Sensitivity tests on relations between tsunami signal and seismic rupture characteristics: The 26 December 2004 Indian Ocean event case study

Abstract

The long wave elevation of a tsunami is closely related to the characteristics of its triggering source. Tide gauges, sea level anomaly altimeters can all be used to measure the amplitude of the wave. Numerical modeling can also be used to approximate tsunami propagation based upon a certain parameterisation of the source describing the mode of generation. Once a robust numerical model has been developed, the simulated wave sequence and the various hydrodynamic observations can be compared to develop a better characterization of the tsunami source. This procedure may be used to refine the description of a tsunami source derived from seismological instrumentations. Numerical sensitivity tests of a tsunami propagation model were used to address whether a simple tide gauge record may help in better identifying the nature of the rupture process. Specifically, four different pure thrust faultings – reverse/normal faults and two opposite dipping orientations – of the 26 December 2004 Indian Ocean tsunami were simulated. The model chosen for the investigation used the representation of Okada, Y., [1985. Surface deformation due to shear and tensile faults in a half-space. Bull. Seism. Soc. Am. 75 (4), 1135–1154] to describe the rupture process and the Funwave numerical model to simulate tsunami propagation. The author finds that it is possible to identify the best-fitted scenario among the four, depending on the nature of the leading wave (crest or trough) and the ratio between the first crest amplitudes. It depends, however, on the dipping amount as the trough/crest dipole reverses at around 43°. Consequently, the depth of the earthquake (location of the epicenter within the interplate slab) also controls the nature of the leading wave (crest or depression).