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Mitchell, EK, Fialko Y, Brown KM.  2016.  Velocity-weakening behavior of Westerly granite at temperature up to 600 degrees C. Journal of Geophysical Research-Solid Earth. 121:6932-6946.   10.1002/2016jb013081   AbstractWebsite

The deep limit to seismicity in continental crust is believed to be controlled by a transition from velocity-weakening to velocity-strengthening friction based on experimental measurements of the rate dependence of friction at different temperatures. Available experimental data on granite suggest a transition to stable creep at about 350 degrees C (approximate to 15km depth). Here we present results from unconfined experiments on Westerly granite at both dry and hydrated conditions that show increasingly unstable slip (velocity-weakening behavior) at temperature up to 600 degrees C. A comparison of previously published experimental results with those presented in this study suggests that the rate and state friction parameters strongly depend on normal stress and pore pressure at high (>400 degrees C) temperature, which may help explain regional variations in the depth distribution of earthquakes in continental crust. Temperature dependence of the rate and state friction parameters may also contribute to strong dynamic weakening observed in high-speed friction experiments on crystalline rocks such as granite and gabbro.

S
Samsonov, SV, Feng WP, Fialko Y.  2017.  Subsidence at Cerro Prieto Geothermal Field and postseismic slip along the Indiviso fault from 2011 to 2016 RADARSAT-2 DInSAR time series analysis. Geophysical Research Letters. 44:2716-2724.   10.1002/2017gl072690   AbstractWebsite

We present RADARSAT-2 Differential Interferometric Synthetic Aperture Radar (DInSAR) observations of deformation due to fluid extraction at the Cerro Prieto Geothermal Field (CPGF) and afterslip on the 2010 M7.2 El Mayor-Cucapah (EMC) earthquake rupture during 2011-2016. Advanced multidimensional time series analysis reveals subsidence at the CPGF with the maximum rate greater than 100mm/yr accompanied by horizontal motion (radial contraction) at a rate greater than 30mm/yr. During the same time period, more than 30mm of surface creep occurred on the Indiviso fault ruptured by the EMC earthquake. We performed inversions of DInSAR data to estimate the rate of volume changes at depth due to the geothermal production at the CPGF and the distribution of afterslip on the Indiviso fault. The maximum coseismic slip due to the EMC earthquake correlates with the Coulomb stress changes on the Indiviso fault due to fluid extraction at the CPGF. Afterslip occurs on the periphery of maximum coseismic slip areas. Time series analysis indicates that afterslip still occurs 6years after the earthquake.

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Jiang, JL, Fialko Y.  2016.  Reconciling seismicity and geodetic locking depths on the Anza section of the San Jacinto fault. Geophysical Research Letters. 43:10663-10671.   10.1002/2016gl071113   AbstractWebsite

Observations from the Anza section of the San Jacinto Fault in Southern California reveal that microseismicity extends to depths of 15-18km, while the geodetically determined locking depth is less than similar to 10km. This contrasts with observations from other major faults in the region and also with predictions of fault models assuming a simple layered distribution of frictional properties with depth. We suggest that an anomalously shallow geodetic fault locking may result from a transition zone at the bottom of seismogenic layer with spatially heterogeneous frictional properties. Numerical models of faults that incorporate stochastic heterogeneity at transitional depths successfully reproduce the observed depth relation between seismicity and geodetic locking, as well as complex spatiotemporal patterns of microseismicity with relatively scarce repeating earthquakes. Our models predict propagation of large earthquakes to the bottom of the transition zone, and ubiquitous aseismic transients below the locked zone, potentially observable using high-precision geodetic techniques.