A great earthquake (surface-wave magnitude, 7.8) occurred along the coast of central Chile on 3 March 1985, causing heavy damage to coastal towns. Intense foreshock activity near the epicenter of the main shock occurred for 11 days before the earthquake. The aftershocks of the 1985 earthquake define a rupture area of 170 by 110 square kilometers. The earthquake was forecast on the basis of the nearly constant repeat time (83 +/- 9 years) of great earthquakes in this region. An analysis of previous earthquakes suggests that the rupture lengths of great shocks in the region vary by a factor of about 3. The nearly constant repeat time and variable rupture lengths cannot be reconciled with time- or slip-predictable models of earthquake recurrence. The great earthquakes in the region seem to involve a variable rupture mode and yet, for unknown reasons, remain periodic. Historical data suggest that the region south of the 1985 rupture zone should now be considered a gap of high seismic potential that may rupture in a great earthquake in the next few tens of years.

Tide gage records at Puerto Montt, referenced to a mareograph in Talcahuano, indicate a large (at least 75 cm) postseismic uplift of the region following the 1960 Mw = 9.5 event. Field observations carried out in 1989 at the same locations of previous measurements in 1968 are consistent with tide gage records. The postseismic elevation changes are modeled as the result of propagating creep on the downdip extension of the coseismic fault. For a 30° E fault dip, minimum square error indicates a fault creep velocity of 4–6 km/yr and slip amplitude of 3–5 m.

Rapid onset natural hazards have claimed more than 2.8 million lives worldwide in the past 20 years. This category includes such events as earthquakes, landslides, hurricanes, tornados, floods, volcanic eruptions, wildfires, and tsunamis. Effective hazard mitigation is particularly difficult in such cases, since the time available to issue warnings can be very short or even nonexistent. This paper presents the concept of a local warning system that exploits and integrates the existing technologies of risk evaluation, environmental measurement, and telecommunications. We describe Project THRUST, a successful implementation of this general, systematic approach to tsunamis. The general approach includes pre‐event emergency planning, real‐time hazard assessment, and rapid warning via satellite communication links.

Several seismic gaps are identified along the coast of Chile. The main one is located in the northern part of the country (18 ° S-20 ° S), where a THRUST seismic trigger has been installed; two more triggers will be placed in other seismic gaps. The Standard Operations Plan (SOP) was tested during a disaster simulation exercise based on a major earthquake and tsunami situation. Response actions by governmental and civil agencies were monitored and a performance evaluation was done. Modifications of the SOP were found necessary to adjust the interactions between agencies.

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