Kiholo Bay, Hawaii, earthquake sequence of 2006: Relationship of the main shock slip with locations and source parameters of aftershocks

We study the source process of the Kīholo Bay earthquake (M_W 6.7), which occurred beneath the northwest part of the Island of Hawai‘i on 15 October 2006, and static stress drops of small earthquakes that occurred in 2006 and 2007 around the main shock including aftershocks. We relocate the aftershocks to determine the fault plane from the two nodal planes. The relocated aftershocks define an E‐W trending plane that dips to the south, in good agreement with one of the nodal planes given by the Global Centroid Moment Tensor solution. Waveform inversion is performed with multiple time windows to investigate the rupture speed and the slip distribution of the main shock. Waveforms of an aftershock with M_W 5.2 are used to calculate empirical Green's functions. Our results indicate that the rupture propagated unilaterally to the west with a rupture speed greater than 3.0 km/s (63% of the shear wave velocity). This westward rupture is consistent with the fact that aftershocks are distributed predominantly to the west of the main shock epicenter. Most aftershocks are located on the edge of patches with a large slip, or asperities and some also occur inside the patches. We also estimate static stress drops of 39 earthquakes (2.5 < M_L < 3.5) that occurred in 2006 and 2007 near the source region of the Kīholo Bay earthquake. Static stress drops range from 0.12 to 8.6 MPa and aftershocks around large slip patches of the main shock likely to have larger stress drops.