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Barbot, S, Fialko Y, Sandwell D.  2008.  Effect of a compliant fault zone on the inferred earthquake slip distribution. Journal of Geophysical Research-Solid Earth. 113   10.1029/2007jb005256   AbstractWebsite

We present a new semi-analytic method to evaluate the deformation due to a screw dislocation in arbitrarily heterogeneous and/or anisotropic elastic half plane. The method employs integral transformations to reduce the governing partial differential equations to the integral Fredholm equation of the second kind. Dislocation sources, as well as spatial perturbations in the elastic properties are modeled using equivalent body forces. The solution to the Fredholm equation is obtained in the Fourier domain using a method of successive over-relaxation, and is mapped into the spatial domain using the inverse Fast Fourier Transform. We apply this method to investigate the effect of a soft damage zone around an earthquake fault on the co-seismic displacement field, and on the earthquake slip distribution inferred from inversions of geodetic data. In the presence of a kilometer-wide damage zone with a reduction of the effective shear modulus of a factor of 2, inversions that assume a laterally homogeneous model tend to underestimate the amount of slip in the middle of the seismogenic layer by as much as 20%. This bias may accentuate the inferred maxima in the seismic moment release at depth between 3-6 km suggested by previous studies of large strike-slip earthquakes.

Gonzalez-Ortega, A, Fialko Y, Sandwell D, Nava-Pichardo FA, Fletcher J, Gonzalez-Garcia J, Lipovsky B, Floyd M, Funning G.  2014.  El Mayor-Cucapah ( M-w 7.2) earthquake: Early near-field postseismic deformation from InSAR and GPS observations. Journal of Geophysical Research-Solid Earth. 119:1482-1497.   10.1002/2013jb010193   AbstractWebsite

El Mayor-Cucapah earthquake occurred on 4 April 2010 in northeastern Baja California just south of the U.S.-Mexico border. The earthquake ruptured several previously mapped faults, as well as some unidentified ones, including the Pescadores, Borrego, Paso Inferior and Paso Superior faults in the Sierra Cucapah, and the Indiviso fault in the Mexicali Valley and Colorado River Delta. We conducted several Global Positioning System (GPS) campaign surveys of preexisting and newly established benchmarks within 30km of the earthquake rupture. Most of the benchmarks were occupied within days after the earthquake, allowing us to capture the very early postseismic transient motions. The GPS data show postseismic displacements in the same direction as the coseismic displacements; time series indicate a gradual decay in postseismic velocities with characteristic time scales of 669days and 203days, assuming exponential and logarithmic decay, respectively. We also analyzed interferometric synthetic aperture radar (InSAR) data from the Envisat and ALOS satellites. The main deformation features seen in the line-of-sight displacement maps indicate subsidence concentrated in the southern and northern parts of the main rupture, in particular at the Indiviso fault, at the Laguna Salada basin, and at the Paso Superior fault. We show that the near-field GPS and InSAR observations over a time period of 5months after the earthquake can be explained by a combination of afterslip, fault zone contraction, and a possible minor contribution of poroelastic rebound. Far-field data require an additional mechanism, most likely viscoelastic relaxation in the ductile substrate.

Fialko, Y, Rivera L, Kanamori H.  2005.  Estimate of differential stress in the upper crust from variations in topography and strike along the San Andreas fault. Geophysical Journal International. 160:527-532.   10.1111/j.1365-246X.2004.02511.x   AbstractWebsite

The major bends of the San Andreas fault in California are associated with significant variations in the along-fault topography. The topography-induced perturbations in the intermediate principal stress may result in the rotation of the fault with respect to the maximum compression axis provided that the fault is non-vertical, and the slip is horizontal. The progressive fault rotation may produce additional topography via thrust faulting in the adjacent crust, resulting in a positive feedback. The observed rotation of the fault plane due to the along-fault variations in topography is used to infer the magnitude of the in situ differential stress. Our results suggest that the average differential stress in the upper crust around the San Andreas fault is of the order of 50 MPa, implying that the effective fault strength is about a factor of two lower than predictions based on Byerlee's law and the assumption of hydrostatic pore pressure.

Fialko, Y, Simons M.  2001.  Evidence for on-going inflation of the Socorro magma body, New Mexico, from interferometric synthetic aperture radar imaging. Geophysical Research Letters. 28:3549-3552.   10.1029/2001gl013318   AbstractWebsite

Interferometric synthetic aperture radar (In-SAR) imaging of the central Rio Grande rift (New Mexico, USA) during 1992-1999 reveals a crustal uplift of several centimeters that spatially coincides with the seismologically determined outline of the Socorro magma body, one of the largest currently active magma intrusions in the Earth's continental crust. Modeling of interferograms shows that the observed deformation may be due to elastic opening of a sill-like intrusion at a rate of a few millimeters per year. Despite an apparent constancy of the geodetically determined uplift rate, thermodynamic arguments suggest that it is unlikely that the Socorro magma body has formed via steady state elastic inflation.

Fialko, Y.  2004.  Evidence of fluid-filled upper crust from observations of postseismic deformation due to the 1992 M(w)7.3 Landers earthquake. Journal of Geophysical Research-Solid Earth. 109   10.1029/2004jb002985   AbstractWebsite

Postseismic deformation due to the 1992 M(w)7.3 Landers, southern California, earthquake is investigated using the entire catalog of the ERS synthetic aperture radar (SAR) data, and GPS measurements made between 1992 and 1999. The stacked interferometric SAR (InSAR) data spanning the time period of 7 years between the Landers and the Hector Mine earthquakes reveal a transient postseismic deformation with a characteristic decay time of several years. The horizontal displacements measured with GPS exhibit somewhat smaller decay times of 1-2 years. I use a slip model of the Landers earthquake that fits all available geodetic data [Fialko, 2004] to calculate and compare permanent postseismic displacements due to viscoelastic and poroelastic relaxation. Viscoelastic models assuming weak mantle or lower crust do not agree with the InSAR data in the limit of complete relaxation, implying large (>10 years) relaxation times, essentially nonlinear rheology, or an appreciable yield strength of the lower lithosphere. A combination of poroelastic relaxation above the brittle-ductile transition and localized shear deformation on and below the Landers rupture is able to explain most of the available geodetic data. The InSAR data suggest that pore fluids and interconnected pore space are ubiquitously present throughout the seismogenic layer up to depth of 15 km or greater. The effective hydraulic diffusivity of the upper crust inferred from the kinetics of surface deformation is of the order of 0.1-1 m(2)/s, consistent with the laboratory, field, and deep borehole measurements. The post-Landers geodetic data suggest that discrete narrow fault zones extend into the lower crust and perhaps the uppermost mantle, thus lending support to a "block tectonics'' model of the Eastern California Shear Zone.

Ujiie, K, Tsutsumi A, Fialko Y, Yamaguchi H.  2009.  Experimental investigation of frictional melting of argillite at high slip rates: Implications for seismic slip in subduction-accretion complexes. Journal of Geophysical Research-Solid Earth. 114   10.1029/2008jb006165   AbstractWebsite

Discovery of pseudotachylytes from exhumed accretionary complexes indicates that frictional melting occurred along illite-rich, argillite-derived slip zones during subduction earthquakes. We conducted high-velocity friction experiments on argillite at a slip rate of 1.13 m/s and normal stresses of 2.67-13.33 MPa. Experiments show slip weakening followed by slip strengthening. Slip weakening is associated with the formation and shearing of low-viscosity melt patches. The subsequent slip strengthening occurred despite the reduction in shear strain rate due to the growth (thickening) of melt layer, suggesting that the viscosity of melt layer increased with slip. Microstructural and chemical analyses suggest that the viscosity increase during the slip strengthening is not due to an increase in the volume fraction of solid grains and bubbles in the melt layer but could be caused primarily by dehydration of the melt layer. Our experimental results suggest that viscous braking can be efficient at shallow depths of subduction-accretion complexes if substantial melt dehydration occurs on a timescale of seismic slip. Melt lubrication can possibly occur at greater depths within subduction-accretion complexes because the ratio of viscous shear to normal stress decreases with depth. Argillite-derived natural pseudotachylytes formed at seismogenic depths in subduction-accretion complexes are more hydrous than the experimentally generated pseudotachylytes and may be evidence of nearly complete stress drop.