2:15 PM - 2:30 PM
[SSS08-20] Blind thrust faults beneath the western Ishikari plain revealed by high-resolution shallow seismic reflection profiling, Hokkaido
Keywords:active fault, Blind thrust, Active fold, Ishikari plain, Hokkaido, Seismic reflection profiling
Data processing using Super X, a commercial software package from JGI Inc., generate depth-converted seismic sections. Data processing included the compilation of field data, coherent noise reduction to suppress surface waves, direct waves and ground roll, 2D binning, deconvolution, static corrections, CDP stacking, 2D migration and depth conversion (e.g., Yilmaz, 2001). Applying deconvolution, bandpass filter, and static correction to the seismic data successfully improved the quality of the seismic imaging and enhanced the seismic reflections. We also carried out refraction analysis on first arrivals to estimate the weathering layers to explain space-variant delays in every seismic trace. As a result, the quality of the shallow portions of the stacked seismic profiles was significantly improved.
The seismic sections illuminate the detailed subsurface structure to depth of ca. 3 km beneath the western Ishikari plain. The preliminary interpreted depth-converted sections correlated with nearby Neogene stratigraphy indicates shallowly to moderately east-dipping blind thrust faults and pairs of overlying fault-related anticlines that deform Plesitocene to Pliocene sedimentary units. We will mainly discuss (1) the shallow structural characteristics of the active blind thrust based on our interpretation of the 2D seismic data in combination with the Neogene stratigraphy, (2) structural relations to deeper structures obtained by the new deep seismic profile (Sato et al., 2018), and (3) and structural relations to southerly plunging active anticlines located north of the seismic lines that deform late Pleistocene marine terrace deposits (Komatsubara and Anzai, 1998).