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The 26 January 1700 Cascadia Earthquake as Part of an Event Sequence

Session: Earthquake Science, Hazards and Policy in Cascadia I

Type: Oral

Date: 4/20/2021

Presentation Time: 03:15 PM Pacific

Description: 

Coastal subsidence, dating of soil samples and tree rings, and sedimentological evidence of a tsunami point to coseismic activity on a sizable portion of the Cascadia subduction zone circa 1700. Documents from Japan reveal that on January 26^th of that year there were tsunami impacts across distant locations in the country and modeling shows that a large Cascadia earthquake is the source. The prevailing hypothesis is that only a single large event rupturing the entire plate boundary explains this. Here we simulate tens of thousands of ruptures and compute their subsidence and tsunami signals and show that it is possible that the 1700 earthquake was instead part of a sequence of several earthquakes. Partial rupture of the megathrust in one large ~M8.7+ earthquake explains the tsunami in Japan and a part of the coastal subsidence. As many as four more earthquakes with M<8.6 can complete the coseismic subsidence signal without their tsunamis being large enough to be recorded in Japan. Given the spatial gaps in the subsidence data it is also possible that short segments of the megathrust have remained unbroken. The findings have significant implications for Cascadia geodynamics and how earthquake and tsunami hazards in the region are quantified.

Presenting Author: Diego Melgar

Student Presenter: No

Authors