Aug. 18, 2009 The Mission Creek and Banning faults are two principal strands of the San Andreas fault zone in the northern Coachella Valley of southern California. The two faults merge at depth to form one fault zone, according to a new analysis of the fault geometry near Desert Hot Springs. The refined understanding of the fault zone has implications for regional earthquake hazards and local groundwater resources, according to a new article.
The structural characteristics of the San Andreas fault in the northern Coachella Valley strongly influence the seismic hazard of the area. In contrast to previous studies, this analysis by Rufus D. Catchings, et al., suggests the Mission Creek fault is a near-vertical or slightly southwest-dipping fault, implying that the northeastern part of the city of Desert Hot Springs is not on a hanging wall, suggesting that the northeastern part of the city should not experience increased shaking due to the hanging wall effect -- or the increased shaking associated with the upper wall of an inclined fault.
In contrast, the thick accumulation of low-velocity sediments southwest of the Mission Creek fault will likely amplify seismic waves, resulting in strong shaking in the southwestern part of the city of Desert Hot Springs and much of the northern Coachella Valley.
The authors of this paper suggest a more complete understanding of the fault geometry and shallow basin structures are needed in order to better mitigate the hazard to lifeline structures (natural gas lines, I-10 freeway, electrical lines, Colorado River Aqueduct, etc.) that serve large population centers in southern California.
Rufus D. Catchings, Michael J. Rymer, Mark R. Goldman and Gini Gandhok, U.S. Geological Survey were authors of the Bulletin of the Seismological Society of America paper, "San Andreas Fault Geometry at Desert Hot Springs, California, and Its Effects on Earthquake Hazards and Groundwater"
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