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Attenuation of the South American Lithosphere

Description: 

Using the amplitudes of regional phases (Pg, Pn, Lg, Sn), we have developed a comprehensive attenuation model of the lithosphere in South America. By using seismic data recorded by stations from multiple networks, we obtain excellent path coverage of the whole continent, including in the eastern portions that are relatively aseismic. We then use a multi-phase amplitude tomography to determine Qp and Qs in the crust and upper mantle over a broad frequency band (0.5-10 Hz). We observe many expected features, including lower Q (higher attenuation) in the active Andes orogenic belt and higher Q (lower attenuation) in the stable craton. Beyond this, however, we see less expected results, including significant variations along the Andes (such as a trend of high Q in the Peruvian and Pampean flat slab regions) and low upper mantle Q extending north from the Rio de la Plata craton along the Chaco and Pantanal basins, which is associated with thinner lithosphere than adjoining regions of the South American platform. Our preliminary results suggest regional variations within the Amazon craton: relatively lower average Q values in the Guyana shield compared with higher average Q in the Central Brazil shield (north and south of the Amazon river, respectively). This is also consistent with the average lithospheric thicknesses inferred from surface-wave tomography. As in other areas of the world, we find that attenuation is highly sensitive to the thermal structure, with warmer regions of more recent tectonic activity having lower Q than older and colder stable continental regions.

Session: Crustal Imaging of High Seismic Hazard Regions

Type: Oral

Date: 4/20/2023

Presentation Time: 11:00 AM (local time)

Presenting Author: Michael E. Pasyanos

Student Presenter: No

Invited Presentation: 

Authors