HR: 11:00h
AN: G42A-03    [Abstracts]
TI: Kinematics of the 1975 Kalapana, Hawaii Earthquake
AU: * Owen, S E
EM: owen@terra.usc.edu
AF: Univ. of Southern California, 3651 Trousdale Parkway, Los Angeles, CA 90089 United States
AU: Burgmann, R
EM: burgmann@seismo.berkeley.edu
AF: Univ. of California, Berkeley, 389 McCone Hall, Berkeley, CA 94720 United States
AB: Earthquakes on Kilauea Volcano can be even more hazardous than volcanic eruptions. The most recent large earthquake was the 1975 Kalapana quake, which generated a locally damaging tsunami, over 8 meters of horizontal displacement and 3 meters of subsidence at the coast. The magnitude estimates for this earthquake range from M$_{s}$7.2 to M$_{w}$7.7. The complexity of the seismic data is matched by the complex surface deformation that was observed with a combination of leveling, tilt and Electronic Distance Measurements (EDM). The geodetic data shows evidence of collapse of the caldera due to magma withdrawal, localized subsidence over the rift zone, shallow slumping along the Hilina Pali, and displacement on the basal detachment fault. We model the summit caldera, rift zones and basal detachment fault as dislocations in an elastic half-space to better quantify the sources of deformation related to this catastrophic event. Using inversion techniques that allow us to let the data constrain the geometry and magnitude of these sources, we find 0.04 km$^{3}$ of magma withdrawal at the summit, between 3-5 m of opening along the rift zone and 7.1 m of slip along the basal detachment at 8.3 km depth. Models that allow for finer spatial resolution of slip on the detachment show that the largest slip occurred west of the hypocenter, along the region of the fault below the coast, and that the majority of the fault slip occurred south of the region of aftershocks and background seismicity. Our best-fitting model has a geodetic moment of 4.1 10$^{20}$ N m (M$_{w}$7.7), which is consistent with tsunami models and recent analysis of long period seismic data. The residual displacements of sites located in the hanging wall of the Hilina Pali slump system, which were not used in the inversion of the other sources, suggest that triggered shallow slumping contributed several meters of horizontal displacement to the coseismic displacement at these sites.
DE: 8400 VOLCANOLOGY
DE: 1200 GEODESY AND GRAVITY
DE: 1242 Seismic deformations (7205)
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting