Recursos de colección

Caltech Authors (142.336 recursos)

Repository of works by Caltech published authors.

Group = Seismological Laboratory

Mostrando recursos 1 - 20 de 897

  1. Evidence for strong lateral seismic velocity variation in the lower crust and upper mantle beneath the California margin

    Lai, Voon Hui; Graves, Robert W.; Wei, Shengji; Helmberger, Don
    Regional seismograms from earthquakes in Northern California show a systematic difference in arrival times across Southern California where long period (30–50 s) SH waves arrive up to 15 s earlier at stations near the coast compared with sites towards the east at similar epicentral distances. We attribute this time difference to heterogeneity of the velocity structure at the crust–mantle interface beneath the California margin. To model these observations, we propose a fast seismic layer, with thickness growing westward from the San Andreas along with a thicker and slower continental crust to the east. Synthetics generated from such a model are...

  2. Probabilistic imaging of tsunamigenic seafloor deformation during the 2011 Tohoku-oki Earthquake

    Jiang, Junle; Simons, Mark
    Diverse observations from the 2011 M_w 9.0 Tohoku-oki earthquake pointed to large coseismic fault slip proximal to the Japan Trench. This seismic failure prompted a reevaluation of the conventional view that the outer forearc is generally aseismic. However, the nature of near-trench fault slip during this event remains debated, without consensus on whether slip peaked at the trench or at greater depths. Here we develop a probabilistic approach to image the spatiotemporal evolution of coseismic seafloor displacement from near-field tsunami observations. In a Bayesian framework, we sample ensembles of nonlinear source models parameterized to focus on near-trench features, incorporating the uncertainty...

  3. Seismic imaging of the metamorphism of young sediment into new crystalline crust in the actively rifting Imperial Valley, California

    Han, Liang; Hole, John A.; Stock, Joann M.; Fuis, Gary S.; Williams, Colin F.; Delph, Jonathan R.; Davenport, Kathy K.; Livers, Amanda J.
    Plate-boundary rifting between transform faults is opening the Imperial Valley of southern California and the rift is rapidly filling with sediment from the Colorado River. Three 65–90 km long seismic refraction profiles across and along the valley, acquired as part of the 2011 Salton Seismic Imaging Project, were analyzed to constrain upper crustal structure and the transition from sediment to underlying crystalline rock. Both first arrival travel-time tomography and frequency-domain full-waveform inversion were applied to provide P-wave velocity models down to ∼7 km depth. The valley margins are fault-bounded, beyond which thinner sediment has been deposited on preexisting crystalline rocks....

  4. Active tectonics in the Gulf of California and seismicity (M > 3.0) for the period 2002–2014

    Castro, R. R.; Stock, J. M.; Hauksson, E.; Clayton, R. W.
    We present a catalog of accurate epicenter coordinates of earthquakes located in the Gulf of California (GoC) in the period 2002–2014 that permits us to analyze the seismotectonics and to estimate the depth of the seismogenic zone of this region. For the period April 2002 to December 2014 we use body-wave arrival times from regional stations of the Broadband Seismological Network of the GoC (RESBAN) operated by CICESE to improve hypocenter locations reported by global catalogs. For the northern region of the GoC (30°N–32°N) we added relocated events from the 2011-Hauksson-Yang-Shearer, Waveform Relocated Earthquake Catalog for Southern California (Hauksson et...

  5. Earthquake ground motion amplification for surface waves

    Bowden, Daniel C.; Tsai, Victor C.
    Surface waves from earthquakes are known to cause strong damage, especially for larger structures such as skyscrapers and bridges. However, common practice in characterizing seismic hazard at a specific site considers the effect of near-surface geology on only vertically propagating body waves. Here we show that surface waves have a unique and different frequency-dependent response to known geologic structure and that this amplification can be analytically calculated in a manner similar to current hazard practices. Applying this framework to amplification in the Los Angeles Basin, we find that peak ground accelerations for certain large regional earthquakes are underpredicted if surface...

  6. Sound velocity and density of magnesiowüstites: Implications for ultralow-velocity zone topography

    Wicks, June; Jackson, Jennifer M.; Sturhahn, Wolfgang; Zhang, Dongzhou
    We explore the effect of Mg/Fe substitution on the sound velocities of iron-rich (Mg_(1 – x),Fe_x)O, where x=0.84, 0.94, and 1.0. Sound velocities were determined using nuclear resonance inelastic x-ray scattering as a function of pressure, approaching those of the lowermost mantle. The systematics of cation substitution in the Fe-rich limit has the potential to play an important role in the interpretation of seismic observations of the core-mantle boundary. By determining a relationship between sound velocity, density, and composition of (Mg,Fe)O, this study explores the potential constraints on ultralow-velocity zones at the core-mantle boundary.

  7. Widespread compression associated with Eocene Tonga-Kermadec subduction initiation

    Sutherland, R.; Collot, J.; Bache, F.; Henrys, S.; Barker, D.; Browne, G. H.; Lawrence, M. J. F.; Morgans, H. E. G.; Hollis, C. J.; Clowes, C.; Mortimer, N.; Rouillard, P.; Gurnis, M.; Etienne, S.; Stratford, W.
    Eocene onset of subduction in the western Pacific was accompanied by a global reorganization of tectonic plates and a change in Pacific plate motion relative to hotspots during the period 52–43 Ma. We present seismic-reflection and rock sample data from the Tasman Sea that demonstrate that there was a period of widespread Eocene continental and oceanic compressional plate failure after 53–48 Ma that lasted until at least 37–34 Ma. We call this the Tectonic Event of the Cenozoic in the Tasman Area (TECTA). Its compressional nature is different from coeval tensile stresses and back-arc opening after 50 Ma in the...

  8. Active Faulting in Northern Turkey

    Allen, Clarence R.
    The North Anatolian fault zone of Turkey has become widely publicized in recent years because of the remarkable series of earthquakes that began along it in 1939 -- most of which have been associated with dextral surface displacements that have successively delineated the fault trace from east to west (Ketin and Roesli, 1953; Ambraseys and Zátopek, 1968). It is not so generally recognized that even prior to 1939 the fault zone could easily have been recognized on the basis of abundant and through-going features of Quaternary displacements, and that the North Anatolian fault is almost completely analogous to the better-known active transcurrent faults of the circum-Pacific region, such as...

  9. Studies of sonic booms with seismic networks

    Sturtevant, Bradford; Cates, Joseph E.; Kanamori, Hiroo
    Seismographs are sufficiently sensitive to detect ground motions induced by atmospheric pressure waves, so seismic networks have the potential to monitor sonic booms over large areas of the United States. They are especially well suited for the analysis of long‐range sonic‐boom propagation. Ground motion or displacement data provide accurate arrival times and useful estimates of wave amplitude and waveform. The instrumentation is most sensitive to the disturbance produced by the arrival of sonic booms at the measuring station, thus serving as sonic‐boom event recorders, but seismographs have also detected seismic waves remotely generated by anomalous coupling of sonic boom into...

  10. Estimates of aseismic slip associated with small earthquakes near San Juan Bautista, CA

    Hawthorne, J. C.; Simons, M.; Ampuero, J.-P.
    Postseismic slip observed after large (M > 6) earthquakes typically has an equivalent moment of a few tens of percent of the coseismic moment. Some observations of the recurrence intervals of repeating earthquakes suggest that postseismic slip following small (M ≾ 4) earthquakes could be much larger—up to 10 or 100 times the coseismic moment. We use borehole strain data from U.S. Geological Survey strainmeter SJT to analyze deformation in the days before and after 1000 1.9 < M < 5 earthquakes near San Juan Bautista, CA. We find that on average, postseismic strain is roughly equal in magnitude to...

  11. Estimates of aseismic slip associated with small earthquakes near San Juan Bautista, CA

    Hawthorne, J. C.; Simons, M.; Ampuero, J.-P.
    Postseismic slip observed after large (M > 6) earthquakes typically has an equivalent moment of a few tens of percent of the coseismic moment. Some observations of the recurrence intervals of repeating earthquakes suggest that postseismic slip following small (M ≾ 4) earthquakes could be much larger—up to 10 or 100 times the coseismic moment. We use borehole strain data from U.S. Geological Survey strainmeter SJT to analyze deformation in the days before and after 1000 1.9 < M < 5 earthquakes near San Juan Bautista, CA. We find that on average, postseismic strain is roughly equal in magnitude to...

  12. Mapping Coherent, Time-Varying Wavefronts from the Tohoku Tsunami into Enhanced, Time-Dependent Warning Messages

    Shi, J.; Kohler, M. D.; Sutton, J. N.; Ampuero, J.-P.
    Recent results are presented to illustrate how predictions of tsunami wave impact and tsunami warning mes-sages can be improved by including information about multiple, large-amplitude wave arrivals over longer time durations and at refined spatial resolution. A deployment of ocean bottom seismometers off the coast of southern California recorded the March 2011 Tohoku tsunami on 22 differential pressure gauges. The pressure gauge tsu-nami records across the entire array show multiple large-amplitude, coherent phases arriving one hour to more than 36 hours after the initial tsunami phase. Analysis of the pressure gauge recordings reveals possible locations of the geographical sources that...

  13. Dense Building Instrumentation Application for City-Wide Structural Health Monitoring

    Massari, A.; Kohler, M.; Clayton, R.; Guy, R.; Heaton, T.; Bunn, J.; Chandy, K. M.; Demetri, D.
    The Community Seismic Network (CSN) has partnered with the NASA Jet Propulsion Laboratory (JPL) to initiate a campus-wide structural monitoring program of all buildings on the premises. The JPL campus serves as a proxy for a densely instrumented urban city with localized vibration measurements collected throughout the free-field and built environment. Instrumenting the entire campus provides dense measurements in a horizontal geospatial sense for soil response; in addition five buildings have been instrumented on every floor of the structure. Each building has a unique structural system as well as varied amounts of structural information via structural drawings, making several levels...

  14. From the seismic cycle to long-term deformation: linking seismic coupling and Quaternary coastal geomorphology along the Andean Megathrust

    Saillard, M.; Audin, L.; Rousset, B.; Avouac, J.-P.; Chlieh, M.; Hall, S. R.; Husson, L.; Farber, D. L.
    Measurement of interseismic strain along subduction zones reveals the location of both locked asperities, which might rupture during Megathrust earthquakes, and creeping zones, which tend to arrest such seismic ruptures. The heterogeneous pattern of interseismic coupling presumably relates to spatial variations of frictional properties along the subduction interface and may also show up in the forearc morphology. To investigate this hypothesis, we compiled information on the extent of earthquake ruptures for the last 500 years and uplift rates derived from dated marine terraces along the South American coastline from central Peru to Southern Chile. We additionally calculated a new interseismic coupling...

  15. Evolution of seismicity near the southernmost terminus of the San Andreas Fault: Implications of recent earthquake clusters for earthquake risk in southern California

    Hauksson, Egill; Meier, Men-Andrin; Ross, Zachary E.; Jones, Lucile M.
    Three earthquake clusters that occurred in the direct vicinity of the southern terminus of the San Andreas Fault (SAF) in 2001, 2009, and 2016 raised significant concern regarding possible triggering of a major earthquake on the southern SAF, which has not ruptured in more than 320 years. These clusters of small and moderate earthquakes with M ≤ 4.8 added to an increase in seismicity rate in the Brawley seismic zone that began after the 1979 Mw6.5 Imperial Valley earthquake, in contrast to the quiet from 1932 to 1979. The clusters so far triggered neither small nor large events on the SAF. The mostly...

  16. Seismic array constraints on reach-scale bedload transport

    Schmandt, B.; Gaeuman, D.; Stewart, R.; Hansen, S. M.; Tsai, V. C.; Smith, J.
    Measurements and mechanical models of heterogeneous bedload transport in rivers remain basic challenges for studies of landscape evolution and watershed management. A 700 m reach of the Trinity River (northern California, USA), a large gravel-bed river, was instrumented with an array of 76 seismographs during a dam-controlled flood and gravel augmentation to investigate the potential for out-of-stream monitoring. The temporal response to gravel augmentation during constant discharge provides strong evidence of seismic sensitivity to bedload transport and aids in identification of the seismic frequencies most sensitive to bedload in the study area. Following gravel augmentations, the seismic array reveals a...

  17. Continuum viscoplastic simulation of a granular column collapse on large slopes: μ(I) rheology and lateral wall effects

    Martin, N.; Ionescu, I. R.; Mangeney, A.; Bouchut, F.; Farin, M.
    We simulate here dry granular flows resulting from the collapse of granular columns on an inclined channel (up to 22°) and compare precisely the results with laboratory experiments. Incompressibility is assumed despite the dilatancy observed in the experiments (up to 10%). The 2-D model is based on the so-called μ(I) rheology that induces a Drucker-Prager yield stress and a variable viscosity. A nonlinear Coulomb friction term, representing the friction on the lateral walls of the channel, is added to the model. We demonstrate that this term is crucial to accurately reproduce granular collapses on slopes ≳10°, whereas it remains of...

  18. Gutenberg–Richter law for deep earthquakes revisited: A dual-mechanism hypothesis

    Zhan, Zhongwen
    Deep earthquake b values appear to vary with slab thermal state and earthquake magnitude. The physical reason for the variations and the relation with deep rupture mechanisms are still unclear. Here I confirm the spatial variations of b value and the dependence on slab temperature using about 40 yr of data from the Global Centroid Moment Tensor catalog. A new bimodal pattern is observed for the 500–700 km depth range: b is close to 1 in the cold Tonga slab, while in warmer slabs (e.g., South America, Japan–Kuril, Izu–Bonin–Mariana), b is close to 0.5 for intermediate magnitudes (M_w 5.3–6.5) and...

  19. Continental rupture and the creation of new crust in the Salton Trough rift, Southern California and northern Mexico: Results from the Salton Seismic Imaging Project

    Han, Liang; Hole, John A.; Stock, Joann M.; Fuis, Gary S.; Kell, Annie; Driscoll, Neal W.; Kent, Graham M.; Harding, Alistair J.; Rymer, Michael J.; González-Fernández, Antonio; Lázaro-Mancilla, Octavio
    A refraction and wide-angle reflection seismic profile along the axis of the Salton Trough, California and Mexico, was analyzed to constrain crustal and upper mantle seismic velocity structure during active continental rifting. From the northern Salton Sea to the southern Imperial Valley, the crust is 17–18 km thick and approximately one-dimensional. The transition at depth from Colorado River sediment to underlying crystalline rock is gradual and is not a depositional surface. The crystalline rock from ~3 to ~8 km depth is interpreted as sediment metamorphosed by high heat flow. Deeper felsic crystalline rock could be stretched preexisting crust or higher-grade metamorphosed sediment....

  20. Tectonic evolution and deep mantle structure of the eastern Tethys since the latest Jurassic

    Zahirovic, Sabin; Matthews, Kara J.; Flament, Nicolas; Müller, R. Dietmar; Hill, Kevin C.; Seton, Maria; Gurnis, Michael
    The breakup of Pangea in the Jurassic saw the opening of major ocean basins at the expense of older Tethyan and Pacific oceanic plates. Although the Tethyan seafloor spreading history has been lost to subduction, proxy indicators from multiple generations of Tethyan ribbon terranes, as well as the active margin geological histories of volcanism and ophiolite obduction events can be used to reconstruct these ancient oceanic plates. The plate reconstructions presented in this study reconcile observations from ocean basins and the onshore geological record to provide a regional synthesis, embedded in a global plate motion model, of the India-Eurasia convergence...

Aviso de cookies: Usamos cookies propias y de terceros para mejorar nuestros servicios, para análisis estadístico y para mostrarle publicidad. Si continua navegando consideramos que acepta su uso en los términos establecidos en la Política de cookies.