新庄盆地東部活褶曲群を横切る反射法地震探査

概要

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Late Quaternary, active folds are well developed in the eastern part of the Shinjo Basin, central northern Honshu, Japan. To reveal the geometry of the folds, seismic reflection profiling was undertaken across the NS-trending folds in the eastern Shinjo Basin. The total length of the seismic line is about 14 km. The seismic source was amini-vibrator truck with 30 seconds of 10-80 Hz signals at 30m intervals. The signal was recorded on 120 and 180 channels by a 15-m group interval of 10 3Hz geophones. The seismic reflection profiles portray the style of folds down to 1.5km in depth. The Neogene basin fill forms asynmetrical fault-related folds associated with an east dipping reverse fault on their western flanks. The range boundary fault (Kyodanbara fault) is demonstrated in the seismic section as an east dipping reverse fault at about 40℃. Based on the fold geometry and prevailing bedding slip, it is interpreted that the Tominami anticline was formed by flexural-slip folding, and the competent layer was a Pliocene sandstone unit. No obvious growth strata are recognized in the seismic sections, suggesting that the main phase of folding and faulting occurred after deposition of the Dokuzawa Formation.
東京大学の論文
2007-03-14