High-Resolution Locations of Triggered Earthquakes and Tomographic Imaging of Kilauea Volcano's South Flank

High-Resolution Locations of Triggered Earthquakes and Tomographic Imaging of Kilauea Volcano's South Flank Histogram of seismicity deeper than 6 km from the HVO catalog, showing the increase in seismicity following the SSE.
Kilauea’s south flank is the source of historic tsunamigenic earthquakes and is unusual in that it is one of the few non-subduction zone settings in which slow slip events (SSEs) have been observed to date. These SSEs have been observed every one to two years since 1997 and trigger earthquakes island-ward of the slip area. However, the exact locations of the triggered seismicity and the slow slip relative to the decollement fault underlying the south flank have been uncertain.
</p><p>A temporary network of 20 seismometers, termed the SEQ network, was deployed on Kilauea’s south flank to record the SSE that was predicted to occur in March 2007. Although the SSE did not occur until June 17 2007, the temporary SEQ network recorded over 3000 earthquakes, including those triggered by the SSE. We relocate hypocenters of volcano-tectonic earthquakes and invert simultaneously for P- and S-wave velocity structure using waveform cross-correlation and double-difference tomography using data from the SEQ network, as well as data from the permanent Hawaii Volcano Network (HVO) network, with additional data from other previous temporary arrays. The best-constrained hypocenters are those recorded by both the SEQ and HVO networks, which show the decollement as a subhorizontal layer of seismicity at 8 km depth that is several hundred meters (or less) thick in most areas. The eastern portion of the decollement shows little topography, while the western portion is gently dipping to the southeast, possibly due to a buried seamount. The seismicity triggered by the June 2007 SSE includes over 400 earthquakes overlapping with the southern edge of the decollement seismicity, indicating that both the slow slip and the triggered seismicity occur on the decollement.
</p><p>A shallower swarm of earthquakes also occurred at 2 to 7 km depth in April 2007 near Apua Point, and may have been indirectly triggered by the Mw 8.1 Solomon Islands earthquake at ~6000 km distance, which occurred 48 hours prior to the beginning of the swarm. The locations and focal mechanisms of these earthquakes indicate that they likely occurred on the Hilina Pali fault along a dip angle of 30°.
</p><p>Acknowledgements: This work was supported by NSF grant EAR-0910352, with instruments supplied by PASSCAL and AVO.</p>


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