Structure of the Suasselkä postglacial fault in northern Finland obtained by analysis of local events and ambient seismic noise
Afonin, Nikita; Kozlovskaya, Elena; Kukkonen, Ilmo; DAFNE/FINLAND Working Group (2017-04-18)
Afonin, N., Kozlovskaya, E., Kukkonen, I., and DAFNE/FINLAND Working Group: Structure of the Suasselkä postglacial fault in northern Finland obtained by analysis of local events and ambient seismic noise, Solid Earth, 8, 531-544, https://doi.org/10.5194/se-8-531-2017, 2017.
© Author(s) 2017. This work is distributed under the Creative Commons Attribution 3.0 License.
Understanding the inner structure of seismogenic faults and their ability to reactivate is particularly important in investigating the continental intraplate seismicity regime. In our study we address this problem using analysis of local seismic events and ambient seismic noise recorded by the temporary DAFNE array in the northern Fennoscandian Shield. The main purpose of the DAFNE/FINLAND passive seismic array experiment was to characterize the present-day seismicity of the Suasselkä postglacial fault (SPGF), which was proposed as one potential target for the DAFNE (Drilling Active Faults in Northern Europe) project. The DAFNE/FINLAND array comprised an area of about 20 to 100 km and consisted of eight short-period and four broadband three-component autonomous seismic stations installed in the close vicinity of the fault area. The array recorded continuous seismic data during September 2011–May 2013. Recordings of the array have being analysed in order to identify and locate natural earthquakes from the fault area and to discriminate them from the blasts in the Kittilä gold mine. As a result, we found a number of natural seismic events originating from the fault area, which proves that the fault is still seismically active. In order to study the inner structure of the SPGF we use cross-correlation of ambient seismic noise recorded by the array. Analysis of azimuthal distribution of noise sources demonstrated that during the time interval under consideration the distribution of noise sources is close to the uniform one. The continuous data were processed in several steps including single-station data analysis, instrument response removal and time-domain stacking. The data were used to estimate empirical Green’s functions between pairs of stations in the frequency band of 0.1–1 Hz and to calculate corresponding surface wave dispersion curves. The S-wave velocity models were obtained as a result of dispersion curve inversion. The results suggest that the area of the SPGF corresponds to a narrow region of low S-wave velocities surrounded by rocks with high S-wave velocities. We interpret this low-velocity region as a non-healed mechanically weak fault damage zone (FDZ) formed due to the last major earthquake that occurred after the last glaciation.
DAFNE/FINLAND Working Group
The DAFNE/FINLAND Working Group consists of the following individuals: Ilmo Kukkonen (University of Helsinki, Department of Physics, Helsinki, Finland), Pekka Heikkinen (University of Helsinki, Institute of Seismology, Helsinki, Finland), Kari Komminaho (University of Helsinki, Institute of Seismology, Helsinki, Finland), Elena Kozlovskaya (Oulu Mining School, University of Oulu/ Geological Survey of Finland, Oulu, Finland), Riitta Hurskainen (Sodankylä Geophysical Observatory, University of Oulu, Oulu, Finland), Tero Raita (Sodankylä Geophysical Observatory, University of Oulu, Oulu, Finland), Hanna Silvennoinen (Sodankylä Geophysical Observatory, University of Oulu, Oulu, Finland).
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