Statistical precursors of a strong earthquake on April 6, 2009 on the Apennine Peninsula

The article discusses the possibility of formulating a conclusion about the transition in early April 2009 to an exceptional state of the geophysical system in an area with a radius of about several hundred kilometers from Rome. This fact preceded the tragic earthquake on April 6, 2009, which led to large casualties in the Italian city of L’Aquila. This conclusion was obtained based on an analysis of the statistics of the critical frequency of the ionosphere. In the course of calculations, in particular, phenomena with a high degree of determinism that preceded the specified seismic event were detected. The fact of their existence with a high probability indicates the occurrence of an exclusive state of the regional geophysical system in the period of about several days before this event. It was depicted that the identified phenomena precede a significant number of seismic events. Based on the analysis of variations in the statistics of the critical frequency of the ionosphere in the Apennine region in 2007–2011, including those preceding the earthquake near the city of L’Aquila on April 6, 2009, an algorithm was formulated to detect a significant probability of transition to an exclusive state of the corresponding local segment of the geophysical system. The approach proposed in the article can be used to compile a short-term that is, calculated for the coming days, forecast of the existence of a significant probability of the occurrence of seismic events of large magnitude in various regions of the world.