Rupture propagation of recent large TsE off-coast Sumatra and Java

The spatio-temporal evolution of the three recent tsunamogenic earthquakes (TsE)off-coast N-Sumatra (Mw9.3), 28/03/2005 (Mw8.5) off-coast Nias, on 17/07/2006(Mw7.7) off-coast Java. Start time, duration, and propagation of the rupture areretrieved. All parameters can be obtained rapidly after recording of the first-arrival phases in near-real time processing. We exploit semblance analysis, backpropagation and broad-band seismograms within 30°-95° distance. Image enhancement is reached by stacking the semblance of arrays within different directions.For the three events, the rupture extends over about 1150, 150, and 200km,respectively. The events in 2004, 2005, and 2006 had source durations of at least 480s, 120s, and 180s, respectively. We observe unilateral rupturepropagation for all events except for the rupture onset and the Nias event, where there is evidence for a bilateral start of the rupture. Whereas average rupture speed of the events in 2004 and 2005 is in the order of the S-wave speed (≈2.5-3km/s), unusually slow rupturing (≈1.5 km/s) is indicated for the July 2006 event.For the July 2006 event we find rupturing of a 200 x 100 km wide area in at least 2 phases with propagation from NW to SE. The event has somecharacteristics of a circular rupture followed by unilateral faulting withchange in slip rate. Fault area and aftershock distribution coincide. Spatial and temporal resolution are frequency dependent. Studies of a Mw6.0 earthquake on 2006/09/21 and one synthetic source show a ≈1° limit in resolution.Retrieved source area, source duration as well as peak values for semblance andbeam power generally increase with the size of the earthquake making possible anautomatic detection and classification of large and small earthquakes.