Electrical Conductive Fluidized Zones and Their Influence on the Earthquake Nucleation, Growth, and Arrest Processes of the 2016 Kumamoto Earthquake Sequence, Kyushu Island, Japan

Crustal earthquake ruptures tend to nucleate near fluidized zones. However, it is relatively unknown whether fluidized zones can further promote or arrest these ruptures. We image the electrical resistivity structure around the focal area of the 2016 Kumamoto earthquake sequence by using 200 sites broad-band magnetotelluric data, and discuss its quantitative relationship to earthquake nucleation, growth, and arrest processes. The result shows that the earthquake hypocenters are all located within 10 km from low-resistivity fluidized zones < 30Ωm. The ruptures that nucleated along the outer edge of the low-resistivity fluidized zones tended to become large earthquakes, whereas those that initiated either distal to or within the fluidized zones did not. The ruptures were arrested by high-temperature (>400°C) fluidized zones, whereas shallower low-temperature (200°C–400°C) fluidized zones either promoted or arrested the ruptures. These results suggest that the distribution of mid-crustal fluids contributes to the nucleation, growth, and arrest of crustal earthquakes.