Mapping normal faults on the outer slope of the western Kuril Trench based on recent seismic reflection and bathymetric data

Abstract To obtain novel information regarding normal faults that could cause tsunamis and large earthquakes on the outer slopes of the Kuril Trench, recently acquired multichannel seismic reflection (MCS) and bathymetric data are processed in this study to interpret the normal faults on the outer slope of the western Kuril Trench from near the Erimo Seamount to near the Nosappu Fracture Zone. This work also assesses the distribution and characteristics of the faults through comparisons with previous studies on the outer slope faults of the Japan Trench. The results of this study show that faulting starts approximately 100 km seaward of the trench axis, and a comparison with the normal fault distributions on the outer slope of the Japan Trench presented in previous studies reveals that the outer slope region of the Kuril Trench is narrower and more densely faulted than that of the Japan Trench. Additionally, the seismic and bathymetric data show that the Erimo and Takuyo-Daiichi Seamounts are deformed by normal faults. However, the number of faults in the seamount areas is lower than that in areas without them, which also affects the scale of the fault throws. The results of the MCS survey reveal that the thickness of the oceanic crust varies between 6 and 10 km due to the presence of these seamounts. Considering the positions of the outer swells presented in previous studies, the results suggest that the crustal and plate structures in the study area influence the distribution and formation of faults on the outer slope of the Kuril Trench. Graphical Abstract