Large Events, Seismic Gaps, and Stress Diffusion in Central Chile
The time and space distribution of rupture segments along south-central Chile suggest the high probability of of a large magnitude earthquake occurring in the proposed seismic gap (34.3°–37.2°S) located between the 1960 and 1985 rupture regions. Three lines of evidence support the occurrence of a magnitude 8+ event within the next couple of decades. First the repeat time of large magnitude earthquakes is 90±6 years; the last such shock was in 1928. The second line of evidence is related to a possible cause-effect relationship between events within the gap. The distribution of events exhibits a coupling of earthquakes from north to south. The average inter-occurrence time is 16 ±6 years and the last quake in the northern part was in 1985. The last line of evidence arises from an analysis of all the data in this century. A southward migration of ca. 7 km/year is apparent in the sequence indicating that the possible “stress front” will arrive at the seismic gap within the first decade of the next century. The observed velocities and recurrence periods are consistent with a stress diffusion model. This analysis by no means excludes the possibility of earlier activity, such as occurred in 1971 prior to the 1985 mainshock.
KeywordsRupture Zone North Anatolian Fault Rupture Length Southward Migration Chilean Earthquake
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