HR: 1340h
AN: V53C-1420    [Abstracts]
TI: Distribution and geometry of magma bodies within Hawaiian volcanic edifices inferred from 3-D seismic velocity and density models
AU: * Park, J
EM: samabar@rice.edu
AF: Rice University, Department of Earth Science, Rice University, 6100 Main Street, Houston, TX 77005, United States
AU: Zelt, C A
EM: czelt@rice.edu
AF: Rice University, Department of Earth Science, Rice University, 6100 Main Street, Houston, TX 77005, United States
AU: Morgan, J K
EM: morganj@rice.edu
AF: Rice University, Department of Earth Science, Rice University, 6100 Main Street, Houston, TX 77005, United States
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: Kauahikaua, J P
EM: jimk@usgs.gov
AF: U.S. Geological Survey, Hawaiian Volcano Observatory, P.O. Box 51, Hawaii National Park, HI 96718, United States
AB: Magmatic intrusions within active Hawaiian volcanoes, e.g., Kilauea and Mauna Loa, often result in measurable surface deformation. However, constraining the source of such deformation is often difficult, and dependent upon assumptions regarding source mechanism, geometry and depth. Estimates for these parameters can be improved by independent constraints on the distribution and geometry of magma bodies within the volcanic edifices. Here, we present seismic P-wave velocity and density models of the onshore and offshore regions around the Island of Hawaii, including parts of Hualalai, Mauna Kea, Mauna Loa, and Kilauea volcanoes, and Loihi seamount. The velocity and density models suggest that the distribution and geometry of magma bodies within the volcanic edifices, indicated by high-velocity and high-density anomalies, might be deeply related to the surface deformation. The velocity model was determined by tomographic inversion of ~200,000 first-arrival traveltime picks of earthquakes and airgun shots recorded by the Hawaiian Volcano Observatory (HVO). The summits of Mauna Loa and Kilauea are underlain by localized high-velocity anomalies of 4.0-4.3 km/s just a few km below the surface, probably indicating shallow summit magma reservoirs responsible for localized inflation and deflation cycles. More extensive high-velocity anomalies of 6.5-7.0 km/s occur beneath the active rift zones of Kilauea, Mauna Loa, and Loihi, and are attributed to intrusive complexes comprising both dense dikes and olivine cumulates precipitated from long-lived deep magma chambers. These deeper bodies are responsible for the outward creep of the volcanic edifices, and probably also upper flank subsidence. Interestingly, the high-velocity bodies are not continuous, but commonly occur as discrete features, which may account for deformation partitioning along the volcano flanks. Kilauea's east rift zone (ERZ) shows two zones of high velocities, one near the summit and upper ERZ and one beneath the lower ERZ, with a region of low velocities beneath the central ERZ. Mauna Loa's lower southwest rift zone (SWRZ) is marked by a prominent high-velocity zone, lacking along the central and upper SWRZ. Mauna Loa's northeast rift zone shows high-velocity materials offset to the south of the current vent trend. High-velocity regions also occur without obvious surface expression, for example, beneath the south flanks of Hualalai, Mauna Kea, and Mauna Loa. These point to buried rift zones, unrelated to the current trends of surface vents on these volcanoes. The density structure of the island and its surroundings is obtained by converting the seismic velocity model to a density model using an empirical relationship. This relationship defines an initial/reference model for the 3-D inversion of onshore and offshore gravity data. The final inversion yields density anomalies that provide additional constraints on material properties. The largest positive density anomalies are observed beneath the summits and upper rift zones of Mauna Loa, Kilauea and Loihi, possibly due to the molten condition of the underlying magma cumulates. In contrast, the high-velocity features beneath the south flank of Mauna Loa yield densities consistent with their velocities, and are thus interpreted to reflect solidified magma cumulates and dike swarms along the old rift zone, resisting flank deformation.
DE: 7200 SEISMOLOGY
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8180 Tomography (6982, 7270)
DE: 8400 VOLCANOLOGY
DE: 8439 Physics and chemistry of magma bodies
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting