The Crustal Stress Field Inferred From Focal Mechanisms In Northern Chile

We study the spatial variability of the crustal stress in northern Chile. A margin-parallel compressive crustal stress regime is inferred along the coastal region between 19 degrees and 23.5 degrees S, similar to stress observations in Cascadia and Japan. The Andean Precordillera shows a distinct stress field associated with a strike-slip faulting regime around 21 degrees S. These results are constrained by over a decade of observations, for which earthquake catalogs report thousands of events in the continental crust. We present focal mechanisms for 817 of these crustal earthquakes, including mechanism qualities. The best mechanisms were grouped and inverted to infer the stress-field variability. We interpret the margin-parallel compression to be caused by the concave shape of the margin and the locking of the plate interface. The inferred strike-slip regime in the Andes agrees with previous studies and has been proposed to be mostly caused by local stresses imposed by a thicker crust.