California Integrated Seismic Network (CISN) Local Magnitude Determination in California and Vicinity

Abstract

Determining local magnitude (M_L) in a manner that is uniform and internally consistent for earthquakes throughout California and the vicinity is an important component of the California Integrated Seismic Network (CISN). We present a new local magnitude attenuation function and corresponding station adjustments that are valid throughout California. The new attenuation function is an analytic function of the radial hypocentral distance between 1 and 500 km. Associated station adjustments are also available for 1185 horizontal seismometer and accelerometer channels from five seismic networks operating in California. The new attenuation function and adjustments provide several advantages to CISN. They allow a more robust M_L computation, the M_Ls are more consistent between northern and southern California than they have been in the past, and because adjustments are now available for more station-network-channel-location codes (SNCLs), M_Ls can be computed for small earthquakes in more locations than was previously possible. In addition to describing our method for calibrating the new CISN M_L, we also present a tool for adding adjustments for new or upgraded stations.