Universidad de los Andes, Bogotá, Colombia
The physical mechanism of intermediate-depth earthquakes is still under debate. In contrast to conditions in the crust and shallow lithosphere, at temperatures and pressures corresponding to depths >50 km one would expect rocks to yield by creep or flow and not by brittle failure, so there has to be a physical mechanism that allows for brittle or brittle-like failure for intermediate-depth earthquakes. Two such mechanisms have been proposed: dehydration embrittlement and thermal shear runaway. Earthquake nests represent a region with high earthquake concentration that is isolated from nearby activity. I will discuss general observations on the three famous intermediate-depth earthquake nests – Vrancea, Hindu-Kush and Bucaramanga. The emphasis will be on the Bucaramanga nest (Colombia) and how high-resolution seismological observations (tectonic setting, precise earthquake locations, focal mechanisms, stress drops, etc.) may provide key constraints on the mechanism responsible. Given the nature and characteristics of this nest, it can be thought as natural laboratory for understanding the physics of intermediate-depth earthquakes.