Fault reactivation linked to rapid ice-mass removal from the Southern Patagonian Icefield (48–52°S)

Abstract

The Southern Patagonian Icefield (SPI) lies above an area of slow convergence between Antarctic and South-America plates, where limited seismicity is recorded by global and regional seismic networks. To understand the seismic behavior of this zone, we analyze two years of continuous broad-band data recorded by 27 seis­mometers, deployed around the SPI. Substantial ice loss coupled with the unusually low viscosity of the un­derlying mantle is causing a rapid uplift. Our findings indicate that most of the seismicity occurs in the upper crust, likely associated with the (re)activation of regional compressive structures. However, earthquakes immediately beneath the SPI generally are shallower and show normal or strike-slip faulting. We suggest that this activity is promoted as a response to the crustal relaxation after rapid ice removal of SPI. The almost complete absence of interplate and intraslab events is consistent with a locked megathrust fault interface, highlighting the similarity of this region with the Cascadia subduction zone.