Postglacial Faults in Fennoscandia: Targets for scientific drilling

Abstract

During the last stages of the Weichselian glaciation (ca. 9,000-15,000 years B.P.), reduced ice loads and glacially affected stress fields resulted in active faulting in Fennoscandia with fault scarps up to 160 km long and up to 30 m high. These postglacial (PG) faults are usually SE dipping, SW-NE oriented thrusts, and represent reactivated, pre-existing crustal discontinuities. Postglacial faulting indicates that the glacio-isostatic compensation is not only a gradual viscoelastic phenomenon, but also includes unexpected violent earthquakes, suggestively larger than other known earthquakes in stable continental regions. We explore here possibilities and benefits for investigating, via scientific drilling, the characteristics of postglacial faults in northern Fennoscandia, including their structure and rock properties, present and past seismic activity and state of stress, as well as hydrogeology and associated deep biosphere. The research is anticipated to advance science in neotectonics, hydrogeology and deep biosphere studies, and provide important information for nuclear waste disposal, petroleum exploration on the Norwegian continental shelf and studies of mineral resources in PG fault areas.

Reflection seismic studies over the end-glacial Burträsk fault, Skellefteå, Sweden

“…This result has important implications for determining the state of stress required to activate the faults and is being followed up by seismological observations using a system of permanent and temporary seismological stations (Karlsson et al, 2010). In addition, there is now an international initiative underway to drill into some of the end-glacial faults in the Nordic countries (Kukkonen et al, 2010) in a systematic manner.…”

Postglacial Fault Drilling in Northern Europe: Workshop in Skokloster, Sweden

“…Methods applied in PG fault research so far include bedrock and Quaternary field geology, trenching, seismicity, airborne and ground geophysics, and shallow drilling to about 500 m (Kukkonen et al, 2010). Revealing the mechanisms and processes related to PG faulting is highly relevant for understanding seismicity in these intraplate areas.…”

“…Existing shallow cores (Kukkonen et al, 2010) should be re-examined with modern mineralogical and isotope methods. Pre-drilling science should also include re-analysis of stress field measurements (Bäckblom and Stanfors, 1989;Bjarnason et al, 1989).…”

“…1, 2; Olesen et al, 1992;Lagerbäck and Sundh, 2008;Kukkonen et al, 2010). Assuming that these distinct faults were formed in single events, they would represent earthquakes with magnitudes of up to 7-8 (Bungum and Lindholm, 1997;Kuivamäki et al, 1998).…”

Structure of the Suasselkä postglacial fault in northern Finland obtained by analysis of local events and ambient seismic noise

“…Postglacial (PG) faults there were formed during the last stages of the Weichselian glaciation (ca. 9000-15 000 years BP), when reduced ice load and relaxation of accumulated tectonic stress resulted in rapid up- lift in Fennoscandia and large-magnitude earthquakes with M w of 7-8.2 (Wu et al, 1999;Olesen et al, 2004;Kukkonen et al, 2010). The length of the PGFs may vary from 2 to 150 km and the maximum height of the fault scarps from 1 to 12 m, and up to 30 m in the extreme cases (see compilation in Olesen et al, 2004).…”