Massive EQ (M > 8) expected to occur within next 30 - 100 years along San Andreas fault in California. Regular pattern of massive EQ's along San Andreas fault every 60 - 200 yrs. Last M = 8 EQ in central CA was 1906 (San Francisco). Last M = 8 EQ in southern CA was in 1857. ~Recent EQ's of Loma Prieta + Northridge, CA were not "The Big One".
II) EQ Prediction
Iben Browning, climatologist who made advance forecast of 50% probability of EQ on New Madrid fault on specific day (Dec. 3, 1990). It didn't happen. Used alignment of planets + moon to exert tidal pressure + create EQ susceptibility. No scientific basis for this method; no pattern between tides + EQ's and tides do not generate enough force to begin movement along faults.
Clues for EQ prediction
A) Seismic gap - seismically active region that hasn't experienced large EQ for long time (stress building up). Example = Parkfield, CA along San Andreas Fault (moderate EQ every 22 yrs, but overdue).
B) Observation of precursor phenomena (events that sometimes
occur before major EQ's)
A) Long-range Predictions
1) Specific Date + Place in Distant Future = no success
2) Range of Dates (10's of yrs) (e.g., 90% chance at Parkfield, CA over next 30 yrs; uses seismic gap information) = sometimes successful
B) Short-range Predictions (uses observation of precursor phenomena) = sometimes successful
China - 1975 successful prediction; 1976 (Tangshan 250,000 deaths) unsuccessful prediction