| Summary: | A major (M_W 7.9) intraplate earthquake ruptured the Pacific plate seaward of the Alaska subduction zone near Kodiak Island on 23 January 2018. The aftershock seismicity is diffuse, with both NNW†and ENEâ€trending distributions, while longâ€period point source moment tensors have nearâ€horizontal compressional and tensional principal strain axes and significant nonâ€doubleâ€couple components. Backprojections from three largeâ€aperture networks indicate sources of shortâ€period radiation not aligned with the best doubleâ€couple fault planes. A suite of finiteâ€fault rupture models with one to four faults was considered, and a fourâ€fault model, dominated by rightâ€lateral slip on an SSE trending, westwardâ€dipping fault, is compatible with most seismic, GPS, and tsunami data. However, the precise geometry, timing, and slip distribution of the complex set of faults is not well resolved. The sequence appears to be the result of intraplate stresses influenced by slab pull, the 1964 Alaska earthquake, and collision of the Yakutat terrane in northeastern Alaska. © 2018 American Geophysical Union. Received 31 JUL 2018; Accepted 4 SEP 2018; Accepted article online 10 SEP 2018; Published online 22 SEP 2018. The Incorporated Research Institutions for Seismology (IRIS) data management service (DMS) (http://www.iris.edu/hq/) was used to access the seismic data from Global Seismic Network and Federation of Digital Seismic Network stations. Broadband data from China were obtained from the Data Management Centre of China National Seismic Network at Institute of Geophysics, Chinese Earthquake Administration (doi:10.11998/SeisDmc/SN, http://www.seisdmc.ac.cn). GPS rapid solutions estimated by Tom Herring were accessed from the UNAVCO webpage (https://www.unavco.org). Tsunami waveform data were obtained from the NOAA National Data Buoy Center (http://www.ndbc.noaa.gov/) and Ocean Networks Canada (https://dmas.uvic.ca/). K. D. Koper kindly provided his backprojection software and training in its use. We thank editor Gavin ...
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