3D Deformation Fields Over Southern California From InSAR and GPS

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Non-technical summaryGeodesy -- the study of the shape of the Earth and its changes over time -- helps researchers gain insight into how the Earth's surface deforms in response to faulting, volcanism, hydrologic cycles, landslides, and human activity. Observations of deformation can inform assessments of the hazard associated with individual faults or volcanoes, models of the forces driving plate tectonics, as well as identification of new modes of deformation such as the slow slip events now observed at subduction zones and strike-slip faults worldwide. However, the available data are rarely optimal for the studies that rely on them -- campaign and continuous GPS observations are at isolated points that are usually separated by 10s of km or more, and place less of a constraint on deformation in the vertical direction than in horizontal ones. Space-based geodetic imaging such as Interferometric Synthetic Aperture Radar (InSAR) provides observations over large areas (100s of km) at high spatial resolution (few 10s of meters), but only constrains a near-vertical component of deformation and lacks the temporal resolution of continuous GPS. Tradeoffs between potential models of behavior can usually be greatly reduced when observations of more than one component of the 3D deformation field are available. This project is providing key information about how best to combine these diverse data.Southern California, with its high population density and complex, evolving network of faults, is a region where spatially dense 3-dimensional observations of ground displacements are particularly important. In many cases, the long-term rate and even the fault plane geometry of structures that make up the San Andreas system are poorly understood, as is the manner in which parallel faults accommodate the plate motion over time. The characteristics of the seismic cycle along these faults -- how regular they are, whether earthquakes occur in clusters along one fault followed by hiatuses during which activity shifts to a different structure, etc. -- are necessary inputs into attempts to assess seismic hazard in the region. Technical DescriptionThis project involves assimilation of available GPS and InSAR data into a combined, 3-dimensional map of ground deformation over a study region within Southern California, taking full advantage of the complementary strengths of the two data types. The proposed work includes close examination of the characteristics of seasonal signals, data quality and anthropogenic sources of ground deformation that may contaminate the tectonic signal as well as being of interest in their own right. This project focuses on the transition from the Los Angeles basin through Banning Pass down through the Salton Trough -- an area of interest both because it covers the southern San Andreas fault, but also because it is expected to experience vertical deformation due to both the convergence across many faults in the region and anthropogenic withdrawal of subsurface fluids. The project is developing combined models, and making available to the wider community the underlying data, the models, and the software used to generate those models those models. The project is also supporting the training of a graduate student and formal outreach to female high school students at the CURIE program for STEM development.