Fault model of the 1771 Yaeyama earthquake along the Ryukyu Trench estimated from the devastating tsunami

Abstract

The 24 April 1771 Yaeyama earthquake generated a large tsunami with a maximum runup of 30 m, causing significant damage in south Ryukyu, Japan, despite the weak ground shaking. Previously proposed mechanisms of the tsunami include intraplate faulting or submarine landslide in the forearc slope. In this study, I estimate the fault parameters of the 1771 earthquake by numerically computing the tsunami heights and comparing them with the recorded heights. The result indicates that the source fault of the tsunami is very close to the Ryukyu Trench. The results are consistent with a thrust‐faulting earthquake that had a fault‐width of less than 50 km. The 1771 Yaeyama tsunami was caused by a tsunami earthquake (Mw = 8.0) that occurred in the subducted sediments beneath the accretionary wedge.