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Surface-Wave Relocation and Characterization of the October 2023 Izu Islands, Japan Earthquake Swarm

Description: 

From October 1-8, 2023, a moderate-magnitude (4.1 < M <= 6.1) earthquake swarm occurred in the Izu Islands region of Japan. The swarm included 151 shallow events (depth < 30 km) catalogued by the U.S. Geological Survey and was categorized by three M >= 6 earthquakes and a cluster of 15 M 4.3 to M 5.4 earthquakes. Many of the earthquakes in the final cluster generated subsequent T-phases and were associated with tsunami waves, one of which had a maximum amplitude of 60 centimeters. However, tsunamigenesis for moderate-magnitude earthquakes is unlikely and suggests that the ocean displacements were generated from a volcanic or landslide source. Shallow-depth earthquakes in the Izu Islands region occur near seamounts and volcanic islands, but the precise characterization of volcano-related seismicity can be challenging with no local seismic monitoring. Leveraging a surface-wave relative relocation approach, we estimated precise epicentroid locations of seismic events from the swarm using over 100,000 regional-to-teleseismic surface-wave relative time shifts. Epicentroid locations show a north-northwest migration of earthquakes over eight days that initiated to the west of the Sofugan seamount. Moment tensor solutions for several swarm events are consistent with normal-faulting source mechanisms, while others are consistent with a vertical tension axis compensated-linear-vector-dipole (CLVD). The locations of epicentroids with CLVD mechanisms relative to those with normal-faulting mechanisms suggest the presence of two different but concurrent volcanic processes. The linear positioning of the normal-faulting events and the presence of CLVD mechanisms are consistent with diking activity and caldera collapse, respectively. Our relative relocation analysis of the Izu Islands swarm demonstrates the ability of surface-wave analysis to measure volcanic unrest and characterize subsequent volcanic behavior. Implemented in near real-time, surface-wave relative relocation may improve volcano monitoring efforts by providing more precise earthquake locations, time history, and characterization of seismicity in remote areas.

Session: Multidisciplinary Approaches for Volcanic Eruption Forecasting [Poster Session]

Type: Poster

Date: 5/2/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Chanel

Student Presenter: No

Invited Presentation: 

Authors