Ground Displacement Analysis of the 1975 Kalapana Earthquake (South Flank of Kīlauea Volcano) Using Air Photo Correlation.

Abstract:

The Kīlauea volcano is composed of several structural components, with the Kīlauea caldera, the East and Southwest Rift Zones, the Koa‘e and the Hilina fault systems and a deep detachment related to a volcano flank instability. The origin, the relation and the evolution of the active fault systems on the south flank (e.g. Koa‘e and Hilina) is still poorly understood, including its role in magma storage in the area and the overall flank instability evolution. Here we focus on the magnitude 7.7 earthquake that occurred on 29 November 1975 that triggered ground displacement of several meters all over the south flank of Kilauea volcano. Ground displacement occurred along a 25 km long sector of the Hilina and Holei fault system with vertical and horizontal displacement along preexisting fault scarp. Our aim is to extract and quantify the displacement that occurred during the event using air photo correlation and geodetic data and better understand the overall volcano flank dynamics.

To quantify the coseismic ground displacement, we use an optical imagery correlation technique. We analyzed the 1975 earthquake using 12 and 15 photos for the pre-event (October 1974 and July 1975, respectively) and 6 and 12 photos for the post-event time period (December 1976 and March 1977, respectively). Results show ground displacements of several meters on Kīlauea’s south flank (Hilina fault system and Holei Pali), in agreement with EDM measurements of 8 meters horizontal displacement measured at the coastline. These data will later be integrated with leveling data to provide better quantification and constraints on ground deformation during the event.