Reliable Fault Modeling of an Mw 7.1 Earthquake in Hyuganada Sea on 8 August 2024 by Offshore Tsunami Data From New Seafloor Network N‐net and Onshore GNSS Data

Abstract We investigated tsunamis of an Mw 7.1 earthquake in the Hyuganada Sea in 2024, observed by a new dense and wide seafloor observation network, N‐net, installed in the western Nankai Trough. A joint inversion of the offshore tsunami and onshore GNSS data revealed a maximum slip of 2.4 m with a significant slip near the centroid from the teleseismic analysis. The joint inversion provided reliable constraints for both up‐dip and down‐dip extents of the fault, while the inversions using either data set showed limitations in the fault constraint. Comparisons with past earthquakes indicate the 2024 earthquake ruptured part of the asperity of the 1961 earthquake but not those of the 1996 earthquakes. Our fault modeling jointly using offshore and onshore data suggests the interplate seismic coupling ratio in this region is <0.4, which was much smaller than those in the anticipated megathrust earthquake source region in the Nankai Trough.