Refraction Microtremor Analysis of Areas Surrounding California State University San Bernardino

Event Center A&B

The San Andreas Fault stretches for over 800 miles through the state of California with varying regions of activity and rupture. Running along the foothills of the San Bernardino Mountains, areas in close proximity to the San Andreas Fault Zone may be subject to site amplification of ground motion caused by seismic activity via wave propagation through the subsurface. Low shear velocity of the subsurface and subsequent seismic activity have been known to present significant geological hazards, which have begun to be addressed via the Alquist-Priolo Earthquake Faulting Zone Act and the National Earthquake Hazards Reduction Program (NEHRP). This study focuses on refraction microtremor analysis (ReMi) of the top 30 meters (Vs30) of the subsurface in Northern San Bernardino; more specifically, areas encompassing California State University, in close proximity to the San Andreas Fault. ReMi profiles were situated 0.3 to 1.5 miles away from the San Andreas Fault, and in some instances, strategically positioned next to housing developments and structures. Phase velocity dispersion curves were generated by processing ReMi seismic data and subsequently inverted for shear wave velocity profiles. The geologic units in the study area consist of young alluvium and wash deposits, as well as older alluvial fan deposits. The goal of this study is to construct a Site Classification map based upon NEHRP site class ranking to show various average velocity profiles across a given area, and allow for the identification of possible high amplification zones.