Decadal variation of crustal deformation in California inferred from EDM and GPS and its implication to seismic hazard

Zheng-Kang Shen, & Yuehua Zeng

Published August 15, 2018, SCEC Contribution #8693, 2018 SCEC Annual Meeting Poster #132

Prior to GPS, the Electronic Distance Meter (EDM, or Trilateration) technique was used from the 1960s to early 1990s to measure crustal deformation across major faults in California. Although the data may not be as accurate as GPS (relative uncertainties of 10e-7 vs 10e-8), inclusion and careful analysis of the EDM data can still effectively extend the observation time span from the last 2-3 decades to the last half century. This provides a unique opportunity to examine the temporal evolution of the deformation field in California, particularly along the San Andreas fault. A preliminary analysis of the EDM data has indeed shown signs of such a deformation rate change, with the overall relative motion determined by EDM measurements in the 1970s-1980s a couple of millimeters per year slower than that measured by GPS in recent years across the Mojave and Coachella sections of the San Andreas fault. This change of deformation rate is consistent with our recent study of seismicity and geodetic strain patterns, which demonstrated that earthquakes of M≥4.0 in California and Nevada became significantly more concentrated along the San Andreas fault system for the period of 1990 to 2013 than for the period of 1933 to late 1980s. It also showed that the seismicity rate for events of M>6.5 was more than doubled for the later period than for the earlier period (Zeng et al., 2018). The geodetic and seismic results seem to lend support to a model of accelerated seismicity late into the earthquake cycle, suggesting increased seismic risk in California.

Reference
Zeng, Y., M. D. Petersen, and Z.-K. Shen, Earthquake potential in California-Nevada implied by correlation of strain rate and seismicity, Geophys. Res. Lett., doi:10.1002/2017GL075967, 45(4), 1778-1785, 2018.

Key Words
EDM, GPS, Deformation, Decadal Change, Earthquake Potential

Citation
Shen, Z., & Zeng, Y. (2018, 08). Decadal variation of crustal deformation in California inferred from EDM and GPS and its implication to seismic hazard. Poster Presentation at 2018 SCEC Annual Meeting.

Related Projects & Working Groups
Tectonic Geodesy