HR: 0800h
AN: V21D-0649    [Abstracts]
TI: A Closer Look at Recent Deep Mauna Loa Seismicity
AU: * Okubo, P G
EM: pokubo@usgs.gov
AF: U S Geological Survey, Hawaiian Volcano Observatory P O Box 51, Hawaii National Park, HI 96718 United States
AU: Wolfe, C J
EM: cecily@soest.hawaii.edu
AF: Hawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, Honolulu, HI 96822 United States
AU: Nakata, J S
EM: jnakata@usgs.gov
AF: U S Geological Survey, Hawaiian Volcano Observatory P O Box 51, Hawaii National Park, HI 96718 United States
AU: Koyanagi, S K
EM: koyanagi@usgs.gov
AF: U S Geological Survey, Hawaiian Volcano Observatory P O Box 51, Hawaii National Park, HI 96718 United States
AU: Uribe, J O
EM: juribe@usgs.gov
AF: U S Geological Survey, Hawaiian Volcano Observatory P O Box 51, Hawaii National Park, HI 96718 United States
AB: In 2002, Mauna Loa Volcano showed signs of reawakening, some 18 years since its last eruption in 1984. First, in April, a brief flurry of microearthquakes occurred at cataloged depths from 25 to 55 km beneath Mauna Loa's summit caldera. Then in May 2002, after the microearthquake swarm had ended, geodetic monitors across Mauna Loa's summit caldera registered a change, from line-length shortening to extension, interpreted as reinflation of a magma body approximately 4 km beneath the volcano's summit. Accordingly, the Hawaiian Volcano Observatory issued advisories related to Mauna Loa's stirring. In July 2004, HVO began to record deep long-period (LP) earthquakes beneath Mauna Loa. Historically, interpretations of such seismicity patterns have associated LP source volumes with magma chambers and magma pathways. Over a few weeks, this seismicity dramatically jumped to levels of several dozen per day. Between the months of July and December 2004, nearly 2000 Mauna Loa LPs were located between roughly 25 km and greater than 60 km depths by HVO seismic analysts. In late December, these earthquakes rather abruptly ceased, and their levels have remained low ever since. We seek a more detailed understanding of how these earthquakes may factor into Mauna Loa's eruptive framework. Given that their first arrivals are typically emergent, hypocentral estimates using only P-wave first-arrival times of LP earthquakes are often marginally constrained. With such hypocentral estimates, it is difficult to establish clear relationships among the earthquake locations themselves, or between the earthquakes and other processes like crustal extension or magma accumulation or withdrawl. Building on earlier applications to deep earthquakes in Hawaii and LP earthquakes beneath Kilauea, we are reexamining this unprecedented Mauna Loa deep seismicity with waveform correlation and precise earthquake relocation techniques. Work to date reveals that, although the waveform correlation coefficients are low, a significant subset of the deep Mauna Loa LPs can be relocated to improve our understanding of the remarkable 2004 swarm. We are currently seeking stronger resolution to determine whether the waveform data are consistent with the vertically extended, conduit-like source distributions suggested by the catalog locations or, alternatively, whether the events are consistent with one or more narrowly extended point sources.
DE: 7280 Volcano seismology (8419)
DE: 8419 Volcano monitoring (7280)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005