Seasonal Variation of Strain in Central California and its Correlation with Seismicity

Meredith L. Kraner, William C. Hammond, Corné Kreemer, & Ilya Zaliapin

Submitted August 14, 2017, SCEC Contribution #7655, 2017 SCEC Annual Meeting Poster #212

Our recently completed analysis of seasonal strain in Central California using horizontal GPS data shows positive extensional dilatational strain peaking in the dry season (August/September) and negative contractional strain peaking in the wet season (February/March) across the creeping section of the San Andreas Fault. The timing of this observed seasonal strain is seemingly out of phase with the expected pattern associated with elastic loading of the Great Valley of California. In addition, no seasonality in dilatation is observed across the locked section of the San Andreas Fault south of Cholame, CA. We use the GPS Imaging technique to confirm our seasonal strain result and place it in the context of seasonal deformation in the southwestern United States. This processing technique can generate an image of vertical displacement based on weighted medians while remaining insensitive to outliers. It confirms that the location of the horizontal seasonal strain effect across the creeping section is well correlated with the location of highest vertical seasonal amplitude.

Furthermore, we investigate possible reasons for the abrupt change in seasonality between the creeping and non-creeping sections of the San Andreas Fault and look for potential correlations with seismicity. Several tests are performed to relate seismicity data to our estimates of seasonal strain. After declustering the seismicity catalog, we bin the earthquakes by month and latitude to spatially match the peak regions of seasonal strain in our study region. We also explore several methods to assess the statistical significance of our result.

Kraner, M. L., Hammond, W. C., Kreemer, C., & Zaliapin, I. (2017, 08). Seasonal Variation of Strain in Central California and its Correlation with Seismicity. Poster Presentation at 2017 SCEC Annual Meeting.

Related Projects & Working Groups
Stress and Deformation Over Time (SDOT)