Large heterogeneous structure beneath the Atotsugawa Fault, central Japan, revealed by seismic refraction and reflection experiments

Electrical Resistivity Structure Around the Atotsugawa Fault, Central Japan, Revealed by a New 2‐D Inversion Method Combining Wideband‐MT and Network‐MT Data Sets

“…(2010) and Iidaka et al. (2015), the low‐velocity areas appear to be broadly distributed under the AF and the TOFZ. Because large amounts of aqueous fluid contribute to low velocity, as well as low‐electrical resistivity, a local concentration of aqueous fluid beneath the UF, AF, and TOFZ is inconsistent with the seismic velocity structure, in which localized velocity anomalies under the respective faults are not noticeable.…”

“…Therefore, we interpreted that the conductive areas at the deep extension of the UF, AF, and TOFZ indicate the localized ductile shear zones at the deep extension of the faults, where connected fluid networks are maintained because of stable slips. As suggested by Nakajima et al (2010) and Iidaka et al (2015), aqueous fluid in the lower crust of the study area would reduce the mechanical strength of the lower-crustal rocks (Bürgmann & Dresen, 2008). However, the electrical resistivity structure obtained by this study implies that the strain is not uniformly distributed in the lower crust but is localized at the deep extension of the UF, AF, and TOFZ, thus supporting the localized stable slip model proposed by Mizuno et al (2005) and Imanishi et al (2011).…”

“…(2010) and Iidaka et al. (2015) suggested that the fluid originating from the subducting PHS rises through the mantle wedge by upwelling flow and is consequently supplied to the lower crust around the AF. The fluid is probably generated by the dehydration of hydrous minerals such as serpentine and chlorite on top of the PHS (Iwamori, 1998).…”

“…The strain accumulation at the upper crust of the AF is considered to be caused by a mechanically weak zone with low viscosity in the lower crust (e.g., Iidaka et al, 2015;Nakajima et al, 2010). From the results of finite element modeling, Mizuno et al (2005) suggested that the stress field around the fault can be explained by the superposition of the stress field associated with regional deformation and the stable slip along the deep extension of the fault.…”

“…In addition, Goto et al (2005) and Yoshimura et al (2009) showed only the crustal electrical resistivity structure because the MT response functions for periods longer than several thousands of seconds could not be well estimated. Nakajima et al (2010) and Iidaka et al (2015) suggested that the aqueous fluid in the lower crust under the study areas is originated from the water dehydrated from the subducting Philippine Sea slab (PHS), which is located down to a depth of about 140 km under the north of the Chubu region (Nakajima et al, 2009). Therefore, to better understand the root of the aqueous fluid in the lower crust, it is important to investigate the electrical resistivity structure down to the upper mantle.…”