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Jacobs, A, Sandwell D, Fialko Y, Sichoix L.  2002.  The 1999 (M-w 7. 1) Hector Mine, California, earthquake: Near-field postseismic deformation from ERS interferometry. Bulletin of the Seismological Society of America. 92:1433-1442.   10.1785/0120000908   AbstractWebsite

Interferometric synthetic aperture radar (InSAR) data over the area of the Hector Mine earthquake (M-w 7.1, 16 October 1999) reveal postseismic deformation of several centimeters over a spatial scale of 0.5 to 50 km. We analyzed seven SAR acquisitions to form interferograms over four time periods after the event. The main deformations seen in the line-of-sight (LOS) displacement maps are a region of subsidence (60 mm LOS increase) on the northern end of the fault, a region of uplift (45 mm LOS decrease) located to the northeast of the primary fault bend, and a linear trough running along the main rupture having a depth of up to 15 mm and a width of about 2 km. We correlate these features with a double left-bending, right-lateral, strike-slip fault that exhibits contraction on the restraining side and extension along the releasing side of the fault bends. The temporal variations in the near-fault postseismic deformation are consistent with a characteristic time scale of 135 + 42 or - 25 days, which is similar to the relaxation times following the 1992 Landers earthquake. High gradients in the LOS displacements occur on the fault trace, consistent with afterslip on the earthquake rupture. We derive an afterslip model by inverting the LOS data from both the ascending and descending orbits. Our model indicates that much of the afterslip occurs at depths of less than 3 to 4 km.

Hearn, EH, Fialko Y.  2009.  Can compliant fault zones be used to measure absolute stresses in the upper crust? Journal of Geophysical Research-Solid Earth. 114   10.1029/2008jb005901   AbstractWebsite

Geodetic and seismic observations reveal long-lived zones with reduced elastic moduli along active crustal faults. These fault zones localize strain from nearby earthquakes, consistent with the response of a compliant, elastic layer. Fault zone trapped wave studies documented a small reduction in P and S wave velocities along the Johnson Valley Fault caused by the 1999 Hector Mine earthquake. This reduction presumably perturbed a permanent compliant structure associated with the fault. The inferred changes in the fault zone compliance may produce a measurable deformation in response to background (tectonic) stresses. This deformation should have the same sense as the background stress, rather than the coseismic stress change. Here we investigate how the observed deformation of compliant zones in the Mojave Desert can be used to constrain the fault zone structure and stresses in the upper crust. We find that gravitational contraction of the coseismically softened zones should cause centimeters of coseismic subsidence of both the compliant zones and the surrounding region, unless the compliant fault zones are shallow and narrow, or essentially incompressible. We prefer the latter interpretation because profiles of line of sight displacements across compliant zones cannot be fit by a narrow, shallow compliant zone. Strain of the Camp Rock and Pinto Mountain fault zones during the Hector Mine and Landers earthquakes suggests that background deviatoric stresses are broadly consistent with Mohr-Coulomb theory in the Mojave upper crust (with mu >= 0.7). Large uncertainties in Mojave compliant zone properties and geometry preclude more precise estimates of crustal stresses in this region. With improved imaging of the geometry and elastic properties of compliant zones, and with precise measurements of their strain in response to future earthquakes, the modeling approach we describe here may eventually provide robust estimates of absolute crustal stress.

Trugman, DT, Shearer PM, Borsa AA, Fialko Y.  2016.  A comparison of long-term changes in seismicity at The Geysers, Salton Sea, and Coso geothermal fields. Journal of Geophysical Research-Solid Earth. 121:225-247.   10.1002/2015jb012510   AbstractWebsite

Geothermal energy is an important source of renewable energy, yet its production is known to induce seismicity. Here we analyze seismicity at the three largest geothermal fields in California: The Geysers, Salton Sea, and Coso. We focus on resolving the temporal evolution of seismicity rates, which provides important observational constraints on how geothermal fields respond to natural and anthropogenic loading. We develop an iterative, regularized inversion procedure to partition the observed seismicity rate into two components: (1) the interaction rate due to earthquake-earthquake triggering and (2) the smoothly varying background rate controlled by other time-dependent stresses, including anthropogenic forcing. We apply our methodology to compare long-term changes in seismicity to monthly records of fluid injection and withdrawal. At The Geysers, we find that the background seismicity rate is highly correlated with fluid injection, with the mean rate increasing by approximately 50% and exhibiting strong seasonal fluctuations following construction of the Santa Rosa pipeline in 2003. In contrast, at both Salton Sea and Coso, the background seismicity rate has remained relatively stable since 1990, though both experience short-term rate fluctuations that are not obviously modulated by geothermal plant operation. We also observe significant temporal variations in Gutenberg-Richter b value, earthquake magnitude distribution, and earthquake depth distribution, providing further evidence for the dynamic evolution of stresses within these fields. The differing field-wide responses to fluid injection and withdrawal may reflect differences in in situ reservoir conditions and local tectonics, suggesting that a complex interplay of natural and anthropogenic stressing controls seismicity within California's geothermal fields.

Fialko, Y, Simons M, Agnew D.  2001.  The complete (3-D) surface displacement field in the epicentral area of the 1999 M(w)7.1 Hector Mine earthquake, California, from space geodetic observations. Geophysical Research Letters. 28:3063-3066.   10.1029/2001gl013174   AbstractWebsite

We use Interferometric Synthetic Aperture Radar (InSAR) data to derive continuous maps for three orthogonal components of the co-seismic surface displacement field due to the 1999 M-w 7.1 Hector Mine earthquake in southern California. Vertical and horizontal displacements are both predominantly antisymmetric with respect to the fault plane, consistent with predictions of linear elastic models of deformation for a strike-slip fault. Some deviations from symmetry apparent in the surface displacement data may result from complexity in the fault geometry.

Simons, M, Fialko Y, Rivera L.  2002.  Coseismic deformation from the 1999 M-w 7.1 Hector Mine, California, earthquake as inferred from InSAR and GPS observations. Bulletin of the Seismological Society of America. 92:1390-1402.   10.1785/0120000933   AbstractWebsite

We use interferometric synthetic aperture radar (InSAR) and Global Positioning System (GPS) observations to Investigate static deformation due to the 1999 M-w 7.1 Hector Mine earthquake, that occurred in the eastern California shear zone. Interferometric decorrelation, phase, and azimuth offset measurements indicate regions of surface and near-surface slip, which we use to constrain the geometry of surface rupture. The inferred geometry is spatially complex, with multiple strands. The southern third of the rupture zone consists of three subparallel segments extending about 20 km in length in a N45degreesW direction. The central segment is the simplest, with a single strand crossing the Bullion Mountains and a strike of N10degreesW. The northern third of the rupture zone is characterized by multiple splays, with directions subparallel to strikes in the southern and central. The average strike for the entire rupture is about N30degreesW. The interferograms indicate significant along-strike variations in strain which are consistent with variations in the ground-based slip measurements. Using a variable resolution data sampling routine to reduce the computational burden, we invert the InSAR and GPS data for the fault geometry and distribution of slip. We compare results from assuming an elastic half-space and a layered elastic space. Results from these two elastic models are similar, although the layered-space model predicts more slip at depth than does the half-space model. The layered model predicts a maximum coseismic slip of more than 5 In at a depth of 3 to 6 km. Contrary to preliminary reports, the northern part of the Hector Mine rupture accommodates the maximum slip. Our model predictions for the surface fault offset and total seismic moment agree with both field mapping results and recent seismic models. The inferred shallow slip deficit is enigmatic and may suggest that distributed inelastic yielding occurred in the uppermost few kilometers of the crust during or soon after the earthquake.

Tong, XP, Sandwell DT, Fialko Y.  2010.  Coseismic slip model of the 2008 Wenchuan earthquake derived from joint inversion of interferometric synthetic aperture radar, GPS, and field data. Journal of Geophysical Research-Solid Earth. 115   10.1029/2009jb006625   AbstractWebsite

We derived a coseismic slip model for the M(w) 7.9 2008 Wenchuan earthquake on the basis of radar line-of-sight displacements from ALOS interferograms, GPS vectors, and geological field data. Available interferometric synthetic aperture radar (InSAR) data provided a nearly complete coverage of the surface deformation along both ascending (fine beam mode) and descending orbits (ScanSAR to ScanSAR mode). The earthquake was modeled using four subfaults with variable geometry and dip to capture the simultaneous rupture of both the Beichuan fault and the Pengguan fault. Our model misfits show that the InSAR and GPS data are highly compatible; the combined inversion yields a 93% variance reduction. The best fit model has fault planes that rotate from shallow dip in the south (35 degrees) to nearly vertical dip toward the north (70 degrees). Our rupture model is complex with variations in both depth and rake along two major fault strands. In the southern segment of the Beichuan fault, the slip is mostly thrust (<13 m) and occurred principally in the upper 10 km of the crust; the rupture progressively transformed to right-lateral strike slip as it propagated northeast (with maximum offsets of 7 m). Our model suggests that most of the moment release was limited to the shallow part of the crust (depth less than 10 km). We did not find any "shallow slip deficit" in the slip depth distribution of this mixed mechanism earthquake. Aftershocks were primarily distributed below the section of the fault that ruptured coseismically.

Fialko, Y, Simons M.  2000.  Deformation and seismicity in the Coso geothermal area, Inyo County, California: Observations and modeling using satellite radar interferometry. Journal of Geophysical Research-Solid Earth. 105:21781-21793.   10.1029/2000jb900169   AbstractWebsite

Interferometric synthetic aperture radar (InSAR) data collected in the Coso geothermal area, eastern California, during 1993-1999 indicate ground subsidence over a similar to 50 km(2) region that approximately coincides with the production area of the Coso geothermal plant. The maximum subsidence rate in the peak of the anomaly is similar to 3.5 cm yr(-1), and the average volumetric rate of subsidence is of the order of 10(6) m(3) yr(-1). The radar interferograms reveal a complex deformation pattern, with at least two irregular subsidence peaks in the northern part of the anomaly and a region of relative uplift on the south. We invert the InSAR displacement data for the positions, geometry, and relative strengths of the deformation sources at depth using a nonlinear least squares minimization algorithm. We use elastic solutions for a prolate uniformly pressurized spheroidal cavity in a semi-infinite body as basis functions for our inversions. Source depths inferred from our simulations range from 1 to 3 km, which corresponds to the production depths of the Coso geothermal plant. Underpressures in the geothermal reservoir inferred from the inversion are of the order of 0.1-1 MPa (except a few abnormally high underpressures that are apparently biased toward the small source dimensions). Analysis of the InSAR data covering consecutive time intervals indicates that the depths and/or horizontal extent of the deformation sources may increase with time. This increase presumably reflects increasing volumes of the subsurface reservoir affected by the geothermal exploitation. We show that clusters of microearthquakes associated with the geothermal power operation may result from perturbations in the pore fluid pressure, as well as normal and shear stresses caused by the deflation of the geothermal reservoir.

Fialko, Y, Khazan Y, Simons M.  2001.  Deformation due to a pressurized horizontal circular crack in an elastic half-space, with applications to volcano geodesy. Geophysical Journal International. 146:181-190.   10.1046/j.1365-246X.2001.00452.x   AbstractWebsite

We consider deformation due to sill-like magma intrusions using a model of a horizontal circular crack in a semi-infinite elastic solid. We present exact expressions for vertical and horizontal displacements of the free surface of a half-space, and calculate surface displacements for a special case of a uniformly pressurized crack. We derive expressions for other observable geophysical parameters, such as the volume of a surface uplift/subsidence, and the corresponding volume change due to fluid injection/withdrawal at depth. We demonstrate that for essentially oblate (i.e. sill-like) source geometries the volume change at the source always equals the volume of the displaced material at the surface of a half-space. Our solutions compare favourably to a number of previously published approximate models. Surface deformation due to a 'point' crack (that is, a crack with a large depth-to-radius ratio) differs appreciably from that due to an isotropic point source ('Mogi model'). Geodetic inversions that employ only one component of deformation (either vertical or horizontal) are unlikely to resolve the overall geometry of subsurface deformation sources even in a simplest case of axisymmetric deformation. Measurements of a complete vector displacement field at the Earth's surface may help to constrain the depth and morphology of active magma reservoirs. However, our results indicate that differences in surface displacements due to various axisymmetric sources may be subtle. In particular, the sill-like and pluton-like magma chambers may give rise to differences in the ratio of maximum horizontal displacements to maximum vertical displacements (a parameter that is most indicative of the source geometry) that are less than 30 per cent. Given measurement errors in geodetic data, such differences may be hard to distinguish.

Fialko, Y, Sandwell D, Agnew D, Simons M, Shearer P, Minster B.  2002.  Deformation on nearby faults induced by the 1999 Hector Mine earthquake. Science. 297:1858-1862.   10.1126/science.1074671   AbstractWebsite

Interferometric Synthetic Aperture Radar observations of surface deformation due to the 1999 Hector Mine earthquake reveal motion on several nearby faults of the eastern California shear zone. We document both vertical and horizontal displacements of several millimeters to several centimeters across kilometer-wide zones centered on pre-existing faults. Portions of some faults experienced retrograde (that is, opposite to their long-term geologic slip) motion during or shortly after the earthquake. The observed deformation likely represents elastic response of compliant fault zones to the permanent co-seismic stress changes. The induced fault displacements imply decreases in the effective shear modulus within the kilometer-wide fault zones, indicating that the latter are mechanically distinct from the ambient crustal rocks.

Guterman, VG, Fialko YA, Khazan YM.  1996.  Dome structures above sill-like crustal intrusions: A quantitative model fo preseismic uplift. Part 2. Geofizicheskii Zhurnal. 18:62-69.
Guterman, VG, Fialko YA, Khazan YM.  1996.  Dome structures above sill-like crustal intrusions: A quantitative model fo preseismic uplift. Part I. Geofizicheskii Zhurnal. 18:35-43.
Takeuchi, CS, Fialko Y.  2012.  Dynamic models of interseismic deformation and stress transfer from plate motion to continental transform faults. Journal of Geophysical Research-Solid Earth. 117   10.1029/2011jb009056   AbstractWebsite

We present numerical models of earthquake cycles on a strike-slip fault that incorporate laboratory-derived power law rheologies with Arrhenius temperature dependence, viscous dissipation, conductive heat transfer, and far-field loading due to relative plate motion. We use these models to explore the evolution of stress, strain, and thermal regime on "geologic" timescales (similar to 10(6)-10(7) years), as well as on timescales of the order of the earthquake recurrence (similar to 10(2) years). Strain localization in the viscoelastic medium results from thermomechanical coupling and power law dependence of strain rate on stress. For conditions corresponding to the San Andreas fault (SAF), the predicted width of the shear zone in the lower crust is similar to 3-5 km; this shear zone accommodates more than 50% of the far-field plate motion. Coupled thermomechanical models predict a single-layer lithosphere in case of "dry" composition of the lower crust and upper mantle, and a "jelly sandwich" lithosphere in case of "wet" composition. Deviatoric stress in the lithosphere in our models is relatively insensitive to the water content, the far-field loading rate, and the fault strength and is of the order of 10(2) MPa. Thermomechanical coupling gives rise to an inverse correlation between the fault slip rate and the ductile strength of the lithosphere. We show that our models are broadly consistent with geodetic and heat flow constrains from the SAF in Northern California. Models suggest that the regionally elevated heat flow around the SAF may be at least in part due to viscous dissipation in the ductile part of the lithosphere.

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.

Fialko, Y, Simons M, Khazan Y.  2001.  Finite source modelling of magmatic unrest in Socorro, New Mexico, and Long Valley, California. Geophysical Journal International. 146:191-200.   10.1046/j.1365-246X.2001.00453.x   AbstractWebsite

We investigate surface deformation associated with currently active crustal magma bodies in Socorro, New Mexico, and Long Valley, California, USA. We invert available geodetic data from these locations to constrain the overall geometry and dynamics of the inferred deformation sources at depth. Our brst-fitting model for the Socorro magma body is a sill with a depth of 19 km, an effective diameter of 70 km and a rate of increase in the excess magma pressure of 0.6 kPa yr(-1). We show that the corresponding volumetric inflation rate is similar to6 x 10(-3) km(3) yr(-1), which is considerably less than previously suggested. The measured inflation rate of the Socorro magma body may result from a steady influx of magma from a deep source, or a volume increase associated with melting of the magma chamber roof (i.e. crustal anatexis). In the latter case, the most recent major injection of mantle-derived melts into the middle crust beneath Socorro map have occurred within the last several tens to several hundreds of years. The Synthetic Interferometric Aperture Radar (InSAR) data collected in the area of the Long Valley caldera, CA, between June 1996 and July 1998 reveal an intracaldera uplift with a maximum amplitude of similar to 11 cm and a volume of 3.5 x 10(-2) km(3). Modelling of the InSAR data suggests that the observed deformation might be due to either a sill-like magma body at a depth of similar to 12 km or a pluton-like magma body at a depth of similar to8 km beneath the resurgent dome. Assuming that the caldera fill deforms as an isotropic linear elastic solid, a joint inversion of the InSAR data and two-colons laser geodimeter data (which provide independent constraints on horizontal displacements at the surface) suggests that the inferred magma chamber is a steeply dipping prolate spheroid with a depth of 7-9 km and an aspect ratio in excess of 2:1. Our results highlight the need for large radar look angles and multiple look directions in future InSAR missions.

Barbot, S, Fialko Y.  2010.  Fourier-domain Green's function for an elastic semi-infinite solid under gravity, with applications to earthquake and volcano deformation. Geophysical Journal International. 182:568-582.   10.1111/j.1365-246X.2010.04655.x   AbstractWebsite

We present an analytic solution in the Fourier domain for an elastic deformation in a semi-infinite solid due to an arbitrary surface traction. We generalize the so-called Boussinesq's and Cerruti's problems to include a restoring buoyancy boundary condition at the surface. Buoyancy due to a large density contrast at the Earth's surface is an approximation to the full effect of gravity that neglects the perturbation of the gravitational potential and the change in density in the interior. Using the perturbation method, and assuming that the effect of gravity is small compared to the elastic deformation, we derive an approximation in the space domain to the Boussinesq's problem that accounts for a buoyancy boundary condition at the surface. The Fourier- and space-domain solutions are shown to be in good agreement. Numerous problems of elastostatic or quasi-static time-dependent deformation relevant to faulting in the Earth's interior (including inelastic deformation) can be modelled using equivalent body forces and surface tractions. Solving the governing equations with the elastic Green's function in the space domain can be impractical as the body force can be distributed over a large volume. We present a computationally efficient method to evaluate the elastic deformation in a 3-D half space due to the presence of an arbitrary distribution of internal forces and tractions at the surface of the half space. We first evaluate the elastic deformation in a periodic Cartesian volume in the Fourier domain, then use the analytic solutions to the generalized Boussinesq's and Cerruti's problems to satisfy the prescribed mixed boundary condition at the surface. We show some applications for magmatic intrusions and faulting. This approach can be used to solve elastostatic problems involving spatially heterogeneous elastic properties (by employing a homogenization method) and time-dependent problems such as non-linear viscoelastic relaxation, poroelastic rebound and non-steady fault creep under the assumption of spatially homogeneous elastic properties.

Fialko, Y.  2007.  Fracture and Frictional Mechanics - Theory. Treatise on geophysics. 4( Schubert G, Ed.)., Amsterdam ; Boston: Elsevier
Khazan, YM, Fialko YA.  1995.  Fracture Criteria at the Tip of Fluid-Driven Cracks in the Earth. Geophysical Research Letters. 22:2541-2544.   10.1029/95gl02547   AbstractWebsite

The effect of high confining pressure on fluid-filled crack growth is considered. Exact solutions are given for a two-dimensional horizontal crack in an infinite elastic body using the approximation of Dugdale-Barenblatt (DB) model. It is shown that for equilibrium cracks (i.e. for cracks on the verge of propagation) the large-scale crack characteristics, such as fluid overpressure, apparent fracture toughness, maximum opening of the crack and crack volume, grow with increase of confining pressure. These effects result from a pressure induced fracture resistance (PIFR). If basic parameters of the DB model (tensile strength and critical crack opening displacement) are independent of confining pressure then PIFR dominates over intrinsic rock strength starting from quite shallow depth (tens to hundreds of meters).

Mitchell, EK, Fialko Y, Brown KM.  2015.  Frictional properties of gabbro at conditions corresponding to slow slip events in subduction zones. Geochemistry Geophysics Geosystems. 16:4006-4020.   10.1002/2015gc006093   AbstractWebsite

We conducted a series of experiments to explore the rate and state frictional properties of gabbro at conditions thought to be representative of slow slip events (SSEs) in subduction zones. The experiments were conducted using a heated direct shear apparatus. We tested both solid and simulated gouge samples at low effective normal stress (5-30 MPa) over a broad range of temperatures (20-600 degrees C) under dry and hydrated conditions. In tests performed on dry solid samples, we observed stable sliding at low temperatures (20-150 degrees C), stick slip at high temperatures (350-600 degrees C), and a transitional "episodic slow slip'' behavior at intermediate temperatures (200-300 degrees C). In tests performed on dry gouge samples, we observed stable sliding at all temperatures. Under hydrated conditions, the gouge samples exhibited episodic slow slip and stick-slip behavior at temperatures between 300 and 500 degrees C. Our results show a decrease in the rate parameter (a - b) with temperature for both solid and gouge samples; friction transitions from velocity strengthening to velocity weakening at temperature of about 150 degrees C for both solid and gouge samples. We do not observe transition to velocity-strengthening friction at the high end of the tested temperature range. Our results suggest that the occurrence of slow slip events and the downdip limit of the seismogenic zone on subduction megathrusts cannot be solely explained by the temperature dependence of frictional properties of gabbro. Further experimental studies are needed to evaluate the effects of water fugacity and compositional heterogeneity (e. g., the presence of phyllosilicates) on frictional stability of subduction megathrusts.

Fialko, Y, Khazan Y.  2005.  Fusion by earthquake fault friction: Stick or slip? Journal of Geophysical Research-Solid Earth. 110   10.1029/2005jb003869   AbstractWebsite

[1] Field observations of pseudotachylites and experimental studies of high-speed friction indicate that melting on a slipping interface may significantly affect the magnitude of shear stresses resisting slip. We investigate the effects of rock melting on the dynamic friction using theoretical models of shear heating that couple heat transfer, thermodynamics of phase transitions, and fluid mechanics. Results of laboratory experiments conducted at high ( order of m/s) slip velocities but low ( order of MPa) normal stresses suggest that the onset of frictional melting may give rise to substantial increases in the effective fault strength, presumably due to viscous effects. However, extrapolation of the modeling results to in situ conditions suggests that the efficiency of viscous braking is significantly reduced under high normal and shear stresses. When transient increases in the dynamic fault strength due to fusion are not sufficient to inhibit slip, decreases in the effective melt viscosity due to shear heating and melting of clasts drastically decrease the dynamic friction, resulting in a nearly complete stress drop ("thermal runaway''). The amount of energy dissipation associated with the formation of pseudotachylites is governed by the temperature dependence of melt viscosity and the average clast size in the fault gouge prior to melting. Clasts from a coarse-grained gouge have lower chances of survival in a pseudotachylite due to a higher likelihood of nonequilibrium overheating. The maximum temperature and energy dissipation attainable on the fault surface are ultimately limited by either the rock solidus ( via viscous braking, and slip arrest) or liquidus ( via thermal runaway and vanishing resistance to sliding). Our modeling results indicate that the thermally activated fault strengthening and rupture arrest are unlikely to occur in most mafic protoliths but might be relevant for quartz-rich rocks, especially at shallow (< 5 - 7 km) depths where the driving shear stress is relatively low.