SeismoTeCH

SeismoTeCH is a project of the Swiss Geophysical Commission (SGPK), funded by the Swiss Federal Office of Topography, swisstopo. In addition to the SED, further project partners are the University of Bern (Structural Geology Group of Prof. Marco Herwegh), swisstopo and the University of Fribourg (Structural Geology Group of Prof. Jon Mosar). SeismoTeCH is a follow-up of the previous “Seismotectonic Atlas of Switzerland” project, which was initiated in 1997 and led by Adrian Pfiffner (University of Bern) and Nicholas Deichmann (SED). The project aims to provide a new seismotectonic characterization of Switzerland by integrating various datasets from geology, geophysics (mainly seismology) and geodesy. The primary target of this project is to gain an improved understanding of the relationship between faults mapped at the Earth’s surface and present-day seismotectonic processes generating seismicity at depth. The SeismoTeCH project is subdivided into several work packages distributed among the project partners, leading to products such as a fault database for Switzerland.

The SED is involved in several work packages and contributes several new crustal models and earthquake catalogs resulting from state-of-the-art processing of seismological data. In the framework of this project, new 3D crustal P- and S-wave velocity models as well as seismic attenuation (Qp, Qs) models were computed. These models provide new insights into the crustal structure and petrophysical properties of the Central Alps and their northern foreland and allow for a refined interpretation of seismotectonic processes in Switzerland. Furthermore, the new 3D velocity models lead to improved hypocenter accuracy and improved take-off angles required for the computation of high-resolution focal mechanisms. In addition, the SED develops a consistently relocated earthquake catalog that combines absolute and relative hypocenter relocation methods. The final relocated hypocenter catalog is linked to an expanded and revised catalog of high-quality focal mechanism (more than 500 first-motion based mechanisms and more than 70 moment-tensor solutions). This “Seismotectonic Earthquake Catalog of Switzerland” (SECOS) forms the input data for a hypocenter-based 3D imaging of active faults, a new method developed by Sandro Truttmann in the framework of his PhD and the SeismoTeCH project at the University of Bern. The method was successfully applied at different scales to image the fine-scale structure of fault systems north of the Rhone Valley in southwest Switzerland. In combination with stress orientations derived from an updated inversion of focal mechanisms performed in the Master Thesis of Julia Heilig at the SED, the imaged fault orientations allow estimates of potential slip and dilation tendencies. Both parameters are important information for future seismic hazard assessments as well as geothermal exploration in the region.

Within the framework of the SeismoTeCH project, the SED also performed an in-depth seismotectonic analysis of an unusually shallow earthquake sequence in the Jura region (northwestern Switzerland). That study provides evidence for active shallow thrust-faulting in the Jura fold-and-thrust belt north of the Central Alps. In addition, several novel seismological methods were developed, tested and evaluated in the framework of the SeismoTeCH project to extend seismotectonic catalogs in future. That included, for instance, improved methods for the detection and location of micro-seismic earthquakes leading to enhance earthquake catalogs as well as novel methods to derive first-motion focal mechanism and moment tensors.