title: A recent deep earthquake doublet in light of long-term evolution of Nazca subduction.
abstract: Earthquake faulting at ~600 km depth remains puzzling. Here we present a new kinematic interpretation of two Mw7.6 earthquakes of November 24, 2015. In contrast to teleseismic analysis of this doublet, we use regional seismic data providing robust two-point source models, further validated by regional back-projection and rupture-stop analysis. The doublet represents segmented rupture of a ∼30-year gap in a narrow, deep fault zone, fully consistent with the stress field derived from neighbouring 1976-2015 earthquakes. Seismic observations are interpreted using a geodynamic model of regional subduction, incorporating realistic rheology and major phase transitions, yielding a model slab that is nearly vertical in the deep-earthquake zone but stagnant below 660 km, consistent with tomographic imaging. Geodynamically modelled stresses match the seismically inferred stress field, where the steeply down-dip orientation of compressive stress axes at ∼600 km arises from combined viscous and buoyant forces resisting slab penetration into the lower mantle and deformation associated with slab buckling and stagnation. Observed fault-rupture geometry, demonstrated likelihood of seismic triggering, and high model temperatures in young subducted lithosphere, together favour nanometric crystallisation (and associated grain-boundary sliding) attending high-pressure dehydration as a likely seismogenic mechanism, unless a segment of much older lithosphere is present at depth.
authors.affiliation: Charles University, Prague, Czech Republic.
authors.forename: J
authors.initials: J
authors.lastname: Zahradník
authors.affiliation: Charles University, Prague, Czech Republic.
authors.forename: H
authors.initials: H
authors.lastname: Čížková
authors.affiliation: Northwestern University, USA.
authors.forename: C R
authors.initials: CR
authors.lastname: Bina
authors.affiliation: University of Patras, Greece.
authors.forename: E
authors.initials: E
authors.lastname: Sokos
authors.affiliation: Charles University, Prague, Czech Republic.
authors.forename: J
authors.initials: J
authors.lastname: Janský
authors.affiliation: Geophysical Institute of Peru, Lima, Peru.
authors.forename: H
authors.initials: H
authors.lastname: Tavera
authors.affiliation: Seismological Observatory, University of Brasilia, Brazil.
authors.forename: J
authors.initials: J
authors.lastname: Carvalho