Global Positioning System Velocity Profile for the Imperial Transect: Reconciling Earthquake Depths with a Steep Velocity Gradient.

Event Center BC

In this study, GPS data and elastic modeling were used to infer fault slip rates by generating a velocity profile across the Pacific-North American plate boundary from faults in the Imperial Valley including the Agua Blanca, San Miguel, Elsinore, San Jacinto, Imperial and an Unnamed Fault east of the Imperial Fault. The results show that the Imperial and San Jacinto faults play the primary role in the steep gradient of the transect’s velocity profile. Aseismic creep was allowed in the uppermost crust of the models for the Imperial Fault in order to fit the very steep velocity profile in the vicinity of that fault. The best-fitting model has 15 mm/ yr of shallow aseismic creep above a locked zone that extends from 12-18 km depth, and 18 mm/yr of aseismic creep below the locked zone. This model also has 25 mm/yr of creep on the San Jacinto Fault, below a locked zone that extends from the surface down to 20 km depth.