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Joint Meeting Pacific Section, AAPG & Cordilleran Section GSA April 29–May 1, 2005, San José, California

An Alternate Fluid Dynamic Tectonic Model That Explains Possible Precursory Hints of the December 22, 2003 San Simeon Earthquake

Lou Blanck and Brian Bode
Earth Design, Inc, 370 Weymouth Street, Cambria, CA 93428, [email protected]
Cambria Community Service District, PO Box 65, Cambria, CA 93428

The December 22, 2003 earthquake was preceded by a series of fluid dynamic changes that still have hydrogeologic implications to the region. Nine days prior to the earthquake, unexplained gasses were noted in Cambria East Village basements. Midnight before the 10:16 AM magnitude 6.5 event, large gas bubbles tossed around a live aboard boat moored in Morro Bay. The San Simeon earthquake occurred approximately 45 minutes after a 7-foot high tide. Approximately one-half hour before the San Simeon earthquake, a sonic-like event was widely perceived along the Central Coast as an earthquake, and at San Simeon cove, rumbling from the ground is heard from the time of the sonic-like event until the magnitude 6.5 earthquake. The earthquake results in the offset of a well casing near the intersection of State Highways 1 and 46 on the Fiscilini Ranch. All of these events and many of the aftershocks occurred West of the East dipping Oceanic fault. Subsequently, and in some cases immediately prior to the earthquake, the area experienced spring flow from springs that had stopped flowing approximately 40 years ago. Several hot sulfur water springs re-appeared in the Paso Robles area, including one in the City Hall parking lot. Spring flow increase into Santa Rosa Creek is significant enough to provide sufficient water supply for Cambria during the 2004 drought and had unusual sustained flow. However, San Simeon Creek North of Cambria and closer to the epicenter had a nearly typical flow for 2004. Pumping through the 2004 drought, indicated a change in available non-precipitation water unlike any since records have been kept in Cambria for Santa Rosa Creek. Many of the observations imply Cambria fault involvement in the earthquake. Future precursor research should monitor fluid dynamic events, at least for coastal thrust faults.

Posted with permission of The Geological Society of America; abstract also online (http://gsa.confex.com/gsa/2005CD/finalprogram/abstract_85802.htm). © Copyright 2005 The Geological Society of America (GSA).