Seismic Swarm Analysis: S20080527.1 Near Westmorland, California
On 27 May 2008, an earthquake swarm designated S20080527.1 was recorded 14 km NNW of Westmorland, California. The sequence began at 09:47 and concluded at 19:21, encompassing a total of 47 events over 9 hours and 34 minutes. All events exhibited low magnitudes, with the strongest reaching 2.6, and occurred at shallow depths predominantly between 0 and 7 km.
The swarm displayed a rapid onset with multiple events clustered in the first hour, followed by episodic bursts through the afternoon. Notable activity included four events of magnitude 1.9 between 11:14 and 11:15, and two magnitude-2.6 shocks at 11:52:57 and 11:54:57. Depths remained consistently shallow, suggesting activity within the upper crustal layers typical of the Imperial Valley region.
This swarm aligns with the broader seismic character of the Imperial Valley, situated within the Salton Trough at the southern terminus of the San Andreas fault system. The area experiences frequent swarm-type seismicity driven by the interaction of the Pacific and North American plates along a network of strike-slip faults, including the Brawley and Imperial faults. Geothermal processes and fluid migration in the subsurface further contribute to clustered, low-magnitude event sequences rather than isolated large ruptures.
Historical records indicate that 11 swarms have occurred in the region since 1 January 2000. These include single swarms in 2000, 2001, 2002, 2004, and 2008, with three each in 2003 and 2005. Such recurrent swarm activity underscores the persistent tectonic strain and hydrothermal influences that characterize the Westmorland vicinity.
The 2008 swarm's parameters, including its brief duration and modest energy release, are consistent with patterns observed in prior Imperial Valley sequences. No events exceeded magnitude 3.0, minimizing potential for significant surface effects while highlighting the value of continuous monitoring for understanding fault behavior and fluid dynamics in this tectonically active zone.
References
- SeismoSight internal swarm classification records for S20080527.1
- USGS Earthquake Catalog for Imperial Valley, California (background regional context)