Facility Support: Pinon Flat Observatory - Longbase Strainmeters Interim Operation

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1533790AgnewThis grant support continuity of operations and maintenance of the Pinon Flat Observatory (PFO) long-baseline laser strainmeters (3) and one long baseline tiltmeter for a period of forty months (congruent with the expiration of the GAGE Facility Cooperative Agreement EAR-1261833). PFO is the only location in which three LSM?s allow the full strain tensor to be measured with a long-term stability that matches GPS, with a short-term sensitivity orders of magnitude better than GPS, and without the calibration concerns and hydrologic effects present on borehole strainmeters. The unmatched "temporal depth" of the PFO data (including a number of environmental sensors) makes it possible to evaluate a range of new signals and to identify patterns which appear only over very long times. PFO LSMs have detected repeated aseismic signals triggered by local earthquakes, observed seven times over the last 22 years, and thought to be caused by aseismic slip within the Anza gap of the nearby San Jacinto Fault. The LSM data extend back to the early 1970?s, and in improved form (fully-anchored) back to the mid-1980?s. The PFO LSM time series observations are unique in the world and are in a strategic area of the transform fault system that runs throughout southern and into northern California and that remains a serious and potent seismic hazard for a large population base in the U.S. The extreme sensitivity of in vacuo laser interferometric crustal displacement gradient measurements such as at PFO offers the real possibility of witnessing seismic precursors within the Anza seismic gap. The Anza gap is seismically quiet compared to regions of the transform fault system to the south and the north. This area is certainly potentially ripe for a major earthquake though it may be an area of the transform that accommodates strain accumulation largely through aseismic slip. However, if a major earthquake in the region should occur, the loss of the important long time series PFO LSM data sets would be less than unfortunate given the marginal costs of keeping it running until other sources of support might be found post-September 2018. This support is congruent with NSFs mission of promoting the progress of science and may well advance the national health, prosperity and welfare in terms of advancing knowledge about seismic hazards and hazard mitigation.***