3-D finite-element modelling of deformation and stress associated with faulting: effect of inhomogeneous crustal structures

Abstract

S U M M A R YModelling of deformation and stress caused by earthquake faulting (or fault motion) based on a homogeneous elastic half-space model does not include crustal rigidity layering and lateral variations. Geological data and seismic surveys indicate that the crust is elastically inhomogeneous, and that rigidity layering and heterogeneities are likely to affect the magnitude and pattern of deformation and stress. We use the finite-element method (FEM) to investigate deformation and stress generated by strike-slip, tensile and thrust faulting, considering rigidity layering in the crust. For a fault with a dimension of 25 × 10 km and a slip value of 0.5 m cutting through the top 10 km of the crust, the deformation and stress change associated with the three modes of faulting are calculated for an island arc crustal structure represented by three models of rigidity layering. The results indicate:(i) The maximum effect in horizontal displacements due to crustal layering for the investigated models is 19.7 mm and 28.8 mm for strike-slip and tensile faulting, respectively. For thrust faulting, the effect is up to 58.3 mm. This remarkable effect is due to the offset of layers by thrust faulting, which dynamically changes the crustal structure both horizontally and vertically. (ii) The maximum effect in vertical deformation due to crustal rigidity layering for strike-slip and tensile faulting is 5 mm. In contrast, the effect for thrusting is 30.3 mm. (iii)The effect in the shear stress change at a depth of 7.5 km for the different styles of faulting ranges from 0.02 MPa to 0.10 MPa.An additional modelling analysis of subduction thrusting at the Japan trench with a detailed structural model based on seismic surveys further confirms the significant distortion caused by a homogeneous model that ignores crustal structural information. Overall, the effect of crustal rigidity layering is at least 20 per cent for surface deformation and 15 per cent for stress changes at depth. In light of the present accuracy of global positioning system (GPS) observations (±2 mm) and the estimate of stress change required for earthquake hazard analysis (ca 0.01 MPa), the results from the numerical experiments indicate that crust inhomogeneity (rigidity layering and lateral variations) should be included in any quantitative models of faulting.

Dynamic simulation of interactions between major earthquakes on the Xianshuihe fault zone

“…To check the reliability of the results, we calculate fields of displacement and stress produced by the same dislocation on the same fault in the half-space elastic medium by using Okada's method [11] . Following some others [12,39] , we present comparison between distribution of displacement and maximum shear stress on the surface in Figure 5. It shows that the results derived from finite element method and classic analysis method are consistent.…”

“…Some researchers [9,10] studied the triggering mechanism between major earthquakes along the Xianhuihe fault zone by using the homogeneous elastic dislocation model [11] . However, if the media is assumed to be half-spatially homogeneous in the dislocation model, the difference is big between the results derived from homogeneous dislocation model and elastic layered model [12] . In addition, the influence degree on the subsequence earthquakes along the fault zone by the interaction between major earthquakes was ignored in previous study.…”

Earthquake Mechanism and Seafloor Deformation for Tsunami Generation

“…Rather than using an elastic half-space or layered-earth model, realistic geologic structures and heterogeneous physical properties can be used to calculate seafloor displacement, most often by finite element methods (Geist and Yoshioka 1996;Masterlark 2003;Zhao et al 2004). Static elastic deformation models developed for the Nankai subduction zone were adapted to calculate tsunami Encyclopedia of Earthquake Engineering DOI 10.1007/978-3-642-36197-5_296-1 # Springer-Verlag Berlin Heidelberg (outside the USA) 2014 generation along the Cascadia subduction zone (Geist and Yoshioka 1996).…”

Effect of heterogeneities on evaluating earthquake triggering of volcanic eruptions

“…However, seismic surveys and geological investigations have indicated that the subsurface include various scales of heterogeneities which might have the influence on the estimation of the stress fields in the subsurface generated by earthquakes. Zhao et al (2004) investigated deformation and stress generated by strike-slip, tensile and thrust faulting, considering the rigidity layering in the crust. They showed that the surface deformation and stress changes are distorted by the ignorance of crustal structural information.…”