HR: 1330h
AN: OS22B-1159    [PDF]
TI: Boussinesq Modeling of the Complex 1975 Kalapana, Hawaii Geological Event
AU: * Grilli, S T
EM: grilli@oce.uri.edu
AF: Department of Ocean Engineering, University of Rhode Island, Narragansett, RI 02882 United States
AU: Watts, P
EM: phil.watts@appliedfluids.com
AF: Applied FLuids Engineering, PMB \#237, 5710 E 7th Street, Long Beach, CA 90803 United States
AU: Day, S J
EM: s.day@ucl.ac.uk
AF: Benfield Greig Hazard Research Centre, Department of Earth Sciences, University College, London, S01 United Kingdom
AU: Kirby, J T
EM: kirby@udel.edu
AF: Center for Applied Coastal Research, University of Delaware, Newark, DE 19716 United States
AB: The potential for a catastrophic flank collapse of Kilauea, on the southern edge of the big island of Hawaii, has occupied scientists for decades. The tsunami hazard from such a potential collapse is hard to conceive of, and therefore deserves serious consideration. The 1975 Kalapana earthquake and tsunami may offer insight into the mechanics of Kilauea collapse, especially when combined with recent marine geology interpretations. The 1975 event is admittedly not of the scale of a catastrophic flank collapse. The reason why this insight is possible is because the tsunami observations and records constrain volcano failure, while at the same time supporting a new interpretation of volcano structures. Therefore, water wave information can also provide geological information. The flank of Kilauea is a complex structure, presumably capable of emitting seismic waves along multiple faults during an adjustment of the volcano flank. This has been recognized through a debate among seismologists as to the frequency content and orientation of a fault plane based on seismic records. We resolve the debate between two competing seismic mechanisms by accepting both. We recognize a steeply dipping fault just off of Halape that can explain high frequency earthquake content, as well as a shallow dipping thrust complex near the base of Kilauea that can explain low frequency earthquake content. Each earthquake provides a distinct tsunami source. The former tsunami source is necessary to explain eyewitness observations at Halape, while the latter is necessary to explain the far-field tsunami records. The two faults are apparently linked by a slumping of the Kilauea flank that ranges from the Hilina Pali system down to the base of Kilauea at over 5000 m deep. The slump, while not a new idea for the 1975 event, provides a third and essential tsunami source. The slump appears to be seismically quiet, which seems possible given recent observations of Kilauea displacement. We generate the three tsunami sources using TOPICS (which is based on fully nonlinear potential flow computations) and simulate tsunami propagation and inundation with the higher-order Boussinesq model FUNWAVE. The simulation results reproduce runups based on detailed accounts of survivors at Halape, in the near-field. They also describe maximum runup above sea level around the big island of Hawaii, including at Hilo. By far the nicest result is that our simulations of the 1975 event quite well reproduce the tide gauge records measured at Hilo (Big Island), Honolulu (Oahu), and Kahalui (Maui), the last two being in the far-field. The agreement of the numerical simulation results with observations supports our interpretation of Kilauea structures, even if overly simplistic as of now. These results raise doubt as to the potential for catastrophic collapse of the Kilauea flank.
DE: 4255 Numerical modeling
DE: 4564 Tsunamis and storm surges
DE: 7223 Seismic hazard assessment and prediction
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting