We invert continuously operating Global Positioning System (cGPS) data obtained between 2007 and 2019 to quantify non steady‐state horizontal strain anomalies in California. Our long‐wavelength transient strain model shows seasonal and multiannual variations in horizontal strain anomalies within the plate boundary zone. During the summer, in general, a zone of extensional dilatation develops along the San Andreas Fault zone and Sierra Nevada, whereas contractional dilatation develops along the Eastern California Shear Zone (ECSZ) north of 36.5°N. The patterns of dilatational strain are opposite during the winter. We find that these seasonal strain anomaly patterns vary in magnitude, depending on precipitation intensity in California. Investigating hydrologic loading models and their horizontal elastic responses reveal that water mass loads on the surface from the precipitation in California are the major sources of the observed long‐wavelength horizontal transient strains. We show, however, that a heavy damping in the inversion of the cGPS data is required for the long‐wavelength horizontal strain solutions to best match with the expected elastic response from hydrologic loading. Appropriate fitting of the horizontal cGPS yields amplified horizontal strain signals in the Sierra Nevada, along regions adjacent to the San Andreas Fault, and within the ECSZ. The larger‐than‐expected amplitudes may be associated with poroelastic responses or thermoelastic changes that are superimposed on the hydrologic response. We demonstrate that there is a persistent sharp boundary of horizontal dilatational strain domains at the transition between the High Sierra and Basin and Range Province, caused by the sharp gradient in hydrologic loading there.

Interferometric Synthetic Aperture Radar (InSAR) observations constrain displacement of the Earth's surface toward or away from the satellite, and are inherently a one-dimensional observation defined by the projection of the true, 3-dimensional (3-D) ground displacement field onto the orientation of the line-of-sight (LOS) vector between the satellite and the ground (e.g., Bürgmann et al., 2000). However, interpretations of the deformation within a given region usually benefit from constraints on the full 3-D displacement field (e.g., Fialko et al., 2001;Funning et al., 2005;Wright et al., 2004) or require well-characterized physical models of the processes driving the deformation (e.g., fault source geometry, aquifer characteristics, crustal rigidity). These models are not always available or well understood and the Earth is far more complex in reality than its representation in models (e.g., Caricchi et al., 2014;Chester & Chester, 2000;Hearn & Bürgmann, 2005). To address this limitation, researchers have combined measurements from multiple observation geometries (particularly from ascending and descending satellite paths) as well as other products derived from the Synthetic Aperture Radar (SAR) imagery (described below) to infer the 3-D displacement field and its variations over time (e.g.

Dense spatial and temporal coverage of continuous global positioning system (cGPS) measurement enables rigorous investigations of time-dependent surface strain anomaly patterns in California. Observed by cGPS, the seasonality in the crustal nontectonic strain and the associated stress changes are attributable to the Earth's elastic response (Farrell, 1972) to time-varying loading sources on the surface, such as hydrologic loads (e.g., Argus et al., 2014), atmospheric pressure (e.g., Gao et al., 2000, and thermoelastic loads (e.g., Ben-Zion & Allam, 2013;Prawirodirdjo et al., 2006). Furthermore, studies have reported that cGPS measurements can also capture multiyear variations in crustal strain due to drought and anomalously heavy precipitation in California (e.g.,

In this study, we perform a 2‐frequency sequential receiver function stacking investigation in Southern California. The resulting Moho depths exhibit similar patterns to previous studies while the crystalline crustal Vp/Vs values show more regional variations. Most Vp/Vs variations can be explained by compositional differences. We observe a dichotomy in Moho depth, Vp/Vs, and crustal strain rates between the Peninsular Ranges and Southern San Andreas Fault system. Comparisons between strain rates, Vp/Vs, and temperature suggest that crustal compositional variations may have played a more critical role in influencing the crustal strain rate variations in the Peninsular Ranges and Southern San Andreas than temperature. The structural and compositional variations provide a new insight into the causes of the migration of the Southern San Andreas Fault system and the formation of the “Big Bend.”