Mwpd: A Duration-Amplitude Procedure for Rapid Determination of Earthquake Magnitude and Tsunamigenic Potential from P Waveforms
Anthony Lomax - A Lomax Scientific, Mouans-Sartoux, France. www.alomax.net, anthony@alomax.net
Alberto Michelini - Istituto Nazionale di Geofisica e Vulcanologia, Roma, Italy
This article has been published in Geophysical Journal International of the Royal Astronomical Society and Blackwell Publishing:
- Lomax,
A. and A. Michelini (2009),
Mwpd: A
Duration-Amplitude Procedure for Rapid Determination of
Earthquake Magnitude and Tsunamigenic Potential from P Waveforms,
Geophys. J. Int.,176,
200-214. (PDF)
- (PDF Poster AGU 2007)
- (PDF Poster AGU 2007)
October, 2007
Abstract
- We
present a duration-amplitude procedure for rapid determination of
an earthquake moment magnitude, Mwpd,
from P-wave
recordings at teleseismic distances. The Mwpd
magnitude
can be obtained within 20 minutes or less after the event origin
time since the required data is available in near-real time. The
procedure determines apparent source durations, T0,
from high-frequency, P-wave
records, and estimates moments through integration of broadband
displacement waveforms over the interval tP
to
tP+T0,
where tP
is
the P
arrival
time. We apply the duration-amplitude methodology to a number of
recent, large earthquakes (Global Centroid-Moment Tensor
magnitude, MwCMT,
6.6 to 9.3) with diverse source types. The results show that a
scaling of the moment estimates for interplate thrust and
possibly tsunami earthquakes is necessary to best match MwCMT.
With this scaling, Mwpd
matches
MwCMT
typically
within ﾱ0.2
magnitude units, with a standard deviation of σ=0.10,
outperforming other approaches to rapid magnitude determination.
In addition, Mwpd
does
not exhibit saturation for the largest events, or, equivalently,
ΔM=Mwpd-MwCMT
does not
become more negative with
increasing MwCMT.
The explicit use of the source duration for integration of
displacement seismograms, the moment scaling, and other
characteristics of the duration-amplitude methodology make it an
extension of the widely used, Mwp,
rapid-magnitude procedure.
The obtained durations and duration-amplitude moments allow rapid
estimation of the energy-to-moment ratio Θ
used
for identification of tsunami earthquakes. The need for a moment
scaling for interplate thrust and possibly tsunami earthquakes
may have important implications for the source physics of these
events.
Figure
Duration-amplitude magnitude Mwpd from this study compared to CMT magnitude MwCMT.
Event symbols are: interplate thrust events (blue inverted triangles); tsunami earthquakes (red squares); other event types (green diamonds). IThe value MwCMT=9.3 for 2004.12.26 Sumatra-Andaman is from Tsai et al. (2005).