Recursos de colección

Caltech Authors (171.365 recursos)

Repository of works by Caltech published authors.

Group = Seismological Laboratory

Mostrando recursos 1 - 20 de 401

  1. Seismotectonics of the Coso Range–Indian Wells Valley region, California: Transtensional deformation along the southeastern margin of the Sierran microplate

    Unruh, Jeffrey R.; Hauksson, Egill; Monastero, Francis C.; Twiss, Robert J.; Lewis, Jonathan C.
    Space-based geodetic observations show that the Coso Range and Indian Wells Valley lie along the southeastern margin of the Sierra Nevada–Central Valley (i.e., “Sierran”) microplate, which moves ~13–14 mm/yr northwest with respect to stable North America. Detailed kinematic analysis of seismicity indicates that active crustal extension in the Coso Range occurs in a right-lateral transtensional regime along the eastern border of the Sierran microplate. The Airport Lake fault in the northern Indian Wells Valley and the Owens Valley fault are the major strike-slip faults along the eastern margin of the Sierran microplate south and north, respectively, of the Coso Range. Patterns of...

  2. Community seismic network and localized earthquake situational awareness

    Kohler, M. D.; Guy, R.; Bunn, J.; Massari, A.; Clayton, R.; Heaton, T.; Chandy, K. M.; Ebrahimian, H.; Dorn, C.
    Community-hosted seismic networks are a solution to the need for large numbers of sensors to operate over a seismically active region in order to accurately measure the size and location of an earthquake, assess resulting damage, and provide alerts. The Community Seismic Network is one such strong-motion network, currently comprising hundreds of elements located in California. It consists of low-cost, three-component, MEMS accelerometers capable of recording accelerations up to twice the level of gravity. The primary product of the network is to produce measurements of shaking of the ground and multiple locations of every upper floor in buildings, in the...

  3. Observations of ocean tidal load response in South America from subdaily GPS positions

    Martens, Hilary R.; Simons, Mark; Owen, Susan; Rivera, Luis
    We explore Earth's elastic deformation response to ocean tidal loading (OTL) using kinematic Global Positioning System (GPS) observations and forward-modelled predictions across South America. Harmonic coefficients are extracted from up to 14 yr of GPS-inferred receiver locations, which we estimate at 5 min intervals using precise point positioning. We compare the observed OTL-induced surface displacements against predictions derived from spherically symmetric, non-rotating, elastic and isotropic (SNREI) Earth models. We also compare sets of modelled predictions directly for various ocean-tide and Earth-model combinations. The vector differences between predicted displacements computed using separate ocean-tide models reveal uniform-displacement components common to all stations...

  4. Early melt season velocity fields of Langjökull and Hofsjökull, central Iceland

    Minchew, Brent; Simons, Mark; Hensley, Scott; Björnsson, Helgi; Pálsson, Finnur
    We infer the horizontal velocity fields of the ice caps Langjökull and Hofsjökull, central Iceland, using repeat-pass interferometric synthetic aperture radar (InSAR). NASA’s uninhabited aerial vehicle synthetic aperture radar (UAVSAR) acquired airborne InSAR data from multiple vantage points during the early melt season in June 2012. We develop a Bayesian approach for inferring three-dimensional velocity fields from multiple InSAR acquisitions. The horizontal components generally agree with available GPS measurements wherever ice motion is well constrained by InSAR observations. We provide evidence that changes in volumetric moisture content near the glacier surface induce phase offsets that obfuscate the vertical component of...

  5. The influence of carbonate platform interactions with subduction zone volcanism on palaeo-atmospheric CO_2 since the Devonian

    Pall, Jodie; Zahirovic, Sabin; Doss, Sebastiano; Hassan, Rakib; Matthews, Kara J.; Cannon, John; Gurnis, Michael; Moresi, Louis; Lenardic, Adrian; Müller, R. Dietmar
    The CO_2 liberated along subduction zones through intrusive/extrusive magmatic activity and the resulting active and diffuse outgassing influences global atmospheric CO_2. However, when melts derived from subduction zones intersect buried carbonate platforms, decarbonation reactions may cause the contribution to atmospheric CO_2 to be far greater than segments of the active margin that lacks buried carbon-rich rocks and carbonate platforms. This study investigates the contribution of carbonate-intersecting subduction zones (CISZs) to palaeo-atmospheric CO_2 levels over the past 410 million years by integrating a plate motion and plate boundary evolution model with carbonate platform development through time. Our model of carbonate platform...

  6. Application of wavefield compressive sensing in surface wave tomography

    Zhan, Zhongwen; Li, Qingyang; Huang, Jianping
    Dense arrays allow sampling of seismic wavefield without significant aliasing, and surface wave tomography has benefitted from exploiting wavefield coherence among neighbouring stations. However, explicit or implicit assumptions about wavefield, irregular station spacing and noise still limit the applicability and resolution of current surface wave methods. Here, we propose to apply the theory of compressive sensing (CS) to seek a sparse representation of the surface wavefield using a plane-wave basis. Then we reconstruct the continuous surface wavefield on a dense regular grid before applying any tomographic methods. Synthetic tests demonstrate that wavefield CS improves robustness and resolution of Helmholtz tomography...

  7. GPlates – Building a Virtual Earth Through Deep Time

    Müller, R. Dietmar; Cannon, John; Qin, Xiaodong; Watson, Robin J.; Gurnis, Michael; Williams, Simon; Pfaffelmoser, Tobias; Seton, Maria; Russell, Samuel H. J.; Zahirovic, Sabin
    GPlates is an open‐source, cross‐platform plate tectonic geographic information system, enabling the interactive manipulation of plate‐tectonic reconstructions and the visualization of geo‐data through geological time. GPlates allows the building of topological plate models representing the mosaic of evolving plate boundary networks through time, useful for computing plate velocity fields as surface boundary conditions for mantle convection models and for investigating physical and chemical exchanges of material between the surface and the deep Earth along tectonic plate boundaries. The ability of GPlates to visualize sub‐surface 3D scalar fields together with traditional geological surface data enables researchers to analyze their relationship through...

  8. Toward a Global Horizontal and Vertical Elastic Load Deformation Model Derived from GRACE and GNSS Station Position Time Series

    Chanard, Kristel; Fleitout, Luce; Calais, Eric; Rebischung, Paul; Avouac, Jean-Philippe
    We model surface displacements induced by variations in continental water, atmospheric pressure, and nontidal oceanic loading, derived from the Gravity Recovery and Climate Experiment (GRACE) for spherical harmonic degrees two and higher. As they are not observable by GRACE, we use at first the degree‐1 spherical harmonic coefficients from Swenson et al. (2008, https://doi.org/10.1029/2007JB005338). We compare the predicted displacements with the position time series of 689 globally distributed continuous Global Navigation Satellite System (GNSS) stations. While GNSS vertical displacements are well explained by the model at a global scale, horizontal displacements are systematically underpredicted and out of phase with GNSS...

  9. A long-lived Indian Ocean slab: Deep dip reversal induced by the African LLSVP

    Wang, Huilin; Wang, Yaoyi; Gurnis, Michael; Zahirovic, Sabin; Leng, Wei
    A slab-like high seismic velocity anomaly (referred as SEIS) has been inferred beneath the central-southern Indian Ocean in a recent tomographic inversion. Although subduction has previously been suggested regionally by surface observations, the new inversion is consistent with a north-dipping slab extending from the upper mantle to the core mantle boundary (CMB). We propose that SEIS anomaly originated from an oceanic plate in the Paleo-Tethys that was consumed by a south-dipping intra-oceanic subduction zone during the Triassic and Jurassic periods. SEIS challenges traditional concepts of the dynamics of slab descent by its relatively shallow depths and a present-day polarity opposite...

  10. Comparing dune migration measured from remote sensing with sand flux prediction based on weather data and model, a test case in Qatar

    Michel, Sylvain; Avouac, Jean-Philippe; Ayoub, François; Ewing, Ryan C.; Vriend, Nathalie; Heggy, Essam
    This study explores validating and calibrating the wind regime predicted by Global Circulation Models (GCM) on Earth and other planets using optical remote sensing of dune dynamics. We use Spot-5 images to track the migration of 64 Barchan dunes in Qatar using the COSI-Corr technique. We estimate the volume of the dunes using a scaling law calibrated from one particular dune, which was surveyed in the field. Using volume and migration rate, we determine the sand flux from a single dune, Q_(Dunes), and scale this estimate to the whole dune field. We compare the measured sand flux with those derived...

  11. Contrasting river incision in north and south Tian Shan piedmonts due to variable glacial imprint in mountain valleys

    Malatesta, Luca C.; Avouac, Jean-Philippe
    Fluvial terraces carved by incising rivers are widely used to investigate external forcing by climate and tectonics. In the Eastern Tian Shan (Central Asia), the north piedmont rivers are much more deeply incised (mean: 124 m) compared to the south piedmont (mean: 17 m) despite very similar tectonic and climatic settings. We attribute the incision contrast to a difference in glacial imprint between southern and northern catchments. Whereas the upper halves of the valleys in the northern higher subrange are formerly glaciated, wide and gently sloping, U-shaped valleys flowing into V-shaped valleys, the valleys of the lower southern subrange are...

  12. Observations and modeling of long-period ground-motion amplification across northeast China

    Chen, Haichao; Tsai, Victor C.; Niu, Fenglin
    Basin resonances can significantly amplify and prolong ground shaking, and accurate site‐amplification estimates are crucial for mitigating potential seismic hazards within metropolitan basins. In this work, we estimate the site amplification of long‐period (2–10 s) ground motions across northeast China for both surface waves and vertically incident shear waves. The spatial distribution of relatively large site amplifications correlates strongly with known sedimentary basins for both wave types. However, the site response of surface waves is typically twice as high as that of shear waves at most basin sites. We further show that these site‐amplification features can be well explained by...

  13. A comparison between rate-and-state friction and microphysical models, based on numerical simulations of fault slip

    van den Ende, M. P. A.; Chen, J.; Ampuero, J.-P.; Niemeijer, A. R.
    Rate-and-state friction (RSF) is commonly used for the characterisation of laboratory friction experiments, such as velocity-step tests. However, the RSF framework provides little physical basis for the extrapolation of these results to the scales and conditions of natural fault systems, and so open questions remain regarding the applicability of the experimentally obtained RSF parameters for predicting seismic cycle transients. As an alternative to classical RSF, microphysics-based models offer means for interpreting laboratory and field observations, but are generally over-simplified with respect to heterogeneous natural systems. In order to bridge the temporal and spatial gap between the laboratory and nature, we...

  14. P-wave arrival picking and first-motion polarity determination with deep learning

    Ross, Zachary E.; Meier, Men-Andrin; Hauksson, Egill
    Determining earthquake hypocenters and focal mechanisms requires precisely measured P‐wave arrival times and first‐motion polarities. Automated algorithms for estimating these quantities have been less accurate than estimates by human experts, which is problematic for processing large data volumes. Here, we train convolutional neural networks to measure both quantities, which learn directly from seismograms without the need for feature extraction. The networks are trained on 18.2 million manually picked seismograms for the southern California region. Through cross‐validation on 1.2 million independent seismograms, the differences between the automated and manual picks have a standard deviation of 0.023 seconds. The polarities determined by...

  15. The Seismic Signature of Debris Flows: Flow Mechanics and Early Warning at Montecito, California

    Lai, Voon Hui; Tsai, Victor C.; Lamb, Michael P.; Ulizio, Thomas P.; Beer, Alexander R.
    Debris flows are concentrated slurries of water and sediment that shape the landscape and pose a major hazard to human life and infrastructure. Seismic ground motion‐based observations promise to provide new, remote constraints on debris flow physics, but the lack of data and a theoretical basis for interpreting them hinders progress. Here we present a new mechanistic physical model for the seismic ground motion of debris flows and apply this to the devastating debris flows in Montecito, California on 9 January 2018. The amplitude and frequency characteristics of the seismic data can distinguish debris flows from other seismic sources and...

  16. Diverse volumetric faulting patterns in the San Jacinto fault zone

    Cheng, Yifang; Ross, Zachary E.; Ben-Zion, Yehuda
    We examine locations, magnitudes and faulting types of post‐2000 earthquakes in the trifurcation area of San Jacinto fault zone to clarify basic aspects of failure processes in the area. Most M ≥3.5 events have strike‐slip mechanisms, occur within 1 km of the main faults (Clark, Buck Ridge, and Coyote creek) and have hypocenter depths of 10‐13 km. In contrast, many smaller events have normal source mechanisms and hypocenters in intra‐fault areas deeper than 13 km. Additional small events with hypocenter depth < 13 km occur in off‐fault regions and have complex geometries including lineations normal to the main faults. Five...

  17. A Review of Geological Evidence for Recurrence Times of Large Earthquakes

    Sieh, Kerry E.
    The geological record of the past several thousand years contains valuable information for evaluating the earthquake potential of the earth's major fault systems. Geologists have begun to characterize past and, presumably, future behavior of active faults and recurrence intervals for large earthquakes by studying 1) uplifted marine terraces, 2) fault‐scarp morphology, 3) physiographic features offset along faults, and 4) faulted or otherwise deformed young sediments. Along the convergent plate margins of Alaska and Japan, for example, studies of uplifted marine terraces have aided in evaluating the likelihood of imminent rupture of faults in two seismic gaps. In Nevada, Utah, and eastern...

  18. Plate Supduction and Prediction of Earthquakes Along the Middle America Trench

    McNally, Karen C.
    Results of detailed studies of seismic slip, tectonic structures, fault mechanisms, and rupture patterns along various segments of the Middle America Trench provide a tectonic framework for analyzing long, intermediate, and short term patterns of seismicity preceding large (M_s ≥ 7), shallow earthquakes. Long term. Average repeat times of 33±8 yrs for earthquakes M_s ≥ 7.5 since 1898 and 35±24 yrs since 1540 indicate that the 81 yr history (1898 to 1979) may be adequate for estimating temporal deficiencies in seismic slip. Seismic slip rates are spatially nonuniform on a scale of 100 km and forecasts are only valid when local...

  19. Strongly Anisotropic Magnesiowüstite in Earth's Lower Mantle

    Finkelstein, Gregory J.; Jackson, Jennifer M.; Said, Ayman; Alatas, Ahmet; Leu, Bogdan M.; Sturhahn, Wolfgang; Toellner, Thomas S.
    The juxtaposition of a liquid iron‐dominant alloy against a mixture of silicate and oxide minerals at Earth's core–mantle boundary is associated with a wide range of complex seismological features. One category of observed structures is ultralow‐velocity zones, which are thought to correspond to either aggregates of partially molten material or solid, iron‐enriched assemblages. We measured the phonon dispersion relations of (Mg,Fe) O magnesiowüstite containing 76 mol% FeO, a candidate ultralow‐velocity zone phase, at high pressures using high energy‐resolution inelastic x‐ray scattering. From these measurements, we find that magnesiowüstite becomes strongly elastically anisotropic with increasing pressure, potentially contributing to a significant...

  20. 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.

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