Recursos de colección

Caltech Authors (144.724 recursos)

Repository of works by Caltech published authors.

Group = Seismological Laboratory

Mostrando recursos 1 - 20 de 911

  1. 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.

  2. 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...

  3. 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...

  4. 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...

  5. Absence of remote earthquake triggering within the Coso and Salton Sea geothermal production fields

    Zhang, Qiong; Lin, Guoqing; Zhan, Zhongwen; Chen, Xiaowei; Qin, Yan; Wdowinski, Shimon
    Geothermal areas are long recognized to be susceptible to remote earthquake triggering, probably due to the high seismicity rates and presence of geothermal fluids. However, anthropogenic injection and extraction activity may alter the stress state and fluid flow within the geothermal fields. Here we examine the remote triggering phenomena in the Coso geothermal field and its surrounding areas to assess possible anthropogenic effects. We find that triggered earthquakes are absent within the geothermal field but occur in the surrounding areas. Similar observation is also found in the Salton Sea geothermal field. We hypothesize that continuous geothermal operation has eliminated any...

  6. Intraslab rupture triggering megathrust rupture coseismically in the 17 December 2016 Solomon Islands M_w 7.9 earthquake

    Lay, Thorne; Ye, Lingling; Ammon, Charles J.; Kanamori, Hiroo
    The 17 December 2016 Solomon Islands earthquake (M_w 7.9) initiated ~103 km deep in the subducting Solomon Sea slab near the junction of the Solomon Islands and New Britain trenches. Most aftershocks are located near the Solomon Islands plate boundary megathrust west of Bougainville, where previous large interplate thrust faulting earthquakes occurred in 1995 (M_w 7.7) and 1971 (M_w 8.0). Teleseismic body wave modeling and aftershock relocations indicate that the initial 30 s of the 2016 rupture occurred over depths of 90 to 120 km on an intraslab fault dipping ~30° to the southwest, almost perpendicular to the dipping slab interface. The next...

  7. Dynamically triggered slip on a splay fault in the Mw 7.8, 2016 Kaikoura (New Zealand) earthquake

    Hollinsworth, James; Ye, Lingling; Avouac, Jean-Philippe
    We investigate the Mw 7.8, 2016 Kaikoura (New Zealand) earthquake using optical satellite imagery and seismology to reveal the main features of the rupture process. Correlation of Landsat8 images reveals a 30-40 km surface rupture on the Kekerengu Fault and Jordan Thrust, with up to 12 m of right-lateral slip. A previously unrecognized conjugate strike-slip fault, the Papatea Fault, also slipped co-seismically (3-4 m). The global CMT centroid indicates both thrust and right-lateral slip, and is located ~100 km NE of the mainshock epicenter. The significant non-double-couple component of the gCMT (25%) suggests the mainshock is not well represented by a single planar fault....

  8. Lithospheric radial anisotropy beneath the Gulf of Mexico

    Chu, Risheng; Ko, Justin Yen-Ting; Wei, Shengji; Zhan, Zhongwen; Helmberger, Don
    The Lithosphere–Asthenosphere Boundary (LAB), where a layer of low viscosity asthenosphere decouples with the upper plate motion, plays an essential role in plate tectonics. Most dynamic modeling assumes that the shear velocity can be used as a surrogate for viscosity which provides key information about mantle flow. Here, we derive a shear velocity model for the LAB structure beneath the Gulf of Mexico allowing a detailed comparison with that beneath the Pacific (PAC) and Atlantic (ATL). Our study takes advantage of the USArray data from the March 25th, 2013 Guatemala earthquake at a depth of 200 km. Such data is...

  9. Rate-and-state friction properties of the Longitudinal Valley Fault from kinematic and dynamic modeling of seismic and aseismic slip

    Thomas, Marion Y.; Avouac, Jean-Philippe; Lapusta, Nadia
    The Longitudinal Valley Fault (LVF, Taiwan) is a fast slipping fault (∼5 cm/yr), which exhibits both seismic, and aseismic slip. Geodetic and seismological observations (1992-2010) were used to infer the temporal evolution of fault slip [Thomas et al., 2014a]. This kinematic model is used here to estimate spatial variations of steady-state velocity dependence of fault friction and to develop a simplified fully-dynamic rate-and-state model of the LVF. Based on the postseismic slip, we estimate that the rate-and-state parameter (a – b) σ[over-bar] decreases from ∼1.2 MPa near the surface to near velocity-neutral at 19 km depth. The inferred (a −...

  10. 3D velocity field time series using synthetic aperture radar: application to tidal-timescale ice-flow variability in Rutford Ice Stream, West Antarctica

    Milillo, Pietro; Minchew, Brent; Agram, Piyush; Riel, Bryan; Simons, Mark
    We present a general method for retrieving time-series of three component surface velocity field vector given a set of continuous synthetic aperture radar (SAR) acquisitions collected from multiple geometries. Our algorithm extends the single-line-of-sight mathematical framework developed for time-series analysis using interferometric SAR (InSAR) to three spatial dimensions. The inversion is driven by a design matrix corresponding to a dictionary of displacement functions parameterized in time. The resulting model minimizes a cost function using a non-regularized least-squares method. We applied our method to Rutford ice stream (RIS), West Antarctica, using a set of 101 multi-track multi-angle COSMO-SkyMed displacement maps generating...

  11. Earthquake supercycles on the Mentawai segment of the Sunda megathrust in the seventeenth century and earlier

    Philibosian, Belle; Sieh, Kerry; Avouac, Jean-Philippe; Natawidjaja, Danny H.; Chiang, Hong-Wei; Wu, Chung-Che; Shen, Chuan-Chou; Daryono, Mudrik R.; Perfettini, Hugo; Suwargadi, Bambang W.; Lu, Yanbin; Wang, Xianfeng
    Over at least the past millennium, the Mentawai segment of the Sunda megathrust has failed in sequences of closely timed events rather than in single end-to-end ruptures—each the culmination of an earthquake “supercycle.” Here we synthesize the sixteenth- and seventeenth-century coral microatoll records into a chronology of interseismic and coseismic vertical deformation. We identify at least five discrete uplift events in about 1597, 1613, 1631, 1658, and 1703 that likely correspond to large megathrust ruptures. This sequence contrasts with the following supercycle culmination, which involved only two large ruptures in 1797 and 1833. Fault slip modeling suggests that together the...

  12. 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...

  13. 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...

  14. 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....

  15. 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...

  16. 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...

  17. 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.

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

    Wicks, June K.; 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.

  19. 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...

  20. 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...

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