A new coda-duration magnitude scale for northern Baja California, Mexico

In northern Baja California, coda-durations of seismic signals recorded in the sediments of the Mexicali-Imperial Valley (MIV) are longer than those recorded on the granitic Peninsular Ranges of Baja California (PRBC). The source-receiver distance and the local geology conditions also affect coda duration. Using data from earthquakes in the 1.8-to-5.8-magnitude range, we performed a multiple regression analysis to get two new duration magnitude relationships as follows: M-D = - (1.56 +/- 0.21) + (2.44 +/- 0.13) log tau + (0.0023 +/- 0.0004)tau + S, for PRBC, and M-D = - (1.27 +/- 0.38) + (2.31 +/- 0.20) log tau + (0.0012 +/- 0.0004)tau + S, for MIV, where tau and S are lapse-time values and station corrections, respectively. Station corrections range from -0.60 to +0.19. The new magnitudes are calibrated with a local magnitude scale previously defined for the region.