan subduction zones from Tohoku to Izu have been broadened and the amplitude has been decayed. These characteristics can be due to anelasticity in the propagating

A. Shito; H. Kawakatsu; K. Obara

2005-01-01

272

Acoustic material signature of a layered plate  

NASA Astrophysics Data System (ADS)

A technique is presented for the theoretical calculation of the acoustic material signature (AMS) of a multilayered plate with its bottom surface free of traction. The layers are composed of homogeneous isotropic linearly elastic materials and are assumed to be firmly bonded at the interfaces. The plate model can serve to represent either a self supporting membrane, or a multilayered composite with extensive debonding on a plane parallel to the layers. Calculated AMS curves are presented for a uniform plate, a two layered plate and a two layered half-space at 60 MHz exciting frequency. The striking differences in these curves indicate the possibility of using them as quantitative diagnostics for extensive debonding in a layered specimen.

Kundu, T.; Mal, A. K.

273

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

274

The History of the Pacific Superplume  

NASA Astrophysics Data System (ADS)

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

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

2001-12-01

275

Hyperbolic Interfaces  

NASA Astrophysics Data System (ADS)

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

Giomi, Luca

2012-09-01

276

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

National Technical Information Service (NTIS)

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

B. H. Erickson

1974-01-01

277

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

NASA Astrophysics Data System (ADS)

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

Gordon, R. G.

2009-05-01

278

Determination of the contact stress distribution in pin loaded orthotropic plates  

Microsoft Academic Search

An analytical solution for determining the stresses in pin loaded orthotropic plates is presented using Lekhnitskii's complex stress function approach which satisfies the displacement boundary conditions along the contact zone of the hole contour. The method is established on the notion that the contact boundary at the pin-plate interface of the loaded plate is unknown a priori and must be

Neville A. Tomlinson

2006-01-01

279

Development and application of automation control system to plate production line  

Microsoft Academic Search

The automation control system to plate production line is developed independently. The whole system is divided into several levels and control functions are put into effect by the basic automation system, process automation system and human-machine-interface (HMI) system. Plate production thickness accuracy depends on the Automatic Gauge Control (AGC) function in the basic automation system for the plate mill area.

Zhi-jie Jiao; Chun-yu he; Jun Wang; Zhong Zhao

2010-01-01

280

Debonding of FRP-plated reinforced concrete beam, a bond-slip analysis. I. Theoretical formulation  

Microsoft Academic Search

External bonding of FRP plates or sheets has emerged as a popular method for strengthening reinforced concrete. Debonding along the FRP–concrete interface can lead to premature failure of the structure. In this study, a bond-slip model is established to study the interface debonding induced by a flexural crack in a FRP-plated concrete beam. The reinforced concrete beam and FRP plate

Jialai Wang

2006-01-01

281

Resource Interfaces  

Microsoft Academic Search

We present a formalism for specifying component interfaces that expose component requirements on limited resources. The formal- ism permits an algorithmic check if two or more components, when put together, exceed the available resources. Moreover, the formalism can be used to compute the quantity of resources necessary for satisfying the requirements of a collection of components. The formalism can be

Arindam Chakrabarti; Luca De Alfaro; Thomas A. Henzinger; Mariëlle Stoelinga

2003-01-01

282

Eastern Pacific Ocean Conference  

NASA Astrophysics Data System (ADS)

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

283

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.

284

Growth Plate Fractures  

MedlinePLUS

... Harris classification of growth plate fractures. Type I Fractures These fractures break through the bone at the ... and completely disrupting the growth plate. Type II Fractures These fractures break through part of the bone ...

285

Segmented Clutch Plates.  

National Technical Information Service (NTIS)

The patent application relates to a segmented annular clutch plate for use in any conventional clutch plate mechanism. The segments are of equal arcuate dimension so that they are interchangeable. Each segment possesses the same annular uniformily serrate...

E. F'Geppert

1981-01-01

286

Button/Plate Yielding  

SciTech Connect

An aluminum button and plate were yielded to compare the experimental and calculated button to plate stress ratios. Using the fact that compressive stress is directly proportional to area and load, the calculated button to plate stress ratio is equal to the plate to button area ratio for a constant load. The loads that caused the button and plate to yield were estimated from a load test cell graph obtained from the materials testing facility. The button was simply compressed, but the plate was compressed with a steel cylinder of the same diameter as the aluminum button. The experimental and calculated stress ratios for the button and plate are the same within experimental error. The equation for the plate bearing area is therefore correct.

Wintercorn, S.; /Fermilab

1987-06-17

287

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.

288

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

289

The challenge of reconstructing the Phanerozoic sea level and the Pacific Basin tectonics  

NASA Astrophysics Data System (ADS)

The relationships between the interior dynamics of our planet and global sea level can be unravelled when plate-tectonic reconstructions are available for the entire Earth. A review of global tectonics reveals significant deficiencies in our understanding of the geodynamic evolution of the Pacific (Panthalassa or Proto-Pacific) during the Cambrian-Jurassic time-span. This particular, but major, shortcoming presents a true challenge for modern geoscientists, who are encouraged to produce a detailed plate-tectonic reconstruction of the Pacific for the pre-Cretaceous in order to advance our understanding of Phanerozoic sea-level change. A set of approaches, including geological/geophysical modelling, investigation of accretionary prisms, palaeobiogeographical studies, and careful examination of eustatic sea-level changes, are proposed that will help geoscientists tackle the challenge of understanding how Pacific geodynamics affected global sea level during the Phanerozoic.

Ruban, Dmitry A.; Conrad, Clinton P.; van Loon, A. J. (Tom)

2010-12-01

290

Pacific Pediatric Advanced Care Initiative.  

National Technical Information Service (NTIS)

The Pacific Pediatric Advanced Care Initiative establishes an advanced care Center with ECLS support in Hawaii to support the Pacific Rim. The Center will advance the science of Pediatric Advanced Care through new basic science and simulation research, wh...

L. Burgess

2010-01-01

291

Pacific Pediatric Advanced Care Initiative.  

National Technical Information Service (NTIS)

The Pacific Pediatric Advanced Care Initiative establishes an advanced care Center with ECLS support in Hawaii to support the Pacific Rim. The Center will advance the science of Pediatric Advanced Care through new basic science and simulation research, wh...

L. Burgess

2009-01-01

292

Accelerated plate tectonics.  

PubMed

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

Anderson, D L

1975-03-21

293

Optimal truss plates  

Microsoft Academic Search

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

Nathan Wicks; John W Hutchinson

2001-01-01

294

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.

295

Plate Tectonic Theory  

NSDL National Science Digital Library

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

Louie, John

296

Plate Tectonic Primer  

NSDL National Science Digital Library

This site gives an in-depth look at the theory of plate tectonics and how it works. The structure of the Earth is discussed, with brief rock type descriptions. The structure of the lithosphere, plate boundaries, interplate relationships, and types of plates are all covered in detail.

Fichter, Lynn

297

Off-axis crustal thickness across and along the east pacific rise within the MELT area  

PubMed

Wide-angle seismic data along the Mantle Electromagnetic and Tomography (MELT) arrays show that the thickness of 0.5- to 1. 5-million-year-old crust of the Nazca Plate is not resolvably different from that of the Pacific Plate, despite an asymmetry in depth and gravity across this portion of the East Pacific Rise. Crustal thickness on similarly aged crust on the Nazca plate near a magmatically robust part of the East Pacific Rise at 17 degrees15'S is slightly thinner (5.1 to 5.7 kilometers) than at the 15 degrees55'S overlapping spreading center (5.8 to 6.3 kilometers). This small north-south off-axis crustal thickness difference may reflect along-axis temporal variations in magma supply, whereas the across-axis asymmetry in depth and gravity must be caused by density variations in the underlying mantle. PMID:9596565

Canales; Detrick; Bazin; Harding; Orcutt

1998-05-22

298

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

299

Electrical conductivity at around 400 km depth in the western Pacific subduction region (Invited)  

Microsoft Academic Search

The western Pacific area is a field of significant mantle downwelling. The old Pacific plate (125-150 Ma) subducts at the Kurile-Japan, Izu-Bonin, and Mariana trenches. The slabs penetrating into the mantle beneath the back arc regions were imaged as high-velocity anomalies by seismic tomography (e.g., Fukao et al., 2001; Obayashi et al., 2009). The high-velocity anomalies tend to be distributed

K. Baba; H. Utada; H. Shimizu

2010-01-01

300

The challenge of reconstructing the Phanerozoic sea level and the Pacific Basin tectonics  

Microsoft Academic Search

The relationships between the interior dynamics of our planet and global sea level can be unravelled when plate-tectonic reconstructions are available for the entire Earth. A review of global tectonics reveals significant deficiencies in our understanding of the geodynamic evolution of the Pacific (Panthalassa or Proto-Pacific) during the Cambrian-Jurassic time-span. This particular, but major, shortcoming presents a true challenge for

Dmitry A. Ruban; Clinton P. Conrad

2010-01-01

301

Shear-wave splitting and implications for mantle flow beneath the MELT region of the east pacific rise  

PubMed

Shear-wave splitting across the fast-spreading East Pacific Rise has been measured from records of SKS and SKKS phases on the ocean-bottom seismometers of the Mantle Electromagnetic and Tomography (MELT) Experiment. The direction of fast shear-wave polarization is aligned parallel to the spreading direction. Delay times between fast and slow shear waves are asymmetric across the rise, and off-axis values on the Pacific Plate are twice those on the Nazca Plate. Splitting on the Pacific Plate may reflect anisotropy associated with spreading-induced flow above a depth of about 100 km, as well as a deeper contribution from warm asthenospheric return flow from the Pacific Superswell region. PMID:9596569

Wolfe; Solomon

1998-05-22

302

The Fate of Unsubducted Fragments of the Farallon Plate  

NASA Astrophysics Data System (ADS)

The Monterrey, Guadalupe, and Magdalena microplates all ceased subducting before the Farallon-Pacific spreading centers disappeared beneath the North American continent, leaving behind plate fragments that became incorporated into the Pacific plate as spreading ceased. Spreading directions changed dramatically on the Monterrey and Magdalena spreading centers, suggesting that the Farallon slab detached from the microplate fragments before or during the cessation of spreading. Although the sinking Farallon plate must have detached from all three microplates, it is not known where the detachments occurred and how much of the young slab was left behind still attached to the unsubducted surface microplates. After the microplates were incorporated into the Pacific plate, the plates moved relative to North America on predominantly strike- slip faults, as much as 820 km in the case of the Monterrey microplate. Did the slab fragments move along with the fossil microplates and coastal crustal blocks? We address the fate of the unsubducted fragments by looking for associated seismic velocity anomalies using teleseismic Rayleigh wave tomography and the stations of the USArray, NARS-Baja and RESBAN arrays. There are high velocity anomalies landward of each of the fossil oceanic microplates, indicating that slab fragments translated along with the surface plates. At least in the case of the Guadalupe plate, high shear velocity anomalies continue to depths exceeding 100 km, suggesting that the leading edge of the microplate slab was shoved downward into the mantle or that thermally induced density contrasts induced downward convection. We estimate how much slab may have remained attached to the surface microplate by integrating the velocity anomaly over the volume of the anomalous region.

Wang, Y.; Forsyth, D.; Savage, B.

2008-12-01

303

Circum-Pacific modes of subduction, collision, and metallogenesis  

Microsoft Academic Search

Tectonic processes in trench-arc-back-arc regions, as depicted on the Plate-Tectonic Map of the Circum-Pacific Region, are controlled by different modes of subduction. In one end member, the Chilean or high-stress subduction zone, the stress regime in the overriding lithosphere is compressive; whereas in the other end member, the Mariana or low-stress subduction zone, extensional tectonics prevails. The two modes are

C. Nishiwaki; S. Uyeda

1986-01-01

304

Protandry in Pacific salmon  

Microsoft Academic Search

Protandry, the earlier arrival of males to the spawning grounds than females, has been reported in several studies of Pacific salmon (Oncorhynchus spp.). However, the reasons for protandry in salmon are poorly understood and little is known about how protandry varies among and within populations. In this study, protandry was quantified in a total of 105 years using gender-specific timing

Yolanda Morbey

2000-01-01

305

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

306

Plastic in the Pacific  

NSDL National Science Digital Library

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

Kqed

2012-08-08

307

Pacific basin energy  

SciTech Connect

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

Not Available

1980-01-01

308

OCLC in Asia Pacific.  

ERIC Educational Resources Information Center

Discusses the Online Computer Library Center (OCLC) and the changing Asia Pacific library scene under the broad headings of the three phases of technology innovation. Highlights include WorldCat and the OCLC shared cataloging system; resource sharing and interlibrary loan; enriching OCLC online catalog with Asian collections; and future outlooks.…

Chang, Min-min

1998-01-01

309

The Pacific Climate Workshops  

NASA Astrophysics Data System (ADS)

In 1984, a workshop was held on climate variability in the eastern North Pacific and western North America. From it has emerged an annual series of workshops held at the Asilomar Conference Center, Monterey Peninsula, Calif. The workshops have been largely sponsored by the U.S. Geological Survey (USGS). The third workshop in the series was held March 25-28, 1986.

Mooers, Christopher N. K.; Peterson, D. H.; Cayan, Daniel R.

310

Discovering Plate Boundaries  

NSDL National Science Digital Library

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

Henning, Alison

311

Multicolor printing plate joining  

NASA Astrophysics Data System (ADS)

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.

1984-03-01

312

Mantle Convection Moving Plates  

NSDL National Science Digital Library

This demonstration models the manner in which the convection currents in the mantle of the Earth cause movement of the plates. Convection currents in the mantle were thought, for many years, to be solely responsible for plate tectonic movements, with the movement taking rocks down at destructive margins and new rocks forming when plates spread. It is now thought likely that there are three possible driving mechanisms for plate tectonics. In addition to movement of mantle convection currents as shown in this demonstration, scientists also consider the mass of the subducted plate (the sinking slab) at the subduction zone dragging the surface part of the plate across the surface and the new plate material sliding off the higher oceanic ridges at constructive margins.

313

Characterization of the upper surface of the Philippine Sea plate beneath Kanto, central Japan: insight from seismic reflection profiling  

NASA Astrophysics Data System (ADS)

Beneath metropolitan Tokyo, the Philippine Sea plate (PHS) has been subducted on the Pacific plate (PAC). Due to shallow subduction of Philippine Sea plate (PHS), intraslab earthquake of PHS can also produce significant damage of Tokyo metropolitan area. To construct source fault models, we have carried out seismic reflection profiling since 2002 and acquired seismic reflection data from 9 seismic lines, including 2009 Sagami trough and 2010 Kujukuri seismic survey. Due to strong impedance contrast of plate interface, the upper surface of PHS was imaged down to maximum 40 km in depth. The obtained seismic profiles portrayed the shallow geometry of the PHS. The combined seismic section from Izu peninsula to Tokyo (2009 Sagami trough and 2003 Tokyo bay seismic sections) shows strong reflectivity in the deeper part (17 to 27 km) and also shallower part (5 to 10 km). Base on the co-seismic displacement of the 1923 Kanto earthquake (M7.9) and slip-deficit rate determined by GPS observations, the asperity zone is clearly identified along the combined seismic line. By comparison, the zone of asperity is marked by the area of low reflectivity, relatively flat geometry and Vp > 6 km/sec. The subducted PHS slab beneath Kanto consists of fore-arc and volcanic-arc of young geologic age. The slab geometry obtained by seismic reflection suggests strong deformation. Three seismic lines across the north to northwestern part of the Izu collision zone demonstrate the ridge shaped antiform of the PHS slab. Judging from overall geometry of PHS slab beneath Kanto, the deformation of the slab probably produced by the northward subduction of PHS (> 1 Ma) and interaction with underlying cold PAC slab.

Sato, H.; Abe, S.; Iwasaki, T.; Kurashimo, E.; Okaya, D. A.; Sakai, S.; Kawanaka, T.; Hirata, N.

2010-12-01

314

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

315

Physical characteristics of subduction interface type seismogenic zones revisited  

Microsoft Academic Search

Based on global earthquake catalogs, the hypocenters, nodal planes, and seismic moments of worldwide subduction plate interface earthquakes were extracted for the period between 1900 and 2007. Assuming that the seismogenic zone coincides with the distribution of 5.5 ? M < 7 earthquakes, the subduction interface seismogenic zones were mapped for 80% of the trench systems and characterized with geometrical

Arnauld Heuret; Serge Lallemand; Francesca Funiciello; Claudia Piromallo; Claudio Faccenna

2011-01-01

316

Deep non-volcanic tremor of circum-Pacific subduction zones  

NASA Astrophysics Data System (ADS)

Non-volcanic tremor was first discovered in SW Japan. The preponderance of evidence indicates that tremor consists of swarms of deep low frequency earthquakes (LFEs) that occur as shear slip on the deep extension of the plate interface. Since being discovered in Japan, non-volcanic tremor has been detected in many other circum-Pacific subduction zones. Studies to date indicate that the results from Japan will generalize to other locales. In this study we present an update of LFE activity during non-volcanic tremor in four subduction zones: April 2006 southwest Japan, July 2004 northern Cascadia, July 2000 south-central Alaska, and May 2007 Costa Rica. We detect LFEs within tremor using the network autocorrelation of tremor waveforms in vicinity of the tremor source, and once the LFEs are detected, we measure phase arrival times and locate them using methods that are used to locate ordinary earthquakes. Our preliminary results suggest non-volcanic tremor is primarily composed of LFEs. A more complete understanding of where tremor occurs, and just as importantly where it doesn’t, is key to developing a comprehensive understanding of tremor and its relationship to regular earthquakes.

Brown, J. R.; Beroza, G. C.

2009-12-01

317

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

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

318

WFPDB: European Plate Archives  

NASA Astrophysics Data System (ADS)

The Wide-Field Plate Database (WFPDB) gives an inventory of all wide-field (>~ 1 sq. deg) photographic observations archived in astronomical institutions over the world. So it facilitates and stimulates their use and preservation as a valuable source of information for future investigations in astronomy. At present WFPDB manages plate-index information for 25% of all existing plates providing on-line access from Sofia (http://www.skyarchive.org/search) and in CDS, Strasbourg. Here we present the new development of WFPDB as an instrument for searching of long term brightness variations of different sky objects stressing on the European photographic plate collections (from existing 2 million wide-field plates more than 55% are in Europe: Germany, Russia, Ukraine, Italy, Czech Republic, etc.). We comment examples of digitization (with flatbed scanners) of the European plate archives in Sonneberg, Pulkovo, Asiago, Byurakan, Bamberg, etc. and virtual links of WFPDB with European AVO, ADS, IBVS.

Tsvetkov, Milcho

2007-08-01

319

Embodied User Interfaces: Towards Invisible User Interfaces  

Microsoft Academic Search

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

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

1998-01-01

320

Imprint of the North American plate in Siberia revealed by GPS  

NASA Astrophysics Data System (ADS)

GPS observations in east Siberia combined with global observations, collected 1995-2002, place constraints on the geometry and motions of the Eurasian, North American, and Pacific plates in east Asia. By comparing velocities relative to Eurasia and to North America, we conclude that east Siberia to the east of the Cherskiy Range belongs to the North American plate, hypothesized 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 Okhotsk and Amurian, can neither be resolved nor excluded by the GPS velocities.

Steblov, G. M.; Kogan, M. G.; King, R. W.; Scholz, C. H.; Bürgmann, R.; Frolov, D. I.

2003-09-01

321

Florida: A Jurassic transform plate boundary  

NASA Astrophysics Data System (ADS)

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

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

1984-09-01

322

Physical controls of magmatic productivity at Pacific-type convergent margins: Numerical modelling  

Microsoft Academic Search

We use a coupled petrological–thermomechanical model of subduction with spontaneous slab bending to investigate magmatic productivity at active continental margins. The model is designed to simulate fossil Pacific-type margins that have a broad well-developed fore-arc accretionary wedge system. The degree of plate coupling strongly depends on the dimensionless ratio (RH2O) between the plate convergence rate and the water propagation velocity.

Weronika Gorczyk; Arne P. Willner; Taras V. Gerya; James A. D. Connolly; Jean-Pierre Burg

2007-01-01

323

Seismic properties of the Eltanin Transform System, South Pacific  

NASA Astrophysics Data System (ADS)

We present a compilation of the seismic properties of the Eltanin Transform Fault (TF) system, compelled by the recent discovery of the Hollister Ridge and the possibility of a change of plate kinematics pattern in the region. The Hollister Ridge is a major volcanic system located on the Western flank of the Pacific-Antarctic Ridge (PAR), immediately south of the Eltanin Fracture Zones (FZs). We find or confirm two anomalous characteristics: the occurrence of seven normal faulting events on the transform segments, expressing extension across the plate boundary in the azimuth N26°W, and more than 90% deficiency in the seismic moment released during strike-slip events on the transforms, as compared to the rate expected from kinematic models. Other seismic properties are typical of the seismicity of a fast-spreading mid-ocean ridge (MOR) system. In particular, we could not document a single teleseismically recorded event on the Hollister Ridge; earthquakes are confined to narrow TFs with no activity present on the ridge segments. The transform events have regular frequency-moment statistics, and we could not document any significantly slow sources. These seismic properties generally support conventional plate tectonics models such as NUVEL-1, and cannot be reconciled with a proposed reorientation of the Pacific plate 4 Ma ago.

Okal, Emile A.; Langenhorst, Amy R.

2000-05-01

324

Acceleration of metal plates  

SciTech Connect

High-explosive charges have been used to accelerate stainless steel plates to velocities of 6-7 km/s. A two-stage system has been used in which the first stage is a plane-wave detonating system that accelerates the plate down a short barrel. The second stage consists of a hollow cylindrical charge through which the moving plate passes. After an adjustable delay this charge is detonated on the outer circumference of the entry side of the charge. Flash radiographs and witness plates show no breakup in the first stage but bowing and frequent breakup in the second stage. 6 figs.

Marsh, S.P.; McQueen, R.G.; Tan, T.H.

1989-01-01

325

Plate Motion Calculator  

NSDL National Science Digital Library

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

Estey, Lou

326

CALUTRON FACE PLATE  

DOEpatents

The construction of a removable cover plate for a calutron tank is described. The plate is fabricated of a rectangular frame member to which is welded a bowed or dished plate of thin steel, reinforced with transverse stiffening ribs. When the tank is placed between the poles of a magnet, the plate may be pivoted away from the tank and magnet and is adapted to support the ion separation mechanism secured to its inner side as well as the vacuum load within the tank.

Brobeck, W.M.

1959-08-25

327

Surface preparation and plating  

SciTech Connect

This chapter covers electroplating and electroless nickel plating since coatings of this type play an important role in diamond turning technology. Items to be discussed include preparation of substrates prior to coating, plating defects such as pits and nodules and their influence on optics, the influence of stress in coatings, plating details for copper, gold, silver, and electroless nickel, and the importance of additives and their influence on grain size and structure of deposits. Some comments are made on future challenges that could be presented to the plating community to further improve the quality of coatings applied for diamond turning purposes. 60 references, 8 figures, 9 tables.

Dini, J.W.; Waldrop, F.B.; Reno, R.W.

1982-10-06

328

PLATES WITH OXIDE INSERTS  

DOEpatents

Planar-type fuel assemblies for nuclear reactors are described, particularly those comprising fuel in the oxide form such as thoria and urania. The fuel assembly consists of a plurality of parallel spaced fuel plate mennbers having their longitudinal side edges attached to two parallel supporting side plates, thereby providing coolant flow channels between the opposite faces of adjacent fuel plates. The fuel plates are comprised of a plurality of longitudinally extending tubular sections connected by web portions, the tubular sections being filled with a plurality of pellets of the fuel material and the pellets being thermally bonded to the inside of the tubular section by lead.

West, J.M.; Schumar, J.F.

1958-06-10

329

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

PubMed Central

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

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

2005-01-01

330

Effect of variations in the plate modulus of elasticity on the failure modes of FRP plated R.C. beams  

Microsoft Academic Search

In the absence of FRP plate\\/glue\\/concrete interface bond failure (i.e. interfacial debonding), eight possible flexural modes of failure are identified for reinforced concrete beams experiencing lateral loading, and strengthened in flexure with external FRP or steel plates glued to their soffits. All possible changes in such modes of failure, as a result of variations in the modulus of elasticity of

Mahmoud Hassanen; M. Raoof

2007-01-01

331

Late mesozoic-quaternary plate tectonics and the Geysers-Clear Lake geothermal anomaly, Northern Coast Ranges, California (Abstract)  

Microsoft Academic Search

The development of structures related to the Geysers-Clear Lake geothermal anomaly can be explained in terms of relative motions of the North American and Pacific plates. Hypothetically, plate convergence during Late Jurassic to mid-Tertiary time produced a west-stepping subduction zone that thrust successively younger plates of sediments and volcanic rocks of the Franciscan assemblage eastward beneath oceanic crust and depositionally

1977-01-01

332

Empowerment at Pacific Gas & Electric.  

ERIC Educational Resources Information Center

|Pacific Gas and Electric's employee involvement program aggressively focuses on customer service, performance measurement tied to management bonuses, and commitment to change in the organizational culture. (SK)|

Kaufman, Steven B.

1991-01-01

333

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.

334

Plate Tectonics with GIS  

Microsoft Academic Search

The concept of Plate Tectonics involves piecing together a wide variety of evidence to build a picture. This includes the location of earthquakes, volcanoes, mountains, fossils, and other paleoclimate data. The theory of Plate Tectonics is driven by information that is attached to a location. Even further, the theory is driven by looking and analyzing all these pieces of information

Nate Ruder

2006-01-01

335

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.

336

Energy resources of Pacific Coast of Colombia  

SciTech Connect

Despite failure of modest exploration efforts to yield commercial hydrocarbon production in the Choco-Pacific coastal basin of Colombia, recent geophysical, geochemical, and surface geologic investigations indicate a potential for petroleum accumulations, which could be related to fields located on the western basins of Ecuador that in fact constitute an extension of the Colombian Pacific geologic scheme. The Choco-Pacific coastal basin of Colombia covers an area of approximately 70,000 km/sup 2/, of which 14,000 km/sup 2/ lies offshore. The structural style of this area corresponds to a convergent plate basin created over folded oceanic sediments and adjacent to the subduction zone. Such a framework could be conducive to an attractive array of potential hydrocarbon-bearing traps. Geochemical knowledge of potential source rocks of Cretaceous and early Tertiary age confers an added attraction to the area. Most evaluations reveal kerogen-rich, gas-prone organic matter. Nevertheless, the existence of oil seeps from Cretaceous outcrops could indicate sufficient thermal maturity for oil generation. Adequate reservoirs could be found in sandy or calcareous rocks of late Eocene to Oligocene age, predominantly of marine origin with an estimated thickness exceeding 20,000 ft. Colombia has been one of the leading world producers of gold and platinum, mostly derived from the vast alluvial cover of the onshore area of the basin. In rocks cropping out in the Western Cordillera (eastern margin of the basin), deposits of potentially commercial value of porphyry copper and molybdenum, as well as massive sulfur, manganese, and bauxite, have been found.

Bueno Salazar, R.

1986-07-01

337

The 1990 Western Pacific Geophysics meeting  

NASA Astrophysics Data System (ADS)

The 1990 Western Pacific Geophysics Meeting was held in Kanazawa, Japan from 15-21 Aug. 1990. This was the first meeting of a new series of meetings for the American Geophysical Union, and it proved to be very successful in terms of the scientific program and attendance, which included over 1,000 participants. The intent of this meeting was an effort on the part of the American Geophysical Union (AGU) and several Japanese geophysical societies to gather individual Earth and space scientists at a major scientific meeting to focus on geophysical problems being studied in the western Pacific rim. The meeting was organized along the lines of a typical AGU annual meeting with some invited talks, many contributed talks, poster sessions, and with emphasis on presentations and informal discussions. The program committee consisted of scientists from both the U.S. and Japan. This meeting provided ample opportunities for U.S. and Japanese scientists to get to know each other and their works on a one-to-one basis. It was also a valuable opportunity for students studying geophysics to get together and interact with each other and with scientists from both the U.S. and Japan. There were 939 abstracts submitted to the conference and a total of 102 sessions designed as a result of the abstracts received. The topics of interest are as follows: space geodetic and observatory measurements for earthquake and tectonic studies; gravity, sea level, and vertical motion; variations in earth rotation and earth dynamics; sedimentary magnetism; global processes and precipitation; subsurface contaminant transport; U.S. Western Pacific Rim initiatives in hydrology; shelf and coastal circulation; tectonics, magmatism, and hydrothermal processes; earthquake prediction and hazard assessment; seismic wave propagation in realistic media; and dynamics and structure of plate boundaries and of the Earth's deep interior.

338

Sizing plate heat exchangers  

SciTech Connect

Since their commercial debut in the 1930s, plate heat exchangers have found widespread use in the chemical process industries (CPI). Today, more than two dozen firms market this space-saving and highly efficient type of heat exchanger. One reason for the popularity of plate heat exchangers is that their overall heat-transfer coefficient (U) is superior to that of shell-and-tube heat exchangers [1,2,3,4]. In clean water-to-water service, for example, a shell-and-tube heat exchanger has a U value of 350 Btu/ft[sup 2]-h-F, much lower than the 1,000 of a plate design at the same pressure drop. However, the plate heat exchanger's much higher U values also mean that fouling factors have a much greater effect on calculations of exchanger surface area. The right fouling factor is the key to specifying plate heat exchanger areas correctly.

Kerner, J. (Alberts and Associates, Inc., Philadelphia, PA (United States))

1993-11-01

339

Plate tectonics of the Scotia Sea  

NASA Astrophysics Data System (ADS)

The opening of the Scotia Sea ended a period of direct terrestrial connection between Antarctica and South America that had started with the amalgamation of Gondwana, and inaugurated the more recent period during which high latitude oceanic circulation between the Pacific and Atlantic oceans increased. The consequences of these changes have been suggested to include the end of terrestrial biogeographic communication across the region in Paleogene times, and the subsequent onset of southern polar isolation, bottom water formation, and Antarctic glaciation by early Neogene times. These events, responding to the configuration of land and sea, would ultimately have been governed by the configuration of continental crustal units around the margins of the Scotia Sea, which in turn responded primarily to plate motions and the associated plate boundary processes. This presentation will put forward a model for the region's tectonic development that is derived largely from marine and satellite-derived geophysical data within it, and surrounding it. In this model, the Scotia Sea develops by extension of existing continental crust and accretion of new oceanic crust around the margins of a core of Jurassic-Cretaceous oceanic crust that formed and was abandoned within the region as a result of large-scale rotation of the South American plate around the northern end of the Antarctic Peninsula in Cretaceous times. The later extension and accretion happened in response to the westwards (since ~50 Ma) and eastwards (since ~17 Ma) motions of southernmost South America and the subduction-related ancestral South Sandwich Trench away from its western and eastern edges. Whilst these events are broadly consistent with what is known about disruption of the biogeographic 'Scotia Portal' in the region, they imply that the onset of Pacific to Atlantic oceanographic connectivity pre-dated, and thus cannot have directly influenced, the onset of Antarctic glaciation.

Eagles, Graeme

2013-04-01

340

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

Microsoft Academic Search

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

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

2004-01-01

341

A new estimate for present-day Cocos-Caribbean plate motion: Implications for slip along the Central American volcanic arc  

Microsoft Academic Search

Velocities from 153 continuously-operating GPS sites on the Caribbean, North American, and Pacific plates are combined with 61 newly estimated Pacific-Cocos seafloor spreading rates and additional marine geophysical data to derive a new estimate of present-day Cocos-Caribbean plate motion. A comparison of the predicted Cocos-Caribbean direction to slip directions of numerous shallow-thrust subduction earthquakes from the Middle America trench between

Charles DeMets

2001-01-01

342

A new estimate for present-day Cocos-Caribbean Plate motion: Implications for slip along the Central American Volcanic Arc  

Microsoft Academic Search

Velocities from 153 continuously-operating GPS sites on the Caribbean, North American, and Pacific plates are combined with 61 newly estimated Pacific-Cocos seafloor spreading rates and additional marine geophysical data to derive a new estimate of present-day Cocos-Caribbean plate motion. A comparison of the predicted Cocos-Caribbean direction to slip directions of numerous shallow-thrust subduction earthquakes from the Middle America trench between

Charles DeMets

2001-01-01

343

Plate Tectonics: A Continuous Process  

NSDL National Science Digital Library

This page provides an introduction to plate tectonics for secondary students. Topics include plate motions, the layers of the Earth and oceanic versus continental plates. A set of links provides access to material on the processes of plate tectonics occuring at plate boundaries, zones of movement and instability.

344

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

345

Trench migration and upper plate strain over a convecting mantle  

NASA Astrophysics Data System (ADS)

Trench motion and upper plate deformation ultimately respond to mantle flow. Herein I build upon the mantle flow model results of Conrad and Behn (2010) and compute the drag forces underneath all plates, and show that they control the dynamics of plates and plate boundaries. The small misfit angle between between the traction azimuths of mantle traction and absolute plate motion corroborates the idea that convective mantle drag is a prominent driver of plate tectonics. Less intuitive is the fact that the interplay between the drag forces from the upper and lower plates, that amounts to -5 to 8.5 TN/m (per unit trench length), dictates both trench migration rates and upper plate deformation. At odds with the classic view that assigns the prime role to the idiosyncrasies of subduction zones (slab age, interplate friction, water content etc), I find that the intrinsic properties of subduction zones in fact only modulate this behavior. More specifically, the mean value of the integrated trenchward mantle drag force from the lower and upper plates (from -2 to 6.5 TN/m) controls upper plate deformation. Conversely, it is the difference between the lower and upper plates mantle drag forces (from -3 to 10 TN/m) that controls trench migration rates. In addition, I find that a minimum trenchward force of ~2.5 TN/m must be supplied by mantle drag before trenches can actually advance, and before upper plates undergo compression. This force results from the default tendency of slabs to rollback when solely excited by their own buoyancy, and is thus the effective tensional force that slab pull exerts on the plate interface.

Husson, Laurent

2013-04-01

346

Interface dissolution control of the 14 C profile in marine sediment  

Microsoft Academic Search

The process of carbonate dissolution at the sediment-water interface has two possible endmember boundary conditions. Either the carbonate particles dissolve mostly before they are incorporated into the sediment by bioturbation (interface dissolution), or the vertical mixing is rapid relative to their extermination rate (homogeneous dissolution). In this study, a detailed radiocarbon profile was determined in deep equatorial Pacific sediment that

Robin S. Keir; Robert L. Michel

1993-01-01

347

Library Status: U. S. Pacific and Selected Pacific Areas.  

National Technical Information Service (NTIS)

The current status of library holdings, services, and activities in the U.S. Pacific and other areas of the Pacific (New Zealand, the Cook Islands, Fiji, Tonga, and Papua New Guinea) are described. Medical library resources are a major focus, but all type...

J. Sirois

1973-01-01

348

The role of slabs and oceanic plate geometry in the net rotation of the lithosphere, trench motions, and slab return flow  

NASA Astrophysics Data System (ADS)

Absolute plate motion models with respect to a deep mantle reference frame (e.g., hot spots) typically contain some net rotation (NR) of the lithosphere. Global mantle flow models for the present-day plate setting reproduce similarly oriented NRs but with amplitudes significantly smaller than those found in some high NR Pacific hot spot reference frames. It is therefore important to understand the mechanisms of NR excitation, which we attempt here with two-dimensional cylindrical models of an idealized Pacific domain. We study the influence of slab properties, oceanic ridge position, continental keels, and a weak asthenospheric layer on NR and trench migration. Fast slab return flow develops in models with stiff slabs and moderate slab dips. Rapid NRs, comparable to the high NR Pacific hot spot reference frames, are primarily induced by asymmetric slab dips, in particular a shallow slab beneath South America and a steep slab in the western Pacific. A scaling relationship links the amplitude of NR to plate size, slab dip angle, and slab viscosity. Asymmetric ridge positions also promote NR through asymmetric plate sizes. Continental keels have less impact, in contrast to what has been found in earlier global studies. Several models yield unidirectional Pacific trench motions, such as slab advance in the western Pacific and, simultaneously, slab retreat in the eastern Pacific. Our model provides a physical explanation for NR generation in the present-day Pacific setting and hints at mechanisms for the temporal evolution of the basin.

GéRault, M.; Becker, T. W.; Kaus, B. J. P.; Faccenna, C.; Moresi, L.; Husson, L.

2012-04-01

349

A teleseismic shear-wave splitting study to investigate mantle flow around South America and implications for plate-driving forces  

Microsoft Academic Search

Closure of the Pacific Ocean basin by the convergence of its surrounding plates, some of which have deep continental roots, implies that there is net mass flux out of the mantle under the Pacific. Here we report on a shear-wave splitting study designed to test the prediction that there should be flow around its southern margin. Our results show no

George Helffrich; Douglas A. Wiens; Emilio Vera; Sergio Barrientos; Patrick Shore; Stacey Robertson; Rodrigo Adaros

2002-01-01

350

Laminar forced convection conjugate heat transfer over a flat plate  

NASA Astrophysics Data System (ADS)

Coupled heat transfer between laminar forced convection along and conduction inside a flat plate wall is theoretically studied. The laminar convective boundary layer is analyzed by employing the integral technique. The energy equations for the fluid and the plate wall are combined under the condition of the continuity in the temperature and heat flux at the fluid-solid interface. The analysis results in a simple formal solution. Expressions have been obtained for calculating local Nusselt number, wall heat flux and temperature along the plate, all are functions of the local Brun number, Brx, which is a measure of the ratio of the thermal resistance of the plate to that of the convective boundary layer. The results indicate that for Brx>=0.15, neglecting the plate resistance will results in an error of more than 5% in Nusselt number. Comparison of the present solution with other previous studies has been made. The solution may be of a considerable theoretical and practical interest.

Mosaad, M.

351

The dynamic response of inelastic, delaminated composite plates  

SciTech Connect

The dynamic behavior of metal matrix composite (MMC) plates is considered. In particular, the influence of inelastic deformations and delamination at the interfaces of the lamina on the macroscopic and local response of Al{sub 2}O{sub 3}/Al plates are studied. The work is carried out using a recently developed plate theory which models both delamination and localized history-dependent effects such, as inelasticity. A linear debonding model for the interface is employed for the current work. The theory models both the initiation and growth of delaminations without imposing any restrictions on the location, size, or direction of growth of the delamination. In the current work the response of the individual lamina in the plate are modeled using the Method of Cells (MOC) micromechanical model. The inelastic behavior in the matrix is modeled using the unified viscoplastic theory of Bodner and Partom. The behavior of a Al{sub 2}O{sub 3}/Al plate under dynamic cylindrical bending subjected to a ramp and hold type of loading is examined. For simplicity, the plate is assumed to be composed of a cross-ply layup. It is shown that both inelastic deformations and delamination have a strong influence on dynamic plate behavior. The inelastic deformations have strong effect on the axial displacement while delamination has greater influence on the deflection.

Williams, T.O.; Addessio, F.L. [Los Alamos National Lab., NM (United States). Theoretical Div.

1997-04-01

352

Pacific rim lures explorationists  

SciTech Connect

The Pacific Rim has been far and away the most attractive hunting ground for explorationists in the past year. Observers point to political initiatives coupled with a growing demand as igniting the region's numerous hydrocarbon possibilities. This paper describes some of the new incentives and the resultant exploration results and developments in China, Thailand, Malaysia, Indonesia, and Vietnam. A major sign of the region's political maturity is the willingness for the countries involved to solve the longstanding disputes over the claims in hydrocarbon-prone South China Sea.

Nation, L.

1991-09-01

353

Arctic Oil And Gas Resources Energy Resources Map Circum-Pacific Region, Arctic Sheet  

Microsoft Academic Search

The Arctic Energy-Resources Map published in 2000 covers the North Pacific Ocean, the Arctic Ocean, part of the North Atlantic Ocean and surrounding land. The map shows oil and gas fields, oil sand, oil shale, coal deposits, geothermal energy sites, onshore and offshore thickness of sedimentary rocks, and active tectonic plate boundaries. Background data on land are from the Arctic

Kenneth J. Drummond

354

Electrical Conductivity and Anisotropy in Pacific Lithosphere: CSEM Results from APPLE  

Microsoft Academic Search

Strain associated with plate formation at mid-ocean ridge spreading centers may influence electrical conductivity at various depths in the lithosphere, and may leave an anisotropic fabric frozen in place. By measuring lithospheric electrical conductivity and anisotropy, insight may be gained regarding the formation and evolution of oceanic crust and mantle. Controlled-source electromagnetic (CSEM) sounding of 35 Ma Pacific lithosphere was

J. Behrens; S. Constable; M. Everett; L. MacGregor

2003-01-01

355

Large-scale motion between Pacific and Atlantic hotspots  

NASA Astrophysics Data System (ADS)

STUDIES of true polar wander (TPW), the rotation of the solid Earth with respect to the spin axis1, have suggested that there has been 10-15° of relative motion over the past 130 Myr (refs 2-4). In such studies, the orientation of the spin axis is recovered from continental palaeomagnetic poles (corrected for relative plate motions), and compared with a deep-mantle reference frame defined by hotspot locations. But deducing relative plate motions becomes increasingly difficult for older (Mesozoic) time periods, hindering tests of TPW on timescales comparable to those of large-scale mantle convection; moreover, the assumption of hotspot fixity is controversial5,6. We examine here a more direct approach7,8, using palaeolatitudes derived from Pacific guyots. Contrary to predictions from TPW models, these data suggest only minor latitudinal shifts of Pacific hotspots during the Cretaceous period. Instead of TPW, relative motion between the Atlantic and Pacific hotspot groups9 is required at a velocity of approximately 30 mm yr-1, more than 50% larger than previously proposed5.

Tarduno, John A.; Gee, Jeff

1995-11-01

356

Geochemical zoning of volcanic chains associated with Pacific hotspots  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

357

The cascading effects of absolute reference frames and geomagnetic polarity timescales on global plate motions  

NASA Astrophysics Data System (ADS)

Global plate motion models use Africa and the Pacific as the base of plate rotation hierarchies, with many other plates moving relative to them. Relative plate motions in the Mesozoic are generally well resolved where seafloor spreading histories are preserved to the present-day. However, the choice of absolute reference frames, whether they are fixed-hotspot, moving-hotspot, true-polar wander-corrected or pure paleomagnetic, can have significant consequences for the absolute plate velocities of smaller plates that are at the mercy of the cascading effects of movement within a complex plate motion hierarchy. We use GPlates to sample plate velocities through time at equally spaced mesh nodes that are contained within continuously closing plate polygons. We calculate root-mean square plate velocities to isolate the effects of different absolute reference frames on absolute plate velocity trends. Apart from being a quality-control tool for the creation of global plate motion models, this approach allows us to track the source of plate velocity spikes, some of which may be indicative of plate reorganisation events. We use a similar approach to test whether alternative geomagnetic polarity time-scales introduce or help reduce anomalous plate velocity fluctuations in global plate motion models. The choice of timescales can affect the seafloor spreading rates partitioned across stage rotations and models of sea level change. Such a workflow may help test alternative timescales, in order to study the model-dependence and controversies that have recently surfaced regarding proposed plate reorganisation events and the mid-Cretaceous seafloor spreading pulse.

Zahirovic, S.; Seton, M.; Müller, R. D.; Torsvik, T. H.

2011-12-01

358

Pixelated neutron image plates  

NASA Astrophysics Data System (ADS)

Neutron image plates (NIPs) have found widespread application as neutron detectors for single-crystal and powder diffraction, small-angle scattering and tomography. After neutron exposure, the image plate can be read out by scanning with a laser. Commercially available NIPs consist of a powder mixture of BaFBr : Eu2+ and Gd2O3 dispersed in a polymer matrix and supported by a flexible polymer sheet. Since BaFBr : Eu2+ is an excellent x-ray storage phosphor, these NIPs are particularly sensitive to ggr-radiation, which is always present as a background radiation in neutron experiments. In this work we present results on NIPs consisting of KCl : Eu2+ and LiF that were fabricated into ceramic image plates in which the alkali halides act as a self-supporting matrix without the necessity for using a polymeric binder. An advantage of this type of NIP is the significantly reduced ggr-sensitivity. However, the much lower neutron absorption cross section of LiF compared with Gd2O3 demands a thicker image plate for obtaining comparable neutron absorption. The greater thickness of the NIP inevitably leads to a loss in spatial resolution of the image plate. However, this reduction in resolution can be restricted by a novel image plate concept in which a ceramic structure with square cells (referred to as a 'honeycomb') is embedded in the NIP, resulting in a pixelated image plate. In such a NIP the read-out light is confined to the particular illuminated pixel, decoupling the spatial resolution from the optical properties of the image plate material and morphology. In this work, a comparison of experimentally determined and simulated spatial resolutions of pixelated and unstructured image plates for a fixed read-out laser intensity is presented, as well as simulations of the properties of these NIPs at higher laser powers.

Schlapp, M.; Conrad, H.; von Seggern, H.

2004-09-01

359

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

360

Parallel Fin ORU Thermal Interface for space applications  

NASA Astrophysics Data System (ADS)

The Parallel Fin Thermal Interface has been developed as an Orbital Replaceable Unit (ORU) interface. The interface transfers heat from an ORU baseplate to a Heat Acquisition Plate (HAP) through pairs of fins sandwiched between insert plates that press against the fins with uniform pressure. The insert plates are spread apart for ORU baseplate separation and replacement. Two prototype interfaces with different fin dimensions were built (Model 140 and 380). Interfacing surface samples were found to have roughnesses of 56 to 89 nm. Conductance values of 267 to 420 W/sq m C were obtained for the 140 model in vacuum with interface pressures of 131 to 262 kPa (19 to 38 psi). Vacuum conductances ranging from 176 to 267 W/sq m F were obtained for the 380 model at interface pressures of 97 to 152 kPa (14 and 22 psi). Correlations from several sources were found to agree with test data within 20 percent using thermal math models of the interfaces.

Stobb, C. A.; Limardo, Jose G.

1992-07-01

361

Visualizing Earthquakes at Divergent Plate Margins  

NSDL National Science Digital Library

This screenshot from the visualization shows both continental rift zones, and ocean spreading centers, both types of divergent plate boundaries. The visualization shows how earthquakes at all types of divergent margins are shallow and have a low-magnitude. Click the image to enlarge or view the MP4 movie (MP4 Video 79.3MB Aug22 11).The purpose of this activity is to introduce students to the distribution and characteristics of earthquakes associated with divergent plate boundaries. Students will learn about how the magnitude and distribution of earthquakes at divergent boundaries are related to processes that occur at these boundaries and to the geometry and position of the two diverging plates. Because the depth of earthquakes can be difficult for students to visualize in 2D representations, this activity allows students to visualize the 3D distribution of earthquakes within Earth's surface, which is essential for understanding how different types of earthquakes occur in different tectonic settings. Locations featured in the visualization include the Mid-Atlantic Ridge, the East Pacific Rise, and the East African Rift Zone. Talking points and questions are included to facilitate using this visualization as part of an interactive lecture. In addition to playing back the visualization, instructors can also download the visualization software and data set and explore it themselves.

Harwood, Cara

362

Halfway There: An EarthScope Plate Boundary Observatory Progress Report  

Microsoft Academic Search

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

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

2006-01-01

363

Pacific Northwest Resources Inventory Demonstration  

Microsoft Academic Search

The Pacific Northwest Land Resource Inventory Demonstration project is being carried out jointly by NASA, the U.S. Department of the Interior (USDI) and Pacific Northwest Regional Commission (PNRC) through the technical capability provided by NASA, USDI and contractor support. The project is designed to demonstrate to users from state and local agencies in Washington, Oregon, and Idaho the cost effective

J. D. Nichols

1976-01-01

364

Business in the Asia Pacific  

Microsoft Academic Search

The success of western business in the Asia Pacific region depends to a large degree on the capacity of western firms to learn new approaches to doing business in the region and to adopt new styles of management practice, business operations, and strategy. Business in Asia Pacific seeks to address this need by providing a useful insight into the international

Sonia El-Kahal

365

Tropical Cyclones - Central Pacific (1981).  

National Technical Information Service (NTIS)

Brief descriptions are given of Tropical Storm Greg (August 20-22, 1981) and Tropical Storm Jova (September 18-20, 1981) which took place in the Central Pacific. Verification statistics show that the 24-hour Central Pacific Hurricane Center (CPHC) forecas...

A. K. T. Chun

1982-01-01

366

Pacific Northwest: paradise lost  

SciTech Connect

An influx of new residents to the Pacific Northwest is changing social patterns and is endangering the region's valued wilderness and resources. A growing population and a feeling that the national govenment is more exploitive than conserving of its resources combines with a political tension between progressive populism and conservative Mormon influences to make residents wary of either newcomers or new prosperity. The abundant hydro power is threatened as power demand increases and utilities, industries, and the state and local governments compete for their fair share. A plan to restructure the Bonneville Power Administration (BPA) has been introduced in Congress to give it a single appointed administrator with the authority to decide how power will be distributed and which new power sources to develop. Concern about the two national nuclear waste repositories at Hanford and Idaho Falls led to a six-month moratorium at Hanford to warn the government that the site was not intended to be a permanent solution. A legislative proposal to set up regional nuclear parks will not relieve the Pacific Northwest's problems for some time. Leaders blame the policymakers for looking on the area as too remote and underpopulated to worry about. 18 references (DCK)

Thomas, W.V.

1980-04-18

367

High loading uranium plate  

SciTech Connect

Two embodiments of a high uranium fuel plate are disclosed which contain a meat comprising structured uranium compound confined between a pari of diffusion bonded ductile metal cladding plates uniformly covering the meat, the meat hiving a uniform high fuel loading comprising a content of uranium compound greater than about 45 Vol. % at a porosity not greater than about 10 Vol. %. In a first embodiment, the meat is a plurality of parallel wires of uranium compound. In a second embodiment, the meat is a dispersion compact containing uranium compound. The fuel plates are fabricated by a hot isostatic pressing process.

Wiencek, T.C.; Domagala, R.F.; Thresh, H.R.

1990-10-16

368

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.

369

Mountains and Moving Plates  

NSDL National Science Digital Library

These are the lecture notes for a class on plate tectonics and mountain building which is taught at the University of Wisconsin-Madison. The course describes the connections between the earth's tectonic plates, earthquakes, and its many mountain ranges. Topics include basic geography, the structure of the earth's interior, the relationships between the seismic cycle, volcanism, and plate movements, erosion of mountains, and mass wasting. Links are provided to additional resources, including aerial photos of geologic features, an interactive map of geology and topography of the United States, and a glossary.

370

Hybrid Interface Automata for Component Interfaces  

Microsoft Academic Search

The modelling and verifying of hybrid systems attract more and more attentions recently. Hybrid automaton is widely used to model discrete and continuous behaviors of hybrid systems. In this paper, a hybrid interface automaton(HIA) is proposed based on hybrid automaton to model the interface behaviors of hybrid components. According to the interface type of components, we define two kinds of

Dehui Du; Jing Liu

2011-01-01

371

The North Pacific Gyre Mode  

NASA Astrophysics Data System (ADS)

Discussion of North Pacific Decadal decadal variability has focused primarily on the Pacific Decadal Oscillation, the leading mode of sea surface temperature anomalies north of the tropics. The PDO appears to result from a superposition of SST pattern forced by the North Pacific atmosphere due to its intrinsic dynamics and teleconnected from the tropics, with a regional impact of the ocean circulation in the frontal regions associated with the Kuroshio/Oyashio and their extensions into the interior. Recent modeling, however, suggest that previously unexplained decadal changes of salinity, nutrient upwelling and chlorophyl in the California Current are not dominated by the PDO. Rather, these are associated with a mode of variability associated with wind driven changes of the North Pacific Gyre. Consideration of this mode variability may thus be important to understand present and future variations of the North Pacific ecosystem, and in the interpretation of climate proxies.

Schneider, N.; di Lorenzo, E.

2007-12-01

372

77 FR 31329 - Pacific Fishery Management Council; Public Meeting  

Federal Register 2010, 2011, 2012, 2013

...0648-XC046 Pacific Fishery Management Council; Public Meeting...The Pacific Fishery Management Council's (Pacific...to review background material on Pacific Halibut...address: Pacific Fishery Management Council, 7700 NE Ambassador...Director, Office of Sustainable Fisheries,...

2012-05-25

373

Structural geomorphology of a fast-spreading rise crest: The East Pacific Rise near 3°25?S  

Microsoft Academic Search

A deeply-towed instrument package was used in a detailed survey of the crest of the East Pacific Rise (EPR) near 3°25'S, where the Pacific and Nazca plates are separating at 152 mm\\/yr. A single 90 km-long traverse of the rise crest extends near-bottom observations onto the rise flanks. A ridge at the spreading axis is defined by its steep regional

Peter Lonsdale

1977-01-01

374

Paleomagnetism and Plate Tectonics.  

National Technical Information Service (NTIS)

Paleomagnetism and plate tectonics are combined in a new procedure for producing paleogeographic reconstructions of the evolution of present day world geography from proto-continents. For each geologic epoch, the continents are first subjected to rotation...

J. Francheteau

1970-01-01

375

Plate Thermometer: Practical Aspects.  

National Technical Information Service (NTIS)

Fire resistance furnaces have different thermal properties and expose test specimens to different heating conditions if controlled by temperature readings by ordinary TC's. The so called Plate Thermometer PT has therefore been introduced. Several investig...

U. Wickstroem

1997-01-01

376

My Plate Food Guide  

MedlinePLUS

... health problems like heart disease, diabetes, and even depression. Aim to get at least 60 minutes of moderate to vigorous exercise every day. Practical Advice on Eating Right and Exercise The USDA's MyPlate website offers lots of ...

377

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

378

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

379

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

380

Seismology and Plate Tectonics  

Microsoft Academic Search

This introduction to seismological theory and the principles of plate tectonics also develops a practical approach to the interpretation of seismograms for physicists and mathematicians as well as geologists.

David Gubbins

1990-01-01

381

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

382

The biogeochemistry of aluminum in the Pacific Ocean  

NASA Astrophysics Data System (ADS)

Vertical distributions and horizontal surface transects of dissolved and particulate Al at several locations in the Pacific Ocean are presented here. Concentrations of dissolved Al in the Pacific range from 0.3 to 5 nmol/kg in the surface waters, from 0.1 to 1 nmol/kg in mid-depths, and from 0.5 to 2 nmol/kg in the deep waters. From these data and published data from other regions, it is evident that Al has a unique oceanic chemistry relative to that of other metals. External sources and rapid particle scavenging throughout the water column are the major controls on dissolved Al distributions in the oceans. Vertical profiles generally exhibit a surface maximum, a mid-depth minimum, and increasing concentrations toward the sediment-water interface. This suggests two sources of dissolved Al, one to the surface waters and one to the deep waters. Concentrations of dissolved Al in surface waters are lowest within the eutrophic, low-salinity California Current (0.3-1 nmol/kg) and increase westwardly into the subtropical gyre of the North Pacific (~ 5 nmol/kg). Values in the South Pacific gyre are fivefold lower. These horizontal trends indicate that the primary source of dissolved Al to the surface waters of the central Pacific is from eolian input. Dissolved Al supplied by rivers to the eastern North Pacific appears to be rapidly scavenged in estuaries and/or the highly productive coastal region. The source of dissolved Al to the deep waters is not known, but could be due to a flux out of the sediments or a remineralization process. Suspended particulate Al concentrations increase with depth at all stations and decrease with distance from the ocean boundary. Surface values range from ~ 1.5 nmol/kg near shore to ~ 0.3 nmol/kg in the central gyres of the Pacific. Deep water concentrations range from ~ 22 nmol/kg near shore to ~ 4 nmol/kg in the North Pacific central gyre, and decrease to ~ 1.3 nmol/kg in the South Pacific central gyre. Observed distributions indicate that suspended particulate Al varies with the intensity of bottom sediment resuspension and the horizontal mixing of the resulting ``nepheloid layer'' out from ocean boundary regions. Particle residence times estimated are consistent with other reported values.

Orians, Kristin J.; Bruland, Kenneth W.

1986-07-01

383

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

ERIC Educational Resources Information Center

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

Maidment, Ewan

1998-01-01

384

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

ERIC Educational Resources Information Center

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

Maidment, Ewan

1998-01-01

385

Polygonal Fresnel zone plates  

NASA Astrophysics Data System (ADS)

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

Alda, Javier; González, Francisco Javier

2009-08-01

386

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.

387

Analysis of thermal conductance of contacts with interstitial plates  

Microsoft Academic Search

An analytical and experimental analysis has been carried out for the prediction of contact conductance with interstitial plates and an expression has been developed in terms of known properties and parameters. The model assumes that the interface is composed of similar macroscopic and microscopic contact elements. These elements are considered to be made up of two cylindrical solids having a

T. N. Veziroglu; H. Yuncu; S. Kakac

1976-01-01

388

The East Pacific Rise: An Active Not Passive Spreading System  

NASA Astrophysics Data System (ADS)

Traditional plate tectonic interpretations of mid-oceanic ridges regard spreading as an entirely passive phenomenon. From this one would assume that the oceanic ridges will move over the mantle in response to the geodynamics of the diverging plates, and do not remain fixed spatially over any protracted period of time. An analysis of the kinematics of ridge motions in the Indo-Atlantic hotspot frame of reference since 83 Ma generally supports this view, with the notable exception of the East Pacific Rise (EPR). The Pacific-Nazca/Farallon segment of the EPR north of Easter Island (27°S) is oriented essentially N-S, and has produced more than 9500km of E-W spreading in the past 80 Ma, making it the dominant ridge in the world's plate system over this interval of time. Yet despite the large amount of E-W divergence, the spreading center has maintained its longitudinal position to within <±250 km of the current ridge axis. Global mantle convective flow modeling indicates that the EPR, unlike any other extensive segment of the mid-oceanic ridge system, is underlain by an active upwelling system extending from the core-mantle boundary to the surface. We suggest that the lack of E-W motion of the EPR apparent from the kinematics is a consequence of these mantle dynamics; this ridge is thus not behaving as a passive plate boundary, but is actively and directly linked to, and controlled by, whole mantle upwelling. This observation overturns the notion that ridges are always entirely passive features of the plate system. Subduction of the northern EPR beneath western North America has thus resulted in the overriding of an active upwelling system that has contributed significantly to the evolution of Basin and Range kinematics and superimposed dynamics, including significant contributions from dynamic topography.

Rowley, D. B.; Rowan, C. J.; Forte, A. M.; Moucha, R.; Grand, S. P.; Simmons, N. A.

2011-12-01

389

Slab identification in the lower mantle beneath the Americas from seismic tomography and plate history reconstruction  

NASA Astrophysics Data System (ADS)

We combine results from seismic tomography and published plate motion histories to investigate the structure and evolution of slabs of subducted lithosphere in the lower mantle beneath North- and South America. We constructed models of 3-D variations in propagation speed of P and S waves through travel time inversion. Using broadband waveform cross-correlation, we measured 37,000 differential travel times (P1-P2 and S1-S2) for pairs of stations and 2,000 PcP-P and ScS-S times from single station records. The earthquakes and receivers are located along a wide corridor from Alaska to South America. We invert the data simultaneously to obtain P and S-wave velocity models. Synthetic tests were performed to assess image quality. We interpret slab structures and unravel subduction history by comparing our Vs tomographic images with reconstructed plate motion from present-day up to 100 Ma. Convergence of the Pacific with respect to North and South America is computed using two approaches: (1) by considering the Pacific and Indo-Atlantic hotspot reference frames and (2) by using the plate circuit passing through Antartica, but there is little difference between the two approaches for ages yonger than 80 Ma. In the upper part of the lower mantle we recognize the imprint of the most recent phase of the plate history. Around 800 km depth, four distinctive fast anomalies can be associated with subduction of the Nazca and Cocos plates beneath South and Central America respectively, the Juan de Fuca plate beneath North America, and the Pacific plate beneath the Aleutian islands arc. In the lowermost mantle, the large fast anomalies which is most pronounced in the S-wave models can be associated with Late Cretaceous subduction of the Farallon plate beneath the Aleutian islands and most of the Americas, and perhaps with the Phoenix plate beneath the southern part of South America. Near 2000 km depth, the images record the fragmentation of the proto Farallon plate into the Kula plate in the North and the Farallon plate in the North-East since 80 Ma. Around 1000 km depth, we observe separated fast anomalies interpreted as the Kula-Pacific, the Juan de Fuca, and the Farallon slabs. This interpretation is validated by comparing the volume and length of slabs estimated from the tomographic images and from plate history reconstruction.

Ren, Y.; Stutzmann, E.; van der Hilst, R.; Besse, J.

2005-12-01

390

The effect of nonlinear contact upon natural frequency of delaminated stiffened composite plate  

Microsoft Academic Search

The effect of nonlinear contact upon natural frequency of the stiffened composite plate with pre-damages, such as delamination of skin panel and\\/or debonding interfaces between skin panel and stiffeners, is studied by the finite element method, based on hump resonance principle. A formula of element stiffness and mass matrices for the composite stiffened plates is deduced by using the first

Haoran Chen; Man Wang; Ruixiang Bai

2006-01-01

391

Vibrations of rectangular plates reinforced by any number of beams of arbitrary lengths and placement angles  

Microsoft Academic Search

This paper presents an analytical method for the vibration analysis of plates reinforced by any number of beams of arbitrary lengths and placement angles. Both the plate and stiffening beams are generally modeled as three-dimensional (3-D) structures having six displacement components at a point, and the coupling at an interface is generically described by a set of distributed elastic springs.

Hongan Xu; Jingtao Du; W. L. Li

2010-01-01

392

Buckling of laminated sandwich plates with soft core based on an improved higher order zigzag theory  

Microsoft Academic Search

An improved higher order zigzag theory is presented and it is applied to study the buckling of laminated sandwich plates. The present theory satisfies the conditions of transverse shear stress continuity at all the layer interfaces including transverse shear stress free conditions at the top and bottom surfaces of the plate. The variation of in-plane displacements through thickness direction is

M. K. Pandit; B. N. Singh; A. H. Sheikh

2008-01-01

393

Monitoring the northern Chile megathrust with the Integrated Plate boundary Observatory Chile (IPOC)  

Microsoft Academic Search

The oceanic Nazca plate subducts beneath the continental South American plate by recurrent rupture of large segments of its interface. The resulting earthquakes are among the largest and most frequent on Earth. Along the Chilean and southern Peruvian margin, all sizeable segments have ruptured at least once in the past 150 years for which there exist historic and\\/or instrumental records.

Bernd Schurr; Günter Asch; Beatrice Cailleau; Guillermo Chong Diaz; Sergio Barrientos; Jean-Pierre Vilotte; Onno Oncken

2010-01-01

394

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

Microsoft Academic Search

Fast convergence between the oceanic Nazca and the continental South American plate is accommodated by recurrent rupture of large segments of the two plates' interface. The resulting earthquakes are among the largest and, for their sizes, most frequent on Earth. Along the Chilean and southern Peruvian margin, all segments have ruptured at least once in the past 150 years for

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

2009-01-01

395

Vibration Equations of Thick Rectangular Plates Using Mindlin Plate Theory  

Microsoft Academic Search

Problem statement: Rectangular steel plates are widely used in variou s steel structures and steel industries. For a proper design of steel plate structures and efficient use of material, the behavior, strength, buckling and post-buckling char acteristics of plates should be accurately determined. Approach: Considering the significance of this matter, later al vibration of thick rectangular plates was studied on

S. A. Sadrnejad; A. Saedi Daryan; M. Ziaei

396

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

397

Pacific Decadal Variability: The Tropical Pacific Mode and the North Pacific Mode(.  

NASA Astrophysics Data System (ADS)

Pacific decadal variability is studied in a series of coupled global ocean-atmosphere simulations aided by two `modeling surgery' strategies: partial coupling (PC) and partial blocking (PB). The PC experiments retain full ocean-atmosphere coupling in selected regions, but constrain ocean-atmosphere coupling elsewhere by prescribing the model climatological SST to force the atmospheric component of the coupled system. In PB experiments, sponge walls are inserted into the ocean component of the coupled model at specified latitudinal bands to block the extratropical-tropical oceanic teleconnection.Both modeling and observational studies suggest that Pacific decadal variability is composed of two distinct modes: a decadal to bidecadal tropical Pacific mode (TPM) and a multidecadal North Pacific mode (NPM). The PC and PB experiments showed that the tropical Pacific mode originates predominantly from local coupled ocean-atmosphere interaction within the tropical Pacific. Extratropical-tropical teleconnections, although not a necessary precondition for the genesis of the tropical decadal variability, can enhance SST variations in the Tropics. The decadal memory in the Tropics seems to be associated with tropical higher baroclinic modes. The North Pacific mode originates from local atmospheric stochastic processes and coupled ocean-atmosphere interaction. Atmospheric stochastic forcing can generate a weaker NPM-like pattern in both the atmosphere and ocean, but with no preferred timescales. In contrast, coupled ocean-atmosphere feedback can enhance the variability substantially and generate a basin-scale multidecadal mode in the North Pacific. The multidecadal memory in the midlatitudes seems to be associated with the delayed response of the subtropical/subpolar gyre to wind stress variation in the central North Pacific and the slow growing/decaying of SST anomalies that propagate eastward in the Kuroshio Extension region. Oceanic dynamics, particularly the advection of the mean temperature by anomalous meridional surface Ekman flow and western boundary currents, plays an important role in generating the North Pacific mode.

Wu, L.; Liu, Z.; Gallimore, R.; Jacob, R.; Lee, D.; Zhong, Y.

2003-04-01

398

Double plate system with a discontinuity in the elastic bonding layer  

Microsoft Academic Search

The double plate system with a discontinuity in the elastic bonding layer of Winker type is studied in this paper. When the\\u000a discontinuity is small, it can be taken as an interface crack between the bi-materials or two bodies (plates or beams). By\\u000a comparison between the number of multifrequencies of analytical solutions of the double plate system free transversal vibrations

2007-01-01

399

Temperature cycling effects between Sn\\/Pb solder and electroless copper plated AIN substrate  

Microsoft Academic Search

Thermal cycling effects on Sn\\/Pb solder and electroless Cu-plated AIN substrates are investigated. X-ray diffraction patterns reveal the existence of Cu2O for the electroless Cu-plated AIN after thermal cycling in an environmental chamber. Moisture in the chamber results in the oxidation of electroless plated Cu and fracture takes place at the Cu2O\\/Cu interface. The oxidation of Cu is also confirmed

Bi-Shiou Chiou; Jiann-Haur Chang; Jenq-Gong Duh

1995-01-01

400

Thermal characterization of a liquid cooled AlSiC base plate with integral pin fins  

Microsoft Academic Search

In this study, we present the thermal analysis and experimental performance assessment of an aluminum silicon carbide (AlSiC) metal matrix composite (MMC) base plate with integral cooling fins. By attaching a pin-finned base plate to an open-chambered flow-through heat sink, the mechanical interface between the base plate and cooling medium is eliminated. This reduces the overall thermal resistance and improves

Kevin A. Moores; Yogendra K. Joshi; Gerhard H. Schiroky

2001-01-01