Constraints on Crustal Structure in the Vicinity of the Adriatic Indenter (European Alps) From Vp and Vp/Vs Local Earthquake Tomography. Issue 2 (17th February 2022)

• Record Type: Journal Article
• Authors: Jozi Najafabadi, Azam; Haberland, Christian; Le Breton, Eline; Handy, Mark R.; Verwater, Vincent F.; Heit, Benjamin; Weber, Michael
• Is Part Of: Journal of geophysical research. Volume 127:Issue 2(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-02-17
• Subjects: European Alps -- crustal structure -- subduction -- seismic tomography -- body waves; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2021JB023160
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: In this study, 3‐D models of P‐wave velocity ( Vp ) and P‐wave and S‐wave ratio ( Vp / Vs ) of the crust and upper mantle in the Eastern and eastern Southern Alps (northern Italy and southern Austria) were calculated using local earthquake tomography (LET). The data set includes high‐quality arrival times from well‐constrained hypocenters observed by the dense, temporary seismic networks of the AlpArray AASN and SWATH‐D. The resolution of the LET was checked by synthetic tests and analysis of the model resolution matrix. The small inter‐station spacing (average of ∼15 km within the SWATH‐D network) allowed us to image crustal structure at unprecedented resolution across a key part of the Alps. The derived P velocity model revealed a highly heterogeneous crustal structure in the target area. One of the main findings is that the lower crust is thickened, forming a bulge at 30–50 km depth just south of and beneath the Periadriatic Fault and the Tauern Window. This indicates that the lower crust decoupled both from its mantle substratum as well as from its upper crust. The Moho, taken to be the iso‐velocity contour of Vp = 7.25 km/s, agrees with the Moho depth from previous studies in the European and Adriatic forelands. It is shallower on the Adriatic side than on the European side. This is interpreted to indicate that the European Plate is subducted beneath the Adriatic Plate in the Eastern and eastern Southern Alps. Plain Language Summary: Energy released by earthquakes is converted to seismic waves that radiate through the Earth. Here, we study two types of waves (P and S) in the Eastern and eastern Southern Alps (northern Italy and southern Austria). The aim is to investigate the subsurface structure beneath the mountains. The P‐wave and S‐wave propagate at different velocities between the earthquakes and seismometers. Given the origin time and locations of earthquakes, seismometer coordinates, and wave arrival times, we can calculate the P‐wave velocity ( Vp ) and the P‐wave and S‐wave velocity ratio ( Vp / Vs ) of the subsurface volume. Therefore, our velocity model allows for imaging the crust at unprecedented resolution. Moreover, an important structure within the Earth, the boundary between the crust and mantle or the so‐called Moho, can be inferred by the study of the waves. Our results show that during collision and formation of the Eastern and eastern Southern Alps, the lower crust of the Adriatic Plate thickened due to decoupling from both the mantle and upper crust within the orogen. The Moho is shallower on the Adriatic side than on the European side. A possible interpretation is that the European Plate subducted under the Adriatic Plate in the Eastern and eastern Southern Alps. Key Points: Vp and Vp / Vs models of the crust and upper mantle were calculated in the Eastern and eastern Southern Alps using a high‐quality data set The simultaneous inversion of 3‐D velocity models and earthquake parameters were performed using the well‐established SIMUL2000 algorithm The structure of Alpine orogenic crust including the tip of the Adriatic Indenter is revealed with the Vp model