Analysis of seismic attenuation in the earthquake swarm area near Werdau

• Applicant: Professor Dr. Ulrich Wegler
• Subject Area: Geophysics
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 422215003

The earthquake swarm area of West-Bohemia/Vogtland was and is an object of intense geoscientific investigations. However, little attention has been paid so far to other small swarm earthquake areas in the surroundings of this main zone of activity as well as to the connection to the Leipzig-Regensburg fault zone. In the project submitted here, we propose to carry out a detailed analysis of the northernmost known earthquake swarm area near Werdau (western Saxony). The goal is to reveal differences and similarities as well as possible connections between both swarm earthquake areas, and finally, to improve our understanding of fluid induced seismicity in intracontinental settings. To image the fluids, which are believed to be the cause of the earthquake swarms, we will invert for the 3D seismic attenuation structure of the Werdau earthquake swarm area using local earthquakes. In a first step, we will apply radiative transfer theory to separate intrinsic absorption and scattering attenuation, to analyze the frequency dependence of attenuation, as well as to invert for detailed source spectra and for frequency dependent seismometer site response factors. To solve the elastic equation of radiative transfer we will apply, for the first time, an improved Monte-Carlo algorithm, which is able to separately invert for intrinsic and scattering attenuation in different depths. To do so, we will extend one of the leading existing algorithms to allow the computation of energy propagation in arbitrary depth dependent velocity and attenuation models. Such kind of algorithms will be useful beyond this particular project, to obtain reliable 1D attenuation models of the Earth's crust. In a second step, we will conduct a 3D attenuation tomography for P- and S-waves, to detect areas of increased fluid content. The combination of the two techniques of radiative transfer theory and attenuation tomography is another technical goal. The respective strengths of the two methods will be combined for the first time, to develop an optimized joint inversion strategy. Results will be compared with existing velocity models (vP and vP/vS ) and jointly interpreted. Such techniques to image fluid flow in the subsurface and its joint interpretation with fluid induced seismicity will play a major role also beyond this project. Especially, we refer to the social relevance with respect to the technical use of the subsurface and to anthropogenic fluid induced seismicity, e.g. in the context of geothermal power plants, carbon capture and sequestration, as well as hydraulic fracturing.

• DFG Programme: Research Grants