[S-CG52] 変動帯ダイナミクス

[SCG52-23] Shallow aseismic creep of the Western Nagaoka Plain Fault Zone based on dense GNSS observation

*鷺谷 威¹ (1.名古屋大学減災連携研究センター)

キーワード：GNSS、非地震性クリープ、長岡平野西縁断層帯

The Western Nagaoka Plain Fault Zone is located along the western edge of the Nagaoka plain and the eastern foothill of the Nishiyama hill in the Niigata prefecture, including the Katakai and the Torigoe faults as a part of it. This area has been well known for its active tectonic features such as active folding. On the other hand, surface creep has not been identified by the geomorphological or geodetic studies. We have been continuing dense GNSS observations around the fault zone since 2010. Though the observed displacements mainly reflect coseismic as well as postseismic signal of the 2011 Tohoku-oki earthquake, in this study, we focus on local deformation feature by analyzing the baseline length changes of neighboring GNSS sites. Among various short baselines, multiple baselines crossing the surface trace of the Katakai and Torigoe faults exhibit significant shortening at a rate of ~0.3 ppm/year. Such a localized shortening can be reproduced only by shallow aseismic creeping of those faults. According to preliminary elastic dislocation modeling, the shallow limit of the creeping needs to be shallower than 1 km depth and the estimated slip rate is around 5 mm/year. Estimated fault behavior is in general consistent with active tectonic feature and can be interpreted as detection of long-term deformation with a geodetic approach.