Ground deformation associated with the 1975 magnitude-7.2 earthquake and resulting changes in activity of Kilauea Volcano, Hawaii.

Abstract

A magnitude-7.2 earthquake on November 29, 1975, the largest in Hawaii in over a century, was associated with large-scale deformation of the entire S flank of Kilauea Volcano. Since the 1975 earthquake, deformation patterns on Kilauea Volcano have changed notably. Previously, rates of horizontal and vertical deformation at the summit were very high (several mm/day) in the 20th century, mainly reflecting inflation-deflation cycles related to eruptive activity as magma accumulated in or was withdrawn from a 2-3 km deep magma reservoir centered near the summit. Since the earthquake, deformation patterns have been complex. The volcano has failed to maintain sustained inflation cycles similar to those of the recent past, and the dominant deformation pattern has been seaward displacement of the S flank, presumably reflecting ongoing adjustments to effects of the 1975 earthquake. In September 1977, Kilauea erupted along its middle E rift zone after the longest period of inactivity in 10 years. No summit inflation preceded this eruption, which, nevertheless, may indicate the beginning of stabilization and return of the volcano to a more typical deformation pattern.-from Authors