Crustal Structure of the Incoming Iquique Ridge Offshore Northern Chile

The Peru-Chile subduction zone hosts M > 8 earthquakes as well as multiple ridges on the downgoing Nazca plate, making this region well suited for investigating the formation, evolution, and potential impacts of subducting features on seismogenesis. To evaluate the physical properties and structural variability of the Iquique Ridge offshore northern Chile, we present a P wave velocity model of the Nazca plate and Iquique Ridge outboard of the 2014 M 8.1 Iquique earthquake sequence. 2D tomographic inversions of P wave traveltime data from the 2016 PICTURES (Pisagua/Iquique Crustal Tomography to Understand the Region of the Earthquake Source) controlled-source experiment indicate that the Iquique Ridge is characterized by significant crustal thickening relative to typical Nazca plate oceanic crust, with a maximum thickness of similar to 13 km beneath the most prominent portion of the Iquique Ridge and outer rise. Reduced upper crustal seismic velocities extend from the ridge eastward to the trench, which may indicate increased fracturing and/or hydration during plate bending. Corresponding multi-channel seismic reflection data show along-profile structural variation as well, including an intermittent Moho reflector near the onset of crustal thickening and faulting along the landward slope. The structural heterogeneity entering the Peru-Chile Trench has potential implications for slip behavior at depth assuming that the anomalous crustal structure continues beneath the forearc. We suggest that the increased buoyant normal force associated with discrete subducted Iquique Ridge seamounts similar to the zone of thick crust imaged here could lead to localized increased interplate coupling, while entrained sediment and fractured/altered crust could facilitate aseismic slip.

Automated summary

This study investigates the physical properties and structural variability of the Iquique Ridge offshore northern Chile, and finds that the ridge has a thickened crust and reduced upper crustal seismic velocities, which may have potential implications for the slip behavior at depth.