Three-dimensional FEM derived elastic Green's functions for the coseismic deformation of the 2005M_w8.7 Nias-Simeulue, Sumatra earthquake

Abstract

Using finite element models (FEMs), we examine the sensitivity of surface displacements to the location of fault slip, topography, and three‐dimensional variations in elastic moduli in the context of a 2‐D infinite thrust fault. We then evaluate the impact of these factors and fault geometry on surface displacements and estimates of the distribution of coseismic slip associated with the 2005 Mw 8.7 Nias‐Simeulue, Sumatra earthquake. Topographic effects can be significant near the trench, where bathymetric gradients are highest and the fault is closest to the free surface. Variations in Young's modulus can significantly alter predicted deformation. Surface displacements are relatively insensitive to perturbations in Poisson's ratio for shear sources, but may play a stronger role when the source has a dilatational component. If we generate synthetic displacements using a heterogeneous elastic model and then use an elastic half‐space or layered earth model to estimate the slip distribution and fault geometry, we find systematic residuals of surface displacements and different slip patterns compared to the input fault slip model. The coseismic slip distributions of the 2005 earthquake derived from the same fault geometry and different material models show that the rupture areas are narrower in all tested heterogeneous elastic models compared to that obtained using half‐space models. This difference can be understood by the tendency to infer additional sources in elastic half‐space models to account for effects that are intrinsically due to the presence of rheological gradients. Although the fit to surface observations in our preferred 3‐D FEM model is similar to that from a simple half‐space model, the resulting slip distribution may be a more accurate reflection the true fault slip behavior.

A Feasibility Study of an FEM Simulation Used in Co-Seismic Deformations: A Case Study of a Dip-Slip Fault

“…They found the maximum difference is about 5% and mainly localized near the trench where the topographic gradient is highest. Basically the present conclusions coincide with that of Hsu et al (2011), although both studies are made for different targets and different topographical models. Thus, we conclude that the terrain effect must be considered in the application of dislocation theory to calculate the co-seismic and post seismic deformation.…”

“…Results show that the relative impact is 9.05% of the horizontal direction and 2.95% of the vertical direction. Hsu et al (2011) also studied the impact of topography on surface displacement using a three-dimensional FEM calculation for the 2005 M w 8.7 Nias-Simeulue, Sumatea earthquake. They found the maximum difference is about 5% and mainly localized near the trench where the topographic gradient is highest.…”

Coseismic deformation due to the 2011 Tohoku-oki earthquake: influence of 3-D elastic structure around Japan

“…Conversely, the consideration of a strong slab (a slab with increased rigidity) in the coseismic inversion was shown to lead to a decrease in inferred seismic moment compared to a homogeneous model (Hsu et al 2011;Kyriakopoulos et al 2013). Consideration of surface topography and lateral heterogeneity from seismic tomography was also found to lead to a better fit to the observed coseismic surface displacements (Pulvirenti et al 2014;Romano et al 2014).…”

“…Thus, for the same slip, the movement of the hanging wall should increase (cf. Hsu et al 2011). Both effects exist in the HOM → LYR and LYR → SLAB steps.…”

An adjoint-based FEM optimization of coseismic displacements following the 2011 Tohoku earthquake: new insights for the limits of the upper plate rebound

“…As well known in literature (e.g., Cattin et al, 1999;Masterlark 2003;Aloisi et al, 2011;Hsu et al, 2011), the simple analytical model approach (homogeneous, isotropic, Poisson-solid half-space assumption) has in fact strong limitations and introduces significant displacement prediction errors (with respect to measurement uncertainties). In particular, Cattin et al (1999) found that rigidity contrasts, existing within the upper crust can increase the horizontal displacements for a given slip model by up to 40%.…”