The 2018 Mw 7.9 Offshore Kodiak, Alaska, Earthquake: An Unusual Outer Rise Strike-Slip Earthquake

The rupture process of the 2018 M-w 7.9 offshore Kodiak (Alaska) earthquake is still in hot dispute because of a lack of offshore observations, thus causing difficulties for understanding seismogenic tectonics and tsunami hazards. In this study, teleseismic body waves, high-rate GPS, seismic waves preceding tsunami waves, static GPS, and tsunami data are jointly used to resolve the faulting geometry and coseismic slip distribution of the offshore Kodiak earthquake. Tests of a series of finite fault rupture models illustrate that an optimal five-fault model can reconcile all available data sets well. The results reveal that the asperity on each fault segment is located near the hypocenter, with peak slip of similar to 7.8 m. The aftershock loci appear to be complementary to the mainshock slips, demonstrating the velocity-strengthening regions that predominantly slip aseismically. Based on a tectonic stress field analysis, we propose that the 2018 Kodiak earthquake is attributed to a combination of enhanced tensional stress following the 1964 M-w 9.2 Alaska earthquake and compressional stress produced by the collision of the Yakutat terrane with North America.