Source fault of the Iwate-Miyagi Nairiku Earthquake in 2008 estimated by distribution of heights of fluvial terraces

Tajikara, Masayoshi; Ikeda, Yasutaka*; Nohara, Tsuyoshi   

We estimated distribution of uplift rates during the last 150 kyrs around the focal region of the Iwate-Miyagi Nairiku Earthquake in 2008 (occurred at June 14, 2008; Mj 7.2, Mw 6.9), based on relative heights of fluvial/marine terraces. Active fault has not been mapped around this area, because clear fault scarp with large displacement does not exist. We showed that the uplift rates vary around the focal region and that the variation of uplift rates is related to the activities of the source fault of the Iwate-Miyagi Nairiku Earthquake in 2008. We estimated the vertical displacement rate of this fault as 0.4-0.5 mm/yr, based on difference of uplift rates on the both side of the source fault. We considered that the existence of (blind) active fault can be estimated even in the area with no clear fault scarp, by clarifying the distribution of uplift rates based on heights of fluvial/marine terraces.