Closing the gap in a double seismic zone: Properties and origin of intraslab seismicity in Northern Chile
Abstract
Double seismic zones (DSZs) of intermediate-depth intraslab seismicity are observed in many subduction zones, and have been related to isothermal dehydration reactions in the downgoing crust and mantle lithosphere. Intermediate-depth seismicity in Northern Chile, however, exhibits a seismicity pattern that substantially deviates from a classical DSZ. Whereas two parallel seismicity planes are present in the updip part of the slab, these abruptly change into a 25-30 km thick, homogeneously seismically active volume at a depth of 80-100 km. Seismicity rate and moment release dramatically increase in this depth interval. Analyzing 11 years of high-resolution hypocenter locations (>130k events), >600 moment tensors, statistical properties of different seismicity populations as well as receiver functions and seismic velocities from double-difference tomography, and combining these pieces of evidence with petrophysical arguments, we derive a possible model that explains the distinct pattern of seismicity in Northern Chile. The highly active seismicity cluster is situated where heat input from the mantle wedge commences (as seen in seismic attenuation images), and where downdip extension in the slab due to slab pull is at its maximum (as seen from moment tensors and slab geometry). These conditions could set the stage for a sudden burst of kinetically delayed metamorphic and/or dehydration reactions, which feature negative volume change that further increases slab pull, which leads to a positive feedback loop. Analysis of seismicity distributions from other subduction zones shows that such a process may be superimposed onto the classical DSZ processes globally, but in most cases it is much more subtle than in Northern Chile.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T12C..07S
- Keywords:
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- 8104 Continental margins: convergent;
- TECTONOPHYSICSDE: 8170 Subduction zone processes;
- TECTONOPHYSICS