Crustal structure of the Dinarides: new insights from the receiver functions and ambient noise tomography 

Abstract

The Dinarides, located at the eastern edge of the Adriatic Sea, are the focus of ongoing geophysical research due to their complex tectonic characteristics and distinctive structural transition zones. Prior investigations have identified a two-layered crust with variable thickness, featuring a transitional zone between Dinaric and Pannonian crust. Recent studies have introduced the concept of a deep-seated Dinaric crustal root, marked by a discernible transition to shallower crust along the northern edge. This study includes two complementary research approaches to advance our understanding of the Dinarides' crustal structure: receiver function analysis and ambient noise tomography. The P receiver function method was applied to 123 seismic stations across the broader Dinaric area, involving 1234 teleseismic earthquakes recorded from 2016 to 2023. Results are presented through cross-sectional CCP stacking images, offering a comprehensive visualization of the converted Ps phase crucial for mapping significant crustal discontinuities. Additionally, seven years of continuous data, recorded from 2016 to the end of 2022 at 121 seismic stations, were utilized to calculate phase velocities of surface waves. Eikonal tomography was applied to both Rayleigh and Love waves, with local dispersion curves independently inverted for each surface wave type. The outcomes provide distributions of vertically and horizontally polarized shear-wave velocities, presented as maps at various depths and cross-sectional profiles, contributing to an in-depth exploration of shear-wave velocities across the entire region. The results reveal intriguing insights: a pronounced high-velocity anomaly beneath the Dinarides at shallower depths, a significant low-velocity anomaly in the mid-crust beneath the Dinarides for vertically polarized shear waves, and a distinct, localized thick low-velocity anomaly beneath the NW Dinarides for horizontally polarized shear waves. These findings collectively suggest complex variations in crustal thickness and seismic properties, particularly thickening crust toward the Southern and Inner Dinarides.