Block tectonics of the island of Hawaii from a focal mechanism analysis of basal slip

The southern third of the island of Hawaii is composed of at least three rigid blocks: Kilauea Volcano's south flank, Mauna Loa Volcano's southeast flank, and Mauna Loa Volcano's west flank. Analysis of earthquake focal mechanisms suggests that Kilauea's south flank, the most mobile of these blocks, is moving seaward perpendicular to its east rift zone along a southeasterly course at an azimuth of 155 ± 5°. Mauna Loa's southeastern flank is also moving in a southeasterly direction, although at a slightly more easterly azimuth of 140 ± 5°. Although data are sparse on the western flank of Mauna Loa due to low seismicity and inadequate seismic network station density, the available data suggest that this region is translating seaward along a generally westerly azimuth. Relative differences in these translational azimuths may represent oblique opening across the boundaries between these regions, the active rift zones of Kilauea and Mauna Loa Volcanoes.