Foreshock Phenomenon And Characteristics Of The Global Earthquakes M≥7

Foreshock is the most effective impending seismic prediction indicator which is acknowledged in earthquake academic world. In order to study the foreshock phenomena and characteristics of the global M≥7 earthquakes, this article selects the 1977-2014 M≥7 earthquakes, based on seismic source physics defining of foreshocks, and according to the definition from 553 times(478 group) seismic case selected 64 groups of foreshocks earthquake cases, accounting for 13.4% of the total seismic events. By using statistical method, the studies have investigated such statistical propreties of foreshocks in terms of magnitudes and occurrence times, and have found the foreshocks and main shock on the distribution of interval shorter and dense. Foreshocks mainly occurs within 10 days before the main shock, and in this time period, seismic activity have apparent acceleration; space distance general within 30 km; general terms of magnitudes between 0.5～2.5; In 92% of the foreshocks earthquake cases in maximum foreshocks and main shocks types of focal mechanism are the same.Through studying the area A、B and Mw 9.0 earthquake on March 11,2011 Japan, Mw 8.0 earthquake on February 6,2013 Solomon island and Mw 8.2 earthquake on April 1,2014 Chile of phenomena and characteristics of foreshocks, the study shows that foreshocks has the following characteristics:Foreshocks and main shocks focal mechanism have consistency; Foreshocks is a high degree of clustering in time and space, before the main earthquake, the earth activity has significantly accelerated phenomenon; The spatial distribution of banding phenomenon occurs after speeding up; Moderate and small earthquakes moves towards near the main epicenter at the speed of thousands of meters into the future before the main shock; Abnormal b value occurs at centrum origin before strong earthquakes happen. The foreshocks are recognized by the above phenomena, according to the time interval, the advantage of the space distance and magnitude difference distribution of main shock to a certain degree of forecasting, even though the main time interval of magnitudes and space distance are not related with original earthquake magnitude.