Spatial extent of a hydrothermal system at Kilauea Volcano, Hawaii, determined from array analyses of shallow long-period seismicity - 2. Results

Array data from a seismic experiment carried out at Kilauea Volcano, Hawaii , in February 1997, are analyzed by the frequency-slowness method. The slow ness vectors are determined at each of three small-aperture seismic antenna s for the first arrivals of 1129 long-period (LP) events and 147 samples of volcanic tremor. The source locations are determined by using a probabilis tic method which compares the event azimuths and slownesses with a slowness vector model. The results show that all the LP seismicity, including both discrete LP events and tremor, was generated in the same source region alon g the east flank of the Halemaumau pit crater, demonstrating the strong rel ation that exists between the two types of activities. The dimensions of th e source region are approximately 0.6 x 1.0 x 0.5 km. For LP events we are able to resolve at least three different clusters of events. The most activ e cluster is centered similar to 200 m northeast of Halemaumau at depths sh allower than 200 m beneath the caldera floor. A second cluster is located b eneath the northeast quadrant of Halemaumau at a depth of similar to 400 m. The third cluster is <200 m deep and extends southeastward from the northe ast quadrant of Halemaumau. Only one source zone is resolved for tremor. Th is zone is coincident with the most active source zone of LP events, northe ast of Halemaumau. The location, depth, and size of the source region sugge st a hydrothermal origin for all the analyzed LP seismicity.