Lithosphere strain rate and stress field orientations near the Alpine arc in Switzerland

N. Houlié,M. Rothacher,J. Woessner,D. Giardini

doi:10.1038/s41598-018-20253-z

N. Houlié, M. Rothacher + Show 2 more

Open Access

https://doi.org/10.1038/s41598-018-20253-z

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Abstract

In this study we test whether principal components of the strain rate and stress tensors align within Switzerland. We find that 1) Helvetic Nappes line (HNL) is the relevant tectonic boundary to define different domains of crustal stress/surface strain rates orientations and 2) orientations of T- axes (of moment tensor solutions) and long-term asthenosphere cumulative finite strain (from SKS shear wave splitting) are consistent at the scale of the Alpine arc in Switzerland. At a more local scale, we find that seismic activity and surface deformation are in agreement but in three regions (Basel, Swiss Jura and Ticino); possibly because of the low levels of deformation and/or seismicity. In the Basel area, deep seismicity exists while surface deformation is absent. In the Ticino and the Swiss Jura, where seismic activity is close to absent, surface deformation is detected at a level of ~2 10−8/yr (~6.3 10−16/s).

Highlights

In order to understand the tectonics acting in the central Alps in Switzerland, we 1) map the strain rate field measured using GPS during the last 2 decades, 2) investigate whether the Helvetic Nappes (HN) can be associated with changes of orientations of the principal components of the strain tensors and 3) at last, by comparing those with orientations of P-/T- axes, and fast axes of shear waves splittings, we discuss whether the orientations of principal components of the stress tensors constrained by moderate magnitude seismic events (Ml > 2.0) are compatible with mantle deformation observed in the region[63]
Shear and extension rates dominate compression rates (Fig. 4a–d). This observation fits well with a crustal seismicity mostly composed of strike-slip events and with previous studies focusing on long-term deformation of central and western Alps[75,76]
The HN cannot be seen as a limit across which strain rates vary

Summary

Introduction

In order to understand the tectonics acting in the central Alps in Switzerland, we 1) map the strain rate field measured using GPS during the last 2 decades, 2) investigate whether the HN can be associated with changes of orientations of the principal components of the strain tensors and 3) at last, by comparing those with orientations of P-/T- axes, and fast axes of shear waves splittings, we discuss whether the orientations of principal components of the stress tensors constrained by moderate magnitude seismic events (Ml > 2.0) are compatible with mantle deformation observed in the region[63]. The alignment of maximum shortening directions with SH and P- orientations would imply that the lithosphere strain rates and crustal stress fields are consistent.

Results

Conclusion