Tsunami early warning using earthquake rupture duration

Anthony Lomax - ALomax Scientific, Mouans-Sartoux, France. www.alomax.net, anthony@alomax.net

Alberto Michelini - Istituto Nazionale di Geofisica e Vulcanologia, Roma, Italy

Published in Geophysical Research Letters:

Lomax, A. and A. Michelini (2009), Tsunami early warning using earthquake rupture duration, Geophys. Res. Lett., 36, L09306, doi:10.1029/2009GL037223. (article: http://www.agu.org/journals/gl/gl0909/2009GL037223 login & password: 50757847) ) (PDF Talk EGU 2009)

Effective tsunami early warning for coastlines near a tsunamigenic earthquake requires notification within 5-15 minutes. We have shown recently that tsunamigenic earthquakes have an apparent rupture duration, T0, greater than about 50 s. Here we show that T0 gives more information on tsunami importance than moment magnitude, Mw, and we introduce a procedure using seismograms recorded near an earthquake to rapidly determine if T0 is likely to exceed T=50 or 100 s. We show that this duration-exceedance” procedure can be completed within 3-10 min after the earthquake occurs, depending on station density, and that it correctly identifies most recent earthquakes which produced large or devastating tsunamis. This identification forms a complement to initial estimates of the location, depth and magnitude of an earthquake to improve the reliability of tsunami early warning, and, in some cases, may make possible such warning.

Auxiliary material: readme.txt.

Example 1: Tsunamigenic and non-tsunamigenic earthquakes with similar magnitudes

Evolution for 10 min after OT of the T0>50 s exceedance level (L50) calculation for: (upper) 2006.07.17, Mw7.7, T0=180 s, tsunami importance It=18, Indonesia tsunami earthquake, and (lower) 2009.03.19, Mw7.6, T0=39 s, tsunami importance It=1, Tonga Islands interplate thrust. Blue lines show P-arrival times for each station; red, yellow or green horizontal bars show the station exceedance levels, l50, starting at its first reported time (about 60 s after the corresponding P time). Histogram shows l50 values at 600s; the median (50 percentile) and bounds (20 and 80 percentile), respectively, for L50 are indicated by solid and dotted white lines on the main plot and as a colored diamond and error bar. Red indicates l50(or L50)≥1 (likely that T0>50 s and It≥2); yellow indicates 0.7≤l50(or L50)<1 (possible that T0>50 s and It≥2); green indicates l50(or L50)≤0.7 (unlikely that T0>50 s or It≥2). For both events the L50 values have stabilized by 4-6 min after OT.

Example 2: Real-time monitoring (available at: http://s3.rm.ingv.it/D-E.php)

Comprehensive information about exceedance level is provided by a time-sliding displays such the following: