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Caltech Authors (167.915 recursos)

Repository of works by Caltech published authors.

Group = Seismological Laboratory

Mostrando recursos 1 - 20 de 376

  1. Strong anisotropic flow in a finely layered asthenosphere

    Honda, Satoru
    We derive the long wave length equivalents of the constitutive relations for finely stratified fluids as suggested by Saito and Abe [1984]. The results show the transversely isotropic relations characterized by two effective viscosities. One is associated with shear stress applied on the plane parallel to the layering and the other is with normal stress applied perpendicular to the layering. If thin soft layers exist in the low velocity zone, there may be a significant difference in these two viscosities. A simple calculation simulating mantle flow with large apparent anisotropy shows the possible existence of convection having large aspect ratio.

  2. Machine Learning Seismic Wave Discrimination: Application to Earthquake Early Warning

    Li, Zefeng; Meier, Men-Andrin; Hauksson, Egill; Zhan, Zhongwen; Andrews, Jennifer
    Performance of earthquake early warning (EEW) systems suffers from false alerts caused by local impulsive noise from natural or anthropogenic sources. To mitigate this problem, we train a Generative Adversarial Network (GAN) to learn the characteristics of first‐arrival earthquake P waves, using 300,000 waveforms recorded in southern California and Japan. We apply the GAN critic as an automatic feature extractor and train a Random Forest classifier with about 700,000 earthquake and noise waveforms. We show that the discriminator can recognize 99.2% of the earthquake P waves and 98.4% of the noise signals. This state‐of‐the‐art performance is expected to reduce significantly...

  3. Transient reactivation of a deep-seated landslide by undrained loading captured with repeat airborne and terrestrial lidar

    Booth, Adam M.; McCarley, Justin; Hinkle, Jason; Shaw, Susan; Ampuero, Jean-Paul; Lamb, Michael P.
    Landslides reactivate due to external environmental forcing or internal mass redistribution, but the process is rarely documented quantitatively. We capture the three‐dimensional, 1‐m resolution surface deformation field of a transiently reactivated landslide with image correlation of repeat airborne lidar. Undrained loading by two debris flows in the landslide's head, rather than external forcing, triggered reactivation. After that loading, the lower 2 km of the landslide advanced by up to 14 m in 2 yrs before completely stopping. The displacement field over those 2 yrs implies that the slip surface gained 1 kPa of shear strength, which was likely accomplished by...

  4. An anisotropic contrast in the lithosphere across the central San Andreas fault

    Jiang, Chengxin; Schmandt, Brandon; Clayton, Robert W.
    Seismic anisotropy of the lithosphere and asthenosphere were investigated with a dense broadband seismic transect nearly orthogonal to the central San Andreas fault (SAF). A contrast in SK(K)S splitting was found across the SAF, with a clockwise rotation of the fast orientation ~26° closer to the strike of the SAF and greater delay times for stations located within 35 km to the east. Dense seismograph spacing requires heterogeneous anisotropy east of the SAF in the uppermost mantle or crust. Based on existing station coverage, such a contrast in splitting orientations across the SAF may be unusual along strike and its...

  5. Equations of state and anisotropy of Fe-Ni-Si alloys

    Morrison, Rachel A.; Jackson, Jennifer M.; Sturhahn, Wolfgang; Zhang, Dongzhou; Greenberg, Eran
    We present powder x‐ray diffraction data on bcc‐ and hcp‐structured Fe_(0.91)Ni_(0.09) and Fe_(0.8)Ni_(0.1)Si_(0.1) at 300 K up to 167 GPa and 175 GPa, respectively. The alloys were loaded with tungsten powder as a pressure calibrant and helium as a pressure transmitting medium into diamond anvil cells, and their equations of state and axial ratios were measured with high statistical quality. These equations of state are combined with thermal parameters from previous reports to improve the extrapolation of the density, adiabatic bulk modulus, and bulk sound speed to the pressures and temperatures of Earth's inner core. We propagate uncertainties and place...

  6. Exploring new drilling prospects in the southwest Pacific

    Gallagher, S. J.; Exon, N.; Seton, M.; Ikehara, M.; Hollis, C. J.; Arculus, R.; D'Hondt, S.; Foster, C.; Gurnis, M.; Kennett, J. P.; McKay, R.; Malakoff, A.; Mori, J.; Takai, K.; Wallace, L.
    A major International Ocean Discovery Program (IODP) workshop covering scientific ocean drilling in the southwest Pacific Ocean was held in Sydney, Australia, in late 2012. The workshop covered all fields of geoscience, and drilling targets in the area from the Equator to Antarctica. High-quality contributions and a positive and cooperative atmosphere ensured its success. The four science themes of the new IODP science plan were addressed. An additional resource-oriented theme considered possible co-investment opportunities involving IODP vessels. As a result of the workshop, existing proposals were revised and new ones written for the April 2013 deadline. Many of the proposals...

  7. Global tectonic reconstructions with continuously deforming and evolving rigid plates

    Gurnis, Michael; Yang, Ting; Cannon, John; Turner, Mark; Williams, Simon; Flament, Nicolas; Müller, R. Dietmar
    Traditional plate reconstruction methodologies do not allow for plate deformation to be considered. Here we present software to construct and visualize global tectonic reconstructions with deforming plates within the context of rigid plates. Both deforming and rigid plates are defined by continuously evolving polygons. The deforming regions are tessellated with triangular meshes such that either strain rate or cumulative strain can be followed. The finite strain history, crustal thickness and stretching factor of points within the deformation zones are tracked as Lagrangian points. Integrating these tools within the interactive platform GPlates enables specialized users to build and refine deforming plate...

  8. The Chilean GNSS Network: Current Status and Progress toward Early Warning Applications

    Báez, J. C.; Leyton, F.; Troncoso, C.; del Campo, F.; Bevis, M.; Vigny, C.; Moreno, M.; Simons, M.; Kendrick, E.; Parra, H.; Blume, F.
    Chile is one of the world’s most seismically active regions and is therefore extensively studied by the earthquake sciences. The great length of the country hosts a variety of measurement systems allowing for the characterization of earthquake processes over a wide range of timescales and in different phases of the seismic cycle. Starting in the early 1990s, several research groups began to deploy continuously operating geodetic networks in Chile, forming the core of the modern network of Global Navigation Satellite Systems (GNSS) receivers used to monitor geodynamics from the southern tip of the Americas to the central Andes. Today, the...

  9. Finite-fault source inversion using adjoint methods in 3D heterogeneous media

    Somala, Surendra Nadh; Ampuero, Jean-Paul; Lapusta, Nadia
    Accounting for lateral heterogeneities in the 3-D velocity structure of the crust is known to improve earthquake source inversion, compared to results based on 1-D velocity models which are routinely assumed to derive finite-fault slip models. The conventional approach to include known 3-D heterogeneity in source inversion involves pre-computing 3-D Green’s functions, which requires a number of 3-D wave propagation simulations proportional to the number of stations or to the number of fault cells. The computational cost of such an approach is prohibitive for the dense data sets that could be provided by future earthquake observation systems. Here, we propose...

  10. Reducing process delays for real-time earthquake parameter estimation – An application of KD tree to large databases for Earthquake Early Warning

    Yin, Lucy; Andrews, Jennifer; Heaton, Thomas
    Earthquake parameter estimations using nearest neighbor searching among a large database of observations can lead to reliable prediction results. However, in the real-time application of Earthquake Early Warning (EEW) systems, the accurate prediction using a large database is penalized by a significant delay in the processing time. We propose to use a multidimensional binary search tree (KD tree) data structure to organize large seismic databases to reduce the processing time in nearest neighbor search for predictions. We evaluated the performance of KD tree on the Gutenberg Algorithm, a database-searching algorithm for EEW. We constructed an offline test to predict peak...

  11. Constraints on Transient Viscoelastic Rheology of the Asthenosphere From Seasonal Deformation

    Chanard, Kristel; Fleitout, Luce; Calais, Eric; Barbot, Sylvain; Avouac, Jean-Philippe
    We discuss the constraints on short‐term asthenospheric viscosity provided by seasonal deformation of the Earth. We use data from 195 globally distributed continuous Global Navigation Satellite System stations. Surface loading is derived from the Gravity Recovery and Climate Experiment and used as an input to predict geodetic displacements. We compute Green's functions for surface displacements for a purely elastic spherical reference Earth model and for viscoelastic Earth models. We show that a range of transient viscoelastic rheologies derived to explain the early phase of postseismic deformation may induce a detectable effect on the phase and amplitude of horizontal displacements induced...

  12. Giant earthquakes on quiet faults governed by rheological transitions

    van den Ende, Martijn P. A.; Chen, Jianye; Ampuero, Jean-Paul; Niemeijer, André R.
    The apparent stochastic nature of earthquakes poses major challenges for earthquake forecasting attempts. Physical constraints on the seismogenic potential of major fault zones may greatly aid in improving seismic hazard assessments, but the mechanics of earthquake nucleation and rupture are obscured by the enormous complexity that natural faults display. In this study, we investigate the mechanisms behind giant earthquakes by employing a microphysically based seismic cycle simulator. This microphysical approach is directly based on the mechanics of friction as inferred from laboratory tests, and can explain a broad spectrum of fault slip behaviour. We show that exceptionally large, fault-spanning earthquakes...

  13. A Suite of Exercises for Verifying Dynamic Earthquake Rupture Codes

    Harris, Ruth A.; Bai, Kangchen; Ampuero, Jean-Paul
    We describe a set of benchmark exercises that are designed to test if computer codes that simulate dynamic earthquake rupture are working as intended. These types of computer codes are often used to understand how earthquakes operate, and they produce simulation results that include earthquake size, amounts of fault slip, and the patterns of ground shaking and crustal deformation. The benchmark exercises examine a range of features that scientists incorporate in their dynamic earthquake rupture simulations. These include implementations of simple or complex fault geometry, off‐fault rock response to an earthquake, stress conditions, and a variety of formulations for fault...

  14. Compositional heterogeneity near the base of the mantle transition zone beneath Hawaii

    Yu, Chunquan; Day, Elizabeth A.; de Hoop, Maarten V.; Campillo, Michel; Goes, Saskia; Blythe, Rachel A.; van der Hilst, Robert D.
    Global seismic discontinuities near 410 and 660 km depth in Earth’s mantle are expressions of solid-state phase transitions. These transitions modulate thermal and material fluxes across the mantle and variations in their depth are often attributed to temperature anomalies. Here we use novel seismic array analysis of SS waves reflecting off the 410 and 660 below the Hawaiian hotspot. We find amplitude–distance trends in reflectivity that imply lateral variations in wavespeed and density contrasts across 660 for which thermodynamic modeling precludes a thermal origin. No such variations are found along the 410. The inferred 660 contrasts can be explained by mantle...

  15. Preliminary observations from the use of US-Soviet Joint Seismic Program data to model upper mantle triplications beneath Asia

    Garnero, E. J.; Helmberger, D. V.; Burdick, L. J.
    New short-period waveform data from the US-Soviet Joint Seismic Program (JSP) make possible investigations of Asian upper mantle structure. the goal of this paper is to explore the potential use of the newly available JSP data to gain a qualitative view of upper mantle structure beneath Asia, and to facilitate more detailed future detailed future upper mantle studies. In a reconnaissance approach, waveform upper mantle studies. In a reconnaissance approach, waveform predictions from upper mantle P-wave velocity models of previous studies are compared to the JSP data to investigate regional differences in the central Asian upper mantle. Data coverage brackets...

  16. Detection of Artificially Generated Seismic Signals using Balloon-borne Infrasound Sensors

    Krishnamoorthy, Siddharth; Komjathy, Attila; Pauken, Michael T.; Cutts, James A.; Garcia, Raphael F.; Mimoun, David; Cadu, Alexandre; Sournac, Anthony; Jackson, Jennifer M.; Lai, Voon Hui; Bowman, Daniel C.
    We conducted an experiment in Pahrump, Nevada, in June 2017, where artificial seismic signals were created using a seismic hammer, and the possibility of detecting them from their acoustic signature was examined. In this work, we analyze the pressure signals recorded by highly sensitive barometers deployed on the ground and on tethers suspended from balloons. Our signal processing results show that wind noise experienced by a barometer on a free‐flying balloon is lower compared to one on a moored balloon. This has never been experimentally demonstrated in the lower troposphere. While seismoacoustic signals were not recorded on the hot air...

  17. Constraints on small-scale heterogeneity in the lowermost mantle from observations of near podal PcP precursors

    Zhang, Baolong; Ni, Sidao; Sun, Daoyuan; Shen, Zhichao; Jackson, Jennifer M.; Wu, Wenbo
    Volumetric heterogeneities on large (∼>1000 km) and intermediate scales (∼>100 km) in the lowermost mantle have been established with seismological approaches. However, there are controversies regarding the level of heterogeneity in the lowermost mantle at small scales (a few kilometers to tens of kilometers), with lower bound estimates ranging from 0.1% to a few percent. We take advantage of the small amplitude PcP waves at near podal distances (0–12°) to constrain the level of small-scale heterogeneity within 250 km above the CMB. First, we compute short period synthetic seismograms with a finite difference code for a series of volumetric heterogeneity...

  18. Global variations of large megathrust earthquake rupture characteristics

    Ye, Lingling; Kanamori­, Hiroo; Lay, Thorne
    Despite the surge of great earthquakes along subduction zones over the last decade and advances in observations and analysis techniques, it remains unclear whether earthquake complexity is primarily controlled by persistent fault properties or by dynamics of the failure process. We introduce the radiated energy enhancement factor (REEF), given by the ratio of an event’s directly measured radiated energy to the calculated minimum radiated energy for a source with the same seismic moment and duration, to quantify the rupture complexity. The REEF measurements for 119 large [moment magnitude (M_w) 7.0 to 9.2] megathrust earthquakes distributed globally show marked systematic regional...

  19. The Effects of Fault Roughness on the Earthquake Nucleation Process

    Tal, Yuval; Hager, Bradford H.; Ampuero, Jean Paul
    We study numerically the effects of fault roughness on the nucleation process during earthquake sequences. The faults are governed by a rate and state friction law. The roughness introduces local barriers that complicate the nucleation process and result in asymmetric expansion of the rupture, nonmonotonic increase in the slip rates on the fault, and the generation of multiple slip pulses. These complexities are reflected as irregular fluctuations in the moment rate. There is a large difference between first slip events in the sequences and later events. In the first events, for roughness amplitude b_r ≤ 0.002, there is a large...

  20. The 2015 Gorkha (Nepal) earthquake sequence: I. Source modeling and deterministic 3D ground shaking

    Wei, Shengji; Chen, Meng; Wang, Xin; Graves, Robert; Lindsey, Eric; Wang, Teng; Karakaş, Çağıl; Helmberger, Don
    To better quantify the relatively long period (< 0.3 Hz) shaking experienced during the 2015 Gorkha (Nepal) earthquake sequence, we study the finite rupture processes and the associated 3D ground motion of the Mw7.8 mainshock and the Mw7.2 aftershock. The 3D synthetics are then used in the broadband ground shaking in Kathmandu with a hybrid approach, summarized in a companion paper (Chen and Wei, 2017, submitted together). We determined the coseismic rupture process of the mainshock by joint inversion of InSAR/SAR, GPS (static and high-rate), strong motion and teleseismic waveforms. Our inversion for the mainshock indicates unilateral rupture towards the...

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