INTEGRATE: GFZ

Integrated 3D structural, thermal, gravity and rheological modeling of the Alps and their forelands – INTEGRATE

a) Thickness of the crust across the modelled area overlain with vertical displacement rates (Sternai et al., 2019). b) Average density of the crust across the modelled area overlain with geodetically derived horizontal surface strain distribution (Sánchez et al., 2018) and seismic events of a moment magnitude larger than 6 (Fäh et al., 2011; Stucchi et al., 2012; Grünthal et al., 2013). From Spooner et al. (2019) *(GFZ/Sektion 4.5)*

A North to South cross section through the structural model, showing the isotherms for 275°C, 450°C and 600°C and seismicity from the International Seismological Centre (International Seismological centre, 2020) that lay within 20 km distance of the section. From Spooner et al. (2020) *(GFZ/Sektion 4.5)*

As a part of the DFG priority program 2017 4D Mountain Building (4D-MB) this project aims to obtain a better understanding of the crust and the uppermost mantle beneath the Alpine orogen and its forelands and to better explain the distribution of deformation and seismicity throughout the region. Therefore, we integrate geoscientific observations with process modelling to predict the 3D lithosphere configuration in the area.

Dr. Cameron C. Spooner developped a first lithosphere-scale 3D model of the Alps and their forlands in the frame of his PhD thesis. This model resolves two sedimentary units, a heterogenuous crustal configuration and the lithsopheric mantle.

Geoscientific observations publicly available so far on properties of the sediments and the crystalline crust (geometry, seismic velocities, and densities) with seismologically derived heterogeneities in the sub-crustal mantle are combined into a consistent data-based 3D structural model that resolves the first-order contrasts in physical properties of the units composing the orogen and the forelands. The derived structural model is then constrained by 3D gravity modelling, with the resulting density model validated by modern satellite fields. Such a combined model provides a reference for other types of data processing and is a crucial step forward in deciphering where deep-seated mass changes occur within the orogen. This 3D model (Spooner et al., 2019a) has then been compared to a historical dataset of high magnitude earthquakes (> M6) as a first step of relating crustal structure to seismicity localisation (Spooner et al., 2019b).

To further interrogate the causes of seismicity localisation the steady-state conductive lithospheric temperature field was calculated based on petrological assumptions on the composition of the crust and mantle derived from the density model and seismic velocities. The model is validated with a dataset of wellbore temperatures from across the region. A strong link between regional temperatures and seismicity was identified (Spooner et al., 2020) and work utilising the 3D density and thermal models to calculate 3D variations of the long term lithospheric strength is ongoing, in order to discuss how it impacts the location of seismicity.

The project contributes to two major themes of the priority program 4D-MB: For “Theme 3: deformation of the crust and mantle during mountain building”, the project provides the configuration of the different crustal units and of the lithospheric mantle and the isostatic and rheological conditions of the orogen-foreland system at the present day.

For “Theme 4: motion patterns and seismicity”, the outcomes of the project will support identifying spatial patterns of faulting and seismicity in relation to the rheological configuration, the variations of flexural rigidity across the system and the distribution of contrasts in physical properties in the crust as well as the lithospheric mantle. In response to its regional character, the project links with the different activity fields of 4D-MB and a continuous exchange of observations and modelling results with many working groups in 4D-MB can support data processing and interpretation.

Partners: Hajo Götze, Jörg Ebbing, Josef Sebara and the Alp-Array Gravity Research Group

Publications:

Spooner, C., Scheck-Wenderoth, M., Cacace, M., Anikiev, D. (2022): How Alpine seismicity relates to lithospheric strength? - International Journal of Earth Sciences, 111, 1201-1221.
https://doi.org/10.1007/s00531-022-02174-5

Degen, D., Spooner, C., Scheck-Wenderoth, M., Cacace, M. (2021): How biased are our models? – a case study of the alpine region. - Geoscientific Model Development, 14, 11, 7133-7153.
https://doi.org/10.5194/gmd-14-7133-2021

Spooner, C., Scheck-Wenderoth, M., Cacace, M., Anikiev, D. (2020): 3D-ALPS-TR: A 3D thermal and rheological model of the Alpine lithosphere.
https://doi.org/10.5880/GFZ.4.5.2020.007

Spooner, C., Scheck-Wenderoth, M., Götze, H., Ebbing, J., Hetényi, G. 3D Gravity Constrained Model of Density Distribution Across the Alpine Lithosphere. GFZ Data Services, https://doi.org/10.5880/GFZ.4.5.2019.004, 2019a.

Spooner, C., Scheck-Wenderoth, M., Götze, H., Ebbing, J. and Hetényi, G. Density distribution across the Alpine lithosphere constrained by 3-D gravity modelling and relation to seismicity and deformation. Solid Earth, 10(6), pp.2073-2088, https://doi.org/10.5194/se-10-2073-2019, 2019b.

Spooner, C., Scheck-Wenderoth, M., Cacace, M., Götze, H. and Luijendijk, E. The 3D thermal field across the Alpine orogen and its forelands and the relation to seismicity. Global and Planetary Change, 193, p.103288, https://doi.org/10.1016/j.gloplacha.2020.103288, 2020.

See also our project on the North Alpine Foreland

overview