2014年11月22日長野県北部の地震（Mw 6.2）に よって出現した神城断層沿いの地表地震断層の分布と性状

抄録

The surface rupture associated with the 22 November 2014 Nagano-ken-hokubu earthquake of Mj = 6.7(Mw = 6.2) occurred on the previously mapped Kamishiro fault, the northernmost section of the ItoigawaShizuoka Tectonic Line active fault system (ISTL). This is the first surface-rupturing earthquake occurred on one of the ~110 major inland active faults intensively evaluated by the Headquarters for Earthquake Research Promotion. We mapped the locations of the surface breaks along the rupture zone immediately after the earthquake, using handy GPS equipment. We also measured vertical and horizontal displacements at these sites using a conventional tape, folding ruler, simple hand level, and handheld laser finder. As a result, we found a N-S trending 9.2-km-long surface rupture and ground deformations mostly along the pre-existing scarp of the Kamishiro fault. Most of the surface ruptures involved flexural and warped surface deformation associated with significant contraction near the fault tip and local extension on the bended hanging wall. Observed deformation suggests that dip of the reverse fault changes to low-angle at shallow depth and deform unconsolidated sediments in the basins. The rupture trace is not simple: there are several short subsidiary faults including three rupture traces involving back-thrust faulting in the northern part. These features and the mapped distribution indicate an east-dipping reverse fault (east side up), which is consistent with early aftershock distribution and a geodetically inferred source fault. However, the amount of displacement associated with the 2014 earthquake was much smaller than the ones expected from previously conducted geomorphological and paleo-seismological studies. To seek the reason why we overestimated the rupture dimension, we need more peleo-seismic data (event age and displacement) and perform further tectonic geomorphological analyses.