Regional Crustal Imaging by Multi-Mode Inversion of Surface Wave Dispersion Curves

Session: Waveform Cross-Correlation-Based Methods in Observational Seismology [Poster]
Type: Poster
Date: 4/30/2020
Time: 08:00 AM
Room: Ballroom
Description: 

Seismic noise correlation functions are widely used to extract surface wave dispersion information. Most tomographic applications consider that the resulting dispersion curves are mainly composed of fundamental-mode surface waves, and disregard the contribution of higher modes. However, several studies have shown that higher modes can be predominant over certain frequency ranges, depending on the local shear-wave velocity structure. Furthermore, higher mode surface waves have been shown to be sensitive to structures where the velocity decreases with depth.

In this work, we present an inversion scheme aimed at exploiting the additional information provided by the higher modes. Phase wave velocities are measured directly from the cross-correlation spectra, since this method does not depend on the far-field approximation and allows us to collect accurate measurements for closely-spaced stations. A standard tomographic algorithm is used to produce a set of phase velocity maps, which are then used in a non-linear inversion to find 1D shear-wave velocity structure at regularly-spaced locations. In the non-linear inversion, the forward modeling accounts for the presence of higher modes by combining the dispersion curves and medium response functions of the fundamental and higher modes into a single, apparent dispersion curve. Finally, a 3D model is built by linear interpolation of the 1D models.

We apply the described approach to data acquired by the SISCAN and MISTERIOS seismic networks, deployed between 2014 and 2018 in the Basque-Cantabrian Zone (N Spain). The crustal structure in this region shows a high complexity as a result of an intense process of crustal stretching in the Mesozoic and a later contractional deformation during the Alpine orogenic event that gave rise to the Pyrenean-Cantabrian mountain belt. Previous works point to the presence of an indentation of the European margin lower crust into the Iberian crust, creating velocity inversions with depth. Our results support these interpretations but provide a new, detailed velocity model for the entire area.

Presenting Author: Marco Pilz

Authors