SCEC Award Number 16073 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Pinon Flat Observatory: Continuous Monitoring of Crustal Deformation
Name Organization
Frank Wyatt University of California, San Diego Duncan Agnew University of California, San Diego
Other Participants
SCEC Priorities 1d, 2c, 5a SCEC Groups Seismology, SDOT, Geodesy
Report Due Date 03/15/2017 Date Report Submitted 03/28/2017
Project Abstract
Crustal deformation measurements at Pinon Flat Observatory (PFO), and at other sites not supported by SCEC, provide data on otherwise unobservable deformation changes and the fault processes that produce them. In particular, we have identified a repeated pattern of rapid aseismic strain following large local earthquakes in 2001, 2005, and 2013 in the Anza area, as well as after the 1992 Joshua Tree, 1999 Hector Mine, and 2010 2010 El-Mayor/Cucapah earthquakes - though not after the 1987 Superstition Hills or 1992 Landers earthquakes. We attribute this to triggered aseismic slip on the San Jacinto fault at seismogenic depths. We have also observed longer-term strain changes, in particular from October 2010 through October 2011, that can be explained by aseismic slip equivalent to a magnitude 5.8 event at the location of the 2005 earthquake.
Intellectual Merit This project continues the operation of the three longbase laser strainmeters (LSM's) and one fully-anchored long fluid tiltmeter (LFT) at PFO. These systems have provided data that are unique in quality, completeness, and length, and give an unequalled view of aseismic and seismic deformations throughout the earthquake cycle.
Broader Impacts This effort provides (I) paradigmatic datasets of strain and tilt used for training researchers in this field, or for new areas of research; (II) information on the design and construction of long-base and other sensors for future replication or improvement; and (III) a readily accessible field site that can be used as a training ground for undergraduate and graduate students in a variety of solid-earth studies.
Exemplary Figure Figure 5 of Technical Report. Caption (from report text):
Comparison strainmeter measurements showing that there are variations in even the long-base strains, if these are measured over parallel but different baselines, over distances much shorter than the 730 m LSM's. Along the NW-SE strainmeter, the same seismic signal is recorded with about 7% larger amplitude on the TOFS: a result that initially suggested a systematic error. But along the EW baseline the two agree to within 1%. We now believe that these differences are real, and occur because of slight elastic inhomogeneities on the scale of hundreds of meters.