Tsunamis (seismic sea waves) are generated by sudden vertical motion of the sea floor.
Because the Fairweather and Denali/Chatham Strait fault systems are strike-slip (sideways
motion parallel to the fault), they are not likely to generate tsunamis. However, earthquake
ground shaking can indirectly cause locally generated waves by triggering landslides in the steep
terrain nearby. If a major landslide enters sea water or occurs on the seafloor, a large local wave
can be generated that can be devastating to people and facilities along nearby shorelines. There is
little warning because the waves can travel from the source to nearby coastal areas in a matter of
minutes. Areas most vulnerable are deep bays and inlets adjacent to steep slopes. In these semienclosed
basins, the water can oscillate to create a large wave, called a seiche, which can impact
the shorelines several times before dissipating. The waves that destroyed much of old Valdez
after the great 1964 earthquake were caused by an earthquake-triggered submarine slide. In 1958,
an earthquake on the Fairweather fault triggered a large landslide that crashed into the head of
Lituya Bay, generating a wave that stripped trees to an elevation of 1,700 ft. on the opposite
shoreline.
