Seismic evidence on the complex rupture system of the 23 January 2018 MW 7.9 offshore Kodiak event.

In this study, we probe the formation mechanisms of the 23 January 2018 Mw7.9 Kodiak earthquake in the Gulf of Alaska region from detailed structural analysis, combined with the regional crustal stress status evaluation via seismology methods measured by the b‐value imaging. The large earthquake not only aroused heated debate due to its intraplate deformation and complex rupture system approaching to the Aleutian subduction zone, but also the complex rupture system. Aftershocks of this event propagated along the ENE‐striking and NNW‐striking fractures in planar view, whereas it shows double‐layer seismicity zones at depth. The b‐value image indicates the highly fractured crustal stress status above 12 km and above 25 km, respectively, while the faulting was locked at a depth between 12 and 20 km. We suggest that mantle peridotite serpentinization induced the aseismic zone gap. Besides, the bathymetric map, the multichannel profiles, and the sub‐bottom seismic evidence across the study area have shown the sinistral seismogenic strike‐slip faults may have been reactivated from the deep‐seated oceanic fracture zones involving the subduction front. In addition, all these faults conjunction has formed the topographic uplift or fault blocks and contribute to the complex earthquake ruptures. [ABSTRACT FROM AUTHOR]