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Satellite synthetic aperture radar (SAR) interferometry shows that the magnitude 7.6 Manyi earthquake of 8 November 1997 produced a 170-kilometer-long surface break with up to 7 meters of left-lateral slip, reactivating a N76 degrees E quaternary fault in western Tibet. The radar interferometric map reveals asymmetric, along-strike displacement profiles between the two sides of the surface rupture, a pattern that cannot be explained with linear elastic theory. This observation suggests that the elastic moduli of the crust in tension and in compression are different because of the presence of cracks in the crust at shallow depth. A model indicates that a ratio of 2 between compressive and tensile elastic moduli can account for the observed asymmetry, a ratio that is consistent with laboratory and borehole measurements.

[1] The 14 November 2001, M w = 7.8, Kokoxili earthquake ruptured more than 400 km of the westernmost stretch of the left-lateral Kunlun fault in northern Tibet. Interferometric synthetic aperture radar data from descending orbits, along four adjacent tracks covering almost the entire rupture, and 1-m pixel Ikonos satellite images are used to map the rupture geometry and the surface displacements produced by the event.Interferograms are then inverted to solve for coseismic slip on the fault at depth. The radar data show that the rupture connected the Heituo fault, where the earthquake initiated, to the main Kunlun fault, cutting across a pull-apart trough in between the two strike-slip faults. The fault model includes two vertical sections extending to a depth of 20 km and discretized into 5 km  5 km patches. Using a nonnegative least squares method that includes an appropriate degree of smoothing, we solve for the left-lateral slip on each fault patch. Our solution shows that the largest slip occurred at depths between 0 and 5 km, reaching '8 m in two areas, 200 and 250 km east of the earthquake epicenter. Significant slip took place below 10 km at both ends of the rupture. Slip appears to have been highly variable along the fault, defining six sections of major moment release. These sections correspond to six subsegments of the Kunlun fault system, defined from the surface morphology of the fault. This suggests that fault geometry exerted a predominant influence on controlling the rupture propagation.

We use global positioning system (GPS) geodesy and synthetic aperture radar (SAR) interferometry to distinguish between interseismic strain accumulation and anthropogenic motion in metropolitan Los Angeles. We establish a relationship between horizontal and vertical seasonal oscillations of the Santa Ana aquifer, use this relationship to infer cumulative horizontal anthropogenic motions from cumulative vertical motions caused by water and oil resource management, and estimate horizontal interseismic velocities corrected for anthropogenic effects. Vertical anthropogenic rates from 1992 to 1999 are slower than 3 mm yr−1 in the Santa Ana and San Gabriel aquifers and faster than 5 mm yr−1 in the Chino aquifer and in many oil fields. Inferred horizontal anthropogenic velocities are faster than 1 mm yr−1 at 18 of 46 GPS sites. Northern metropolitan Los Angeles is contracting, with the 25 km south of the San Gabriel Mountains shortening at 4.5 ± 1 mm yr−1 (95% confidence limits). The thrust fault in an elastic edge dislocation model of the observed strain is creeping at 9 ± 2 mm yr−1 beneath and north of a position 6 ± 2 km deep and 8 ± 8 km north of downtown Los Angeles. The model fault is near the Los Angeles segment of the Puente Hills thrust but south of the Sante Fe Springs segment of the thrust. Disagreement between the 6 km locking depth in the model and the 15 km seismogenic depth inferred from earthquakes suggests that the elastic continuum model may be unsatisfactory; models with different stiffnesses of sedimentary basin and crystalline basement must be investigated.

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