On the Manifestation of Precursors of Strong Earthquakes (<i>M</i><sub>W</sub> ≥ 6.6) in Kamchatka

A review of work on the search for earthquake precursors during the period of detailed seismological observations in the Kamchatka Peninsula in 1962–2022 is presented in comparison with the cumulative graph of seismic energy release and the most powerful earthquakes. A feature of the observation network for earthquake precursors is the location of most “non-seismological” types of observations in a small area of the Petropavlovsk-Kamchatsky test site (PKTS). Analysis of the 14 types of seismic, geophysical and geochemical precursors before seven 2005–2022 shallow and intermediate earthquakes with МW = 6.6–7.7 showed an increase in the number of precursors N with an increase in the parameter MW / lgdh (dh is the hypocentral distance to the center of PKTS in km), which characterizes the relative intensity of earthquake preparation in the PKTS area. Such a relationship between N and MW/lgdh traced for interplate (subduction) earthquakes in the Kamchatka fragment of the Kuril-Kamchatka Island arc as well as consistent with the manifestations of precursors in 1987–2004 and reflects the integrated manifestation of precursors before earthquakes that are the strongest and closest to the PKTS territory. Before such events, the effect of integrated manifestation of precursors (EIMP) was observed in no less than 80% of the precursors of all considered in this work. For such earthquakes, the ratio between the hypocentral distance dh and the size of the earthquake source L (km) is dh / L = 3.8–1.6, i.e., the manifestation of EIMP is characteristic of the near and middle (intermediate) zone of the future earthquake. Using the example of four separate types of precursors, it is shown that their threshold values dh / L = 5.0–8.5 for events with МW ≥ 6.6. If, during seismic forecasting, the EIMP is diagnosed in real time, then using the threshold value dh / L ≤ 3.8 set for it, it is possible to significantly reduce the estimate of the distance of a future strong earthquake from the PKTS area and the Petropavlovsk-Yelizovo urban agglomeration, compared with the use of data on individual types of precursors.