Finite element analysis of crustal deformation in the Ou Backbone Range, northeastern Japan, with non-linear visco-elasticity and plasticity: effects of non-uniform thermal structure

Bunichiro Shibazaki,Kazuteru Garatani,Hiroshi Okuda

doi:10.1186/bf03352713

Abstract

AbstractA finite element analysis with non-linear visco-elasticity and plasticity was carried out with the aim of constructing a model of the slip and deformation processes in the deeper parts of the seismogenic zones of inland earthquakes. Our finite element code is based on the GeoFEM parallel finite element code and was developed using plug-ins to adopt several non-linear functions. We consider the effects of geothermal structures in the crust in a compressional tectonic setting to model the deformation and faulting that occur around the Ou Backbone Range in northeastern Japan. We set an area of high geothermal gradient in the center of the model. The numerical results show that shortening deformation due to non-linear viscous flow occurs in the high-temperature area in the lower part of the crust, which results in shear faulting in the upper part of the crust. In the case where the crust comprises two layers—the upper crust (quartz diorite) and the lower crust (wet diabase)—a weak viscous zone appears in the lower part of the upper crust and a strong viscous or plastic zone appears at the upper part of the lower crust. Our numerical results are able to explain the deformation and faulting that occur around the Ou Backbone Range in northeastern Japan.

Highlights

In the case of interplate earthquakes, stress is believed to accumulate as a result of a fault slip being held back relative to the plate motion
The differences in temperatures between the center of the model and the surrounding region in the lower crust determine the degree of localization in both the shortening deformation zone in the lower crust and the plastic deformation zone in the upper crust. 3.3.2 Two-layer crust In case 6, we consider a twolayer crust: a wet granite layer for the upper crust and a wet diabase layer for the lower crust
To simulate the deformation and faulting processes in the crust, we used non-linear finite element method (FEM) codes that were developed based on the GeoFEM platform, which includes functions of non-linear viscoelasticity, plasticity, and the approximate analysis for large deformation

Summary

Introduction

In the case of interplate earthquakes, stress is believed to accumulate as a result of a fault slip being held back relative to the plate motion. Iio and Kobayashi (2002) reviewed several models for the generation processes of large intraplate earthquakes, two of which are end member models. In one of these, where stress is uniformly loaded over a broad region and low-strength pre-existing faults exist in the upper crust, intraplate earthquakes are generated on the pre-existing faults, and faulting in the upper crust controls the lower crustal flow. Johnston and Kanter (1990) found that intraplate earthquakes in stable continental crust are commonly associated with the pre-existing weak zones which are ancient rift zones. In the second end member model, in which a local weak zone exists in the lower crust and deformation concentrates on this zone, the localized deformation results in the concen-

Methods

Findings

Conclusion