Location of Long Period events belo Kilauea using seismic amplitudes and precise relative relocation.

International audienceWe present methods for improving the location of long-period (LP) events, deep andshallow, recorded below Kilauea Volcano by the permanent seismic network. LP eventsmight be of particular interest to understanding eruptive processes as their sourcemechanism is assumed to directly involve fluid transport. However, it is usually difficultor impossible to locate their source using traditional arrival time methods because ofemergent wave arrivals. At Kilauea, similar LP waveform signatures suggest the existenceof LP multiplets. The waveform similarity suggests spatially close sources, while catalogsolutions using arrival time estimates are widely scattered beneath Kilauea’s summitcaldera. In order to improve estimates of absolute LP location, we use the distribution ofseismic amplitudes corrected for station site effects. The decay of the amplitude as afunction of hypocentral distance is used for inferring LP location. In a second stage, weuse the similarity of the events to calculate their relative positions. The analysis of theentire LP seismicity recorded between January 1997 and December 1999 suggests that avery large part of the LP event population, both deep and shallow, is generated by a smallnumber of compact sources. Deep events are systematically composed of a weak high-frequency onset followed by a low-frequency wave train. Aligning the low-frequencywave trains does not lead to aligning the onsets indicating the two parts of the signal aredissociated. This observation favors an interpretation in terms of triggering and resonanceof a magmatic conduit. Instead of defining fault planes, the precise relocation ofsimilar LP events, based on the alignment of the high-energy low-frequency wave trains,defines limited size volumes