Spatiotemporal Correlation Between Seasonal Variations in Seismicity and Horizontal Dilatational Strain in California

Corné Kreemer, & Ilya Zaliapin

Published September 27, 2018, SCEC Contribution #8125

We extract significant spatially-coherent strain variations from horizontal seasonal GPS displacements in the American Southwest. The dilatational strain is largest (~5×10−9) in northern California with maximum margin-normal contraction and extension in spring and fall, respectively, consistent with the Earth’s surface going down and up at those times. The northern California signal has a phase-shift with that in southern California and the Great Basin. The intensity in mainshocks, aftershocks, as well as in the relative number of larger earthquakes, are in phase with the inferred Coulomb stress on the San Andreas fault system in northern California. In southern California, the same correlations exist except not with mainshock intensity. This suggests that a seasonal increase in fault-normal extension may or may not trigger mainshocks, but when an earthquake happens at those times, the favorable stress regime allows for a higher aftershock productivity and for earthquakes to grow larger than they otherwise would.

Citation
Kreemer, C., & Zaliapin, I. (2018). Spatiotemporal Correlation Between Seasonal Variations in Seismicity and Horizontal Dilatational Strain in California. Geophysical Research Letters, 45(18), 9559-9568. doi: 10.1029/2018GL079536.