Abstract
We present a procedure for rapid determination of an earthquake moment magnitude, M wp, at regional distances from the P ‐wave first arrivals based on Tsuboi et al. (1995, 1999) and Kanjo et al. (2006). We apply an automated window‐length selection and use a variable P ‐wave velocity instead of a constant value to make a better estimation for M wp magnitude. This procedure is applied to 46 earthquakes with magnitude ( M w) greater than 4.8, which have been recorded and analyzed for Global Centroid Moment Tensor (Global CMT; the Global Centroid Moment Tensor Project database was searched using www.globalcmt.org/CMTsearch.html [last accessed July 2012]) solutions between 2008 and 2011 by the Prime Ministry Disaster and Emergency, Presidency National Earthquake Department (AFAD). Our results show good agreement between the M wp and M w magnitudes (about ±0.27 mu), and we expect this procedure can be used for the rapid determination of moment magnitudes of regional earthquakes. Effective emergency response for large regional destructive earthquakes requires accurate information about the size and location of event within a few minutes. The 23 October 2011 M w 7.1 Van, Turkey earthquake was a destructive regional earthquake that needed rapid determination of the moment magnitude because the local ( M L) and duration ( M D) magnitudes determined by national network operators were underestimated. The widely used M wp moment magnitude algorithm (Tsuboi et al. , 1995, 1999) considers very broadband, P ‐wave displacement seismogram to approximate far‐field source time functions. These displacement seismograms are integrated and corrected for geometrical spreading and an average radiation pattern to obtain scalar moments at each station. Application of the standard moment magnitude formula, averaging over stations, and applying a magnitude correction (Whitmore et al. , 2002), gives a moment magnitude, M wp, for an event. We introduce a procedure to …
Published Version
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