Abstract
We investigated tombstone fall-down rates from November 30 to December 2 in 2014 to estimate the distribution of the ground motion intensity around the near source region of the 2014 Northern Nagano Prefecture Earthquake (MJ6.7), Japan. In addition, we conducted microtremor observations and evaluated horizontal-to-vertical spectral ratios (H/V) to interpret the spatial distribution of the intensity in terms of ground vibration characteristics. In Hakuba-mura Horinouchi where wooden houses were heavily damaged, tombstone fall-down rates were 100%. This result corresponded to seismic intensity 7 (in the 0-7 Japanese scale) according to previous studies. H/V amplitudes of this area were found to be significantly different from other areas such as Hakuba-mura Oide or Otari-mura, and this difference can be considered to be due to the difference in subsurface geology. In Hakuba-mura Oide where obvious surface faults were found, the tombstone fall-down rates of hanging-wall side were 13-56% (averaged seismic intensity 6-), and those of foot-wall side were 0-23% (averaged seismic intensity 5+). We also investigated tombstone fall-down rates also in Otari-mura, Ogawa-mura and Nagano-shi. Based on these results, we showed the spacial variation of the ground motion, corresponding to seismic intensity from 5- up to 7, around the near source region.
