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ABSTRACT: Towards In Situ Monitoring of Active Submarine Volcanoes: A Progress Report

F. Wyatt, G. Sasagawa, H. Staudigel

Hydrovolcanic explosions of active shallow submarine volcanoes (e.g., Krakatoa) and tsunamis triggered by slope instabilities of active oceanic volcanoes provide a serious threat for many population centers and navigation, in particular for the Circum-Pacific region. Seismic methods and measurement of ground tilt have been very successfully employed in subaerial volcano monitoring and in the prediction of major eruptions of many volcanoes, but have never been applied to submarine volcanoes.

Development of a prototype tiltmeter-Ocean Bottom Seismograph (Tilt-OBS) is nearing completion and is scheduled for field testing in April 1990. The package consists of and involves a modified Scripps OBS and a high precision bubble tiltmeter. The tiltmeter measurement circuitry was modified from a design by James Westphal (CalTech), most successfully used to monitor Mount St. Helens. The electronics are especially adapted to the low power consumption needs of a long-term ocean bottom experiment. Inside the capsule, an automated leveling platform is attached to the seismometer housing, which allows for leveling the tilt sensors to within 6 µrad. Initial laboratory testing was successful in measuring the local tilt in our coastline vault (approx. 3 µrad p-p). So far, long-ter stability appears to be about 5 µrad/ week, as measured inside the OBS capsule. Initial seafloor results may be plagued by instability of the capsules' contact with the (hard-rock) ocean bottom. For continuous monitoring of submarine volcanoes, we envisage powering the system through a battery pack in a buoy-mooring that could also serve as a continuous data relay to shore stations.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990