Mw8.6 Sumatra Earthquake and Tsunami, 11 April 2012, 08:38 UTC

Early-est: Rapid location, tsunami potential and magnitude determinations in real-time

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

Alberto Michelini - Istituto Nazionale di Geofisica e Vulcanologia, Roma, Italy, alberto.michelini@ingv.it

During the earthquake and tsunami in Sumatra, the Early-est Earthquake Monitor implementing the rapid magnitude and tsunami warning algorithms described in our recent papers (see below) was running in real-time at ALomax Scientific and at the INGV seismic center in Rome.

The Early-est monitor first located the M8.6 mainshock at origin time (OT) +4min, and indicated:

A high tsunami warning level of Td*T50Ex=11 at OT+5min,
Mwpd=8.6-9.0 and earthquake rupture duration T0=130-150s at OT+5min to OT+10min, stabilizing to Mwpd=8.8 and T0=170s thereafter,
SW-NE extensional first-motion faulting mechanism at OT+6min, stabilizing to a strike-slip mechanism at OT+10min and thereafter.

We note that:

The Td*T50Ex=11 tsunami warning level is not high for an M8.6 event, consistent with the moderate size tsunami generated by this earthquake.
The Mwpd=8.8 magnitude and T0=170s duration estimates provided early information on the true size and extent of the earthquake rupture; these rapid measures should be useful during future large earthquakes for regional tsunami warning, and early shakemap, finite-fault and tsunami forecast modeling.
The Early-est monitor greatly overestimated the magnitude of the M8.2 aftershock at 10:43 UTC (due to overlapping surface waves from the earlier M8.6 mainshock), and the monitor miss-associated late phases from the M8.6 mainshock into false events with large magnitude or high tsunami potential. The problems are consequences of Early-est being a new, prototype and fully automatic system with no manual editing of results; solutions to these and related problems are available, but will be time consuming to implement and test.

Early-est Earthquake Monitor real-time display at origin time + 5min

Early-est Earthquake Monitor real-time display at origin time + 10min

INGV Early-est Earthquake Monitor: http://early-est.rm.ingv.it
ALomax Scientific Early-est Earthquake Monitor: http://early-est.alomax.net

References:

Lomax, A. and A. Michelini (2012), Tsunami early warning within 5 minutes, PAGEOPH, submitted.

Lomax, A. and A. Michelini (2011), Tsunami early warning using earthquake rupture duration and P-wave dominant period: the importance of length and depth of faulting, Geophys. Journal Int., first published on-line Jan. 20, 2011, DOI: 10.1111/j.1365-246X.2010.04916.x. (further information)

Lomax, A. and A. Michelini (2009), Tsunami early warning using earthquake rupture duration, Geophys. Res. Lett., 36, L09306, doi:10.1029/2009GL037223. (further information)

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. (further information)