Official earthquake prediction procedure in Greece

Abstract

Since Jan. 19, 1983, the authors have been operating a telemetric network of electrotelluric stations in Greece. The real-time observation of specific pre-seismic variations in the electric field of the earth (seismic electric signals, SES) allows us to predict the time, epicenter and magnitude of an impending earthquake (EQ). Initially the predictions were announced by expediting telegrams prior to the event. After the Ministry of Public Works established the Earthquake Prediction Council (EPC) in September 1985, predictions were dealt with in special sessions of the council prior to the occurrence of an earthquake. It was decided to announce only EQ's with an expected magnitude M s ⩾ 4.8 for epicenters predicted within or near the perimeter surrounding the network of measuring stations, and M s > 5 for EQ's predicted outside the perimeter. This procedure was followed from September 1985 to March 18, 1986 with the following results. 1. (1) Within the network. Only one EQ (with M s = 4.9) occurred during the period mentioned. The prediction of the magnitude was accurate to within a few tenths of a magnitude-unit, while the epicenter was predetermined to within some tens of kilometers. No predictions were made that were not followed by earthquakes. 2. (2)Outside the network. Three EQ's with M s = 5.4, 5.2, and 5.3 occurred on Nov. 9, Dec. 18, and Dec. 23, 1985, respectively. The first was missed. The magnitudes of the other two were predicted to be M s = 5.2 and 5.5 respectively. The corresponding epicentral coordinates were forecast with an accuracy of 150 and 160 km respectively. The sessions were discontinued on March 18, 1986. On March 24, 1986, a M s = 6.1 EQ was predicted and directly announced to the Ministry of Public Works. The event occurred on March 29 with the predicted magnitude and less than 50 km from the predicted epicenter.