abstract

The hypocenters of 43 earthquakes on Kilauea Volcano were analyzed in detail in order to examine the accuracy of hypocenters determined with data from tripartite arrays and to look for evidence of zones of abnormally high or low velocity in a region of complex crustal structure. Ten vertical and two horizontal seismometers were operated on the south flank of Kilauea within the seismic network of the Hawaiian Volcano Observatory. A number of combinations of the temporary stations were treated as separate tripartite arrays. The sides of each tripartite array were 1 to 2 km long. Azimuths and apparent velocities of P-wave fronts observed at these arrays generally agreed well with the values predicted from hypocenters calculated using data from as many as 20 stations. Some observed azimuths differed from the predicted values by over 40° and some apparent velocities differed by nearly a factor of 2. These differences are consistent with the travel-time residuals found when the hypocenters are located with all available data. They can be attributed to local zones of abnormally high or low velocity or to changes in the thicknesses of the assumed crustal layers. Waves that travel through the east and southwest rift zones arrive relatively early and the waves traveling through the Kaoiki fault zone arrive late. Refraction data were compiled to obtain a new average crustal structure. When small tripartite arrays are used to locate shallow earthquakes, a crustal structure with a linear increase in velocity should be assumed in order to calculate unique hypocenters and to obtain less scatter in a group of hypocenters.

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