Historical tsunami observability for Izu–Bonin–Mariana sources

Abstract

AbstractThe Izu–Bonin–Mariana Subduction System (IBM) is one of the longest subduction zones in the world with no instrumental history of shallow focus, great earthquakes (Mw > 8). Over the last 50 years, researchers have speculated on the reason for the absence of large magnitude, shallow seismicity on this plate interface, exploring factors from plate age to convergence rate. We approach the question from a different point of view: what if the IBM has hosted great earthquakes and no documentable evidence was left? To address the question of observability, we model expected tsunami wave heights from nine great earthquake scenarios on the IBM at selected locations around the Pacific Basin with an emphasis on locations having the possibility for a long, written record. Many circum-Pacific locations have extensive written records of tsunami run-up with some locations in Japan noting tsunami back to 684 CE. We find that most IBM source models should theoretically be observable at historically inhabited locations in the Pacific Basin. Surprisingly, however, some IBM source models for earthquakes with magnitudes as high as Mw 8.7 produce tsunami wave heights that would be essentially unobservable at most historically populated Pacific Basin locations. These scenarios aim to provide a constraint on the upper bound for earthquake magnitudes in the IBM over at least the past 400 years. Graphical Abstract