Detection and Modeling of the Tsunami Generated by 2013 Okhotsk Deep Focus Earthquake

Abstract:

The May 24, 2013 moment magnitude (M_W) 8.3 Sea of Okhotsk deep earthquake is the largest deep focused earthquake on record. This event is the only great (Mw > 8.0) earthquake in the past two decades to rupture at a depth greater than 300 km and is the only deep earthquake to be detected by modern geodetic tools such as DART pressure sensors, continuous GPS, and GRACE. Continuous GPS stations along the Kamchatka Peninsula and Kuril Islands recorded sub-centimeter static displacements including subsidence across the peninsula, inferring a spatially extensive region of uplift within the Sea of Okhotsk likely generating a low-amplitude, but long-wavelength tsunami wave. We use water column height changes recorded at 10 regional DART pressure sensors, to evaluate the detectability and usability of these tsunami sensors in identifying tsunami waves from such deep earthquakes. Of the 10 sites, only 2 were triggered by the event, enabling capture of high-rate (one sample per minute) pressure data. The remaining sites reported at the background rate of 15 minutes per sample. From these sensors we observed sub-centimeter tsunami waves, in general agreement with synthetics computed using normal mode theory, following the framework of Ward (1980). Additionally, despite remaining at the low-frequency background rate, we were able to identify wave periods around 9000 s across multiple DART stations. We will report on our observations of the long-period tsunami waves from these sensors, and our analysis of how they compare to both reported, and our best-fit determination of the Okhotsk earthquake focal mechanism and location.