Sunday, May 24, 2015

 

 



Soy un nuevo usuario

Olvidé mi contraseña

Entrada usuarios

Lógica Matemáticas Astronomía y Astrofísica Física Química Ciencias de la Vida
Ciencias de la Tierra y Espacio Ciencias Agrarias Ciencias Médicas Ciencias Tecnológicas Antropología Demografía
Ciencias Económicas Geografía Historia Ciencias Jurídicas y Derecho Lingüística Pedagogía
Ciencia Política Psicología Artes y Letras Sociología Ética Filosofía
 

rss_1.0 Recursos de colección

Caltech Authors (106,101 recursos)
Repository of works by Caltech published authors.

Group = Caltech Tectonics Observatory

Mostrando recursos 1 - 20 de 270

1. Numerical modeling of long-term earthquake sequences on the NE Japan megathrust: Comparison with observations and implications for fault friction - Cubas, Nadaya; Lapusta, Nadia; Avouac, Jean-Philippe; Perfettini, Hugo
We use numerical modeling to investigate fault properties that explain key features of the 2011 Mw 9.0 Tohoku-Oki earthquake as well as the overall regional behavior of the NE Japan megathrust. In particular, we study the possibility that slip near the trench resulted from thermal pressurization on a shallow patch of the megathrust, and investigate whether low-velocity friction on that patch is rate-strengthening or rate-weakening. Our models also contain a deeper rate-weakening patch, not prone to efficient thermal pressurization, to account for the moderate-sized interplate seismicity. We produce earthquake sequences and aseismic slip in our models using 2D dynamic simulations...

2. Static Laboratory Earthquake Measurements with the Digital Image Correlation Method - Rubino, V.; Lapusta, N.; Rosakis, A. J.; Leprince, S.; Avouac, J. P.
Mapping full-field displacement and strain changes on the Earth’s surface following an earthquake is of paramount importance to enhance our understanding of earthquake mechanics. Currently, aerial and satellite images taken pre- and post-earthquake can be processed with sub-pixel correlation algorithms to infer the co-seismic ground deformations (e.g., [1, 2]). However, the interpretation of this data is not straightforward due to the inherent complexity of natural faults and deformation fields. To gain understanding into rupture mechanics and to help interpret complex rupture features occurring in nature, we develop a laboratory earthquake setup capable of reproducing displacement and strain maps similar to...

3. Seismic structure in southern Peru: evidence for a smooth contortion between flat and normal subduction of the Nazca Plate - Dougherty, Sara L.; Clayton, Robert W.
Rapid changes in slab geometry are typically associated with fragmentation of the subducted plate; however, continuous curvature of the slab is also possible. The transition from flat to normal subduction in southern Peru is one such geometrical change. The morphology of the subducted Nazca Plate along this transition is explored using intraslab earthquakes recorded by temporary regional seismic arrays. Observations of a gradual increase in slab dip coupled with a lack of any gaps or vertical offsets in the intraslab seismicity suggest warping of the slab. Concentrations of focal mechanisms at orientations which are indicative of slab bending are also...

4. Origin of the modern Chiapanecan Volcanic arc in southern México inferred from thermal models - Manea, Vlad C.; Manea, Marina
In southern México, the subducting Cocos slab drastically changes its geometry: from a flat slab in central México to a ∼45° dip angle beneath Chiapas. Also, the currently active volcanic arc, the modern Chiapanecan volcanic arc, is oblique and situated far inland from the Middle America trench, where the slab depth is ∼200 km. In contrast, the Central America volcanic arc is parallel to the Middle America trench, and the slab depth is ∼100 km. A two-dimensional steady-state thermomechanical model explains the calc-alkaline volcanism by high temperature (∼1300 °C) in the mantle wedge just beneath the Central America volcanic arc...

5. Shallow Rupture of the 2011 Tarlay Earthquake (M_w 6.8), Eastern Myanmar - Wang, Yu; Lin, Yu-Nung Nina; Simons, Mark; Tun, Soe Thura
We use L‐band Advanced Land Observation Satellite PALSAR data to infer the distribution of subsurface fault slip during the Tarlay earthquake (M_w 6.8) in eastern Myanmar. We find the total length of surface rupture is approximately 30 km, with nearly 2 m maximum surface offset along the westernmost section of the Nam Ma fault (the Tarlay segment). Finite‐fault inversions constrained by Interferometric Synthetic Aperture Radar (InSAR) and pixel‐tracking data suggest that fault slip is concentrated within the upper 10 km of the crust. Maximum slip exceeds 4 m at a depth between 3 and 5 km. Comparison between field measurements...

6. A physical model for seismic noise generation by turbulent flow in rivers - Gimbert, Florent; Tsai, Victor C.; Lamb, Michael P.
Previous studies suggest that the seismic noise induced by rivers may be used to infer river transport properties, and previous theoretical work showed that bedload sediment flux can be inverted from seismic data. However, the lack of a theoretical framework relating water flow to seismic noise prevents these studies from providing accurate bedload fluxes and quantitative information on flow processes. Here we propose a forward model of seismic noise caused by turbulent flow. In agreement with previous observations, modeled turbulent flow-induced noise operates at lower frequencies than bedload-induced noise. Moreover, the differences in the spectral signatures of turbulent flow-induced and...

7. Diagnosing Source Geometrical Complexity of Large Earthquakes - Rivera, L.; Kanamori, H.
We investigated the possible frequency dependence of the moment tensor of large earthquakes by performing W phase inversions using teleseismic data and equally-spaced narrow, overlapping frequency bands. We investigated frequencies from 0.6 to 3.8 mHz. Our focus was on the variation with frequency of the scalar moment, the amount of non-double-couple, and the focal mechanism. We applied this technique to 30 major events in the period 1994–2013 and used the results to detect source complexity. Based on the results, we classed them into three groups according to the variability of the source parameters with frequency: simple, complex and intermediate. Twelve...

8. Rupture and variable coupling behavior of the Mentawai segment of the Sunda megathrust during the supercycle culmination of 1797 to 1833 - Philibosian, Belle; Sieh, Kerry; Avouac, Jean-Philippe; Natawidjaja, Danny H.; Chiang, Hong-Wei; Wu, Chung-Che; Perfettini, Hugo; Shen, Chuan-Chou; Daryono, Mudrik R.; Suwargadi, Bambang W.
We refer to periods of subduction strain accumulation beneath the Mentawai Islands, Sumatra, as “supercycles,” because each culminates in a series of partial ruptures of the megathrust in its final decades. The finale of the previous supercycle comprised two giant earthquakes in 1797 and 1833 and whatever happened in between. This behavior between two great ruptures has implications for how the megathrust will behave between its more recent partial failure, during the M_w 8.4 earthquake of 2007, and subsequent large ruptures. We synthesize previously published coral microatoll records and a large new coral data set to constrain not only these...

9. Lithological control on the deformation mechanism and the mode of fault slip on the Longitudinal Valley Fault, Taiwan - Thomas, Marion Y.; Avouac, Jean-Philippe; Gratier, Jean-Pierre; Lee, Jian-Cheng
The Longitudinal Valley Fault (LVF) in Taiwan is creeping at shallow depth along its southern half, where it is bounded by the Lichi Mélange. By contrast, the northern segment of the LVF is locked where it is bounded by forearc sedimentary and volcanoclastic formations. Structural and petrographic investigations show that the Lichi Mélange most probably formed as a result of internal deformation of the forearc when the continental shelf of South China collided with the Luzon arc as a result of the subduction of the South China Sea beneath the Philippine Sea Plate. The forearc formations constitute the protolith of...

10. Upper mantle surprises derived from the recent Virginia earthquake waveform data - Chu, Risheng; Helmberger, Don; Gurnis, Michael
Recent high resolution regional waveform modeling reveals that the lithosphere beneath the North American craton is subdivided into an upper nearly uniform layer and a lower layer with a high velocity gradient. The boundary occurs at about a depth of 115 km and is responsible for 8° discontinuity in seismic record sections that is often observed in craton environments. Unexpectedly, we find seismic velocities in the lower layer significantly reduced along a corridor from the New Madrid rift zone to Virginia. This reduced velocity in the lower lithosphere may be associated with a possible historic hotspot activity. We also find...

11. Modeling deformation induced by seasonal variations of continental water in the Himalaya region: Sensitivity to Earth elastic structure - Chanard, K.; Avouac, J. P.; Ramillien, G.; Genrich, J.
Strong seasonal variations of horizontal and vertical positions are observed on GPS time series from stations located in Nepal, India, and Tibet (China). We show that this geodetic deformation can be explained by seasonal variations of continental water storage driven by the monsoon. For this purpose, we use satellite data from the Gravity Recovery and Climate Experiment to determine the time evolution of surface loading. We compute the expected geodetic deformation assuming a perfectly elastic Earth model. We consider Green's functions, describing the surface deformation response to a point load, for an elastic homogeneous half-space model and for a layered...

12. Spatiotemporal evolution of seismic and aseismic slip on the Longitudinal Valley Fault, Taiwan - Thomas, Marion Y.; Avouac, Jean-Philippe; Champenois, Johann; Lee, Jian-Cheng; Kuo, Long-Chen
The Longitudinal Valley Fault (LVF) in eastern Taiwan is a high slip rate fault (about 5 cm/yr), which exhibits both seismic and aseismic slip. Deformation of anthropogenic features shows that aseismic creep accounts for a significant fraction of fault slip near the surface, whereas a fraction of the slip is also seismic, since this fault has produced large earthquakes with five M_w>6.8 events in 1951 and 2003. In this study, we analyze a dense set of geodetic and seismological data around the LVF, including campaign mode Global Positioning System(GPS) measurements, time series of daily solutions for continuous GPS stations (cGPS),...

13. Response of rate-and-state seismogenic faults to harmonic shear-stress perturbations - Ader, Thomas J.; Lapusta, Nadia; Avouac, Jean-Philippe; Ampuero, Jean-Paul
Field and laboratory observations show that seismicity has non-trivial period-dependent response to periodic stress perturbations. In Nepal, seismicity shows significant variations in response to annual monsoon-induced stress variations but not to semidiurnal tidal stresses of the same magnitude. Such period dependence cannot be explained by the Coulomb failure model and spring-slider rate-and-state model (SRM). Here, we study seismicity response to periodic stress perturbations in a 2-D continuum model of a rate-and-state fault (that is, a finite rate-and-state fault). We find that the resulting seismicity indeed exhibits nearly periodic variations. Their amplitude is maximum at a certain period, T_a, and decreases...

14. Zircon age and oxygen isotopic correlations between Bouse Formation tephra and the Lawlor Tuff - Harvey, Janet C.
The Bouse Formation in the lower Colorado River trough holds an important record of the onset of the modern drainage patterns in the southwestern United States. It comprises calcareous and clastic infill deposited during flooding of several basins, including the Bristol and Blythe subbasins of Lake Bouse. An intercalated ash bed, which is key to constraining its depositional age, is exposed in two locations, Buzzards Peak and Amboy. Comparative zircon tephrochronology by secondary ion microprobe analysis of U-Pb zircon crystallization ages, U-Th trace element abundances, and oxygen isotopic composition confirm a correlation between the Bouse Formation tephra and the 4.834...

15. From deep to modern time along the western Sierra Nevada Foothills of California, San Joaquin to Kern River drainages - Saleeby, Jason; Saleeby, Zorka; Sousa, Frank
This two day field trip presents an overview of ~ 500 m.y. of diverse geologic history along the southwestern Sierra Nevada Foothills, with focus on several profound geologic features that distinguish this part of the western foothills. These features include (1) a highly deformed oceanic Moho section through the Kings River ophiolite, interpreted as a Carboniferous abyssal core complex; (2) Permo-Carboniferous ophiolitic mélange interpreted to have formed and been emplaced along the SW Cordilleran edge transform, along which the early Mesozoic convergent margin initiated; (3) Early Cretaceous mafic rocks of the western Sierra Nevada batholith, which also characterize much of the Great Valley basement; (4) evidence for 1000-m-scale...

16. Pliocene–Quaternary subsidence and exhumation of the southeastern San Joaquin Basin, California, in response to mantle lithosphere removal - Cecil, M. Robinson; Saleeby, Z.; Saleeby, J.; Farley, K. A.
Thermomechanical models of mantle lithosphere removal from beneath the southern Sierra Nevada region, California (USA), predict a complex spatiotemporal pattern of vertical surface displacements. We evaluate these models by using (U-Th)/He thermochronometry, together with other paleothermometry estimates, to investigate such topographic transients. We target Tertiary strata from the Kern arch, a crescent-shaped active uplift located in the southeastern San Joaquin Basin, along the western flank of the southern Sierra Nevada. Kern arch stratigraphy provides a unique record of subsidence and exhumation in a sensitive region immediately adjacent to the delaminating mantle lithosphere at depth. Detrital apatite (U-Th)/He ages from Oligocene–Miocene...

17. Active tectonics and earthquake potential of the Myanmar region - Wang, Yu; Sieh, Kerry; Tun, Soe Thura; Lai, Kuang-Yin; Myint, Than
This paper describes geomorphologic evidence for the principal neotectonic features of Myanmar and its immediate surroundings. We combine this evidence with published structural, geodetic, and seismic data to present an overview of the active tectonic architecture of the region and its seismic potential. Three tectonic systems accommodate oblique collision of the Indian plate with Southeast Asia and extrusion of Asian territory around the eastern syntaxis of the Himalayan mountain range. Subduction and collision associated with the Sunda megathrust beneath and within the Indoburman range and Naga Hills accommodate most of the shortening across the transpressional plate boundary. The Sagaing fault...

18. Imaging subducted slab structure beneath the Sea of Okhotsk with teleseismic waveforms - Zhan, Zhongwen; Helmberger, Donald V.; Li, Dunzhu
The structure of subducted slabs is not well imaged in most global tomographic models with anomalies typically less than 1%. Synthetic waveforms for such models are not noticeably different from their 1D reference models. In contrast, we find that observed teleseismic waveforms sampling slabs in the down-dip direction display multipathing features indicative of substantial structure. Such waveform complexity patterns appear distinctly different for various source locations with outer-rise events generally displaying relatively simple waveforms. Here, we model these waveform patterns for a portion of the Kuril subduction zone. The best fitting slab models have relatively fast cores (∼5%) with smooth...

19. The seismic cycle in the area of the 2011 M_w9.0 Tohoku-Oki earthquake - Perfettini, H.; Avouac, J. P.
We model seismic and aseismic slip on the Japan megathrust in the area of the M_w9.0, 2011 Tohoku-Oki earthquake based on daily time series from 400 GPS stations of the GEONET network and campaign measurements of six sea floor displacements. The coseismic and postseismic slip distributions are inverted simultaneously using principal component analysis-based inversion method (PCAIM). Exploring a wide range of boundary conditions and regularization constraints, we found the coseismic slip distribution to be quite compact with a peak slip between 30 and 50 m near the trench. Our model shows deep afterslip fringing the downdip edge of the coseismic...

20. Seismicity and structure in central Mexico: Evidence for a possible slab tear in the South Cocos plate - Dougherty, Sara L.; Clayton, Robert W.
The morphology of the transition from flat to normal subduction in eastern central Mexico is explored using intraslab earthquakes recorded by temporary and permanent regional seismic arrays. Observations of a sharp transition in slab dip near the abrupt end of the Trans-Mexican Volcanic Belt (TMVB) suggest a possible slab tear located within the subducted South Cocos plate. The eastern lateral extent of a thin ultra-slow velocity layer (USL) imaged atop the Cocos slab in recent studies along the Meso America Subduction Experiment array is examined here using additional data. We find an end to this USL which is coincident with...

Página de resultados:
 

Busque un recurso