The great earthquakes of 21–22 May, 19 in west-central Chile were accompanied tectonic displacements and intense, predominantly shallow (h≤70 km), aftershock activity. They affected a region more than 2 km wide and about 1000 km long that along the continental margin between 37° 46° S latitude. Studies of shorelines levelling data in this region indicate that vertical deformation involved a broad downwarp and two flanking upwarps. The structures lie roughly between and parallel the Peru-Chile Trench and Andeanchain. Vertical tectonic displacements to sea level resulted in: (1) uplift of at least 5 m on offshore islands, at some points along mainland coast, and on at least part of contiguous continental shelf; (2) subsidence as much as 2.7 m in a zone 75–110 km that extends eastward from the vicinity of outer coast almost to the western margin of borders the downwarp on the east.