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Local changes of sea level before large earthquakes in South America

GEOPHYSIKALISCHES INSTITUT UNIVERSITÄT KARLSRUHE, 75 KARLSRUE WEST (21), HERTZSTR 16, BAU42, Germany

Abstract

Vertical movements of the crust along the South American west coast are estimated from mean annual sea level (MASL). At an average distance of 400 km, 13 stations recorded sea level more or less continuously since 1941. The standard deviation of MASL from 20-year means is typically about 3 cm. Using reference stations reduces the standard deviation to 0.5 to 1.5 cm and therefore elevation changes of 3 cm can be resolved with 99 per cent confidence, if they last for more than 5 years. At Chimbote (Peru) uplift of about 5 cm was recorded in 1961. Six and nine years later the 1966 and 1970 Peru earthquakes (M = 7.6 and 7.8) occurred at distances of 130 and 23 km, respectively. An uplift of about 3 cm appears to have preceded the Antofagasta earthquake (M = 6.8) by 6 years. At 100 km north of the 1960 Chile rupture (M = 8.6) sea level remained unchanged between 1955 and 1970. Because all tide gauge stations in South America are located in active tectonic areas it is difficult to identify small land elevation changes by comparison with reference stations.

Footnotes

^* Present address: The Cooperative Institute for Research in Environmental Sciences, University of Colorado/NOAA, Boulder, Colorado 80302.

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