Mud-Mark-Based Estimations of Mass-Wasting Processes Caused by the 2008 Iwate-Miyagi Nairiku Earthquake, Japan

A 7.2 Magnitude (Moment Magnitude Mw: 6.8) earthquake occurred in the south inland of Iwate prefecture at 8:43 JST on June 14, 2008. Its epicenter was about 10 km northeast of Mt. Kurikoma, an active Nasu volcanic belt composite volcano whose lava flows from several eruption centers covering underlying crumbly secondary volcaniclastic deposits. Thus, the earthquake caused over 3000 mass-wasting events in its epicentral area, encompassing the Kurikoma Volcano’s flank on the hanging side of the seismic fault. Though these mass-wasting events were blamed as the primary cause of deaths in this earthquake, they left tremendous marks of soil deformations and tsunami (seiche) runups along a dam reservoir. The earthquake thus provided unique opportunities to gain insights into the dynamics of the mass-wasting events. The traces of two highly significant mass-wasting events, namely a debris flow that buried the Komano-Yu hot spring inn and a landslide mass of about 70 million m3 that induced a tsunami in the reservoir of Aratozawa dam, were highlighted in this paper. This paper reviews the findings from our observations in the referred papers. It also compares our findings with the other researchers’ inferences from different approaches.