Effects of Depth of Fault Slip and Continental Shelf Geometry on the Generation of Anomalously Long‐Period Tsunami by the July 2020 <i>M</i> w 7.8 Shumagin (Alaska) Earthquake

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