Seismic imaging of the Izu-Oshima volcano using dense onshore-offshore datasets
Abstract
The Izu-Oshima volcano is an active stratovolcano of the Izu-Bonin arc offshore Japan, that last erupted in 1986-1990. Imaging viscoelastic structures of the volcano and surrounding tectonic settings is essential to understand the volcanic system of the Izu-Oshima volcano. We analyze a unique seismic dataset acquired in 2009, and aim to image both regional tectonic and local volcanic structures by exploiting active, earthquake, and ambient noise data. We use 4 days of seismic data recorded using existing 36 seismographs, 286 temporary geophones, and 37 temporary Ocean Bottom Seismographs (OBSs). During the period, large-volume air-gun sources and explosives were densely excited for a total of 1234 times along the OBS line and around the island.
The seismic record contains varieties of waveforms excited by air guns, ambient noise, small volcanic earthquakes, and a few regional earthquakes. We observe quite complicated waveforms; highly fluctuating first arrivals, significant amount of reflections/refractions, shadow zones arising from low velocity structures associated with magma conduits or the topography of the volcano, and strong but localized attenuation of waves propagating across a conduit. By cross-correlating ambient noise data, we extract coherent surface and body waves across the island with good signal to noise ratio. We use the OBS array data to image regional velocity structures, and the onshore seismographs and geophones to delineate detailed local velocity and attenuation structures of the volcano. We estimate P-wave structures from active shot data, and S-wave structures from the correlated noise data. By combining P- and S-wave information, we can infer subsurface pressure and fluid distribution of the volcanic system. Then we locate the spatial distribution of volcanic earthquakes, and illustrate relationships with the obtained structures. The comprehensive analysis of the seismic waveforms will lead us to discuss the subsurface physical condition of the volcanic system.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.V51G0213N
- Keywords:
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- 3613 Subduction zone processes;
- MINERALOGY AND PETROLOGY;
- 8170 Subduction zone processes;
- TECTONOPHYSICS;
- 8185 Volcanic arcs;
- TECTONOPHYSICS;
- 8413 Subduction zone processes;
- VOLCANOLOGY