Diagnosis of time of increased probability of strong earthquakes in the Jordan-Dead Sea rift zone

We have explored the possibility of intermediate-term earthquake prediction in the Jordan-Dead Sea rift region using the CN algorithm (Keilis-Borok et al., 1988). This algorithm is designed to identify the Time of Increased Probability (TIP) of the occurrence of strong earthquakes, defined by the conditionM ≥ M₀, where M is the earthquake magnitude and M₀ is a numerical threshold chosen for the considered region. The area under diagnosis includes Israel, most of Lebanon and the eastern parts of Jordan and Syria. Three strong earthquakes defined by the condition M₀ = 5 occurred in this area during the period July 1964-June 1990. By applying the CN algorithm with unchanged standard parameters, we found that two of the strong earthquakes were within the range of corresponding TIP intervals. These intervals extend far beyond the time of the occurrence of the strong earthquakes and represent about 40.5% of the total time. However, the TIP duration is considerably reduced to about 12.9% of the total time, when the threshold of the TIP termination rule is slightly changed. Although this a posteriori change violates the formal standard application of the CN algorithm, the results seem to be encouraging since false alarms did not appear at random, and the excessive TIP duration has a simple and rather obvious explanation. However, it seems that the conditions for the determination of TIPs in the CN algorithm should be modified accordingly.