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Crustal and Uppermost Mantle Structure North of the Gloria Fault Inferred From OBS-Recorded Surface Waves

Description: 

The DOCTAR array encompassed 12 broadband Ocean Bottom Seismometers (OBSs) that operated on the seafloor for ~1 year north of the Gloria fault, at the African-Eurasia plate boundary in the north Atlantic. The array had short inter-station distances of 10-20 km and aimed mainly at the application of array techniques to teleseismic data and to study the seismicity of the Gloria fault. However, the data recorded by this array can also be used to study the shallow Earth structure. Here, we analysed the dispersion of surface waves from both ambient noise (short periods, <14 s) and from teleseismic earthquakes (longer periods, > 14 s). Based on the inferred surface wave dispersion observations, we then computed first a 1D vertically layered model for the entire region, and subsequently a 3D laterally varying model of S-wave velocities.

The 1D Vs model shows a top layer of sediments with a low Vs of 1.05 km/s; this low velocity is in agreement with previous observations for the region and likely results from the presence of water in the sediments. Below the sediments, Vs increases in the crust from 3.3 to 4.5 kms. We find an unusual high velocity of 4.9 km/s in a 20 km thick layer at depths between 16 km and 36 km. We suggest that this unusual fast velocity indicates the presence of harzburgite, which is formed as a residue of enhanced mantle melting. We hypothesize that such enhanced melting might have resulted from the proximity between the slow-spreading mid-Atlantic ridge and the Azores mantle plume. A low-velocity zone is then found deeper, at 70 km depth, which we associate with the LAB. The 3D models shows that the shallow crustal is mostly horizontally layered below the DOCTAR array. However, it also shows some small-amplitude oscillations of the crustal structure.

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020), LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020).

Session: Seismology in the Oceans: Pacific Hemisphere and Beyond - I

Type: Oral

Date: 5/2/2024

Presentation Time: 09:00 AM (local time)

Presenting Author: Susana

Student Presenter: No

Invited Presentation: 

Authors