09:45 〜 10:00
[S08-17] Stress Change Driven Afterslip Following the 2016 Central Tottori Earthquake
The analysis of GNSS observations in the coseismic and postseismic period of the 2016 Central Tottori earthquake (Mw6.2) revealed a complementary spatial pattern between the coseismic and postseismic slip distributions on the fault plane (Meneses-Gutierrez et al., 2019 JGR). These results suggested afterslip driven by coseismic stress change, in agreement with velocity-strengthening friction laws, often invoke to explain postseismic deformation (Marone et al., 1991). However, a quantitative relation between the coseismic deformation and the mechanism driving postseismic deformation of the 2016 Central Tottori earthquake has not been established.
We perform a geodetic inversion of a dense GNSS network to estimate the coseismic slip distribution on the fault plane of the 2016 Central Tottori earthquake in an elastic half-space using the method of Yabuki and Matsu’ura (1992). Using the stress change calculated from the aforementioned coseismic slip distribution, we construct the expected afterslip stress drop in the postseismic period (Saito and Noda, 2022 JGR). For this purpose, we assume that the observed positive coseismic stress change at shallow depths (~1 MPa) works as the stress drop in the afterslip. Next, we obtain the afterslip distribution by inverting the stress drop distribution. In doing this, we assume that the slip direction in the postseismic period is consistent with that of the subfaults in the coseismic period.
Large afterslip is restricted to shallow depths (<3 km) in agreement with previous studies. The maximum postseismic slip is 20 cm and the moment magnitude is Mw 5.3 (1.47 x 1017 N·m) when we assume a rigidity of 30 GPa. The moment magnitude of our slip distribution constructed from the coseismic stress change is smaller than the resulting from the conventional geodetic data inversion (Mw 5.55, 2.17x1017 N·m), however, we found that our model can well reproduce the horizontal postseismic displacement near the source region, quantitatively demonstrating the afterslip driven by coseismic stress change.
We perform a geodetic inversion of a dense GNSS network to estimate the coseismic slip distribution on the fault plane of the 2016 Central Tottori earthquake in an elastic half-space using the method of Yabuki and Matsu’ura (1992). Using the stress change calculated from the aforementioned coseismic slip distribution, we construct the expected afterslip stress drop in the postseismic period (Saito and Noda, 2022 JGR). For this purpose, we assume that the observed positive coseismic stress change at shallow depths (~1 MPa) works as the stress drop in the afterslip. Next, we obtain the afterslip distribution by inverting the stress drop distribution. In doing this, we assume that the slip direction in the postseismic period is consistent with that of the subfaults in the coseismic period.
Large afterslip is restricted to shallow depths (<3 km) in agreement with previous studies. The maximum postseismic slip is 20 cm and the moment magnitude is Mw 5.3 (1.47 x 1017 N·m) when we assume a rigidity of 30 GPa. The moment magnitude of our slip distribution constructed from the coseismic stress change is smaller than the resulting from the conventional geodetic data inversion (Mw 5.55, 2.17x1017 N·m), however, we found that our model can well reproduce the horizontal postseismic displacement near the source region, quantitatively demonstrating the afterslip driven by coseismic stress change.