Imaging the crust and uppermost mantle structure of Portugal (West Iberia) with seismic ambient noise

Abstract

Summary We present a new high-resolution three-dimensional (3D) shear wave velocity (Vs) model of the crust and uppermost mantle beneath Portugal, inferred from ambient seismic noise tomography. We use broadband seismic data from a dense temporary deployment covering the entire Portuguese mainland between 2010 and 2012 in the scope of the WILAS project. Vertical component data are processed using phase correlation and phase weighted stack to obtain Empirical Green functions (EGF) for 3900 station pairs. Further, we use a random sampling and subset stacking strategy to measure robust Rayleigh wave group velocities in the period range 7–30 s and associated uncertainties. The tomographic inversion is performed in 2 steps: First, we determine group velocity lateral variations for each period. Next, we invert them at each grid point using a new trans-dimensional inversion scheme to obtain the 3D shear wave velocity model. The final 3D model extends from the upper crust (5 km) down to the uppermost mantle (60 km) and has a lateral resolution of ∼50 km. In the upper and middle crust, the Vs anomaly pattern matches the tectonic units of the variscan massif and alpine basins. The transition between the Lusitanian Basin and the Ossa Morena Zone is marked by a contrast between moderate and high velocity anomalies, in addition to two arched earthquake lineations. Some faults, namely the Manteigas-Vilariça-Bragança fault and the Porto-Tomar-Ferreira do Alentejo fault, have a clear signature from the upper crust down to the uppermost mantle (60 km). Our 3D shear wave velocity model offers new insights into the continuation of the main tectonic units at depth and contributes to better understanding the seismicity of Portugal.

Crustal and uppermost mantle structure of Cape Verde from ambient noise tomography

“…To obtain a 3D model of S-wave velocity we followed a commonly applied surface wave tomography two-step approach. In the first step, we computed maps with the lateral variation of group-velocity, as a function of period, using the Fast Marching Surface Tomography (FMST) method of Rawlinson and Sambridge (2005); in the second step, we inverted the group-velocity maps by using a transdimensional inversion technique to obtain the local S-wave velocity at each grid-point as a function of depth (Haned et al 2016;Silveira et al, 2022).…”

“…Next, the group-velocity maps were inverted to obtain the tomographic S-wave velocity model as described in Haned et al (2016) and Silveira et al (2022). The inversion performed here is identical to the one applied in Silveira et al (2022).…”

“…Next, the group-velocity maps were inverted to obtain the tomographic S-wave velocity model as described in Haned et al (2016) and Silveira et al (2022). The inversion performed here is identical to the one applied in Silveira et al (2022). For this study a water layer was included on the a priori model and the group velocity measurements were only considered below 0.1 Hz.…”

Variscan Inheritance Induces Alpine Upper Crustal Delamination in East Spanish‐Portuguese Central System

“…Since the main Variscan trend is NW–SE, seismic lines were run NE‐SW, that is, parallel to the SPCS, and therefore, not suitable for determining its deep structure. This tendency changed in recent times (Andrés et al., 2019, 2020; Silveira et al., 2022). Accordingly, previous crustal models, deduced from indirect methods, need to be revisited.…”

“…2020; Silveira et al, 2022). Accordingly, previous crustal models, deduced from indirect methods, need to be revisited.…”