Volcanic Earthquakes and Tremor at Kilauea Volcano. Hawaii-Their Source Mechanisms

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We made an experiment during January 8,1996 to February 10 in the summit area of Kilauea volcano, Hawaii, which consisted of deployment of dense arrays of seismographs in three configurations which recorded simultaneously . All were arranged to optimally record earthquakes that occur beneath the summit caldera of Kilauea. The first array was a seismic antenna of 31 3-component instruments arranged in a semi-circle, with a spacing of about 50 m between arcs of stations. The collected signals from the antenna can be tuned to look at the passage of seismic waves across the network. The second component was an array of two circular rings, an inner ring of 8 3-component stations with a diameter of 2 km and an outer ring of 16 3-component stations with a diameter of 4 km, plus one station at the center. This configuration provided excellent azimuthal converage for events occurring near the center of the array. The third part of the array was a dense line of 48 mostly vertical instruments extending to the SSE from the center of the network. The spacing between these instruments was 35 m, chosen to assure wave coherence. This dense linear array was designed to study wave transmission as a function of distance.The principal goal of the experiment was to record volcanic tremor and volcanic earthquakes. The tremor signal was mostly weak during the recording period, except for a 4-hour long swarm on February 1. However, during the experiment hundreds of earthquakes were counted from the HVO network, with numerous earthquakes that occurred beneath other parts of Hawaii Island. Indeed, the data loggers recorded many earthquakes including several long-period volcanic earthquakes and tremor.