Seismic studies on Kilauea Volcano, Hawaii Island

Abstract

This volume contains reports on seismological studies done in conjunction with other geophysical and geochemical studies of the Hawaii Geothermal Project. The studies were conducted on the easternmost portion of the East Rift Zone of Kilauea Volcano, near the eventual site of the initial well, HGP-A, drilled by the Hawaii Geothermal Project. The microearthquake survey by Suyenaga and Furumoto found, among other patterns of seismicity, a small cluster of events at 1-to 3-km depth in the immediate vicinity of HGP-A. Another microearthquake survey conducted by Mattice and Furumoto over a high electrical conductivity anomaly located west of HGP-A found it to be probably more seismically active than the area around the well site. Norris and Furumoto contoured noise levels but found no local amplification at any frequency associated with the geothermal reservoir. However, noise may be associated with magmatic activity. The crustal structure of the area was studied with two sets of seismic refraction profiles reported by Suyenaga and by Broyles. The surface layer has a low but highly variable velocity (0.8 to 1.6 km/sec) and consists of interlayered aa and pahoehoe flows with large voids. A jump in velocity to 2.5 to 3.0 km/sec occurs near sea level and is attributed to saturation of water. A layer of velocity about 5.0 km/sec lies between the 3.0-km/sec and a 7.0-km/sec layer. The latter is interpreted as the dike complex and locally is found as shallow as 2 to 2.5 km. Furumoto combines microearthquake, source mechanism, gravity and thermal data into an interpretation of the process of geothermal reservoir formation in the East Rift Zone.