New Model of the Rupture Surface of the Mw = 7.8 Near Islands Aleutian Earthquake of July 17, 2017 Based on SAR Interferometry

Abstract—A new model of the rupture surface of the Mw = 7.8 Near Islands Aleutian earthquake that occurred on July 17, 2017 in the region of the Commander Islands of the Aleutian Island Arc is presented. The model is based on the displacement fields obtained from Sentinel-1B radar images for the Bering and Mednyi Islands. Among the interferogram pairs calculated from the images covering the period from June 17 to August 28, 2017, the most reliable displacement fields were obtained from the image pair July 11–July 23, 2017. These displacements include coseismic and part of postseismic displacements. The inversion also involved the displacement data recorded by the GNSS GPS stations on the Kamchatka Peninsula, Commander Islands, and the closest to the epicenter Aleutian Islands. Due to the fact that displacements substantially exceeding the noise level were only recorded at two GPS stations on the Bering and Shemya islands, the use of the InSAR data substantially refines the existing earthquake source models. In our models, a seismic rupture zone is approximated by a plane with a length of 370 km along the strike and 19 km along the dip, respectively. Three models have been calculated: a model of uniform displacement across the entire rupture surface; a model in which the rupture surface is divided strikewise into five elements; and a model divided into four elements along the strike and into two levels along the dip, with a total of eight elements. All models demonstrate the same displacement type—right-lateral strike-slip faulting with a relatively small thrust component. According to the constructed models, the displacements in some areas of the rupture surface are slightly smaller than average but, generally, they occur all over the source zone. The models based on satellite geodetic data and on waveform inversion largely agree. The discrepancy between the models utilizing different data types can probably be due to the fact that seismological data characterize the part of the source process that is accompanied by the generation of seismic waves. Surface displacements estimated from InSAR data do not characterize the main event alone but also contain contributions that may reflect various creep processes. The period covered by the radar images also includes the foreshocks with magnitudes up to 6.3 as well as more than 100 aftershocks with magnitudes between 4 to 5.5. Perhaps that is why the displacements obtained in our models are more uniformly distributed over the 370-km rupture surface than in the models based on the waveform analysis.