11:15 AM - 11:30 AM
[SCG56-09] Rheological Heterogeneity with Overlap of Coseismic and Postseismic Slip: 2008 Iwate-Miyagi Nariku Earthquake
Keywords:Simulation, Fault slip, InSAR, GNSS, Caldera
The Iwate-Miyagi Nairiku Earthquake (IMNE) occurred on June 14, 2008 (Mw 6.8). The rupture area stretches along the volcanic front of NE Japan, which introduces rheological heterogeneities. A series of large-scale calderas in the neighboring area adds another complexity to the mechanical response (Takada and Fukushima, 2013). The geometry of the fault system is also complex: ALOS PALSAR images (both InSAR and offset-tracking) revealed the conjugate fault slip (Takada et al., 2009; Abe et al., 2013), which is also supported by the aftershock distributions. Large post-seismic deformation following the mainshock has been detected by GNSS and InSAR (e.g., Iinuma et al., 2009; Ohzono et al., 2012; Takada et al., 2011). Furthermore, using InSAR analysis, we found clear overlaps of coseismic and postseismic areas on the same fault planes (Takei, et al., 2021).
So far, the physical relationship between the abovementioned factors prescribing the complex nature of IMNE has not been proposed. In this study, we construct a physical model using a numerical code Unicycle (Barbot et al., 2017; Moore et al., 2017), a half-analytic viscoelastic solution. In the physical model, we considered, (1) rheological heterogeneity in the proximity of an active volcano (Mt. Kurikoma), and (2) pre-stress that is necessary to explain the overlap of co- and post-seismic slip.
The result shows remarkable post-seismic uplift to the west of Mt. Kurikoma as detected by InSAR, which is caused by kinematic interaction between the post-seismic slip at the deeper portion of the west-dipping fault and low-viscosity material associated with past caldera formation. The spatial heterogeneity of pre-stress strongly affects the post-seismic slip distribution as well as the co-seismic slip pattern, which explains the overlap of co- and post-seismic slip areas. The calculated post-seismic displacements are overall consistent with the observed data.
So far, the physical relationship between the abovementioned factors prescribing the complex nature of IMNE has not been proposed. In this study, we construct a physical model using a numerical code Unicycle (Barbot et al., 2017; Moore et al., 2017), a half-analytic viscoelastic solution. In the physical model, we considered, (1) rheological heterogeneity in the proximity of an active volcano (Mt. Kurikoma), and (2) pre-stress that is necessary to explain the overlap of co- and post-seismic slip.
The result shows remarkable post-seismic uplift to the west of Mt. Kurikoma as detected by InSAR, which is caused by kinematic interaction between the post-seismic slip at the deeper portion of the west-dipping fault and low-viscosity material associated with past caldera formation. The spatial heterogeneity of pre-stress strongly affects the post-seismic slip distribution as well as the co-seismic slip pattern, which explains the overlap of co- and post-seismic slip areas. The calculated post-seismic displacements are overall consistent with the observed data.