Repository of works by Caltech published authors.
Group = Caltech Tectonics Observatory
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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...
Microseismicity and seismotectonics of the South Caspian Lowlands, NE Iran - Nemati, Majid; Hollingsworth, James; Zhan, Zhongwen; Bolourchi, Mohammad Javad; Talebian, Morteza
This paper is concerned with the microseismicity and seismotectonics of the eastern South Caspian Sea region, where the East Alborz mountains descend to meet the South Caspian Lowlands of NE Iran. To better understand the present-day tectonics and seismicity of this region, which includes the cities of Gorgan and Gonbad-e-Qabus (combined population 500 000), we installed a temporary local seismic network across the area for 6 months between 2009 and 2010. We analysed the seismicity and focal mechanisms together with data from the permanent networks of the Institute of Geophysics, University of Tehran (IGUT) and the International Institute of Earthquake...
The lack of correlation between flat slabs and bathymetric
impactors in South America - Skinner, Steven M.; Clayton, Robert W.
Flat slab subduction has been attributed to various causes including mantle wedge dynamics, overriding by the upper plate, age of the subducting plate, and subduction of anomalously thick oceanic crust. One often favored explanation for flat slabs is the subduction of buoyant features on the oceanic plate in the form of an aseismic-ridge or oceanic plateau. We show through plate tectonic reconstructions of the Marquesas, Tuamotu, and Austral plateau, assuming that features on the conjugate plate can be used as proxies for subducted bathymetric anomalies, that there is very little correlation between the subduction of such anomalies and historic zones...
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...
Application of titanium-in-quartz thermobarometry to greenschist facies veins and recrystallized quartzites in the Hsüehshan range, Taiwan - Kidder, S.; Avouac, J.-P.; Chan, Y.-C.
The accuracy, reliability and best practises of Ti-in-quartz thermobarometry (TitaniQ) in greenschist facies rocks have not been established. To address these issues, we measured Ti concentrations in rutile-bearing samples of moderately deformed, partially recrystallized quartzite and vein quartz from the Hsüehshan range, Taiwan. The spread of Ti concentrations of recrystallized grains in quartzite correlates with recrystallized grain size. Recrystallized quartz (grain size ~100–200 μm) that formed during early deformation within the biotite stability field shows a marked increase in intermediate Ti-concentration grains (~1–10 ppm) relative to detrital porphyroclasts (Ti ~0.1–200 ppm). Fine recrystallized quartz (~5% of the samples by area,...
New Radar Interferometric Time
Series Analysis Toolbox Released - Agram, P. S.; Jolivet, R.; Riel, B.; Lin, Y. N.; Simons, M.; Hetland, E.; Doin, M.-P.; Lasserre, C.
Interferometric synthetic aperture radar (InSAR) has become an important geodetic
tool for measuring deformation of Earth’s surface due to various geophysical phenomena,
including slip on earthquake faults, subsurface migration of magma, slow‐moving
landslides, movement of shallow crustal fluids (e.g., water and oil), and glacier flow.
Airborne and spaceborne synthetic aperture radar (SAR) instruments transmit microwaves
toward Earth’s surface and detect the returning reflected waves. The phase of the
returned wave depends on the distance between the satellite and the surface, but it is
also altered by atmospheric and other effects. InSAR provides measurements of surface
deformation by combining amplitude and phase information from two SAR images of
Plate tectonic reconstructions with continuously closing plates - Gurnis, Michael; Turner, Mark; Zahirovic, Sabin; DiCaprio, Lydia; Spasojevic, Sonja; Müller, R. Dietmar; Boyden, James; Seton, Maria; Manea, Vlad Constantin; Bower, Dan J.
We present a new algorithm for modeling a self-consistent set of global plate polygons. Each plate polygon is composed of a finite list of plate margins, all with different Euler poles. We introduce a "continuously closed plate" (CCP), such that, as each margin moves independently, the plate polygon remains closed geometrically as a function of time. This method solves emerging needs in computational geodynamics to combine kinematic with dynamic models. Because they have polygons that are too widely spaced in time and have inconsistent motions between margins and plates, traditional global plate tectonic reconstructions have become inadequate for geodynamics. The...