Subsurface geometry and structural evolution of the eastern margin fault zone of the Yokote basin based on seismic reflection data, northeast Japan

Estimation of the Slip Rate Along the Unruptured Fault Segment of the M7.2 1896 Rikuu Earthquake, Northeast Japan

“…The signatures of active faulting and slip rate estimates are very well documented along the historically active northern ruptured segment of the EFZYB (Imaizumi et al, 1997;Kagohara et al, 2009;Matsuda et al, 1980). However, in our study, which is based on the geomorphic, seismic, and borehole survey data, we provide evidence of Quaternary faulting along the unruptured segment of the EFZYB, along the western margin of the Mahiru Mountain.…”

“…The Shiraiwa, Ota, Senya, and some parts of the Kanazawa Fault were reactivated during the 1896 Rikuu earthquake (M JMA 7.2) but, due to the lack of seismological and geodetic measurement, the earthquake parameters were not constrained (Thatcher et al, 1980). However, the extensive field investigations along the EFZYB rupture zone revealed a surface rupture extending of at least 36 km along the Shiraiwa Fault, Ota Fault, Senya Fault, and along the northern section of the Kanazawa Fault, before terminating along the rest of the Kanazawa Fault (Active Fault Research Group of Japan, 1991; Matsuda et al, 1980 Ozawa et al, 1987;Kagohara et al, 2009) 3. Methods…”

“…Apart from the plate boundary earthquakes, several intraplate earthquakes for example, the 1896 Rikuu earthquake (M7.2) (Matsuda et al., 1980), the 1900 Northern Miyagi earthquake (M7.0), the 1970 Akita‐ken Nantobu earthquake (M6.2) (Hasegawa et al., 1974), the 1998 Iwate volcano earthquake (M6.1) (Miura et al., 2000), and the 2008 Iwate‐Miyagi Nariku earthquake (M7.2) (Matsu'ura & Kase, 2010) have occurred on the faults in the over‐riding plate in the Tohoku region (Figure 1a). The 1896 Rikuu earthquake is one the largest on‐land reverse fault earthquakes in the history of Japan (Matsuda et al., 1980), which ruptured beneath the Ou Backbone Range (OBR) and reactivated the preexisting northern segment of the Eastern Margin Fault Zone of Yokote Basin (EFZYB), while leaving the southern segment unruptured (Kagohara et al., 2009; Matsuda et al., 1980; Miura et al., 2002) (Figures 1a and 1b). Since then, extensive work has been conducted along the ruptured segment of the EFZYB to document the fault slip rate, the timing of the penultimate and the earlier events, and establishing the recurrence interval for large earthquakes (Kagohara et al., 2009; Matsuda et al., 1980; Miura et al., 2002; Research Group for Senya Fault, 1986; Imaizumi et al., 1997; Sato et al., 2002).…”

“…The 1896 Rikuu earthquake is one the largest on‐land reverse fault earthquakes in the history of Japan (Matsuda et al., 1980), which ruptured beneath the Ou Backbone Range (OBR) and reactivated the preexisting northern segment of the Eastern Margin Fault Zone of Yokote Basin (EFZYB), while leaving the southern segment unruptured (Kagohara et al., 2009; Matsuda et al., 1980; Miura et al., 2002) (Figures 1a and 1b). Since then, extensive work has been conducted along the ruptured segment of the EFZYB to document the fault slip rate, the timing of the penultimate and the earlier events, and establishing the recurrence interval for large earthquakes (Kagohara et al., 2009; Matsuda et al., 1980; Miura et al., 2002; Research Group for Senya Fault, 1986; Imaizumi et al., 1997; Sato et al., 2002). Along the southern unruptured segment of EFZYB, some of the pioneering work was conducted by the Active Faults Research Group of Japan (1991), Sawa et al., (2011, 2013), Sugito (2013) to document the probable trace of the active fault, however, the estimation of slip rates and recurrence interval remained largely unresolved.…”

“…The black dots indicate epicenters with M w > 4 < 5.9, whereas red stars indicate the epicenters with M w > 5.9. (b) The generalized X ‐ Y cross‐section across the OBR is adopted from Kagohara et al., (2009), showing a pop‐up structure of the OBR bounded by the KTSFZ toward the east and by the Higashi Chokai san Fault (HCF) toward the west. The Mahiru Mountain is the western segment of OBR bounded to the east by a back‐thrust Kawafune Fault (KF).…”