Moment magnitude scale for local earthquakes in the Petatlan region, Mexico, based on recorded peak horizontal velocity

Abstract

AbstractAssigning moment magnitude to local earthquakes based on peak recorded amplitude and hypocentral distance is the principal concern of this paper. For 38 aftershocks of the Petatlan earthquake (14 March 1979) with moments between 2.8 × 1018 and 1.4 × 1022 dyne-cm, we developed an empirical relationship for the estimation of moment based on peak horizontal velocity (V) and hypocentral distance (R). This empirical relationship in conjunction with the definition of moment magnitude (Hanks and Kanamori, 1979) allows direct estimation of moment magnitude, knowing peak horizontal velocity and hypocentral distance. We call this estimation of moment magnitude “Mw′” to distinguish it from its original definition. Equation for Mw′ for our data set isM w ' = 2 . 2 7 + 0 . 7 7 log ( V ⋅ R ) + 6 . 5 9 × 1 0 - 3 R ,where V is in millimeters/second, and R is in kilometers.In order to be able to estimate the moment magnitude from coda duration (Tc), we sought and found correlation between log(Tc) and log of moment (M0) as followslog M 0 = ( 2 . 2 5 ± 0 . 1 7 ) log ⁡ T c + ( 15.88 ± 0.29 ) ,where M0 is in dyne-cm, and Tc is in seconds.