Application of the Korla volumetric strain to explore the triggering effects of tidal stress on tidal deformation before earthquakes

Abstract

When the fault in a focal area enters the critical state, nonlinear accelerated deformation and disturbance changes may occur during tide-induced loading and unloading. In this study, the anomalies in the Korla volumetric strain caused by earth tide were investigated using a theoretical model of tidal force. Results show that the step changes in the Korla volumetric strain may be triggered by tidal force within a short time frame, ranging from a few to tens of days, prior to a moderate earthquake. The azimuthal angles at the time of step changes are mainly distributed in the ranges of 124–158° and 185–228°, and the azimuth angle at the time of many nearby medium-to-strong earthquakes occurring in this step concentration area, suggesting that the step anomalies in the Korla volumetric strain are closely related to the horizontal tide-induced force in a specific direction. Using the Schuster method, it was found that the tide-induced azimuth angle of the step changes occurred mostly at the minimum value of the solid tide, providing evidences of the modulation of the solid tide. These results may present new ideas for using crustal deformation observations for short-term earthquake predictions.