A two-dimensional seismic investigation of crustal structure under the Hawaiian Islands near Oahu and Kauai

Abstract

Two expanding spread profiles (ESPs) were analyzed in detail to investigate the deep structure of the volcanoes and the underlying oceanic crust near Oahu. A 2.4-km vertical offset in the preexisting crust, inferred to be a large fault zone, was found near the midpoint of one of the profiles. This fault may form the southern wall of a graben or half graben in which Kauai sits. The other profile is located over a shallow 4-km-thick basin filled with volcaniclastics and possibly volcanic flows bordered by the islands of Oahu and Molokai, Penguin Bank, and two buried rift zones. Under this basin the main volcanic edifice is 4 to 5 km thick. The top of the preexisting oceanic crust is 8 to 9 km below sea level and is 3 to 4 km lower than the crust away from the islands. The underlying oceanic crust is 6 to 7 km thick excluding the Moho transition zone, which is of normal thickness and at a depth from 15 to 16 km. -Author