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Title

Seismicity and Velocity Structure of Offshore Hawai`i, including Lo`ihi Submarine Volcano

Date Permissions Signed

5-12-2017

Date of Award

Spring 2017

Document Type

Masters Thesis

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

Caplan-Auerbach, Jacqueline

Second Advisor

Thurber, Clifford H.

Third Advisor

Housen, Bernard Arthur.

Abstract

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

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.

Type

Text

Publisher

Western Washington University

OCLC Number

987856251

Digital Format

application/pdf

Geographic Coverage

Hawaii

Genre/Form

Academic thesis

Language

English

Rights

Copying of this thesis in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this thesis for commercial purposes, or for financial gain, shall not be allowed without the uthor's written permission.