Combining constraints from tsunami modeling and sedimentology to untangle the 1969 Ozernoi and 1971 Kamchatskii tsunamis

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 resultant tsunamis were recorded on tide gauges, but only the 1969 tsunami has cataloged observations of runup, and these observations are limited and questionable. We used a combination of field mapping of tsunami deposits and tsunami modeling to augment this historical record. We mapped tsunami deposits above A.D. 1956 and 1964 volcanic ash layers, along more than 200 km of shoreline. However, the 1969 and 1971 tsunami deposits are not distinguishable in the field. The distribution of tsunami‐deposit elevation has two latitudinal peaks. From 58° to 57° sediment runup typically ranges from 2 to 4 m, decreasing to the south. From 57° to 56° sediment runup typically ranges from 3 to 6 m (maximum more than 10 m), increasing to the south. Models of local runup for the 1969 and 1971 tsunamis explain most of the sediment distribution, differentiate the two tsunamis in some localities, and elucidate the earthquakes' focal mechanisms and rupture areas.