Special Session: 3D/4D Seismic Imaging and Their Interpretation for Seismic Hazard Assessment
Type: Oral
Day: 5/15/2018
Time: 9:15 AM
Room: Tuttle
Abstract
In October 2016, we acquired high-resolution P- and S-wave seismic data along a 120-m-long, SW-NE-trending profile in Napa, California. Our seismic survey was designed to image a strand of the West Napa Fault Zone (WNFZ), which ruptured during the 24 August 2014 Mw 6.0 South Napa Earthquake. We separately acquired P- and S-wave data at every station using multiple hammer hits, which were edited and stacked into individual shot gathers in the lab. Each shot was co-located with and recorded by 118 P-wave (40-Hz) geophones, spaced at 1 m, and by 118 S-wave (4.5-Hz) geophones, spaced at 1 m. We developed both P- and S-wave tomographic velocity models, as well as Poisson’s ratio and a Vp/Vs ratio models. We observed a well-defined zone of elevated Vp/Vs ratios below about 10 m depth, centered beneath the observed surface rupture. P-wave reflection images show that the fault forms a flower-structure in the upper few tens of meters. This method has been shown to delineate fault structures even in areas of rough terrain.
Author(s):
Goldman M. R. USGS - U.S. Geological Survey
Catchings R. D. USGS - U.S. Geological Survey
Chan J. H. USGS - U.S. Geological Survey
Sickler R. R. USGS - U.S. Geological Survey
Nevitt J. USGS - U.S. Geological Survey
Criley C. J. USGS - U.S. Geological Survey
Seismic Imaging of the West Napa Fault in Napa, California
Category
3D/4D Seismic Imaging and Their Interpretation for Seismic Hazard Assessment