A new paper from Dr. Tom Rockwell and others emphasizing the potential danger of an earthquake by rupture of the San Ramon Fault in Santiago, Chile. With two large (Mw ~ 7.5) earthquakes in the past 17–19 k.y.. Generalizing further, despite long return times that might give a false sense of security, our study suggests that thrust faults at fronts of any active orogeny should be regarded as potential sources of large destructive earthquakes.

Probing large intraplate earthquakes at the west flank of the Andes

G. Vargas1Y. Klinger2T.K. Rockwell3S.L. Forman4S. Rebolledo1S. Baize5R. Lacassin2 and R. Armijo2

1Departamento de Geología, CEGA (Andean Geothermal Center of Excellence), Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, 8370450 Santiago, Chile
2Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot, UMR 7154 CNRS, 1 rue Jussieu, F-75005 Paris, France
3Department of Geological Sciences, MC 1020, San Diego State University, San Diego, California 92182, USA
4Department of Geology, Baylor University, One Bear Place #97354, Waco, Texas 76798-7354, USA
5Institut de Radioprotection et de Sûreté Nucléaire, BP 17, 92262 Fontenay-aux-Roses, France


Estimating the potential for the occurrence of large earthquakes on slow-slip-rate faults in continental interiors, away from plate boundaries, is possible only if the long-term geological record of past events is available. However, our knowledge of strong earthquakes appears to be incomplete for thrust faults flanking large actively growing mountain ranges, such as those surrounding Tibet and the Andes Mountains. We present a paleoseismic study of a prominent fault scarp at the west flank of the Andes in Santiago, Chile. The evidence demonstrates recurrent faulting with displacement of ∼5 m in each event. With two large earthquake ruptures within the past 17–19 k.y., and the last event occurring ∼8 k.y. ago, the fault appears to be ripe for another large earthquake (moment magnitude, Mw 7.5). These results emphasize the potential danger of intraplate continental faults, particularly those associated with youthful mountain fronts. 

GeologyG. Vargas, Y. Klinger, T.K. Rockwell, S.L. Forman, S. Rebolledo, S. Baize, R. Lacassin, and R. Armijo, Probing large intraplate earthquakes at the west flank of the Andes, Geology, 17 October 2014, doi:10.1130/G35741.1