Earthquake cycle stress accumulation disparities of the Cajon Pass region

Liliane Burkhard, Bridget R. Smith-Konter, Lauren Ward, Katherine M. Scharer, & David T. Sandwell

Submitted August 15, 2018, SCEC Contribution #8617, 2018 SCEC Annual Meeting Poster #262

As the San Andreas Fault System is known to participate in multi-segmented ruptures, it is important to understand how both fault segment properties and regional rheology can influence earthquake cycle stress accumulation. Here, we investigate stress accumulation rates as a function of depth for the Cajon Pass in southern California, representing a critical junction for possible past and future through-going ruptures. Using a new 4D viscoelastic earthquake cycle model that incorporates heterogeneous rheological constraints of the southern California lithosphere, we estimate stress rate disparities caused by spatial variations in crustal rigidity. We adopt a simplified representation of crustal rigidity derived from provisional heat flow estimates and seismically imaged lithosphere-asthenosphere boundary (LAB) depths. Preliminary estimates of crustal rigidity are slightly higher (~35-40 GPa) than CA average south of the Cajon Pass, due to a combined effect of slightly lower heat flow rates and thicker LAB depths. If these rigidity contrasts are real, they suggest reduced stress accumulation rates (by ~2-5 kPa/yr) south of the Mojave segment (i.e., on the San Bernardino (San Andreas) and Claremont (San Jacinto) segments), in a region that already hosts lower stress rates due to fault strain accommodated over the multiple paralleling segments. Over 100-200 year earthquake cycle time scales, accumulated stress could be reduced by at least 1 MPa on these segments, making the occurrence of major through-going ruptures less frequent at this earthquake gate junction. Moreover, longer earthquake recurrence times are needed to accumulate several MPa of stress along these segments south of the Cajon Pass, and may be a natural response of crustal rigidity variations in southern California.

Key Words
Earthquake cycle, stress accumulation, Cajon Pass, SAFS

Citation
Burkhard, L., Smith-Konter, B. R., Ward, L., Scharer, K. M., & Sandwell, D. T. (2018, 08). Earthquake cycle stress accumulation disparities of the Cajon Pass region. Poster Presentation at 2018 SCEC Annual Meeting.


Related Projects & Working Groups
San Andreas Fault System (SAFS)