Coseismic deformation of the 2001 M_w = 7.8 Kokoxili earthquake in Tibet, measured by synthetic aperture radar interferometry

Abstract

[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.

Deeper penetration of large earthquakes on seismically quiescent faults

“…The slip model constrained by InSAR measurements (53) suggests that while most slip occurs within the upper 10 km, significant slip penetrates below 10 km near the rupture end (Fig. S7).…”

Crustal–lithospheric structure and continental extrusion of Tibet

“…Recent large earthquakes on this fault include the M w 8.1 Kokoxili event, which ruptured a 300 km portion of the western end of the fault in 2001 (Lasserre et al 2005), and two earlier earthquakes along the central segment in 1963 (M w 7.1) and 1937 (M w 7.5). Therefore the central and western segments of the fault have had at least four large earthquakes in the past century whereas the eastern segment appears to have had little historical seismicity (Kirby et al 2007).…”

3-D coseismic displacement field of the 2005 Kashmir earthquake inferred from satellite radar imagery

“…This process is recursively executed until the size of the quadrant equals to a given minimum. In this study, we only use the data in a 110 × 90-km box around the fault, and the pixels closer than 1 km to the fault are eliminated to take into account uncertainties on the fault location (Lasserre et al, 2005). The ratio of valid pixels in a quadrant must be higher than a given level, e.g., 0.8 in this study, to deal with the irregular boundaries in the deformation maps (Masterlark and Lu, 2004).…”