Differences in tsunami generation between the December 26, 2004 and March 28, 2005 Sumatra earthquakes

Abstract

Source parameters affecting tsunami generation and propagation for the M w > 9.0 December 26, 2004 and the M w = 8.6 March 28, 2005 earthquakes are examined to explain the dramatic difference in tsunami observations. We evaluate both scalar measures (seismic moment, maximum slip, potential energy) and finite-source representations (distributed slip and far-field beaming from finite source dimensions) of tsunami generation potential. There exists significant variability in local tsunami runup with respect to the most readily available measure, seismic moment. The local tsunami intensity for the December 2004 earthquake is similar to other tsunamigenic earthquakes of comparable magnitude. In contrast, the March 2005 local tsunami was deficient relative to its earthquake magnitude. Tsunami potential energy calculations more accurately reflect the difference in tsunami severity, although these calculations are dependent on knowledge of the slip distribution and therefore difficult to implement in a real-time system. A significant factor affecting tsunami generation unaccounted for in these scalar measures is the location of regions of seafloor displacement relative to the overlying water depth. The deficiency of the March 2005 tsunami seems to be related to concentration of slip in the down-dip part of the rupture zone and the fact that a substantial portion of the vertical displacement field occurred in shallow water or on land. The comparison of the December 2004 and March 2005 Sumatra earthquakes presented in this study is analogous to previous studies comparing the 1952 and 2003 Tokachi-Oki earthquakes and tsunamis, in terms of the effect slip distribution has on local tsunamis. Results from these studies indicate the difficulty in rapidly assessing local tsunami runup from magnitude and epicentral location information alone.

Experiments on generation of surface waves by an underwater moving bottom

“…bottom motions (not shown), times at which extrema of E K occur are different from the half-sine case, 5 but the contrast of kinetic energy behaves similarly withτ .…”

Tsunami inundation modeling for western Sumatra

“…In this respect, the coast near Bengkulu resembles the west coast of Aceh, as devastated in 2004 by the impact of waves that were not affected by the presence of offshore islands. By contrast, the Padang coast is analogous to the coast of North Sumatra, which suffered far less devastating tsunami inundation in 2005, ascribable at least in part to the presence of the large island of Nias between itself and the region of maximum seafloor uplift (10,24,25). Supporting information (SI) Movies 1-10 are related to tsunami wave propagation and inundation for a subset of the cases described here.…”

Field Survey of the March 28, 2005 Nias-Simeulue Earthquake and Tsunami

“…The larger runup from the smaller 2007 earthquake can be explained by differences in the location of the largest seafloor deformation. In 2005, a large fraction of the coseismic uplift occurred under northern Nias and southern Simuelue Islands (BRIGGS et al, 2006) and did not contribute to tsunami generation (KAJIURA, 1981;GEIST et al, 2006b), whereas in 2007, the uplift occurred underwater, along the bathymetric rise extending southeast from the Mentawai group towards Enggano Island FUJII and SATAKE, 2008;LORITO et al, 2008;KONCA et al, 2008). That both events had a relatively small far field signature can be explained by the reasoning above for 2005 and by the overall smaller magnitude (M o = 0.5 9 10 29 vs. 1.1 9 10 29 dyn-cm) of the 2007 event with the largest coseismic deformation occurring under relatively shallow (200-500 m depth) water.…”