9:15 AM - 9:30 AM
[SSS11-02] Very shallow S-wave seismic reflection survey across the Dainenjiyama fault in Nagamachi–Rifu Line fault zone, Northeast Japan
Keywords:Very shallow S-wave seismic reflection survey, Dainenjiyama fault, Nagamachi–Rifu Line fault zone
Nagamachi-Rifu Line fault zone has a 40 km length and extended from Matsushima town to Murata town in Miyagi prefecture, northeast Japan. In the middle of the fault zone, several active fault, Shishiochizaka fault, Dainenjiyama fault, and Nagamachi-Rifu Line (Miyagino flexure) are located parallel with each other. The Dainenjiyama fault for this research is east dipping back-thrust for the master fault of Nagamachi-Rifu Line (Miyagino flexure), which has continuous fault scarp in topography.
Around Tsutsuji-gaoka area in Miyagino district in Sendai city, outcrop of Dainenjiyama fault was reported by Kosaka et al. (2014), which is located beside our seismic survey line. Kosaka et al. (2014) estimated the existence of another reverse fault at the base of topographic fault scarp, because of the scarp height across the Dainenjiyama fault is significantly greater than the displacement from outcrop.
To reveal the detail location of active fault and its shallow geological structure, we execute the very shallow S-wave seismic reflection survey across the Dainenjiyama fault. It is important things for the disaster prevention and mitigation to find out the detail location of active fault and its subsurface geological structure.
We conducted a very shallow seismic survey in May, 2022. The source and receiver interval were both 1 m. The source used in the seismic survey was portable vibrator (CAG, OYO). Sweep length was 8 sec and frequency range beginning at 10 Hz up to 100 Hz. The receiver was GS20-DM (natural frequency, 14 Hz, Geometrics Inc.). We used 120-ch of receivers (roll-on mode) using Geode recording system (Geometrics Inc.) with 0.5 msec sampling rate. Observations of the seismic survey were carried out through nighttime to avoid the environmental noise and traffic noise.
The seismic reflection data we observed was processed with standard common mid-point (CMP) method using seismic processing software SuperX-C (JGI Inc.). The CMP spacing was 0.5 m.
In the seismic reflection profile, two clear reverse faults were imaged with dislocation of continuous strong reflector in the Mukaiyama Fm. One is located imaged at the center of profile which is corresponding to outcrop reported by Kosaka et al. (2014). Another reverse fault was imaged at the western side of profile, which is located at the base of scarp for Dainenjiyama fault.
Reference:
Kosaka et al., Fault Exposure of Dainenjiyama Fault Across Urban District of Sendai City, Northeast Japan, J. Japan Soc. Eng. Geol., 55, 166-176, 2014.
Around Tsutsuji-gaoka area in Miyagino district in Sendai city, outcrop of Dainenjiyama fault was reported by Kosaka et al. (2014), which is located beside our seismic survey line. Kosaka et al. (2014) estimated the existence of another reverse fault at the base of topographic fault scarp, because of the scarp height across the Dainenjiyama fault is significantly greater than the displacement from outcrop.
To reveal the detail location of active fault and its shallow geological structure, we execute the very shallow S-wave seismic reflection survey across the Dainenjiyama fault. It is important things for the disaster prevention and mitigation to find out the detail location of active fault and its subsurface geological structure.
We conducted a very shallow seismic survey in May, 2022. The source and receiver interval were both 1 m. The source used in the seismic survey was portable vibrator (CAG, OYO). Sweep length was 8 sec and frequency range beginning at 10 Hz up to 100 Hz. The receiver was GS20-DM (natural frequency, 14 Hz, Geometrics Inc.). We used 120-ch of receivers (roll-on mode) using Geode recording system (Geometrics Inc.) with 0.5 msec sampling rate. Observations of the seismic survey were carried out through nighttime to avoid the environmental noise and traffic noise.
The seismic reflection data we observed was processed with standard common mid-point (CMP) method using seismic processing software SuperX-C (JGI Inc.). The CMP spacing was 0.5 m.
In the seismic reflection profile, two clear reverse faults were imaged with dislocation of continuous strong reflector in the Mukaiyama Fm. One is located imaged at the center of profile which is corresponding to outcrop reported by Kosaka et al. (2014). Another reverse fault was imaged at the western side of profile, which is located at the base of scarp for Dainenjiyama fault.
Reference:
Kosaka et al., Fault Exposure of Dainenjiyama Fault Across Urban District of Sendai City, Northeast Japan, J. Japan Soc. Eng. Geol., 55, 166-176, 2014.