Rapid estimation of rupture extent for large earthquakes: Application to the 2004, M9 Sumatra‐Andaman mega‐thrust

Abstract

Rapid estimation of the rupture extent of large earthquakes is critical for tsunami warning and emergency response. The hypocenter of a distant earthquake is determined from the first seismic P waves within about 15 minutes after the event. However, methods for determining the size and rupture extent of very large earthquakes rely on long period recordings and aftershock locations, which are not available until several hours or more after the event. Here we introduce a method for rapid estimation of the rupture termination location for large earthquakes based on short period, P‐wave recordings, available about 30 minutes after an event. The hypocenter and the rupture termination location provide estimates of the extent of rupture and the event size. Application to the 2004, M9 Sumatra‐Andaman earthquake gives a rupture termination location near the Andaman Islands, about 1100 km north of the hypocenter, and a rupture duration of about 8 minutes.

Analysis of Rupture Directivity for the 2004 Sumatra Earthquake from the Rayleigh-Wave Phase Velocity

“…The av er age rup ture ve loc ity (3.1 km sec ) de ter mined by the whole source du ration. The for mer seems con sis tent with the re sults from multi ple event anal y sis (Tsai et al 2005) and the lat ter is in agree ment with pre vi ous stud ies from hydroacoustic data and re gional seis mic net work (Guilbert et al 2005;Ishii et al 2005;Krüger and Ohrnberger 2005;Lomax 2005;. Also, the es ti mated rup ture length (1164-km) agrees well with a re sult de rived from high-fre quency P-wave energy ra di a tion .…”

“…The mis fit is de fined as mis fit = 1 + g, where g is the cor re la tion co ef fi cient be tween the ob served and pre dicted data. The es ti mated source-pro cess time of 463.0 sec is in good agree ment with that ob tained in other stud ies, ~430 -515 sec (Guilbert et al 2005;Ishii et al 2005;Krüger and Ohrnberger 2005;Lomax 2005;. The optimal rup ture az i muth, 336°, mea sured clock wise from the north, ap prox i mates the strike of the fault plane so lu tion as re ported in the Har vard CMT cat alog.…”

“…The rup ture time for the 2004 Su ma tra earth quake is thus 371.0 sec, and the rup ture ve loc ity is es ti mated to be nearly 3.1 km sec -1 . This is higher than that de ter mined in other stud ies (Guilbert et al 2005;Ishii et al 2005;Krüger and Ohrnberger 2005;Lomax 2005;Ni et al 2005). How ever, mul ti ple CMT source anal y sis (Tsai et al 2005) im plied an av er age rup ture ve loc ity of ~3.0 -3.1 km sec -1 for the 2004 Su ma tra earthquake.…”

“…Re cently, stud ies of high-fre quency en ergy ra di a tion from P-waves, as well as hydroacoustic data have con firmed the rup ture length to be 1100 -1300 km (Guilbert et al 2005;Ishii et al 2005;Krüger and Ohrnberger 2005;Lomax 2005;Ni et al 2005). The source-pro cess time is 430 -515 sec, with an av er age es ti mated rup ture ve loc ity from 2.3 to 2.8 km sec -1 (Guilbert et al 2005;Ishii et al 2005;Krüger and Ohrnberger 2005;Lomax 2005;Ni et al 2005). Ammon et al (2005) de rived the slip dis tri bu tion on the fault plane from the deconvolution of sur face waves.…”

The Energy Radiated by the 26 December 2004 Sumatra–Andaman Earthquake Estimated from 10-Minute P-Wave Windows

“…Indeed, the duration, as constrained by several studies of bandlimited data, far exceeded that of any earthquake encountered to date. Lomax (2005) and Krüger and Ohrnberger (2005) exploit the fact that later arrivals (primarily PP and PPP) are depleted of high-frequency energy by virtue of ray paths that propagate multiple times in an attenuating upper mantle. After high-pass filtering of seismic records the decay of the Pwave signal can be easily seen.…”