Abstract
Evaluating the transfer of stresses from megathrust earthquakes to adjacent segments is fundamental to assess seismic hazard. Here, we use a 3D forward model as well as GPS and seismic data to investigate the transient deformation and Coulomb Failure Stresses (CFS) changes induced by the 2010 Maule earthquake in its northern segment, where the Mw 8.3 Illapel earthquake occurred in 2015. The 3D model incorporates the coseismically instantaneous, elastic response, and time-dependent afterslip and viscoelastic relaxation processes in the postseismic period. We particularly examine the impact of linear and power-law rheology on the resulting postseismic deformation and CFS changes that may have triggered the Illapel earthquake. At the Illapel hypocenter, our model results in CFS changes of ∼0.06 bar due to the coseismic and postseismic deformation, where the coseismic deformation accounts for ∼85% of the total CFS changes. This is below the assumed triggering threshold of 0.1 bar and, compared to the annual loading rate of the plate interface, represents a clock advance of approximately only 2 months. However, we find that sixteen events with Mw ≥ 5 in the southern region occurred in regions of CFS changes > 0.1 bar, indicating a potential triggering by the Maule event. Interestingly, while the power-law rheology model increases the positive coseismic CFS changes, the linear rheology reduces them. This is due to the opposite polarity of the postseismic displacements resulting from the rheology model choice. The power-law rheology model generates surface displacements that fit better to the GPS-observed landward displacement pattern.
Highlights
Given that the afterslip distributions from both rheology model cases show similar magnitude and patterns in the closest region to the Illapel segment (Figure 2), the main deviations in their resulting horizontal displacement patterns are due to differences in location of viscous relaxation from the rheology model choice
We examine the co- and postseismic deformation and stress change pattern on the Illapel segment induced by the 2010 Maule earthquake using a 3D geomechanical-numerical model with linear and power-law rheology
Our results show that the postseismic horizontal deformation patterns in the Illapel segment are sensitive to the choice of the rheology model
Summary
Megathrust earthquakes induce local and large-scale deformations (e.g., Hu et al, 2004; Vigny et al, 2011; Moreno et al, 2012), which may last several decades due to viscoelastic relaxation (Khazaradze et al, 2002; Hu et al, 2004; Wang et al, 2012). At neighboring segments of the rupture area, the GPS horizontal displacements exhibit landward motion (Heki and Mitsui, 2013; Tomita et al, 2015; Klein et al, 2016; Loveless, 2017; Melnick et al, 2017), as envisioned by Anderson (1975). While the trenchward motion patterns are mostly attributed to afterslip on the fault interface and viscous relaxation in the lower crust and upper mantle (e.g., Hu et al, 2004; Hergert and Heidbach, 2006; Wang et al, 2012; Peña et al, 2019, 2020), the driving mechanisms controlling landward patterns following megathrust earthquakes are currently a matter of controversial debate. Other authors have proposed that the slab pull balance of forces after large earthquakes is the driving mechanism of the GPSobserved postseismic landward patterns (Heki and Mitsui, 2013; Yuzariyadi and Heki, 2020)
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