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Source inversion of W phase: speeding up seismic tsunami warning

Kanamori, Hiroo and Rivera, Luis (2008) Source inversion of W phase: speeding up seismic tsunami warning. Geophysical Journal International, 175 (1). pp. 228-238. ISSN 0956-540X. doi:10.1111/j.1365-246X.2008.03887.x.

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W phase is a long period phase arriving before S wave. It can be interpreted as superposition of the fundamental, first, second and third overtones of spheroidal modes or Rayleigh waves and has a group velocity from 4.5 to 9 km s^−1 over a period range of 100–1000 s. The amplitude of long period waves better represents the tsunami potential of an earthquake. Because of the fast group velocity of W phase, most of W phase energy is contained within a short time window after the arrival of the P wave. At a distance of 50°, W phase energy is contained within 23 min after the origin time which is the distinct advantage of using W phase for rapid tsunami warning purposes. We use a time domain deconvolution method to extract W phases from the broad-band records of global seismic networks. The bandwidth of W phase is approximately from 0.001 to 0.01 Hz, and we bandpass filter the data from 0.001 to 0.005 Hz in most cases. Having extracted W phase from the vertical component records, we perform a linear inversion using a point source to determine Mw and the source mechanism for several large earthquakes including the 2004 Sumatra–Andaman earthquake, the 2005 Nias earthquake, the 2006 Kuril Is. earthquake and the 2007 Sumatra earthquake. W phase inversion yields reliable solutions and holds promise of the use of W phase for rapid assessment of tsunami potential.

Item Type:Article
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Kanamori, Hiroo0000-0001-8219-9428
Rivera, Luis0000-0002-0726-5445
Additional Information:© 2008 RAS. Accepted 2008 June 12. Received 2008 June 12; in original form 2008 April 2. We thank Göran Ekström and an anonymous reviewer for helpful comments on the original manuscript, and Rhett Butler for helpful technical discussion on global seismic network data. This work made use of GMT and SAC software and Federation of Digital Seismic Networks (FDSN) seismic data. The Incorporated Research Institutions for Seismology (IRIS) Data Management System (DMS) was used to access the data.
Subject Keywords:Tsunamis; Earthquake source observations; Surface waves and free oscillations; Wave propagation, Early warning.
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Record Number:CaltechAUTHORS:KANgji08
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13494
Deposited On:23 Apr 2009 19:10
Last Modified:08 Nov 2021 22:38

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