Caltech Authors
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Repository of works by Caltech published authors.
Group = Caltech Tectonics Observatory
Mostrando recursos 1 - 20 de 213
1.
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...
2.
Stalled slab dynamics - Burkett, Erin; Gurnis, Michael
Recent seismic imaging of the mantle beneath western North America reveals complexities interpreted as structures ranging from plumes to lithospheric drips and slab fragments. A prominent high-velocity "curtain" beneath Idaho has been interpreted as a remnant of the subducted Farallon plate left dangling within the upper mantle since >40 Ma. Consequently, using numerical models, we explore the rheological, chemical, geometrical, and dynamic conditions under which a slab fragment might persist in the mantle for tens of millions of years. With thermal buoyancy alone, stalled slabs extending to 500 km depth tend to detach and sink vertically within ∼17 m.y. for...
3.
Locating a scatterer in the active volcanic area of Southern Peru from ambient noise cross-correlation - Ma, Yiran; Clayton, Robert W.; Tsai, Victor C.; Zhan, Zhongwen
We report on a strong scatterer of seismic energy in the 5–10 s period range located in the volcanic arc of Southern Peru. It is superficially like an active noise source in that it produces a continuous signal that arrives earlier than the inter-station surface wave in the noise cross-correlations. However, it is clearly determined to be a scatterer based on the coda arrivals observed in the cross-correlations, and the fact that it scatters waves from earthquake sources. We model the scatterer as a cylinder approximately 5 km in diameter with a shear wave velocity 30 per cent lower than the background...
4.
Large-scale adaptive mantle convection simulation - Burstedde, Carsten; Stadler, Georg; Alisic, Laura; Wilcox, Lucas C.; Tan, Eh; Gurnis, Michael; Ghattas, Omar
A new generation, parallel adaptive-mesh mantle convection code, Rhea, is described and benchmarked. Rhea targets large-scale mantle convection simulations on parallel computers, and thus has been developed with a strong focus on computational efficiency and parallel scalability of both mesh handling and numerical solvers. Rhea builds mantle convection solvers on a collection of parallel octree-based adaptive finite element libraries that support new distributed data structures and parallel algorithms for dynamic coarsening, refinement, rebalancing and repartitioning of the mesh. In this study we demonstrate scalability to 122 880 compute cores and verify correctness of the implementation. We present the numerical approximation...
5.
Mantle transition zone shear velocity gradients beneath USArray - Schmandt, Brandon
Broadband P-to-s scattering isolated by teleseismic receiver function analysis is used to investigate shear velocity (V_S) gradients in the mantle transition zone beneath USArray. Receiver functions from 2244 stations were filtered in multiple frequency bands and migrated to depth through P and S tomography models. The depth-migrated receiver functions were stacked along their local 410 and 660 km discontinuity depths to reduce stack incoherence and more accurately recover the frequency-dependent amplitudes of P410s and P660s. The stacked waveforms were inverted for one-dimensional V_S between 320 and 840 km depth. First, a gradient-based inversion was used to find a least-squares solution...
6.
An asperity model for fault creep and interseismic deformation
in northeastern Japan - Kanda, Ravi V. S.; Hetland, Eric A.; Simons, Mark
We explore the potential geodetic signature of mechanical stress shadows surrounding inferred major seismic asperities along the Japan-Kurile subduction megathrust. Such stress shadows result from a decrease in creep rates late in the interseismic period. We simplify the rupture history along this megathrust as the repeated rupture of several asperities, each with its own fixed recurrence interval. In our models, megathrust creep throughout the interseismic period evolves according to velocity strengthening friction, as opposed to common kinematic back-slip models of locked or partially locked (i.e. coupled) regions of the megathrust. Such backslip models are usually constrained by onshore geodetic data...
7.
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...
8.
Structure of the subduction system in southern Peru from seismic array data - Phillips, Kristin; Clayton, Robert W.; Davis, Paul; Tavera, Hernando; Guy, Richard; Skinner, Steven; Stubailo, Igor; Audin, Laurence; Aguilar, Victor
The subduction zone in southern Peru is imaged using converted phases from teleseismic P, PP, and PKP waves and Pwave tomography using local and teleseismic events with a linear array of 50 broadband seismic stations spanning 300 km from the coast to near Lake Titicaca. The slab dips at 30° and can be observed to a depth of over 200 km. The Moho is seen as a continuous interface along the profile, and the crustal thickness in the back-arc region (the Altiplano) is 75 km thick, which is sufficient to isostatically support the Andes, as evidenced by the gravity. The...
9.
Deformation during the 1975–1984 Krafla rifting crisis, NE Iceland, measured from historical optical imagery - Hollingsworth, James; Leprince, Sébastien; Ayoub, François; Avouac, Jean-Philippe
We measure the displacement field resulting from the 1975–1984 Krafla rifting crisis, NE Iceland, using optical image correlation. Images are processed using the COSI-Corr software package. Surface extension is accommodated on normal faults and fissures which bound the rift zone, in response to dike injection at depth. Correlation of declassified KH-9 spy and SPOT5 satellite images reveals extension between 1977–2002 (2.5 m average opening over 80 km), while correlation of aerial photos between 1957–1990 provide measurements of the total extension (average 4.3 m opening over 80 km). Our results show ∼8 m of opening immediately north of Krafla caldera, decreasing...
10.
Postseismic deformation following the 1999 Chi-Chi earthquake,
Taiwan: Implication for lower-crust rheology - Rousset, Baptiste; Barbot, Sylvain; Avouac, Jean-Philippe; Hsu, Ya-Ju
On 1999 September 21, the Mw 7.6 Chi-Chi earthquake ruptured a segment of the
Chelungpu Fault, a frontal thrust fault of the Western Foothills of Taiwan. The stress
perturbation induced by the rupture triggered a transient deformation across the island,
which was well recorded by a wide network of continuously operating GPS stations.
The analysis of more than ten years of these data reveals a heterogeneous pattern of
postseismic displacements, with relaxation times varying by a factor of more than ten,
and large cumulative displacements at great distances, in particular along the Longitudinal
Valley in eastern Taiwan, where relaxation times are also longer. We show that while
afterslip...
11.
From basalts to boninites: The geodynamics of volcanic expression during induced subduction initiation - Leng, Wei; Gurnis, Michael; Asimow, Paul
Subduction initiation may unfold via different pathways in response to plate strength, plate age, and driving mechanism. Such pathways influence volcanism on the overriding plate and may be preserved in the sequence of erupted volcanic products. Here, we parameterize melting in a mechanical model to determine the volcanic products that form in response to different subduction initiation modes. We find that with a mode of continuous initiation with infant-arc spreading, the foundering of the subducting slab and water release from the slab govern a succession from basalts with compositions similar to mid-ocean-ridge basalts (MORB) to boninites. The modeled transition from...
12.
Epeirogenic transients related to mantle lithosphere removal in
the southern Sierra Nevada region, California, part I:
Implications of thermomechanical modeling - Saleeby, J.; Le Pourhiet, L.; Saleeby, Z.; Gurnis, M.
The putative Pliocene–Quaternary removal of mantle lithosphere from beneath the southern Sierra Nevada region (California, USA) is investigated by the iteration of thermal-mechanical models that incorporate and are tested against a range of data that are geologically observable, including rock uplift and basin subsidence data, structural and compositional data on crustal architecture, and a synthesis of seismic data that image lower crust–upper mantle structure of the region. The primary focus is testing model results with rock uplift and basin subsidence data. The initial state of our models recognizes that (1) the sub–Sierra Nevada batholith mantle lithosphere, including a substantial thickness...
13.
Sea level and vertical motion of continents from dynamic earth models since the Late Cretaceous - Spasojevic, Sonja; Gurnis, Michael
Dynamic earth models are used to better understand the impact of mantle dynamics on the vertical motion of continents and regional and global sea level change since the Late Cretaceous. A hybrid approach combines inverse and forward models of mantle convection and accounts for the principal contributors to long-term sea level change: the evolving distribution of ocean floor age, dynamic topography in oceanic and continental regions, and the geoid. We infer the relative importance of dynamic versus other factors of sea level change, determine time-dependent patterns of dynamic subsidence and uplift of continents, and derive a sea level curve.
We find...
14.
Anomalously steep dips of earthquakes in the 2011 Tohoku-Oki source region and possible explanations - Zhan, Zhongwen; Helmberger, Don; Simons, Mark; Kanamori, Hiroo; Wu, Wenbo; Cubas, Nadaya; Duputel, Zacharie; Chu, Risheng; Tsai, Victor C.; Avouac, Jean-Philippe; Hudnut, Kenneth W.; Ni, Sidao; Hetland, Eric; Culaciati, Francisco H. Ortega
The 2011 M_w 9.1 Tohoku-Oki earthquake had unusually large slip (over 50 m) concentrated in a relatively small region, with local stress drop inferred to be 5–10 times larger than that found for typical megathrust earthquakes. Here we conduct a detailed analysis of foreshocks and aftershocks (M_w 5.5–7.5) sampling this megathrust zone for possible clues regarding such differences in seismic excitation. We find that events occurring in the region that experienced large slip during the M_w 9.1 event had steeper dip angles (by 5–10°) than the surrounding plate interface. This discrepancy cannot be explained by a single smooth plate interface....
15.
Magmatic growth and batholithic root development
in the northern Sierra Nevada, California - Cecil, M. R.; Rotberg, G. L.; Ducea, M. N.; Saleeby, J. B.; Gehrels, G. E.
In contrast to the much-studied central and southern Sierra Nevada, relatively little is known about the growth and petrogenesis of the batholith in its northern reaches, making it difficult to evaluate range-wide, spatiotemporal trends in batholithic development and the regional extent of eclogite root production and/or loss. New U-Pb ages from northern Sierra plutons reveal a shift between the age of Cretaceous magmatism recorded in the northern Sierra and the timing of an apparent flare-up in the main batholith, indicating that: (1) the northern batholith was more spatially dispersed and emplaced into regions beyond the modern topographic range, and (2)...
16.
Sea level and vertical motion of continents from dynamic
earth models since the Late Cretaceous - Spasojevic, Sonja; Gurnis, Michael
Dynamic earth models are used to better understand the impact of mantle dynamics on the vertical motion of continents and regional and global sea level change since the Late Cretaceous. A hybrid approach combines inverse and forward models of mantle convection and accounts for the principal contributors to long-term sea level change: the evolving distribution of ocean floor age, dynamic topography in oceanic and continental regions, and the geoid. We infer the relative importance of dynamic versus other factors of sea level change, determine time-dependent patterns of dynamic subsidence and uplift of continents, and derive a sea level curve.
We find...
17.
Multi-scale dynamics and rheology of mantle flow with plates - Alisic, Laura; Gurnis, Michael; Stadler, Georg; Burstedde, Carsten; Ghattas, Omar
Fundamental issues in our understanding of plate and mantle dynamics remain unresolved, including the rheology and state of stress of plates and slabs; the coupling between plates, slabs and mantle; and the flow around slabs. To address these questions, models of global mantle flow with plates are computed using adaptive finite elements, and compared to a variety of observational constraints. The dynamically consistent instantaneous models include a composite rheology with yielding, and incorporate details of the thermal buoyancy field. Around plate boundaries, the local resolution is 1 km, which allows us to study highly detailed features in a globally consistent...
18.
Constraints from rocks in the Taiwan orogen on crustal stress
levels and rheology - Kidder, Steven; Avouac, Jean-Philippe; Chan, Yu-Chang
Taiwan's Hsüehshan range experienced penetrative coaxial deformation within and near the brittle-plastic transition between ∼6.5 and 3 Ma. This recent and short-lasting deformation in an active, well-studied orogen makes it an ideal natural laboratory for studying crustal rheology. Recrystallized grain size piezometry in quartz and Ti-in-quartz thermobarometry yield peak differential stresses of ∼200 MPa at 250–300°C that taper off to ∼80 MPa at ∼350°C and ∼14 MPa at ∼400–500°C. Stress results do not vary with lithology: recrystallized quartz veins in slates and metasiltstones yield equivalent stresses as recrystallized grains in quartzites. A minimum strain rate of 2.9 × 10^(−15) s^(−1)...
19.
The role of velocity-neutral creep on the modulation of tectonic tremor activity by periodic loading - Ader, Thomas J.; Ampuero, Jean-Paul; Avouac, Jean-Philippe
Slow slip events and associated non-volcanic tremors are sensitive to oscillatory stress perturbations, such as those induced by tides or seismic surface waves. Slow slip events and tremors are thought to occur near the seismic-aseismic transition regions of active faults, where the difference a − b = ∂μ/∂lnV between the sensitivity of friction to slip rate and fault state, which characterizes the stability of slip, can be arbitrarily small. We investigate the response of a velocity-strengthening fault region to oscillatory loads through analytical approximations and spring-slider simulations. We find that fault areas that are near velocity-neutral at steady-state, i.e., ∂μ...
20.
Distribution of hydrous minerals in the subduction system beneath Mexico - Kim, YoungHee; Clayton, Robert W.; Jackson, Jennifer M.
Teleseismic converted phases are used to probe the composition of the downgoing oceanic crust as a function of depth along the Cocos slab in central and southern Mexico. Previously, modeling of the receiver function (RF) conversion amplitude of the flat Cocos slab beneath central Mexico at 45 km depth revealed a thin low-velocity upper oceanic crust of a thickness of 4±1 km, which has much lower seismic velocities (∼20–30% reduction in shear wave velocities) than (normal) lower crust. High Vp/Vs ratio (∼2.0) also suggested a large concentration of hydrous minerals such as talc in combination of high pore-fluid pressure in...
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