Seismic Attenuation Structure of Nazca Plate Subduction Zone in Southern Peru

Date: 4/25/2019

Time: 05:00 PM

Room: Cascade II

Significant subduction-zone complexity in southern Peru has been attributed to the subducting Nazca Ridge along the South American margin between 10°S and 20°S latitude. In this study, we provide the first attenuation models (Qp, Qs, and Qp/Qs structures) that represent complex Nazca Plate subduction system associated with the passage of Nazca Ridge. The subduction geometry of the Nazca Plate changes from nearly horizontal in NW to normal-dip in SE in southern Peru, and present location of Nazca Ridge coincides with the southern end of the flat slab segment (Hampel 2002).

We use data from three temporary seismic arrays (PeruSE, PULSE, and CAUGHT) and one permanent station to estimate seismic attenuation in terms of quality factors, Qp and Qs using P and S phases, respectively. We measure t*, which is integrated attenuation through the seismic raypath between the regional earthquakes and stations. The measured t* are inverted to construct 3-D Qp, Qs and Qp/Qs models. Our Qp and Qs models from the inversion recover features that can be closely associated with slab morphology and dynamics, as well as geological features in the upper plate. Our Q models show well-defined along-arc slab structure in high Q overall, and also show several notable differences between the flat slab region (above 15°S latitude) and normal-dip slab region. First, high-Q anomaly in the lower crust below the region including Lake Titicaca (below 16°S latitude) may correspond to Brazilian shield. Second, low Q near and above the subducting plate beneath the volcanic arc can be related to the slab dehydration. Third, relatively low Q features in the subducting plate in the region above 12°S latitude extend laterally about 200 km from the trench. This may be a feature related to delayed eclogitization process, which can explain the flat slab geometry, or the tear of the slab.

Presenting Author: Hyoihn Jang

Authors