A Method for Rapid Estimation of Moment Magnitude for Early Tsunami Warning Based on Coastal GPS Networks

Abstract

The recent great earthquakes of 26 December 2004 (Sumatra, Indonesia, Mw 9.2), 26 February 2010 (Maule, Chile, Mw 8.8), and 11 March 2011 (Tohoku-oki, Japan, Mw 9.0) have once again brought to the forefront the urgent need for early tsunami warning. These warnings mostly rely on magnitude and location of an earthquake. A large/great magnitude subduction-zone earthquake with rupture area extending up to the trench is potentially a tsunamigenic event. The appropriate magnitudes for tsunami warning are those that are based on long-period seismic waves (Abe 1979), e.g. , the moment magnitude, Mw (Kanamori 1977). Recently, W -phase (the long-period wave that arrives between P and S waves) has been used to compute Mw (Kanamori and Rivera 2008; Hayes et al. 2009). This magnitude can be determined in a relatively short time. For example, the first moment tensor solutions of the Tohoku-oki earthquake, based on inversion of W -phase at teleseismic distances, became available in 20 min (Duputel et al. 2011). For this reason, Mw computed from W -phase is especially useful for tsunami alerts at distant sites. It is at local distances that early tsunami warning becomes difficult. Even then, Mw based on inversion of W -phase recorded at regional distances may be useful. Tests show that Mw of Mexican subduction thrust earthquakes, based on W -phase recorded on broadband, regional seismograms, can be estimated in ∼7 min after the occurrence of the event (Perez-Campos et al. 2010). In recent years there has been an increase in GPS stations along the coastal region of some subduction zones. Some of these stations are operated in continuous mode (either in real-time high-rate mode or periodic low-rate download mode), and others in campaign mode. Static displacement vectors obtained from GPS data …