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FIRE - Reflection seismics

mapIn 2001, an extensive new lithosphere project FIRE ( Finnish Reflection Experiment) was launched by a national consortium (Geological Survey of Finland, Institute of Seismology of the University of Helsinki, Institute of Geosciences and the Sodankylä Geophysical Observatory of the University of Oulu ) for the period of 2001 to 2005. The project has carried out crustal scale reflection seismic work on four transects in the Finnish part of the Fennoscandian Shield. The seismic fieldwork was contracted to the Russian company Spetsgeofyzika. The project consists of four FIRE transects with a total length of 2135 km. In 2001, 400 km of reflection profile along FIRE1 extending from the Archean Karelian craton in eastern Finland to the Central Finland continental-arc complex was acquired. In 2002, two transects were measured; FIRE-2 extending from the Central Finland continental arc complex to the Southern Finland arc complex, and FIRE-3 from the Archean Karelian craton via the Central Finland arc complex to the Pohjanmaa schist belt. In 2003, the fourth transect, FIRE-4 was measured in northern Finland. It started from the Archean Karelian craton and continued through the Paleoproterozoic Peräpohja schist belt, Lapland granitoid complex, Kittilä greenstone belt, Lapland granulite belt and it was terminated on the Archean craton in the northern most tip of Finland. In addition, high resolution reflection seismic works were carried out in Outokumpu ore province in eastern Finland and Suhanko area in southern Lapland. Suhanko area is known for its layered mafic intrusions. The interpretation and correlation with other geological and geophysical data sets is going on within the FIRE consortium research groups.

The seismic measurements were carried out using Vibroseis method. The crustal scale seismic signal was produced with five 14.5 ton vibrators. The applied signal was a linear sweep ranging from 12 to 80 Hz. The sweep duration and the correlated record length were 30 s, which corresponds to about 90 km in depth. Using 360 active channels at 50 m intervals and shot points at 100 m intervals, the resulting fold is 90 at most.

Pekka Heikkinen
Annakaisa Korja
Timo Tiira
Jukka Keskinen

Geologica Survey of Finland
University of Oulu:
- Division of Geophysics
- Sodankylä Geophysical observatory
Spetsgeofizika, Russia

Korja, A., Kukkonen, I.T., Heikkinen, P., Ekdahl, E., Hjelt, S.-E., Yliniemi, J., Lahtinen, R., Berzin, R. and FIRE Working Group, 2003. FIRE - Suomen kallioperän heijastusluotaustutkimukset. In: Kaila, K. ja Korja, T.: Geofysiikan päivät XXI, Oulussa 22.-23.05.2003. Geofysiikan seura, Oulu. s. 63-66.

Kukkonen, I., Heikkinen, P., Ekdahl, E., Korja, A., Hjelt, S.-E., Yliniemi, J., Berzin, R. and FIRE Working Group, 2002. Project FIRE: Deep Seismic Reflection Sounding in Finland 2001-2005. In: Lahtinen, R., Korja, A., Arhe, K., Eklund, O., Hjelt, S.-E., and Pesonen, L.J. 2002 (Eds.). Lithosphere 2002 - Second Symposium on the Structure, Composition and Evolution of the Lithosphere in Finland. Programme and Extended Abstracts, Espoo, Finland, November 12-13, 2002. Instit. Seismology, Univ. Helsinki, Report S-42, s. 67-70.