Seismic Swarm PS20080320.1: Analysis of Events Near Hotan, China

The seismic swarm designated PS20080320.1 occurred 226 km southeast of Hotan in Xinjiang, China, within a tectonically active zone shaped by the ongoing collision between the Indian and Eurasian plates. This region lies along the northern margin of the Tibetan Plateau, where thrust faults and strike-slip systems accommodate crustal shortening and lateral extrusion. The swarm spanned 22 hours and 19 minutes, from 22:32 on 20 March 2008 to 20:52 on 21 March 2008, registering 12 earthquakes.

The sequence initiated with a magnitude 7.2 mainshock at a depth of 10 km. Subsequent events included magnitudes of 5.3, 5.0, 5.2, 5.0, 5.6, 5.1, 5.3, 5.0, 5.2, 5.2, and 5.0, with most hypocenters at 10 km depth and two deeper events at 21 km and 37 km. This pattern reflects typical aftershock decay following a large thrust or strike-slip rupture, with energy release concentrated in the shallow crust.

Geologically, the area forms part of the Kunlun fault system and adjacent structures that have produced significant historical seismicity. The 2008 mainshock aligns with regional deformation rates of several millimeters per year, driven by northward indentation of the Indian plate. Paleoseismic records indicate recurrent large events along these faults over the Holocene, underscoring the persistent hazard in this intraplate setting.

No other magnitude 7 or greater earthquakes have occurred within 50 km of the swarm center since 2000. The 34 km offset between the recorded mainshock and swarm centroid suggests minor migration of activity along the fault plane, consistent with stress triggering in a heterogeneous crust.

This swarm provides insight into clustered seismicity in compressional regimes, where a single large event can trigger a brief cascade of moderate aftershocks without evolving into a prolonged sequence. Monitoring data from regional networks continue to refine models of fault interaction in the Hotan sector.

References

USGS Earthquake Catalog China Earthquake Administration reports SeismoSight internal classification data