Validation of 3D velocity models using earthquakes with shallow slip: case study of the Mw6.0 2014 South Napa, California, event

Walter Imperatori, & Frantisek Gallovic

Submitted August 12, 2016, SCEC Contribution #6596, 2016 SCEC Annual Meeting Poster #288

Three-dimensional velocity models constitute a key element in strong ground motion modelling, e.g., earthquake hazard assessment. Their validation is typically based on modelling weak earthquakes with foci limited to depths greater than ~5km. However, ruptures during moderate and large earthquakes can propagate to shallower depths (and eventually reach the surface). For such shallow sources velocity models may not be validated with sufficient accuracy. In this respect, we conduct a series of tests based on the Mw6.0 2014 South Napa earthquake, which was characterised by a very shallow slip asperity, to assess the performance of the USGS 3D San Francisco Bay area velocity model within 20km fault distance. Our study indicates that the velocity model performs generally well with some exceptions, where large amplitude surface waves not present in the observed data are systematically excited. We exclude that more complex fault geometries or slightly deeper slip could result in a better fit of the observed data. Contrarily, we demonstrate that smoothing the velocity model (i.e. reducing the strong velocity contrasts between basin fill and bedrock) effectively attenuates the spurious oscillations.

Citation
Imperatori, W., & Gallovic, F. (2016, 08). Validation of 3D velocity models using earthquakes with shallow slip: case study of the Mw6.0 2014 South Napa, California, event. Poster Presentation at 2016 SCEC Annual Meeting.


Related Projects & Working Groups
Ground Motion Simulation Validation (GMSV)