Source properties of two microearthquakes at Kilauea Volcano, Hawaii

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Abstract
The source-time functions of two microearthquakes with magnitudes 2.1 and 2.3 at Kilauea Volcano, Hawaii, are determined by using the deconvolution technique. P-wave seismograms of a smaller event with magnitude 1.6 in a nearby location are treated as empirical Green's functions and deconvolved from the waveforms of the larger earthquakes by spectral division. From the time-domain analysis of the source-time functions, some of the source properties, such as the complexity and directivity, and some of the source parameters, such as pulse width, rise time, and source dimension, are determined. With a good azimuthal distribution of stations, the direction and magnitude of rupture velocity are estimated for one of the events. The rupture direction is about N85°W and rupture velocity is 0.75 Vs, assuming Vp = 1.73 Vs. The result for direction agrees with one of the nodal planes of the focal mechanism. Our results indicate that there exist obvious variations in rupture durations for nearby small events with similar seismic moments, suggesting significant differences in the static stress drops. The stress drops of two events (1.5 and 16.5 bar) estimated from the rise times differ by an order of magnitude, implying heterogeneity of the stress distribution over this small area.