Observation of Spatiotemporal Creep Rate Variation Along Southern San Andreas and San Jacinto Faults from InSAR Time Series and Repeating Earthquakes

Abstract:

Understanding the spatiotemporal distribution of the aseismic slip rate variation on the fault over various depths is essential for quantifying the earthquake potential (Avouac, 2015). Here we investigate the creep rate variation of the southern San Andreas Fault (SAF), which is near the end of its interseismic period (Brothers et al. 2011; Philibosian et al. 2011). Currently, there is only a few observation of short-term creep rate variation along the southern SAF (Tymofyeyeva et al., 2019) and the nearby San Jacinto Fault. In this study, we develop a new multitemporal SAR interferometric framework that combines the concept of permanent and distributed scatterers to identify a large set of elite pixels in all terrain. This new approach also implements a spatial patch-wise 2D smoothing spline combined with a temporal 1D continuous wavelet to remove the atmospheric delay in SAR interferograms. This processing framework is applied to a large set of SAR images acquired by Sentinel-1A/B during late-2014 till mid-2019 to obtain surface deformation time series along the southern SAF and San Jacinto Fault at a high resolution and precision. Besides geodetic observation, we search for characteristically repeating earthquakes (CREs) that can provide additional constraint on spatio-temporal distributions of aseismic slip. Our primary interest is in long-lived CREs that will be associated with creeping faults. Using the Southern California Seismic Network catalog (1981-2018) with magnitude >=1.0, 505 sequences of CREs with life spans greater than 100 days have been identified. We will further investigate the relationship between surficial fault slip rate from geodetic data and creep within the fault zone inferred from the characteristic repeating earthquake. These analyses have the potential to advance our understanding of the mechanism of crustal strain accumulation on faults and release over various spatial and temporal scales.