Long‐term changes in the Coulomb failure function on inland active faults in southwest Japan due to east‐west compression and interplate earthquakes

Abstract

Inland earthquake activity in and around the Kinki region, southwest Japan, increases in the period from several decades before to about a decade after the occurrence of great interplate earthquakes along the Nankai Trough. To quantitatively investigate this relationship, we calculated long-term changes in the Coulomb failure function (ΔCFF) on inland active faults in this region with viscoelastic slip response functions. As sources for the change in CFF, we investigated east-west compression within the Niigata-Kobe Tectonic Zone (NKTZ), historical interplate earthquakes and interseismic locking along the Nankai Trough subduction zone, and historical inland earthquakes in this region. Among these sources, the NKTZ east-west compression is the primary cause of the long-term changes in CFF. The changes in CFF due to interplate earthquakes are mostly negative on reverse faults and positive on strike-slip faults. This result suggests that the inland reverse faulting activity mostly increases before interplate earthquakes and decreases after the earthquakes, whereas strike-slip activity is mostly suppressed before interplate earthquakes and increases thereafter. This suggestion is supported by spatiotemporal pattern of historical inland earthquakes if focal mechanisms of historical earthquakes correspond to fault geometries in the region. The calculated changes in CFF are usually consistent with the occurrence of historical inland earthquakes. If we use the change in shear stress instead of the change in CFF, this consistency is enhanced, which suggests low apparent coefficients of friction in this region.

Shear Strain Energy Change Caused by the Interplate Coupling Along the Nankai Trough: An Integration Analysis Using Stress Tensor Inversion and Slip‐Deficit Inversion

“…In fact, the seismicity in Wakayama showed significant quiescence after the 1944 Tonankai earthquake (e.g., Kanamori, ; Yoshioka & Hashimoto, ). Past studies reported that the seismic activation and quiescence in the inland area were associated with Nankai Trough earthquakes (e.g., Ogata, ; Shikakura et al, ). The stress fluctuation caused by the interplate locking and the huge Nankai Trough earthquakes significantly affects the occurrence time of the inland earthquakes.…”

Driving Stress and Seismotectonic Implications of the 2013 Mw5.8 Awaji Island Earthquake, Southwestern Japan, Based on Earthquake Focal Mechanisms Before and After the Mainshock

“…Mitogawa and Nishimura (2020) showed that a model incorporating the viscoelasticity successfully reproduces the activation of shallow inland earthquakes, not only before but also after the interplate earthquakes. Under a more realistic model setting, Shikakura et al (2014) explained this feature by computing the long-term viscoelastic Coulomb stress change on inland earthquake faults. They incorporated all possible deformation sources: the E-W compression observed as the Niigata-Kobe Tectonic Zone (Sagiya et al 2000), historical…”

“…Regarding an additional loading stress of the Awaji Island earthquake, we evaluated the Coulomb stress change (∆CFF) and its evolution after the Kobe earthquake, following the approach from Ohtani and Imanishi (2019). We assumed a one-dimensional viscoelastic structure used in Shikakura et al (2014), in which the thickness of the elastic layer is 35 km and the Maxwell viscosity of the viscoelastic layer is 5.0×10 18 Pa s. For the fault slip of the Kobe earthquake, we used a finite fault source model derived from the inversion of the near-source strong motion data (Ide and Takeo 1997). Most of the slip exists beneath Awaji Island, which is a feature commonly found in other slip models (Wald 1996;Koketsu et al 1998;Sekiguchi et al 2000).…”

Driving stress and seismotectonic implications of the 2013 Mw5.8 Awaji Island earthquake, southwestern Japan, based on earthquake focal mechanisms before and after the mainshock

“…Regarding an additional loading stress of the Awaji Island earthquake, we evaluated the Coulomb stress change () and its evolution after the Kobe earthquake, following the approach from Ohtani and Imanishi (2019). We assumed a one-dimensional viscoelastic structure used in Shikakura et al (2014), in which the thickness of the elastic layer is 35 km and the Maxwell viscosity of the viscoelastic layer is 5.0×10 18 Pa s. For the fault slip of the Kobe earthquake, we used a nite fault source model derived from the inversion of the near-source strong motion data (Ide and Takeo 1997). Most of the slip exists beneath Awaji Island, which is a feature commonly found in other slip models (Wald 1996;Koketsu et al 1998;Sekiguchi et al 2000).…”