← Back to Gallery

Session: Imaging Subduction Zones

Type: Oral

Date: 4/25/2019

Time: 04:30 PM

Room: Cascade II

Investigating Anomalous Crustal Thickness of the Subducting Iquique Ridge

The Iquique Ridge (IR) is a broad bathymetric high on the subducting Nazca plate that serves as a potential source of crustal heterogeneity influencing seismogenesis along the Peru-Chile Trench. Lithospheric buoyancy and reduced seismic velocities of the IR swell are thought to be produced by over thickened crust or anomalously low density mantle, either of which could affect interplate coupling where the ridge is subducted but has not yet been explored with comprehensive subsurface imaging. The nearby, prominent Nazca and Juan-Fernández Ridges, show thick crust with low lithospheric velocities explained by different sources, including underplated magma and hydrated upper mantle respectively. The subduction of both features has been associated with changes in seismicity and slab geometry. Here, we present a P-wave velocity model of the Nazca plate and incoming IR neighboring the 2014 Mw 8.1 Iquique earthquake rupture zone. This model is 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. Arrivals from eight ocean bottom seismometers (OBS) cover an uninterrupted ~220 km profile, with dense ray coverage of both crustal and upper mantle phases at up to ~70 km offset. Our resulting model shows at least a kilometer of crustal thickening relative to typical Nazca plate oceanic crust, with a maximum overall thickness of ~10 km beneath the IR and prominent outer rise. We also resolve shallow crustal velocities approaching the trench beneath the faulted landward slope. To further investigate the source of these velocity variations, we use coincident multi-channel seismic (MCS) shots recorded on a 12.5 km streamer, enhancing the imaging resolution of the shallow structure. Information about velocity and faulting structure from the combined MCS and wide-angle data should help characterize inputs to the subduction system and constrain controls on seismogenesis within the 2014 Iquique earthquake rupture segment.

Presenting Author: Emma K. Myers

Additional Authors