11:00 〜 11:15
[SGD03-08] Mechanics-Based Analysis Linking Coseismic Slip and Afterslip in Intraplate Earthquakes
キーワード：Afterslip, Stress drop, Intraplate earthquakes, 2016 Central Tottori earthquake
Multiple studies have shown that kinematic afterslip distributions sometimes display spatial patterns that complement coseismic slip areas. This has been interpreted as evidence of afterslip driven by coseismic stress changes (e.g., Shen et al., 1994; Hern et al., 2002). However, the mechanical and quantitative relationship between the mainshock and the subsequent afterslip remains unclear. Evaluating fault parameters such as stress drop and strain energy change is key to clarifying the mechanics that link coseismic slip and afterslip.
This study aims to develop a mechanical model where the coseismic slip provides enough energy to drive the afterslip of inland earthquakes. Within this framework, we assume that the afterslip (i.e., the stress drop associated with the afterslip) occurs in areas of positive shear stress change due to coseismic slip along the fault; moreover, the slip direction must be consistent with the coseismic slip. We conduct a stress change inversion of postseismic observations in these areas (Saito and Noda, 2022), and using these results, we obtain the associated afterslip distribution.
We apply our method to the 2016 Mw6.1 Central Tottori earthquake in Japan, a left-lateral strike-slip fault-type earthquake that caused significant near-field coseismic and postseismic deformation recorded by a dense GNSS network, and for which stress-driven afterslip based on kinematic modeling has been suggested (Meneses-Gutierrez et al., 2019). Our estimated model accurately reproduces the horizontal postseismic displacement near the source region of the 2016 earthquake and illustrates a complementary spatial pattern between the kinematic coseismic slip and afterslip distributions. Moreover, unlike conventional inversion results, our study provides a quantitative spatial relationship between stress drops and changes in shear strain energy between the mainshock and afterslip, demonstrating that coseismic slip can provide sufficient strain energy to drive afterslip. Since the method proposed in this study yields a coseismic-afterslip model that is consistent with both reasonable mechanical conditions and observed GNSS data, it helps bridge the gap between observational kinematic results and simulation-based mechanical research.
This study aims to develop a mechanical model where the coseismic slip provides enough energy to drive the afterslip of inland earthquakes. Within this framework, we assume that the afterslip (i.e., the stress drop associated with the afterslip) occurs in areas of positive shear stress change due to coseismic slip along the fault; moreover, the slip direction must be consistent with the coseismic slip. We conduct a stress change inversion of postseismic observations in these areas (Saito and Noda, 2022), and using these results, we obtain the associated afterslip distribution.
We apply our method to the 2016 Mw6.1 Central Tottori earthquake in Japan, a left-lateral strike-slip fault-type earthquake that caused significant near-field coseismic and postseismic deformation recorded by a dense GNSS network, and for which stress-driven afterslip based on kinematic modeling has been suggested (Meneses-Gutierrez et al., 2019). Our estimated model accurately reproduces the horizontal postseismic displacement near the source region of the 2016 earthquake and illustrates a complementary spatial pattern between the kinematic coseismic slip and afterslip distributions. Moreover, unlike conventional inversion results, our study provides a quantitative spatial relationship between stress drops and changes in shear strain energy between the mainshock and afterslip, demonstrating that coseismic slip can provide sufficient strain energy to drive afterslip. Since the method proposed in this study yields a coseismic-afterslip model that is consistent with both reasonable mechanical conditions and observed GNSS data, it helps bridge the gap between observational kinematic results and simulation-based mechanical research.