Locked segment is the geological structure that governs the generation of tectonic earthquakes. As such， studying the energy conversion and allocation principle during the damage process of locked segment can make enhanced insights into its damage behavior and energy evolution mechanism. Based on the energy conservation principle， the relationship between conversion and allocation of elastic strain energy stored in a locked segment during crack propagation was elucidated， and a formula for calculating the radiated seismic energy generated from a cracking event in the locked segment was proposed. Hereby， using the brittle failure theory of multiple locked segments of seismogenic faults， the magnitude criterion for identifying a mainshock was derived， the equivalence between the cumulative Benioff strain ratio and the shear strain ratio was demonstrated， and the methods for calculating the source parameters of cracking event in a locked segment were presented. Case studies show that the methods are reliable. The present results have broad application prospects in identification of mainshock， estimation and verification of source parameters.
