Geodetic Evidence for a Blind Fault Segment at the Southern End of the San Jacinto Fault Zone

Ekaterina Tymofyeyeva, & Yuri Fialko

Published January 27, 2018, SCEC Contribution #7275

The San Jacinto Fault (SJF) splits into several active branches south of Anza, including the Clark fault and the Coyote Creek fault. The Clark fault is believed to terminate at the southern tip of the Santa Rosa mountains, with the Coyote Creek fault being the main strand at the southern end of the SJF [Jennings, 1994]. Space geodetic observations have revealed high gradients in the InSAR line-of-sight (LOS) velocity to the east of the Coyote Creek fault, possibly indicating a ”blind” continuation of the Clark fault further to the south [Fialko, 2006; Lindsey and Fialko, 2013a]. We present new InSAR and GPS data that confirm high deformation rates along the southern extent of the Clark fault. We derive maps of horizontal and vertical average velocities by combining data from the ascending and descending satellite orbits with an additional constraint provided by the azimuth of the horizontal component of secular velocities from GPS data. The resulting high-resolution surface velocities are differentiated to obtain maps of shear strain rate at various spatial wavelengths. Joint inversions of InSAR and GPS data suggest that the hypothesized blind segment of the Clark fault and the Coyote Creek fault have slip rates of 12 ± 4 mm/yr and 5 ± 4 mm/yr, respectively. The blind southern segment of the Clark fault thus appears to be the main active strand of the SJF, posing a currently unrecognized seismic hazard.

Citation
Tymofyeyeva, E., & Fialko, Y. (2018). Geodetic Evidence for a Blind Fault Segment at the Southern End of the San Jacinto Fault Zone. Journal of Geophysical Research: Solid Earth, 123(1), 878-891. doi: 10.1002/2017JB014477.