Abstract
The crustal seismogenic thickness (CST) has direct implications on the
magnitude and occurrence of crustal earthquakes, and therefore, on the
seismic hazard of high-populated regions. Amongst other factors, the
seismogenesis of rocks is affected by in-situ conditions (temperature
and state of stress) and by their heterogeneous composition. Diverse
laboratory experiments have explored the frictional behavior of the most
common materials forming the crust and upper most mantle, which are
limited to the scale of the investigated sample. However, a workflow to
up-scale and validate these experiments to natural geological conditions
of crustal and upper mantle rocks is lacking. We used NW South America
as a case-study to explore the spatial variation of the CST and the
potential temperatures at which crustal earthquakes occur, computing the
3D steady-state thermal field taking into account lithology-constrained
thermal parameters. Modelled hypocentral temperatures show a general
agreement with the seismogenic windows of rocks and mineral assemblies
expected in the continental crust. A few outliers in the hypocentral
temperatures showcase nucleation conditions consistent with the
seismogenic window of olivine-rich rocks, and are intepreted in terms of
uncertainties in the Moho depths and/or in the earthquake hypocenters,
or due to the presence of ultramafic rocks within the allochthonous
crustal terranes accreted to this complex margin. Our results suggest
that the two largest earthquakes recorded in the region (Murindo
sequence, in 1992) nucleated at the lower boundary of the seismogenic
crust, highlighting the importance of considering this transition into
account when characterizing seismogenic sources for hazard assessments.