These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Plate Tectonics: Diverging, Converging, and Transform Boundaries  

NSDL National Science Digital Library

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

2

From Convergence to Subduction - Plate Boundary Formation through New Zealand  

NASA Astrophysics Data System (ADS)

In contrast to the normal 'Wilson cycle' sequence of subduction leading to continental collision and associated mountain building, the evolution of the New Zealand plate boundary in the Neogene reflects the converse - initially a period of continental convergence that is followed by the emplacement of subduction. Plate reconstructions allow us to place limits on the location and timing of the continental convergence and subduction zones and the migration of the transition between the two plate boundary regimes. Relative plate motions and reconstructions since the Early to Mid-Miocene require significant continental convergence in advance of the emplacement of the southward migrating Hikurangi subduction - a sequence of tectonism seen in the present plate boundary geography of Hikurangi subduction beneath North Island and convergence in the Southern Alps along the Alpine Fault. In contrast to the transition from subduction to continental convergence where the leading edge of the upper plate is relatively thin and deformable, the transition from a continental convergent regime, with its associated crustal and lithospheric thickening, to subduction of oceanic lithosphere requires substantial thinning (removal) of upper plate continental lithosphere to make room for the slab. The simple structure of the Wadati-Benioff zone seen in the present day geometry of the subducting Pacific plate beneath North Island indicates that this lithospheric adjustment occurs quickly. Associated with this rapid lithospheric thinning is the development of a series of ephemeral basins, younging to the south, that straddle the migrating slab edge. Based on this association between localized vertical tectonics and slab emplacement, we argue that the tectonic history of these basins record the effects of lithospheric delamination driven by the southward migrating leading edge of the subducting Pacific slab. Although the New Zealand plate boundary is often described as simply two subduction zones linked by the transpressive Alpine Fault, in actuality the present is merely a snapshot view of an ongoing and complex evolution from convergence to subduction.

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

2007-12-01

3

Composite transform-convergent plate boundaries: description and discussion  

USGS Publications Warehouse

The leading edge of the overriding plate at an obliquely convergent boundary is commonly sliced by a system of strike-slip faults. This fault system is often structurally complex, and may show correspondingly uneven strain effects, with great vertical and translational shifts of the component blocks of the fault system. The stress pattern and strain effects vary along the length of the system and change through time. These margins are considered to be composite transform-convergent (CTC) plate boundaries. Examples are given of structures formed along three CTC boundaries: the Aleutian Ridge, the Solomon Islands, and the Philippines. The dynamism of the fault system along a CTC boundary can enhance vertical tectonism and basin formation. This concept provides a framework for the evaluation of petroleum resources related to basin formation, and mineral exploration related to igneous activity associated with transtensional processes. ?? 1992.

Ryan, H.F.; Coleman, P.J.

1992-01-01

4

Tectonic Plates and Plate Boundaries  

NSDL National Science Digital Library

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

2005-12-17

5

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

6

External Resource: Plate Tectonics: Diverging, Converging, and Transform Boundaries  

NSDL National Science Digital Library

This activity allows learners to explore the meaning of plate tectonics, to distinguish the different layers of the Earth, to model the effects caused by plate movements, to explore the reasons for earthquakes and volcanoes, and to discovering how conver

1900-01-01

7

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

8

Subduction at Convergent Boundary  

NSDL National Science Digital Library

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

9

Holocene turbidites reveal earthquake supercycles at a slow convergence plate boundary (Northern Algeria)  

NASA Astrophysics Data System (ADS)

Ongoing evidence for earthquake clustering calls upon records over numerous earthquake cycles to improve seismic hazard assessments, especially at places where recurrence times overstep historical records. Here, we show that meaningful information of large earthquakes recurrence intervals over several seismic cycles may be obtained using turbidite record offshore the Algerian margin. The Africa-Eurasia plate boundary is slowly convergent (~3mm/yr), with deformation in the investigated margin segment accommodated mainly onland, along thrusts and strike-slip faults. Historically, two relatively large earthquakes stroke the area in 1954 (Orléansville M6.7) and 1980 (El Asnam M7.3). Holocene turbidites emplaced offshore are triggered by thirteen earthquakes. Most of them tune to paleoseismic record of the El Asnam fault onland, whereas two are slightly diachronous (<100 yrs), and likely result from bursts of activity on nearby faults. Turbidites depict a bimodal distribution over ~8 kyrs that support the concepts of earthquake supercycles and rupture synchronization between nearby faults. Thirteen coastal paleoquakes underpin clusters of 3 to 6 events with mean recurrence intervals of ~300-600 years, separated by two periods of quiescence of ~1.7 ka without major events on any fault. They imply alternation of broad phases of strain loading and shorter phases of strain release along the fault network. More generally, our results demonstrate that fault slip rates are time-dependent and that earthquake occurrence might be strain-predictable rather than time- or slip-predictable. Turbidite paleoseismology investigation is ongoing on an adjacent margin segment where the Boumerdes M6.9 earthquake occurred in 2003. Preliminary results retrieved the traces of historical earthquakes, and established Holocene time-series. They support a similar bimodal seismic distribution, suggesting that earthquake supercycling should be a major strain release process along the Africa-Eurasia plate boundary.

Ratzov, Gueorgui; Cattaneo, Antonio; Babonneau, Nathalie; Yelles, Karim; Bracene, Rabah; Lateb, Tassadite; Déverchere, Jacques

2014-05-01

10

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

NSDL National Science Digital Library

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

Anne Egger

2003-03-18

11

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

Microsoft Academic Search

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

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

2005-01-01

12

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

Microsoft Academic Search

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

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

2005-01-01

13

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

E-print Network

of oceanic subduction, (3) an episode of continental subduction, during which the trench absorbs all: Plate boundary-- general (3040); KEYWORDS: subduction, collision, continental subduction, oceanic of an oceanic basin. However, several orders of evidence indicate that arrival at the trench of a continental

14

Tectonic Plates and Plate Boundaries (WMS)  

NSDL National Science Digital Library

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

Eric Sokolowsky

2004-06-14

15

Thermal Structure of Convergent Plate Boundaries Incorporating the Heat of Melting and Crustal Accretion  

NASA Astrophysics Data System (ADS)

Numerical models that include magmatic effects of crustal accretion are used to explore the temperature structure of convergent boundaries. In our models, melt forms at the water saturated solidus near the slab, rises vertically, and freezes in the crust. Freezing also occurs at the water saturated solidus at the top of the mantle wedge. Crustal accretion rates and arc widths are prescribed from the measured thickness of crust and the duration of convergence in well studied convergent boundaries. In our models, the rate of crustal accretion, the depth distribution of magmatic intrusion in the crust, and the total volume of crustal material emplaced are important parameters. However, slab age and dip have relatively small influences on crustal temperatures and heatflow. Crustal temperatures resulting from the combined effects of magmatic accretion and heat advected by flow in the mantle wedge, are comparable to those inferred from metamorphic constraints, with temperatures in the lower crust approaching the water saturated basalt solidus. Calculated surface heat flows also agree with measured values in magmatic arcs. Crustal accretion reduces temperatures in the mantle due to the extraction of latent heat where melt is forming. The downward displacement of mantle associated with burial by emplaced crust also reduces mantle temperatures in the top of the wedge. Mantle temperatures in the top of the wedge are not high enough to reach mantle temperature estimates based on assumed melt-mantle equilibration. Depending on the rate of melt transfer into the crust, some melt generated may freeze in the mantle at the upper water saturated solidus. This may have implications for geochemical constraints on melting. Our models suggest that even with a significant fraction of melt freezing in the upper mantle, flow through the wedge permits only a modest temperature increase.

Walsh, F.; Parmentier, E.

2011-12-01

16

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

NASA Technical Reports Server (NTRS)

The northwesternmost part of the Sagami trough, a part of the Philippine Sea-Eurasian plate boundary, was ruptured during the great South Kanto earthquake in 1923. Very extensive and frequent geodetic measurements of crustal deformation have been made in the South Kanto district since the 1890's, and these constitute the most complete data set on crustal movements in the world. These data were reanalyzed and interpreted and according to our interpretation indicate the following sequence of events. The coseismic movements were due to oblique thrust and right lateral slip of about 8 m on a fault outcropping at the base of the Sagami trough. This was followed by postseismic deformation resulting from reversed afterslip of 20-60 cm that occurred at an exponentially decaying rate in time. The interseismic deformation is produced by steady subduction at a rate of about 1.8 cm/yr. During subduction the top 10-15 km of the plate boundary is apparently locked, while deeper parts slip aseismically at an irregular rate. No significant precursory deformation was observed. The recurrence time for 1923 type earthquakes is 200-300 years. The Boso and Miura peninsulas are broken into a series of fault-bound blocks that move semi-independently of the surrounding region. The subduction zone itself, where it is exposed on land, is shown to be a wide zone encompassing several faults that are active at different times.

Scholz, C. H.; Kato, T.

1978-01-01

17

Characterizing Plate Boundaries  

NSDL National Science Digital Library

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

Bill Hirt

18

Focal Mechanisms at the convergent plate boundary in Southern Aegean, Greece.  

NASA Astrophysics Data System (ADS)

Greece is characterized by high seismicity, mainly due to the collision between the European and the African lithospheric plates and the dextral strike slip motion along the North Anatolia Fault zone and North Aegean Trough. The subduction of the Eastern Mediterranean oceanic plate along the Hellenic Arc under the Aegean microplate along with the accompanied roll back of the descending slab is considered the main tectonic feature of the region (Papazachos and Comninakis 1971; Makropoulos and Burton 1984; Papazachos et al. 2000a, b). The divergent motion between the Aegean block and mainland Europe is indicated by an extension zone in the northern Aegean, with Crete and Aegean diverging from mainland Europe at a rate of about 3.5 cm yr-1 with Africa moving northward relative to Europe at a rate of about 1 cm yr-1 (Dewey et al., 1989; Papazachos et al., 1998; Mc-Clusky et al., 2000; Reilinger et al., 2006). In this tectonically complicated area diverge types of deformation are manifested, in addition to the dominant subduction processes. Aiming to shed more light in the seismotectonic properties and faulting seismological data from the Hellenic Unified Seismological Network (HUSN) were selected and analyzed for determining focal mechanisms using the method of moment tensor inversion, additional to the ones being available from the routine moment tensor solutions and several publications. Thus, 31 new fault plane solutions for events with magnitude M>4.0, are presented in this study, by using the software of Ammon (Randall et al., 1995). For this scope the data from at least 4 stations were used with an adequate azimuthal coverage and with an epicentral distance not more than 350 km. The preparation of the data includes the deconvolution of instruments response, then the velocity was integrated to displacement and finally the horizontal components were rotated to radial and transverse. Following, the signal was inverted using the reflectivity method of Kennett (1983) as implemented by Randall (1994) in order to determine Green's functions. Initially, iterative inversions were performed considering a crude depth interval of 5 km and the relative misfit functions were computed. In a second stage, inversions were performed considering a finer depth interval of 1-2 km around the depth where the lowest misfit was exhibited. During the analysis different velocity models were used (Karagianni et al., 2005; Novotny et al., 2001; Papazachos et al., 1997). This research has been funded by the European Union (European Social Fund) and Greek national resources under the framework of the "THALES Program: SEISMO FEAR HELLARC" project of the "Education & Lifelong Learning" Operational Programme.

Moshou, Alexandra; Papadimitriou, Eleftheria; Drakatos, George; Evangelidis, Christos; Karakostas, Vasilios; Vallianatos, Filippos; Makropoulos, Konstantinos

2014-05-01

19

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.

Michael Kerwin

20

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

21

Visualizing Earthquakes at Convergent Plate Margins  

NSDL National Science Digital Library

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

Cara Harwood

22

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.

23

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

NSDL National Science Digital Library

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

24

Mapping Plate Boundaries  

NSDL National Science Digital Library

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

Rurik Johnson

2009-11-12

25

Discovering Plate Boundaries  

NSDL National Science Digital Library

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

26

Discovering Plate Boundaries  

NSDL National Science Digital Library

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

Dale Sawyer

1997-09-15

27

Seismic gaps and plate tectonics: Seismic potential for major boundaries  

Microsoft Academic Search

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

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

1979-01-01

28

Uplift of Zagros Mountains slows plate convergence  

NASA Astrophysics Data System (ADS)

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

Balcerak, Ernie

2013-05-01

29

The seismotectonics of plate boundaries  

NASA Technical Reports Server (NTRS)

Research on the seismotectonics of plate boundaries is summarized. Instrumental development and an observational program designed to study various aspects of the seismotectonics of southern California and the northern Gulf of California are described. A unique superconducting gravimeter was further developed and supported under this program for deployment and operation at several sites. Work on Earth tides is also discussed.

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

1981-01-01

30

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.

Brian Hampton

31

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

NASA Astrophysics Data System (ADS)

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

Kopf, Achim

2013-11-01

32

Plate Boundary Observatory in Taiwan  

NASA Astrophysics Data System (ADS)

The island of Taiwan is situated in the plate boundary zone between the Eurasian and the Philippine Sea plates. The Philippine Sea plate is subducting northwestward underneath the Eurasian plate along the Ryukyu Trench in the north, while the Eurasian plate underthrusts the Philippine Sea plate along the Manila Trench in the south. Taking advantage of the extremely high strain rate in the Taiwan area, an integrated National Science Council project, Plate Boundary Observatory in Taiwan (PBOT), was initiated following the idea of US PBO. The scientific goal of PBOT is to observe the crustal deformation on various temporal and spatial scales in the Taiwan plate boundary zone employing available state of the art techniques for measuring crustal strain. The techniques include seismology, Global Positioning System (GPS), Interferometric Synthetic Aperture Radar (InSAR), borehole strainmeter, and earthquake geology. They are complementary to each other and form a complete spectrum of measuring various periods of crustal strain. The process of crustal deformation is generally quite slow. To obtain a reliable result, we usually need to persist in the observations for several years or even decades. Thus the PBOT should be a long-term project. In the first phase of 3 years period from 2003 to 2006, we will focus on the two areas, i.e. the plate suture zone in the Longitudinal Valley area and the western Taiwan where the higher seismic hazard is expected. A five-year national program, entitled ­Program for Earthquake and Active-fault Research (PEAR)­" was initiated after the disastrous 1999 Chi-Chi earthquake (Mw 7.6). As part of the PEAR, a dense continuous GPS array consisting of 150 new and about 50 pre-existing stations will be completed in the Taiwan area by the end of 2005 through a joint effort by the Central Weather Bureau and the Institute of Earth Sciences, Academia Sinica. The 50 new stations are going to be evenly distributed around the Taiwan Island. The other 100 stations will be densely deployed near the major active faults and potential earthquake source areas. The enormous continuous GPS data collected by the array will give us the unprecedented opportunity to study the crustal deformation in Taiwan. The near real time spatial and temporal variations of crustal strain can be realized and their correlation with seismic activity will be studied. Using GPS data from the dense array, the slow slip events related to fault-creep and subduction may be detected. In the event of a major earthquake, the continuous GPS array provides the precise measurements of preseismic, coseismic, and postseismic deformations. It may shed light on the process of strain accumulation and energy release through an earthquake cycle. The present-day fault-slip rates of major active faults in Taiwan will be estimated. These results provide the important information for seismic risk analysis and lead to the effective reduction of earthquake disaster

Yu, S.; Tsai, C.

2003-12-01

33

Introduction to the special issue on convergent plate margin dynamics Convergent plate margins are arguably the most complicated and  

E-print Network

Preface Introduction to the special issue on convergent plate margin dynamics Convergent plate in this special issue provide many new insights into a variety of geological, geophysical and geodynamical buoyancy forces across the passive margin (Mart et al., 2005; Goren et al., 2008). In this special issue

Rawlinson, Nick

34

Introduction Myanmar, also known as Burma, is located at the plate boundary between the Indian and  

E-print Network

the Indian and Sunda plates. It is one of the most tectonically active regions in Southeast Asia. During1 Chapter 1 Introduction Myanmar, also known as Burma, is located at the plate boundary between-going oblique convergence and extrusion processes between the Indian, Eurasian and Sunda plates. Although

Winfree, Erik

35

Convergent plate margin dynamics: New perspectives from structural geology, geophysics and geodynamic modelling  

NASA Astrophysics Data System (ADS)

Convergent plate margins occur when two adjoining tectonic plates come together to form either a subduction zone, where at least one of the converging plates is oceanic and plunges beneath the other into the mantle, or a collision zone, where two continents or a continent and a magmatic arc collide. Convergent plate margins are arguably the most complicated and dynamic plate boundaries on Earth and have been the subject of many investigations and discussions since the advent of plate tectonic theory. This paper provides a historical background and a review of the development of geological and geodynamic theories on convergent plate margins. Furthermore, it discusses some of the recent advances that have been made in the fields of structural geology, geophysics and geodynamics, which are fundamental to our understanding of this phenomenon. These include: (1) the finding that plates and plate boundaries move at comparable velocities across the globe; (2) the emerging consensus that subducted slabs are between two to three orders of magnitude stronger than the ambient upper mantle; (3) the importance of lateral slab edges, slab tearing and toroidal mantle flow patterns for the evolution of subduction zones; and (4) clear evidence from mantle tomography that slabs can penetrate into the lower mantle. Still, many first-order problems regarding the geodynamic processes that operate at convergent margins remain to be solved. These include subduction zone initiation and the time of inception of plate tectonics, and with it convergent plate margins, on Earth. Fundamental problems in orogenesis include the mechanism that initiated Andean mountain building at the South American subduction zone, the potential episodicity of mountain building with multiple cycles of shortening and extension, and the principal driving force behind the construction of massive mountain belts such as the Himalayas-Tibet and the Andes. Fundamental questions in subduction dynamics regard the partitioning of subduction into a trench and plate component, and the distribution of energy dissipation in the system. In seismic imaging, challenges include improving resolution at mid to lower mantle depth in order to properly understand the fate of slabs, and better constraining the 3-D flow-related anisotropic structure in the surrounding mantle. Future insights into such fundamental problems and into the regional and global dynamics of convergent plate margins will likely be obtained from integrating spatio-temporal data, structural geological data, geophysical data and plate kinematic data into plate tectonic reconstructions and three-dimensional geodynamic models of progressive deformation.

Schellart, W. P.; Rawlinson, N.

2010-03-01

36

Question of the Day: Plate Boundary Characteristics  

NSDL National Science Digital Library

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

37

Statistical tests of additional plate boundaries from plate motion inversions  

NASA Technical Reports Server (NTRS)

The application of the F-ratio test, a standard statistical technique, to the results of relative plate motion inversions has been investigated. The method tests whether the improvement in fit of the model to the data resulting from the addition of another plate to the model is greater than that expected purely by chance. This approach appears to be useful in determining whether additional plate boundaries are justified. Previous results have been confirmed favoring separate North American and South American plates with a boundary located beween 30 N and the equator. Using Chase's global relative motion data, it is shown that in addition to separate West African and Somalian plates, separate West Indian and Australian plates, with a best-fitting boundary between 70 E and 90 E, can be resolved. These results are generally consistent with the observation that the Indian plate's internal deformation extends somewhat westward of the Ninetyeast Ridge. The relative motion pole is similar to Minster and Jordan's and predicts the NW-SE compression observed in earthquake mechanisms near the Ninetyeast Ridge.

Stein, S.; Gordon, R. G.

1984-01-01

38

The Rivera-Cocos Plate Boundary Revisited  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

39

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

E-print Network

1 Boundary knot method: A meshless, exponential convergence, integration-free, and boundary an inherently meshless, exponential convergence, integration-free, boundary-only collocation techniques, and meshless (meshfree). However, the use of artificial boundary outside physical domain has been a major

40

Convergent plate margin dynamics: New perspectives from structural geology, geophysics and geodynamic modelling  

E-print Network

: Convergent plate margin Subduction Collision Orogenesis Slab Plate tectonics Convergent plate margins occur when two adjoining tectonic plates come together to form either a subduction zone, where at least one and discussions since the advent of plate tectonic theory. This paper provides a historical background

Rawlinson, Nick

41

Viscoelastic deformation near active plate boundaries  

NASA Technical Reports Server (NTRS)

Model deformations near the active plate boundaries of Western North America using space-based geodetic measurements as constraints are discussed. The first six months of this project were spent gaining familarity with space-based measurements, accessing the Crustal Dynamics Data Information Computer, and building time independent deformation models. The initial goal was to see how well the simplest elastic models can reproduce very long base interferometry (VLBI) baseline data. From the Crustal Dynamics Data Information Service, a total of 18 VLBI baselines are available which have been surveyed on four or more occasions. These data were fed into weighted and unweighted inversions to obtain baseline closure rates. Four of the better quality lines are illustrated. The deformation model assumes that the observed baseline rates result from a combination of rigid plate tectonic motions plus a component resulting from elastic strain build up due to a failure of the plate boundary to slip at the full plate tectonic rate. The elastic deformation resulting from the locked plate boundary is meant to portray interseismic strain accumulation. During and shortly after a large interplate earthquake, these strains are largely released, and points near the fault which were previously retarded suddenly catch up to the positions predicted by rigid plate models. Researchers judge the quality of fit by the sum squares of weighted residuals, termed total variance. The observed baseline closures have a total variance of 99 (cm/y)squared. When the RM2 velocities are assumed to model the data, the total variance increases to 154 (cm/y)squared.

Ward, S. N.

1986-01-01

42

The strength of large-scale plate boundaries: Constraints from the dynamics of the Philippine Sea plate since ~5 Ma  

NASA Astrophysics Data System (ADS)

Friction controls most of the strength of tectonic plate boundaries, and thus the force mutually exchanged between plates. Estimates of the plate-boundary friction-coefficient are therefore of paramount importance to our understanding of the lithosphere torque balance. However, several lines of evidence indicate that the friction-coefficient of plate margins is significantly lower than is measured in laboratory experiments performed on fractured rocks. This poses a significant limit to extrapolation from the laboratory scale to the large-scale of Earth's lithosphere. The record of past and present-day plate motions represents an efficient probe into the torque balance of plate tectonics, because plate-motions readjust virtually instantaneously to temporal changes in driving and resisting forces. Here I derive inferences on the strength of large-scale plate boundaries by focusing on the convergence of the fast-moving Philippine Sea plate towards Eurasia, since subduction initiation ~5 Myr ago. Because at the present-day the Philippine slab reaches depths shallower than the 410-km transition zone in the upper mantle, its weight is unlikely to provide sufficient driving force to shear the trailing plate over the viscous mantle at the observed rates. Using global models of the coupled mantle/lithosphere system, I argue that frictional coupling with the Pacific and Eurasia plates is the main driver for the dynamics of the Philippine Sea plate. This allows me to infer that the friction-coefficient of large-scale plate boundaries is in range 0.01 to 0.07, and that the amount of sediments entering plate margins efficiently modulates the friction-coefficient, contributing significantly to its lateral variations. Importantly, I corroborate my conclusions by focusing on the present-day vertical deformation of the Philippine Sea/Eurasia margin, evident from observed trench-parallel gravity anomalies.

Iaffaldano, G.

2012-12-01

43

The strength of large-scale plate boundaries: Constraints from the dynamics of the Philippine Sea plate since ˜5 Ma  

NASA Astrophysics Data System (ADS)

Friction controls most of the strength of tectonic plate boundaries, and thus the force mutually exchanged between plates. Estimates of the plate-boundary friction-coefficient are therefore of paramount importance to our understanding of the lithosphere torque balance. However, several lines of evidence indicate that the friction-coefficient of plate margins is significantly lower than is measured in laboratory experiments on fractured rocks. This poses a significant limit to extrapolation from the laboratory scale to the large-scale of Earth's lithosphere. The record of past and present-day plate motions represents an efficient probe into the torque balance of plate tectonics, because plate-motions readjust virtually instantaneously to temporal changes in driving and resisting forces. Here I derive inferences on the strength of large-scale plate boundaries by focusing on the convergence of the fast-moving Philippine Sea plate towards Eurasia, since subduction initiation ˜5 Myr ago. Because at the present-day the Philippine slab reaches depths shallower than the 410-km transition zone in the upper mantle, its weight is unlikely to provide sufficient driving force to shear the trailing plate over the viscous mantle at the observed rates. Using global models of the coupled mantle/lithosphere system, I argue that frictional coupling with the Pacific and Eurasia plates is the main driver for the dynamics of the Philippine Sea plate. This allows me to infer that the friction-coefficient of large-scale plate boundaries is in range 0.01-0.07, and that the amount of sediments entering plate margins efficiently modulates the friction-coefficient, contributing significantly to its lateral variations. Importantly, I corroborate my conclusions by looking at the present-day vertical deformation of the Philippine Sea/Eurasia margin, evident from observed trench-parallel gravity anomalies.

Iaffaldano, Giampiero

2012-12-01

44

Plate TectonicsPlate Tectonics Plate TectonicsPlate Tectonics  

E-print Network

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

Siebel, Wolfgang

45

Crustal deformation and volcanism at active plate boundaries  

NASA Astrophysics Data System (ADS)

Most of Earth's volcanoes are located near active tectonic plate boundaries, where the tectonic plates move relative to each other resulting in deformation. Likewise, subsurface magma movement and pressure changes in magmatic systems can cause measurable deformation of the Earth's surface. The study of the shape of Earth and therefore studies of surface deformation is called geodesy. Modern geodetic techniques allow precise measurements (˜1 mm accuracy) of deformation of tectonic and magmatic systems. Because of the spatial correlation between tectonic boundaries and volcanism, the tectonic and volcanic deformation signals can become intertwined. Thus it is often important to study both tectonic and volcanic deformation processes simultaneously, when one is trying to study one of the systems individually. In this thesis, I present research on crustal deformation and magmatic processes at active plate boundaries. The study areas cover divergent and transform plate boundaries in south Iceland and convergent and transform plate boundaries in Central America, specifically Nicaragua and El Salvador. The study is composed of four main chapters: two of the chapters focus on the magma plumbing system of Hekla volcano, Iceland and the plate boundary in south Iceland; one chapter focuses on shallow controls of explosive volcanism at Telica volcano, Nicaragua; and the fourth chapter focuses on co- and post-seismic deformation from a Mw = 7.3 earthquake which occurred offshore El Salvador in 2012. Hekla volcano is located at the intersection of a transform zone and a rift zone in Iceland and thus is affected by a combination of shear and extensional strains, in addition to co-seismic and co-rifting deformation. The inter-eruptive deformation signal from Hekla is subtle, as observed by a decade (2000-2010) of GPS data in south Iceland. A simultaneous inversion of this data for parameters describing the geometry and source characteristics of the magma chamber at Hekla, and geometry and secular rates across the plate boundary segments, reveals a deep magma chamber under Hekla and gives a geodetic estimate of the current location of the North-America Eurasian plate boundary in south Iceland. Different geometries were tested for Hekla's magma chamber: spherical, horizontally elongated ellipsoidal, and pipe-like magma chambers. The data could not reliably distinguish the actual geometry; however, all three models indicate magma accumulation near the Moho (˜20-25 km) under Hekla. The February -- March 2000 eruption of Hekla gave another opportunity to image the magmatic system. In Chapter 5, I used co-eruptive GPS and InSAR displacements, borehole strain, and tilt measurements to jointly invert for co-eruptive deformation associated with the 2000 eruption and found a depth of approximately 20 km for the magma chamber, in accordance with my previous results. Telica is a highly seismically active volcano in Nicaragua. The seismicity is mostly of shallow (<2 km deep) origin, and shows a high variability in terms of the number of seismic events per time unit. The highest rates exceed one earthquake per minute averaged over 24 hours, but overall trends in seismic activity, as observed since 1993, do not have an obvious correlation with eruptive activity. This variability causes difficulties for hazard monitoring of Telica. Telica erupted in a small (VEI 2) explosive eruption in 2011. Eruptions of this style and size seem to occur on decadal time scales at Telica. In Chapter 3, I used an extensive multidisciplinary data set consisting of seismic and GPS data, multivariate ash analysis, SO2 measurements, fumarole temperatures, and visual observations, to show that the eruption was essentially an amagmatic eruption of hydrothermally altered materials from the conduit, and that short-term sealing of hydrothermal pathways led to temporary pressure build-up, resulting in the explosions. No significant crustal deformation was detected before or during the eruption, in accordance with low (<2 km) plume heights and small (<105 m3) eruptive

Geirsson, Halldor

46

Diffuse oceanic plate boundaries: Strain rates, vertically averaged rheology, and comparisons with narrow plate boundaries and stable plate interiors  

NASA Astrophysics Data System (ADS)

Diffuse plate boundaries occur in both oceanic and continental lithosphere and cover ? 15% of Earth's solid surface. The fastest plate speeds accommodated across diffuse oceanic plate boundaries are ? 15 mm/yr. The smallest strain rates averaged across narrow plate boundaries are at least 102 times larger than the largest strain rates across diffuse oceanic plate boundaries and at least 102 times larger than those across stable plate interiors. The effective viscosity (?eff) of the lithosphere is estimated from the ratio of vertically averaged shear stresses to strain rates for three tectonic settings: (i) oceanic transform fault zones, for which ?eff = 3 ×1016 to 5×1019 Pa s, comparable to estimates for the asthenosphere, (ii) diffuse oceanic plate boundaries, for which ?eff = 1×1023 to 6×l023 Pa s, ? 10 times larger than for diffuse continental plate boundaries, and (iii) stable plate interiors, for which ?eff = 1x1024 to 2×1027 Pa s. The rheology of oceanic lithosphere over times longer than earthquake cycles is modeled as a plastic layer overlying a layer that deforms by creeping flow [Martinod and Davy, 1992]. Oceanic lithosphere deforms when the yield strength of the upper lithosphere is exceeded. The vertically averaged rheology of deforming oceanic lithosphere can be approximated by a power-law fluid for which ?. ? (?s)n where ?. is the rate of shear strain and ?s is the shear stress. If the ratio of the yield strength of the upper lithosphere to the force required to deform the lower lithosphere at a strain rate of 10-16 s-1 is varied from 10-2 to 102 , the calculated value of n varies from ?3 to ?300. The map-view aspect ratio of a deforming zone in a thin sheet of power-law fluid is proportional to n-½ [England et al., 1985]. A profile of displacement versus distance inferred from a seismic profile across the Central Indian Basin (India-Capricorn diffuse oceanic plate boundary), where the lithosphere is about 60-Myr old, indicates that the lithosphere is being deformed in response to a rigid moving boundary near the north end of the basin. If so, the vertically averaged rheology of the lithosphere in the Central Indian Basin is described by a power-law fluid with n?8, which suggests that the yield strength of the upper lithosphere is a few times larger than the force required to deform the lower lithosphere. Owing to a lack of data, other diffuse oceanic plate boundaries can at best be interpreted qualitatively. Whereas the total aspect ratios (total along-strike length / total across-strike width) for diffuse oceanic plate boundaries in 60- to 90-Myr-old lithosphere are 1.25-1.8, they are 0.73-0.82 in young lithosphere adjacent to an active mid-ocean ridge, The latter aspect ratios suggest smaller values of n, indicating a relatively weaker brittle upper lithosphere relative to the force required to deform the lower lithosphere, similar to results for diffuse continental plate boundaries, for which n?3 [England and Molnar, 1991]. In contrast, the East Africa Rift has a large aspect ratio, 2.3, which suggests its lithosphere behaves more like 60- to 90-Myr-old oceanic lithosphere than like other diffuse continental plate boundaries.

Gordon, Richard G.

47

Three-Dimensional Particle Dynamics Simulations of Oblique Plate Convergence Using Bonded Particle Assemblages  

NASA Astrophysics Data System (ADS)

Many convergent boundaries around the world exhibit significant curvature (e.g., Himalayas, Caribbean Arc, Aleutian arc), resulting in spatially varying convergence directions. The along-strike transitions from normal convergence to oblique convergence can produce a range of deformation structures reflecting the degree of strain partitioning along the boundary, including strike-parallel extension and strike-slip faulting. To explore the geometry and controls on these structures in more detail, and to better resolve the stresses and strains responsible for such deformation, we have carried out three-dimensional particle dynamics simulations using the discrete element method (DEM). Simulations are carried out in a numerical sandbox scaled to 20 km wide by 60 km long. A curved vertical wall of particles defines the backstop, which emerges through a fixed planar wall of particles into a layer of particles sedimented under gravity. Furthermore, particles have been bonded together to simulate cohesive rock, allowing brittle failure to occur and persistent faults to develop. The geometries and slip directions of these deformation structures can be resolved in detail using visualization tools provided by Generic Mapping Tools (GMT) and Earth Vision (EV). We extract and display specific particle properties (e.g., displacements and strains) and assemblage attributes (e.g., stress components) to fully interpret and analyze the deformation history and stress evolution of the growing wedge. Spaced imbricate thrust faults develop at the head of the backstop, where convergence is normal, whereas distinct strike-slip faults develop along the lateral margins. As expected, the oblique convergent zones exhibit more complicated deformation, including dip-slip faults and en-echelon extensional fault arrays. We compare the emergent structures with examples from analogous plate boundaries to assess the validity of the models.

Tate, G. W.; Morgan, J. K.

2008-12-01

48

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

49

The transpressive tectonics and large earthquake distribution along the plate boundary in North Africa  

NASA Astrophysics Data System (ADS)

The Tell Atlas and Rif Mountains of northern Africa have been the site of several large and moderate seismic events in the last decades. However, the thrust and fold system of NW Algeria experienced the largest earthquakes in the last centuries along the Africa-Eurasia plate boundary. This shallow seismic activity was very often associated with surface faulting and deformation as for the Mw 7.3 El Asnam (10/10/1980) and the Mw 6.8 Zemmouri-Boumerdes (21/05/2003) earthquakes. We study the active tectonics along the plate boundary in North Africa from the seismicity database, individual large and moderate earthquakes, the seismic moment tensor summation, the geodetic measurements (GPS and InSAR) and the structural and kinematic of active faults. Neotectonic structures and significant seismicity (Mw>5) indicate that coeval east-west trending right-lateral faulting and NE-SW thrust-related folding result from the oblique convergence at the plate boundary. A simple modeling of block tectonics suggests that transpression and block rotation govern the mechanics of the Africa - Eurasia plate boundary in the Tell Atlas and Rif Mountains. The tectonic restraining bend of NW Algeria combined with the ~ 5 mm/yr convergence between Africa and Eurasia justify the large seismic activity on the thrust and fold system of the Tell Atlas and the relatively passive active deformation along the adjacent sections of the plate boundary.

Meghraoui, Mustapha; Pondrelli, Silvia

2010-05-01

50

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

E-print Network

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

Cerveny, Vlastislav

51

Earthquakes, Plate Boundaries, and Depth Indiana Standard Indicators  

E-print Network

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

Polly, David

52

The Plate Boundary Observatory: Data Management Progress and Highlights  

Microsoft Academic Search

The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, is designed to study the three- dimensional strain field resulting from deformation across the active boundary zone between the Pacific and North American plates in the western United States. To meet these goals, UNAVCO will install 880 continuous GPS stations, 103 borehole strainmeter stations, 28 tiltmeters, and five laser

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

2007-01-01

53

Identifying Plate Tectonic Boundaries for a Virtual Ocean Basin  

NSDL National Science Digital Library

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

Stephen Reynolds

54

Structures and kinematics in the northeastern Mediterranean: A study of an irregular plate boundary  

NASA Astrophysics Data System (ADS)

Extensional structures are prominent in the northeastern Mediterranean, a unique sector of the Africa-Eurasia plate convergence zone. To explain this paradoxical situation, we analyse here the young tectonics of this region by examining its structural elements and plate kinematics. Offshore multichannel seismic reflection profiles and onland geology show that the stuctural settings are different on the two sides of the northeastern Mediterranean triple junction (AFR-ARB-ANA). On the east, stuctures controlled by strike-slip and by compression coexist, whereas on the west compression is not very conspicuous. Here, deep basins separated by a partly submerged ridge are prominent. We interpret the ridge, which comprises the Kyrenia- Misis-Andirin Unit at its core, as a large flower structure which extends from southeastern Turkey to Cyprus; the Adana-Cilicia and the Iskenderun-Latakia-Mesaoria Basins on its flanks are interpreted as due to extension. This interpretation agrees with the relative motions between the Africa, Arabia, Eurasia and Anatolia plates in this region. Analysis of the local plate kinematics reveals that strike-slip predominates along the southern boundary of the Anatolia plate in this region, as a result of Anatolia's westward escape. East of the triple junction this motion is associated with comparable shortening transverse to the plate boundary, whereas west of the triple junction the motion transverse to the plate boundary varies between slight compression to extension, depending mainly on the local strike of the plate boundaries. These variations, calculated from regional data, correlate well with the observed structural changes along the northeastern Mediterranean sector of the plate convergence zone. The structural-kinematic analysis explains both the lateral changes in the deformation style and the existence of local extension in the northeastern Mediterranean.

Kempler, Ditza; Garfunkel, Zvi

1994-06-01

55

Submarine Volcanic Cones in the Central Aleutian Arc: Relationship to Arc Rifting and Oblique Plate Convergence  

NASA Astrophysics Data System (ADS)

Plate convergence along the 2200km Aleutian Arc varies from orthogonal at the Alaskan Peninsula to fully strike-slip on the west end of the arc. Deformation response of the upper plate to oblique convergence appears to accelerate markedly between Adak (177W) and Amchitka Pass (180W). On a regional scale, this deformation appears to be concentrated at the boundaries of crustal blocks, with clockwise rotation and westward translation [Geist et al., Tectonics 7, 327-341, 1988]. In the block rotation model, extensional rift structures develop between the blocks in arc-normal orientation. Summit basins develop at the northern, trailing edge of the blocks in arc-parallel orientation. These summit basins are located near or within the volcanic front. Thus structures in the upper plate driven by oblique convergence are predicted to interact with arc volcanism. We report on multibeam mapping in 2003-2004 and ROV Jason II dives in 2004. The data reveal locations and patterns of fault structures, volcanic cones, and lithologies in several locations critical to understanding the arc's response to oblique convergence. A large submarine volcano, named Amchixtam Chaxsxii in the Unangan language, was mapped next to Semisopochnoi Island. Additional small cones are identified on the flank of Tanaga Volcano, and near Bobrof Volcano on possible fault structures. The largest extensional `block boundary' is located at Amchitka Pass; in this area the seafloor is offset by a network of faults. Small volcanic cones are clustered at these faults. Some show signs of erosion and mass wasting; others, especially deeper ones, are intact. Surfaces are dominated by `a`a flows and spatter, and have light sediment cover and moderately fresh lavas. Our mapping focused on specific sites that were chosen to be representative, and suggests that (1) small, probably monogenetic cones are common; (2) the cones occur preferentially in areas of extensional faulting in the volcanic front; (3) these cones are present largely because of oblique convergence and arc deformation. Geochemical analyses will test their relationship to nearby subaerial arc volcanoes.

Reynolds, J. R.; Greene, G.; Krutikov, L.; Vallier, T. L.

2004-12-01

56

Statistical tests of additional plate boundaries from plate motion inversions  

Microsoft Academic Search

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

Seth Stein; R. G. Gordon

1984-01-01

57

Study on plate silencer with general boundary conditions  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

58

Macrobrecciation at a Plate Boundary: The Iskenderun Block  

NASA Astrophysics Data System (ADS)

The area of intersection of the East Anatolian and the Dead Sea fault zones in southeast Turkey and northwest Syria represents the intersection of three tectonic Plates: African,Anatolian, and Arabian. Widespread deformation occurs in the area of the plate triple junction including the presence of multiple faults bounding plate fragments along the plate tectonic boundaries. Earthquake fault plane solutions and epicenter clustering in the area of the intersectiong fault zones has been used to identify plate fragments. This study delineates a plate boundary near the mouth of the Gulf of Iskenderun based on linear trends in epicenters and the orientation of fault plane solution nodal planes. The boundary located near the mouth of the Gulf of Iskenderun is proposed to be the southern boundary of a plate fragment roughly the size of the state of Delaware, herein named the Iskenderun block. Plate motions and moho depths suggest that the Iskenderun block is a promontory that was originally joined to the African plate and has been caught up in the deformation at the Anatolian-Arabian-African triple junction and has been subsequently torn from the African plate.

Sine, C. R.; Brumbaugh, D. S.

2004-12-01

59

Partial and Complete Rupture of the Indo-Andaman Plate Boundary 1847-2004  

Microsoft Academic Search

We review seismicity along the Nicobar\\/Andaman plate boundary prior to the Mw=9 earthquake of 26 December 2004, with particular attention to reverse slip in the central and northern parts of the rupture zone 600-1300 km north from the epicenter. Slip is partitioned between convergence and strike-slip motion, which in the northern Andamans is assisted by back-arc spreading. Subduction zone earthquakes

R. Bilham; R. Engdahl; N. Feldl; S. P. Satyabala

2005-01-01

60

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

61

Distributed Roughness Receptivity in a Flat Plate Boundary Layer  

E-print Network

manufactured using rapid prototyping and installed flush with the wall in a flat plate boundary layer. The main objective was to compare the wakes of the discrete roughness and the combined roughness to examine if the distributed roughness shields...

Kuester, Matthew Scott

2014-04-18

62

Calibrated Plate Boundary Observatory Borehole Strainmeter Data  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

63

Diffuse Plate Boundary Seismicity and Triple Junction Stability  

NASA Astrophysics Data System (ADS)

Diffuse plate boundaries extend over broad deformation zones hundreds to thousands of kilometers wide. For example, the boundaries are diffuse between Australia and India, North America and South America, and Nubia and Somalia. Relative velocities are slow across these regions because the pole of rotation for the plate pair is located within or near the diffuse plate boundary. This geometry causes extension on one side and compression on the other side of the pole; earthquake focal mechanisms confirm this observation. Diffuse triple junctions exist where a diffuse plate boundary meets a regular narrow plate boundary. Diffuse triple junction stability can be assessed by extending the McKenzie and Morgan (Nature, 1969) velocity vector method. In this method, lines on a map represent narrow plate boundaries and a triangle of vectors indicates relative motions between plates. In contrast, a diffuse (D) plate boundary differs from a narrow ridge (R), transform fault (F), or trench (T); it cannot be represented as a single line on a map or a unique vector on a velocity vector diagram. Because ongoing deformation is distributed over a broad zone, the diffuse boundary is drawn as a broad zone on the velocity vector diagram, and a range of stability lines is necessary to represent motions that remain in this zone. This "stability zone" usually encompasses the stability lines of the remaining two plate boundaries where they intersect. This indicates that diffuse triple junctions are stable for a wide range of plate boundary orientations. For example, in a standard velocity vector diagram, the three plate boundaries meeting at the Australia-Eurasia-India triple junction are represented as trenches. The diffuse Australia-India plate boundary, however, may be drawn along an edge or through the center of the diffuse deformation zone. On a velocity vector diagram, the diffuse plate boundary is represented as a broad "stability zone" extending between the northern and southern edges of the diffuse deformation. Because the stability zone encompasses the intersecting lines representing the other two plate boundaries, this trench-trench-diffuse (TTD) triple junction is stable. The diffuse plate boundary extends west to the Central Indian ridge where it forms either a ridge-ridge-diffuse (RRD), ridge-fault-diffuse (RFD), or fault-fault-diffuse (FFD) triple junction. All combinations are stable. Similarly, the Caribbean-North America-South America TTD triple junction and all RRD, RFD, and FFD combinations at the Africa-North America-South America triple junction are stable. The RFD and FFD triple junction combinations are stable for an Antarctica-Nubia-Somalia triple junction extending between 26 and 32 degrees east along the Southwest Indian ridge. The RRD geometry is stable through most of this region, but is unstable near 26 degrees east.

Wetzel, L. R.; Frohlich, C.

2005-12-01

64

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

65

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

PubMed

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

Apperson, K D

1991-11-01

66

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

67

A diffuse plate boundary model for Indian Ocean tectonics  

NASA Technical Reports Server (NTRS)

It is suggested that motion along the virtually aseismic Owen fracture zone is negligible, so that Arabia and India are contained within a single Indo-Arabian plate divided from the Australian plate by a diffuse boundary. The boundary is a zone of concentrated seismicity and deformation commonly characterized as 'intraplate'. The rotation vector of Australia relative to Indo-Arabia is consistent with the seismologically observed 2 cm/yr of left-lateral strike-slip along the Ninetyeast Ridge, north-south compression in the Central Indian Ocean, and the north-south extension near Chagos.

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

1985-01-01

68

Dynamic behaviour of thin composite plates for different boundary conditions  

NASA Astrophysics Data System (ADS)

In the context of composite materials technology, which is increasingly present in industry, this article covers a topic of great interest and theoretical and practical importance. Given the complex design of fiber-reinforced materials and their heterogeneous nature, mathematical modeling of the mechanical response under different external stresses is very difficult to address in the absence of simplifying assumptions. In most structural applications, composite structures can be idealized as beams, plates, or shells. The analysis is reduced from a three-dimensional elasticity problem to a oneor two-dimensional problem, based on certain simplifying assumptions that can be made because the structure is thin. This paper aims to validate a mathematical model illustrating how thin rectangular orthotropic plates respond to the actual load. Thus, from the theory of thin plates, new analytical solutions are proposed corresponding to orthotropic rectangular plates having different boundary conditions. The proposed analytical solutions are considered both for solving equation orthotropic rectangular plates and for modal analysis.

Sprintu, Iuliana; Rotaru, Constantin

2014-12-01

69

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

PubMed

On 1 April 2007 a great, tsunamigenic earthquake (moment magnitude 8.1) ruptured the Solomon Islands subduction zone at the triple junction where the Australia and Solomon Sea-Woodlark Basin plates simultaneously underthrust the Pacific plate with different slip directions. The associated abrupt change in slip direction during the great earthquake drove convergent anelastic deformation of the upper Pacific plate, which generated localized uplift in the forearc above the subducting Simbo fault, potentially amplifying local tsunami amplitude. Elastic deformation during the seismic cycle appears to be primarily accommodated by the overriding Pacific forearc. This earthquake demonstrates the seismogenic potential of extremely young subducting oceanic lithosphere, the ability of ruptures to traverse substantial geologic boundaries, and the consequences of complex coseismic slip for uplift and tsunamigenesis. PMID:19359581

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

2009-04-10

70

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

71

The lithospheric geodynamics of plate boundary transpression in New Zealand: Initiating and emplacing subduction along the Hikurangi margin, and the tectonic evolution of the Alpine Fault system  

NASA Astrophysics Data System (ADS)

In contrast to the normal 'Wilson cycle' sequence of subduction leading to continental collision and associated mountain building, the evolution of the New Zealand plate boundary in the Neogene reflects the converse—initially a period of continental convergence that is followed by the emplacement of subduction. Plate reconstructions allow us to place limits on the location and timing of the continental convergence and subduction zones and the migration of the transition between the two plate boundary regimes. Relative plate motions and reconstructions since the Early to Mid-Miocene require significant continental convergence in advance of the emplacement of the southward migrating Hikurangi subduction—a sequence of tectonism seen in the present plate boundary geography of Hikurangi subduction beneath North Island and convergence in the Southern Alps along the Alpine Fault. In contrast to a transition from subduction to continental convergence where the leading edge of the upper plate is relatively thin and deformable, the transition from a continental convergent regime, with its associated crustal and lithospheric thickening, to subduction of oceanic lithosphere requires substantial thinning (removal) of upper plate continental lithosphere to make room for the slab. The simple structure of the Wadati-Benioff zone seen in the present-day geometry of the subducting Pacific plate beneath North Island indicates that this lithospheric adjustment occurs quickly. Associated with this rapid lithospheric thinning is the development of a series of ephemeral basins, younging to the south, that straddle the migrating slab edge. Based on this association between localized vertical tectonics and slab emplacement, the tectonic history of these basins records the effects of lithospheric delamination driven by the southward migrating leading edge of the subducting Pacific slab. Although the New Zealand plate boundary is often described as simply two subduction zones linked by the transpressive Alpine Fault, in actuality the present is merely a snapshot view of an ongoing and complex evolution from convergence to subduction.

Furlong, Kevin P.; Kamp, Peter J. J.

2009-09-01

72

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

NASA Astrophysics Data System (ADS)

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

Eagles, Graeme; Scott, Benjamin G. C.

2014-12-01

73

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

E-print Network

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

Till, Christy B

2011-01-01

74

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

NASA Technical Reports Server (NTRS)

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

Fitch, T. J.

1971-01-01

75

Linking mantle dynamics, plate tectonics and surface processes in the active plate boundary zones of eastern New Guinea (Invited)  

NASA Astrophysics Data System (ADS)

Eastern New Guinea lies within the rapidly obliquely converging Australian (AUS)- Pacific (PAC) plate boundary zone and is characterized by transient plate boundaries, rapidly rotating microplates and a globally significant geoid high. As the AUS plate moved northward in the Cenozoic, its leading edge has been a zone of subduction and arc accretion. The variety of tectonic settings in this region permits assessment of the complex interplay among mantle dynamics, plate tectonics, and surface processes. Importantly, the timescale of tectonic events (e.g., subduction, (U)HP exhumation, seafloor spreading) are within the valid bounds of mantle convection models. A record of changes in bathymetry and topography are preserved in high standing mountain belts, exhumed extensional gneiss domes and core complexes, uplifted coral terraces, and marine sedimentary basins. Global seismic tomography models indicate accumulation of subducted slabs beneath eastern New Guinea at the bottom of the upper mantle (i.e., <660km depth). Some of the deeply subducted material may indeed be buoyant subducted AUS continental margin (to depths of ~250-300 km), as well as subducted continental material that has reached the point of no return (i.e., > 250-300 km). Preliminary global-scale backward advected mantle convection models, driven by density inferred from joint seismic-geodynamic tomography models, exhibit large-scale flow associated with these subducted slab remnants and predict the timing and magnitude (up to 1500 m) of dynamic topography change (both subsidence and uplift) since the Oligocene. In this talk we will explore the effects of large-scale background mantle flow and plate tectonics on the evolution of topography and bathymetry in eastern New Guinea, and discuss possible mechanisms to explain basin subsidence and surface uplift in the region.

Baldwin, S.; Moucha, R.; Fitzgerald, P. G.; Hoke, G. D.; Bermudez, M. A.; Webb, L. E.; Braun, J.; Rowley, D. B.; Insel, N.; Abers, G. A.; Wallace, L. M.; Vervoort, J. D.

2013-12-01

76

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

PubMed Central

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

Qin, Zhengrong; Wang, Qingshan

2014-01-01

77

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

Microsoft Academic Search

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

S. E. Olds

2010-01-01

78

Crustal motion studies in the southwest Pacific: Geodetic measurements of plate convergence in Tonga, Vanuatu and the Solomon Islands  

NASA Astrophysics Data System (ADS)

The southwest Pacific is one of the most tectonically dynamic regions on Earth. This research focused on crustal motion studies in three regions of active Pacific-Australia plate convergence in the southwest Pacific: Tonga, the New Hebrides (Vanuatu) and the Solomons Islands. In Tonga, new and refined velocity estimates based on more than a decade of Global Positioning System (GPS) measurements and advanced analysis techniques are much more accurate than previously reported values. Convergence rates of 80 to 165 mm/yr at the Tonga trench represent the fastest plate motions observed on Earth. For the first time, rotation of the Fiji platform relative to the Australian plate is observed, and anomalous deformation of the Tonga ridge was also detected. In the New Hebrides, a combined GPS dataset with a total time series of more than ten years led to new and refined velocity estimates throughout the island arc. Impingement of large bathymetric features has led to arc fragmentation, and four distinct tectonic segments are identified. The central New Hebrides arc segment is being shoved eastward relative to the rest of the arc as convergence is partitioned between the forearc (Australian plate) and the backarc (North Fiji Basin) boundaries due to impingement of the d'Entrecasteaux Ridge and associated Bougainville seamount. The southern New Hebrides arc converges with the Australian plate more rapidly than predicted due to backarc extension. The first measurements of convergence in the northern and southernmost arc segments were also made. In the Solomon Islands, a four-year GPS time series was used to generate the first geodetic estimates of crustal velocity in the New Georgia Group, with 57--84 mm/yr of Australia-Solomon motion and 19--39 mm/yr of Pacific-Solomon motion being observed. These velocities are 20--40% lower than predicted Australia-Pacific velocities. Two-dimensional dislocation models suggest that most of this discrepancy can be attributed to locking of the San Cristobal trench and elastic strain accumulation in the forearc. Anomalous motion at Simbo island is also observed.

Phillips, David A.

79

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

Microsoft Academic Search

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

G. M Stampfli; G. D. Borel

2002-01-01

80

Boundary element method for 3-D cracks in a plate  

NASA Technical Reports Server (NTRS)

Fundamental solutions which automatically satisfy boundary conditions at the interfaces of an elastic plate perfectly bonded to two elastic halfspaces are implemented in a three-dimensional BEM for crack problems. The BEM features a new integration scheme for highly singular kernels. The capability is achieved through a part analytic and part numerical integration procedure, such that the analytic part of the integration is similar for all slip/opening variations. Part-through elliptic cracks in an elastic plate with traction-free surfaces are analyzed and the SIF values along the crack front are found to compare favorably with the numerical SIF results of Raju and Newman (1979).

Fares, N.; Li, V. C.

1988-01-01

81

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

E-print Network

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

Smith-Konter, Bridget

82

Predicted and measured plate velocities induced by turbulent boundary layers  

NASA Astrophysics Data System (ADS)

A method for the prediction of velocity levels of a fuselage plate excited by turbulent boundary layers is described. The aim is to identify a method for the prediction of the relative changes of the velocity levels caused by variations of plate geometry and flight conditions. The Corcos, Efimtsov and Chase models are used to characterize the dynamic surface pressure cross-spectra. Predicted results using these models are compared with the result of in-flight measurements of plate velocities. It is found that the Corcos model gives the best agreement with the measured results for three different flight conditions. The Efimtsov extension and Chase models tend to underestimate the plate response in the lower frequency range. It is evident that the velocity level of the plate elements of the fuselage very much depends on the speed of the aircraft. An increase of the speed of the aircraft by 10% is likely to increase the plate velocity level by 3 dB and a reduction of the speed by 10% would give a reduction of 3 dB.

Liu, Bilong; Feng, Leping; Nilsson, Anders; Aversano, Marco

2012-11-01

83

Tectonics of the Nazca-Antarctic plate boundary  

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

84

Imprints of weak lithospheric plate boundaries in the observed geoid.  

NASA Astrophysics Data System (ADS)

The observed geoid is highly sensitive to both: density-viscosity variations within the Earth and lithosphere dynamics. While geoid undulations induced by the mantle dynamics is a subject of numerous studies, the effect of plate tectonics on the geoid and dynamic topography remains an open issue. In present study we investigate a joint effect of weak zones, dividing lithospheric plates, and lateral viscosity variations (LVV) in the whole mantle on the observed geoid. A new numerical technique is based on the substantially revised method introduced by Zhang and Christensen (1993) for solving the Navier-Stokes-Poisson equations in the spectral domain with strong LVV. Weak plate boundaries (WPB) are introduced based on the integrated global model of plate boundary deformations GSRM (Kreemer et al., 2003). We show that the effect of WPB on the geoid is significant and reaches -40 m to 70 m with RMS ~20 m. Maximal WPB-related anomalies are observed over large subduction zones in South America and the Southwestern Pacific in agreement with previous studies. The positive geoid anomaly in South America could be explained largely by a dynamic effect of decoupling of the Nazca and South American plates. Mid-ocean ridges are mostly characterized by negative changes of the geoid compared to the model without WPB. The amplitude of the effect depends on the viscosity contrasts across WPB until its value reaches the limit of 2.5-3 orders of magnitude. This value might be considered as the level at which plates are completely decoupled. The effect of WPB alone, exceeds the effect of LVV in the whole mantle and generally does not correlate with it. However, inclusion of LVV reduces the geoid perturbations due to WPB by about 10 m. Therefore, it is important to consider all these factors together. The geoid changes mainly result from changes of the dynamic topography, which are about -300 to +500 m. The obtained results show that including WPB may significantly improve the reliability of instantaneous global dynamic models. References Zhang, S., and U. Christensen (1993), Some effects of lateral viscosity variations on geoid and surface velocities induced by density anomalies in the mantle, Geophys. J. Int., 114(3), 531-547 Kreemer, C., W. E. Holt, and A. J. Haines (2003), An integrated global model of present-day plate motions and plate boundary deformation, Geophys. J. Int., 154(1), 8-34

Petrunin, Alexey G.; Kaban, Mikhail K.; Schmeling, Harro; Shahraki, Meysam

2014-05-01

85

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

Microsoft Academic Search

The results of detailed investigation into the geometry of distribution of earthquakes around and below the volcanoes Korovin, Cleveland, Makushin, Yake-Dake, Oshima, Lewotobi, Fuego, Sangay, Nisyros and Montagne Pelée at convergent plate margins are presented. The ISC hypocentral determinations for the period 1964–1999, based on data of global seismic network and relocated by Engdahl, van der Hilst and Buland, have

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

2004-01-01

86

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

Microsoft Academic Search

The results of detailed investigation into the geometry of distribution of earthquakes around and below the volcanoes Korovin, Cleveland, Makushin, Yake-Dake, Oshima, Lewotobi, Fuego, Sangay, Nisyros and Montagne Pelée at convergent plate margins are presented. The ISC hypocentral determinations for the period 1964-1999, based on data of global seismic network and relocated by Engdahl, van der Hilst and Buland, have

Ales Spicák; Václav Hanus; Jirí Vanek

2004-01-01

87

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

Microsoft Academic Search

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

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

1996-01-01

88

Sharp Lithosphere-asthenosphere Boundaries of Oceanic Plates  

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

89

An Introduction to Plate Tectonics  

NSDL National Science Digital Library

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

90

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

NASA Astrophysics Data System (ADS)

The Australia-Pacific-Antarctic plate circuit has long been a weak link in global plate reconstruction models for Cenozoic time. The time period spanning chron 20 to chron 7 (43-25 Ma) is particularly problematic for global plate models because seafloor spreading was occurring in two poorly constrained regions in the Southwest Pacific - the Macquarie Basin southwest of New Zealand, and the Adare Basin north of the Ross Sea, Antarctica. I present a new shipboard dataset collected aboard several recent geophysical cruises which places important constraints on the tectonic evolution of these two regions. Utilizing multibeam bathymetry, magnetic, gravity, and seismic data in the Macquarie Basin, I am able to locate tectonic features and magnetic anomalies with greater accuracy than was previously possible. These tectonic features and magnetic anomalies are then used to calculate relative motion between the Australia and Pacific Plates for chrons 18-11 (40-30 Ma). I use revised locations of the rifted margins along the boundary of the Macquarie Basin to determine a best-fit pre-rift reconstruction for this region. During this same time period, seafloor spreading between East and West Antarctica was occurring along the Adare Trough, an extinct spreading center located north of the Ross Sea. Motion along the Adare Trough accounts for roughly 180 km of previously unrecognized motion between East and West Antarctica. I present multibeam and seismic data in the Adare Basin that place constraints on the timing and character of motion along this plate boundary.

Keller, William R.

91

Formation of plate boundaries: The role of mantle volatilization  

NASA Astrophysics Data System (ADS)

In the early Earth, convection occurred with the accumulation of thick crust over a weak boundary layer downwelling into the mantle (Davies, G.F., 1992. On the emergence of plate tectonics. Geology 20, 963-966.). This would have transitioned to stagnant-lid convection as the mantle cooled (Solomatov, V.S., Moresi, L.-N., 1997. Three regimes of mantle convection with non-Newtonian viscosity and stagnant lid convection on the terrestrial planets. Geophys. Res. Lett. 24, 1907-1910.) or back to a magma ocean as the mantle heated (Sleep, N., 2000. Evolution of the mode of convection within terrestrial planets. J. Geophys. Res. 105(E7): 17563-17578). Because plate tectonics began operating on the Earth, subduction must have been initiated, thus avoiding these shifts. Based on an analogy with the continental crust subducted beneath Hindu Kush and Burma, we propose that the lithosphere was hydrated and/or carbonated by H2O-CO2 vapors released from magmas generated in upwelling plumes and subsequently volatilized during underthrusting, resulting in lubrication of the thrust above, and subduction of the lithosphere along with the overlying thick crust. Once subduction had been initiated, serpentinized forearc mantle may have formed in a wedge-shaped body above a dehydrating slab. In relict arcs, suture zones, or rifted margins, any agent that warms and dehydrates the wedge would weaken the region surrounding it, and form various types of plate boundaries depending on the operating tectonic stress. Thus, once subduction is initiated, formation of plate boundaries might be facilitated by a major fundamental process: weakening due to the release of pressurized water from the warming serpentinized forearc mantle.

Seno, Tetsuzo; Kirby, Stephen H.

2014-02-01

92

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

E-print Network

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

Bretherton, Christopher S.

93

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.

Timothy Heaton

94

Turbulent thermal boundary layer on a permeable flat plate  

SciTech Connect

Scaling laws are established for the profiles of temperature, turbulent heat flux, rms temperature fluctuation, and wall heat transfer in the turbulent boundary layer on a flat plate with transpiration. In the case of blowing, the temperature distribution represented in scaling variables outside the viscous sublayer has a universal form known from experimental data for flows over impermeable flat plates. In the case of suction, the temperature distribution is described by a one-parameter family of curves. A universal law of heat transfer having the form of a generalized Reynolds analogy provides a basis for representation of the heat flux distributions corresponding to different Reynolds numbers and transpiration velocities in terms of a function of one variable. The results are obtained without invoking any special closure hypotheses.

Vigdorovich, I. I. [Moscow State University, Institute of Mechanics (Russian Federation)], E-mail: vigdorovich@imec.msu.ru

2007-06-15

95

Measuring Transient Signals in Plate Boundary Faults Zones with Strainmeters  

NASA Astrophysics Data System (ADS)

One of the fundamental goals the U.S. National Science Foundation (NSF) funded Earthscope program was to provide a high-quality, continuous geodetic data set that would allow the scientific community to study the evolution of plate boundary zones. Of particular importance was enabling investigation of the role aseismic transient deformation plays in the release of accumulated stress. For example, to allow the comparison of the amount of strain released through Episodic Tremor and Slip (ETS) events to that released in subduction zone earthquakes or, provide the ability to geodetically illuminate the kinematics of fault creep in strike-slip fault zones. The ability to easily integrate these measurements with compatible geophysical data sets was also an essential objective. With goals such as these in mind NSF funded the Plate Boundary Observatory (PBO) to record the continuous deformation field across the western US Plate Boundary. PBO, built and operated by UNAVCO, now consists of over 1100 GPS stations, 76 co-located borehole strain and seismic sites, 6 long baseline strainmeters, Depending on the scientific questions being addressed sites may also have tiltmeter, meteorological, pore pressure and meteorological instrumentation. This presentation will focus on the transient deformation signals recorded by the PBO strainmeter network. PBO strainmeters, which excel in recording signals on the order of nanostrain over hours, have provided unprecedented temporal resolution of aseismic transients such as ETS events in the Cascadia subduction zone, creep signals along the central section of the San Andreas fault system and tsunami generated strain waves. UNAVCO is responsible not only for the ongoing operation of PBO but also the generation of data products associated with each instrument type. In this presentation we will highlight some of the transient signals these instruments have captured, outline the processing steps required to extract these signals data and describe the strainmeter data products produced by UNAVCO.

Hodgkinson, Kathleen; Mencin, Dave; Phillips, David; Henderson, Brent; Gottlieb, Mike; Gallaher, Warren; Johnson, Wade; Pyatt, Chad; Van Boskirk, Elizabeth; Fox, Otina; Mattioli, Glen; Meertens, Chuck

2014-05-01

96

Flat plate turbulent boundary-layer control using vertical LEBUs  

NASA Astrophysics Data System (ADS)

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

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

97

Crustal motion along the Eurasia-Nubia plate boundary in the Calabrian Arc and Sicily and active extension in the Messina Straits from GPS measurements  

Microsoft Academic Search

We investigate crustal deformation along the Eurasia-Nubia plate boundary in Calabria and Sicily revealed by the GPS velocity field obtained by the combination of continuous site velocities with previous results from episodic campaigns. We recognize two distinct crustal domains characterized by different motions and styles of deformation. Convergence in Sicily is taken up by crustal shortening along the former Tyrrhenian

Nicola D’Agostino; Giulio Selvaggi

2004-01-01

98

Features on Venus generated by plate boundary processes  

NASA Technical Reports Server (NTRS)

Various observations suggest that there are processes on Venus that produce features similar to those associated with plate boundaries on earth. Synthetic aperture radar images of Venus, taken with a radar whose wavelength is 12.6 cm, are compared with GLORIA images of active plate boundaries, obtained with a sound source whose wavelength is 23 cm. Features similar to transform faults and to abyssal hills on slow and fast spreading ridges can be recognized within the Artemis region of Venus but are not clearly visible elsewhere. The composition of the basalts measured by the Venera 13 and 14 and the Vega 2 spacecraft corresponds to that expected from adiabatic decompression, like that which occurs beneath spreading ridges on earth. Structures that resemble trenches are widespread on Venus and show the same curvature and asymmetry as they do on earth. These observations suggest that the same simple geophysical models that have been so successfully used to understand the tectonics of earth can also be applied to Venus.

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

1992-01-01

99

Stress accumulation and release at complex transform plate boundaries  

SciTech Connect

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

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

1992-10-01

100

The GEORED and Plate Boundary Observatory Engineer Exchange Program  

NASA Astrophysics Data System (ADS)

In early 2007, the Colombian Institute of Geology and Mining - INGEOMINAS initiated GEORED (Geodesia: Red de Estudios de Deformación) in order to increase the knowledge of the geodynamics of northwestern South America. GEORED is an essential tool for determining crustal deformation and is primary in the analysis of inter- plate and intraplate deformation and the present seismic cycle. Some of the objectives of the project are to improve the technical, scientific, and operational capabilities of Colombian scientists regarding tectonic and volcanic deformation in Colombia, to implement a Colombian GPS permanent network for the study of geodynamics, with near real-time data retrieval and processing, and to establish a high precision geodetic reference frame for multipurpose activities within INGEOMINAS. Phase 1 of GEORED, which includes the installation of 30 permanent GPS stations in Colombia, will commence in early 2007. The Plate Boundary Observatory (PBO), part of the larger NSF-funded EarthScope project managed by UNAVCO, will study the three-dimensional strain field resulting from active plate boundary deformation across the Western United States. PBO is a large construction project involving the reconnaissance, permitting, installation, documentation, and maintenance of 875 permanent GPS stations scheduled for completion in September 2008. PBO is currently in the fourth year of the project, with over 550 GPS stations completed to date. INGEOMINAS recently became a member of the UNAVCO consortium. UNAVCO has been working with INGEOMINAS by providing technical support for the GEORED project relating to GPS receiver specifications. In the spirit of collaboration and outreach, INGEOMINAS and UNAVCO will begin an engineer exchange program starting in early summer 2007. The purpose of this outreach program is to provide a mechanism for the exchange of ideas relating to GPS station construction techniques, hardware designs, data communications, and data archiving based upon the UNAVCO PBO experience and based upon the extensive INGEOMINAS experience in installing scientific instrumentation in remote locations and difficult conditions. The Plate Boundary Observatory and GEORED will provide a natural laboratory for training in GPS construction techniques.

Feaux, K.; Mora-Paez, H.

2007-05-01

101

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

E-print Network

velocity structure of the crust and upper mantle of the Caribbean-South American boundary region-South American plate boundary have been largely limited to either broad regional, or very local studies [MalaveUpper mantle structure beneath the Caribbean-South American plate boundary from surface wave

Niu, Fenglin

102

Has the plate boundary shifted from central Hokkaido to the eastern part of the Sea of Japan?  

NASA Astrophysics Data System (ADS)

A NS trending Cenozoic fold-and-thrust belt has developed in the western part of the Hidaka Collision Zone (HCZ), central Hokkaido, Japan. A quantitative estimation of the late Cenozoic convergence rate at the front of the Hidaka thrust system is important in revealing the plate tectonic framework around northern Japan. High-resolution seismic reflection profiling across the active fault-related folds was carried out to ascertain the temporal change in the crustal shortening rate. Overlapping ramp anticlines and growth folds within thrust sheets were examined using balanced cross-sections combined with industry seismic and drilling data. The rate of shortening was examined using a 3.5 Ma horizon and late Quaternary horizons at 115 and 41 ka. These horizons show that the convergence rate of the Hidaka thrust system has not decreased during the last 3.5 Ma. This suggests that the plate boundary between the Eurasian (Amurian) and North American (Okhotsk) plates has not jumped from the central part of Hokkaido to the eastern part of the Sea of Japan since 3.5 Ma and that a significant amount of plate convergence is still being absorbed in the Hidaka Collision Zone.

Kato, Naoko; Sato, Hiroshi; Orito, Masayuki; Hirakawa, Kazuomi; Ikeda, Yasutaka; Ito, Tanio

2004-09-01

103

Comparison of Modern Zn-Ba-Pb Ore Deposits at Convergent Plate Margins and Fe-Cu-Zn Deposits at Divergent Plate Margins  

Microsoft Academic Search

At divergent plate margins, black smoke forms immediately on contact of ascending hydrothermal solutions with sea water. The black smoke, consisting mainly of black ore (BO) and barite ore (BaO), is rapidly dispersed in seawater leaving behind a dominantly yellow ore (YO). At convergent plate margins, on the other hand, zinc sulfides and associated chalcophilic elements start depositing within the

G. P. Glasby

2008-01-01

104

Major earthquakes occur regularly on an isolated plate boundary fault.  

PubMed

The scarcity of long geological records of major earthquakes, on different types of faults, makes testing hypotheses of regular versus random or clustered earthquake recurrence behavior difficult. We provide a fault-proximal major earthquake record spanning 8000 years on the strike-slip Alpine Fault in New Zealand. Cyclic stratigraphy at Hokuri Creek suggests that the fault ruptured to the surface 24 times, and event ages yield a 0.33 coefficient of variation in recurrence interval. We associate this near-regular earthquake recurrence with a geometrically simple strike-slip fault, with high slip rate, accommodating a high proportion of plate boundary motion that works in isolation from other faults. We propose that it is valid to apply time-dependent earthquake recurrence models for seismic hazard estimation to similar faults worldwide. PMID:22745426

Berryman, Kelvin R; Cochran, Ursula A; Clark, Kate J; Biasi, Glenn P; Langridge, Robert M; Villamor, Pilar

2012-06-29

105

Modeling surface deformations at complex strike-slip plate boundaries  

NASA Technical Reports Server (NTRS)

Two new versions of the physical base-traction model of Li and Rice (1987) have been developed to study the loading processes and surface deformation near plate boundaries with geometric complexities, including a shallow creeping fault segment and two subparallel faults. Predictions of surface velocity and surface slip rate for the region between the San Andreas fault and the Pacific coast at the latitude of the Parkfield-Cholame segment using model parameters based on geologic, geodetic, and seismic considerations were found to be in good agreement with contemporary geodetic field data (not used in constrainning model parameters). Also, predicted surface velocity for the Salton Sea-Coachella Valley area were fit to recently derived contemporary geodetic data and very large baseline interferometry data, althoug here the model parameters are not well constrained.

Li, Victor C.; Lim, Hun Seng

1988-01-01

106

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

107

Coseismic slip resolution along a plate boundary megathrust: the Nankai Trough, southwest Japan  

USGS Publications Warehouse

Geodetic survey measurements are used to estimate the coseismic slip distribution in the 1944 Tonankai (Mw=8.1) and 1946 Nankaido (Mw=8.3) earthquakes and to assess quantitatively the degree to which this slip is resolved on the plate boundary megathrust. Data used include 798 angle changes from triangulation surveys, 328 leveling section differences, and 5 coseismic tidal gage offsets. Many of the nominally coseismic triangulation data span ?50 years, nearly half the earthquake cycle, and correction for interseismic deformation using post-1950 observations is applied. Microseismicity is used to define the configuration of the plate boundary interface and approximate it with a continuous, multisegment fault model. Because the onshore geodetic data have very limited resolving power for offshore fault segments, offshore coseismic slip was constrained by Satctke's [1993] estimation based on tsunami data. The majority of the coseismic slip occurs between 15 and 25 km depth. Although resolution declines toward the trench axis, it is sufficiently good to define two distinct high-slip regions, one off southeastern Shikoku Island (11 m maximum) and the other offshore of Kii Peninsula (3 m maximum). The slip magnitude off southeastern Shikoku, coupled with the plate convergence rate, would imply an recurrence interval of about 270 years, much-longer than the average repeat time of ?120 years for historical great earthquakes on the Nankai Trough. However, the maximum coseismic slip is sensitive to the assumed fault geometry, and slippage on trough-parallel splay faults could significantly decrease the maximum slip to about 6 m.

Sagiya, Takeshi; Thatcher, Wayne

1999-01-01

108

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

109

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

NASA Astrophysics Data System (ADS)

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

Kirby, S. H.

2006-12-01

110

Convergence to Equilibrium for the Cahn-Hilliard Equation with Wentzell Boundary Condition  

E-print Network

In this paper we consider the Cahn-Hilliard equation endowed with Wentzell boundary condition which is a model of phase separation in a binary mixture contained in a bounded domain with permeable wall. Under the assumption that the nonlinearity is analytic with respect to unknown dependent function, we prove the convergence of a global solution to an equilibrium as time goes to infinity by means of a suitable \\L ojasiewicz-Simon type inequality with boundary term. Estimates of convergence rate are also provided.

Wu, Hao

2007-01-01

111

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

NASA Technical Reports Server (NTRS)

According to the slip partitioning concept, the trench parallel component of relative plate motion in regions of oblique convergence is accommodated by strike-slip faulting in the overriding continental lithosphere. The pattern of postseismic surface deformation due to viscoelastic flow in the lower crust and asthenosphere following a major earthquake on such a fault is modified from that predicted from the conventual elastic layer over viscoelastic halfspace model by the presence of the subducting slab. The predicted effects, such as a partial suppression of the postseismic velocities by 1 cm/yr or more immediately following a moderate to great earthquake, are potentially detectable using contemporary geodetic techniques.

Cohen, Steven C.

1999-01-01

112

Free Vibration Analysis of Kirchoff Plates with Damaged Boundaries by the Chebyshev Collocation Method  

E-print Network

Free Vibration Analysis of Kirchoff Plates with Damaged Boundaries by the Chebyshev Collocation for the free vibration analysis of slender Kirchoff plates with both mixed and damaged boundaries an important role in applications of mechanical, aerospace and civil engineering. Studying the free vibration

Butcher, Eric A.

113

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

Microsoft Academic Search

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

Vladimir Kostoglodov

1988-01-01

114

Average properties of compressible laminar boundary layer on flat plate with unsteady flight velocity  

NASA Technical Reports Server (NTRS)

The time-average characteristics of boundary layers over a flat plate in nearly quasi-steady flow are determined. The plate may be either insulated or isothermal. The time averages are found without specifying the plate velocity explicitly except that it is positive and has an average value.

Moore, Franklin K; Ostrach, Simon

1957-01-01

115

Free vibrations of thermally stressed orthotropic plates with various boundary conditions  

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

116

Convergence of the wave equation damped on the interior to the one damped on the boundary  

NASA Astrophysics Data System (ADS)

In this paper, we study the convergence of the wave equation with variable internal damping term ?(x)u to the wave equation with boundary damping ?(x)??u when (?(x)) converges to ?(x)?? in the sense of distributions. When the domain ? in which these equations are defined is an interval in R, we show that, under natural hypotheses, the compact global attractor of the wave equation damped on the interior converges in X=H(?)×L(?) to the one of the wave equation damped on the boundary, and that the dynamics on these attractors are equivalent. We also prove, in the higher-dimensional case, that the attractors are lower-semicontinuous in X and upper-semicontinuous in H(?)×H(?).

Joly, Romain

117

Convergence of spectral methods for hyperbolic initial-boundary value systems  

NASA Technical Reports Server (NTRS)

A convergence proof for spectral approximations is presented for hyperbolic systems with initial and boundary conditions. The Chebyshev collocation is treated in detail, but the final result is readily applicable to other spectral methods, such as Legendre collocation or tau-methods.

Gottlieb, D.; Lustman, L.; Tadmor, E.

1986-01-01

118

Obduction at plate boundaries : thermo-mechanical modelling  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

119

Characteristics of transition in a flat-plate boundary layer  

NASA Astrophysics Data System (ADS)

A direct numerical simulation of the spatially evolving transition in a flat-plate boundary layer is performed in the region of ( 115000<= Re_x<= 340000 ) with ( 1537× 99× 128 ) grid points. Inflow disturbances, similar to the two dimensional T-S wave combined with three dimensional waves, are generated on the upstream wall through time-dependent localized blowing and suction. A ( ? ) vortex, consisting of two legs, is identified at a downstream location of blowing and suction. Soon a hairpin vortex, consisting of a head and two legs, is formed from the ( ? ) vortex through the self induction mechanism. At a later time new hairpin vortices are successively produced behind the first hairpin vortex. At the final stage six hairpin vortices are observed. As the vortices move downstream in time, the legs of the ( ? ) vortex get stronger and become quasi-streamwise vortices, while the head of the hairpin vortex changes into an ( ? ) shape. Near the end of the computational domain the hairpin vortices and quasi-streamwise vortices are entangled with each other and convect downstream together; these phenomena are compared with the characteristics of a turbulent spot. It is shown that the spikes and saw-tooth like jumps in the streamwise velocity signals, observed in experiments, are associated with the heads and legs of the hairpin vortices, respectively.

Choi, Myung-Ryul; Choi, Haecheon; Kang, Shin-Hyoung

1998-11-01

120

On the instability of boundary layers on heated flat plates  

NASA Technical Reports Server (NTRS)

The stability of a boundary layer on a heated flat plate is investigated in the linear regime. The flow is shown to be unstable to longitudinal vortex structures which in general develop in a nonparallel manner in the streamwise direction. Solutions of the nonparallel equations are obtained numerically at O(1) values of the appropriate stability parameter, i.e., the Grashof number. The particular cases investigated relate to the situations when the instability is induced by localized or distributed wall roughness or nonuniform wall heating. The case when the vortices are induced by freestream disturbances is also considered. The fastest growing mode is found to be governed by a quasi-parallel theory at high wavenumbers. The wavenumber and growth rate of the fastest growing mode are found in closed form. At low wavenumbers the vortex instability is shown to be closely related to Tollmein-Schlichting waves. The effect of wall heating or cooling on the latter type of instability is discussed.

Hall, Philip; Morris, Helen

1992-01-01

121

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

NASA Astrophysics Data System (ADS)

Global Positioning System (GPS) measurements made in 1991, 1992 and 1993 provide preliminary estimates of slip distribution between the Australian and Pacific plates in Irian Jaya, Indonesia. We interpret the GPS results with constraints from earthquake mechanisms and slip vectors, recent marine surveys, and geology. Three GPS sites in southeastern Irian Jaya show motions that are within 10 mm/yr of the expected motion of Australia. A coast-to-coast N-S baseline along 140.5°E crosses all known onland regions of active deformation but reveals no more than 15 mm/yr of shortening and 20 mm/yr of left-lateral shear in the 27-month period. The remaining 40 mm/yr of expected convergence between the Pacific and Australian plates probably occurs at the New Guinea trough. GPS sites on the island of Biak, at 136°E, and at Sorong, near the western tip of Bird's Head (at 131°E), both move 90-100 mm/yr in a WSW direction relative to Irian Jaya, but less than 15 mm/yr relative to each other. These sites are on either side of the Sorong fault and demonstrate that it is not presently the major boundary between the Australian and Pacific plates. Instead the plate boundary is now south of the Sorong and Biak sites. Earthquakes suggest possible structures that accomodate motion between Bird's Head and Australia but the relative importance of them remains uncertain.

Puntodewo, S. S. O.; McCaffrey, R.; Calais, E.; Bock, Y.; Rais, J.; Subarya, C.; Poewariardi, R.; Stevens, C.; Genrich, J.; Fauzi; Zwick, P.; Wdowinski, S.

1994-10-01

122

Analysis of turbulent free-convection boundary layer on flat plate  

NASA Technical Reports Server (NTRS)

A calculation was made for the flow and heat transfer in the turbulent free-convection boundary layer on a vertical flat plate. Formulas for the heat-transfer coefficient, boundary layer thickness, and the maximum velocity in the boundary layer were obtained.

Eckert, E R G; Jackson, Thomas W

1950-01-01

123

Understanding Plate Motions  

NSDL National Science Digital Library

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

124

An EarthScope Plate Boundary Observatory Progress Report  

NASA Astrophysics Data System (ADS)

UNAVCO is building and operating the Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project to understand the structure, dynamics, and evolution of the North American continent. When complete in October 2008, the 875 GPS, 103 strain and seismic, and 28 tiltmeters stations will comprise the largest integrated geodetic and seismic network in United States and the second largest in the world. Data from the PBO network will facilitate research into plate boundary deformation with unprecedented scope and detail. As of 1 September 2007, UNAVCO had completed 680 PBO GPS stations and had upgraded 89% of the planned PBO Nucleus stations. Highlights of the past year's work include the expansion of the Alaska subnetwork to 95 continuously-operating stations, including coverage of Akutan and Augustine volcanoes and reconnaissance for future installations on Unimak Island; the installation of nine new stations on Mt. St. Helens; and the arrival of 33 permits for station installations on BLM land in Nevada. The Augustine network provided critical data on magmatic and volcanic processes associated with the 2005-2006 volcanic crisis, and has expanded to a total of 11 stations. Please visit http://pboweb.unavco.org/?pageid=3 for further information on PBO GPS network construction activities. As of September 2007, 41 PBO borehole stations had been installed and three laser strainmeter stations were operating, with a total of 60 borehole stations and 4 laser strainmeters expected by October 2007. In response to direction from the EarthScope community, UNAVCO installed a dense network of six stations along the San Jacinto Fault near Anza, California; installed three of four planned borehole strainmeter stations on Mt. St. Helens; and has densified coverage of the Parkfield area. Please visit http://pboweb.unavco.org/?pageid=8 for more information on PBO strainmeter network construction progress. The combined PBO/Nucleus GPS network provides 350 GB of raw standard rate data, with special downloads of more than 250 GB of high-rate GPS data following large earthquakes in Russia, Tonga, and Peru, as well as for community requests. The standard rate GPS data are processed routinely to generate data products including station position time series, velocity vectors, and related information, and all data products are available from the UNAVCO Facility archive. The PBO seismic network seismic network has provided 201 GB of raw data, which are available via Antelope and Earthworm from PBO and via the IRIS Data Management Center (DMC); we provide data to seismic networks operated from Caltech, UCSD, UCSB, University of Washington, and the Pacific Geosciences Center in Sidney, BC. The PBO strainmeter network has provided 93 GB of raw data, available in both raw native format and SEED format from the Northern California Earthquake Data Center and the IRIS DMC, along with higher-level products such as cleaned strain time series and related information. Please visit http://pboweb.unavco.org/gps_data and http://pboweb.unavco.org/strain_data for more information on PBO GPS and strainmeter/seismic data products, respectively.

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

2007-12-01

125

Convergence  

Microsoft Academic Search

A key economic issue is whether poor countries or regions tend to grow faster than rich ones: are there automatic forces that lead to convergence over time in the levels of per capita income and product? We use the neoclassical growth model as a framework to study convergence across the 48 contiguous U.S. states. We exploit data on personal income

Robert J. Barro; Xavier Sala-i-Martin

1992-01-01

126

The Earthscope Plate Boundary Observatory Akutan Alaskan Volcano Network Installation  

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

127

Overview on the Plate Boundaries Along the Western Mexican Pacific Margin  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

128

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

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

129

Inter- and intra-plate deformation at North American plate boundaries  

NASA Technical Reports Server (NTRS)

Alaska tectonics and earthquake hazard studies; Southern California tectonics (block rotation); spreading near the Salton Trough; California plate motion (fault zone kinematics); and Caribbean plate motion investigations are examined.

Beavan, John

1986-01-01

130

Diurnal cycle in convergence patterns in the boundary layer east of the Andes and convection  

NASA Astrophysics Data System (ADS)

The South American Low-Level Jet Experiment (SALLJEX) provided a unique dataset to investigate the existence of a mesoscale low-level circulation and of a diurnal cycle in its related convergence pattern over the Southeastern South American region east of the Andes, as well as its relationship with deep convection during the warm season. The present paper builds upon high-resolution analyses produced, assimilating the data collected during the SALLJEX field campaign using BRAMS, and explores their capability to reproduce mesoscale circulations not resolved by the low density observational network available in this region. Results of the analyses show a diurnal oscillation signal in the mean boundary layer convergence pattern over the plains with a nocturnal (daytime) convergence (divergence) maximum. These results are coherent with previous findings of a nocturnal phase in the mature stage of organized deep convection and related precipitation in subtropical latitudes east of the Andes during the warm season. The diurnal cycle of convergence/divergence in the boundary layer is described over a 15-day period, during which different synoptic conditions occurred. During weakly forced environments a regime characterized by nocturnal eastward anomaly flow and convergence and daytime westward anomaly flow and divergence related to a mesoscale northwestern mountain-central plain flow regime dominates over the plains between the Andes Mountains, the Parana River Valley, and the southern Brazil mountain range. In contrast, during synoptic conditions dominated by the presence of a deep thermal low over northwestern Argentina and a related low-level jet, convergence at night is mainly accomplished by the predominantly meridional low-level jet, which exhibits an anomalous weak wind speed diurnal cycle with respect to its summer climatological mean. On the other hand daytime divergence is completely produced by the zonal wind component as in the previous synoptic situation. Mesoscale circulations are altered (still effecting mean divergence in the domain, which exhibits a diurnal oscillation) upon the initiation of deep convective circulations in the evening in an increasingly convectively unstable atmosphere driven by a persistent horizontal advection of heat and moisture at low levels and forced by convergence generated by the low-level jet and the presence of a frontal zone. Convection intensifies at night when its related convergence over the plains comes in phase with the convergence related to the nocturnal maximum in the low-level jet.

Nicolini, Matilde; Skabar, Yanina García

2011-06-01

131

Isla del Coco, on Cocos Plate, Converges with Isla de San Andrés, on the Caribbean Plate, at 78 mm/yr  

NASA Astrophysics Data System (ADS)

Isla del Coco is the only land mass of the Cocos Plate that emerges above sea level. This makes it the only place where Cocos Plate motion can be measured using Global Navigation Satellite System (GNSS) monitoring. Global Positioning System (GPS) observations have been carried out sporadically over more than two decades on Isla del Coco, allowing precise measurement of the motion of the Cocos Plate. Recently, in May 2011, a continuous GPS station was built and instrumented at Isla del Coco, in Wafer Bay, by OVSICORI UNA and UNAVCO, as part of the COCONet regional GNSS network. Position time series from this CGPS station (ISCO: Isla del Coco) show a steady motion of Isla del Coco at a speed of 90.9±1.5mm/yr in the N35oE direction in ITRF2008 and convergence with the Caribbean Plate at 78±1mm/yr. This result is consistent with the findings of the earliest GPS studies, and agrees within uncertainty with the estimated convergence rate of 76.4±2.6 mm/yr of the MORVEL plate motion model. MORVEL is based on an average over the last 780,000 years, and our result suggests that Cocos Caribbean plate motions have been constant over that time interval.

Protti, M.; Gonzalez, V. M.; Freymueller, J. T.; Doelger, S.

2013-05-01

132

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

Microsoft Academic Search

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

William R. Keller

2005-01-01

133

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

NASA Astrophysics Data System (ADS)

The Netherlands Leeward Antilles volcanic island arc is an ideal natural laboratory to study the evolution of the Caribbean-South American plate boundary. The Leeward Antilles islands (Aruba, Curacao, and Bonaire) are located offshore western Venezuela, within the obliquely convergent diffuse plate boundary zone. Outcrop analysis, microthermometry, and 2D marine seismic reflection data provide evidence of three generations of regional deformation since the Late Cretaceous. Outcrop analysis of structural features, including faults, joints, and veins, characterizes the kinematic history of the islands. Fluid inclusion analysis of quartz and calcite veins coupled with apatite fission-track dating provides the island exhumation history. Finally, marine reflection seismic data processing and interpretation of newly acquired data elucidates offshore structures to integrate with our onshore results. The oldest regional deformation, resulting in both ductile (D1) and brittle (F 1) structures, is attributed to displacement partitioning along the arcuate Caribbean plate boundary. Associated crustal thinning initiated island exhumation, at a rate of 0.18 km/my, from a maximum burial depth of 6 km in the Late Cretaceous (˜89 Ma). Coeval with D1/F1 deformation and exhumation, stretching of the island arc resulted in extensive basin rifting that separated the island blocks. At ˜55 Ma, a change in the relative motion of the Caribbean plate altered plate boundary dynamics. Displacement along the right-lateral Caribbean transform fault and Oca - San Sebastian - El Pilar strike-slip fault system created a wrench tectonic regime within the diffuse plate boundary zone. A second generation of brittle structures (F2) developed while the islands were at a maximum burial depth of 2 km during the Paleocene/Eocene. Since ˜45 Ma, continued motion along the strike-slip fault systems and oblique plate convergence resulted in the youngest generation of structural features (F3). Regional tectonics control the ongoing steady-state exhumation of the islands at a rate of 0.04 km/my. Most recently, the northeast escape of the Maracaibo block also drives deformation within the diffuse plate boundary zone. Overall, the Caribbean-South American plate boundary geometry has evolved with diachronous deformation, from west to east, accompanied by 135° of clockwise block rotation during collision and accretion of the Leeward Antilles since the Late Cretaceous.

Beardsley, Amanda Gail

2007-12-01

134

Recovering physical property information from subduction plate boundaries using 3D full-waveform seismic inversion  

NASA Astrophysics Data System (ADS)

Our understanding of subduction margin seismogenesis has been revolutionised in the last couple of decades with the discovery that the size of the seismogenic zone may not be controlled simply by temperature and a broad spectrum of seismic behaviour exists from stick-slip to stable sliding. Laboratory and numerical experiments suggest that physical properties, particularly fluid pressure may play an important role in controlling the seismic behaviour of subduction margins. Although drilling can provide information on physical properties along subduction thrust faults at point locations at relatively shallow depths, correlations between physical properties and seismic velocity using rock physics relationships are required to resolve physical properties along the margin and down-dip. Therefore, high resolution seismic velocity models are key to recovering physical property information at subduction plate boundaries away from drill sites. 3D Full waveform inversion (FWI) is a technique pioneered by the oil industry to obtain high-resolution high-fidelity models of physical properties in the sub-surface. 3D FWI involves the inversion of low-frequency (>2 to <7 Hz), early arriving (principally transmitted) seismic data, to recover the macro (intermediate to long-wavelength) velocity structure. Although 2D FWI has been used to improve velocity models of subduction plate boundaries before, 3D FWI has not yet been attempted. 3D inversions have superior convergence and accuracy, as they sample the subsurface with multi-azimuth multiply-crossing wavefields. In this contribution we perform a suite of synthetic tests to investigate if 3D FWI could be used to better resolve physical property information along subduction margin plate boundaries using conventionally collected 3D seismic data. We base our analysis on the Muroto Basin area of the Nankai margin and investigate if the acquisition parameters and geometry of the subduction margin render 3D seismic data collected across this basin in 1999 suitable for future 3D FWI. We build a 3D model of the sub-surface based on an existing velocity model that was used to migrate these data (Tsuji et al. 2000, JGR). We then add a low P-wave velocity layer along the décollement, which is supported by ODP core data but does not feature in the current seismic velocity model, to test if it could be recovered using 3D FWI. We use the same acquisition parameters as in the 1999 seismic survey (including a 6 km long streamer) to generate a fully-elastic synthetic seismic dataset, added noise and inverted the windowed transmitted arrivals only. We also ran a suite of resolution tests across the model. The results show that 3D FWI of conventionally collected 3D seismic data across the Muroto Basin would be capable of resolving variations in P-wave velocity along the décollement of the order of half the seismic wavelength at the plate boundary. This is a significant improvement on conventional travel-time tomography which resolves to the Fresnel width. In this presentation we will also postulate on the optimal 3D FWI experiment design for the next generation of 3D seismic surveys across subduction margins as a guide for those embarking on new data collection.

Bell, R. E.; Morgan, J. V.; Warner, M.

2013-12-01

135

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

USGS Publications Warehouse

THE Cascadia subduction zone, a region of converging tectonic plates along the Pacific coast of North America, has a geological history of very large plate-boundary earthquakes1,2, but no such earthquakes have struck this region since Euro-American settlement about 150 years ago. Geophysical estimates of the moment magnitudes (Mw) of the largest such earthquakes range from 8 (ref. 3).to 91/2 (ref. 4). Radiocarbon dating of earthquake-killed vegetation can set upper bounds on earthquake size by constraining the length of plate boundary that ruptured in individual earthquakes. Such dating has shown that the most recent rupture, or series of ruptures, extended at least 55 km along the Washington coast within a period of a few decades about 300 years ago5. Here we report 85 new 14C ages, which suggest that this most recent rupture (or series) extended at least 900 km between southern British Columbia and northern California. By comparing the 14C ages with written records of the past 150 years, we conclude that a single magnitude 9 earthquake, or a series of lesser earthquakes, ruptured most of the length of the Cascadia subduction zone between the late 1600s and early 1800s, and probably in the early 1700s.

Nelson, A.R.; Atwater, B.F.; Bobrowsky, P.T.; Bradley, L.-A.; Clague, J.J.; Carver, G.A.; Darienzo, M.E.; Grant, W.C.; Krueger, H.W.; Sparks, R.; Stafford, T.W., Jr.; Stuiver, M.

1995-01-01

136

Skin friction and Reynolds stress measurements for a turbulent boundary layer following manipulation using flat plates  

NASA Technical Reports Server (NTRS)

Research has been undertaken to experimentally study the alterations in turbulent boundary-layer properties due to turbulence manipulation using thin flat plates. Plate geometry and placement within the boundary layer were selected to coincide with recent studies. Direct, local measurements of skin friction and Reynolds stresses were made within the boundary layer downstream of the manipulator devices for cases with an approach momentum thickness Reynolds number of 3700. A strong tendency for recovery of the Reynolds stresses was observed, accompanied by local skin-friction reductions of up to 15 percent. The mean velocity profile in the manipulated flow displayed the same similarity shape in the logarithmic region as a natural boundary layer, but had an enhanced wake component. The results indicate that the plate wake plays an important role in the boundary layer response to this sort of manipulation.

Westphal, R. V.

1986-01-01

137

Inter- and intra-plate deformation at North American plate boundaries  

NASA Technical Reports Server (NTRS)

A geodetic network which spans the region between San Francisco and Lake Tahoe has been measured 5 times completely with triangulation in 1880, 1922, 1929, 1943, 1963. A resurvey with the Global Positioning System (GPS) in 1991 allows the formation of 1 coseismic and 4 interseismic epochs. The data from this network provide a unique opportunity to examine the temporal and spatial evolution of the strain field associated with the 1906 San Francisco earthquake in particular and with the Pacific-North American plate boundary in general. Calculations of strain rate from the network data lead to the following conclusions. (1) There is no resolvable (greater than 0.05 microradians/yr) strain in between Sutter Buttes and the Sierra Nevada. (2) Throughout the time since the 1906 earthquake, a region extending at least as far east as the westernmost Great Valley has been undergoing deformation related to Pac:Nam interaction and the associated earthquake cycle. (3) In the time and space of overlap, our results agree with those from the United States Geological Survey (USGS) trilateration data. Both data sets indicate that strain must be accumulating to the east of Vaca. (4) The San Andreas discrepancy cannot be accommodated in the Great Valley at the 1 sigma level of our results. It is possible to absorb it in that region at the 2 sigma level. (5) Strain rate is elevated in the years following the earthquake and decays slowly with time. It is possible that the rate in the Coast Ranges increases until around 1950 and then decays. With the exception of one epoch, strain rate in the Coast Ranges is consistently fault parallel, shows no sign changes, and is consistent with monotonic strain accumulation.

Beavan, John; Gilbert, Lewis E.; Scholz, Chris

1992-01-01

138

Convergence  

NASA Astrophysics Data System (ADS)

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

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

2005-09-01

139

Hunting the European-Adriatic plate boundary in Eastern Alps: a receiver function perspective  

NASA Astrophysics Data System (ADS)

The type of collision between the European and the Adriatic plates in the easternmost portion of the Alps is one the most intriguing questions regarding the Alpine evolution. The interaction between the two plates is controversial all along the Alpine chain, e.g. changes of subduction polarity have been argued, but never clarified. This study focuses on the crust-mantle boundary, and on the differences between the European and Adriatic plate structures along a North-South oriented Receiver-Function profile from the Bohemian Massif to the Adriatic Sea. A seismically anisotropic layer is observed on top of the Moho interface from the Adriatic Sea to one of the major tectonic lines of the area, the SEMP fault. A seismically anisotropic upper mantle is detected at the boundary of the two plates, belonging to Europe and downgoing beneath Adria. These anisotropic features witness a different response to deformation of the two plates. The plate boundary appears to extend further north than the recognized boundary on surface, raising new questions on the deep interaction between the two plates.

Bianchi, I.; Bokelmann, G. H.; Behm, M.

2012-12-01

140

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

NASA Astrophysics Data System (ADS)

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

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

2007-02-01

141

Convergence  

NASA Astrophysics Data System (ADS)

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

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

2005-06-01

142

Convergence  

NASA Astrophysics Data System (ADS)

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

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

2005-08-01

143

Kinematics to dynamics in the New Zealand plate-boundary zone  

NASA Astrophysics Data System (ADS)

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

Lamb, S. H.

2013-12-01

144

Analytical solutions to the fundamental frequency of arbitrary laminated plates under various boundary conditions  

NASA Astrophysics Data System (ADS)

In recent years, as the composite laminated plates are widely used in engineering practice such as aerospace, marine and building engineering, the vibration problem of the composite laminated plates is becoming more and more important. Frequency, especially the fundamental frequency, has been considered as an important factor in vibration problem. In this paper, a calculation method of the fundamental frequency of arbitrary laminated plates under various boundary conditions is proposed. The vibration differential equation of the laminated plates is established at the beginning of this paper and the frequency formulae of specialty orthotropic laminated plates under various boundary conditions and antisymmetric angle-ply laminated plates with simply-supported edges are investigated. They are proved to be correct. Simple algorithm of the fundamental frequency for multilayer antisymmetric and arbitrary laminated plates under various boundary conditions is studied by a series of typical examples. From the perspective of coupling, when the number of laminated plates layers N > 8-10, some coupling influence on the fundamental frequency can be neglected. It is reasonable to use specialty orthotropic laminated plates with the same thickness but less layers to calculate the corresponding fundamental frequency of laminated plates. Several examples are conducted to prove correctness of this conclusion. At the end of this paper, the influence of the selected number of layers of specialty orthotropic laminates on the fundamental frequency is investigated. The accuracy and complexity are determined by the number of layers. It is necessary to use proper number of layers of special orthotropic laminates with the same thickness to simulate the fundamental frequency in different boundary conditions.

Luo, Yingqin; Hong, Ming; Liu, Yuan

2015-03-01

145

Kinematics to dynamics in the New Zealand plate-boundary zone  

NASA Astrophysics Data System (ADS)

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

Lamb, Simon

2014-05-01

146

The effect of rectangular synthetic jet to the flat plate boundary layer in low Reynolds number  

NASA Astrophysics Data System (ADS)

The objective of this study is investigating the impact of synthetic jet on the boundary layer and optimising the slot yaw angle (?). A rectangular synthetic jet with yaw angle relative to freestream is applied for flat plate boundary layer control. Various slot yaw angles are applied to find optimized amount and their impacts on the boundary layer are measured using a boundary layer probe with 2-D traversing system. The slot yaw angles are varied from 0°~90°. The assessment carried out using non-dimensional velocity profiles and lateral relative velocity (u/U) contours.

Kim, Young-Hwan

2012-04-01

147

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

NASA Technical Reports Server (NTRS)

Commonly used one dimensional geoid models predict that the isostatic geoid anomaly over old ocean basins for the boundary layer thermal model of the lithosphere is a factor of two greater than that for the plate model. Calculations presented, using the spherical analogues of the plate and boundary layer thermal models, show that for the actual global distribution of plate ages, one dimensional models are not accurate and a spherical, fully three dimensional treatment is necessary. The maximum difference in geoid heights predicted for the two models is only about two meters. The thermal structure of old lithosphere is unlikely to be resolvable using global geoid anomalies. Stripping the effects of plate aging and a hypothetical uniform, 35 km, isostatically-compensated continental crust from the observed geoid emphasizes that the largest-amplitude geoid anomaly is the geoid low of almost 120 m over West Antarctica, a factor of two greater than the low of 60 m over Ceylon.

Hager, B. H.

1981-01-01

148

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

NASA Technical Reports Server (NTRS)

Weak shock-wave interactions with boundary layers on a flat plate were investigated experimentally in Mach 8 variable-density tunnel for plate-length Reynolds numbers. The undisturbed boundary layers were laminar over the entire plate length. Pressure and heat-transfer distributions were obtained for wedge-generated incident shock waves that resulted in pressure rises ranging from 1.36 to 4.46 (both nonseparated and separated boundary-layer flows). The resulting heat-transfer amplifications ranged from 1.45 to 14. The distributions followed established trends for nonseparated flows, for incipient separation, and for laminar free-interaction pressure rises. The experimental results corroborated established trends for the extent of the pressure rise and for certain peak heat-transfer correlations.

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

1974-01-01

149

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

NASA Technical Reports Server (NTRS)

Work is devoted to study of free-stream vorticity normal to leading edge interaction with boundary layer over plate and resulting flow distortion influence on laminar-turbulent transition. In experiments made the wake behind the vertically stretched wire was used as a source of vortical disturbances and its effect on the boundary layer over the horizontally mounted plate with various leading edge shapes was investigated. The purpose of experiments was to check the predictions of theoretical works of M.E. Goldstein, et. al. This theory shows that small free-stream inhomogeneity interacting with leading edge produces considerable distortion of boundary layer flow. In general, results obtained confirms predictions of Goldstein's theory, i.e., the amplification of steady vortical disturbances in boundary layer caused by vortex lines stretching was observed. Experimental results fully coincide with predictions of theory for large Reynolds number, relatively sharp leading edge and small disturbances. For large enough disturbances the flow distortion caused by symmetric wake unexpectedly becomes antisymmetric in spanwise direction. If the leading edge is too blunt the maximal distortion takes place immediately at the nose and no further amplification was observed. All these conditions and results are beyond the scope of Goldstein's theory.

Kogan, M. N.; Ustinov, M. V.

1997-01-01

150

Analytical solutions for bending analysis of rectangular laminated plates with arbitrary lamination and boundary conditions  

Microsoft Academic Search

The intent of the present study is to employ the extended Kantorovich method for semi-analytical solutions of laminated composite\\u000a plates with arbitrary lamination and boundary conditions subjected to transverse loads. The method based on separation of\\u000a spatial variables of displacement field components. Within the displacement field of a first-order shear deformation theory,\\u000a a laminated plate theory is developed. Using the

Ali Mohammad Naserian Nik; Masoud Tahani

2009-01-01

151

Null-Field Integral Equation Approach for Plate Problems With Circular Boundaries  

Microsoft Academic Search

In this paper, a semi-analytical approach for circular plate problems with multiple cir- cular holes is presented. Null-field integral equation is employed to solve the plate prob- lems while the kernel functions in the null-field integral equation are expanded to degen- erate kernels based on the separation of field and source points in the fundamental solution. The unknown boundary densities

Jeng-Tzong Chen; Chia-Chun Hsiao; Shyue-Yuh Leu

2006-01-01

152

Velocity Distribution in the Boundary Layer of a Submerged Plate  

NASA Technical Reports Server (NTRS)

This report deals with the measurement of the velocity distribution of the air in the velocity of a plate placed parallel to the air flow. The measurements took place in a small wind tunnel where the diameter of the entrance cone is 30 cm and the length of the free jet between the entrance and exit cones is about 2.5 m. The measurements were made in the free jet where the static pressure was constant, which was essential for the method of measurement used.

Hansen, M

1930-01-01

153

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

NASA Astrophysics Data System (ADS)

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

Wortel, M. J.; Govers, R. M.; van Benthem, S.

2013-12-01

154

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

155

Convergence  

NSDL National Science Digital Library

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

156

Converging shear rheometer  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

157

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

E-print Network

The unsteady boundary layer behavior on the concave surface of a curved plate is investigated. Detailed experimental investigations are carried out to study the effect of unsteady wakes on the boundary layer transition under varying wake passing...

Read, Robert Kevin

1997-01-01

158

Rayleigh phase velocities in the upper mantle of the Pacific-North American plate boundary in southern California  

NASA Astrophysics Data System (ADS)

The Pacific-North America plate boundary, located in Southern California, presents an opportunity to study a unique tectonic process that has been shaping the plate tectonic setting of the western North American and Mexican Pacific margin since the Miocene. This is one of the few locations where the interaction between a migrating oceanic spreading center and a subduction zone can be studied. The rapid subduction of the Farallon plate outpaced the spreading rate of the East Pacific Rise rift system causing it to be subducted beneath southern California and northern Mexico 30 Ma years ago. The details of microplate capture, reorganization, and lithospheric deformation on both the Pacific and North American side of this boundary is not well understood, but may have important implications for fault activity, stresses, and earthquake hazard analysis both onshore and offshore. We use Rayleigh waves recorded by an array of 34 ocean bottom seismometers deployed offshore southern California for a 12 month duration from August 2010 to 2011. Our array recorded teleseismic earthquakes at distances ranging from 30° to 120° with good signal-to-noise ratios for magnitudes Mw ? 5.9. The events exhibit good azimuthal distribution and enable us to solve simultaneously for Rayleigh wave phase velocities and azimuthal anisotropy. Fewer events occur at NE back-azimuths due to the lack of seismicity in central North America. We consider seismic periods between 18 - 90 seconds. The inversion technique considers non-great circle path propagation by representing the arriving wave field as two interfering plane waves. This takes advantage of statistical averaging of a large number of paths that travel offshore southern California and northern Mexico allowing for improved resolution and parameterization of lateral seismic velocity variations at lithospheric and sublithospheric depths. We present phase velocity results for periods sampling mantle structure down to 150 km depth along the west coast margin. With this study, we seek to understand the strength and deformation of the Pacific oceanic lithosphere resulting from plate convergence and subduction beneath Southern California 30 Ma as well as translational stresses present today. We also test for predictions of several geodynamic models which describe the kinematic mantle flow that accompanies plate motion within this area including passive mantle drag due to Pacific plate motion and toroidal flow in the western U.S. region that may extend offshore.

Escobar, L.; Weeraratne, D. S.; Kohler, M. D.

2013-05-01

159

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

NASA Astrophysics Data System (ADS)

The western edge of the Indian plate is a transform plate boundary similar to the San Andreas Fault in that it lies mostly on land, has a similar expected slip rate, accommodates restraining bends, and contains segments that may slip aseismically by surface creep. Tectonic models of the western edge of India must also account for the absence of significant seismic moment release in the past century along the Chaman Fault, the transform boundary between Asia and India. I discuss modern and historical data from India and Pakistan that provide new constraints on deformation within this 100--250 km wide plate boundary. Geological and plate-closure estimates suggest sinistral slip of 19--35 mm/yr since the Oligocene across the Chaman Fault system. Analysis of space-based geodetic data suggests a prevalence of shallow locking depths and an upper limit of approximately 19.5 mm/yr of sinistral motion across the Chaman Fault System south of Afghanistan. In the past century, the region between the Chaman Fault System and the Indus Plain near Quetta, Pakistan, has experienced numerous earthquakes with a larger total moment release than an equivalent length of the Himalaya in the same period, comparable to a single Mw 8:0. Of this moment release, 90% has occurred more than 70 km east of the Chaman fault. In this region, GPS data have captured slip partitioning across the plate boundary suggesting that long-term sinistral slip is shared between the Chaman and Ghazaband fault systems. Additionally, a combination of GPS and InSAR analysis of a pair of Mw 6:4 earthquakes NE of Quetta in 2008 suggests that they occurred on a parallel pair of sinistral faults, rather than the dextral mechanism suggested by their NW-SE trending fault planes. I find that "bookshelf faulting" occurs in a zone NE of Quetta that includes several previous instrumental and historical earthquakes. This geodetic view of deformation in Pakistan differs from that derived from the instrumental seismic record, but is consistent with the sparse historical record of earthquakes in the past two millennia, and has important implications for assessment of seismic hazards in Pakistan.

Szeliga, W. M.

160

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

Microsoft Academic Search

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

J. Purbolaksono; M. H. Aliabadi

2005-01-01

161

Upper boundary of the Pacific plate subducting beneath Hokkaido, Japan, estimated from ScSp phase  

NASA Astrophysics Data System (ADS)

Three-dimensional geometry of the upper boundary of the Pacific plate subducting beneath Hokkaido, Japan, was obtained using the ScSp phase: the phase converted from ScS (S wave reflected at the core-mantle boundary) to P wave at the plate boundary. Taking the advantage of a dense seismic network, "Hi-net", recently deployed across the Japanese islands, we applied several seismic array analyses to the recorded waveform data for a large nearby deep earthquake, in order to enhance very weak ScSp signals in the original records. At first, we set up five blocks for the region in plate dip directions. After aligning the travel times of ScS and stacking seismograms among stations in a given sub-block perpendicular to each dip direction, we searched for the optimal plate model (i.e., two-dimensional geometry of the upper boundary) for each block. The model was parameterized by seven depth grids, and seismograms were stacked based on the travel time of ScSp as a time lag of each sub-block, so that the optimal model would yield the maximum spectral energy of ScSp after stacking. This model parameter search was conducted, using ray tracings of ScSp with a reference velocity model and a non-linear inversion scheme (Neighbourhood Algorithm). The optimal model of each block was combined each other by cubic spline interpolation, in order to construct an overall three-dimensional geometry of the upper boundary of the plate. Next, we performed the frequency-wavenumber ( f- k) spectral analysis to refine the above result. Assuming each station as a reference point, we made beam output from records of its adjacent stations as a function of wavenumber vector ( kx, ky) and frequency. The peak of its power spectrum was considered to represent the wavenumber vector of ScSp, that is, azimuth of arrival and slowness, so that we can estimate the position and depth of the corresponding ScS- ScSp conversion. In the frequency range from 0.5 to 1.5 Hz, we could estimate the conversion points for 21 stations or hypothetical arrays, and revised the geometry of the upper boundary obtained by the non-linear stacking approach in the previous step. The final plate model was compared with the distribution of intraplate earthquakes in the Pacific plate. This comparison clearly reveals that the upper seismic zone merges with the lower from 150 to 200 km in depth, deviating systematically away from the upper boundary where the boundary is slightly bumped in a convex manner.

Osada, Kinue; Yoshizawa, Kazunori; Yomogida, Kiyoshi; Suetsugu, Daisuke; Bina, Craig; Inoue, Toru; Wiens, Douglas; Jellinek, Mark

2010-11-01

162

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

163

Geometrically nonlinear dynamic response of stiffened plates with moving boundary conditions  

NASA Astrophysics Data System (ADS)

An approach is presented to investigate the nonlinear vibration of stiffened plates. A stiffened plate is divided into one plate and some stiffeners, with the plate considered to be geometrically nonlinear, and the stiffeners taken as Euler beams. Lagrange equation and modal superposition method are used to derive the dynamic equilibrium equations of the stiffened plate according to energy of the system. Besides, the effect caused by boundary movement is transformed into equivalent excitations. The first approximation solution of the non-resonance is obtained by means of the method of multiple scales. The primary parametric resonance and primary resonance of the stiffened plate are studied by using the same method. The accuracy of the method is validated by comparing the results with those of finite element analysis via ANSYS. Numerical examples for different stiffened plates are presented to discuss the steady response of the non-resonance and the amplitude-frequency relationship of the primary parametric resonance and primary resonance. In addition, the analysis on how the damping coefficients and the transverse excitations influence amplitude-frequency curves is also carried out. Some nonlinear vibration characteristics of stiffened plates are obtained, which are useful for engineering design.

Ma, NiuJing; Wang, RongHui; Han, Qiang; Lu, YiGang

2014-08-01

164

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

SciTech Connect

Research on the seismotectonics of plate boundaries is summarized. Instrumental development and an observational program designed to study various aspects of the seismotectonics of southern California and the northern Gulf of California are described. A unique superconducting gravimeter was further developed and supported under this program for deployment and operation at several sites. Work on Earth tides is also discussed.

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

1981-06-01

165

Influence of diameter and boundary conditions on low velocity impact response of CFRP circular laminated plates  

Microsoft Academic Search

Low velocity and low energy impact tests were carried out on CFRP circular laminated plates, in order to investigate the effect of specimen dimensions and boundary conditions on dynamic behaviour and material damage. Two different diameters and constraints were tested. Numerical simulations of specimen impact response were performed by a finite element program and compared to experimental results. Tests indicated

Giangiacomo Minak; Daniele Ghelli

2008-01-01

166

Thermal State of the Seismogenic Plate Boundary in Southern Chile, 36 -- 46 °S  

Microsoft Academic Search

According to current models of great subduction earthquakes, the area of the ruptured zone, and therefore the magnitude of the event, is controlled by the thermal structure of the plate boundary; updip and downdip limits of the seismogenic zone coincide with temperatures of 100 - 150 °C and 350 - 450°C, respectively. From this point of view, the 1960 Chile

M. Heesemann; I. Grevemeyer; H. W. Villinger; E. Contreras-Reyes; M. Scherwath; D. Völker

2006-01-01

167

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

Microsoft Academic Search

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

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

1993-01-01

168

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

Microsoft Academic Search

Large and intermediate-scale tectonic features such as subduction zones, large igneous provinces, rifts, and diffuse plate boundary zones are often seen to have a magnetic signature visible from the perspective of near-Earth magnetic field satellites such as CHAMP and Orsted. Why do these tectonic features have a magnetic signature, while others do not? A new model of the lithospheric field

M. E. Purucker; K. A. Whaler

2008-01-01

169

The Plate Boundary Observatory as a Network for Water Cycle Studies  

Microsoft Academic Search

Measurements of soil moisture, snow, and vegetation are needed at various spatial and temporal scales to study the water and carbon cycle. Here we outline ways in which the ~1100 GPS receivers that make up the Plate Boundary Observatory can be used to provide daily measurements of soil moisture, snow, and vegetation water content. Our work is based on using

K. M. Larson; E. E. Small; J. J. Braun; E. D. Gutmann; M. W. Williams; V. U. Zavorotny; B. Munson; A. L. Bilich; F. G. Nievinski; J. Normandeau; S. Doelger

2009-01-01

170

Scaling Analysis of the Thermal Boundary Layer Adjacent to an Abruptly Heated Inclined Flat Plate  

Microsoft Academic Search

The natural convection thermal boundary layer adjacent to an abruptly heated inclined flat plate is investigated through a scaling analysis and verified by numerical simulations. In general, the development of the thermal flow can be characterized by three distinct stages, i.e. a start-up stage, a transitional stage and a steady state stage. Major scales including the flow velocity, flow development

S. C. Saha; C. Lei; J. C. Patterson

171

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

Microsoft Academic Search

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

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

2010-01-01

172

A family of laminar boundary layers along a semi-infinite flat plate  

Microsoft Academic Search

A new similarity solution is obtained for flow of a uniform stream past an aligned, semi-infinite flat plate. The fluid is incompressible, of constant density, and constant absolute viscosity. A detailed examination is made of flows involving steady rates of accretion and of ablation at the leading edge. Both the classical Blasius boundary layer and the Rayleigh-Stokes shear layer are

L. Todd

1997-01-01

173

Completion of the 16 station Plate Boundary Observatory (PBO) network on Mt. St. Helens, WA  

Microsoft Academic Search

The Plate Boundary Observatory (PBO), part of the larger NSF-funded EarthScope project, is completing year 3 of the installation phase of 852 continuously operating GPS stations in the Western United States. Some of these GPS stations are focused specifically on centers of volcanic activity. Mt. St. Helens is one of these volcanic areas of interest in the Pacific Northwest (PNW)

K. Austin; K. Hafner; K. Fengler; S. Doelger

2006-01-01

174

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

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

175

Hypocenter distribution of plate boundary zone off Fukushima Japan derived from ocean bottom seismometer data  

Microsoft Academic Search

Microearthquake observation using Ocean Bottom Seismometers (OBSs) was carried out to obtain a detailed distribution of microearthquakes beneath the area off Fukushima, in the middle section of the Japan Trench in the summer of 1997. The observation period spanned approximately one month. Almost all of the well-determined hypocenters occurred in the vicinity of the plate boundary in this region (approximately

Masanao Shinohara; Ryota Hino; Takashi Yoshizawa; Minoru Nishino; Kiyoshi Suyehiro

2005-01-01

176

India and Sunda plates motion and deformation along their boundary in Myanmar determined by GPS  

E-print Network

India and Sunda plates motion and deformation along their boundary in Myanmar determined by GPS with respect to mainland India. Including these points, using a longer time span than previous studies-day Indian motion. Our results confirm that the current motion of India is slower than predicted by the NUVEL

Socquet, Anne

177

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

NASA Astrophysics Data System (ADS)

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

Olds, S. E.

2010-12-01

178

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

NASA Astrophysics Data System (ADS)

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

Benthem, Steven; Govers, Rob; Wortel, Rinus

2014-05-01

179

The Northwestern (Maghreb) boundary of the Nubia (Africa) Plate  

NASA Astrophysics Data System (ADS)

A study of the present compressional deformation of the Northwestern (Maghreb) Nubia (Africa) margin is derived from the analysis of more than 20,000 km of seismic profiles. In the western part the compression is distributed in a large zone with on-land compression in Algeria, mainly strike-slip deformation on the Algerian margin and folds and strike-slip faulting in Eastern Spain. In the middle of the Algerian margin, around Algiers, the evidences of compression become more obvious. In this area a ridge trending N-S that is interpreted as a middle to late Miocene spreading center interacted with the transpressional margin that trends E-W. North of the location of the Boumerdes-Zemmouri earthquake the oceanic crust is deformed by blind thrusts up to 60 km from the coast. These thrusts are south dipping and with the northward dipping thrusts located onshore form a wedge that maybe a positive flower structure at a crustal scale related to the right-lateral transpression of the margin. In the eastern part of the Northwestern (Maghreb) Nubia (Africa) Deformed Belt, off eastern Algeria and Tunisia, the deformation is more intense but limited to the north by the continental slope. Large late Miocene Tortonian folds are cut by the Messinian erosional surface but the present deformation is also evident. It is suggested that the deformation with a double vergence may be followed up to the north of Sicily. After the docking (18 Ma) of the Kabylies to the Africa Plate, the crust has been thinned and the Algerian Basin opened during the middle-late Miocene with an E-W direction. From the late Miocene to the Present the margin has been rethickened by transpression and uplifted.

Mauffret, Alain

2007-01-01

180

The delamination effect in laminated von Kármán plates under unilateral boundary conditions. A variational-hemivariational inequality approach  

Microsoft Academic Search

This paper deals with the delamination effect for laminated plates undergoing large displacements (v. Kármán plates). The interaction between the laminae due to the binding material as well as the delamination effect are described by means of a nonmonotone, possibly multivalued law, while on the boundary of each lamina general unilateral boundary conditions obeying monotone laws are assumed to hold.

P. D. Panagiotopoulos; G. E. Stavroulakis

1990-01-01

181

Block kinematics of the PacificNorth America plate boundary in the southwestern United States from inversion of GPS,  

E-print Network

Block kinematics of the Pacific­­North America plate boundary in the southwestern United States­North America plate boundary in the southwestern United States from inversion of GPS, seismological of the southwestern United States (30°­41°N) is represented by a finite number of rotating, elastic-plastic spherical

McCaffrey, Robert

182

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

NASA Technical Reports Server (NTRS)

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

Bischke, R. E.

1974-01-01

183

The Theory of Plate Tectonics  

NSDL National Science Digital Library

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

184

Measurements of strain at plate boundaries using space based geodetic techniques  

NASA Technical Reports Server (NTRS)

We have used the space based geodetic techniques of Satellite Laser Ranging (SLR) and VLBI to study strain along subduction and transform plate boundaries and have interpreted the results using a simple elastic dislocation model. Six stations located behind island arcs were analyzed as representative of subduction zones while 13 sites located on either side of the San Andreas fault were used for the transcurrent zones. The length deformation scale was then calculated for both tectonic margins by fitting the relative strain to an exponentially decreasing function of distance from the plate boundary. Results show that space-based data for the transcurrent boundary along the San Andreas fault help to define better the deformation length scale in the area while fitting nicely the elastic half-space earth model. For subduction type bonndaries the analysis indicates that there is no single scale length which uniquely describes the deformation. This is mainly due to the difference in subduction characteristics for the different areas.

Robaudo, Stefano; Harrison, Christopher G. A.

1993-01-01

185

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

USGS Publications Warehouse

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

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

1992-01-01

186

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

PubMed

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

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

2009-04-24

187

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

NASA Astrophysics Data System (ADS)

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

Landes, M.; Pavlis, G. L.

2008-12-01

188

Tectonics of the Easter plate  

NASA Technical Reports Server (NTRS)

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

Engeln, J. F.; Stein, S.

1984-01-01

189

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

190

Plate Borders and Mountain Building  

NSDL National Science Digital Library

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

Schlumberger Excellence in Educational Development, Inc.

191

Late Cretaceous to mid Eocene plate boundaries in the southwest Pacific  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

192

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

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

193

A modelling study of vertical surface displacements at convergent plate margins  

E-print Network

of the overriding plate margin. This subsidence is reduced when roll-back takes place in a land-locked basin setting. Subduction zone roll-back due to sinking of the negatively buoyant subducting plate induces subsidence, finite element method, subduction, subsidence, uplift. 1 I N T R O D U C T I O N 1.1 Aims and approach

Buiter, Susanne

194

Estimating the convergence rate for eigenfrequencies of anisotropic plates with variable thickness  

NASA Astrophysics Data System (ADS)

Estimates of the differences between rescaled eigenvalues of the spectral problem for a thin anisotropic plate and eigenvalues of its two-dimensional models are obtained with bounds expressed in terms of the plate's thickness and attributes of the limit eigenvalue. To cite this article: S.A. Nazarov, C. R. Mecanique 330 (2002) 603-607.

Nazarov, Serguei A.

195

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

196

Structure and lithology of the Japan Trench subduction plate boundary fault  

NASA Astrophysics Data System (ADS)

The 2011 Mw9.0 Tohoku-oki earthquake ruptured to the trench with maximum coseismic slip located on the shallow portion of the plate boundary fault. To investigate the conditions and physical processes that promoted slip to the trench, Integrated Ocean Drilling Program Expedition 343/343T sailed 1 year after the earthquake and drilled into the plate boundary ˜7 km landward of the trench, in the region of maximum slip. Core analyses show that the plate boundary décollement is localized onto an interval of smectite-rich, pelagic clay. Subsidiary structures are present in both the upper and lower plates, which define a fault zone ˜5-15m thick. Fault rocks recovered from within the clay-rich interval contain a pervasive scaly fabric defined by anastomosing, polished, and lineated surfaces with two predominant orientations. The scaly fabric is crosscut in several places by discrete contacts across which the scaly fabric is truncated and rotated, or different rocks are juxtaposed. These contacts are inferred to be faults. The plate boundary décollement therefore contains structures resulting from both distributed and localized deformation. We infer that the formation of both of these types of structures is controlled by the frictional properties of the clay: the distributed scaly fabric formed at low strain rates associated with velocity-strengthening frictional behavior, and the localized faults formed at high strain rates characterized by velocity-weakening behavior. The presence of multiple discrete faults resulting from seismic slip within the décollement suggests that rupture to the trench may be characteristic of this margin.

Kirkpatrick, James D.; Rowe, Christie D.; Ujiie, Kohtaro; Moore, J. Casey; Regalla, Christine; Remitti, Francesca; Toy, Virginia; Wolfson-Schwehr, Monica; Kameda, Jun; Bose, Santanu; Chester, Frederick M.

2015-01-01

197

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

Microsoft Academic Search

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

E. Gnos; A. Immenhauser; Tj. Peters

1997-01-01

198

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

NASA Technical Reports Server (NTRS)

A flight experiment was conducted to investigate the pressure distribution, local-flow conditions, and boundary-layer transition characteristics on a large flat plate in flight at supersonic speeds up to Mach 2.00. The tests used a NASA testbed aircraft with a bottom centerline mounted test fixture. The primary objective of the test was to characterize the local flow field in preparation for future tests of a high Reynolds number natural laminar flow test article. A second objective was to determine the boundary-layer transition characteristics on the flat plate and the effectiveness of using a simplified surface coating. Boundary-layer transition was captured in both analog and digital formats using an onboard infrared imaging system. Surface pressures were measured on the surface of the flat plate. Flow field measurements near the leading edge of the test fixture revealed the local flow characteristics including downwash, sidewash, and local Mach number. Results also indicated that the simplified surface coating did not provide sufficient insulation from the metallic structure, which likely had a substantial effect on boundary-layer transition compared with that of an adiabatic surface. Cold wall conditions were predominant during the acceleration to maximum Mach number, and warm wall conditions were evident during the subsequent deceleration.

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

2012-01-01

199

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

200

The optimal rate of convergence of the p-version of the boundary element method in two dimensions  

E-print Network

with weakly singular or hypersingular operators, the solutions on polygonal domains have singularities for approximation errors in the p-version of the boundary element method for hypersingular and weakly singular integral operators on polygons. We prove the optimal rate of convergence for the p-version in the energy

Heuer, Norbert

201

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

SciTech Connect

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

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

1993-02-01

202

A preliminary investigation of boundary-layer transition along a flat plate with adverse pressure gradient  

NASA Technical Reports Server (NTRS)

Boundary-layer surveys were made throughout the transition region along a smooth flat plate placed in an airstream of practically zero turbulence and with an adverse pressure gradient. The boundary-layer Reynolds number at the laminar separation point was varied from 1,800 to 2,600. The test data, when considered in the light of certain theoretical deductions, indicated that transition probably began with separation of the laminar boundary layer. The extent of the transition region, defined as the distance from a calculated laminar separation point to the position of the first fully developed turbulent boundary-layer profile, could be expressed as a constant Reynolds number run of approximately 70,000. Some speculations are presented concerning the application of the foregoing concepts, after certain assumptions have been made, to the problem of the connection between transition on the upper surface of an airfoil at high angles of attack and the maximum lift.

Von Doenhoff, Albert E

1938-01-01

203

Dynamic Stability Optimization of Laminated Composite Plates under Combined Boundary Loading  

NASA Astrophysics Data System (ADS)

Dynamic stability and design optimization of laminated simply supported plates under planar conservative boundary loads are investigated in current study. Examples can be found in internal connecting elements of spacecraft and aerospace structures subjected to edge axial and shear loads. Designation of such elements is function of layup configuration, plate aspect ratio, loading combinations, and layup thickness. An optimum design aims maximum stability load satisfying a predefined stable vibration frequency. The interaction between compound loading and layup angle parameter affects the order of merging vibration modes and may stabilize the dynamic response. Laminated plates are assumed to be angle-plies symmetric to mid-plane surface. Dynamic equilibrium PDE has been solved using kernel integral transformation for modal frequency values and eigenvalue-based orthogonal functions for critical stability loads. The dictating dynamic stability mode is shown to be controlled by geometric stiffness distributions of composite plates. Solution of presented design optimization problem has been done using analytical approach combined with interior penalty multiplier algorithm. The results are verified by FEA approach and stability zones of original and optimized plates are stated as final data. Presented method can help designers to stabilize the dynamic response of composite plates by selecting an optimized layup orientation and thickness for prescribed design circumstances.

Shafei, Erfan; Kabir, Mohammad Zaman

2011-12-01

204

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

E-print Network

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

L. Petrova; B. Pavlov

2008-01-18

205

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

E-print Network

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

Petrova, L

2008-01-01

206

Boundary element formulation for planar time-dependent inelastic deformation of plates with cutouts  

SciTech Connect

A boundary element formulation for planar, time-dependent, inelastic deformation problems for bodies with cutouts is presented in this paper. A stress function description for these nonlinear problems leads to a nonhomogeneous biharmonic equation for the stress function rate. An integral representation of the solution uses modified kernels which guarantee that the cutout boundary is traction free for all time. This incorporation of the effect of the cutout on the stress field into the kernels leads to an accurate determination of stresses in the near field of the cutout. Illustrative analytical examples for circular plates with circular cutouts are presented in this paper. In a companion paper, numerical solutions are presented for problems of finite plates with very narrow elliptic cutouts. These problems are of considerable importance in inelastic fracture.

Mukherjee, S.; Morjaria, M.

1980-02-01

207

Geodetic observations in Iceland: divergent plate boundary influenced by a hotspot  

NASA Astrophysics Data System (ADS)

The mid Atlantic ridge, separating the Eurasian and North American tectonic plates, is mostly buried below the Atlantic. There are, however, a few places where subaerial exposure of the mid-oceanic rift system allows geodetic observations of the deformation associated with the plate boundary. Iceland is the largest portion of the system emerged above sea level, a consequence of excessive volcanism caused by the interaction of a mantle plume with the mid-oceanic ridge. Iceland is therefore a unique site to study processes associated with divergent plate boundaries, and the effects of the plume-ridge interaction. A network of continuous GPS stations have been operating in Iceland since 1995 when the first station was installed in Reykjavik. Since then, stations have been added to the network at different points in time, with over 70 stations presently in operation. The network has been used e.g. for studies of deformation associated with the divergent plate boundary, micro-plate formation due to rift jumps, the plate-spreading deformation cycle associated with rifting episodes, strain rates and stress accumulation on transform zones connecting the ridge segments and deformation due to magmatic processes. In addition the GPS network is used in studies of the deformation associated with mass variations of Iceland's glaciers. The continuous GPS network serves as monitoring tool in Iceland, both for volcanic and seismic hazards but also as a research tool. In the recent Futurvolc project, which partly builds on EPOS, the data from the continuous GPS network along with data from the seismic network and InSAR observations, will serve as the main input in joint analyses of long and short term magma movements in volcanic regions. The establishment of the continuous GPS network in Iceland has provided an ideal tool to further increase our understanding of the geodynamic processes associated with divergent plate boundaries and plume-ridge interaction as well as establishing a background velocity field, serving as the backbone for detailed geodetic studies of individual processes.

Ofeigsson, Benedikt Gunnar; Hreinsdóttir, Sigrun; Sigmundsson, Freysteinn; Arnadottir, Thora; Vogfjord, Kristin; Geirsson, Halldor; Einarsson, Pall; Jonsson, Sigurjon; Villemin, Thierry; Fjalar Sigurdsson, Sigurdur; Roberts, Matthew; Sturkell, Erik; Lafemina, Peter C.; Bennett, Richard; Voelksen, Christof; Valsson, Gudmundur; Sigurdsson, Thorarinn

2013-04-01

208

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

NASA Astrophysics Data System (ADS)

On 1 April 2014, Northern Chile was struck by a magnitude 8.1 earthquake following a protracted series of foreshocks. The Integrated Plate Boundary Observatory Chile monitored the entire sequence of events, providing unprecedented resolution of the build-up to the main event and its rupture evolution. Here we show that the Iquique earthquake broke a central fraction of the so-called northern Chile seismic gap, the last major segment of the South American plate boundary that had not ruptured in the past century. Since July 2013 three seismic clusters, each lasting a few weeks, hit this part of the plate boundary with earthquakes of increasing peak magnitudes. Starting with the second cluster, geodetic observations show surface displacements that can be associated with slip on the plate interface. These seismic clusters and their slip transients occupied a part of the plate interface that was transitional between a fully locked and a creeping portion. Leading up to this earthquake, the b value of the foreshocks gradually decreased during the years before the earthquake, reversing its trend a few days before the Iquique earthquake. The mainshock finally nucleated at the northern end of the foreshock area, which skirted a locked patch, and ruptured mainly downdip towards higher locking. Peak slip was attained immediately downdip of the foreshock region and at the margin of the locked patch. We conclude that gradual weakening of the central part of the seismic gap accentuated by the foreshock activity in a zone of intermediate seismic coupling was instrumental in causing final failure, distinguishing the Iquique earthquake from most great earthquakes. Finally, only one-third of the gap was broken and the remaining locked segments now pose a significant, increased seismic hazard with the potential to host an earthquake with a magnitude of >8.5.

Schurr, Bernd; Asch, Günter; Hainzl, Sebastian; Bedford, Jonathan; Hoechner, Andreas; Palo, Mauro; Wang, Rongjiang; Moreno, Marcos; Bartsch, Mitja; Zhang, Yong; Oncken, Onno; Tilmann, Frederik; Dahm, Torsten; Victor, Pia; Barrientos, Sergio; Vilotte, Jean-Pierre

2014-08-01

209

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

Microsoft Academic Search

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

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

2007-01-01

210

Repeating earthquakes and quasi-static slip on the plate boundary east off northern Honshu, Japan  

Microsoft Academic Search

We have investigated spatio-temporal variation in small repeating earthquake activity in the 1989 earthquake swarm and used them to infer quasi-static slip distribution on the plate boundary off Sanriku, northern Honshu, Japan. Seismicity and inferred quasi-static slip accelerations propagated to the west and to the south during the swarm activity to trigger the occurrence of the largest earthquake (M7.1). To

Toru Matsuzawa; Naoki Uchida; Toshihiro Igarashi; Tomomi Okada; Akira Hasegawa

2004-01-01

211

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

Microsoft Academic Search

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

L. Petrova; B. Pavlov

2008-01-01

212

Goringe-Alboran-Tell tectonic zone: A transpression system along the Africa-Eurasia plate boundary  

Microsoft Academic Search

Neotectonic structures distributed from the Goringe bank to the Tell Atlas mountains show that the Africa-Eurasia plate boundary in the western Mediterranean corresponds to an east-west trending deforming zone (Goringe-Alboran-Tell). Main Pliocene and Quaternary tectonic structures of the northern Atlas Mountains are northeast-southwest striking fault-related folds, similar to that of El Asnam, and are related to north-south to northwest-southeast compressional

Jean Luc Morel; Mustapha Meghraoui

1996-01-01

213

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

Microsoft Academic Search

The Plate Boundary Observatory (PBO), part of the NSF-funded EarthScope project, will complete the installation of a fourteen station GPS network on Unimak Island, Alaska in August, 2008. The primary data communications goal of the project is to design and implement a robust data communications network capable of downloading 15-sec daily GPS files and streaming 1 Hz GPS data, via

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

2008-01-01

214

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

PubMed

Steady two dimensional MHD laminar free convective boundary layer flows of an electrically conducting Newtonian nanofluid over a solid stationary vertical plate in a quiescent fluid taking into account the Newtonian heating boundary condition is investigated numerically. A magnetic field can be used to control the motion of an electrically conducting fluid in micro/nano scale systems used for transportation of fluid. The transport equations along with the boundary conditions are first converted into dimensionless form and then using linear group of transformations, the similarity governing equations are developed. The transformed equations are solved numerically using the Runge-Kutta-Fehlberg fourth-fifth order method with shooting technique. The effects of different controlling parameters, namely, Lewis number, Prandtl number, buoyancy ratio, thermophoresis, Brownian motion, magnetic field and Newtonian heating on the flow and heat transfer are investigated. The numerical results for the dimensionless axial velocity, temperature and nanoparticle volume fraction as well as the reduced Nusselt and Sherwood number have been presented graphically and discussed. It is found that the rate of heat and mass transfer increase as Newtonian heating parameter increases. The dimensionless velocity and temperature distributions increase with the increase of Newtonian heating parameter. The results of the reduced heat transfer rate is compared for convective heating boundary condition and found an excellent agreement. PMID:23166688

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

2012-01-01

215

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

PubMed Central

Steady two dimensional MHD laminar free convective boundary layer flows of an electrically conducting Newtonian nanofluid over a solid stationary vertical plate in a quiescent fluid taking into account the Newtonian heating boundary condition is investigated numerically. A magnetic field can be used to control the motion of an electrically conducting fluid in micro/nano scale systems used for transportation of fluid. The transport equations along with the boundary conditions are first converted into dimensionless form and then using linear group of transformations, the similarity governing equations are developed. The transformed equations are solved numerically using the Runge-Kutta-Fehlberg fourth-fifth order method with shooting technique. The effects of different controlling parameters, namely, Lewis number, Prandtl number, buoyancy ratio, thermophoresis, Brownian motion, magnetic field and Newtonian heating on the flow and heat transfer are investigated. The numerical results for the dimensionless axial velocity, temperature and nanoparticle volume fraction as well as the reduced Nusselt and Sherwood number have been presented graphically and discussed. It is found that the rate of heat and mass transfer increase as Newtonian heating parameter increases. The dimensionless velocity and temperature distributions increase with the increase of Newtonian heating parameter. The results of the reduced heat transfer rate is compared for convective heating boundary condition and found an excellent agreement. PMID:23166688

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

2012-01-01

216

Plate motions: fundamentals  

E-print Network

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

Déverchère, Jacques

217

The October 28, 2012 Mw 7.8 Haida Gwaii underthrusting earthquake and tsunami: Slip partitioning along the Queen Charlotte Fault transpressional plate boundary  

NASA Astrophysics Data System (ADS)

The Pacific/North American plate boundary is undergoing predominantly right-lateral strike-slip motion along the Queen Charlotte and Fairweather transform faults. The Queen Charlotte Fault (QCF) hosted the largest historical earthquake in Canada, the 1949 MS 8.1 strike-slip earthquake, which ruptured from offshore northern Haida Gwaii several hundred kilometers northwestward. On January 5, 2013 an Mw 7.5 strike-slip faulting event occurred near the northern end of the 1949 rupture zone. Along central and southern Haida Gwaii the relative plate motion has ?20% oblique convergence across the left-stepping plate boundary. There had been uncertainty in how the compressional component of plate motion is accommodated. The October 28, 2012 Mw 7.8 Haida Gwaii earthquake involved slightly (?20°) oblique thrust faulting on a shallow (?18.5°) northeast-dipping fault plane with strike (?320°) parallel to the QCF, consistent with prior inferences of Pacific Plate underthrusting beneath Haida Gwaii. The rupture extended to shallow depth offshore of Moresby Island beneath a 25-30 km wide terrace of sediments that has accumulated in a wedge seaward of the QCF. The shallow thrusting caused seafloor uplift that generated substantial localized tsunami run-up and a modest far-field tsunami that spread across the northern Pacific, prompting a tsunami warning, beach closure, and coastal evacuation in Hawaii, although ultimately tide gauges showed less than 0.8 m of water level increase. The mainshock rupture appears to have spread with a ?2.3 km/s rupture velocity over a length of ?150 km, with slip averaging 3.3 m concentrated beneath the sedimentary wedge. The event was followed by a substantial aftershock sequence, in which almost all of the larger events involve distributed intraplate normal faulting extending ?50 km oceanward from the QCF. The highly oblique slip partitioning in southern Haida Gwaii is distinctive in that the local plate boundary-parallel motion on the QCF may be accommodated either by infrequent large strike-slip ruptures or by aseismic creep, as seems to be the case for deeper oblique relative plate motion beneath Haida Gwaii, while the sedimentary terrace accumulates plate boundary-perpendicular compressional strain that releases in almost pure thrust faulting earthquakes, seaward of the QCF.

Lay, Thorne; Ye, Lingling; Kanamori, Hiroo; Yamazaki, Yoshiki; Cheung, Kwok Fai; Kwong, Kevin; Koper, Keith D.

2013-08-01

218

Neogene tectonic stress fields of northeast Honshu Arc and implications for plate boundary conditions  

NASA Astrophysics Data System (ADS)

More than 3300 metalliferous veins were analyzed to reconstruct the Neogene tectonic stress field of the northeast Honshu Arc using basic fracture mechanics. The veins are grouped into a dominant NE system and subordinate E-W, N-S and NW systems. The NE system is associated with assemblages of conjugate strike-slip faults and extension joints or normal faults which were formed during a period from 15 to 5 Ma. The fractures suggest that ?1or?2 was oriented ENE and ?3 was oriented NNW. ?3 is thought to have been tensional, because no veins are associated with thrust faults. This stress orientation is neither perpendicular nor parallel to the axis of the Japan Trench where the Pacific plate was moving west-northwest and was subducted under the northeast Honshu Arc. The inconsistency between the stress orientation and the plate kinematics can be explained by the dynamic effects related to other plate boundaries surrounding the northeast Honshu Arc, namely compression on the Hokkaido Axial Zone and the Itoigawa-Shizuoka Tectonic Line. In addition, the triple junction of the Japan Trench, Izu-Bonnin Trench and the Sagami Trough was probably located 300-400 km northeast from its present position and the subduction zone of Nankai Trough-Sagami Trough is assumed to have been a tensional plate boundary. The reconstructed stress field is consistent with transtensional backarc rifting at about 15 Ma.

Otsuki, Kenshiro

1990-09-01

219

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

NASA Astrophysics Data System (ADS)

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

Avalos, George

2006-06-01

220

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

E-print Network

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

Paris-Sud XI, Université de

221

3D geometry of the strain-field at transform plate boundaries: Implications for seismic rupture  

SciTech Connect

We examine the amplitude and distribution of slip on vertical frictionless faults in the zone of concentrated shear strain that is characteristic of transform plate boundaries. We study both a 2D and a 3D approximation to this strain field. Mean displacements on ruptures within the zone of concentrated shear strain are proportional to the shear strain at failure when they are short, and are limited by plate displacements since the last major earthquake when they are long. The transition between these two behaviors occurs when the length of the dislocation approaches twice the thickness of the seismogenic crust, approximately the breadth of the zone of concentrated shear strain observed geodetically at transform plate boundaries. This result explains the observed non-linear scaling relation between seismic moment and rupture length. A geometrical consequence of the 3D model, in which the strain-field tapers downward, is that moderate earthquakes with rupture lengths similar to the thickness of the crust tend to slip more at depth than near the surface. Seismic moments estimated from surface slip in moderate earthquakes (M less than or equal to 7) will thus be underestimated. Shallow creep, if its along-strike dimension is extensive, can reduce a surface slip deficit that would otherwise develop on faults on which M less than 7 events are typical. In the absence of surface creep or other forms of off-fault deformation great earthquakes may be necessary features of transform boundaries with downward-tapering strain-fields.

Bodin, P.; Bilham, R. [Univ. of Memphis, Memphis, TN (United States)] [Univ. of Memphis, Memphis, TN (United States); [Univ. of Colorado, Boulder, CO (United States)

1994-11-01

222

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

223

Critical exponents from parallel plate geometries subject to periodic and antiperiodic boundary conditions  

NASA Astrophysics Data System (ADS)

We introduce a renormalized one-particle irreducible, 1PI, vertex part scalar field theory setting in momentum space to computing the critical exponents ? and ?, at least at two-loop order, for a layered parallel plate geometry separated by a distance L, with periodic as well as antiperiodic boundary conditions on the plates. We utilize massive and massless fields in order to extract the exponents in independent ultraviolet and infrared scaling analysis, respectively, which are required in a complete description of the scaling regions for finite size systems. We prove that fixed points and other critical amounts either in the ultraviolet or in the infrared regime dependent on the plates boundary condition are a general feature of normalization conditions. We introduce a new description of typical crossover regimes occurring in finite size systems. Avoiding these crossovers, the three regions of finite size scaling present for each of these boundary conditions are shown to be indistinguishable in the results of the exponents in periodic and antiperiodic conditions, which coincide with those from the (bulk) infinite system.

da Silva, José B.; Leite, Marcelo M.

2012-04-01

224

Convergence of a non-stiff boundary integral method for interfacial flows with surface tension  

NASA Astrophysics Data System (ADS)

Boundary integral methods to simulate interfacial flows are very sensitive to numerical instabilities. In addition, surface tension introduces nonlinear terms with high order spatial derivatives into the interface dynamics. This makes the spatial discretization even more difficult and, at the same time, imposes a severe time step constraint for stable explicit time integration methods. A proof of the convergence of a reformulated boundary integral method for two-density fluid interfaces with surface tension is presented. The method is based on a scheme introduced by Hou, Lowengrub and Shelley [J. Comp. Phys. 114 (1994), pp. 312-338] to remove the high order stability constraint or stiffness. Some numerical filtering is applied carefully at certain places in the discretization to guarantee stability. The key of the proof is to identify the most singular terms of the method and to show, through energy estimates, that these terms balance one another. The analysis is at a time continuous-space discrete level but a fully discrete case for a simple Hele-Shaw interface is also studied. The time discrete analysis shows that the high order stiffness is removed and also provides an estimate of how the CFL constraint depends on the curvature and regularity of the solution. The robustness of the method is illustrated with several numerical examples. A numerical simulation of an unstably stratified two-density interfacial flow shows the roll-up of the interface; the computations proceed up to a time where the interface is about to pinch off and trapped bubbles of fluid are formed. The method remains stable even in the full nonlinear regime of motion. Another application of the method shows the process of drop formation in a falling single fluid.

Ceniceros, H. D.; Hou, T. Y.

1998-01-01

225

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

NASA Technical Reports Server (NTRS)

A flight experiment was conducted to investigate the pressure distribution, local flow conditions, and boundary-layer transition characteristics on a large flat plate in flight at supersonic speeds up to Mach 2.0. The primary objective of the test was to characterize the local flow field in preparation for future tests of a high Reynolds number natural laminar flow test article. The tests used a F-15B testbed aircraft with a bottom centerline mounted test fixture. A second objective was to determine the boundary-layer transition characteristics on the flat plate and the effectiveness of using a simplified surface coating for future laminar flow flight tests employing infrared thermography. Boundary-layer transition was captured using an onboard infrared imaging system. The infrared imagery was captured in both analog and digital formats. Surface pressures were measured with electronically scanned pressure modules connected to 60 surface-mounted pressure orifices. The local flow field was measured with five 5-hole conical probes mounted near the leading edge of the test fixture. Flow field measurements revealed the local flow characteristics including downwash, sidewash, and local Mach number. Results also indicated that the simplified surface coating did not provide sufficient insulation from the metallic structure, which likely had a substantial effect on boundary-layer transition compared with that of an adiabatic surface. Cold wall conditions were predominant during the acceleration to maximum Mach number, and warm wall conditions were evident during the subsequent deceleration. The infrared imaging system was able to capture shock wave impingement on the surface of the flat plate in addition to indicating laminar-to-turbulent boundary-layer transition.

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

2012-01-01

226

Polynomial decay rate of a thermoelastic Mindlin–Timoshenko plate model with Dirichlet boundary conditions  

NASA Astrophysics Data System (ADS)

In this article, we are concerned with the polynomial stabilization of a two-dimensional thermoelastic Mindlin-Timoshenko plate model with no mechanical damping. The model is subject to Dirichlet boundary conditions on the elastic as well as the thermal variables. The work complements our earlier work in Grobbelaar-Van Dalsen (Z Angew Math Phys 64:1305-1325, 2013) on the polynomial stabilization of a Mindlin-Timoshenko model in a radially symmetric domain under Dirichlet boundary conditions on the displacement and thermal variables and free boundary conditions on the shear angle variables. In particular, our aim is to investigate the effect of the Dirichlet boundary conditions on all the variables on the polynomial decay rate of the model. By once more applying a frequency domain method in which we make critical use of an inequality for the trace of Sobolev functions on the boundary of a bounded, open connected set we show that the decay is slower than in the model considered in the cited work. A comparison of our result with our polynomial decay result for a magnetoelastic Mindlin-Timoshenko model subject to Dirichlet boundary conditions on the elastic variables in Grobbelaar-Van Dalsen (Z Angew Math Phys 63:1047-1065, 2012) also indicates a correlation between the robustness of the coupling between parabolic and hyperbolic dynamics and the polynomial decay rate in the two models.

Grobbelaar-Van Dalsen, Marié

2015-02-01

227

Seismotectonics of the Lwandle-Nubia plate boundary between South Africa and the Southwest Indian Ridge  

NASA Astrophysics Data System (ADS)

The Lwandle (LW) plate shares a boundary with the Nubia (NU) plate, extending from a diffuse triple junction with the Rovuma plate in Southern Mozambique to a triple junction with the Antarctic plate along a segment of the Southwest Indian Ridge (SWIR). The LW-NU boundary terminates in the ~750 km-long, complex transform of the Andrew Bain Fracture Zone (ABFZ), but its exact locus is still unclear. Recent works locate it along the eastern boundary of the submarine Mozambique Ridge, parallel to the pre-existing, oceanic transform-fault fabric. However, an early concept of the LW block ('ambiguous region' of Hartnady, 1990, Fig. 2) indicates a more westerly trajectory in the north that includes parts of South Africa, with a southerly extension across old oceanic crust of the submarine Natal Valley and Transkei Basin. This proposed boundary is marked by several, aligned epicentres of moderate to strong earthquakes (1941, 1942, 1956, 1969, 1972, 1975, 1981 and 1989). Our re-examination of seismographic records from the 1975 'intraplate' earthquake (-37.62°N, 30.98°E, mb5.0), in the oceanic crust of the distal Transkei Basin, shows a thrust-faulting focal mechanism along a nodal plane striking N272°E. The largest (ML4.2) of a series of three small earthquakes in the Natal Valley in 2009, close to a zone of recent seafloor deformation mapped in 1992, has similar first-motion patterns at Southern African seismograph stations. When the 1975 slip-vector result (N173°E) is combined with a normal-faulting slip vector (N078°E) from a 1986 onland earthquake (-30.53°N, 28.84°E, mb5.0) near the Lesotho-KZN border, and both are incorporated into the wider data-set previously used to solve for East African Rift kinematics, they produce a LW-NU rotation pole that is located south of Africa, near the Agulhas Plateau, and approximately 950 km from the Natal Valley deformation zone. The modeled low rate of right-lateral, LW-NU slip (~0.50-0.75 mm/yr) across this LW-NU boundary segment suggests that the 1972, 1981 and nearby 2009 earthquakes are instances of a 'long aftershock sequence' in the source zone of the 1850 'i-Nyikima' event, which was felt over a very wide region of the Eastern Cape Colony, and the adjacent territories of British Kaffraria and Pondoland. This remarkable historic shaking appears to have been caused by a great (Mw8.0+), oceanic event along a segment of the LW-NU boundary, resembling the 1942 SWIR event along the ABFZ and the recent (2012 March 11) North Indian Ocean events along the incipient boundary between the Indian and Australian plates. This new interpretation has implications for the re-assessment of seismic and submarine-landslide (tsunami) hazard along the SE continental margin of South Africa. Reference Hartnady CJH (1990). Seismicity and plate boundary evolution in southeastern Africa. S. Afr. J. Geol. 93, 473 484.

Hartnady, Chris; Okal, Emile; Calais, Eric; Stamps, Sarah; Saria, Elifuraha

2013-04-01

228

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

E-print Network

The effect of unsteady periodic wakes on heat transfer and boundary layer transition was investigated on a constant curvature heat transfer curved plate in a subsonic wind tunnel facility. The local heat transfer coefficient distribution...

Wright, Lance Cole

1996-01-01

229

Evolution of the boundary between the Philippine Sea Plate and Australia: palaeomagnetic evidence from eastern Indonesia  

NASA Astrophysics Data System (ADS)

The boundary between the Philippine Sea and Australian plates is the left-lateral Sorong Fault system of eastern Indonesia. Until recently, modelling this boundary for the period before about 5 Ma was difficult; the Tertiary motion of the Philippine Sea Plate was uncertain and palaeomagnetic data from areas adjacent to the fault were lacking. Recent geological and palaeomagnetic studies of the area north of the Sorong Fault have elucidated the Tertiary motion history of the Philippine Sea Plate, providing a reference for examining movements within the fault system. We report new palaeomagnetic data from within the Sorong Fault Zone, from the islands of Taliabu and Obi. Taliabu is part of the Sula Platform and is considered to be derived from Australia. Pelagic limestones from the Upper Cretaceous Tanamu Formation of Taliabu yielded a direction of D = 329.1°, I = -34.9° implying counter-clockwise rotation and a formation latitude of 19 ± 5°S. Sula and Misool are postulated to be part of a single microcontinent which had a different Late Cretaceous-mid-Tertiary movement history from Australia. The Sula Platform was transported to its present position by movement along the Sorong Fault system in the Late Miocene. Obi includes rocks of Philippine Sea and Australian origin; all the new sites are in rocks of Philippine Sea Plate origin. Since the Early Neogene the Philippine Sea Plate, which includes all islands north of the Sorong Fault, has rotated 40° clockwise and moved 10-15° northwards. Philippine Sea Plate rocks within the Sorong Fault Zone record similar latitude shifts, but different rotations. In north Obi, the Upper Oligocene Anggai River Formation and the Middle Miocene Woi Formation record ˜ 60° and ˜ 30° counter-clockwise rotations, respectively. The sense of rotation is consistent with motion within a left-lateral fault system, with the Philippine Sea and Australian plates providing the shear couple. In contrast, the Woi Formation in southeast Obi records 15-20° clockwise rotation; this area is separated from the zone of counter-clockwise movement in north Obi by a strand of the Sorong Fault. Arc volcaniclastic rocks from the Upper Cretaceous Leleobasso Formation of northwest Obi have a primary magnetisation with a mean direction of D = 357.1°, I = -21.9°. These rocks formed at ˜ 11°N or ˜ 11°S, depending on the interpreted rotation history, and indicate a Pacific rather than Indian Ocean origin. A volcanic arc at the southern edge of the Philippine Sea Plate collided with eastern New Guinea at ˜ 25 Ma. The Philippine Sea-Australia plate boundary then changed from subduction to strike-slip, as the Philippine Sea Plate began its Neogene rotation, initiating the Sorong Fault system. We suggest that many of the arc fragments in the New Guinea orogenic belt originated in the southern Philippine Sea Plate arc which has subsequently been dismembered by strike-slip faulting.

Ali, Jason R.; Hall, Robert

1995-12-01

230

The influence of decoupling along plate boundaries on the mode of deformation and the geometry of collisional-type mountain belts  

NASA Astrophysics Data System (ADS)

The consequences of decoupling between weak orogenic wedges and strong adjacent foreland plates are investigated by means of lithospheric-scale analogue modeling. Decoupling is implemented in the three layer models by lubrication of the inclined boundary between the strong foreland and a weak orogenic wedge. Plate boundaries are orthogonal to the convergence direction. Experimental results show that strong decoupling between the foreland and the orogenic wedge leads to underthrusting of the former underneath the orogenic wedge, deformation of the orogenic wedge itself by folding, shearing and minor backthrusting. Shortening is mainly taken up along the main overthrust, the decoupled boundary, and within the orogenic wedge, leaving the indenter devoid of deformation. As a response to loading a foreland-type basin developed on the underthrusted plate. In contrast, strong coupling between the foreland and the orogenic wedge favors buckling, involving both, the weak zone and the strong plates. The development of topography through time reflects irregular folding (broad antiformal hinges are separated by narrow synforms), which is conditioned by the lateral strength variations from the strong encasing plates to the orogenic wedge. Our results show that (de)coupling between orogenic wedges and adjacent strong plates is a variable that can steer the structural and topographic evolution of collision zones as it controls the mechanisms by which the crust and lithosphere deform. The modelling results have implications for collision zones suggesting that an increase in resistive forces, as exemplified in this study through variable degrees of plate coupling, can lead to a change of the dominant deformation mechanism i.e. from thrusting to folding. Such a change is recorded in the evolution of the Eastern Alps in Europe, where subsidence and uplift/cooling data document the switch from localized deformation within the orogenic wedge proper during the Oligocene to Middle Miocene to orogen-scale uplift and deformation during the Late Miocene to recent. This younger phase of deformation involves the foreland and indenter plates and is interpreted as reflecting a change from a decoupled to a coupled system.

Sokoutis, D.; Willingshofer, E.

2009-04-01

231

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

Microsoft Academic Search

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

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

2003-01-01

232

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

233

What on Earth is Plate Tectonics?  

NSDL National Science Digital Library

This web site was put together by the U.S.G.S. (United States Geological Survey) and the N.P.S. (National Park Service) and provides an overview of plate tectonics. It begins by explaining about the Earth's core, mantle, and crust. It then discusses the crustal plates and the types of plate boundaries (convergent, divergent and transform). The lesson ends with paleogeographic reconstructions of plate distributions from the past 650 million years.

234

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

PubMed

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

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

2010-06-22

235

The boundary between the Indian and Asian tectonic plates below Tibet  

PubMed Central

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

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

2010-01-01

236

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

237

Effect of time-evolving age and convergence rate of the subducting plate on the Cenozoic adakites and boninites  

NASA Astrophysics Data System (ADS)

Partial melting of subducting oceanic crust expressed as high-Mg volcanic rocks such as adakites and boninites has been actively studied for decades, and Lee and King (2010) reported that time-evolving subduction parameters such as the age and the subduction rate of the converging oceanic plate play important roles in transient partial melting of the subducting oceanic crust (e.g., Aleutians). However, few subduction model experiments have considered time-evolving subduction parameters, posing problems for studies of transient partial melting of subducting oceanic crust in many subduction zones. Therefore, we constructed two-dimensional kinematic-dynamic subduction models for the Izu-Bonin, Mariana, Northeast Japan, Kuril, Tonga, Java-Sunda, and Aleutian subduction zones that account for the last 50 Myr of their evolution. The models include the time-evolving age and convergence rate of the incoming oceanic plate, so the effect of time-evolving subduction parameters on transient partial melting of oceanic crust can be evaluated. Our model calculations revealed that adakites and boninites in the Izu-Bonin and Aleutian subduction zones resulted from transient partial melting of oceanic crust. However, the steady-state subduction model using current subduction parameters did not produce any partial melting of oceanic crust in the aforementioned subduction zones, indicating that time-evolving subduction parameters are crucial for modeling transient eruption of adakites and boninites. Our model calculations confirm that other geological processes such as forearc extension, back-arc opening, mantle plumes and ridge subduction are required for partial melting of the oceanic crust in the Mariana, Northeast Japan, Tonga, and southeastern Java-Sunda subduction zones.

Kim, Yoon-Mi; Lee, Changyeol

2014-12-01

238

Relaxation of an unsteady turbulent boundary layer on a flat plate in an expansion tube  

NASA Technical Reports Server (NTRS)

An analysis is presented for the relaxation of a turbulent boundary layer on a semi-infinite flat plate after passage of a shock wave and a trailing driver gas-driven gas interface. The problem has special application to expansion-tube flows. The flow-governing equations have been transformed into the Crocco variables, and a time-similar solution is presented in terms of the dimensionless distance-time variable alpha and the dimensionless velocity variable beta. An eddy-viscosity model, similar to that of time-steady boundary layers, is applied to the inner and outer regions of the boundary layer. A turbulent Prandtl number equal to the molecular Prandtl number is used to relate the turbulent heat flux to the eddy viscosity. The numerical results, obtained by using the Gauss-Seidel line-relaxation method, indicate that a fully turbulent boundary layer relaxes faster to the final steady-state values of heat transfer and skin friction than a laminar boundary layer. The results also give a fairly good estimate of the local skin friction and heat transfer for near steady-flow conditions.

Gurta, R. N.; Trimpi, R. L.

1974-01-01

239

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

240

Flat plate boundary layer transition induced by a controlled near-wall circular cylinder wake  

NASA Astrophysics Data System (ADS)

The flat plate boundary layer transition induced by the wake of a circular cylinder close to the wall is experimentally investigated using particle image velocimetry (PIV) and hydrogen bubble visualization techniques. The wake of the circular cylinder is controlled by a slot synthetic jet at the rear stagnation point of the circular cylinder. It is found that when the synthetic jet is actuated, the wake can be greatly modified. When the excitation frequency of the synthetic jet is set at the natural shedding frequency of the cylinder wake, the symmetrical shedding pattern can be observed. While the excitation frequency increases to be twice of the natural shedding frequency, the wake appears to be antisymmetrical again, but with the shedding frequency locked onto half of the excitation frequency. Flow visualizations show that spanwise secondary vortices can be induced in the near wall region by these large scale vortices in the wake. It is found that the secondary vortices destabilize into streamwise stretched ? vortices as they convect downstream. After the introduction of the synthetic jet, the destabilization process is promoted. By investigating the disturbance growth inside the boundary layer, it reveals that the synthetic jet can cause earlier initialization of the disturbance growth, thus promoting the transition process of the boundary layer. An explanation is provided that the low frequency components of the wake disturbances, which interact with the boundary layer, are enhanced by the introduction of the synthetic jet. Therefore, the destabilization of the secondary vortices is promoted, and disturbance growth in the boundary layer initiates earlier.

He, Guo-Sheng; Wang, Jin-Jun

2015-02-01

241

Contraction along a previously extended plate boundary; analogue modelling of the Iberian - Eurasian suture zone  

NASA Astrophysics Data System (ADS)

The Iberian - Eurasian plate boundary can be roughly subdivided into a continent-continent and a continent-ocean collision zone in the east and west, respectively. This is due to the extensional phase that predates the contraction that formed the present day mountains in the area. A narrow ocean seaway separated the Iberian and Eurasian plates, whereas a wider ocean opened up towards west, where the present day Bay of Biscay lies. The deep seismic structures under the eastern segment show a subduction of the Iberian plate under the Eurasian plate, whereas the western segment is less well constrained and leave room for discussion regarding deep geometries and the nature of the collision zone. An analogue experiment was designed to represent the tectonic setting at the boundary at the culmination of the extensional phase in the early Cretaceous and then contracted to explore how surface topography and deep structures are affected by changes in upper mantle strength and contraction rate. The model is composed of layers of silicone putty and sand, tailored to simulate the assumed lithospheric geometries and strength-viscosity profiles along the plate boundary zone, and comprises two 'continental' plates separated by a thinner 'oceanic' plate that represents the narrow seaway that separated the eastern areas, and opens up to a 30° angle in the west, representing the Bay of Biscay. The experiment floats on a substrate of sodium polytungstate, representing mantle. The experiment was run 24 times, varying the thickness (and thus strength) of the upper mantle lithosphere, and the contraction rate. Keeping all other parameters identical for each experiment, the models were shortened by a computer-controlled jackscrew while time-lapse images were recorded. After completion, the models were saturated with water and frozen, allowing for sectioning and profile inspection. Of the 19 successful iterations of the experiment, three shortening rates were tested, each value representing an order of magnitude higher than the previous, and three thickness values (and thus strength) were applied to the sand layer representing upper mantle lithosphere. The results show how upper mantle strength appears to be the most important factor in determining whether an inversion of subduction direction occurs. A weak upper mantle layer (weaker than the oceanic crust) leads to obduction of the oceanic crust in the western segment of the model, forcing a significantly different scenario compared to observations in NW Spain today. In model iterations where the upper mantle is stronger than the oceanic crust, most model outcomes show a reversal in subduction polarity from northerly in the east, to southerly in the west. The transition zone is located where the narrow, parallel 'seaway' opens up towards west, near the centre of the model. Surface inspection of the models also show consistent patterns of faults breaking the surface, and are comparable to the present day major fault patterns mapped along the Pyrenean and Cantabrian mountains. It is concluded that both deep and surface structures are at least in part a result of the inherent zone of weakness that developed along the Iberian - Eurasian plate boundary.

Midtkandal, I.; Gabrielsen, R. H.; Brun, J.; Huismans, R. S.

2011-12-01

242

Laminar-Boundary-Layer Oscillations and Transition on a Flat Plate  

NASA Technical Reports Server (NTRS)

This is an account of an investigation in which oscillations were discovered in the laminar boundary layer along a flat plate. These oscillations were found during the course of an experiment in which transition from laminar to turbulent flow was being studied on the plate as the turbulence in the wind stream was being reduced to unusually low values by means of damping screens. The first part of the paper deals with experimental methods and apparatus, measurements of turbulence and sound, and studies of transition. A description is then given of the manner in which oscillations were discovered and how they were found to be related to transition, and then how controlled oscillations were produced and studied in detail.

Schubauer, G B; Skramstad, H K

1948-01-01

243

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

Microsoft Academic Search

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

M. Fathizadeh; F. Rashidi

2009-01-01

244

Turbulent boundary-layer along a streamwise bar of a rectangular cross section placed on a flat plate  

Microsoft Academic Search

The three-dimensional turbulent boundary layer developing along a long streamwise bar of a rectangular cross section placed on a flat plate was investigated experimentally. The mean velocity, turbulence intensity and wall shear stress distributions were measured, and the general behavior of the secondary currents accompanying the boundary layer were speculated from the deformation lines of constant velocity and constant turbulence

Y. Furuya; I. Nakamura; M. Miyata; Y. Yama

1977-01-01

245

Evolution of southern Caribbean plate boundary, vicinity of Trinidad and Tobago  

NASA Technical Reports Server (NTRS)

The tectonic evolution of the southeastern corner of the Caribbean is examined, using field data from the El Pilar fault zone of Trinidad and offshore seismic data. It is found that the dominant process in the region's tectonic evolution is strike-slip motion on at least five major fault systems in a 250-km wide east-west-trending plate-boundary zone extending from Grenada in the north to the Orinoco River in the south. The geological effects of this evolution over the past 30 m y are described.

Robertson, Paul; Burke, Kevin

1989-01-01

246

A globally converging secant method with applications to boundary value problems  

NASA Technical Reports Server (NTRS)

This paper presents a new algorithm for solving systems of nonlinear equations, which combines elements of the method of local variations with a sequential secant method. The new algorithm converges superlinearly and its convergence does not depend upon a good initial guess at a solution.

Polak, E.

1974-01-01

247

Relaxation of the accelerating-gas boundary layer to the test-gas boundary layer on a flat plate in an expansion tube  

NASA Technical Reports Server (NTRS)

An analytic investigation of the relaxation of the accelerating-gas boundary layer to the test-gas boundary layer over a flat plate mounted in an expansion tube has been conducted. In this treatment, nitrogen has been considered as the test gas and helium as the accelerating gas. The problem is analyzed in two conically similar limits: (1) when the time lag between the arrival of the shock and the interface at the leading edge of the plate is very large, and (2) when this time lag is negligible. The transient laminar boundary-layer equations of a perfect binary-gas mixture are taken as the flow governing equations. These coupled equations have been solved numerically by Gauss-Seidel line-relaxation method. The results predict the transient behavior as well as the time required for an all-helium accelerating-gas boundary layer to relax to an all-nitrogen boundary layer.

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

1973-01-01

248

Experimental study of boundary layer transition on a heated flat plate  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

249

A Reference Crustal and Plate-Boundary Velocity Model of Japan  

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

250

Tour of Park Geology: Plate Tectonics  

NSDL National Science Digital Library

This National Park Service (NPS) site provides links to geology field notes providing information about National Parks, National Monuments, and National Recreation Areas that have to do with plate tectonics. The site also has illustrations and descriptions of different plate boundaries. The parks are divided into categories depending on which type of plate boundary they are located on. This includes divergent boundaries(active and ancient), convergent boundaries (ocean-ocean, continent-continent, continent-ocean), transform faults, hot spots, and accreted terrains. Parks referenced include Virgin Islands National Park, Florissant Fossil Beds National Monument, Hawaii Volcanoes National Park, and many more.

251

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

USGS Publications Warehouse

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

Schouten, Hans; Klitgord, Kim D.

1982-01-01

252

Chemical and isotopic evidence of gas-influenced flow at a transform plate boundary: Monterey Bay, California  

USGS Publications Warehouse

Chemical and isotopic compositions of pore fluids document upward flow through communities of vesicomyid clams in Monterey Bay, California. Within the clam communities, the sulfate reduction zone is only 10 cm thick, and Ca and Mg concentrations decrease to values as low as 2.2 mM and 34.5 mM, respectively, at depths less than 30 cm below the sediment-water interface. Less than 5 m outside the communities, the base of the sulfate reduction zone is deeper than the greatest penetration of the cores (-30 cm), and Ca and Mg exhibit only minor changes from seawater values. The sediment exhibits no significant variation in grain size, mineralogy, organic carbon, nitrogen, or carbonate content throughout the region. The composition of pore fluid within clam communities results from upward flow of altered fluid rather than different diagenetic reactions within and outside the communities. Isotopically light dissolved inorganic carbon (DIC), with ??13C values ranging from -3.2 to -54.1???, could reflect carbon sources from either oxidized thermogenic methane and/or a mixture of oxidized microbial methane and solid organic carbon. The C1/(C2+C3) ratios (ranging from 34 to 1142) and the hydrogen and carbon isotopic compositions of methane (??D values of -109 to -156???; ??13C values of -30.6 to -86.6???) suggest that methane is primarily microbial but that a minor component could be thermally generated. Any thermogenic methane would have migrated from great depths, possibly >2 km. The presence of methane is likely to contribute to fluid flow by reducing the density of the fluids. Past fluid migration and venting are reflected by widespread carbonate mineralization at the sediment-water interface. This mineralization and the geographic distribution and proportions of microbial and thermogenic methane suggest that vent sites migrate when permeability is reduced during carbonate cementation. These results demonstrate that along with convergent and divergent plate boundaries, transform plate boundaries are characterized by fluid flow and that the flow may be widespread, occurring at sites away from fault zones.

Martin, J.B.; Orange, D.L.; Lorenson, T.D.; Kvenvolden, K.A.

1997-01-01

253

Seismicity and seismotectonics of the diffusive Iberian/African plate boundary: Horseshoe Abyssal Plain and Gorringe Bank  

NASA Astrophysics Data System (ADS)

In the area to the west of the Gibraltar Arc the plate boundary between Africa and Iberia is poorly defined. The deformation in the area is forced by the slow NW-SE convergence of 4 mm/yr between the oceanic domains of Iberia/Eurasia and Africa and is accommodated over a 200 km broad tectonically-active deformation zone. The region, however, is also characterized by large earthquakes and tsunamis, such as the 1969 Mw=7.9 Horseshoe Abyssal Plain earthquake and the November 1, 1755 Great Lisbon earthquake with an estimated magnitude of Mw~8.5. The exact location of the source of the 1755 Lisbon earthquake is still unknown. Recent work may suggest that the event occurred in the vicinity of the Horseshoe fault, an oblique thrust fault. However, estimates of tsunami arrival times suggested a source near the Gorringe Bank, a ~180 km-long and ~70 km-wide ridge that has a relieve of ~5000 m. Deep Sea Drilling (DSDP) and rock samples indicated that the bank is mainly composed of serpentinized peridotites with gabbroic intrusions, perhaps being created by overthrusting of the Horseshoe Abyssal Plain onto the Tagus Abyssal Plain in NW direction. Further, the Horseshoe Abyssal Plain is marked by the presence of compressive structures with a roughly NE-SW orientation and E-W trending, segmented, crustal-scale, strike slip faults that extend from the Gorringe Bank to the Gibraltar Arc in the eastern Gulf of Cadiz, which were called "South West Iberian Margin" or SWIM faults. The fault system may mark a developing Eurasia-Africa plate boundary. Two local seismic networks were operated in the area. First, a network of 14 ocean-bottom seismometers (OBS) was operated between April and October 2012 in the vicinity of the Horseshoe fault between 10°W to 11°W, and 35°50'N to 36°10'N. From October 2013 to March 2014 a second network of 15 OBS monitored seismicity at the Gorringe Bank. Both networks benefitted from seismic stations operated in Portugal. The first network provided in the order of 100 locale earthquakes occurring with the network. Most earthquakes in the Horseshoe occurred at a depth of 40-60 km, either in oceanic or unroofed continental mantle. The large source depth of events observed in the Horseshoe Abyssal Plain supports the idea that large catastrophic earthquakes, like the Great Lisbon earthquake of 1755, may indeed occur in the area.

Grevemeyer, Ingo; Lange, Dietrich; Matias, Luis

2014-05-01

254

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

NASA Astrophysics Data System (ADS)

Although smooth-flat-plate turbulent boundary layers (TBLs) have been studied for nearly a century, measurements at Reynolds numbers typical of marine & aerospace transportation systems are scarce. Experimental results at momentum-thickness Reynolds numbers (Re) up to 150,000 from the US Navy W.B. Morgan Large Cavitation Channel using a polished 12.9-m-long flat-plate test model at water flow speeds up to 20 m/s are presented. Mean velocity profiles were measured 10.7 m from the leading edge of the model over a wall-normal range from less than one wall unit to more than twice the nominal boundary layer thickness using particle-tracking and laser-Doppler velocimetry. Static pressure and average skin-friction were measured independently. A mild favorable pressure gradient led to a flow speed increase of 2.5% over the test surface. The measurements span a factor of three in Re and were fitted to within experimental uncertainty using one set of constants and modern empirical inner- and outer-profile forms based on traditional TBL asymptotics. The fitted profiles satisfy the von-Karman momentum integral to within 1%, and show distinct differences from equivalent zero pressure gradient results. [Supported by DARPA & ONR

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

2010-11-01

255

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

256

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

NASA Astrophysics Data System (ADS)

Homogeneous flow model is used to study the flow and heat transfer of carbon nanotubes (CNTs) along a flat plate subjected to Navier slip and uniform heat flux boundary conditions. This is the first paper on the flow and heat transfer of CNTs along a flat plate. Two types of CNTs, namely, single- and multi-wall CNTs are used with water, kerosene or engine oil as base fluids. The empirical correlations are used for the thermophysical properties of CNTs in terms of the solid volume fraction of CNTs. For the effective thermal conductivity of CNTs, Xue (Phys B Condens Matter 368:302-307, 2005) model has been used and the results are compared with the existing theoretical models. The governing partial differential equations and boundary conditions are converted into a set of nonlinear ordinary differential equations using suitable similarity transformations. These equations are solved numerically using a very efficient finite difference method with shooting scheme. The effects of the governing parameters on the dimensionless velocity, temperature, skin friction, and Nusselt numbers are investigated and presented in graphical and tabular forms. The numerical results of skin friction and Nusselt numbers are compared with the available data for special cases and are found in good agreement.

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

2014-06-01

257

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

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

258

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

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

259

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

260

Convergence results for pseudospectral approximations of hyperbolic systems by a penalty type boundary treatment  

NASA Technical Reports Server (NTRS)

A new method of imposing boundary conditions in the pseudospectral approximation of hyperbolic systems of equations is proposed. It is suggested to collocate the equations, not only at the inner grid points, but also at the boundary points and use the boundary conditions as penalty terms. In the pseudo-spectral Legrendre method with the new boundary treatment, a stability analysis for the case of a constant coefficient hyperbolic system is presented and error estimates are derived.

Funaro, Daniele; Gottlieb, David

1989-01-01

261

Optimizing the electrode size of circular bimorph plates with different boundary conditions for maximum deflection of piezoelectric micromachined ultrasonic transducers.  

PubMed

The effect of plate electrode area on the deflection of a symmetric circular bimorph piezoelectric micromachined ultrasonic transducer (pMUT) with clamped and simply supported boundary conditions was studied for the first time. Distinct plate displacement shape functions were defined for the regions underneath and outside the active electrodes. The plate shape functions were solved analytically using classic plate theory in conjunction with the external boundary conditions and the internal ones between the two regions in order to calculate the exact plate displacement under both external voltage stimulus and acoustic pressure. The model was used to study the effect of the electrode area on the overall plate deflection per unit input voltage such that the electromechanical coupling is optimized. While the center plate deflection increased monotonically with the electrode area for a simply supported plate, it followed a parabolic shape for a clamped one with a maximum deflection when the electrode radius covered 60% of the total plate radius. The simply supported plate exhibited four times the plate deflection capability of its clamped counterpart, when both are operating at their optimal electrode size. Both an experimental clamped bimorph aluminum nitride (AlN) pMUT, recently reported in the literature, and Finite Element Modeling (FEM) were used to verify the developed model. The theoretical model predicted a static displacement per unit voltage of 10.9nm/V and a resonant frequency of 196.5kHz, which were in excellent agreement with the FEM results of 10.32nm/V and 198.5kHz, respectively. The modeling data matched well with the experimental measurements and the error ranged from 2.7-22% due to process variations across the wafer. As such, the developed model can be used to design more sensitive pMUTs or extract the flexural piezoelectric coefficient using piezoelectrically actuated circular plates. PMID:22959848

Sammoura, Firas; Smyth, Katherine; Kim, Sang-Gook

2013-02-01

262

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

NASA Technical Reports Server (NTRS)

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

Sohn, Ki-Hyeon; Reshotko, Eli

1991-01-01

263

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

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

264

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

USGS Publications Warehouse

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

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

2010-01-01

265

Detection of Reflected Waves from Plate Boundary Using ACROSS Source and Seismic Array  

NASA Astrophysics Data System (ADS)

ACROSS (Accurately Controlled and Routinely Operated Signal System) is effective in monitoring temporary changes of Earth's interior. A long-term operation experiment near Nojima fault [Ikuta et al.,2004] detected small temporary changes of travel time of P and S waves at tele-seismic events. Toward Tokai monitoring plan to detect the reflected phases from the top of Philippine Sea Plate and monitor its temporal changes, a mid-term continuous experiment was conducted using ACROSS source and a seismic array. The experiment was operated for the period from Dec. 2004 to Sep.2005 in the Tokai area, Pacific side of the central part of Japan. In this region, the expected Tokai earthquake is a serious concern. In addition, slow slip events and low-frequency tremors are observed in this area. A strong reflected phase from the plate boundary was found by the seismic observation using artificial sources [Iidaka et al.,2003]. The purpose of the experiment is to establish a method to detect and monitor the reflection from the plate boundary using ACROSS. The ACROSS source is located in Toki city and operated by Tono Geoscience Center. The ACROSS source continuously transmits precisely-controlled frequency-modulated signals whose frequency band ranges from 10 to 20 Hz with an interval of 50 seconds. We deployed a short-span seismic array at the distance of 55 km from the ACROSS source. The cross-shaped seismic array spanning 2 km consists of 12 seismometers equipped with an offline data logger, amplifier and solarpanel. We stacked the received signal for a month with an interval of 200 seconds in order to improve signal noise ratio. We extracted a series of line spectrum of ACROSS signal. Transfer function can be obtained by dividing spectrum by the source. Applying inverse Fourier transform, we can obtain the transfer function in time-domain. We identified direct P and S phases by comparing with the standard travel time table by JMA. We also found some coherent later phases. By comparing the travel-time of these phases with the travel-time calculated by ray-tracing with a given structure model, these phases may include the reflection waves from the top of Philippine Sea plate, the Mohorovicic discontinuity and some other physical discontinuities. We calculated the semblance of the later phases to estimate the slowness and the incident angle. A later phase with a low slowness can be found after the direct P phase. We also try to evaluate the temporal change of travel time and waveform. The detail results will be presented in the conference.

Soma, T.; Watanabe, T.; Ikuta, R.; Saiga, A.; Miyajima, R.; Yamaoka, K.; Tsuruga, K.; Kunitomo, T.; Hasada, Y.; Kasahara, J.; Satomura, M.; Kumazawa, M.; Fujii, N.

2005-12-01

266

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

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

267

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

NASA Technical Reports Server (NTRS)

The northern Caribbean plate boundary has been undergoing left lateral strike slip motion since middle Tertiary time. The western part of the boundary occurs in a complex tectonic zone in the continental crust of Guatemala and southernmost Mexico, along the Chixoy-Polochic, Motogua and possibly Jocotan-Chamelecon faults. Prominent lineaments visible in radar imagery in the Neogene volcanic belt of southern Guatemala and western El Salvador were mapped and interpreted to suggest southwest extensions of this already broad plate boundary zone. Because these extensions can be traced beneath Quaternary volcanic cover, it is thought that this newly mapped fault zone is active and is accommodating some of the strain related to motion between the North American and Caribbean plates. Onshore exposures of the Motoqua-Polochic fault systems are characterized by abundant, tectonically emplaced ultramafic rocks. A similar mode of emplacement for these off shore ultramafics, is suggested.

Baltuck, M.; Dixon, T. H.

1984-01-01

268

Numerical model for the generation of the ensemble of lithospheric plates and their penetration through the 660-km boundary  

NASA Astrophysics Data System (ADS)

In the kinematic theory of lithospheric plate tectonics, the position and parameters of the plates are predetermined in the initial and boundary conditions. However, in the self-consistent dynamical theory, the properties of the oceanic plates (just as the structure of the mantle convection) should automatically result from the solution of differential equations for energy, mass, and momentum transfer in viscous fluid. Here, the viscosity of the mantle material as a function of temperature, pressure, shear stress, and chemical composition should be taken from the data of laboratory experiments. The aim of this study is to reproduce the generation of the ensemble of the lithospheric plates and to trace their behavior inside the mantle by numerically solving the convection equations with minimum a priori data. The models demonstrate how the rigid lithosphere can break up into the separate plates that dive into the mantle, how the sizes and the number of the plates change during the evolution of the convection, and how the ridges and subduction zones may migrate in this case. The models also demonstrate how the plates may bend and break up when passing the depth boundary of 660 km and how the plates and plumes may affect the structure of the convection. In contrast to the models of convection without lithospheric plates or regional models, the structure of the mantle flows is for the first time calculated in the entire mantle with quite a few plates. This model shows that the mantle material is transported to the mid-oceanic ridges by asthenospheric flows induced by the subducting plates rather than by the main vertical ascending flows rising from the lower mantle.

Trubitsyn, V. P.; Trubitsyn, A. P.

2014-11-01

269

Inland jump of the Arabian northwest plate boundary from the Levant continental margin to the Dead Sea Transform  

NASA Astrophysics Data System (ADS)

While the breakup of Arabia and Africa began in the early Oligocene, the northwestern boundary of the Arabian Plate along the Dead Sea Transform (DST) formed 10-15 Myr later (early-middle Miocene). During the early stage of breakup the Red Sea Rift continued propagating northwestward, forming the Suez Rift. The present ˜45° northward twist of the plate boundary from the Red Sea toward the Gulf of Eilat (Aqaba) still did not exist. What happened at the northern tip of the Suez Rift at that time? How was strain distributed to its surroundings, and where did the plate boundary continue from there? Here we describe an abandoned segment of the Arabian northwestern plate boundary that extended from the northern tip of the Suez Rift northeastward, along the Levant margin. Seismic data collected offshore Israel support a subsurface, deep-rooted fault zone running along the base of the continental slope. These faults indicate Oligocene transpressional lateral shearing. We propose that during the early stage of continental breakup a left-lateral strike-slip motion of ˜10 km took place along this embryonic plate boundary. Such deep-rooted tectonism implies that unlike the passive situation of the Israel-Sinai continental margin witnessed presently and before the Oligocene, during the early stage of the Africa-Arabia breakup this part of the continental margin was reactivated. We further suggest that the inland jump of the plate boundary toward the DST was not immediate and that during the transitional period the Israel-Sinai triangular block was an independent subplate with deformation all around it.

Gvirtzman, Zohar; Steinberg, Josh

2012-08-01

270

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

NASA Astrophysics Data System (ADS)

Remnants of ocean floor forming the Eastern Ophiolite Belt in Oman and the Western Ophiolite Belt in Pakistan have a common plate-tectonic history culminating in emplacement at the Cretaceous/Tertiary boundary. Fragments of ocean floor in these two belts have ages between 150 and 65 Ma and recorded tectonic events in the early Indian Ocean at 150 Ma, 130-120 Ma, 110-100 Ma and 70-65 Ma. New radiometric and chronostratigraphic ages and paleomagnetic and sedimentary information are used to relocate these ophiolites in the frame of the evolving Indian Ocean, which was characterised by the stepwise breakup of Gondwana at 158 Ma (East and West Gondwana), 130 Ma (Southern Atlantic, breakup of East Gondwana), 95-84 Ma (Madagascar and India/Seychelles), 65 Ma (India and Seychelles) and, finally, at 40 Ma, rifting between Africa and Arabia. The 150-Ma-old oceanic rocks of Masirah Island in Oman originally formed the extension of the basins now preserved along the eastern edge of the Afro-Arabian plate. Masirah drifted together with India-Seychelles when a new ridge formed at approximately 130 Ma separating microplates (e.g., Kabul Block) from the northern edge of Greater India. Parts of this new ocean were later emplaced to form the western ophiolite belt in Pakistan. Consumption of oceanic crust and emplacement of ophiolites during the closure of the Neotethys occurred not only north of India (± Seychelles), but also along two or three subduction zones between the Afro-Arabian plate and India/Seychelles, documented by the formation of metamorphic soles beneath ophiolites. Relics of ocean floor formed approximately 65-70 Ma ago, now form the upper units in the Western Ophiolite belt of Pakistan where they overlie an accretionary prism of pillow lavas of dominantly (Aptian-) Albian age and sedimentary rocks. The breakup of India and the Seychelles at 65 Ma was associated with the eruption of flood basalts (Deccan and Seychelles) and enhanced counter-clockwise movement of India. This breakup possibly caused the Late Jurassic/Early Cretaceous fragments of ocean floor (e.g., Masirah) to be thrust onto the eastern edge of Oman. The ophiolites, which were emplaced onto the western edge of India, drifted as part of this plate farther north where collision with Eurasia and the accreted microplates occurred in the Eocene (˜ 55 Ma).

Gnos, E.; Immenhauser, A.; Peters, Tj.

1997-03-01

271

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

NASA Technical Reports Server (NTRS)

The unsteady laminar boundary layer induced by the flow-initiating shock wave passing over a flat plate mounted in a shock tube was theoretically and experimentally studied in terms of heat transfer rates to the plate for shock speeds ranging from 1.695 to 7.34 km/sec. The theory presented by Cook and Chapman for the shock-induced unsteady boundary layer on a plate is reviewed with emphasis on unsteady heat transfer. A method of measuring time-dependent heat-transfer rates using thin-film heat-flux gages and an associated data reduction technique are outlined in detail. Particular consideration is given to heat-flux measurement in short-duration ionized shocktube flows. Experimental unsteady plate heat transfer rates obtained in both air and nitrogen using thin-film heat-flux gages generally agree well with theoretical predictions. The experimental results indicate that the theory continues to predict the unsteady boundary layer behavior after the shock wave leaves the trailing edge of the plate even though the theory is strictly applicable only for the time interval in which the shock remains on the plate.

Cook, W. J.

1972-01-01

272

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

273

Navier-Stokes simulations of the effects of suction holes on a flat plate boundary layer  

NASA Technical Reports Server (NTRS)

Direct numerical simulations (DNS) of the Navier-Stokes equations are employed to explore the effects of suction holes on transition in a laminar flat plate boundary layer. The Navier-Stokes equations are cast in vorticity-velocity form. Periodicity is imposed in spanwise direction; all other spatial derivatives are discretized with fourth order compact differences. An explicit fourth order Runge-Kutta scheme is employed for the time-integration of the vorticity transport equations. Suction is applied through a row of holes aligned in spanwise direction. For low suction strengths, each hole generates a pair of stable streamwise vortices. When the suction strength exceeds a critical value, the vortices become unstable. For high suction strengths, vortex shedding occurs right at the suction holes. Our numerical findings agree well with experimental observations.

Meitz, Hubert L.; Fasel, Hermann F.

1994-01-01

274

Convergence of a numerical scheme for a nonlinear oblique derivative boundary value problem  

E-print Network

in the modelling of the plasma opening switch [8] and has been studied mathematically in [9], in the case = f(z; x This paper deals with the discretization and the numerical simulation of a nonlin- ear oblique boundary respectively by #28; and #23; the local tangential and inner normal vectors on , this boundary condition

Méhats, Florian

275

Development of the Plate Boundary Observatory GPS Low Latency Salton Trough Radio Network  

NASA Astrophysics Data System (ADS)

UNAVCO is developing a 20 GPS station low latency radio network that spans the San Andreas and San Jacinto faults in the region of highest strain in southern California and the narrowest part of the North America-Pacific plate boundary. The Salton Trough Radio Network (STRN) is instrumented with Ethernet bridge Intuicom EB6+ (900 MHz) radios to transmit a high rate low latency data stream from each permanent GPS site for the purpose of the following: 1) telemeter 15 second data (1 MB/day/station) to the Plate Boundary Observatory archive, 2) accommodate the timely download of 1 and 5 sample per second data following large earthquakes (4 MB/hour/station), and 3) test the UStream of 1Hz BINEX and RTCM data. Three of four phases have been completed. Office radio testing yielded transfer rates of 30-50 KB/s with subsecond latency while streaming 1 Hz data. Latency climbed to ~1.8 seconds while simultaneously streaming 1 Hz and downloading hourly 1 and 5 sample per second data files. Field testing demonstrated rates on the order of 30 KB/s. At present the radios are installed and have transfer rates of 10-40 KB/s between sites that span 10-32 km. The final phase will be the installation of the main telemetry relay where master radios will be connected to a high speed ISP near the town of Brawley. The high-rate low latency UStream data will be available to researchers who are developing prototype earthquake early warning systems in Southern California. A goal of the STRN is to make the data available rapidly enough for GPS-derived coseismic and dynamic displacements to be integrated into early warning system earthquake models. The improved earthquake models will better assist emergency response. UStream data will also aid surveyors who wish to use PBO GPS stations as permanent, high-quality base stations in real-time kinematic surveys.

Walls, C.; Miller, S.; Wilson, B.; Lawrence, S.; Arnitz, E.

2008-05-01

276

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

277

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

278

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 ...

Mrs. Rohlfing

2011-02-03

279

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.

Rita Haberlin

280

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

NASA Astrophysics Data System (ADS)

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

Fernandez, M.; Verges, J.

2013-12-01

281

Summary of the stratigraphy and structural elements related to plate convergence of the Quetta-Muslim Bagh-Sibi region, Balochistan, west-central Pakistan  

USGS Publications Warehouse

The four major faults that bound the structural terrane are the Frontal (F), Ghazaband-Zhob (GZ), Gwal-Bagh (GB), and Chaman (C) faults. Four major periods of deformation are recognized: (1) emplacement of ophiolitic rocks onto the continental margin of the India plate; (2) convergence of the India-Eurasia plates; (3) deposition of Tertiary-Quaternary molasse units followed by major folding and thrusting, and formation of strike-slip faults; and (4) deposition of Pleistocene molasse units with subsequent folding, thrusting, and strike-slip motion that continues to the present.

Maldonado, Florian; Mengal, Jan M.; Khan, Shahid H.; Warwick, Peter D.

2011-01-01

282

Convergence of Sound Waves Radiated from Aerial Ultrasonic Source Using Square Transverse Vibrating Plate with Several Reflective Boards  

Microsoft Academic Search

An ultrasonic source using a metal square vibrating plate radiates extremely intense ultrasonic waves into the air. The plate experiences transverse vibration when a longitudinal vibration is applied to the central point of the plate. In the lattice mode, the nodal positions of the plate take the form of straight lines, creating a lattice-like pattern. The source radiates four directional

Yuu Onishi; Hikaru Miura

2005-01-01

283

Has the plate boundary shifted from central Hokkaido to the eastern part of the Sea of Japan?  

Microsoft Academic Search

A NS trending Cenozoic fold-and-thrust belt has developed in the western part of the Hidaka Collision Zone (HCZ), central Hokkaido, Japan. A quantitative estimation of the late Cenozoic convergence rate at the front of the Hidaka thrust system is important in revealing the plate tectonic framework around northern Japan. High-resolution seismic reflection profiling across the active fault-related folds was carried

Naoko Kato; Hiroshi Sato; Masayuki Orito; Kazuomi Hirakawa; Yasutaka Ikeda; Tanio Ito

2004-01-01

284

Monitoring dynamics of an active plate boundary: Peceneaga-Camena Fault  

NASA Astrophysics Data System (ADS)

Peceneaga-Camena Fault (PCF) is one of the well-known regional faults on the Romanian territory, separating the Central Dobrogea from the North Dobrogea structures. Despite its first mentioning more than hundred years ago, some aspects related to its track, nature and dynamics are still debated. After the first geological models assuming it as a reverse fault, or the overthrust plan along which the Upper Proterozoic Green Schist series of Central Dobrogea overthrusted the North Dobrogea Paleozoic structures, PCF started to be considered more as a strike-slip fault. First geophysical evidence (the international DSS line Calarasi-Galati) revealed a 10 km step along it at the both Conrad and Moho levels, thus advocating for its trans-crustal feature. Later on, the re-interpretation of the data provided by Calixto experiment clearly showed in depth extension of the contact down to more than 150 km. This way it becomes clear the lithospheric nature of PCF, as a plate boundary between Moesian Microplate and East European Plate. Concerning the PCF nature and dynamics, several authors have been previously considered the fault as an active trans-current contact along which its southern flank would be pushed towards NW, thus generating the recent Pleistocene folds in the SE bending zone of East Carpathians. The Baspunar experiment was designed and accomplished in order to bring direct evidence on the active character of the PCF. Geomagnetic investigations conducted under the umbrella of a joint project between the Institute of Geodynamics of the Romanian Academy and the Institute of Geophysics of the Ukrainian Academy of Sciences have revealed the presence of an additional local geomagnetic field, due to the inductive currents circulating along the fault plane, which associates well with its assumed active character. A geodetic experiment, during which two Leica TC &TCR total stations were installed and monitored the distance between the PCF flanks, has brought direct evidence on the active nature of the fault, mainly behaving as a right-lateral trans-current plate boundary, in full agreement with previous geodynamic models based on indirect geological evidence.

Besutiu, Lucian; Zlagnean, Luminita

2010-05-01

285

The giant coastal landslides of Northern Chile: Tectonic and climate interactions on a classic convergent plate margin  

NASA Astrophysics Data System (ADS)

Documented for the first time are an extensive suite of late Neogene giant terrestrial coastal landslides along the classic convergent margin of western South America (18° to 24° south). These are remarkable in terms of their unusual abundance and atypical setting, such failures previously being linked with oceanic volcanic edifices or over-steepened glaciated coastlines. Located within the hyper-arid Coastal Cordillera of the Atacama Desert of Northern Chile we report the presence of more than 60 individual large-scale landslides with individual volumes up to 9 km3 developed over a horizontal coastline distance of some 650 km. These landslides were emplaced as a combination of rock avalanches and multiple rotational failures. The majority terminated directly into the Pacific - likely generating significant tsunami hazard to the Chilean and south Peruvian coastline in a region which is today considered to be part of a notorious seismic gap. The proliferation and scale of these Late Neogene giant landslides in this actively uplifting, hyperarid terrain suggests they are the main geomorphic agent for relief reduction, probably triggered by megathrust earthquakes and potentially providing a unique palaeoseismic archive. The temporal and spatial distribution of these giant landslides corresponds with a period of surface steepening of the forearc wedge in the Central Andes and south to north differential uplift associated with factors such as aseismic ridge subduction. The resulting surface gradient increases, combined with the persistent climatic aridity of the region, have served to limit effective relief-reducing geomorphic processes in this oversteepened terrain to large-scale landsliding. The phenomena documented here geospatially link previously recognised large-scale slope failures from the off-shore environment and higher altitude areas of the Andean forearc, suggesting that large-scale landsliding is capable of transferring sediment on a regional scale to the off-shore Peru-Chile trench. This has implications for the friction of the subducting Nazca plate and associated seismicity and uplift.

Mather, Anne E.; Hartley, Adrian J.; Griffiths, James S.

2014-02-01

286

Turbulent boundary-layer along a streamwise bar of a square cross section placed on a flat plate  

Microsoft Academic Search

The turbulent boundary layer developing along a long streamwise bar with a square cross section placed on a flat plate was investigated experimentally. Measurements were made on the distributions of mean velocities, turbulence intensities and wall stresses. Near the streamwise edge and corner, secondary currents are generated whose directions near the bisectors are away from and toward the wall respectively.

Y. Furuya; I. Nakamura; M. Miyata; Y. Fukuyo

1976-01-01

287

North American plate dynamics  

NASA Technical Reports Server (NTRS)

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

Richardson, Randall M.; Reding, Lynn M.

1991-01-01

288

Real feature of seismicity around Palau trench region, western Pacific: Is Palau trench aseismic silent plate boundary?  

NASA Astrophysics Data System (ADS)

Palau islands locate around plate converging zone in the western Pacific region. In the east off the Palau islands, obvious trench topography is developed whose bathymetry reaches about 6000 meters. Palau trench locates at the west side of Yap trench. However tectonic activity is quite different in the both trenches. Yap trench has active seismic activity associate with subduction process. Plate motion model shows clear convergent relative motion between Pacific plate and Philippine Sea plate at Yap trench. On the other hand, Palau trench doesn't have active seismicity according to ISC catalogue. In ten years in 2000's, only three small earthquakes are reported in ISC catalogue. Historically any great earthquake also is not reported. Recent plate motion model shows very low convergent motion at Palau trench though developed trench structure. Our group operates broadband seismic station at Palau (station code: PALU) for about 15 years. In our instant monitoring, local earthquakes sometime are recognized. We operated additional stations in Palau islands for six months to detect local earthquake and to locate hypocenters. Our objective of the research is evaluation of real seismicity of Palau region and final major interest is to understand tectonic activity of Palau trench. We install minimum network for hypocenter locating in Koror and Babeldaob islands, Palau that its array dimension is about 20 km. We use broadband seismographs and high resolution data loggers with GPS clock and solar power generators. We succeeded continuous recording without any troubles and clips of mass position. By careful motoring, we pick up greater than 70 local earthquakes in only six months. And we also tried to read the P and S wave arrival times. We succeeded to locate 27 hypocenters. The number of seismic events is much higher than initial estimation. The hypocenters locate east coast side of Palau islands where is trench side. The overview of distribution is parallel to trench. Estimated depth is distributed from 20 to 30 km. The determination is inaccurate and sparse distributed, but simple seismograms mean that these are not shallow crustal event. P and S wave amplitude analysis says that dip-slip type fault mechanism is dominant. This seismic activity may be strongly related with subduction process. These earthquakes are magnitude of 2 to 3. Seismicity of Palau area is much higher than initial estimation based on earthquake catalogue. These results mean that Palau trench has latent active seismic process and suggest that the trench may have convergent plate process than general understanding.

Ishihara, Y.; Shito, A.; Tanaka, S.; Suetsugu, D.

2012-12-01

289

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

NASA Astrophysics Data System (ADS)

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

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

1998-03-01

290

The upper boundary of the Philippine sea plate beneath the western Kanto region estimated from S-P-converted wave  

NASA Astrophysics Data System (ADS)

In the Kanto-Tokai district of central Japan, the configuration of the subducting Philippine Sea plate has been estimated using three-dimensional velocity inversions of the seismic wave velocity structure and the distribution of microearthquakes. However, it is difficult to show the configuration of the Philippine Sea plate from the distribution of microearthquakes beneath the western Kanto region, i.e. the Yamanashi and Nagano prefectures, because seismic activity is quite low there. A clear X-phase between P- and S-phases on seismograms from an earthquake is observed at temporary seismological stations located in this area. This X-phase is identified as the S to P converted wave at the upper boundary of the subducting Philippine Sea plate. Thus we have been able to deduce the shape of the Philippine Sea plate and to show that it dips northwest.

Iidaka, T.; Mizoue, M.; Nakamura, I.; Tsukuda, T.; Sakai, K.; Kobayasi, M.; Haneda, T.; Hashimoto, S.

1990-07-01

291

The Quest for the Africa-Eurasia plate boundary West of the Strait of Gibraltar  

NASA Astrophysics Data System (ADS)

A new swath bathymetry compilation of the Gulf of Cadiz Area and SW Iberia is presented. The new map is the result of a collaborative research performed after year 2000 by teams from 7 European countries and 14 research institutions. This new dataset allow for the first time to present and to discuss the missing link in the plate boundary between Eurasia and Africa in the Central Atlantic. A set of almost linear and sub parallel dextral strike-slip faults, the SWIM Faults (SWIM is the acronym of the ESF EuroMargins project "Earthquake and Tsunami hazards of active faults at the South West Iberian Margin: deep structure, high-resolution imaging and paleoseismic signature") was mapped using a the new swath bathymetry compilation available in the area. The SWIM Faults form a narrow band of deformation over a length of 600 km coincident with a small circle centred on the pole of rotation of Africa with respect to Eurasia, This narrow band of deformation connects the Gloria Fault to the Rif-Tell Fault Zone, two segments of the plate boundary between Africa and Eurasia. In addition, the SWIM faults cuts across the Gulf of Cadiz, in the Atlantic Ocean, where the 1755 Great Lisbon earthquake, M~8.5-8.7, and tsunami were generated, providing a new insights on its source location. SWIM Team: E. Gràcia (2), L. Matias (3), P. Terrinha (4), M.A. Abreu (5), G. DeAlteriis(6), J.P. Henriet (7), J.J. Dañobeitia (2), D.G. Masson (8), T. Mulder (9), R. Ramella (10), L. Somoza (11) and S. Diez (2) (2) Unitat de Tecnologia Marina (CSIC), Centre Mediterrani d'Investigacions Marines i Ambientals, Barcelona, Spain (3) Centro Geofísica da Universidade de Lisboa (CGUL, IDL), Lisboa, Portugal (4) National Institute for Engineering, Technology and Innovation (INETI, LATTEX), Departamento de Geologia Marinha, Amadora, Portugal (5) Estrutura de Missão para a Extensão da Plataforma Continental, Lisboa, Portugal (6) Geomare Sud IAMC, CNR, Napoli, Italy (7) Renard Centre of Marine Geology, Dpt. Geology and Soil Science, Gent University, Gent, Belgium (8) National Oceanography Centre, European Way, Southampton, United Kingdom (9) Département de Géologie et Océanographie, Talence Cedex, France (10) Department for the Development of Marine Technology and Research, Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), Sgonico, Italy (11) Geología Marina, Instituto Geológico y Minero de España, Madrid, Spain

Zitellini, N.

2009-04-01

292

The Plate Boundary Observatory Borehole Network: Geologic Resources from Drilling and Logging  

NASA Astrophysics Data System (ADS)

The Plate Boundary Observatory Strainmeter Borehole Network has a total of 79 operational boreholes, with depths drilled from 420 to 800 feet. All drill cuttings, core samples and logs are stored and catalogued. The cuttings for each successful borehole were recently photo documented and will be placed on the UNAVCO website to be readily available to the public, as well as to request samples. The drill cuttings were collected in 10 foot intervals, and in Yellowstone they were collected in five foot intervals. The extent of the borehole network includes sites near the San Jacinto fault, San Andreas Fault, throughout the Cascadia region, Mt St Helens and Yellowstone. These locations provide a wide array of tectonic and volcanic environments. In the case of Yellowstone, the park has not been drilled in for four decades. Due to the circulation of hot fluids, holes are at a shallower depth ( > 420 feet). These cuttings provide a resource of understanding the history and dynamics of fluid interaction in Yellowstone. Along the San Jacinto fault and San Andreas fault, these cuttings can help to build better models of the fault dynamics through evaluating the stratigraphy, fractures, rock strength, structural geology and fluid interaction near and along the fault zones. The stranmeter sites in the Pacific NW were chosen for the subduction zone, and are therefore not near a major plate boundary. They could instead be used to understand local regional fault dynamics, stratigraphy, structural geology and volcanic history of the NW. Presented will be examples of interest from each region, from cuttings, core, logs, to correlated network observations. For example, a site on the San Jacinto fault, near Anza has recorded creep events. This site is the closest to the fault and during drilling fault gouge was observed. While in Parkfield, cuttings and core reveal different fault blocks for sites that are 1000 feet apart in distance. As UNAVCO cannot provide any analysis on these samples, the documentation and variability of these resources will be presented. The availability of these resources and an interest of understanding the hydrology and structural geology could provide new incite for understanding strike slip faulting as well as additional resources for understanding volcanic history.

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

2011-12-01

293

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

294

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

SciTech Connect

Advances in the technology for exploiting resources of the oceans, particularly recovery of hydrocarbons and minerals in deep water, is benefiting a growing number of nations. At the same time, however, economic and political pressures have induced concern and there is now a much increased emphasis on jurisdiction to divide the offshore areas between the 132 coastal nations. Negotiations affect research operations at sea and, in consequence, marine scientists have been made aware of offshore problems as highlighted by the Law of the Sea Treaty (UNCLOS III) and complications arising from the legal versus scientific definitions of continental shelves and margins. The first major offshore boundary case of international scope where plate tectonics has constituted a significant argument is the one recently brought before the International Court of Justice by Libya and Tunisia concerning the delimitation of their continental shelves. Of the two parties, Libya placed the greatest emphasis on this concept as a means to determine natural prolongation of its land territory into and under the sea. Tunisia contested Libya's use of the whole of the African continental landmass as a reference unit; in Tunisia's view, considerations of geography, geomorphology, and bathymetry are at least as relevant as are those of geology. In its landmark judgment (February 1982) - which almost certainly will have far-reaching consequences in future such boundary delimitation cases - the court pronounced that It is the outcome, not the evolution in the long-distant past, which is of importance, and that it is the present-day configuration of the coasts and sea bed which are the main factors to be considered, not geology.

Stanley, D.J.

1983-03-01

295

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

NASA Technical Reports Server (NTRS)

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

Solomon, Sean C.

1987-01-01

296

PBO H2O: Plate Boundary Observatory Studies of the Water Cycle  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

297

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

298

Sinuous breakdown in a flat plate boundary layer exposed to free-stream turbulence  

NASA Astrophysics Data System (ADS)

In a flat plate boundary layer, perturbed with streaks, breakdown occurs due to a secondary instability acting on the streaks. An experimental study using a water channel with static turbulence grid revealed the presence of a sinuous secondary instability mode in the bypass transition process. Five sinuous instabilities are investigated in detail in the horizontal plane. The streamwise length scale of the sinuous instability is around 40?300* and the spanwise scale equals around ?300*. Four main features are found in the underlying streak configuration and developing streak-streak interactions. Firstly, all instabilities arise in a streak configuration where two low-speed streaks are located at a small spanwise distance from each other. Patches of low-speed fluid (forming a discontinuity in the streak pattern) are present in the high-speed streaks surrounding the unstable low-speed streak. As a consequence of the streak-streak interactions at the discontinuities, vortices arise in a staggered configuration. Finally, the vortices develop into three-dimensional structures after which the flow falls apart into smaller three-dimensional flow regions.

Mans, J.; de Lange, H. C.; van Steenhoven, A. A.

2007-08-01

299

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

SciTech Connect

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

Huang, J.; Menard, J.

2006-01-01

300

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

301

The ultra weak variational formulation of thin clamped plate problems  

NASA Astrophysics Data System (ADS)

We develop a new numerical scheme for a fourth order elliptic partial differential equation based on Kirchhoff's thin plate theory. In particular we extend the ultra weak variational formulation (UWVF) to thin plate problems with clamped plate boundary conditions. The UWVF uses a finite element mesh and non-polynomial basis functions. After deriving the new method we then prove L2 norm convergence on the boundary. Finally we investigate numerically the feasibility of the UWVF for both homogeneous and inhomogeneous problems and show examples of p- and h-convergence.

Luostari, Teemu; Huttunen, Tomi; Monk, Peter

2014-03-01

302

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

NASA Technical Reports Server (NTRS)

The NASA/DOSE 'Kinematics of the New Zealand Plate Boundary' experiment is a four-year cooperative Global Positioning System (GPS) experiment involving 6 universities and institutions in New Zealand and the United States. The investigation covers two scales, the first on the scale of plates (approximately 1000 km) and the second is on the scale of the plate boundary zone (approximately 50 km). In the first portion of the experiment, phase A, the objective is to make direct measurements of tectonic plate motion between the Australian and Pacific plates using GPS in order to determine the Euler vector of this plate pair. The phase A portion of this experiment was initiated in December 1992 with the first-epoch baseline measurements on the large scale network. The network will be resurveyed two years later to obtain velocities. The stations which were observed for phase A are shown and listed. Additional regional stations which will be used for this study are listed and are part of either CIGNET or other global tracking networks. The phase A portion of the experiment is primarily the responsibility of the UNAVCO investigators. Therefore, this report concentrates on phase A. The first year of NASA funding for phase A included only support for the field work. Processing and analysis will take place with the second year of funding. The second part of the experiemnt measured relative motion between the Australian and Pacific plates across the pate boundary zone between Hokitika and Christchurch on the South Island of New Zealand. The extent and rate of deformation will be determined by comparisons with historical, conventional surveys and by repeated GPS measurements to be made in two years. This activity was the emphasis of the LDGO portion of the study. An ancillary experiment, phase C, concentrated on plate boundary deformation in the vicinity of Wellington and was done as part of training during the early portion of the field campaign. Details of the objectives of the field investigations are given in the appendix. An overview of the 1992 GPS field program is also given in the appendix.

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

1993-01-01

303

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

E-print Network

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

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

2014-01-01

304

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

305

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

NASA Astrophysics Data System (ADS)

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

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

1997-02-01

306

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

NASA Technical Reports Server (NTRS)

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

Solomon, Sean C.

1987-01-01

307

Crack-Tip Parameters in Polycrystalline Plates with Soft Grain Boundaries  

E-print Network

, who performed in situ fracture toughness experiments on specimens of warm lake ice whose in the statistical distributions of the stress intensity factor of a crack in a polycrystalline plate containing of the uncracked plate and the stress intensity factor of the cracked plate are calculated for selected values

Ballarini, Roberto

308

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

E-print Network

of the 2004 Northern Sumatra, 2010 Chile and 2011 Tohoku-Oki megathrust earthquakes 7 Existing Geophysical Infrastructure and Initiatives in the Pacific devastating megathrust earthquakes off Sumatra, Chile and Japan have raised awareness

Wilcock, William

309

Structure and composition of the plate-boundary slip zone for the 2011 Tohoku-Oki earthquake.  

PubMed

The mechanics of great subduction earthquakes are influenced by the frictional properties, structure, and composition of the plate-boundary fault. We present observations of the structure and composition of the shallow source fault of the 2011 Tohoku-Oki earthquake and tsunami from boreholes drilled by the Integrated Ocean Drilling Program Expedition 343 and 343T. Logging-while-drilling and core-sample observations show a single major plate-boundary fault accommodated the large slip of the Tohoku-Oki earthquake rupture, as well as nearly all the cumulative interplate motion at the drill site. The localization of deformation onto a limited thickness (less than 5 meters) of pelagic clay is the defining characteristic of the shallow earthquake fault, suggesting that the pelagic clay may be a regionally important control on tsunamigenic earthquakes. PMID:24311682

Chester, Frederick M; Rowe, Christie; Ujiie, Kohtaro; Kirkpatrick, James; Regalla, Christine; Remitti, Francesca; Moore, J Casey; Toy, Virginia; Wolfson-Schwehr, Monica; Bose, Santanu; Kameda, Jun; Mori, James J; Brodsky, Emily E; Eguchi, Nobuhisa; Toczko, Sean

2013-12-01

310

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

E-print Network

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

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

2014-03-24

311

Stress triggering of the great Indian Ocean strike-slip earthquakes in a diffuse plate boundary zone  

NASA Astrophysics Data System (ADS)

On April 11, 2012, two great magnitude 8+ earthquakes occurred within a two-hour period off the west coast of northern Sumatra, Indonesia, in the broadly distributed India-Australia plate boundary zone. The magnitude 8.6 mainshock holds the distinction of being both the largest instrumentally recorded strike-slip earthquake and the largest earthquake away from a recognized plate boundary fault. The mainshock involved sequential ruptures of multiple fault planes oriented nearly perpendicular to each other. The adjacent 2004 megathrust earthquake statically loaded the northern Wharton Basin oceanic lithosphere on both of the 2012 mainshock fault plane orientations, and greatly enhanced the rate of earthquake activity in the region for a year. Viscoelastic relaxation of the asthenosphere following the 2004 and 2005 megathrust earthquakes continued to positively stress the offshore region, correlating with the locations of later strike-slip earthquakes, including two magnitude 7+ and the 2012 magnitude 8+ earthquakes.

Wiseman, Kelly; Bürgmann, Roland

2012-11-01

312

Manipulation of an artificial large scale horse-shoe vortex by a thin plate placed in a turbulent boundary layer  

NASA Astrophysics Data System (ADS)

A horseshoe vortex was artificially induced in a fully-developed turbulent boundary layer by injecting a pair of small swirling jets from a flat plate beneath. The artificial vortex grew toward the outer layer and came to have a structure almost the same as the natural coherent bulge as it flowed downstream. A thin manipulator plate was installed parallel to the flat plate and the artificial horseshoe vortex was broken. Velocity-vector plots and the shear-stress contour maps were obtained by the conditional sampling method. When the horseshoe vortex was manipulated, its coherent structure decayed rapidly, and the intensity of the induced shear stress concentrated between its two legs was reduced effectively. These results suggest the possibility of drag reduction by the large-eddy breakup method.

Makita, H.; Sassa, K.; Abe, M.; Itabashi, A.

1987-06-01

313

Characteristics of Plate Boundary Reflected Phases at the Japan Trench Obtained by OBS-Airgun Study in 2001. -Preliminary Results-  

NASA Astrophysics Data System (ADS)

Recent GPS and rapture process studies for large earthquakes suggest that earthquake generation is controlled by the distribution of asperities. Among the subduction zones around the Japanese islands, the subduction zone along the Japan Trench is one of the well studied areas in viewpoint of asperity distribution. The seismic experiment using controlled source-OBS study in 1996 revealed strong correlation between seismic reflection intensity and the seismic activity in 38o40'N and 39o00'N on the forearc slope of the Japan Trench (Fujie et al., 2002). P-wave velocity structure under the NS-line can be represented by horizontal layering structure, and the plate boundary is located at slightly deeper depth than 10 km (Suyehiro and Nishizawa, 1994 and Fujie et al., 2000). In order to study 3-D distribution of seismic reflection intensity at the subdction plate boundary for this region, we carried out a seismic experiment in 2001 in a part of the area of the 1996 experiment, with a denser OBS array. Thirty-nine OBSs were placed on 30 km x 50 km along seven seismic lines. Airguns were used as artificial seismic sources, and their average total chamber volume was 57 liters. While making record sections, each trace was plotted at the mid point between the source and receiver locations so that reflected arrivals were plotted at their approximated reflection points. The distribution of seismic reflection intensity observed in this experiment agreed well with the result of Fujie, 2000. In their results, strong seismic reflections from plate boundary occur at aseismic region. The seismic reflection intensities were found to be largely heterogeneous over the surveyed area. We identified these reflected arrivals as reflections from plate boundary.

Nakamura, M.; Kasahara, J.; Mochizuki, K.; Hino, R.; Nishino, M.; Yamada, T.; Kuwano, A.; Kuno, T.; Sato, T.; Nakamura, Y.; Kanazawa, T.

2002-12-01

314

Using EarthScope Construction of the Plate Boundary Observatory to Provide Locally Based Experiential Education and Outreach  

Microsoft Academic Search

EarthScope is an NSF-funded, national science initiative to explore the structure and evolution of the North American continent and to understand the physical processes controlling earthquakes and volcanoes. This large-scale experiment provides locally based opportunities for education and outreach which engage students at various levels and the public. UNAVCO is responsible for the Plate Boundary Observatory (PBO) component of EarthScope.

M. Jackson; S. Eriksson; K. Barbour; S. Venator; D. Mencin; W. Prescott

2006-01-01

315

Velocity and temperature distribution of air in the boundary layer of a vertical plate for free-convective heat transfer  

E-print Network

VELOCITY AND TEMPERATURE DISTRIBUTION OF AIR IN THE BOUNDARY LAYER OF A VERTICAL PLATE FOR FREE-CONVECTIVE HEAT TRANSFER A Thesis By JEAN MAXIME JOSE JULLIENNE Submitted to . the . Graduate School of the Agricultural. and Mechanical. College...-CONVECTIVE, HEAT TRANSFER A Thesis By JEAN MAXIME JOSE . JULLIENE Approved as to style . and content by: 1tt e ea o Department or tu eat . visor Angnsty 1962 ACKNOWLEDGMENTS This investigation, . designated as a part of Project 0915, was. made possible...

Jullienne, Jean Maxime Jose

1962-01-01

316

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

317

Halfway There: An EarthScope Plate Boundary Observatory Progress Report  

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

318

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

NASA Astrophysics Data System (ADS)

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. The one segment that is most mature for re-rupture stretches for more than 500 km along the northernmost Chilean coast between roughly -23° and -18° latitude. It last broke in 1877 in a magnitude ~8.5 earthquake, triggering a major Tsunami. From the historical record, it has been known to have a recurrence cycle of approximately 110 years. The adjoining segments to the south and north broke rather recently in 1995 and 2001 in M>8 earthquakes and an M 7.7 earthquake intruded into the southern part of the seismic gap in 2007 between Antofagasto and Tocopilla. This makes northern Chile a unique natural laboratory to observe a subduction megathrust at various stages of its seismic cycle. For that purpose, installation of long-term observatories started in 2006 in a close cooperation of the Universidad de Chile (Santiago, Chile), the Universidad Catolica del Norte (Antofagasta, Chile), the Institut de Physique du Globe de Paris (France), and the GFZ German research Centre for Geosciences (Germany). Currently we are operating 17 modern seismological stations equipped with STS-2 broadband seismometers and accelerometers (EPI sensor). At least two more stations will be installed in the near future. Continuous GPS, tilt, creep, climate and magnetotellurics measurements are complementing the seismological part. A majority of the sites provide data near real-time. We will present results of seismic monitoring including analysis of the 2007 M7.7 Tocopilla earthquake sequence that was recorded during the installation stage of the observatory. We relocated the mainshock and about a one thousand aftershocks during the following week using waveform cross-correlation and the double-difference algorithm. Aftershocks reveal that rupture during this earthquake was confined to the deeper part (35 - 55 km depth) of the seismogenic coupling zone, except near the Mejillones peninsula that marks rupture termination in the south. Here earthquake activity reaches to depths of 20 km and even shallower, possibly indicating upper plate activation. The sequence also features an M 6.8 earthquake that broke the oceanic slab on an almost vertical plane at the down-dip end of the megathrust rupture. Confrontation with the aftershock distribution of the 1995 M 8.0 Antofagasta earthquake on the adjoining southern segment reveals an intriguing mirror symmetry with an axis crossing the Mejillones peninsula, emphasizing the penisula's significance as a segment boundary. Since then activity inside the remaining seismic gap to the north picked up with three earthquakes exceeding magnitude 6, maybe heralding the next great rupture.

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

2010-05-01

319

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

NASA Astrophysics Data System (ADS)

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

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

2007-05-01

320

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

321

The EarthScope Plate Boundary Observatory Akutan Alaskan Volcano Tiltmeter Installation  

NASA Astrophysics Data System (ADS)

During August of 2007, the Plate Boundary Observatory (PBO) successfully installed four Applied Geomechanics Lily Self Leveling Borehole Tiltmeters on Akutan Volcano, in the central Aleutian islands of Alaska. All four stations were collocated with existing PBO Global Positioning Systems (GPS) stations installed on the volcano in 2005. The tiltmeters will aid researchers in detecting and measuring flank deformation associated with future magmatic intrusions of the volcano. All four of the tiltmeters were installed by PBO field crews with helicopter support provided by JL Aviation and logistical support from the Trident Seafood Corporation, the City of Akutan, and the Akutan Corporation. Lack of roads and drivable trails on the remote volcanic island required that all drilling equipment be transported to each site from the village of Akutan by slinging gear beneath the helicopter and with internal loads. Each tiltmeter hole was drilled to a depth of approximately 30 feet with a portable hydraulic/pneumatic drill rig. The hole was then cased with splined 2.75 inch PVC. The PVC casing was cemented in place with grout and the tiltmeters were installed and packed with fine grain sand to stabilize the tiltmeters inside the casing. The existing PBO NetRS GPS receivers were configured to collect the tiltmeter data through a spare receiver serial port at one sample per minute and 1 hour files. Data from the GPS receivers and tiltmeters is telemetered directly or through a repeater radio to a base station located in the village of Akutan that transmits the data using satellite based communications to connect to the internet and to the UNAVCO Facility data archive where it is made freely available to the public.

Pauk, B. A.; Gallaher, W.; Dittmann, T.; Smith, S.

2007-12-01

322

Controls on spatial and temporal evolution of prism faulting and relationships to plate boundary slip offshore north-central Sumatra  

NASA Astrophysics Data System (ADS)

Across- and along-strike variations in the morphology and structure of the north-central Sumatran forearc (~1.5°S to 1°N) are broadly coincident with subducting plate topography and an earthquake segment boundary zone below the Batu Islands. We present a detailed interpretation of multichannel streamer seismic reflection data collected offshore north-central Sumatra, to better characterize the morphological and structural variations, provide insight into fault development, and relate structure to plate boundary rupture and seismicity patterns. We interpret two relatively continuous, major fault structures that divide the prism into three strike-parallel belts that can be characterized by the relative fault slip rates along major and minor fault structures. The midslope break fault(s) and upper slope-bounding fault(s) are major, potentially out-of-sequence thrusts accommodating a significant component of the compressional strain. We propose that the upper slope-bounding fault represents the more mature end-member of an evolving fault system. Landward vergent structures are associated with a relatively thin sedimentary section near the deformation front in the center of our study area and suggest a potentially weak shallow plate boundary associated with the subducting Wharton Fossil Ridge.

Cook, Becky J.; Henstock, Timothy J.; McNeill, Lisa C.; Bull, Jonathan M.

2014-07-01

323

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

NASA Technical Reports Server (NTRS)

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

Solomon, Sean C.

1991-01-01

324

MHD Forced Convective Laminar Boundary Layer Flow from a Convectively Heated Moving Vertical Plate with Radiation and Transpiration Effect  

PubMed Central

A two-dimensional steady forced convective flow of a Newtonian fluid past a convectively heated permeable vertically moving plate in the presence of a variable magnetic field and radiation effect has been investigated numerically. The plate moves either in assisting or opposing direction to the free stream. The plate and free stream velocities are considered to be proportional to whilst the magnetic field and mass transfer velocity are taken to be proportional to where is the distance along the plate from the leading edge of the plate. Instead of using existing similarity transformations, we use a linear group of transformations to transform the governing equations into similarity equations with relevant boundary conditions. Numerical solutions of the similarity equations are presented to show the effects of the controlling parameters on the dimensionless velocity, temperature and concentration profiles as well as on the friction factor, rate of heat and mass transfer. It is found that the rate of heat transfer elevates with the mass transfer velocity, convective heat transfer, Prandtl number, velocity ratio and the magnetic field parameters. It is also found that the rate of mass transfer enhances with the mass transfer velocity, velocity ratio, power law index and the Schmidt number, whilst it suppresses with the magnetic field parameter. Our results are compared with the results existing in the open literature. The comparisons are satisfactory. PMID:23741295

Uddin, Md. Jashim; Khan, Waqar A.; Ismail, A. I. Md.

2013-01-01

325

MHD forced convective laminar boundary layer flow from a convectively heated moving vertical plate with radiation and transpiration effect.  

PubMed

A two-dimensional steady forced convective flow of a Newtonian fluid past a convectively heated permeable vertically moving plate in the presence of a variable magnetic field and radiation effect has been investigated numerically. The plate moves either in assisting or opposing direction to the free stream. The plate and free stream velocities are considered to be proportional to x(m) whilst the magnetic field and mass transfer velocity are taken to be proportional to x((m-1)/2) where x is the distance along the plate from the leading edge of the plate. Instead of using existing similarity transformations, we use a linear group of transformations to transform the governing equations into similarity equations with relevant boundary conditions. Numerical solutions of the similarity equations are presented to show the effects of the controlling parameters on the dimensionless velocity, temperature and concentration profiles as well as on the friction factor, rate of heat and mass transfer. It is found that the rate of heat transfer elevates with the mass transfer velocity, convective heat transfer, Prandtl number, velocity ratio and the magnetic field parameters. It is also found that the rate of mass transfer enhances with the mass transfer velocity, velocity ratio, power law index and the Schmidt number, whilst it suppresses with the magnetic field parameter. Our results are compared with the results existing in the open literature. The comparisons are satisfactory. PMID:23741295

Uddin, Md Jashim; Khan, Waqar A; Ismail, A I Md

2013-01-01

326

Unsteady Boundary Layer Flow and Heat Transfer of a Casson Fluid past an Oscillating Vertical Plate with Newtonian Heating  

PubMed Central

In this paper, the heat transfer effect on the unsteady boundary layer flow of a Casson fluid past an infinite oscillating vertical plate with Newtonian heating is investigated. The governing equations are transformed to a systems of linear partial differential equations using appropriate non-dimensional variables. The resulting equations are solved analytically by using the Laplace transform method and the expressions for velocity and temperature are obtained. They satisfy all imposed initial and boundary conditions and reduce to some well-known solutions for Newtonian fluids. Numerical results for velocity, temperature, skin friction and Nusselt number are shown in various graphs and discussed for embedded flow parameters. It is found that velocity decreases as Casson parameters increases and thermal boundary layer thickness increases with increasing Newtonian heating parameter. PMID:25302782

Hussanan, Abid; Zuki Salleh, Mohd; Tahar, Razman Mat; Khan, Ilyas

2014-01-01

327

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

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

328

Global mantle flow simulations with realistic rheologies on adapted meshes with 1km local resolution at plate boundaries  

NASA Astrophysics Data System (ADS)

Accurate simulation of global mantle dynamics requires the resolution of features on very different length and time scales: while faulted plate margins can require a mesh resolution down to ~1km, a significantly coarser mesh (up to 100km) is sufficient away from these local features, for instance in the lower mantle. Simulations on adaptively refined meshes can reduce the number of unknowns drastically: while a uniform mesh with 1km resolution would lead to ~10^12 unknowns, adapted meshes with the same resolution around plate boundaries require only 10^8-10^9 unknowns, rendering such high-resolution simulations possible on large parallel computers. Thus, it is crucial to efficiently carry out large parallel simulations on locally refined meshes. We are developing Rhea, a parallel adaptive finite element mantle convection code that builds on our ALPS framework to efficiently solve global mantle flow problems on parallel supercomputers. Rhea uses the p4est library from ALPS to dynamically adapt meshes based on forests-of-octrees, combined with efficient and scalable iterative solvers for the mass, momentum and energy equations. We present a study of global flow simulations using a realistic nonlinear rheology and a mesh that is sufficiently fine locally to resolve large variations in the viscosity. For these models we carefully incorporate the details of the plate boundaries at a fine scale, and use a thermal model of the seismicity-defined slabs combined with the diffuse temperature profile obtained from tomography in the lower mantle. The rheology law combines Newtonian and non-Newtonian flow along with yielding under high stress. We compare these global models to plate motion data, and assess changes in plate motions as predicted by the models.

Stadler, G.; Burstedde, C.; Wilcox, L. C.; Gurnis, M.; Alisic, L.; Ghattas, O.; Tan, E.; Zhong, S.

2009-12-01

329

Seismo-electromagnetic phenomena in the western part of the Eurasia-Nubia plate boundary  

NASA Astrophysics Data System (ADS)

This paper presents a future research plan that aims to monitor Seismo-electromagnetic (SEM) phenomena in the western part of the Eurasia-Nubia plate boundary (WENP). This region has a significant tectonic activity [1] combined with relatively low electromagnetic noise levels and for that reason presents the possibility to perform high quality SEM measurements. Further, it is known that low-frequency [ultra (ULF), very (VLF), and low-frequencies (LF)] electromagnetic (EM) waves produce more convincing earthquake precursors (compared to higher frequencies) because of less contamination, large skin depth, and low attenuation [2]. Thus, two SEM effects will be considered: ULF electromagnetic field emissions [3], and VLF/LF radio broadcastings [4]. With respect to the ULF measurements, as a start, three ULF sensors are planned to be installed in the South of Iberian Peninsula supported by the existing networks of seismic research stations. Subsequent development of this initial plan could result in the implementation of a lager ULF monitoring network not only in the Iberian Peninsula, but also in the rest of Europe. Possible integration in the SEGMA array is now under consideration. Another perspective is to use a portable station to track seismic events. Regarding the VLF/LF radio broadcastings, a receiver is planned to be mounted in University of Évora. Radio signals from up to 10 transmitters (in these bands) of interest to study the seismic activity in the WENP region will be monitored. Actually, the radio path from the transmitter to the receiver should cross the epicentral area, therefore two possible transmitters are the ones installed in Monaco (France) and Sicily (Italy). Furthermore, the system will integrate the INFREP network and in this context it will not be restricted to WENP region. With the development of these research plans we aim to collect novel SEM data emerging from the seismic activity in the WENP region. We expect to address the time variations of EM properties of the crust/plate in relation with the strain field, and in space in relation with composition and temperature and stress fields. Further, the interplay between atmospheric (and solar) perturbations with crust perturbations will be monitored, to observe geomagnetic perturbations at different locations. Our study will be focused in the analyses of low magnitude earthquakes with M =< 4, these events are frequent in the WENP region, but have been almost completely disregarded in literature [5,6]. [1] J. Borges, A. J. S. Fitas, M. Bezzeghoud, and P. Teves-Costa, Tectonophysics 337, 373 (2001). [2] V. Chauhan, O.P. Singh, V. Kushwah, V. Singh, B. Singh, Journal of Geodynamics 48, 68 (2009). [3] L. Telesca, V. Lapenna, M. Macchiato, and K. Hattori, Earth and Planet. Science Lett. 268, 219 (2008). [4] P. F. Biagi, L. Castellana, T. Maggipinto, D. Loiacono, L. Schiavulli, T. Ligonzo, M. Fiore, E. Suciu, and A. Ermini, Nat. Hazards Earth Syst. Sci. 9, 1551 (2009). [5] A. Rozhnoi , M.S. Solovieva, O.A. Molchanov, and M. Hayakawa, Phys. and Chem. of the Earth 29, 589-598 (2004). [6] K. Hattori, I. Takahashi, C. Yoshino, N. Isezaki, H. Iwasaki, M. Harada, K. Kawabata, E. Kopytenko, Y. Kopytenko, P. Maltsev, V. Korepanov, O. Molchanov, M. Hayakawa, Y. Noda, T. Nagao, S. Uyeda, Physics and Chemistry of the Earth 29, 481-494 (2004).

Gonçalves da Silva, Hugo; Bezzeghoud, Mourad; Biagi, Pier; Namorado Rosa, Rui; Salgueiro da Silva, Manuel; Caldeira, Bento; Heitor Reis, Artur; Borges, José Fernando; Tlemçani, Mouhaydine; Manso, Marco

2010-05-01

330

Uppermost mantle Pn Velocity of the Arabian Plate, a Preliminary study  

NASA Astrophysics Data System (ADS)

The Arabian plate represents a unique tectonic setup. The uniqueness of this plate is its boundaries that constitute the three known types of plate boundaries. The Red Sea and the Gulf of Aden represent the south and southwest plate boundary with Africa plate. Farther north the Dead Sea Fault system represents the remainder of the northwestern boundary with Africa plate. Continent-continent collision along the Bitlis-Zagros Suture zones represents the northern and northeastern boundary with Eurasia plate. Farther south the convergent plate boundary is manifested by the Makran Subduction Zone. Finally, the Owen and Murray Transform Faults represent the southeast boundary of Arabia with India plate. The broad objective of this study is to map uppermost mantle Pn velocity and anisotropy within the Arabian plate and around its boundaries. Zones that are along the north and the northeast boundaries of Arabia plate historically and in recent years has been effected by devastating earthquakes, a recent example is the Bam earthquake on December, 2003. In this region, accurate earthquake location is essential to delineate seismically active zones, where, without proper velocity models for the region, located earthquake may have large location error. In this preliminary study we present uppermost mantle Pn velocity tomography results of the north and northeastern regions of Arabia plate. We used in this study Pn phase data from the bulletins of Oman Seismic Network, Saudi Seismic Network, Kuwait Seismic Network, International Seismological Center and the National Earthquake Information Center,USA.

Al-Lazki, A. I.; Al-Damegh, K. S.; Al-Enizi, A.; Elhusain, I.; Al-Mahrooqi, I.

2005-12-01

331

Performance of BiCG-like iterative solvers with fast multipole boundary element method and improvement of convergence  

Microsoft Academic Search

Iterative solvers are widely used for solving large systems of linear equa- tions, and these are also applied to the systems obtained with the acoustical BEM. Since the convergence rate of the solvers directly affects the computational time, it is desirable to know the convergence behavior. In this paper, we investigate the convergence behavior of BiCG-like iterative solvers towards the

Y. Yasuda; T. Sakuma

332

Completion of the 16 station Plate Boundary Observatory (PBO) network on Mt. St. Helens, WA  

NASA Astrophysics Data System (ADS)

The Plate Boundary Observatory (PBO), part of the larger NSF-funded EarthScope project, is completing year 3 of the installation phase of 852 continuously operating GPS stations in the Western United States. Some of these GPS stations are focused specifically on centers of volcanic activity. Mt. St. Helens is one of these volcanic areas of interest in the Pacific Northwest (PNW) region. The PNW region will complete the installation of a 16 station GPS network on Mt. St. Helens during September 2006. This work also includes the co-location and installation of tiltmeters at four of the existing GPS sites. Network upgrades will be completed to handle the increase in data flow from the new GPS stations as well as the data from the tiltmeters and strainmeters. New GPS site installations include six helicopter accessible sites, and three drive to sites on the south flank of the mountain. Higher elevation sites will be outfitted with an eight battery, three solar panel power array to keep the stations operational during winter months. The remaining sites use a four battery, three solar panel array that has proved sufficient at other GPS locations over the past 2 winters. All stations will communicate via one of 2 radio networks set up on the mountain. The northern radio network transmits data for ten stations through a microwave connection at the Johnston Ridge observatory that also provides communications for PBO strainmeter, tiltmeter and CVO equipment. The remaining 10 stations on the south side of the mountain, are relayed through a hub at Washington State University's Vancouver Campus that is also providing data services for CVO. Results from analysis of data from both PBO and USGS GPS stations on the mountain, show a radially inward and downward motion, with the maximum vertical offsets high on the mountain and the maximum horizontal offsets located at distances of 5-10km from the crater. Displacements are small over the 2004-present eruption with a maximum of 3cm of inward movement. Modeling of the data by Lisowski et al. (AGU 2006) only accounts for a volume loss that is one third of the amount of material erupted. GPS stations installed high on the mountain were subjected to severe winter weather and heavy rime ice accumulations over the last year. This ice build-up caused distortion of the GPS antenna phase center, and blocked sun access to the solar panels at several sites. Due to the large battery storage capacity, very few power failures occurred at these stations. However, the build up of ice on the GPS antennas caused cm-level pseudo-displacements that mask the ground movements associated with the eruption.

Austin, K.; Hafner, K.; Fengler, K.; Doelger, S.

2006-12-01

333

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

334

Electromagnetic imaging the of the Pacific-North American plate boundary in central California, USA  

NASA Astrophysics Data System (ADS)

The continental margin of central California lies adjacent to a segment of the San Andreas fault (SAF) that exhibits a transition between locked behavior south of the town of Cholame, and freely slipping (creeping) behavior north of the town of Parkfield. Recent reports of non-volcanic tremor (NVT) near the town of Cholame represent the first observation of NVT in a strike-slip environment. Dense clusters of tremor episodes located at the northern limit of the locked section of the SAF were found to originate within the ductile lower crust at depths between 15 and 30~km, and have been interpreted as evidence of high pore fluid pressure. An excess of fluids in this region is likely given its history of subduction, which transports large quantities of water into the forearc crust and mantle. We present a study that uses deep electromagnetic imaging methods to estimate the abundance and distribution of pore fluids at depths associated with non-volcanic tremor. This study extends a previously collected terrestrial profile of magnetotelluric (MT) data (Becken et al. 2008, Geophysical Journal International) into the offshore environment. We deployed 21 seafloor instruments that collected controlled-source electromagnetic (CSEM) and MT data in a line extending from the coast near Morro Bay, across the continental shelf, and out onto the Pacific plate. The marine MT data results in apparent resistivity and phase estimates at periods between 1~s and 20,000~s, sufficient for probing the upper 100~km of regional conductivity. A significant coast effect, marked by asymptotic behavior in the TE mode of the MT responses, is observed at the deep water sites. This necessitates accurate bathymetry modeling when inverting. The CSEM transmitter was towed by all receivers broadcasting a compact broadband binary waveform with a 0.25~Hz fundamental frequency. The controlled-source signal is observed above the noisefloor at source-receiver offsets up to 6~km, which provides constraints on the conductivity structure of the upper 3~km of the crust. By extending the preceding line of terrestrial MT measurements to the west, we are able to constrain any differences in crust and mantle conductivity associated with the transition across the continental boundary. Furthermore, we address whether the deeply-sourced fluids migrating into the root of the SAF identified in Becken et al. (2008) are related to the fossil subduction zone. Inversion of this combined data set aims to detect the source region of these deep fluids, put constraints on their abundance, and further reveal any pathways by which they may reach the San Andreas fault.

Wheelock, B. D.; Constable, S.; Key, K. W.

2010-12-01

335

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

NASA Astrophysics Data System (ADS)

The Plate Boundary Observatory (PBO) is the geodetic component of the NSF funded EarthScope Project. The final PBO GPS network will comprise 852 continuously operating GPS stations installed throughout the Western US and Alaska. There are 435 Stations planned for California with 229 of these in Northern California (NCA). This poster will present a progress report and highlights of GPS installations in NCA over the past year. At the end of the second year of the project (10/2006), PBO NCA installed 68 GPS stations. In the third year of the project we installed 56 stations for a total of 124. This total comprises 60% of the along the active transform margin, 15% of the sites on volcanoes and calderas and 44% of the sites covering the extensional regime of the Basin and Range. We have submitted permit applications for all but 40 of the remaining stations proposed for NCA and expect to have these completed in the next few months. A particularly important metric for planning our schedules is the time lag between reconnaissance and permit accepted. This time lag has varied from 1 day to over a year. Our average over the first two years was 192 days from reconnaissance to installation. Other highlights include completing station installations along the Maacama Fault Zone and onshore of the Mendocino Triple Junction. Data from these stations are available from the UNAVCO archive. As part of our operations and maintenance activities we are developing a catalog of the effects of fences, trees and other near-field objects on GPS data quality. We hope to have 190 Stations built by the end of Sept 2007. In order to accomplish this goal, we are working to finalize our reconnaissance and permitting activities for stations located in National Forests and National Parks, installations we expect to complete by September 2007. We expect to be finished with all our reconnaissance activities by spring 2007 after which crews will focus solely on installations and the transition to operations and maintenance mode in 2008.

Coyle, B.; Basset, A.; Williams, T.; Enders, M.; Rogers, J.; Mann, D.; Feaux, K.

2006-12-01

336

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

337

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

338

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

NASA Astrophysics Data System (ADS)

The Pacific Northwest Region (PNW) of the United States contains a variety of geologic regions and tectonic problems. These include the Cascadia Subduction Zone, Mt. St. Helens and the transition to the Basin and Range province. Since September of 2003, the Plate Boundary Observatory (PBO), which is part of the larger NSF-funded EarthScope project, has been installing a network of continuously operating GPS, strainmeter and tiltmeter instruments. There are currently 78 GPS, 13 strainmeter/borehole seismometers, and 4 tiltmeters operating in the PNW region. The data from this network has already been used to study Episodic Tremor Events (ETS) during September 2005 and January 2007, and renewed activity on Mt. St. Helens that began on September 23, 2004. The goal is have 134 continuously operating GPS stations by the end of September 2008. The locations of the GPS stations were determined by scientific committees. Whenever possible, multiple instruments are deployed at the same location, and share power and communications resources. Examples of this are GPS antennas mounted on top of strainmeter boreholes in the forearc region of western Washington and tiltmeters collecting data through GPS receivers on Mt. St. Helens. In addition, a number of stations provide real time kinematic data to professional surveyors within the region. During the fall of 2006, a 16 GPS and 4 tiltmeter station network was completed on Mt. St. Helens. Results from analysis of both PBO and USGS GPS stations on the mountain, show a radially inward and downward motion, with the maximum vertical offsets high on the mountain and the maximum horizontal offsets located at distances of 5-10km from the crater. Displacements are small over the 2004-present eruption with a maximum of 3cm of inward movement. GPS stations installed high on the mountain experience severe weather and heavy rime accumulations for approximately 6 months of the year. Ice build-up causes distortion of the GPS antenna phase center, and sun blockages on solar panels at several sites. Due to the large battery storage capacity, there have been very few power failures, however the build up of ice on the GPS antennas causes cm-level pseudo- displacements that mask the ground movements associated with the eruption.

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

2007-05-01

339

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

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

340

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

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

341

Real time data from the Plate Boundary Observatory continuous GPS network  

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

342

Real Time Data From the Plate Boundary Observatory Continuous GPS Network  

NASA Astrophysics Data System (ADS)

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

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

2009-05-01

343

Plate boundary and major fault system in the overriding plate within the Shumagin gap at the Alaska-Aleutian subduction zone  

NASA Astrophysics Data System (ADS)

Structure in the overriding plate is one of the parameters that may increase the tsunamigenic potential of a subduction zone but also influence the seismogenic behavior and segmentation of great earthquake rupture. The Alaska-Aleutian margin is characterized by along-strike changes in plate interface coupling over relatively small distances. Here, we present trench normal multichannel seismic (MCS) profiles acquired across the Shumagin gap that has not broken in many decades and appears to be weakly coupled. The high fold, deep penetration (636 channel, 8-km long streamer, 6600 cu.in airgun source) MCS data were acquired as part of the ALEUT project. This dataset gives us critical new constraints on the interplate boundary that can be traced over ~100 km distance beneath the forearc with high variation in its reflection response with depth. These profiles also reveal the detailed upper plate fault structure and forearc morphology. Clear reflections in the overriding plate appear to delineate one or more large faults that cross the shelf and the upper slope. These faults are observed 75 km back from the trench and seem to branch at depth and connect to the plate interface within this gap at ~11 s twtt. We compare the reflective structure of these faults to that of the plate boundary and examine where it intersects the megathrust with respect of the expected downdip limit of coupling. We also compare this major structure with the seismicity recorded in this sector. The imaged fault system is associated with a large deep basin (~6s twt) that is an inherited structure formed during the pre-Aleutian period. Basins faults appear to have accommodated primarily normal motion, although folding of sediments near the fault and complicated fault geometries in the shallow section may indicate that this fault has accommodated other types of motion during its history that may reflect the stress-state at the megathrust over time. The deformation within the youngest sediment also suggests also that this fault system might be still active. The coincident wide-angle seismic data coincident with one MCS profile allow the addition of more information about the deep P-wave velocity structure whereas the streamer tomography (Michaelson-Rotermund et al., this session) around the fault system add more detailed view into the complex structure in the shallow portions (upper 2km) of these structures showing a low velocity zone along one large fault suggesting that this fault is still active. These large-scale structures imaged in the overriding plate within the Shumagin gap are probably sufficiently profound to play a major role in the behavior of the megathrust in this area, segmentation of great earthquake rupture area, tsunami generation and may influence the frictional properties of the seismogenic zone at depth.

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

2013-12-01

344

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

NASA Technical Reports Server (NTRS)

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

Ward, Steven N.

1988-01-01

345

Investigations of Suction in a Transitional Flat-Plate Boundary Layer  

Microsoft Academic Search

\\u000a For the maintenance of a laminar boundary layer flow on transonic wings, it is necessary to integrate a boundary layer suction\\u000a unit in the nose region. This concept of the Hybrid Laminar Flow control is realized through a suction area adapted to the\\u000a outer pressure distribution by an array of suction holes. With this, a stabilization of the boundary layer

Stefan Becker; Jovan Jovanovic

2010-01-01

346

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

347

Disruption of Esrom and Ryk identifies the roof plate boundary as an intermediate target for commissure formation.  

PubMed

Growth cones are guided to their final destination by intermediate targets. Here, we identify intermediate targets and signaling components acting on zebrafish habenula commissural axons. Live imaging establishes that axons pause at the medial habenula before and after crossing the roof plate. esrom mutants axons fail to advance beyond the ipsilateral medial habenula. Tsc2 function is reduced in mutant axons, indicating cell autonomous defects in signaling. Consistent with signaling properties changing outside the roof plate, EphB is surface localized on axon segments within a zone demarcated by the medial habenula. wnt4a is expressed in the medial habenula and morpholino knockdown causes loss of the commissure. Electroporation of truncated Ryk causes axons to reenter the midline after reaching the contralateral habenula. These data identify Esrom as a mediator of growth cone navigation at an intermediate target and underscore the importance of midline boundaries as signaling centers for commissure formation. PMID:18060805

Hendricks, Michael; Mathuru, Ajay Sriram; Wang, Hui; Silander, Olin; Kee, Michelle Zhi Ling; Jesuthasan, Suresh

2008-02-01

348

Perturbation analysis of unsteady magnetohydrodynamic convective heat and mass transfer in a boundary layer slip flow past a vertical permeable plate with thermal radiation and chemical reaction  

Microsoft Academic Search

An analytical study for the problem of unsteady mixed convection with thermal radiation and first-order chemical reaction on magnetohydrodynamics boundary layer flow of viscous, electrically conducting fluid past a vertical permeable plate has been presented. Slip boundary condition is applied at the porous interface. The classical model is used for studying the effect of radiation for optically thin media. The

Dulal Pal; Babulal Talukdar

2010-01-01

349

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

USGS Publications Warehouse

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

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

1998-01-01

350

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

351

The Dauki Thrust Fault and the Shillong Anticline: An incipient plate boundary in NE India?  

NASA Astrophysics Data System (ADS)

The Shillong Massif is a regional contractional structure developing across the Assam sliver of the Indian plate near the Eastern Syntaxis between the Himalaya and Burma arcs. Faulting associated with the Shillong Massif is a major source of earthquake hazard. The massif is a composite basement-cored asymmetric anticline and is 100km wide, >350km long and 1.8km high. The high relief southern limb preserves a Cretaceous-Paleocene passive margin sequence despite extreme rainfall while the gentler northern limb is devoid of sedimentary cover. This asymmetry suggests southward growth of the structure. The Dauki fault along the south limb builds this relief. From the south-verging structure, we infer a regional deeply-rooted north-dipping blind thrust fault. It strikes E-W and obliquely intersects the NE-SW margin of India, thus displaying three segments: Western, within continental India; Central, along the former passive margin; and Eastern, overridden by the west-verging Burma accretion system. We present findings from recent geologic fieldwork on the western and central segments. The broadly warped erosional surface of the massif defines a single anticline in the central segment, east of the intersection with the hinge zone of the continental margin buried by the Ganges-Brahmaputra Delta. The south limb of the anticline forms a steep topographic front, but is even steeper structurally as defined by the Cretaceous-Eocene cover. Below it, Sylhet Trap Basalts intrude and cover Precambrian basement. Dikes, presumably parallel to the rifted margin, are also parallel to the front, suggesting thrust reactivation of rift-related faults. Less competent Neogene clastics are preserved only near the base of the mountain front. Drag folds in these rocks suggest north-vergence and a roof thrust above a blind thrust wedge floored by the Dauki thrust fault. West of the hinge zone, the contractional structure penetrates the Indian continent and bifurcates. After branching into the Dapsi Fault, the Dauki Fault continues westward as the erosion-deposition boundary combined with a belt of N-S shortening. The Dapsi thrust fault strikes WNW across the Shillong massif and dips NNE. It is mostly blind below a topographically expressed fold involving basement and passive-margin cover. Recent fieldwork has shown that the fault is better exposed in the west, where eventually Archean basement juxtaposes folded and steeply dipping fluvial sediment. Both Dauki and Dapsi faults probably continue beyond the Brahmaputra River, where extreme fluvial processes mask them. The area between the two faults is a gentle southward monocline with little or no shortening. Thus uplift of this area stems from slip on the Dauki thrust fault, not from pervasive shortening. The Burma foldbelt overrides the Shillong Plateau and is warped but continuous across the eastern segment of the Dauki fault. The Haflong-Naga thrust front north of the Dauki merges with the fold-thrust belt in the Sylhet basin to the south, despite >150km of differential advance due to much greater advance of the accretionary prism in the basin. Where the Dauki and Haflong-Naga thrusts cross, the thrust fronts are nearly parallel and opposite vergence. We trace a Dauki-related topographic front eastward across the Burma Range. This and other evidence suggest that the Dauki Fault continues below the foldbelt.

Ferguson, E. K.; Seeber, L.; Steckler, M. S.; Akhter, S. H.; Mondal, D.; Lenhart, A.

2012-12-01

352

EarthScope's Plate Boundary Observatory as the Mother of Invention (Invited)  

NASA Astrophysics Data System (ADS)

The Plate Boundary Observatory (PBO) component of EarthScope includes a network of over 1,100 permanent, continuously operating GPS stations. After 5 years of site selection, permitting, and construction, the network was completed in 2008. Having such an unprecedented number of high quality stations in western North America has enabled us to image geology in action, as it happens, such as contemporary uplift of the Sierra Nevada, and block rotation in the Walker Lane. Yet, when PBO was in its planning stages, questions were raised as to whether GPS analysis could keep up with the flood of data, while producing results with the highest achievable accuracy. The general consensus was that the challenge would be met by a combination of innovative data processing methods together with the inevitable progress in computer speed and capacity. Various innovations made by the geodetic community over the last decade have enabled massive operational processing of GPS data with high accuracy. For example, now in 2013, the Nevada Geodetic Laboratory operationally produces position time series and quality assurance data from all ~7,000 GPS geodetic stations in the world that make data publicly available. Of these stations, 4,000 have daily time series updated the next day, and 2,000 have 5-minute time series updated within 1-2 hours of real time. The RMS precision of daily positions for well-sited stations are at the level of 1-2 mm horizontal, and 3-6 mm vertical in the International Terrestrial Reference Frame (ITRF). For 5-minute positions, the precision is at the level of 6-12 mm horizontal, and 15-30 mm vertical. Here we review some of the innovations that have made all of this possible, which were in part driven by challenges presented by EarthScope. First of all, at the data processing level, much creative effort went into making computer processing time scale linearly with the number of GPS stations. The Precise Point Positioning (PPP) technique invented in 1997 has been significantly enhanced recently by techniques to resolve integer-cycle ambiguities in the GPS carrier phase data for single stations. PPP with ambiguity resolution now delivers positioning as precise as full-network processing using differenced data, but with processing time that scales linearly with the number of stations. PPP depends critically on accurate GPS orbit and clock modeling and estimation, which in turn depends on the International GNSS Service (IGS) and its ~500-station global network. IGS products have continued to improve over the last decade as a result of innovation in observable modeling, such as the introduction of antenna calibrations, and new satellite force models. At the foundation of this interconnected geodetic system is the ITRF, which depends critically on the synergy of various space-based geodetic techniques, and the IERS Conventions, which ensure accurate models and overall consistency between analysis centers. This 'global geodetic observing system' is monumental in scale, and involves the hard operational work, research and development of the global geodetic community. Indeed, it is the improvements of this system by the innovations of the geodetic community that has enabled EarthScope to meet its scientific requirements.

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

2013-12-01

353

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

354

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

E-print Network

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

Bonnetier, Eric; Milisic, Vuk

2008-01-01

355

Kinematics to dynamics in the New Zealand Plate boundary zone: implications for the strength of the lithosphere  

NASA Astrophysics Data System (ADS)

New Zealand straddles the boundary between the Australian and Pacific Plate. Cenozoic relative plate motion has resulted in a complex pattern of faulting and block rotation in a zone of continental lithosphere up to 250 km wide. I investigate the implications of the short-term kinematics for the strength of the deforming lithosphere. I use a compilation of seismic reflection/refraction studies and high quality receiver function analyses to determine both the regional structure of the crust, which ranges from 20 to 50 km thick, and fields of buoyancy stress (or GPE per unit volume). Deformation over thousands of years is quantified in terms of velocity and strain rate fields, based on an inversion of neotectonic fault slip and palaeomagnetic data, in the context of the short-term relative plate motions. Forces on the subduction megathrust, as well as deviatoric stresses in the behind subduction region, are calculated from simple 2-D force balances across the Hikurangi Margin, given negligible deviatoric stresses at the along-strike transition between backarc extension and compression. Average megathrust shear stresses are in the range 6-15 MPa, and average lithospheric stresses <20 MPa in the overriding plate. The regional lithospheric strength of the plate boundary zone, assuming a viscous rheology (Newtonian or power law), is determined from an inversion of the field of gradients of buoyancy stress (averaged over either the top 25 km of the crust, or 100-km-thick lithosphere) and strain rate, using the thin sheet stress balance equations, calibrated with the subduction force balance analysis. Effective viscosities for the deforming lithosphere and/or crust are in the range 0.1-5 × 1021 Pa s, with marked weakening in zones of high strain rate, and an abrupt transition to viscosities >1022 Pa s at the margins of the rigid plates. If lateral variations in effective viscosity are only due to non-Newtonian behaviour, these data indicate a bulk power law rheology, with exponent n in the range 2-6. Average lithospheric or crustal deviatoric stresses <30 MPa. Such low driving stresses for the deforming crust are likely to be the result of a combination of pore fluid pressures much greater than hydrostatic (?40 per cent lithostatic) and low coefficients of friction (?0.6) on crustal faults.

Lamb, Simon

2015-05-01

356

The boundary layer contribution to intertropical convergence zones in the quasi-equilibrium tropical circulation model framework  

NASA Astrophysics Data System (ADS)

Theories for the position and intensity of precipitation over tropical oceans on climate time scales have a perplexing disagreement between those that focus on the momentum budget of the atmospheric boundary layer (ABL) and those that focus on thermodynamic factors. In the case of narrow intertropical convergence zones (ITCZs), there is some evidence for both classes of theories, and there are large open questions on the interpretation of the moist static energy (MSE) and momentum budgets of these regions. We develop a model in which both types of mechanisms can operate and the interaction between them can be analyzed. The model includes a mixed-layer ABL, coupled to a free troposphere whose vertical structure follows the quasi-equilibrium tropical circulation model (QTCM) of Neelin and Zeng. The case analyzed here is axisymmetric, using a fixed sea surface temperature (SST) lower boundary condition with an idealized off-equatorial SST maximum. We examine a regime with small values of the gross moist stability associated with tropospheric motions, which is realistic but poses theoretical challenges. In both rotating (equatorial ?-plane) and nonrotating cases, the model ITCZ width and intensity are substantially controlled by the horizontal diffusion of moisture, which is hypothesized to be standing in for nonaxisymmetric transients. The inclusion of the ABL increases the amplitude and sharpness of the ITCZ, contributing to the importance of diffusion. Analytical solutions under simplifying assumptions show that the ABL contribution is not singular in the nondiffusive limit; it just features an ITCZ more intense than observed. A negative gross moist stability contribution associated with the flow component driven by ABL momentum dynamics plays a large role in this. Because of the ABL contribution, the flow imports, rather than exports, MSE in the ITCZ, but we show that this can be understood rather simply. The ABL contribution can be approximately viewed as a forcing to the tropospheric thermodynamics. The ABL forcing term is in addition to thermodynamic forcing by net flux terms in the MSE budget, which otherwise is much as in the standard QTCM. The ABL momentum budget suggests that divergent flow in the ABL is controlled to a significant extent by the pressure gradient imprinted on the ABL by the SST gradient—termed the Lindzen Nigam contribution—although we also find that the thermodynamics mediating this is nontrivial, especially in the rotating case. Nonetheless, when this component of the pressure gradient is artificially removed, the peak ITCZ precipitation is reduced by a fraction on the order of 15 to 25%, less than might have been expected based on the diagnosis of the ABL momentum budget.

Sobel, Adam H.; Neelin, J. David.

2006-11-01

357

Scalings for unsteady natural convection boundary layers on an evenly heated plate with time-dependent heating flux.  

PubMed

It is of fundamental significance, especially with regard to application, to fully understand the flow behavior of unsteady natural convection boundary layers on a vertical plate heated by a time-dependent heat flux. Such an understanding is currently scarce. In this paper, the scaling analysis by Lin et al. [Phys. Rev. E 79, 066313 (2009)] using a simple three-region structure for the unsteady natural convection boundary layer of a homogeneous Newtonian fluid with Pr>1 under isothermal heating was substantially extended for the case when the heating is due to a time-varying sinusoidal heat flux. A series of scalings was developed for the thermal boundary thickness, the plate temperature, the viscous boundary thicknesses, and the maximum vertical velocity within the boundary layer, which are the major parameters representing the flow behavior, in terms of the governing parameters of the flow, i.e., the Rayleigh number Ra, the Prandtl number Pr, and the dimensionless natural frequency f(n) of the time-varying sinusoidal heat flux, at the start-up stage, at the transition time scale which represents the ending of the start-up stage and the beginning of the transitional stage of the boundary-layer development, and at the quasi-steady stage. These scalings were validated by comparison to 10 full numerical solutions of the governing equations with Ra, Pr, and f(n) in the ranges 10(6)?Ra?10(9), 3?Pr?100, and 0.01?f_{n}?0.1 and were shown in general to provide an accurate description of the flow at different development stages, except for high-Pr runs in which a further, although weak, Pr dependence is present, which cannot be accurately predicted by the current scaling analysis using the simple three-region structure, attributed to the non-boundary-layer nature of the velocity field with high-Pr fluids. Some scalings at the transition time scale and at the quasi-steady stage also produce noticeable deviations from the numerical results when f(n) is reduced, indicating that there may be a further f(n) dependence of the scalings which also cannot be accurately predicted by the current scaling analysis. PMID:24483563

Lin, Wenxian; Armfield, S W

2013-12-01

358

Free Vibration Analysis of Patch Repaired Plates with a Through Crack by p-Convergent Layerwise Element  

PubMed Central

The high-order layerwise element models have been used for damaged plates and shells in the presence of singularities such as crack, cutout, and delamination. In this study, the extension of a proposed finite element model has been tested for free vibration analysis of composite laminated systems. For the elements, three-dimensional displacement fields can be captured by layer-by-layer representation. For the elements, higher-order shape functions are derived by combination of one- and two-dimensional shape functions based on higher-order Lobatto shape functions, not using pure higher-order three-dimensional shape functions. The present model can relieve difficulty of aspect ratios in modeling very thin thickness of bonding layer. For verification of the model, natural frequencies and corresponding mode shapes are calculated and then compared with reference values for uncracked and cracked plates. Also, the vibration characteristics of one-sided patch repaired plates with a through internal crack are investigated with respect to variation of crack length, size and thickness of patch, and shear modulus of adhesive, respectively. PMID:25215321

Ahn, Jae S.; Yang, Seung H.; Woo, Kwang S.

2014-01-01

359

Free vibration analysis of patch repaired plates with a through crack by p-convergent layerwise element.  

PubMed

The high-order layerwise element models have been used for damaged plates and shells in the presence of singularities such as crack, cutout, and delamination. In this study, the extension of a proposed finite element model has been tested for free vibration analysis of composite laminated systems. For the elements, three-dimensional displacement fields can be captured by layer-by-layer representation. For the elements, higher-order shape functions are derived by combination of one- and two-dimensional shape functions based on higher-order Lobatto shape functions, not using pure higher-order three-dimensional shape functions. The present model can relieve difficulty of aspect ratios in modeling very thin thickness of bonding layer. For verification of the model, natural frequencies and corresponding mode shapes are calculated and then compared with reference values for uncracked and cracked plates. Also, the vibration characteristics of one-sided patch repaired plates with a through internal crack are investigated with respect to variation of crack length, size and thickness of patch, and shear modulus of adhesive, respectively. PMID:25215321

Ahn, Jae S; Yang, Seung H; Woo, Kwang S

2014-01-01

360

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

361

Upper Plate Deformation in Response to Aseismic Ridge Subduction along a Convergent Margin - the Piano Player Model: Osa Peninsula, Costa Rica  

NASA Astrophysics Data System (ADS)

The Osa Peninsula, an outer forearc high ~20 km inboard of the Middle America Trench, is deforming in response to short wavelength variations in the bathymetry on the subducting aseismic Cocos Ridge, an elongate region of thickened crust ( up to 40% thicker) created by motion of the Cocos plate across the Galapagos Hotspot. Plate convergence is nearly orthogonal to the trench at ~90 mm/yr and the plate interface occurs at a depth ~5 km under the peninsula. Relief on the Cocos Ridge locally exceeds 1 km with the dominant topography expressed as two nearly parallel, but locally offset ridges separated by an axial graben. The strike of these features is sub-parallel to the convergence vector. Modern topography of the Osa Peninsula, elevation of the basement rocks (Early to Middle Tertiary Osa Mélange), elevations of late Quaternary marine deposits, and distribution of late Quaternary deformation rates directly mirror the bathymetry on the Cocos Ridge just outboard of the MAT. New geologic mapping, radiometric dating and fission track analysis constrain distribution and rates of deformation on the Osa Peninsula. The Osa Peninsula is fragmented into a complex set of blocks that vary in size from several kms on a side to <10 kms on a side. These blocks, which closely match the size, distribution and shape of bathymetric features on the incoming Cocos Ridge, are bounded by trench parallel and trench perpendicular, high angle, normal and reverse faults that extend to the plate interface, allowing for grossly different deformation histories over short distances. Fission track analyses of 4 sandstone samples from the Osa Mélange suggest that the basement rocks reached maximum burial temperatures of 60-80 ° C indicating burial depths of ~3-4 kms assuming a reasonable geothermal gradient of ~20 °/km. This suggests a very thin margin wedge prior to late Neogene unroofing. Rates of late Quaternary deformation are constrained by over 30 radiocarbon and 5 Optically Stimulated Luminescence (OSL) ages from sections of the shallow marine Armuelles Fm. Deposition and subsequent block deformation of the Armuelles Fm are fundamentally controlled by interaction of eustatic sea level and bathymetry on the subducted Cocos Ridge. Sea level highstands (MIS 1, 3, and 5) allow for deposition of the shallow marine to estuarine Jimenez, Marenco and Rincón members while sea level lowstands allow for subaerial erosion and the development of internal unconformities. Deformation rates for individual blocks range from > 15 mm/yr directly inboard of subducting ridges to < -6 mm/yr directly inboard of axial grabens. These new results imply a model in which the thin, mechanically weak, outer margin, characterized by pervasive, penetrative, brittle deformation of the Osa Melange basement rocks, deforms directly in response to short wavelength, high-relief bathymetric features on the down going plate. In this case bathymetry dominates over basal traction in controlling deformation of the upper plate. Surface uplift or subsidence of the Osa Peninsula, is not significantly driven by shortening within the outer margin nor underplating or subduction erosion at the plate interface, but by the variations in bathymetry, relief, of the subducting Cocos Ridge.

Gardner, T. W.; Fisher, D. M.; Morell, K. D.; Cupper, M. L.

2008-12-01

362

Volcano-tectonic evolution of Santa Maria Island: implications for the Nubia-Eurasia plate boundary in the Azores  

NASA Astrophysics Data System (ADS)

Santa Maria is a key island in the Azores because it has unique position and age: it sits near the eastern portion of an extinct plate boundary, the East Azores Fracture Zone, and ca. 100 km to the west of the junction between the active Terceira Rift and the Gloria fault. It is by far the oldest island in the archipelago, thus recording a story that no other island in the Azores can tell. From morphologic, stratigraphic and new high resolution K-Ar dating, we show that the volcano-tectonic evolution of Santa Maria is marked by the fast construction of two shield volcanoes separated by a volcano-sedimentary complex. The youngest age we measured for the older construction phase is 4.32 × 0.06 Ma. The oldest age of the younger phase is 4.02 × 0.06 Ma, whereas the youngest age we obtained in Santa Maria is 2.84 × 0.04 Ma. From geophysical, bathymetric and our new geochronological data, we propose that the lineament materialized by the S. Jorge graben in the northwest and Santa Maria Island in the southeast is an intermediate rift, which developed between the East Azores Fracture Zone and the Terceira Rift during migration of the Nubia-Eurasia plate