The July 2020 Mw 7.8 Shumagin earthquake occurred in the seismic gap region along the Aleutian subduction zone. This interplate earthquake generated a small tsunami, but with unusual long-period waves ranging between 40 and 90 min. We examined the cause of such an anomalous ocean wave through a source modeling inverted from tsunami and geodetic data. Our model indicates that the plate-boundary rupture area was confined at depths of 20–40 km, although the slip resolvability decreases with depth. The coseismic seafloor displacement predominantly took place on the shallow continental shelf. Therefore, the initial water surface displacement at a mean water depth of ∼200 m is responsible for the long-period waves, because tsunami period is inversely proportional to the square root of water depth. Furthermore, tsunami modeling implies that slip shallower than 20 km depth in the Aleutians would displace the seafloor beyond the continental shelf and generate shorter tsunami periods.
|Journal||Geophysical Research Letters|
|Early online date||31 Jan 2022|
|Publication status||Published - 16 Feb 2022|
- extreme event
- long-period waves
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)