SEDIMENTARY EVIDENCE AND NUMERICAL MODELING OF TSUNAMIS ASSOCIATED WITH LARGE EARTHQUAKES OFF KAMCHATKA IN 1969 AND 1971

Large tsunamigenic earthquakes occurred in 1969 (Mw 7.7) and 1971 (Mw 7.8) along the Bering Sea and northernmost Pacific coast of Kamchatka. Both the earthquakes occurred off of well defined plate boundaries in the region. The 1969 and 1971 tsunamis were recorded on tide gages, but due to sparse population and winter occurrence catalog runup observations are limited to the 1969 tsunami. We used a combination of field mapping of tsunami deposits and tsunami modeling, with MOST, to expand knowledge of runup and geographic extent of these two tsunamis. Field work from the Bering and northern-most Pacific coast showed a deposit of unknown origin deposited post-1956 or post-1964 based on stratigraphic location above tephra. Computer modeling was then used to model the runup of the tsunamis to determine the probable tsunami source of the deposits. Wave heights were highest on the peninsulas near the ruptures of each tsunami. Deposits inferred to correlate with the 1969 tsunami reach elevations over 4m on Ozernoi Cape, and those likely from the 1971 tsunami reach over 13 m on Kamchatskii Cape. There were some regions where the models gave similar heights and we were unable to assign a tsunami source to the deposit. Modeling of initial deformation using earthquake parameters form published studies showed no need to induce a landslide to augment wave height to explain sedimentologically observed heights.