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Caltech Authors (147.820 recursos)

Repository of works by Caltech published authors.

Group = Seismological Laboratory

Mostrando recursos 1 - 20 de 924

  1. Elastic-plastic bending of the lithosphere incorporating rock deformation data, with application to the structure of the Hawaiian archipelago

    Hsi-Ping, Liu; Kosloff, Dan
    An elastic-plastic lithosphere bending model incorporating rock deformation data has been developed for computation of flexure profiles at mid-ocean island chains and at the trenches near the plate boundaries. Flexure of the plate is computed by finite-element numerical solution of Von Kármán's equation for large deflection of plates with a nonlinear material behavior. The elastic part of the constitutive relation is derived from seismology (moduli = 90% of the seismic values) while the strain rate-dependent plastic part is derived from dunite deformation data extrapolated to the appropriate geologic loading rates. As an illustration, the amplitude and the wavelength of the...

  2. Upper limit on damage zone thickness controlled by seismogenic depth

    Ampuero, Jean Paul; Mao, Xiaolin
    The thickness of fault damage zones, a characteristic length of the cross-fault distribution of secondary fractures, significantly affects fault stress, earthquake rupture, ground motions and crustal fluid transport. Field observations indicate that damage zone thickness scales with accumulated fault displacement at short displacements, but saturates at few hundred meters for displacements larger than few kilometers. To explain this transition of scaling behavior, we conduct 3D numerical simulations of dynamic rupture with off-fault inelastic deformation on long strike-slip faults. We find that the distribution of coseismic inelastic strain is controlled by the transition from crack-like to pulse-like rupture propagation associated with saturation...

  3. Dynamic Rupture Simulations Based on the Characterized Source Model of the 2011 Tohoku Earthquake

    Tsuda, Kenichi; Iwase, Satoshi; Uratani, Hiroaki; Ogawa, Sachio; Watanabe, Takahide; Miyakoshi, Jun’ichi; Ampuero, Jean Paul
    The 2011 Off the Pacific Coast of Tohoku earthquake (Tohoku earthquake, M_w 9.0) occurred on the Japan Trench and caused a devastating tsunami. Studies of this earthquake have revealed complex features of its rupture process. In particular, the shallow parts of the fault (near the trench) hosted large slip and long period seismic wave radiation, whereas the deep parts of the rupture (near the coast) hosted smaller slip and strong radiation of short period seismic waves. Understanding such depth-dependent feature of the rupture process of the Tohoku earthquake is necessary as it may occur during future mega-thrust earthquakes in this...

  4. Surface Rupture Effects on Earthquake Moment-Area Scaling Relations

    Luo, Yingdi; Ampuero, Jean-Paul; Miyakoshi, Ken; Irikura, Kojiro
    Empirical earthquake scaling relations play a central role in fundamental studies of earthquake physics and in current practice of earthquake hazard assessment, and are being refined by advances in earthquake source analysis. A scaling relation between seismic moment (M_0) and rupture area (A) currently in use for ground motion prediction in Japan features a transition regime of the form M_0–A^2, between the well-recognized small (self-similar) and very large (W-model) earthquake regimes, which has counter-intuitive attributes and uncertain theoretical underpinnings. Here, we investigate the mechanical origin of this transition regime via earthquake cycle simulations, analytical dislocation models and numerical crack models...

  5. A phase coherence approach to identifying co-located earthquakes and tremor

    Hawthorne, J. C.; Ampuero, J.-P.
    We present and use a phase coherence approach to identify seismic signals that have similar path effects but different source time functions: co-located earthquakes and tremor. The method used is a phase coherence-based implementation of empirical matched field processing, modified to suit tremor analysis. It works by comparing the frequency-domain phases of waveforms generated by two sources recorded at multiple stations. We first cross-correlate the records of the two sources at a single station. If the sources are co-located, this cross-correlation eliminates the phases of the Green’s function. It leaves the relative phases of the source time functions, which should...

  6. Crust and Upper Mantle Seismic Anisotropy Variations from the Coast to Inland in Central and Southern Mexico

    Castillo, Jorge; Pérez-Campos, Xyoli; Valenzuela, Raúl; Husker, Allen; Ferrari, Luca
    Subduction zones are among the most dynamic tectonic environments on Earth. Deformation mechanisms of various scales produce networks of oriented structures and faulting systems that result in a highly anisotropic medium for seismic wave propagation. In this study, we combine shear-wave splitting inferred from receiver functions and the results from a previous SKS-wave study to quantify and constrain the vertically averaged shear wave splitting at different depths along the 100-station MesoAmerican Subduction Experiment (MASE) array. This produces a transect that runs perpendicular to the trench across the flat slab portion of the subduction zone below central and southern Mexico. Strong...

  7. Depth varying rupture properties during the 2015 Mw 7.8 Gorkha (Nepal) earthquake

    Yue, Han; Simons, Mark; Duputel, Zacharie; Jiang, Junle; Fielding, Eric; Liang, Cunren; Owen, Susan; Moore, Angelyn; Riel, Bryan; Ampuero, Jean Paul; Samsonov, Sergey V.
    On April 25th 2015, the Mw 7.8 Gorkha (Nepal) earthquake ruptured a portion of the Main Himalayan Thrust underlying Kathmandu and surrounding regions. We develop kinematic slip models of the Gorkha earthquake using both a regularized multi-time-window (MTW) approach and an unsmoothed Bayesian formulation, constrained by static and high rate GPS observations, synthetic aperture radar (SAR) offset images, interferometric SAR (InSAR), and teleseismic body wave records. These models indicate that Kathmandu is located near the updip limit of fault slip and approximately 20 km south of the centroid of fault slip. Fault slip propagated unilaterally along-strike in an ESE direction...

  8. Characterizing the Kathmandu Valley sediment response through strong motion recordings of the 2015 Gorkha earthquake sequence

    Rajaure, S.; Asimaki, D.; Thompson, E. M.; Hough, S.; Martin, S.; Ampuero, J. P.; Dhital, M. R.; Inbal, A.; Takai, N.; Shigefuji, M.; Bijukchhen, S.; Ichiyanagi, M.; Sasatani, T.; Paudel, L.
    We analyze strong motion records and high-rate GPS measurements of the M 7.8 Gorkha mainshock, M 7.3 Dolakha, and two moderate aftershock events recorded at four stations on the Kathmandu basin sediments, and one on rock-outcrop. Recordings on soil from all four events show systematic amplification relative to the rock site at multiple frequencies in the 0.1–2.5 Hz frequency range, and de-amplification of higher frequencies ( >2.5–10 Hz). The soil-to-rock amplification ratios for the M 7.8 and M 7.3 events have lower amplitude and frequency peaks relative to the ratios of the two moderate events, effects that could be suggestive...

  9. Anomalously large complete stress drop during the 2016 M_w 5.2 Borrego Springs earthquake inferred by waveform modeling and near-source aftershock deficit

    Ross, Z. E.; Kanamori, H.; Hauksson, E.
    The 2016 M_w 5.2 Borrego Springs earthquake occurred in the trifurcation area of the San Jacinto fault zone and generated more than 23,000 aftershocks. We analyze source properties of this earthquake along with 12,487 precisely located aftershock hypocenters to obtain an unusually detailed view of the rupture process and energy budget for this moderate earthquake. Source time functions are obtained using an empirical Green's function approach and are inverted for a slip distribution on the fault plane. The rupture propagated unilaterally to the northwest over a distance of 1.8 km, resulting in clear directivity signals. Two asperities are identified and the...

  10. Intraslab seismicity and thermal stress in the subducted Cocos plate beneath central Mexico

    Manea, Vlad; Manea, Marina; Kostoglodov, Vladimir; Sewell, Granville
    We present a model of the subducting Cocos slab beneath Central Mexico, that provides an explanation for stresses causing the occurrence of the majority of the intraslab earthquakes which are concentrated in a long flat segment. Based on the recently developed thermal models for the Central Mexico subduction zone, the thermal stresses due to non-uniform temperature contrast in the subducting slab are calculated using a finite element approach. The slab is considered purely elastic but due to high temperature at its bottom the behavior is considered as ductile creep. The calculation results show a ∼ 20 km slab core characterized...

  11. Introduction to special issue: "The influence of plate interaction on post-Laramide magmatism and tectonics in Mexico"

    Ferrari, Luca; Stock, Joann M.; Fucugauchi, Jaime Urrutia
    Among convergent margins, Mexico is an excellent site for studying along-strike variation in plate tectonics at the trench and its effect on the accompanying volcanism and tectonics in the overriding plate. The progressive fragmentation and consumption of the Farallon plate and the interaction between the Pacific and North America plates during the Cenozoic produced some unique geologic features. These include the Sierra Madre Occidental, one of the largest silicic igneous provinces on Earth, and the Trans-Mexican Volcanic Belt, a complex continental volcanic arc underlain by two of the youngest slabs in the world. In addition, extension occurred concurrently in much...

  12. Locally and remotely triggered aseismic slip on the central San Jacinto Fault near Anza, CA, from joint inversion of seismicity and strainmeter data

    Inbal, A.; Ampuero, J.-P.; Avouac, J.-P.
    We study deep aseismic slip along the central section of the San Jacinto Fault, near the Anza Seismic Gap, in southern California. Elevated strain-rates following the remote M_w 7.2 April 4, 2010 El Mayor-Cucapah and the local M_w 5.4, July 7, 2010 Collins Valley earthquakes were recorded by Plate Boundary Observatory borehole strain-meters near Anza, and were accompanied by vigorous aftershock sequences. We introduce a method to infer the distribution of triggered aseismic slip from combined seismicity and geodetic data, based on a rate-and-state friction model that maps observed changes in seismicity rates into stress changes. We invert for the cumulative...

  13. Upper mantle P structure on the ocean side of the Japan-Kurile Arc

    Fukao, Yoshio
    Slowness measurements are made for the first and later arrivals of P waves from about seventy Kurile-Kamchatka earthquakes (13° < Δ < 30°) at the Wakayama Micro-Earthquake Observatory, Japan. The experimental error of dT/dd is not more than 3 per cent and the data points suffice to draw a dT/dΔ curve fairly uniquely. In the distance range 4° < Δ < 15° a travel-time curve, including a later arrival branch, is constructed for a specific Kurile event using the records along the Pacific coasts of the Japanese-Kurile islands. The results are inverted to obtain a velocity model for the upper...

  14. Towards adjoint-based inversion of time-dependent mantle convection with non-linear viscosity

    Li, Dunzhu; Gurnis, Michael; Stadler, Georg
    We develop and study an adjoint-based inversion method for the simultaneous recovery of initial temperature conditions and viscosity parameters in time-dependent mantle convection from the current mantle temperature and historic plate motion. Based on a realistic rheological model with temperature-dependent and strain-rate-dependent viscosity, we formulate the inversion as a PDE-constrained optimization problem. The objective functional includes the misfit of surface velocity (plate motion) history, the misfit of the current mantle temperature, and a regularization for the uncertain initial condition. The gradient of this functional with respect to the initial temperature and the uncertain viscosity parameters is computed by solving the...

  15. The relative amplitudes of mantle heterogeneity in P velocity, S velocity and density from free-oscillation data

    Li, X.-D.; Giardini, D.; Woodhouse, J. H.
    Splitting functions retrieved from spectra of the free oscillations are sensitive to the lateral variations in P velocity (α), S velocity (β), and density (ρ) simultaneously. In this study they are used to constrain the values of the ratios d ln α/d ln β and d ln ρ/d ln α for the lower mantle. Assuming that the upper mantle structure is obtainable from model M84A (this is not a crucial assumption as experiments indicate), the optimal value of d ln α/d ln β inferred from the modal data is 0.44 and d ln α/d ln β lies in the interval...

  16. Mantle convection with strong subduction zones

    Conrad, Clinton P.; Hager, Bradford H.
    Because mantle viscosity is temperature‐dependent, cold subducting lithosphere should be strong, which implies that the rapid, localized deformation associated with subduction should strongly resist plate motions. Due to computational constraints, the deformation of a subducting plate cannot be accurately resolved in mantle‐scale convection models, so its effect on convection is difficult to investigate. We have developed a new method for implementing subduction that parametrizes the deformation of the oceanic lithosphere within a small region of a finite element grid. By imposing velocity boundary conditions in the vicinity of the subduction zone, we enforce a geometry for subduction, producing a slab...

  17. A modified first-motion approximation for the synthesis of body-wave seismograms

    Mellman, George R.; Helmberger, Donald V.
    Modified first-motion approximations have been developed for the generation of synthetic body-wave seismograms using the Cagniard-de Hoop method. Comparisons are presented between classical first motion, modified first motion and full Cagniard treatments for problems involving a homogeneous sphere and a triplication in a realistic earth model. Results of these comparisons show that the modified first-motion approximations may be used for a wide variety of geophysically interesting problems with little loss of accuracy compared to the full Cagniard method.

  18. Abundant off-fault seismicity and orthogonal structures in the San Jacinto fault zone

    Ross, Zachary E.; Hauksson, Egill; Ben-Zion, Yehuda
    The trifurcation area of the San Jacinto fault zone has produced more than 10% of all earthquakes in southern California since 2000, including the June 2016 M_w (moment magnitude) 5.2 Borrego Springs earthquake. In this area, the fault splits into three subparallel strands and is associated with broad V_P/V_S anomalies. We synthesize spatiotemporal properties of historical background seismicity and aftershocks of the June 2016 event. A template matching technique is used to detect and locate more than 23,000 aftershocks, which illuminate highly complex active fault structures in conjunction with a high-resolution regional catalog. The hypocenters form dipping seismicity lineations both...

  19. Earthquake rupture below the brittle-ductile transition in continental lithospheric mantle

    Prieto, Germán A.; Froment, Bérénice; Yu, Chunquan; Poli, Piero; Abercrombie, Rachel
    Earthquakes deep in the continental lithosphere are rare and hard to interpret in our current understanding of temperature control on brittle failure. The recent lithospheric mantle earthquake with a moment magnitude of 4.8 at a depth of ~75 km in the Wyoming Craton was exceptionally well recorded and thus enabled us to probe the cause of these unusual earthquakes. On the basis of complete earthquake energy balance estimates using broadband waveforms and temperature estimates using surface heat flow and shear wave velocities, we argue that this earthquake occurred in response to ductile deformation at temperatures above 750°C. The high stress...

  20. A dipping, thick segment of the Farallon Slab beneath Central US

    Sun, Daoyuan; Gurnis, Michael; Saleeby, Jason; Helmberger, Don
    It has been hypothesized that much of the crustal deformation attributed to the Laramide orogeny of the southwest North American Cordillera was caused by dynamic effects induced by the flat subduction of a large oceanic plateau that was embedded within the Farallon plate. Previous studies have identified within the North American mantle a seismic velocity anomaly that plausibly represents the remnants of the subducted plateau. Coupled plate kinematic and dynamic modeling of the anomaly, as well as surface geological findings identify this anomaly as the subducted conjugate to the Shatsky Rise. Here, we find clear evidence for a northeastward dipping...

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