Statistical property of candidate earthquake precursors and its apparent focal mecha- nism dependence

Statistical properties of reported earthquake precursors show apparent focal mechanism dependence. Intensity of anomaly is described by the ′anomaly ratio′ as defined by the number of stations/items reporting anomalies before the target earthquake over the number of stations/items in operation around the target earthquake. Variation of the ′anomaly ratio′ with the magnitude of the target earthquake was studied for dip-slip earthquakes all over China, strike-slip earthquakes in eastern China, and strike-slip earthquakes in western China, respectively. It is observed that for strike-slip earthquakes, the ′anomaly ratio′ increases linearly with the magnitude of the target earthquake, while earthquakes in eastern China and western China have different slopes. For dip-slip earthquakes, however, the ′anomaly ratio′ has no statistically significant change with the magnitude of the target earthquake. Limited data imply that the ′anomaly ratio′ seems proportional to the apparent stress of the target earthquake. The result might be heuristic for the analysis of candidate earthquake precursors.