Implications of the 26 December 2004 Sumatra–Andaman Earthquake on Tsunami Forecast and Assessment Models for Great Subduction-Zone Earthquakes

Abstract

Results from different tsunami forecasting and hazard assessment models are compared with observed tsunami wave heights from the 26 December 2004 Indian Ocean tsunami. Forecast models are based on initial earthquake information and are used to estimate tsunami wave heights during propagation. An empirical forecast relationship based only on seismic moment provides a close estimate to the observed mean regional and maximum local tsunami runup heights for the 2004 Indian Ocean tsunami but underestimates mean regional tsunami heights at azimuths in line with the tsunami beaming pattern (e.g., Sri Lanka, Thailand). Standard forecast models developed from subfault discretization of earthquake rupture, in which deepocean sea level observations are used to constrain slip, are also tested. Forecast models of this type use tsunami time-series measurements at points in the deep ocean. As a proxy for the 2004 Indian Ocean tsunami, a transect of deep-ocean tsunami amplitudes recorded by satellite altimetry is used to constrain slip along four subfaults of the M Ͼ9 Sumatra-Andaman earthquake. This proxy model performs well in comparison to observed tsunami wave heights, travel times, and inundation patterns at Banda Aceh. Hypothetical tsunami hazard assessments models based on endmember estimates for average slip and rupture length (M w 9.0-9.3) are compared with tsunami observations. Using average slip (low end member) and rupture length (high end member) (M w 9.14) consistent with many seismic, geodetic, and tsunami inversions adequately estimates tsunami runup in most regions, except the extreme runup in the western Aceh province. The high slip that occurred in the southern part of the rupture zone linked to runup in this location is a larger fluctuation than expected from standard stochastic slip models. In addition, excess moment release (ϳ9%) deduced from geodetic studies in comparison to seismic moment estimates may generate additional tsunami energy, if the exponential time constant of slip is less than approximately 1 hr. Overall, there is significant variation in assessed runup heights caused by quantifiable uncertainty in both first-order source parameters (e.g., rupture length, slip-length scaling) and spatiotemporal complexity of earthquake rupture.

On the solitary wave paradigm for tsunamis

“…[83] Typical historic fault areas of major earthquakes are listed in, e.g., Geist [1999], and details on the recent Sumatra earthquake can be found in, e.g., Stein and Okal [2005], Hirata et al [2006], Fujii and Satake [2007] and Geist et al [2007].…”

Integration of High-Resolution, Active and Passive Remote Sensing in Support to Tsunami Preparedness and Contingency Planning

“…The worst documented such case occurred in the near field of a M W =8.0 earthquake in 1946 at Unimak Island, Alaska, where the Scotch Cap lighthouse was flushed away by a 35-meter high wave. Reportedly, wave heights for the great Indian Ocean tsunami of 26 th December 2004, may have exceeded 15 m along northern Sumatra coasts (Geist et al, 2007). In Sri Lanka, about 2000 km away from the epicentre of the M W =9.2±0.1 earthquake, largest wave heights may have exceeded 10 m in the East, whereas at least 5000 lives were taken by wavetrains not higher than 4 m, in the South and the Southwest of the island.…”

Numerical simulation of March 11, 2011 Honshu, Japan tsunami

“…They are often employed to derive tsunami Green functions for the estimation of slip distribution along seismic faults or of an initial tsunami distribution [7,8]. They are also used in tsunami hazard assessments for happened and expected future large earthquakes [9,10]. For conventional tsunami simulations, the mass conservation equation that is also called the continuity equation of Shallow Water Equation is…”