Last week's seismic swarm at Bombay Beach along the Salton Sea occurred near the southern tip of the San Andreas fault and a perpendicular fault zone that looks to me like a spreading center or the edge of the Salton trough rift. Denis Norton with Hydrothermals in Stanley, Idaho forwarded this plot he prepared using data from the USGS earthquake catalog.
The black dots are the oldest events, light green are the youngest. Size relates to event magnitudes. View is to the WSW with the blue dot being Bombay Beach.
Denis is examining the nature of geothermal reservoirs and mentioned that the quake swarm to the south looks like what they typically see over cooling magmas. Could something similar be occurring at Bombay Beach? The current swarm seems pretty well constrained horizontally, but stretched out vertically.
If the swarm is related to igneous activity rather than lateral stress buildup on the San Andreas, that may lower the risk of a large earthquake that would hit Southern California and even trigger significant events on faults closer to Arizona.
Ref: Norton, D.L., and Hulen, J.B., 2006. Magma-hydrothermal activity in the Salton
Sea geothermal field, Imperial County, California: Geothermal Resources Council,
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