Premonitory seismicity changes prior to the Parkfield and Coalinga earthquakes in southern California

In this work, we apply the Pattern Informatics technique for evaluating one surface expression of the underlying stress field, the seismicity, in order to study the Parkfield–Coalinga interaction over the years preceding the 1983 Coalinga earthquake. We find that significant anomalous seismicity changes occur during the mid-1970s in this region prior to the Coalinga earthquake that illustrate a reduction in the probability of an event at Parkfield, while the probability of an event at Coalinga is seen to increase. This suggests that the one event did not trigger or hinder the other, rather that the dynamics of the earthquake system are a function of stress field changes on a larger spatial and temporal scale.