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ABSTRACT: Earthquakes radiate from slip on discrete faults, but also commonly involve distributed deformation within a broader fault zone, especially near the surface. Variations in rock strain during an earthquake are caused by heterogeneity in the elastic stress before the earthquake, by variable material properties and geometry of the fault zones, and by dynamic processes during the rupture. Stress changes due to the earthquake slip, both dynamic and static, have long been thought to cause dilatancy in the fault zone that recovers after the earthquake. Decreases in the velocity of seismic waves passing through the fault zone due to coseismic dilatancy have been observed followed by postseismic seismic velocity increases during healing. Dilatancy and its recovery have not previously been observed geodetically. Here we use interferometric analysis of synthetic aperture radar images to measure postseismic surface deformation after the 2003 Bam, Iran, earthquake and show reversal of coseismic dilatancy in the shallow fault zone that causes subsidence of the surface. This compaction of the fault zone is directly above the patch of greatest coseismic slip at depth. The dilatancy and compaction probably reflects distributed shear and damage to the material during the earthquake that heals afterwards. Coseismic and postseismic deformation spread through a fault zone volume may resolve the paradox of shallow slip deficits for some strike-slip fault ruptures.
Nature 04/2009; 458(7234):64-8. · 36.28 Impact Factor
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ABSTRACT: The Pisco earthquake (Mw 8.0; 2007 August 15) occurred offshore of Peru's southern coast at the subduction interface between the Nazca and South American plates. It ruptured a previously identified seismic gap along the Peruvian margin. We use Wide Swath InSAR observations acquired by the Envisat satellite in descending and ascending orbits to constrain coseismic slip distribution of this subduction earthquake. The data show movement of the coastal regions by as much as 85 cm in the line-of-sight of the satellite. Distributed-slip model indicates that the coseismic slip reaches values of about 5.5 m at a depth of ∼18–20 km. The slip is confined to less than 40 km depth, with most of the moment release located on the shallow parts of the interface above 30 km depth. The region with maximum coseismic slip in the InSAR model is located offshore, close to the seismic moment centroid location. The geodetic estimate of seismic moment is 1.23 × 1021 Nm (Mw 8.06), consistent with seismic estimates. The slip model inferred from the InSAR observations suggests that the Pisco earthquake ruptured only a portion of the seismic gap zone in Peru between 13.5° S and 14.5° S, hence there is still a significant seismic gap to the south of the 2007 event that has not experienced a large earthquake since at least 1687.
Geophysical Journal International 01/2008; 174(3):842-848. · 2.42 Impact Factor
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ABSTRACT: Only 87 days after the M w 7.5, 17 August 1999 I ˙ zmit earthquake, the Düzce earthquake ruptured a ca. 40-km-long adjoining strand of the North Anatolian fault (NAF) system to the east. We used displacements of 50 Global Positioning System (GPS) sites together with interferometric synthetic aperture radar (InSAR) range-change data spanning the event to estimate the geometry and slip distribution of the coseismic rupture. Postseismic deformation transients from the Düzce earth-quake and the preceding I ˙ zmit event that are included in some of the measurements are corrected for using dislocation models fit to GPS data spanning the various time periods. Nonlinear inversions for fault geometry indicate that the rupture occurred on a ca. 54 north-dipping oblique normal, right-lateral fault. Distributed-slip inver-sions indicate maximum strike slip near the center of the Düzce fault close to the earthquake hypocenter. Slip magnitude and depth of faulting decrease to the west and east of the hypocenter. Both GPS and InSAR data suggest that normal slip is restricted to the shallow portion of the rupture. The Düzce earthquake had the highest slip-to-rupture-length ratio of any historic earthquake along the NAF.
Bulletin of the Seismological Society of America 03/2002; 92:161-171. · 1.70 Impact Factor
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ABSTRACT: The Hayward fault slips in large earthquakes and by aseismic creep observed along its surface trace. Dislocation models of the surface deformation adjacent to the Hayward fault measured with the global positioning system and interferometric synthetic aperture radar favor creep at similar to 7 millimeters per year to the bottom of the seismogenic zone along a similar to 20-kilometer-long northern fault segment, Microearthquakes with the same waveform repeatedly occur at 4- to 10-kilometer depths and indicate deep creep at 5 to 7 millimeters per year. The difference between current creep rates and the long-term slip rate of similar to 10 millimeters per year can be reconciled in a mechanical model of a freely slipping northern Hayward fault adjacent to the locked 1868 earthquake rupture, which brake the southern 40 to 50 kilometers of the fault. The potential for a major independent earthquake of the northern Hayward fault might be Less than previously thought.
Science 08/2000; 289(5482):1178-1182. · 31.20 Impact Factor
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ABSTRACT: Synthetic aperture radar interferometry (InSAR) from Earth- orbiting spacecraft provides a new tool to map global topography and deformation of the Earth's surface. Radar images taken from slightly different viewing directions allow the construction of digital elevation models of meter-scale accuracy. These data sets aid in the analysis and interpretation of tectonic and volcanic landscapes. If the Earth's surface deformed between two radar image acquisitions, a map of the surface displacement with tens-of-meters resolution and subcentimeter accuracy can be constructed. This review gives a basic overview of InSAR for Earth scientists and presents a selection of geologic applications that demonstrate the unique capabilities of InSAR for mapping the topography and deformation of the Earth.
Annual Review of Earth and Planetary Sciences 01/2000; 28:169-209. · 7.23 Impact Factor
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ABSTRACT: For 3-5 years following the 1989 M=7.1 Loma Prieta earthquake, creep along the southern Hayward fault, California, slowed or ceased. Slip apparently resumed pre-earthquake patterns by 1994 except for a locked ~3-km-long segment at the southern fault tip, that had consistently slipped at ~9 mm/yr before 1989. We use repeated Interferometric Synthetic Aperture Radar (IFSAR) measurements to map active deformation along the Hayward fault while slip rates recovered between 1992 and 1995. Assuming pure strike slip, 1992-to-1995 slip rates estimated from IFSAR range changes are generally consistent with creepmeter and alignment array measurements along much of the fault and confirm the temporary locking of the southernmost fault segment. However, along ~6 km of the Fremont segment IFSAR slip estimates of ~16 mm/yr are at least twice of those measured in the field. Transient vertical slip (northeast side up) of 2-3 mm/yr near the southern tip of the creep patch could explain this observation. First-order boundary element models of a vertical frictionless fault in an elastic half space predict some, but not all of the inferred vertical slip.
Geology 01/1998; 26:559–562. · 3.61 Impact Factor
