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.
The 4 April 2010 Mw=7.2 El Major earthquake in northern Mexico shook the area so violently that it caused eleven faults in southernmost California to slip. The slip on each of these faults was modest, less than an inch, and in most cases less than 1/10". Slip of the small amount is usually confined to the uppermost thousand feet of the surface. Sensitive displacement monitors (creepmeters) on two of the faults indicated that slip occurred within a few seconds of the passage of seismic waves from the earthquake. The project installed another six creepmetersn in apprehension should these faults continue to slip. Fortunately, with the exception of one fault near the Mexico border that slipped 1/6" in a local aftershock in June 1010, stability appears to have been resumed. We discovered that the shape of the US changed in the earthquake as a result of the US/Mexico border being offset by several inches. We also discovered that the northern Jan Jacinto fault may be creeping at a rate of 1/6" each year. As of May 2011, five of the six instruments continue to operate. The locations of creepmeters in southern California are listed in the table below. The first four were in operation before the earthquake. The next five marked by * were installed by the project. coFE Ferrum 33.4572 115.8538 coSC Salt Creek 33.4485 115.8437 coDU Durmid 33.4147 115.7985 coSH Superstition Hills 32.9301 115.7009 coNS* North Shore 33.5307 115.9388 coRR* Ross Road 32.7812 115.4485 coLW* Laguna Salada W 32.6483 115.8790 coLE* Laguna Salada E 32.6643 115.8480 coML* Mystic Lake 33.8965 117.0866
