A large refined catalog of earthquake relocations and focal mechanisms for the Island of Hawai'i and its seismotectonic implications

Abstract

We present high‐quality focal mechanisms based on a refined earthquake location catalog for the Island of Hawai'i, focusing on Mauna Loa and Kīlauea volcanoes. The relocation catalog is based on first‐arrival times and waveform data of both compressional and shear waves for about 180,000 events on and near the Island of Hawai'i between 1986 and 2009 recorded by the seismic stations at the Hawaiian Volcano Observatory. We relocate all the earthquakes by applying ray tracing through an existing three‐dimensional velocity model, similar event cluster analysis, and a differential‐time relocation method. The resulting location catalog represents an expansion of previous relocation studies, covering a longer time period and consisting of more events with well‐constrained absolute locations. The focal mechanisms are obtained based on the compressional‐wave first‐motion polarities and compressional‐to‐shear wave amplitude ratios by applying the HASH program to the waveform cross correlation relocated earthquakes. Overall, the good‐quality (defined by the HASH parameters) focal solutions are dominated by normal faulting in our study area, especially in the active Ka'ōiki and Hīlea seismic zones. Kīlauea caldera is characterized by a mixture of approximately equal numbers of normal, strike‐slip, and reverse faults, whereas its south flank has slightly fewer strike‐slip events. Our relocation and focal mechanism results will be useful for mapping the seismic stress and strain fields and for understanding the seismic‐volcanic‐tectonic relationships within the magmatic systems.

Deep crustal melt plumbing of Bárðarbunga volcano, Iceland

“…Although deep seismic activity is confined to the SE outer flank of Bárðarbunga, this lateral offset is not an unusual observation [ White and McCausland , ]. Other volcanoes such as Askja (Iceland) [ Greenfield and White , ], Kilauea (Hawaii) [ Wright and Klein , ; Bell and Kilburn , ; Wech and Thelen , ; Lin and Okubo , ], Mount St Helens (US) [ Kiser et al ., ], and El Hierro (Canary Islands) [ Klügel et al ., ] also have deep seismicity with similar lateral offsets from the associated volcanoes.…”

Extension parallel to the rift zone during segmented fault growth: application to the evolution of the NE Atlantic

“…Such incremental, non-plane strains within evolving relay zones may be responsible for local instances of basin inversion, reverse and strike-slip faulting in otherwise extensional regimes, and complex compartmentalization characteristics (e.g. Lin and Okubo, 2016;Sachau et al, 2016). Importantly, for basin faults with displacements on the kilometre scale, significant amounts of horizontal bending and rotation are possible, driving associated strains that may go undetected.…”

“…Fault growth models have been derived using natural examples and numerical, or scaled-analogue modelling techniques, in which normal faults grow through stages in which discontinuous segments interact and link across relay zones to form composite structures with fault displacement deficits initially accommodated by soft-linkage rotation and/or material folding (e.g. Trudgill and Cartwright, 1994;Gupta and Scholz, 2000;Peacock, 2002;Long and Imber, 2010).…”

“…In horizontally layered materials, displacement (throw) gradients on adjacent normal faults are commonly accommodated by relay structures (e.g. Peacock and Sanderson, 1991;Childs et al, 1995;Long and Imber, 2010), requiring horizontal axis bending of the host layering (Fig. 1).…”

“…This may be accommodated in this interfault region, or relay zone, through components of elastic and inelastic strain (e.g. Peacock andSanderson, 1991, 1994;Childs et al, 1995;Long and Imber, 2010), and depending on the degree of overlap and separation of individual segments, may lead to different styles of deformation (e.g. Tentler and Acocella, 2010;Long and Imber, 2011;Childs et al, 2017) ( Fig.…”