Using uplifted Holocene beach berms for paleoseismic analysis on the Santa María Island, south-central Chile

Abstract

Major earthquakes (M > 8) have repeatedly ruptured the Nazca-South America plate interface of south-central Chile involving meter scale land-level changes. Earthquake recurrence intervals, however, extending beyond limited historical records are virtually unknown, but would provide crucial data on the tectonic behavior of forearcs. We analyzed the spatiotemporal pattern of Holocene earthquakes on Santa Maria Island (SMI; 37°S), located 20 km off the Chilean coast and approximately 70 km east of the trench. SMI hosts a minimum of 21 uplifted beach berms, of which a subset were dated to calculate a mean uplift rate of 2.3 ± 0.2 m/ky and a tilting rate of 0.022 ± 0.002 °/ky. The inferred recurrence interval of strandline-forming earthquakes is ∼180 years. Combining coseismic uplift and aseismic subsidence during an earthquake cycle, the net gain in strandline elevation in this environment is ∼0.4 m per event. Copyright 2006 by the American Geophysical Union.