Publication Date:
2017-04-04
Description:
We present a duration-amplitude procedure for rapid determination of a moment magnitude,
Mwpd, for large earthquakes using P-wave recordings at teleseismic distances. Mwpd can be
obtained within 20 minutes or less after the event origin time as the required data is currently
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 79 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 ±0.2
magnitude units, with a standard deviation of σ=0.11, equaling or outperforming other
approaches to rapid magnitude determination. Furthermore, Mwpd does not exhibit saturation;
that is, for the largest events, Mwpd does not systematically underestimate MwCMT. The obtained
durations and duration-amplitude moments allow rapid estimation of an energy-to-moment
parameter Θ* used for identification of tsunami earthquakes. Our results show that Θ* ≤ -5.7
is an appropriate cutoff for this identification, but also show that neither Θ* nor Mw is a good
indicator for tsunamigenic events in general. For these events we find that a reliable indicator
is simply that the duration T0 is greater than about 50 sec. 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 need for a moment scaling for interplate thrust
and possibly tsunami earthquakes may have important implications for the source physics of
these events.
Description:
DPC-INGV (2007-2009) S3 Project
Description:
Published
Description:
200-214
Description:
3.1. Fisica dei terremoti
Description:
JCR Journal
Description:
open
Keywords:
earthquakes, Richter magnitude, seismic moment, seismograms, tsunami, earthquakesource mechanism
;
04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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