BRASS: Bright Reflector Characterisation in a Geodynamically Active Region with Recurring Swarm Seismicity

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The West Bohemia/Vogtland region (WB/V) is an area of significant tectonic interest due to its frequent microseismic swarms. Typically, the seismic activity in this region has a low energy release that it is not felt by the local population. However, over the last decade several larger magnitude events occurred in the Nový Kostel swarm region (Czech Republic). These events, along with a recent increase in microseismic activity in Vogtland (Germany) has motivated several new studies. To date, there have been many studies relating to the source of the microseismic swarms. Most of them proposed that fluids migrating from the deeper crust accumulate and trigger the earthquakes. However, the fluid pathways have not been determined and it is not known why the fluids accumulate in these locations. Therefore, this study aims to image the subsurface structures in the vicinity of the swarm zones, and to model the structures in order to determine the overall structural and tectonic conditions within the WB/V region. In order to achieve this goal, two active source seismic profiles from the WB/V region were recently reprocessed by researchers in the Seismics and Seismology Working Group at TU Bergakademie Freiberg. These datasets imaged bright reflectors spatially correlated with the swarm earthquakes. In this study, I will use reflection coefficient modelling to characterise the bright reflectors observed in the active seismic profiles. These reflectors may represent geological and/or structural boundaries which trap fluids and facilitate the microseismic rupturing. Recently, our working group successfully used this method to model and characterise faults in a crystalline environment. Here, I will use this method to model the bright reflectors in the 9HR/91 and MVE-90 profiles, and to determine if they image the same structures. In order to model and map the bright reflectors throughout WB/V, the method will be adapted and applied to earthquake seismograms recorded by local German and Czech seismometers. Based on the modelling results and the reflector map, I will determine if the reflectors are associated with the swarm activity, or represent unrelated structures. This study will be of interest to scientists studying the relationships between fluids and earthquakes. Furthermore, the methodology will be useful to researchers interested in mapping the subsurface structures in regions with a good local seismic network, but little information from active source studies.