Abstract
Online Material: Figures showing local magnitude versus duration; table of station correction coefficients. The earthquake magnitude estimate is a routine task in all seismological observatories. Several magnitude scales are available, based on amplitude measurement of different seismic phases, and/or on total signal duration. Among them, the duration magnitude ( M D) is adopted in many regional networks because it provides a rapid and reliable estimate of the earthquake size through a fairly simple procedure based on the measure of the duration of recorded seismograms. Bisztricany (1958) first demonstrated the existence of a relationship between magnitude and duration, and several authors (e.g., Sole’vev, 1965; Tsumura, 1967; Bakun, 1984; Vidal and Munguia, 2005; Hara, 2007; among many others) later discussed the use of duration of the recorded seismograms as a measure of the event size. Furthermore, in a recent paper, Lomax and Michelini (2009) proposed a duration magnitude procedure for the rapid determination of the moment magnitude, based on the P ‐wave recordings at teleseismic distances, which can be applied for tsunami early warning. In its more general formulation the duration magnitude depends on the ground‐shaking duration, on the hypocentral distance, and accounts for a station correction coefficient. According to Real and Teng (1973) and Hermann (1975), the duration magnitude is defined as ![Graphic][1] (1)in which τ is the signal duration, R is the hypocentral distance, Sc stands for the station correction, and a , b , and c are coefficients to be determined through a regression analysis. The present work has a double goal. First, we present an automatic procedure, which has been specifically developed to measure the earthquake duration, based on the estimate of the signal‐to‐noise ratio (SNR) along the seismic records. We then calibrate a duration magnitude scale for the area monitored by the … [1]: /embed/inline-graphic-1.gif
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