The MAUPASACQ experiment: Preliminary results of a noise-based Rayleigh wave analysis of the Mauleon Basin in western Pyrenees, France
Creators: name: Giannopoulos, Dimitrios
name: Lois, Athanasios
name: Leontarakis, Konstantinos
name: Polychronopoulou, Katerina
name: Martakis, Nikolaos
name: Calassou, Sylvain
name: Collin, Magali
name: Chevrot, Sebastien
name: Sylvander, Matthieu
name: Villaseñor, Antonio
name: Diaz, Jordi
name: Bitri, Adnand
Publisher: name: Zenodo
Year: 2019
Subjects: Ambient Seismic Noise
Ambient Noise Tomography
Pyrenees

description: In the framework of the MAUPASACQ project, a dense seismic network of 440 three-component stations was<br>
deployed throughout the Mauleon Basin, in the northern foothills of the Pyrenees, SW France. The network consisted<br>
of three different types of sensors, namely 190 SG-10 SERCEL geophone nodes, 197 5 Hz SEISMOTECH<br>
short-period sensors and 53 broadband sensors (Guralp CMG-40, Trillium Compact, Trillium 120), and operated<br>
continuously for 6 months, from April 1 until September 30, 2017.<br>
Numerous geological and geophysical observations provide evidence that the Mauleon Basin was created<br>
by the tectonic inversion of a precollisional rift system that was formed between the Iberian and European plates,<br>
involving processes of rift-related mantle exhumation. These observations, among others, characterize the area<br>
under investigation as an ideal locality to study and understand the structural and geodynamic evolution of the<br>
Pyrenean mountain range. The main scientific objective of the MAUPASACQ experiment is to provide new<br>
constraints on this topic, by applying different types of classical imaging techniques that incorporate a number<br>
of Passive Seismic methodologies (i.e. travel time tomography, ambient noise tomography, receiver functions, etc.).<br>
The scope of this work is to illustrate some preliminary observations deriving from the analysis of the ambient<br>
seismic noise field that was recorded in the Mauleon Basin. This was achieved by beamforming and by<br>
using the Rayleigh wave empirical Green’s functions that were estimated by seismic interferometry. Beamforming<br>
analysis provided valuable information about the spatial distribution and the directionality of the ambient noise<br>
sources. The main source region for the primary microseisms (12-20 s) is located to the northwest (N315o),<br>
being present over a larger backazimuth range across the northwest quadrant, while the secondary microseisms<br>
(5-10 s) seem to present two maxima, one in the west (N270o) and a second one in the north-northwest (N350o),<br>
ranging between west-southwest and north directions. Furthermore, 1-day long recordings between all available<br>
vertical components were cross correlated, stacked over the whole recording period, resulting in more than 90000<br>
reference noise cross-correlation stacks. A frequency-time analysis was applied to measure Rayleigh wave group<br>
velocity dispersion curves, which were used to invert for 2D velocity maps in the 1 to 10 s period range. The<br>
results reveal the presence of interesting and distinctive velocity structures, demonstrating a good agreement with<br>
the major geological features that were expected in the area.<br>
The preliminary observations of the current analysis highlight the sufficiency and the potential of the MAUPASACQ<br>
array to use ambient seismic noise recordings as a standalone, as well as a complementary tool towards<br>
the investigation of the shear velocity structure beneath the Mauleon Basin.