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Seismic Attenuation Imaging in the Central Andes Using Local and Teleseismic Earthquake Spectra: Insights Into Fluid Migration in the South Amerian Lithosphere Above the Pampean Flat Slab

Description: 

Hypocenter locations and wavespeed models derived from prior analysis of data recorded by the SIEMBRA and ESP networks located above the Pampean Flat Slab in the Central Andes (Maharaj et al., 2022) revealed evidence for potential fluid migration from the subducted Nazca plate through the upper mantle and lower crust of the South American plate. Because fluids are likely to promote anelasticity, in this study we analyze seismograms from the same networks to examine the potential for attenuation (Q_p and Q_s) imaging to provide additional constraints on this type of devolitization in a flat slab environment.

The methodology we employ combines a local event approach based on that described in Bennington et al (2008) with a teleseismic procedure that follows from an algorithm discussed in Byrnes and Bezada (2020). For local events, earthquake spectra are used to both sequentially and simultaneously solve for source spectral plateau and corner frequency, local receiver response, and the attenuation parameter t*, along with a frequency independent term and accounts for effects such as radiation pattern, the free surface, and geometric spreading. For teleseismic events, we follow Byrnes and Bezada (2020) and model waveforms in the time domain to generate estimates of relative t*, but do so by solving for variations from averaged spectra that form a minimum phase wavelet. We also include receiver site responses as part of the teleseismic procedure. As is the case with arrival time tomography, the joint inversion of local and teleseismic estimates of t* reduces the coupling between the crust and mantle.

Out of the nearly 40,000 events cataloged by Maharaj et al., (2022) from the SIEMBRA and ESP networks, we were able to recover usable spectra from about 500 events dispersed throughout the crust of South America and the subducted Nazca plate. A review of the available teleseismic records shows that a similar number (about 370) are suitable for this joint analysis.

Session: Subduction Zone Structure From Trench to Arc [Poster]

Type: Poster

Date: 4/19/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Andrea P. Navarro-Aranguiz

Student Presenter: Yes

Invited Presentation: 

Authors