Repository of works by Caltech published authors.
Group = Caltech Tectonics Observatory
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Reconstructing Farallon plate subduction beneath North America back to the Late Cretaceous - Liu, Lijun; Spasojevic, Sonja; Gurnis, Michael
Using an inverse mantle convection model that assimilates seismic structure and plate motions, we reconstruct Farallon plate subduction back to 100 million years ago. Models consistent with stratigraphy constrain the depth dependence of mantle viscosity and buoyancy, requiring that the Farallon slab was flat lying in the Late Cretaceous, consistent with geological reconstructions. The simulation predicts that an extensive zone of shallow- dipping subduction extended beyond the flat-lying slab farther east and north by up to 1000 kilometers. The limited region of flat subduction is consistent with the notion that subduction of an oceanic plateau caused the slab to flatten....
Change of apparent segmentation of the San Andreas fault
around Parkfield from space geodetic observations across multiple periods - Barbot, Sylvain; Agram, Piyush; De Michele, Marcello
Sequences of earthquakes are commonly represented as a succession of periods of interseismic stress accumulation followed by coseismic and postseismic phases of stress release. Because the recurrence time of large earthquakes is often greater than the available span of space geodetic data, it has been challenging to monitor the evolution of interseismic loading in its entire duration. Here we analyze large data sets of surface deformation at different key episodes around the Cholame, Parkfield and creeping segments of the San Andreas Fault that show evidence of significant deceleration of fault slip during the interseismic period. We compare the average fault...
Analysis of teleseismic P waves with a 5200-station array in Long Beach, California: Evidence for an abrupt boundary to Inner Borderland rifting - Schmandt, Brandon; Clayton, Robert W.
We analyze teleseismic P waves from four Mw ≥ 6.5 earthquakes recorded by a petroleum industry survey in Long Beach, California. The survey used a 2-D array with up to 5200 seismometers, 120 m mean spacing, and 7 – 10 km aperture. At frequencies near 1 Hz, P wave travel times and amplitudes exhibit coherent lateral variations over scales as short as ~400 m, including locally delayed travel times and increased amplitudes at the crest of the Long Beach anticline. Deeper heterogeneity is indicated by P wave phase velocities that deviate from reference model predictions for events from southwestern azimuths. We postulate that a sharp northeastward...
Generation of talc in the mantle wedge and its role in subduction dynamics in central Mexico - Kim, YoungHee; Clayton, Robert W.; Asimow, Paul D.; Jackson, Jennifer M.
Geophysical evidence shows the presence of low-seismic velocity material at the surface of slabs in subduction zones. In the central Mexican subduction zone this appears as a thin (∼4 km) low-velocity zone that absorbs nearly all of the strain. The P-to-S velocity ratio as a function of S wave velocity distinguishes among the various candidate hydrous (low-strength) minerals; the thin layer in the flat-slab region is most consistent with a layer showing enrichment in talc overlying normal MORB-like gabbro. Based on available thermodynamic data for equilibria for talc, its generation at the trench is nearly impossible, and hence we propose...
Late Pleistocene glacial advances in the western Tibet interior - Amidon, William H.; Bookhagen, Bodo; Avouac, Jean-Philippe; Smith, Taylor; Rood, Dylan
It has long been observed that the timing of glacial advances is asynchronous across the Himalaya–Karakoram–Tibet Plateau (HKTP) but the climatic implications, if any, remain unclear. Resolving this question requires additional glacial chronologies from unique spatial and climatic regimes as well as an analysis of how glaciers within different regimes are likely to have responded to past climate changes. This study presents a ^(10)Be–^(21)Ne chronology from the Mawang Kangri range of western Tibet (∼34°N, 80°E); an arid high-elevation site. We identify advances at ∼123, 83, and 56 kyr, which agree reasonably well with sites in the immediate vicinity, but are...
Megathrust friction determined from mechanical analysis of the forearc in the Maule earthquake area - Cubas, Nadaya; Avouac, Jean-Philippe; Souloumiac, Pauline; Leroy, Yves
The seismogenic potential of a given fault depends essentially on its frictional properties and on the mechanical properties of the medium. Determining the spatio-temporal variations of frictional properties is therefore a key issue in seismotectonics. This study aims to characterize the friction on the South America megathrust in the 2010 Mw 8.8 Maule earthquake area from mechanical analysis of the forearc structure and morphology. Based on the critical taper theory, we first show that the rupture area of the Maule earthquake, also shown to be locked in the interseismic period, coincides with the stable part of the wedge. In the...
Complementary slip distributions of the largest earthquakes
in the 2012 Brawley swarm, Imperial Valley, California - Wei, Shengji; Helmberger, Don; Owen, Susan; Graves, Robert W.; Hudnut, Kenneth W.; Fielding, Eric J.
We investigate the finite rupture processes of two M > 5 earthquakes in the 2012 Brawley swarm by joint inversion of nearby strong motion and high-rate GPS data. Waveform inversions up to 3 Hz were made possible by using a small event (M_w3.9) for path calibration of the velocity structure. Our results indicate that the first (M_w5.3) event ruptured a strong, concentrated asperity with offsets of ~20 cm centered at a depth of 5 km. The subsequent M_w5.4 event occurred 1.5 h later with a shallower slip distribution that surrounds and is complementary to that of the earlier event. The second event...
Rupture complexity of the M_w 8.3 Sea of Okhotsk Earthquake: Rapid triggering of complementary earthquakes? - Wei, Shengji; Helmberger, Don; Zhan, Zhongwen; Graves, Robert
We derive a finite slip model for the 2013 M_w 8.3 Sea of Okhotsk Earthquake (Z = 610 km) by inverting calibrated teleseismic P waveforms. The inversion shows that the earthquake ruptured on a 10° dipping rectangular fault zone (140 km × 50 km) and evolved into a sequence of four large sub-events (E1–E4) with an average rupture speed of 4.0 km/s. The rupture process can be divided into two main stages. The first propagated south, rupturing sub-events E1, E2, and E4. The second stage (E3) originated near E2 with a delay of 12 s and ruptured northward, filling the slip gap between E1 and E2. This kinematic process...
Low friction along the high slip patch of the 2011 Mw 9.0 Tohoku-Oki earthquake required from the wedge structure and extensional splay faults - Cubas, N.; Avouac, J. P.; Leroy, Y. M.; Pons, A.
We analyze the mechanical properties needed to
account for the large shallow slip during the 2011
Tohoku-Oki earthquake and the activation of landward
normal faulting within the forearc. We show that the
morphology and internal structure of the forearc follows
closely the prediction of the critical Coulomb wedge in
horizontal compression, implying a high internal pore
pressure ratio (λ = 0.7 + 0.14/ – 0.48) and a low effective
basal friction (μ^(eff)_b = 0.14 + 0.18/ – 0.04). We then show that the activation of the normal fault requires a lower effective basal friction beneath the outer wedge than beneath the inner wedge (μ_outer ≤ 0.015), possibly due...
Elasticity and lattice dynamics of enstatite at high pressure - Zhang, Dongzhou; Jackson, Jennifer M.; Chen, Bin; Sturhahn, Wolfgang; Zhao, Jiyong; Yan, Jinyuan; Caracas, Razvan
The behavior of synthetic-powdered ^(57)Fe-enriched enstatite (Mg_(0.980)Fe_(0.020(5)))(Mg_(0.760)Fe_(0.240))Si_2O_6 has been explored by X-ray diffraction (XRD) and nuclear resonant inelastic X-ray scattering (NRIXS). The Pbca-structured enstatite sample was compressed in fine pressure increments for our independent XRD measurements. One structural transition between 10.1 and 12.2 GPa has been identified from the XRD data. The XRD reflections observed for the high-pressure phase are best matched with space group P2_1/c. We combine density functional theory with Mössbauer spectroscopy and NRIXS to understand the local site symmetry of the Fe atoms in our sample. A third-order Birch-Murnaghan (BM3) equation of state fitting gives K_(T0)=103±5 GPa and K'_(T0)=13±2...
Spatially variable fault friction derived from dynamic modeling of aseismic afterslip due to the 2004 Parkfield earthquake - Chang, Shu-Hao; Avouac, Jean-Philippe; Barbot, Sylvain; Lee, Jian-Cheng
We investigate fault friction from dynamic modeling of fault slip prior to and following the M_w 6.0 earthquake which ruptured the Parkfield segment of the San Andreas Fault in 2004. The dynamic modeling assumes a purely rate-strengthening friction law, with a logarithmic dependency on sliding rate: μ= μ*+(a-b)ln(v/v*). The initial state of stress is explicitly taken into account, and afterslip is triggered by the stress change induced by the earthquake source model given a priori. We consider different initial stress states and two coseismic models, and invert for the other model parameters using a nonlinear inversion scheme. The model parameters...
New constraints on dike injection and fault slip during the 1975–1984 Krafla rift crisis, NE Iceland - Hollingsworth, J.; Leprince, Sébastien; Ayoub, François; Avouac, Jean-Philippe
Correlation of KH9 spy and SPOT5 satellite images, airphotos, digital elevation model differencing, electronic distance measurement, and leveling survey data is used to constrain the deformation resulting from the 1975–1984 Krafla rifting crisis. We find that diking typically extends to depths of 5 km, while the dike tops range from 0 km in the caldera region to 3 km at the northern end of the rift. Extension is accommodated by diking at depth and normal faulting in the shallowest crust. In the southern section of the Krafla rift, surface opening is 80% of the dike opening at depth. Over the 70–80 km length of...
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,...
Detecting periodicities and declustering in earthquake catalogs using the Schuster spectrum, application to Himalayan seismicity - Ader, Thomas J.; Avouac, Jean-Philippe
We show that the Schuster test alone does not provide a sufficient condition to assert the existence of a periodicity in an earthquake catalog. Such periodicities can be detected by computing a spectrum of Schuster p-values (the probability to observe such a level of periodic variations in a catalog occurring out of a constant seismicity rate). We show that the detection level is slightly period dependent, and we provide an analytical expression relating the amplitude of seismicity-rate variations to the confidence level at which the probability that the observed variations be due to chance can be discarded. The Schuster spectrum...
Lithospheric convective instability could induce creep along part of the San Andreas fault - Le Pourhiet, Laetitia; Saleeby, Jason
Along the western border of the Sierra Nevada microplate, the San Andreas fault (California, United States) is comprised of three segments. Two (north and south segments) are locked and support large earthquakes (e.g., the M 7.7 1906 San Francisco and the M 7.8 1857 Fort Tejon earthquakes), while the central segment, from Parkfield to San Juan Bautista, is creeping. Based on mechanical models, we show that the late Pliocene–Quaternary convective removal (delamination) of the southern Sierra Nevada mantle lithosphere and associated uplift of the Sierra Nevada Mountains causes the Great Valley upper crust to deform by flexure and buckling. Additional...
A review of observations and models of dynamic topography - Flament, Nicolas; Gurnis, Michael; Müller, R. Dietmar
The topography of Earth is primarily controlled by lateral differences in the density structure of the crust and lithosphere. In addition to this isostatic topography, flow in the mantle induces deformation of its surface leading to dynamic topography. This transient deformation evolves over tens of millions of years, occurs at long wavelength, and is relatively small (<2 km) in amplitude. Here, we review the observational constraints and modeling approaches used to understand the amplitude, spatial pattern, and time dependence of dynamic topography. The best constraint on the present-day dynamic topography induced by sublithospheric mantle flow is likely the residual bathymetry...
Temperatures and Fluids on Faults Based on Carbonate Clumped-Isotope Thermometry - Swanson, Erika M.; Wernicke, Brian P.; Eiler, John M.; Losh, Steven
We present results from a carbonate clumped-isotope thermometric study of 42 carbonate samples collected within ∼1 m or less of the Mormon Peak detachment, a large-slip Miocene normal fault in the Basin and Range province of southern Nevada. Samples include cataclastic rocks, narrow vein fillings and larger void-filling carbonates. Our results are consistent with earlier measurements of O and C isotopic ratios and fluid inclusion temperatures, and provide independent constraints on the isotopic composition and temperature of both syntectonic and post-tectonic pore waters. The results reveal a wide range of precipitation temperatures (24 to 137 °C) associated with deformation, and...
Kinematic fault slip evolution source models of the 2008 M7.9 Wenchuan earthquake in China from SAR interferometry, GPS and teleseismic analysis and implications for Longmen Shan tectonics - Fielding, Eric J.; Sladen, Anthony; Li, Zhenhong; Avouac, Jean-Philippe; Bürgmann, Roland; Ryder, Isabelle
The M_w 7.9 2008 Wenchuan earthquake ruptured about 280 km of faults in the Longmen Shan of Sichuan province, China, at the eastern edge of the Tibetan Plateau. We use teleseismic waveforms with geodetic data from Global Positioning System, synthetic aperture radar interferometry and image amplitude correlation to produce a source model of this earthquake. The model describes evolution of fault slip during the earthquake. The geodetic data constrains the spatial distribution of fault slip and the seismic waveforms constrain mostly the time evolution of slip. We find that the earthquake started with largely thrust motion on an imbricate system of...
Evidence of upper-mantle processes related to continental rifting versus oceanic crust in the Gulf of California - Pérez-Campos, Xyoli; Clayton, Robert W.
Receiver functions from teleseismic events, recorded by stations around the Gulf of California,
are used to map the upper-mantle seismic discontinuities. We observe a mean transition zone
thickness comparable to the global average for most of the region. A low-velocity layer is
detected above the 410 discontinuity that varies in thickness along the Gulf of California. The
660 discontinuity shows complex waveforms south of latitude 30◦N as a result of the phase
change of garnet to perovskite. Within the transition zone, a complex behaviour of the receiver
functions is observed mainly at the southern end of the Gulf. The north–south variations of
this zone are likely associated...
Epeirogenic transients related to mantle lithosphere removal in the southern Sierra Nevada region, California: Part II. Implications of rock uplift and basin subsidence relations - Saleeby, J.; Saleeby, Z.; Le Pourhiet, L.
We investigate the putative Pliocene–Quaternary removal of mantle lithosphere from beneath the southern Sierra Nevada region using a synthesis of subsidence data from the Great Valley, and geomorphic relations across the Sierra Nevada. These findings are used to test the results and predictions of thermomechanical modeling of the lithosphere removal process that is specific to the Sierra Nevada, as presented in an accompanying paper referenced here as Part I. Our most successful thermomechanical model and the observational data that it explains are further bundled into an integrated physiographic evolution–geodynamic model for the three-dimensional epeirogenic deformation field that has affected mainly...