RAPID: Fault Creep Following the Mw=7.2 Sierra El Mayor Earthquake of 4 April

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

The investigation has as its objective the rapid deployment of instruments sensitive to the movement of faults of southern California and northern Mexico. These faults all lie to the north of the epicenter of the Mw=7.2 Sierra Mayor earthquake of 4 April 2010, which abruptly increased tectonic stress in southern California, bringing three major US fault-systems closer to failure: the Elsinore, San Jacinto and San Andreas systems. Seismologists believe that fault segments within each of these systems could slip in one or more earthquakes greater than Mw=7 resulting in huge economic losses in the US. At least two of segments were already close to failure prior to the recent earthquake. The surface traces of segments of these three fault systems all slipped a minor amount (by a process of triggered creep) in response to the instantaneous stress released by the April earthquake. and some continue to creep in response both to aftershocks, and to the instantaneous stress during the mainshock. The question arises as to which of these three fault systems is most likely to experience failure in a future earthquake, and several remote sensing and local measurements are being undertaken to identify the most significant stress changes that have now occurred. The instrumentation being installed by the present project (starting less than a week after the earthquake) consists of six buried 20' to 60'-long graphite rods installed obliquely across each fault, and attached firmly to the rock on one side, that are drawn through a telescopic plastic pipe should the fault move. A displacement transducer monitors the displacement of the free end of the rod relative to a second anchor on the remote side of the fault to an accuracy of 1/1000 inch. The displacement is measured every 15 minutes and recorded by a local data logger that operates autonomously from AA cells for up to a year. The data are transmitted through a cell phone every 2 hours to a publicly accessible web site where they may be viewed by the scientific community, by transportation and pipeline authorities, and by members of the public. The latency can be decreased to less than 1 minute by remote command, should anomalous seismic slip occur on any of these monitored faults. In such an event the seismological community will be in an informed position to advise the public concerning increased hazards to lifeline interruptions following an earthquake, far sooner than it takes for members of the public or geologists to inspect the epicenter. The website is https://datagarrison.com/ user=geo, password hobo.