Seismic Swarm PS20080512.1 Near Guangyuan, China

A seismic swarm designated PS20080512.1 was recorded 55 km west of Guangyuan in Sichuan Province, China. The sequence began at 06:41 on 12 May 2008 and concluded at 07:19 on 13 May 2008, encompassing 11 earthquakes over 24 hours and 37 minutes. All events were shallow, with focal depths between 10 km and 18 km, and magnitudes ranging from 5.0 to 5.3.

The swarm unfolded in two main phases. The initial cluster on 12 May featured nine events between 06:41 and 07:05, including multiple magnitude 5.1–5.3 shocks at 10 km depth. Two additional events occurred later that day at 14:15 (magnitude 5.0, 18 km depth) and 15:08 (magnitude 5.1, 10 km depth). The final event, a magnitude 5.0 shock at 10 km depth, took place at 07:19 on 13 May.

This activity occurred within the Longmen Shan fault system, a northeast-trending thrust belt marking the eastern margin of the Tibetan Plateau. The region lies at the boundary where the Indian Plate converges with the Eurasian Plate, driving crustal shortening and uplift at rates of several millimeters per year. The Longmen Shan accommodates oblique reverse faulting, with the 2008 Wenchuan earthquake (magnitude 7.9) demonstrating the zone’s capacity for large-magnitude events.

Geological records indicate that the Longmen Shan has experienced recurrent seismicity throughout the Quaternary. Paleoseismic studies reveal surface-rupturing earthquakes roughly every 1,000–2,000 years on major strands of the fault system. The 2008 Wenchuan mainshock, which nucleated approximately 150 km southwest of the swarm location, triggered widespread aftershock sequences across the fault network, consistent with the timing and character of the PS20080512.1 swarm.

Since 1 January 2000, only one earthquake swarm has been identified in the immediate vicinity according to SeismoSight internal classification—the event documented here. No prior swarms meeting the same criteria have been recorded in the catalog for this sector of the Longmen Shan.

The swarm events were tightly clustered both spatially and temporally, a pattern often associated with fluid migration or static stress transfer following a major regional earthquake. Depths remained predominantly at 10 km, suggesting activation of a mid-crustal segment of the fault zone.

SeismoSight classification data; Longmen Shan fault zone literature (USGS, China Earthquake Administration reports 2008–2023).