Recursos de colección

Caltech Authors (156.041 recursos)

Repository of works by Caltech published authors.

Group = Caltech Tectonics Observatory

Mostrando recursos 1 - 20 de 23

  1. Geologic map of the east-central Meadow Valley Mountains, and implications for reconstruction of the Mormon Peak detachment, Nevada

    Swanson, E.; Wernicke, B. P.
    The role of low-angle faults in accommodating extension within the upper crust remains controversial because the existence of these faults markedly defies extant continuum theories of how crustal faults form, and once initiated, how they continue to slip. Accordingly, for many proposed examples, basic kinematic problems like slip direction, dip angle while active, and magnitude of offset are keenly debated. A well-known example is the Miocene Mormon Peak detachment and overlying Mormon Peak allochthon of southern Nevada (USA), whose origin and evolution have been debated for several decades. Here, we use geologic mapping in the Meadow Valley Mountains to help...

  2. Time scale bias in erosion rates of glaciated landscapes

    Ganti, Vamsi; von Hagke, Christoph; Scherler, Dirk; Lamb, Michael P.; Fischer, Woodward W.; Avouac, Jean-Philippe
    Deciphering erosion rates over geologic time is fundamental for understanding the interplay between climate, tectonic, and erosional processes. Existing techniques integrate erosion over different time scales, and direct comparison of such rates is routinely done in earth science. On the basis of a global compilation, we show that erosion rate estimates in glaciated landscapes may be affected by a systematic averaging bias that produces higher estimated erosion rates toward the present, which do not reflect straightforward changes in erosion rates through time. This trend can result from a heavy-tailed distribution of erosional hiatuses (that is, time periods where no or...

  3. Numerical modeling of long-term earthquake sequences on the NE Japan megathrust: Comparison with observations and implications for fault friction

    Cubas, Nadaya; Lapusta, Nadia; Avouac, Jean-Philippe; Perfettini, Hugo
    We use numerical modeling to investigate fault properties that explain key features of the 2011 Mw 9.0 Tohoku-Oki earthquake as well as the overall regional behavior of the NE Japan megathrust. In particular, we study the possibility that slip near the trench resulted from thermal pressurization on a shallow patch of the megathrust, and investigate whether low-velocity friction on that patch is rate-strengthening or rate-weakening. Our models also contain a deeper rate-weakening patch, not prone to efficient thermal pressurization, to account for the moderate-sized interplate seismicity. We produce earthquake sequences and aseismic slip in our models using 2D dynamic simulations...

  4. Static Laboratory Earthquake Measurements with the Digital Image Correlation Method

    Rubino, V.; Lapusta, N.; Rosakis, A. J.; Leprince, S.; Avouac, J. P.
    Mapping full-field displacement and strain changes on the Earth’s surface following an earthquake is of paramount importance to enhance our understanding of earthquake mechanics. Currently, aerial and satellite images taken pre- and post-earthquake can be processed with sub-pixel correlation algorithms to infer the co-seismic ground deformations (e.g., [1, 2]). However, the interpretation of this data is not straightforward due to the inherent complexity of natural faults and deformation fields. To gain understanding into rupture mechanics and to help interpret complex rupture features occurring in nature, we develop a laboratory earthquake setup capable of reproducing displacement and strain maps similar to...

  5. Static Laboratory Earthquake Measurements with the Digital Image Correlation Method

    Rubino, V.; Lapusta, N.; Rosakis, A. J.; Leprince, S.; Avouac, J. P.
    Mapping full-field displacement and strain changes on the Earth’s surface following an earthquake is of paramount importance to enhance our understanding of earthquake mechanics. Currently, aerial and satellite images taken pre- and post-earthquake can be processed with sub-pixel correlation algorithms to infer the co-seismic ground deformations (e.g., [1, 2]). However, the interpretation of this data is not straightforward due to the inherent complexity of natural faults and deformation fields. To gain understanding into rupture mechanics and to help interpret complex rupture features occurring in nature, we develop a laboratory earthquake setup capable of reproducing displacement and strain maps similar to...

  6. Diagnosing Source Geometrical Complexity of Large Earthquakes

    Rivera, L.; Kanamori, H.
    We investigated the possible frequency dependence of the moment tensor of large earthquakes by performing W phase inversions using teleseismic data and equally-spaced narrow, overlapping frequency bands. We investigated frequencies from 0.6 to 3.8 mHz. Our focus was on the variation with frequency of the scalar moment, the amount of non-double-couple, and the focal mechanism. We applied this technique to 30 major events in the period 1994–2013 and used the results to detect source complexity. Based on the results, we classed them into three groups according to the variability of the source parameters with frequency: simple, complex and intermediate. Twelve...

  7. Response of rate-and-state seismogenic faults to harmonic shear-stress perturbations

    Ader, Thomas J.; Lapusta, Nadia; Avouac, Jean-Philippe; Ampuero, Jean-Paul
    Field and laboratory observations show that seismicity has non-trivial period-dependent response to periodic stress perturbations. In Nepal, seismicity shows significant variations in response to annual monsoon-induced stress variations but not to semidiurnal tidal stresses of the same magnitude. Such period dependence cannot be explained by the Coulomb failure model and spring-slider rate-and-state model (SRM). Here, we study seismicity response to periodic stress perturbations in a 2-D continuum model of a rate-and-state fault (that is, a finite rate-and-state fault). We find that the resulting seismicity indeed exhibits nearly periodic variations. Their amplitude is maximum at a certain period, T_a, and decreases...

  8. Kinematic Inversion of Physically Plausible Earthquake Source Models Obtained from Dynamic Rupture Simulations

    Konca, Ali Ozgun; Kaneko, Yoshihiro; Lapusta, Nadia; Avouac, Jean-Philippe
    One approach to investigate earthquake source processes is to produce kinematic source models from inversion of seismic records and geodetic data. The setup of the inversion requires a variety of assumptions and constraints to restrict the range of possible models. Here, we evaluate to what extent physically plausible earthquake scenarios are reliably restituted in spite of these restrictions. We study which characteristics of ruptures, such as rupture velocity, slip distribution, stress drop, rise time, and slip function, can be reliably determined from the inversion of near‐field seismic and geodetic data. Using spontaneous dynamic rupture simulations, we generate five earthquake scenarios,...

  9. Comparison of average stress drop measures for ruptures with heterogeneous stress change and implications for earthquake physics

    Noda, Hiroyuki; Lapusta, Nadia; Kanamori, Hiroo
    Stress drop, a measure of static stress change in earthquakes, is the subject of numerous investigations. Stress drop in an earthquake is likely to be spatially varying over the fault, creating a stress drop distribution. Representing this spatial distribution by a single number, as commonly done, implies averaging in space. In this study, we investigate similarities and differences between three different averages of the stress drop distribution used in earthquake studies. The first one, Δσ¯¯¯¯¯M, is the commonly estimated stress drop based on the seismic moment and fault geometry/dimensions. It is known that Δσ¯¯¯¯¯M corresponds to averaging the stress drop...

  10. Mitigating artifacts in back-projection source imaging with implications for frequency-dependent properties of the Tohoku-Oki earthquake

    Meng, Lingsen; Ampuero, Jean-Paul; Luo, Yingdi; Wu, Wenbo; Ni, Sidao
    Comparing teleseismic array back-projection source images of the 2011 Tohoku-Oki earthquake with results from static and kinematic finite source inversions has revealed little overlap between the regions of high- and low-frequency slip. Motivated by this interesting observation, back-projection studies extended to intermediate frequencies, down to about 0.1 Hz, have suggested that a progressive transition of rupture properties as a function of frequency is observable. Here, by adapting the concept of array response function to non-stationary signals, we demonstrate that the "swimming artifact", a systematic drift resulting from signal non-stationarity, induces significant bias on beamforming back-projection at low frequencies. We introduce...

  11. Stable creeping fault segments can become destructive as a result of dynamic weakening

    Noda, Hiroyuki; Lapusta, Nadia
    Faults in Earth’s crust accommodate slow relative motion between tectonic plates through either similarly slow slip or fast, seismic-wave-producing rupture events perceived as earthquakes. These types of behaviour are often assumed to be separated in space and to occur on two different types of fault segment: one with stable, rate-strengthening friction and the other with rate-weakening friction that leads to stick-slip. The 2011 Tohoku-Oki earthquake with moment magnitude M_w = 9.0 challenged such assumptions by accumulating its largest seismic slip in the area that had been assumed to be creeping. Here we propose a model in which stable, rate-strengthening behaviour...

  12. Under the Hood of the Earthquake Machine: Toward Predictive Modeling of the Seismic Cycle

    Barbot, Sylvain; Lapusta, Nadia; Avouac, Jean-Philippe
    Advances in observational, laboratory, and modeling techniques open the way to the development of physical models of the seismic cycle with potentially predictive power. To explore that possibility, we developed an integrative and fully dynamic model of the Parkfield segment of the San Andreas Fault. The model succeeds in reproducing a realistic earthquake sequence of irregular moment magnitude (M_w) 6.0 main shocks—including events similar to the ones in 1966 and 2004—and provides an excellent match for the detailed interseismic, coseismic, and postseismic observations collected along this fault during the most recent earthquake cycle. Such calibrated physical models provide new ways...

  13. Spectral-element simulations of long-term fault slip: Effect of low-rigidity layers on earthquake-cycle dynamics

    Kaneko, Y.; Ampuero, J.-P.; Lapusta, N.
    We develop a spectral element method for the simulation of long-term histories of spontaneous seismic and aseismic slip on faults subjected to tectonic loading. Our approach reproduces all stages of earthquake cycles: nucleation and propagation of earthquake rupture, postseismic slip and interseismic creep. We apply the developed methodology to study the effects of low-rigidity layers on the dynamics of the earthquake cycle in 2-D. We consider two cases: small (M ~ 1) earthquakes on a fault surrounded by a damaged fault zone and large (M ~ 7) earthquakes on a vertical strike-slip fault that cuts through shallow low-rigidity layers. Our...

  14. Seasonal variations of observed noise amplitudes at 2–18 Hz in southern California

    Hillers, G.; Ben-Zion, Y.
    We show that noise amplitudes at frequencies above 1 Hz exhibit strong seasonal variations in a broad southern California region. The results are based on 3-component seismic data recorded between 2002 and 2009 by 30 stations. Focusing on continuous 6-hr night-time segments, the seismograms are bandpass-filtered in nine frequency bands between 2 and 18 Hz. Squared amplitudes are median-filtered to reduce the influence of earthquake signals and integrated to yield half-hourly noise energy estimates. The 6-hr minimum energy values are converted back to ground velocity and used as representative daily noise level amplitudes. Notwithstanding various trends, drifts and other transient...

  15. Magnetostratigraphy of the Yaha section, Tarim Basin (China): 11 Ma acceleration in erosion and uplift of the Tian Shan mountains

    Charreau, Julien; Gilder, Stuart; Chen, Yan; Dominguez, Stéphane; Avouac, Jean-Philippe; Sen, Sevket; Jolivet, Marc; Li, Yongan; Wang, Weiming
    We report a magnetostratigraphic and rock magnetic study of the Yaha section, located on the southern flank of the central Tian Shan mountains, Asia. Our results show a two-fold increase in sedimentation rate as well as marked changes in rock magnetic characteristics ca. 11 Ma. After 11 Ma, sedimentation rate remained remarkably constant until at least 5.2 Ma. These findings are consistent with sedimentary records from other sections surrounding the Tian Shan. We conclude that uplift and erosion of the Tian Shan accelerated ca. 11 Ma, long after the onset of the collision between India and Asia, and that the...

  16. Magnetostratigraphy and rock magnetism of the Neogene Kuitun He section (northwest China): implications for Late Cenozoic uplift of the Tianshan mountains

    Charreau, Julien; Chen, Yan; Gilder, Stuart; Dominguez, Stéphane; Avouac, Jean-Philippe; Sen, Sevket; Sun, Dongjiang; Li, Yongan; Wang, Wei-Ming
    In order to better constrain the tectonic evolution of central Asia under the influence of the India–Asia collision, we carried out a magnetostratigraphic study at the Kuitun He section, on the northern flank of the Tianshan range (northwest China). A total of 801 samples were collected from a 1559-m-thick section, which is composed mainly of fluvio-lacustrine sandstone and conglomerate. Stepwise thermal and alternating field demagnetization isolated a linear magnetization component that decays univectorally toward the origin and likely represents a primary magnetization principally carried by magnetite. From this component, 29 magnetic polarity intervals were identified. They correlate between ~3.1 and...

  17. Inferring mantle properties with an evolving dynamic model of the Antarctica-New Zealand region from the Late Cretaceous

    Spasojevic, Sonja; Gurnis, Michael; Sutherland, Rupert
    We show that time-dependent models of mantle upwellings above a cold downwelling in the New Zealand-Antarctica region since 80 Ma can explain anomalous geophysical observations: ~1.0 km of positive residual bathymetry at the Antarctica margin, a large Ross Sea geoid low, 0.5–0.9 km of excess tectonic subsidence of the Campbell Plateau since 80 Ma, and several seismic wave speed anomalies. Model results indicate that the largest mantle upwelling, centered in the Ross Sea, has an average temperature anomaly of 200°C and density anomaly of 0.6%, and it rose from midmantle depths at 80 Ma to a present depth of 400–1000...

  18. Mantle upwellings above slab graveyards linked to the global geoid lows

    Spasojevic, Sonja; Gurnis, Michael; Sutherland, Rupert
    The global geoid is characterized by a semi-continuous belt of lows that surround the Pacific Ocean, including isolated minima in the Indian Ocean, Ross Sea and northeast Pacific and west Atlantic oceans. These geoid lows have been attributed to Mesozoic subduction. Geodynamic models that include slab graveyards in the lower mantle as inferred from seismic topography or from plate reconstructions correctly predict the general trend of geoid minima. However, these models fail to accurately reproduce localized geoid lows in the Indian Ocean, Ross Sea and northeast Pacific Ocean. Here we show that the geoid lows are correlated with high-velocity anomalies...

  19. Towards inferring earthquake patterns from geodetic observations of interseismic coupling

    Kaneko, Yoshihiro; Avouac, Jean-Philippe; Lapusta, Nadia
    Ultimately, seismotectonic studies seek to provide ways of assessing the timing, magnitude and spatial extent of future earthquakes. Ample observations document the spatial variability in interseismic coupling, defined as a degree of locking of a fault during the period of stress build-up between seismic events: fully or nearly locked fault patches are often surrounded by aseismically creeping areas. However, it is unclear how these observations could help assess future earthquakes. Here we simulate spontaneous seismic and aseismic fault slip with a fully dynamic numerical model. Our simulations establish the dependence of earthquake rupture patterns and interseismic coupling on spatial variations...

  20. Mantle upwelling after Gondwana subduction death explains anomalous topography and subsidence histories of eastern New Zealand and West Antarctica

    Sutherland, Rupert; Spasojevic, Sonja; Gurnis, Michael
    West Antarctica and adjacent seafloor have topographic elevations 0.5–1.2 km greater than expected from models of lithospheric age and crustal structure. Ocean crust near New Zealand has no equivalent depth anomaly, but tectonic subsidence histories from Campbell Plateau petroleum wells show anomalously high subsidence rates during the Paleogene, and total subsidence 0.5–0.9 km greater than expected from rift basin models. Geophysical and geochemical anomalies suggest that upward mantle flow supports the anomalous topography beneath Antarctica, and the Campbell Plateau subsidence history indicates that topographic support mechanisms were long lived (>80 Ma) and recoverable over a period of ~30 m.y. as...

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