Drilling Active Faults in Northern Europe

Principal Investigators:
 Ilmo Kukkonen, University of Helsinki, Finland.
 Odleiv Olesen, Geological Survey of Norway.
 Maria Ask, Luleå University of Technology, Sweden.

DAFNE – Drilling into Active Faults in Northern Europe is an ambitious international research project aiming to drill deep research boreholes to depths of 2-3 kilometers in order to study the geology, seismicity, stress field, deep fluid and gas, and microbes in postglacial faults. The project will be carried out in close co-operation with an international team of scientists, research institutes and relevant industry under the auspice of the International Continental Scientific Drilling Program (ICDP). A recent review on postglacial faults is provided in [1] and a workshop report in [2]. The DAFNE proposal is one of the drilling proposals included in the Swedish Deep Drilling Program and its successor, the Swedish Scientific Drilling Program. The project is expected to proceed with seismic monitoring, geophysical and geological mapping of selected structures in 2011-2013, selection of the drilling site in 2013, submission of a full drilling proposal to ICDP in 2014, and drilling in 2015-2016. The estimated cost of drilling is in the range of 1-3 M€ with details depending on drilling technology, depth, number of holes, rock technical conditions, and need of casing as well as logistical requirements.

Background
Northern Fennoscandia experienced an exceptional period of tectonic activity at the end of the last ice age at about 9,000-10,000 years before present [1]. Due to changes in bedrock stress field very strong earthquakes occurred under, or just outside of the withdrawing ice sheet. Today, the resulting structures are sharp discordant fault lines with lengths of 10-150 km and vertical displacements of 1-30 m. At the moment, 14 major structures in Finland, Norway and Sweden are known. Seismic monitoring along some faults have revealed that they are still seismically active with frequent small earthquakes occurring from surface to depths of tens of kilometers and roughly following the structural dip angle of the faults. Furthermore, paleoseismic records reveal that large earthquakes may occur in this area that traditionally is assumed to be dormant. In 1898, an earthquake of estimated magnitude 4.7 resulted in structural damage on buildings [3]. In addition, measurements of in situ stress have been made in one postglacial fault [4]. These results suggest low stress magnitudes and perturbed stress orientations, which are well-known signs of an active fault. The available results indicate that the structures are not dormant, but continuously active from shallow to great depths.

Scientific questions
Some post-glacial faults in Fennoscandia have been investigated extensively including structural geology, geophysical surveys, reflection seismic studies and excavations,  but only occasional with shallow drilling (<100 m). Systematic in-situ information on post-glacial faults at depth will elucidate the following problems:

Schematic picture of a DAFNE drill site. Schematic diagram (NOT ACTUAL DRILL SITE!) of a DAFNE investigation on an aerial photograph of the Pärvie Fault in northern Sweden (Photo: Björn Lund). Inset photo shows the fault scarp of the Pärvie Fault north of Kiruna(Photo: Robert Lagerbäck).
  1. What is the tectonic style, deep structure and depth extent of the post-glacial faults?
  2. Are post-glacial faults still active?
  3. What are the paleoseismic implications of postglacial faults?
  4. Did post-glacial faults reactivate more than once? Is it possible to provide quantitative ages of the tectonic systems hosting post-glacial faults?
  5. What are the present and paleostress fields of post-glacial faults?
  6. How has the faulting affected the rock properties, structure and deformation in and near the fault surface?
  7. What are the hydraulic properties of post-glacial faults, and how did they control fresh glacial meltwater recharge?
  8. What is the composition of groundwater (chemistry, salinity, pH, Eh, gas content) in post-glacial faults?
  9. Is there a deep biosphere in post-glacial faults?

Societal, scientific and industrial relevance
Postglacial faults and related seismic activity are a poorly known component of intraplate seismicity and bedrock response to glacioisostatic rebound which characterizes the geological and topographic environment in all of Fennoscandia. Research on postglacial faults is extremely interesting from the scientific point of view, but it also has great relevance for the society. The understanding of postglacial faulting, particularly factors controlling the location of faults and their earthquake triggers in the previous glaciation are essential for predicting the future behaviour of bedrock during forthcoming glaciations. This is especially important for safe disposal of spent nuclear fuel in bedrock, currently planned and prepared for in Finland and Sweden. Postglacial faulting often has taken place in old reactivated zones of weakness, and at least in central Finnish Lapland, there are orogenic gold deposits located within a postglacial fault structure. Up to 1.3 % copper occurs locally in the soil along the Stuoragurra Fault in Finnmark, Norway, and copper and iron mineralizations are associated with postglacial faults in Sweden. In addition, some postglacial faults are located in the vicinity of active mines in Sweden and Finland. Scientific drilling would offer an opportunity to investigate the influence of these faults on stress field and hazard risk for these mines, especially as the depth of mining is increasing. Further, the present seismic activity of postglacial faults has relevance for hydropower- and tailing dams located in the vicinity of postglacial faults in northern Sweden, Norway and Finland. A deeper insight to neotectonic activity and uplift in the northern Fennoscandian continental area would improve our understanding of how the hydrocarbon resources in the continental shelf in the Barents Sea were formed. Therefore, the suggested research on postglacial faults is expected to have a widespread scientific and societal relevance [1, 2].

[1] Kukkonen, I.T., Olesen, O., Ask, M.V. S. and the PFDP WORKING GROUP (2010) 'Postglacial Faults in Fennoscandia: Targets for scientific drilling‘. GFF, vol. 132: 1, 71 — 81
[2] Kukkonen, I.T., Ask, M.V.S & Olesen O., 2011. Postglacial Fault Drilling in Northern Europe: Workshop in Skokloster, Sweden. Scientific Drilling, No. 11, March 2011, 56-59.
[3] Mäntyniemi, P., 2008. Earthquake of 4 November 1898 in northern Europe: New insights, J. Geophys. Res., vol.113, B11303, doi:10.1029/2007JB005461.
[4] SKB, 2008. Investigations of post-glacial faulting in the Lansja?rv area, northern Sweden. SKB report P-08-79. SKB: Stockholm, Sverige, 192 pp.