Historical Tsunami Observability for Izu-Bonin-Mariana sources: Can an Mw 9.0 hide in the Pacific Ocean

Abstract:

The Izu-Bonin-Mariana Subduction System (IBM) is one of the largest subduction zones in the world with no instrumental history of shallow focus, great earthquakes (Mw > 8). For the last fifty years, researchers have speculated on 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 we just haven’t seen them. Many circum-Pacific locations have extensive written records of tsunami run-up with some locations in Japan noting tsunami back to 684 CE. To address the question of observability, we modeled expected tsunami wave heights for various great earthquake scenarios in the IBM at selected locations around the Pacific Basin with an emphasis on locations having the possibility for a long written record. We find that some IBM source models should theoretically be observable at historically occupied locations in the Pacific Basin. Surprisingly, however, some IBM source models for earthquakes with magnitude greater than Mw 9 produce tsunami wave heights that would be essentially unobservable at historically populated Pacific Basin locations. These scenarios provide for the possibility that a magnitude Mw 9.0 could have occurred in the Pacific Basin in the past 1000 years and have gone unrecorded by humans.