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Master of Science (MS)
Thurber, Clifford H.
Housen, Bernard Arthur.
This study presents the earthquake data collected from a nine month deployment (September 2010 - June 2011) of a temporary ocean bottom seismometer (OBS) network fully surrounding Lo‘ihi submarine volcano, Hawai‘i. This allowed us to widen the aperture of earthquake detection around the Big Island, lower the magnitude detection threshold, and better constrain the hypocentral depths of offshore seismicity that occurs between the OBS network and the Hawaiian Volcano Observatory (HVO) land based network. Although this deployment occurred during a time of volcanic quiescence for Lo‘ihi, it establishes an important basis for background seismicity of the volcano. 463 earthquakes were located using the OBS network, incorporating data from the HVO network where possible. Here we present relocated hypocenters using the double-difference earthquake location algorithm HypoDD (Waldhauser and Ellsworth, 2000), as well as tomographic images for an area 80x80 km2 around the summit of Lo‘ihi. Offshore seismicity during this study is punctuated by events locating in the mantle fault zone 25-40 km deep. These events reflect rupture on preexisting faults in the lower lithosphere caused by stresses induced by volcano loading and flexure of the Pacific Plate (Wolfe, et al., 2004; Pritchard et al., 2007). A shallow cluster of highly-correlated events was located on the western boundary fault of Kilauea’s mobile south flank. Tomography was performed using the double-difference seismic tomography method TomoDD (Zhang and Thurber, 2003) and showed overall velocities to be slower than the regional velocity model (HG50; Klein, 1981) in the shallow lithosphere above 16 km depth. A broad, low-velocity anomaly was observed from 20-40 km deep, and is suggestive of the central plume conduit that supplies magma to the active volcanoes. A localized high-velocity body is observed 4-6 km deep beneath Lo‘ihi’s summit, extending 10 km to the North and South. Following Lo‘ihis active rift zones and crossing the summit, this high-velocity body is characteristic of dense basaltic dikes and magma cumulates. Two low-velocity anomalies are observed below the oceanic crust, interpreted as melt accumulation beneath Lo‘ihi and magmatic underplating beneath Hawai‘i Island.
Western Washington University
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Merz, Dara K., "Seismicity and Velocity Structure of Offshore Hawai`i, including Lo`ihi Submarine Volcano" (2017). WWU Graduate School Collection. 571.