Japan Geoscience Union Meeting 2018

Presentation information

[EJ] Poster

S (Solid Earth Sciences) » S-CG Complex & General

[S-CG57] Dynamics in mobile belts

Wed. May 23, 2018 3:30 PM - 5:00 PM Poster Hall (International Exhibition Hall7, Makuhari Messe)

convener:Yukitoshi Fukahata(Disaster Prevention Research Institute, Kyoto University), Toru Takeshita(Department of Natural History Sciences, Graduate School of Science, Hokkaido University), Hikaru Iwamori(海洋研究開発機構・地球内部物質循環研究分野)

[SCG57-P24] Three dimensional S-wave velocity structure near the fault zones of the 2000 western Tottori earthquake using surface wave tomography

*Yudai Suemoto1, Hiro Nimiya1, Tatsunori Ikeda2, Takeshi Tsuji1,2, Yoshihisa Iio3 (1.Department of Earth Resources Engineering, Kyushu University, 2.International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, 3.Disaster Prevention Research Institute, Kyoto University)

Keywords:Western Tottori prefecture earthquake, surface wave tomography, ambient noise

We applied high-resolution surface wave tomography using ambient noise records to reveal three dimensional S-wave velocity structure in San-in area near the 2000 western Tottori earthquake (Mw6.8). In this area, many earthquakes have been happened by unexplored faults. The recent study using GPS data revealed that strain is accumulated in the San-in area (Nishimura at al., 2017). Therefore, new faults may be generated in the future. To reveal the mechanism of earthquakes, many seismometers were deployed around the western Tottori area. This project is called Manten project (Iio et al., 2017). In this area, P- and S-wave velocity structure at deeper than 3km was estimated by seismic tomography using P- and S-wave first arrival times from local earthquakes (Zhao et al., 2004) but the spatial resolution in shallow structure is limited. In our study, we tried to explore relatively shallow velocity structure and clarify the fault and lithology distribution in this area by using ambient seismic noise obtained from the Manten project. We used continuous seismic data recorded by 129 seismometers during the period from 15th June to 20th September in 2015. We estimated surface wave dispersion curves between two pairs of seismometers by applying the zero-crossing method (Ekström et al., 2009) based on the Spatial Auto Correlation (SPAC) method (Aki, 1957). By using station pairs separated by 10 to 40km, we calculated more than 3000 dispersion curves. We then inferred high-resolution phase velocity maps in the frequency range from 0.3 to 0.7Hz. Three dimensional S-wave velocity distribution was approximately estimated from observed dispersion curves by using empirical relationship between surface wave dispersion curve and S-wave velocity profile (one-third wavelength transformation) (Hayashi, 2008). The velocity boundary observed in our results could be related to the geological boundary in north area. The S-wave velocity distribution we obtained in this study demonstrated that east-west faults are identified as low S-wave velocity. However, the seismogenic fault in the 2000 western Tottori earthquake is located at high S-wave velocity lineament. Our high resolution shallow seismic velocity model (less than 3km depth) estimated using dense seismic array will help for understanding fault characteristics and stress accumulation, and contribute to disaster prevention in San-in area.