07 May 2021

07 May 2021

Review status: this preprint is currently under review for the journal SE.

Imaging structure and geometry of slabs in the greater Alpine area – A P-wave traveltime tomography using AlpArray Seismic Network data

Marcel Paffrath1, Wolfgang Friederich1, and the AlpArray and AlpArray-Swath D working group Marcel Paffrath et al.
  • 1Ruhr-Universität Bochum
  • For further information regarding the team, please visit the link which appears at the end of the paper.

Abstract. We perform a teleseismic P-wave traveltime tomography to examine the geometry and structure of subducted lithosphere in the upper mantle beneath the Alpine orogen. The tomography is based on waveforms recorded at over 600 temporary and permanent broadband stations of the dense AlpArray Seismic Network deployed by 24 different European institutions in the greater Alpine region, reaching from the Massif Central to the Pannonian Basin and from the Po plain to the river Main. Teleseismic traveltimes and traveltime residuals of direct teleseismic P-waves from 331 teleseismic events of magnitude 5.5 and higher recorded between 2015 and 2019 by the AlpArray Seismic Network are extracted from the recorded waveforms using a combination of automatic picking, beamforming and cross-correlation. The resulting database contains over 162.000 highly accurate absolute P-wave traveltimes and traveltime residuals. For tomographic inversion, we define a model domain encompassing the entire Alpine region down to a depth of 600 km. Outside this domain, a laterally homogeneous standard earth model is assumed. Predictions of traveltimes are computed in a hybrid way applying a fast Tau-P method outside the model domain and continuing the wavefronts into the model domain using a fast marching method. For teleseismic inversion, we iteratively invert demeaned traveltime residuals for P-wave velocities in the model domain using a regular discretization with an average lateral spacing of about 25 km and a vertical spacing of 15 km. The inversion is regularized towards an initial model constructed from an a priori model of the crust and uppermost mantle and a standard earth model beneath.

The resulting model provides a detailed image of slab configuration beneath the Alpine and Apenninic orogens. Major features are an overturned Adriatic slab beneath the Apennines reaching down to 400 km depth still attached in its northern part to the crust but exhibiting detachment towards the southeast. A fast anomaly beneath the western Alps indicates a short western Alpine slab that ends at about 100 km depth close to the Penninic front. Further to the east and following the arcuate shape of the western Periadriatic Fault System, a deep-reaching coherent fast anomaly with complex interior stucture generally dipping to the SE down to about 400 km suggests a slab of European origin extending eastward to the Giudicarie fault. This slab is detached from overlying lithosphere at its eastern end below a depth of about 100 km. Further to the east, well-separated from the slab beneath the western and central Alps, another deep-reaching, nearly vertically dipping high-velocity anomaly suggests the existence of a slab beneath the Eastern Alps of presumably European origin which is completely detached from the orogenic root. Our image of this slab does not require a polarity switch because of its nearly vertical dip and full detachment from the overlying lithosphere. Fast anomalies beneath the Dinarides are weak and concentrated to the northernmost part and shallow depths. Low-velocity regions surrounding the fast anomalies beneath the Alps to the west and northwest follow the same dipping trend as the overlying fast ones, indicating a kinematically coherent subducting tectosphere in this region. In contrast, low-velocity anomalies to the east suggest asthenospheric upwelling presumably driven by retreat of the Carpathian slab and extrusion of eastern Alpine lithosphere towards the east while low velocities to the south are presumably evidence of asthenospheric upwelling and mantle hydration due to the backarc position behind the European slab.

Marcel Paffrath et al.

Status: open (until 20 Jun 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on se-2021-58', Anonymous Referee #1, 08 Jun 2021 reply
    • CC1: 'Reply on RC1', Marcel Paffrath, 10 Jun 2021 reply
  • RC2: 'Comment on se-2021-58', Anonymous Referee #2, 13 Jun 2021 reply

Marcel Paffrath et al.

Marcel Paffrath et al.


Total article views: 385 (including HTML, PDF, and XML)
HTML PDF XML Total BibTeX EndNote
303 74 8 385 3 3
  • HTML: 303
  • PDF: 74
  • XML: 8
  • Total: 385
  • BibTeX: 3
  • EndNote: 3
Views and downloads (calculated since 07 May 2021)
Cumulative views and downloads (calculated since 07 May 2021)

Viewed (geographical distribution)

Total article views: 371 (including HTML, PDF, and XML) Thereof 371 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
Latest update: 15 Jun 2021
Short summary
The Alpine mountain belt was formed by the collision of the Eurasian and African plates in the geological past, during which parts of the colliding plates sank into the Earth's mantle. Using seismological data from distant earthquakes recorded by the AlpArray Seismic Network, we have derived an image of the current location of these subducted parts in the Earth's mantle. Their quantity and spatial distribution is key information needed to understand how the Alpine orogen was formed.