2:00 PM - 2:15 PM
[SCG58-07] 3D Distribution of Crustal Fluids in the Central Tohoku Region
Keywords:crustal fluids
Many broadband MT observations have been conducted in the central Tohoku region since 1990 for tectonic studies of volcanoes and inland earthquakes. (e.g., Ogawa et al., 2014). However, the crustal structure of the central Tohoku region has not yet been analyzed on a regional scale. This study aims to elucidate detailed regional crustal structure and mantle structure in three dimensions from broadband MT data of 590 stations over the past 30 years, and to elucidate the three-dimensional distribution of crustal fluids in active volcanic and inland earthquake areas.
We present a 3-D inversion analysis based on data from an area 50 km north-south and 40 km west of the Onikobe caldera. The data used were impedances and tippers for 8 periods from 0.4 to 1,300 s at 410 stations. The WSINV3DMT code (Siripunvaraporn and Egbert, 2009) was used for the analysis, and the impedance and tipper error floors were set to 10% and 20%, respectively. The obtained final model has RMS=2.99.
The final model shows the existence of a continuous low resistivity belt in the SSW-NNE direction along the volcanic arc in the deep crust (20 km to 30 km depth), which is connected to the low resistivity anomaly in the upper mantle shown by Ichiki et al. (2015). In the northern Miyagi Prefecture area on the forearc side, blocky low resistivity anomalies are found in the deep crust and are considered to be fluid uplift zones. These low resistivity anomalies in the deep crust correspond to a widespread strain concentration area along the volcanic arc and the forearc (Miura et al., 2004). The low resistivity zone in the deep crust along the volcanic arc locally rises to a depth of 10 km, branching toward Naruko volcano, Mt. Kurikoma, Onikobe caldera, and Takamatsu-dake. This low resistivity of the volcanic body at 10 km depth correlates well with the subsidence variations in the coseismic volcanoes of the 2011 off the Pacific coast of Tohoku earthquake (Takada and Fukushima, 2013), as estimated by InSAR.
We present a 3-D inversion analysis based on data from an area 50 km north-south and 40 km west of the Onikobe caldera. The data used were impedances and tippers for 8 periods from 0.4 to 1,300 s at 410 stations. The WSINV3DMT code (Siripunvaraporn and Egbert, 2009) was used for the analysis, and the impedance and tipper error floors were set to 10% and 20%, respectively. The obtained final model has RMS=2.99.
The final model shows the existence of a continuous low resistivity belt in the SSW-NNE direction along the volcanic arc in the deep crust (20 km to 30 km depth), which is connected to the low resistivity anomaly in the upper mantle shown by Ichiki et al. (2015). In the northern Miyagi Prefecture area on the forearc side, blocky low resistivity anomalies are found in the deep crust and are considered to be fluid uplift zones. These low resistivity anomalies in the deep crust correspond to a widespread strain concentration area along the volcanic arc and the forearc (Miura et al., 2004). The low resistivity zone in the deep crust along the volcanic arc locally rises to a depth of 10 km, branching toward Naruko volcano, Mt. Kurikoma, Onikobe caldera, and Takamatsu-dake. This low resistivity of the volcanic body at 10 km depth correlates well with the subsidence variations in the coseismic volcanoes of the 2011 off the Pacific coast of Tohoku earthquake (Takada and Fukushima, 2013), as estimated by InSAR.