Active and passive seismic methods for investigating the glacially-triggered Burträsk fault

• Main Author: Beckel, Ruth A.
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Uppsala universitet, Geofysik 2022
• Subjects: Burträsk fault; Glacially-triggered faulting; Crooked-line reflection seismics; Cross-dip correction; Stacking-based location; Microearthquake source observations; Passive seismic imaging; Seismic interferometry; Geophysics; Geofysik; Fennoscandia
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-465855

Glacially-triggered faults are of high scientific interest since their formation was likely accompanied by major earthquakes and they are still a centre of seismicity in northern Fennoscandia, today. Imaging their deeper structure mainly relies on reflection seismics since the method generally has the best resolving power at depth of all geophysical methods. This thesis uses data acquired at the glacially-triggered Burträsk fault to advance active and passive seismic imaging methods and improve the understanding of the area. Reprocessing of a vintage, crooked-line reflection dataset using a newly developed module for a local cross-dip correction improved the quality of the reflection image significantly and provided important 3D information for the interpretation of the fault and its surroundings. A fault segment to the southwest of the profile was imaged with a dip of approximately 50° but the segment intersecting the profile was not imaged, likely due to insufficient shot coverage close to the fault. Since the Burträsk area is seismically the most active area in Sweden, passive imaging using a dataset of local microearthquakes was attempted. As a first step, the earthquakes were re-located using a stacking-based location method. In spite of the poor azimuthal coverage of the array, the method yielded surprisingly good location results within 30–40 km from the array. The most important factors for success proved to be combined P- and S-wave location with down-weighted S-wave signals, and the use of a polarity-sensitive characteristic function. The distribution of the hypocentres confirmed that the trace of the Burträsk fault is the currently active fault plane. Disappointingly, passive seismic processing using reflection seismic interferometry (RSI) did not image the known reflections. To improve the planning of future studies, different aspects of imaging dipping faults with RSI were investigated using synthetic data. The results showed that reconstructing steeply dipping reflections requires sources in the ...