Abstract

The Chilean earthquake sequence of May 21–22, 1960, was accompanied by linear zones of tectonic warping, including both uplift and subsidence relative to sea level. The region involved is more than 200 km wide and about 1000 km long, and lies along the continental margin between latitude 37° and 48° S. Significant horizontal strains accompanied the vertical movements in parts of the subsided zone for which triangulation data are available. Displacements were initiated near the northern end of the deformed region during the opening earthquake of the sequence (Ms ≅ 7.5) on May 21 at 10h 02m 50s GMT and were extended over the remainder of the region during the culminating shock (Ms ≅ 8.5) on May 22 at 19h llm 17s GMT. During the latter event, sudden uplift of adjacent portions of the continental shelf and much or all of the continental slope apparently generated the destructive tsunami that immediately followed the main shock.

Available data suggest that the primary fault or zone of faulting along which displacement occurred probably is a complex thrust fault roughly 1000 km long and at least 60 km wide; it dips eastward at a moderate angle beneath the continental margin and intersects the surface on the continental slope. Dip slip required to satisfy the surface displacements is at least 20 m and perhaps as large as 40 m. There is some evidence that there was a minor component of right-lateral slip on the fault plane.

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