Recursos de colección

Caltech Authors (155.447 recursos)

Repository of works by Caltech published authors.

Group = Seismological Laboratory

Mostrando recursos 1 - 20 de 108

  1. Internal structure of the San Jacinto fault zone at Jackass Flat from data recorded by a dense linear array

    Qiu, H.; Ben-Zion, Y.; Ross, Z. E.; Share, P.-E.; Vernon, F. L.
    The internal structure of the Clark fault in the trifurcation area of the San Jacinto fault zone is imaged using seismograms recorded by a dense linear array (Jackass Flat, JF) crossing the surface trace of the fault and an adjacent array (TR) to the SW. Delay times between phase arrivals associated with ∼3500 local earthquakes and nine teleseismic events are used to estimate velocity variations within the arrays. The teleseismic P waves travel faster beneath the TR than the JF array, in contrast to larger scale tomographic results. Statistical analysis of local P-wave delay times indicates that the entire JF...

  2. Ten kilometer vertical Moho offset and shallow velocity contrast along the Denali fault zone from double-difference tomography, receiver functions, and fault zone head waves

    Allam, A. A.; Schulte-Pelkum, V.; Ben-Zion, Y.; Tape, C.; Ruppert, N.; Ross, Z. E.
    We examine the structure of the Denali fault system in the crust and upper mantle using double-difference tomography, P-wave receiver functions, and analysis (spatial distribution and moveout) of fault zone head waves. The three methods have complementary sensitivity; tomography is sensitive to 3D seismic velocity structure but smooths sharp boundaries, receiver functions are sensitive to (quasi) horizontal interfaces, and fault zone head waves are sensitive to (quasi) vertical interfaces. The results indicate that the Mohorovičić discontinuity is vertically offset by 10 to 15 km along the central 600 km of the Denali fault in the imaged region, with the northern...

  3. Early Neogene foreland of the Zagros, implications for the initial closure of the Neo-Tethys and kinematics of crustal shortening

    Pirouz, Mortaza; Avouac, Jean-Philippe; Hassanzadeh, Jamshid; Kirschvink, Joseph L.; Bahroudi, Abbas
    We study the transition from passive margin to foreland basin sedimentation now exposed in the High Zagros belt to provide chronological constraints on the initial stage of Arabia–Eurasia collision and closure of the Neo-Tethys. We performed magnetostratigraphy and strontium isotope stratigraphy along two sections near the Zagros suture which expose the oldest preserved foreland deposits: the Shalamzar section in the west and the Dehmoord section in the east. The top of the passive margin Asmari formation has an age of 28–29 Ma in the High Zagros and is overlain by foreland deposits with a major basal unconformity representing 7 Myr...

  4. Perturbational and nonperturbational inversion of Rayleigh-wave velocities

    Haney, Matthew M.; Tsai, Victor C.
    The inversion of Rayleigh-wave dispersion curves is a classic geophysical inverse problem. We have developed a set of MATLAB codes that performs forward modeling and inversion of Rayleigh-wave phase or group velocity measurements. We describe two different methods of inversion: a perturbational method based on finite elements and a nonperturbational method based on the recently developed Dix-type relation for Rayleigh waves. In practice, the nonperturbational method can be used to provide a good starting model that can be iteratively improved with the perturbational method. Although the perturbational method is well-known, we solve the forward problem using an eigenvalue/eigenvector solver instead...

  5. How “good” are real-time ground motion predictions from Earthquake Early Warning systems?

    Meier, Men-Andrin
    Real-time ground motion alerts, as can be provided by Earthquake Early Warning (EEW) systems, need to be both timely and sufficiently accurate to be useful. Yet how timely and how accurate the alerts of existing EEW algorithms are is often poorly understood. In part, this is because EEW algorithm performance is usually evaluated not in terms of ground motion prediction accuracy and timeliness but in terms of other metrics (e.g., magnitude and location estimation errors), which do not directly reflect the usefulness of the alerts from an end user perspective. Here we attempt to identify a suite of metrics for...

  6. Aseismic deformation associated with an earthquake swarm in the northern Apennines (Italy)

    Gualandi, A.; Nichele, C.; Serpelloni, E.; Chiaraluce, L.; Anderlini, L.; Latorre, D.; Belardinelli, M. E.; Avouac, J.-P.
    Analyzing the displacement time series from continuous GPS (cGPS) with an Independent Component Analysis, we detect a transient deformation signal that correlates both in space and time with a seismic swarm activity (maximum M_w=3.69 ± 0.09) occurred in the hanging wall of the Altotiberina normal fault (Northern Apennines, Italy) in 2013–2014. The geodetic transient lasted ∼6 months and produced a NW-SE trending extension of ∼5.3 mm, consistent with the regional tectonic regime. The seismicity and the geodetic signal are consistent with slip on two splay faults in the Altotiberina fault (ATF) hanging wall. Comparing the seismic moment associated with the...

  7. Electronic environments of ferrous iron in rhyolitic and basaltic glasses at high pressure

    Solomatova, Natalia V.; Jackson, Jennifer M.; Sturhahn, Wolfgang; Rossman, George R.; Roskosz, Mathieu
    The physical properties of silicate melts within Earth's mantle affect the chemical and thermal evolution of its interior. Chemistry and coordination environments affect such properties. We have measured the hyperfine parameters of iron-bearing rhyolitic and basaltic glasses up to ~120 GPa and ~100 GPa, respectively, in a neon pressure medium using time domain synchrotron Mössbauer spectroscopy. The spectra for rhyolitic and basaltic glasses are well explained by three high-spin Fe^(2+)-like sites with distinct quadrupole splittings. Absence of detectable ferric iron was confirmed with optical absorption spectroscopy. The sites with relatively high and intermediate quadrupole splittings are likely a result of...

  8. Testing monsoonal controls on bedrock river incision in the Himalaya and Eastern Tibet with a stochastic-threshold stream power model

    Scherler, Dirk; DiBiase, Roman A.; Fisher, G. Burch; Avouac, Jean-Philippe
    ^(10)Be-derived catchment average erosion rates from the Himalaya and Eastern Tibet show different relationships with normalized channel steepness index (k_(sn)), suggesting differences in erosional efficiency of bedrock river incision. We used a threshold stream power model (SPM) combined with a stochastic distribution of discharges to explore the extent to which this observation can be explained by differences in the mean and variability of discharge between the two regions. Based on the analysis of 199 daily discharge records (record lengths 3–45 years; average 18.5 years), we parameterized monsoonal discharge with a weighted sum of two inverse gamma distributions. During both high-...

  9. The Earth's Core [Book Review]

    Anderson, Don L.
    The role of the Earth’s core is essential to our understanding of many geophysical and planetary problems. The core is the source of the Earth’s magnetic field and core-mantle coupling is responsible for some of the irregularities in the rotation of the Earth. Knowledge of the core comes from many different fields, of which seismology and geomagnetism are the most important, and discussions of these disciplines form a large part of the book.

  10. Origin of the Earth and Moon [Book Review]

    Anderson, Don L.
    This small book is divided into three sections containing four chapters each. The three sections are entitled Composition and Constitution of the Earth, Origin of the Earth, and The Moon and Planets. The first four chapters cover the same ground in about the same way as the author's 1975 book, Composition and Petrology of the Earth's Mantle. Most of the figures and tables are taken from the previous publication. The main difference is that Ringwood now believes that the light element in the core is oxygen. He previously argued that it was silicon and, later, sulfur. A major conclusion of the first two-thirds...

  11. Singular value decomposition of the velocity-reflector depth tradeoff, Part 2: High-resolution analysis of a generic model

    Stork, Christof
    The symmetries of a block circulant matrix significantly reduce the computational expense of the singular value decomposition (SVD) of the variable velocity inverse problem for a generic reflection seismology model. As a result, the decomposition does not suffer from edge effects or parameterization artifacts that are associated with small model spaces. Using this approach, we study the eigenvector and eigenvalue characteristics for a generic model of a size as large as is used with a variety of iterative inversion techniques (>100 000 parameters). Singular value decomposition of the raypath inverse problem of a discretized generic seismic model having one reflector...

  12. Singular value decomposition of the velocity-reflector depth tradeoff, Part 1: Introduction using a two-parameter model

    Stork, Christof
    A singular value decomposition (SVD) of a two-parameter model serves to introduce several characteristics of a raypath inversion of the standard reflection seismology recording geometry. Two important families of eigenvectors consist of constructive interference and destructive interference of velocity and reflector depth. The eigenvalue that corresponds to the velocity-reflector depth destructive interference is very sensitive to the maximum ray angle in the data. For a cable length equal to twice the reflector depth, the theoretical linear resolution is quite high. The relative weighting between velocity and reflector depth is not critical so long as the weight is near 1.0.

  13. Two regions of seafloor deformation generated the tsunami for the 13 November 2016, Kaikoura, New Zealand earthquake

    Bai, Yefei; Lay, Thorne; Cheung, Kwok Fai; Ye, Lingling
    The 13 November 2016 Kaikoura, New Zealand, M_w 7.8 earthquake ruptured multiple crustal faults in the transpressional Marlborough and North Canterbury tectonic domains of northeastern South Island. The Hikurangi trench and underthrust Pacific slab terminate in the region south of Kaikoura, as the subdution zone transitions to the Alpine fault strike-slip regime. It is difficult to establish whether any coseismic slip occurred on the megathrust from on-land observations. The rupture generated a tsunami well recorded at tide gauges along the eastern coasts and in Chatham Islands, including a ~4 m crest-to-trough signal at Kaikoura where coastal uplift was about 1...

  14. Pulse-Like Partial Ruptures and High-Frequency Radiation at Creeping-Locked Transition during Megathrust Earthquakes

    Michel, Sylvain; Avouac, Jean-Philippe; Lapusta, Nadia; Jiang, Junle
    Megathrust earthquakes tend to be confined to fault areas locked in the interseismic period and often rupture them only partially. For example, during the 2015 M7.8 Gorkha earthquake, Nepal, a slip pulse propagating along strike unzipped the bottom edge of the locked portion of the Main Himalayan Thrust (MHT). The lower edge of the rupture produced dominant high-frequency (>1 Hz) radiation of seismic waves. We show that similar partial ruptures occur spontaneously in a simple dynamic model of earthquake sequences. The fault is governed by standard laboratory-based rate-and-state friction with the ageing law and contains one homogenous velocity-weakening (VW) region...

  15. Aftershocks driven by afterslip and fluid pressure sweeping through a fault-fracture mesh

    Ross, Z. E.; Rollins, C.; Cochran, E. S.; Hauksson, E.; Avouac, J.-P.; Ben-Zion, Y.
    A variety of physical mechanisms are thought to be responsible for the triggering and spatiotemporal evolution of aftershocks. Here we analyze a vigorous aftershock sequence and postseismic geodetic strain that occurred in the Yuha Desert following the 2010 M_w 7.2 El Mayor-Cucapah earthquake. About 155,000 detected aftershocks occurred in a network of orthogonal faults and exhibit features of two distinct mechanisms for aftershock triggering. The earliest aftershocks were likely driven by afterslip that spread away from the mainshock with the logarithm of time. A later pulse of aftershocks swept again across the Yuha Desert with square-root time dependence and swarm-like...

  16. Aftershocks driven by afterslip and fluid pressure sweeping through a fault-fracture mesh

    Ross, Zachary E.; Rollins, Christopher; Cochran, Elizabeth S.; Hauksson, Egill; Avouac, Jean-Philippe; Ben-Zion, Yehuda
    A variety of physical mechanisms are thought to be responsible for the triggering and spatiotemporal evolution of aftershocks. Here we analyze a vigorous aftershock sequence and postseismic geodetic strain that occurred in the Yuha Desert following the 2010 M_w 7.2 El Mayor-Cucapah earthquake. About 155,000 detected aftershocks occurred in a network of orthogonal faults and exhibit features of two distinct mechanisms for aftershock triggering. The earliest aftershocks were likely driven by afterslip that spread away from the main shock with the logarithm of time. A later pulse of aftershocks swept again across the Yuha Desert with square root time dependence...

  17. Single-crystal equations of state of magnesiowüstite at high pressures

    Finkelstein, Gregory J.; Jackson, Jennifer M.; Sturhahn, Wolfgang; Zhang, Dongzhou; Alp, E. Ercan; Toellner, Thomas S.
    Solid solutions of (Mg,Fe)O with high iron enrichment may be an important component of ultralow-velocity zones at Earth’s core-mantle boundary. However, to date there have been few high-precision studies on the elastic properties of these materials. In this study we present results on the compression of (Mg_(0.22)Fe_(0.78))O magnesiowüstite in both neon and helium pressure media using single-crystal diffraction to ~55 GPa. In addition, our sample was characterized by time-domain synchrotron Mössbauer spectroscopy at ambient pressure using an extended time range that resulted in vastly improved energy resolution. The combination of these high-resolution techniques tightly constrains the presence of a defect-structure...

  18. Large earthquakes in the macquarie ridge complex: Transitional tectonics and subduction initiation

    Ruff, Larry J.; Given, Jeffrey W.; Sanders, Chris O.; Sperber, Christine M.
    While most aspects of subduction have been extensively studied, the process of subduction initiation lacks an observational foundation. The Macquarie Ridge complex (MRC) forms the Pacific-Australia plate boundary between New Zealand to the north and the Pacific-Australia-Antarctica triple junction to the south. The MRC consists of alternating troughs and rises and is characterized by a transitional tectonic environment in which subduction initiation presently occurs. There is a high seismicity level with 15 large earthquakes (M>7) in this century. Our seismological investigation is centered on the largest event since 1943: the 25 MAY 1981 earthquake. Love, Rayleigh, andP waves are inverted...

  19. The Caltech digital seismograph

    Miller, Wayne F.
    A digital data logger has been constructed at the California Institute of Technology for recording the signals from long-period Press-Ewing seismometers. Three-component data are continuously digitized at the rate of 10 samples per second with an 86-db dynamic range and stored on magnetic tape. With a tape speed of 0.5 inch/sec, data for a 24-hour period may be recorded on one 10 1/2-inch reel. An editing system is then used to select interesting events and convert them to a form compatible with the IBM 7090 computer for further reduction and analysis.

  20. Explaining Extreme Ground Motion in Osaka Basin during the 2011 Tohoku Earthquake

    Tsai, Victor C.; Bowden, Daniel C.; Kanamori, Hiroo
    Despite being 770 km away from the epicenter, observed ground motions due to the Tohoku Earthquake in the Osaka Basin were unexpectedly large, with an amplification of more than a factor of 20 compared to immediately outside the basin, and including 2.7-m peak-to-peak roof displacements at one high-rise building. The local ground motions exceeded expectations based on standard computations of site response by a factor of 3, predicted frequencies of peak acceleration were off by at least 50%, and such discrepancies have not yet been explained quantitatively. Here, we show that utilizing semi-analytic theory for surface-wave amplification, we are able...

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.