Application of Mwp to the Great December 26, 2004 Sumatra Earthquake

Kenji Kanjo,Seiji Tsuboi,Tomomichi Furudate

doi:10.1186/bf03353368

Abstract

Abstract A great earthquake of Mw9.0 (Harvard) occurred off of northwestern Sumatra on December 26, 2004 (UTC), causing an unprecedented tsunami disaster. An earthquake of Mw8.6 (Harvard) then occurred on March 28, 2005 (UTC), about 160 km to the southeast of the December event’s epicenter. The Matsushiro Seismological Observatory of Japan Meteorological Agency determined magnitudes of M8.8 and M8.7 respectively for these events using the Global Seismic Network’s (GSN) Live Internet Seismic Server (LISS) data. The West Coast/Alaska Tsunami Warning Center (WC/ATWC), and the Pacific Tsunami Warning Center (PTWC) both use Mwp to rapidly evaluate moment magnitude. The WC/ATWC calculated a mean Mwp of 8.0 for the multiple event on Decmber 26, 2004. Using data from the IRIS station MAJO, we determined an Mwp of 8.5 by using a distance-dependent apparent P-wave velocity (α = 0.16Δ + 7.9 km/sec.) instead of a constant apparent P wave velocity (α = 7.9 km/sec), for α in the original equation for Mwp. The corrected Mwp value of 8.5 is much closer to the total moment magnitude of the multiple ruptures of the complex December 26 main-shock, and is useful as a first magnitude estimation to evaluate possible tsunami generation.

Highlights

A great earthquake of Mw9.0 (Harvard) occurred off of northwestern Sumatra (3.30N, 95.96E) at 00:58:53 on December 26, 2004 (UTC) causing an unprecedented tsunami disaster
The results show that Mwp correlates well with Harvard’s Mw’s obtained from their Centroid Moment Tensor (CMT) solutions (Dziewonski et al, 1981)
Summary The Matsushiro Seismological Observatory (MSO) of JMA uses the data from USGS Live Internet Seismic Server (LISS) and IRIS BUD server to determine hypocenter and moment magnitude

Summary

Introduction

A great earthquake of Mw9.0 (Harvard) occurred off of northwestern Sumatra (3.30N, 95.96E) at 00:58:53 on December 26, 2004 (UTC) causing an unprecedented tsunami disaster. The Matsushiro Seismological Observatory of the JMA has been determining hypocenters using a Grid-search method (Furudate, 2002, 2003), and magnitudes using the average of the squared velocity amplitudes for four minutes beginning at the P wave arrival time (Ogahara et al, 2004) using USGS/IRIS, and BUD/IRIS LISS data. Mwp provides an estimate of moment magnitude from the integrated displacement of the initial P waves of a broadband seismic record, or from differences of amplitude with P and pP or sP wave enabling very fast tsunami warnings (Tsuboi et al, 1995, 1999).

Results

Conclusion