INVERTING TSUNAMI DEPOSITS TO THEIR SOURCE VIA TSUNAMI MODELING: SEDIMENTARY GEOLOGY, EARTHQUAKE SEISMOLOGY, AND GEOPHYSICAL FLUID DYNAMICS

Tsunami deposits are a resource for determining earthquake rupture characteristics. The most basic information derived from a tsunami deposit is 1) a tsunami must have reached the location of the deposit, and 2) the deposit's elevation is a minimum estimate of peak tsunami runup at that location. Via tsunami modeling, the size of the tsunami can then be inverted to initial sea-floor disturbance and rupture characteristics of the earthquake. Deposits and other physical evidence in the tsunami nearfield also provide important information for modelers because whereas tsunami models can routinely and reliably predict amplitudes of farfield tsunamis, nearfield tsunami amplitudes are strongly affected by earthquake characteristics such as slip distribution along the rupture length. Farfield modeling can simply use location and seismic moment of an earthquake because with increasing distance from the source, perturbations in the waveform caused by the rupture are overwritten by local effectf of the bathymetry along the travel path of the tsunami. However, in the nearfield, as every earthquake is different, so also will every tsunami be different.

Starting with tsunami deposits, we are using the tsunami model MOST [Method of Splitting Tsunamis] to elucidate several earthquake sources in the Russian Far East, including 1952 Kamchatka-Kurils, 1969 Ozernoi, 1971 Kamchatskiy, 1997 Kronotsky and 2006 middle Kurils. The high elevation of certain tsunami deposits from the Mw 9.0 1952 Kamchatka earthquake lead us to conclude via modeling that there was a region of high slip off south Kamchatka. Modeling of 1969 and 1971 northern Kamchatka tsunamis permits us to distinguish deposits from each in the field, and to elucidate both earthquakes and tsunamis. Deposits from the 1997 Kronotsky tsunami point to a larger local tsunami than catalogued and require a region of high slip at the northern end of the rupture zone. Deposits from and modeling of the 2006 mid-Kurils tsunami will provide a further test of our approach.