Deep fault plane geometry inferred from multiplet relative relocation beneath the south flank of Kilauea

Abstract

Dense microearthquake swarms occur in the upper south flank of Kilauea, providing multiplets composed of hundreds of events. The similarity of their waveforms and the quality of the data have been sufficient to provide accurate relative relocations of their hypocenters. A simple and efficient method has been developed which allowed the relative relocation of more than 250 events with an average precision of about 50 m horizontally and 75 m vertically. Relocation of these events greatly improves the definition of the seismic image of the fault that generates them. Indeed, relative relocations define a plane dipping about 6° northward, although corresponding absolute locations are widely dispersed in the swarm. A composite focal mechanism, built from events providing a correct spatial sampling of the multiplet, also gives a well‐constrained northward dip of about 5° to the near‐horizontal plane. This technique thus collapses the clouds of hypocenters of single‐event locations to a plane coinciding with the slip plane revealed by previous focal mechanism studies. We cannot conclude that all south flank earthquakes collapse to a single plane. There may locally be several planes, perhaps with different dips and depths throughout the south flank volume. The 6° northward‐dipping plane we found is too steep to represent the overall flexure of the oceanic crust under the load of the island of Hawaii. This plane is probably an important feature that characterizes the basal slip layer below the upper south flank of Kilauea volcano. Differences in seismicity rate and surface deformations between the upper and lower south flank could be related to the geometry of this deep fault plane. The present work illustrates how high precision relative relocations of similar events in dense swarms, combined with the analysis of geodetic measurements, can help to describe deep fault plane geometry. Systematic selection and extensive relative relocation of similar earthquakes could be attempted in other well‐instrumented, highly seismic areas to provide reliable basic information, especially useful for understanding of earthquake generation processes.

A reinterpretation of seismicity associated with the January 1983 dike intrusion at Kilauea Volcano, Hawaii

“…The tendency has been to interpret diffuse rift zone seismicity as reflecting deformation of the volume through which magma is flowing [e.g., Ryan et al, 1981;Tilling and Dvorak, 1993]. The earthquake relocations indicate that, as with the south flank events studied by Got et al [1994], the diffuse character of the seismicity is instead likely to be an artifact of location error in the HVO catalog. We propose that most of the intrusioninduced and background seismicity within the rift zones occurs within spatially restricted stress concentrations at the margins of long-lived magma bodies.…”

“…The relocation method [Got et al, 1994] is a three-step process that consists of (1) identifying groups of similar earthquakes (multiplets) by comparing, at each station, the waveforms of all earthquakes; (2) determi'ning the P wave arrival time differences between the multiplet events by cross correlation; and ( Multi. plets were assigned an absolute location by repicking P wave arrivals for the aligned traces and relocating the events with the best signal-to-noise ratio using HYPOINVERSE.…”

Three‐dimensional seismic velocity structure of Mauna Loa and Kilauea volcanoes in Hawaii from local seismic tomography

“…All Rights Reserved. [Got et al, 1994;Got and Okubo, 2003]. Seismicity at Kilauea contains both volcanotectonic and long-period events beneath the summit, with a relatively aseismic zone between 5 and 8 km depth [Klein et al, 1987].…”

Double-difference relocation of earthquakes in central-western China, 1992–1999

“…In the master event technique (Fukao, 1972;Fitch, 1975;Chung, 1976;Yang et al, 1999Yang et al, , 2002, travel time differences are taken between an assigned (master) event and its neighboring events, improving locations for clusters of events that have dimensions smaller than the scale-length of the velocity heterogeneities between sources and receivers. Got et al (1994) extended this idea to include travel time differences not only relative to one event, but between all neighboring events. They used differential times measured by cross-correlation to solve for interevent distances relative to the centroid of a cluster of events.…”