Algorithm MSc or “The Mendocino Scenario” (Kossobokov et al., 1990) was designed by retroactive analysis of the regional seismic catalog prior to the Eureka earthquake (1980, M=7.2) near Cape Mendocino in California, hence its name. Given a TIP diagnosed for a certain territory U at the moment T, the algorithm is designed to find within U a smaller area V where the predicted earthquake can be expected. An application of the algorithm requires a reasonably complete catalog of earthquakes with magnitudes M >= (M0 — 4), which is lower than the minimal threshold usually used by M8.

The essence of MSc can be summarized as follows.

    1. Territory U is coarse-grained into small squares of s x s size. Let (i,j) be the coordinates of the centers of the squares. Within each square (i,j) the number of earthquakes nij(k), aftershocks included, is calculated for consecutive, short time windows, u months long, starting from the time to = (T-6 years) onward, to allow for the earthquakes which contributed to the TIP’s diagnosis; k is the sequence number of a time window. In this way the time-space considered is divided into small boxes (i,j,k) of the size (s x s x u).
    2. «Quiet» boxes are singled out for each small square (i,j); they are defined by the condition that nij(k) is below the Q percentile of nij.
    3. The clusters of q or more quiet boxes connected in space or in time are identified. Area V is the territorial projection of these clusters.

The standard values of parameters adjusted for the case of the Eureka earthquake are as follows: u = 2 months, Q = 10% , q = 4, and s = 3D/16, D being the diameter of the circle used in algorithm M8. Thus, the MSc algorithm outlines such an area of the territory of alarm where the activity is continuously high but it has been interrupted for a short time (the interruption must have a sufficient temporal and/or spatial span). Note that the phenomenon used in the MSc algorithm might reflect the second (shorter-term) stage of premonitory rise of seismic activity near the incipient source of main shock.