Determining the fault dislocations is one of the important factors in the civil engineering design of infrastructures. There are three main methods for this fault dislocation: theoretical, numerical and empirical methods. Theoretical methods explain ground surface deformation due to earthquake based on equilibrium equations. Numerical methods use equilibrium equations and computer program for calculation. In most of the previous studies, linear elasticity and continuum mechanics were considered. Theoretical and numerical methods have some limitations in their calculation and show inconsistency between the reality and the simulation results. The other type of fault dislocation calculation is empirical method which is based on the pervious earthquakes data. In this method based on information about surface deformation, source fault factors, underground geology and geometry empirical relationship proposed. Current empirical relationships don't cover all the factors and they should be improved. The most important factor in ground surface deformation is type of fault; second factor is source fault geometry and displacement, magnitude of earthquake represents these factors. Underground geology and property are in the next level of priority. Based on this model empirical relationship should be proposed.
Fault dislocation induces surface deformations of the ground during large earthquakes. Generally there are two types of surface deformations: discontinuous deformations or fault raptures as shown in Figure 1-A, or continuous deformations which is a continuous bending of the ground without marked discontinuities as shown in Figure 1-B. The determination of the fault dislocation is very important in geology and the civil engineering design of infrastructures. Most of the structural design codes only consider load due to earthquakes. There are few design codes which pay attention to the surface deformation around fault and their effects on the structures. In the case that surface rupture happened as shown in Figure 2-A (The 2008 Wenchuan, China earthquake) the collapse occurred, and in the case that continuous deformation occurred as shown on Figure 2-B (The 1999 Chi-Chi, Taiwan earthquake) the building is safe but it needs to rebuilt. Recent earthquakes provided lots of example of surface deformations causing some damages on buildings, roads and lifelines; therefore increasing knowledge on measurement of fault dislocation is necessary and some effective evaluation methods should be developed. In this paper, the available methods of calculations and predictions of surface deformations due to fault dislocations are discussed.
To understand the ground surface deformation due to earthquake, first the important factors should be known. As shown in the Figure 3 there are three main factors:
underground geologies and geometries and
Source fault is the most important factor in ground surface deformation due to earthquake. As shown in Figure 3 source fault has two main sub-factors: geometry and displacement, the details of each subfactors is shown in Figure 4. The other important factor is underground geologies and properties. Generally there are two main sub-factors: incompetent shallow soil (or shallow soft soil) and competent deep soil (or deep hard soil).