The coefficient of variation representing the non-uniformity of the strain field and its implication to detect earthquake precursor

Before the major earthquake or rock damage occurs, it is often accompanied by a sudden change in the degree of non-uniformity of the strain field. In order to find a stronger non-uniformity signal before the rock failure, the coefficient of variation (C_v) is examined and reformed in this study. We test the C_v calculation way of the "normal-abnormal" model proposed in the previous studies. Based on the analysis of the physical process of rock failure and its relationship to the shear strain field, we construct a new way to calculate the C_v value. The variation of shear strain field on rock sample with the increase of stress is obtained by the digital speckle correlation method (DSCM). The new C_v value calculation way is used to study the non-uniformity of the spatial distribution for the shear strain field. The results show that this C_v calculation way can get more obvious abnormal signals. When the number of observation points are limited, the specific distribution of points can increase the signal strength, which may provide reference for the research on precursor detection of earthquakes.