Rapid Geodetic Assessment of July 2019 Ridgecrest, California Earthquakes

Researchers: Michael Floyd and Thomas Herring, Massachusetts Institute of Technology; Gareth Funning, University of California, Riverside; Yuri Fialko, University of California, San Diego; and Rachel Terry, UNAVCO.

Written by Linda Rowan
25 February 2020

Summary

The July 2019 moment magnitude 6.4 and 7.1 Ridgecrest California earthquakes occurred about 34 hours apart on connected strike-slip faults. Continuous and temporary Global Navigation Satellite Systems (GNSS) sites captured the surface motions during and after the events. In particular, temporary GNSS sites installed near the epicenter of the first earthquake, recorded in exquisite detail the surface motions of the second, larger M7.1 event. The geodetic data provides crucial information about how the faults move during and after an earthquake and how this motion is related to other processes, such as plate tectonics and fault creep.

Observations

The eastern California shear zone is a region of active strike-slip fault motion and an important tectonic region associated with the Pacific-North America plate boundary. The region includes the southern Mojave Desert in California, east of the San Andreas fault system, and extends into western Nevada. The region is estimated to account for about 25 percent of the relative plate motion between the Pacific and North America plates. Continuous and temporary observing monuments, mostly seismic and geodetic, have been installed to measure plate tectonics, active faults and surface changes associated with the Coso geothermal field.

On 4 July 2019, a M6.4 strike slip earthquake occurred near Ridgecrest, California. Continuously monitoring GNSS sites captured the earthquake’s surface motions. Soon after, the rapid deployment of temporary GNSS sites close to the fault was initiated to gather details of any post-event changes. Then about 34 hours later, on 5 July 2019, a M7.1 strike slip earthquake on a connected and nearly perpendicular striking fault occurred. The continuous and temporary GNSS sites were able to capture the earthquake motions in exquisite detail.