A 2D Tomographic P-Wave Velocity Model for the Incoming Nazca Plate Adjacent to the 2014 Iquique Earthquake
Abstract
The 2014 Iquique Mw 8.1 earthquake unexpectedly ruptured only the northern portion of the Peru-Chile seismic gap. The limits of southward propagation and local gravity anomalies suggest a geologic control on slip behavior within the subduction zone. The Iquique Ridge (IR), a broad, bathymetric high on the incoming Nazca plate that roughly spans the entire seismic gap, serves as a potential source of crustal heterogeneity that could influence seismogenesis at depth. Lithospheric buoyancy and previously observed reduced seismic velocities of the IR swell are thought to be produced by isostatically compensated, overthickened crust or anomalously low density mantle due to heating or serpentinization, either of which could influence subsequent interplate coupling. Here, we present a new model of the seismic P-wave velocity structure of the Nazca plate adjacent to the Iquique rupture zone determined from 2D tomographic inversions of travel time data from the 2016 PICTURES (Pisagua/Iquique Crustal Tomography to Understand the Region of the Earthquake Source) experiment. The combination of multichannel seismic (MCS) and ocean bottom seismometer (OBS) data provides an uninterrupted 170 km 2D profile, with dense ray coverage of both Pg and PmP arrivals on six OBS spanning the outer rise to the trench along the IR. Using an initial oceanic crust model determined from shipboard MCS processing, our inversions resolve velocity perturbations that emphasize key structural features of this portion of the Nazca plate. The model provides new information on the limits of plate bending faults and hydration, explores the thickness of the oceanic crust and upper mantle structure of the IR, and highlights the shallow velocity structure of the material trapped within prominent seamounts as seen in preliminary MCS sections. We use our new velocity model along with the coincident MCS reflection profile to characterize properties of the incoming Nazca plate that influence inputs to the subduction system and control seismogenesis within the 2014 Iquique earthquake rupture segment.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T21F0273M
- Keywords:
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- 8104 Continental margins: convergent;
- TECTONOPHYSICSDE: 8170 Subduction zone processes;
- TECTONOPHYSICS