A Seismic Refraction Study of the Koolau Volcanic Plug

Abstract

The seismic data from the GASHOUSE line suppOrt the gravity and magnetic data as indicating a plutonic body occurring beneath the center of the Koolau caldera in the vicinity of Kailua, Oahu. This plug has a velo city greater than 7 krn/sec and adjoins material with a velocity of about 4.6 km / sec at the top and to the southeast. The width of the plug is estimated to be about 6 km down to 3-4 km. Reflections from a horizon greater than 3 km deep may indicate an und erlying magma chamber. The top of the plug is about 1600 m deep. Drilling of this plug would have considerable scientific value both geologically and geophysically. An appropriate drilling site would be at the southwest corner of Kaelepulu Pond, which "lies close to the center of the plug as now defined geophysically. Seismic reflection work directly above the dome is also recommended to test the present estimate of the depth based on refraction results .