High-Resolution Satellite Imagery Mapping of the Surface Rupture and Slip Distribution of the Mw ~7.8, 14 November 2001 Kokoxili Earthquake, Kunlun Fault, Northern Tibet, China
Résumé
The Mw 7.8 Kokoxili earthquake of 14 November 2001, which ruptured a 450-km-long stretch of the sinistral Kunlun strike-slip fault, at the northeastern edge of the Tibet plateau, China, ranks as the largest strike-slip event ever recorded instrumentally in Asia. Newly available high-resolution satellite HRS images (pixel size ≤1 m) acquired in the months following the earthquake proved a powerful tool to complement field investigations and to produce the most accurate map to date of the coseismic displacements along the central Kusai Hu segment of the rupture. The coseismic rupture geometry south and west of Buka Daban Feng, near the earthquake epicenter, was also investigated in detail. Along the Kusai Hu segment, slip partitioning is for the first time observed to occur simultaneously during a single event, with two parallel strands, ~2 km apart, localizing almost pure strike-slip and normal faulting. In all, 83 new HRS coseismic offset measurements, some of which calibrated by field work, show large, well-constrained variations (≥100%) of the slip function over distances of only ~25 km. Tension cracks opening ahead of the shear dislocation and later offset by the upward propagating strike-slip rupture were observed, demonstrating that the rupture front propagated faster at depth than near the surface. The triple junction between the central Kusai Hu segment, the Kunlun Pass fault, where the rupture ended, and the Xidatan-Dongdatan segment, which could be the next segment to fail along the main Kunlun fault, acted as a strong barrier, implying that direct triggering of earthquake rupture on the Xidatan-Dongdatan segment by Kokoxili-type earthquakes may not be the rule.