MAPPING BASIN GEOMETRY WITH A NOVEL JOINT INVERSION OF GRAVITY AND SEISMIC DATA TO ENHANCE THE SALT LAKE VALLEY, UTAH COMMUNITY VELOCITY MODEL

The 2020 M5.7 Magna earthquake within the Salt Lake Valley is a reminder that devastating earthquakes are a real threat in the Intermountain West. Approximately 80% of Utah’s population and much of its economic infrastructure are located within the seismically active Wasatch Front urban corridor. Although much has been learned about the Salt Lake basin over the last several years, its detailed geometry and subsurface structure remain poorly constrained. To better assess potential seismic hazards, a more accurate community velocity model (CVM) is needed for realistic earthquake ground motion simulations for various fault rupture scenarios.

The previous CVM, published in 2008, was constructed using basin-wide gravity surveys and limited local measurements including sonic logs, geology, and seismic data. Because the spatial density of the regional seismicity data was limited, legacy gravity data played an important role in the CVM development. In this study, we have incorporated an additional 1000 gravity measurements collected across the Salt Lake Valley. Basin-wide seismic observations from the Magna earthquake aftershock receiver array added critical observations for improving the accuracy of the CVM.

We leveraged the complementary sensitivity of gravity, seismic, and other relevant geologic data by performing a novel joint inversion of gravity and seismic data to construct a new 3D model of the Salt Lake Basin. This model uses newly collected gravity measurements to validate legacy geophysical data and integrates the new and legacy datasets to improve model precision. We modeled the gravity field with an updated Complete Bouguer Gravity Anomaly map and determined the local gravity anomaly attributed to basin structure by separating the regional field. This model will provide insight into a future CVM revision and benefit the 2.6 million people living within the Wasatch Front urban corridor as this community continues to grow.