Seismic lower crustal reflectivity and signal penetration in the Siljan Ring area, Central Sweden
1998 (English)In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 288, no 1-4, 17-30 p.Article in journal (Refereed) Published
During the period between 1984 and 1990. several rellection seismic profiles, ~ ith a total length of-~ It)() kin, ~,ere shot in the area of the Siljan impact structure. Central Sweden. The aim was to study the F'roterozoic cD'stalline crust, prior to the drilling of a deep well. Parts of this data have been re-processed, addressing questions concerning signal penetration and lower crustal/upper mantle rellectivity, as strong lower crustal retlectivity is often absent on land data from the Baltic Shield. Earlier processing showed clear reflectors at upper crustal levels, some of which have been attributed to dolerites. through tile use of horehole .... ' ,, Ioeem e. At lower crustal levels, the picture was less clear with only diffuse bands of rellectors. We have tried to improve the image of the deeper parts, mainly by using standard processing techniques lor correcting static shills and for spectral balancing. The standard stacked sections show, as before, strong reflectors in the upper crust and some discontinuous events at lower crustal levels, primarily in the time window between I 1 and 14 s TWT. From this v,'e place the base of the crust at 13-14 s TWT (43-47 km at 6.6-6.7 km/sl in this area. There are strong lateral ~ariations in this apparent retlectivity. These variations could, in part, be caused by differences in charge sizes. The depth of signal penetration, estimated through prestack amplitude decay, was not fully sufficient for the smallest charges ~,-. l0 kg). This is supported by coincident stacked sections, where data collected with smaller charges contain less coherent events at Iox~er crustal levels. Some variations in apparent reflectivity are not related to the charge size. The efle'cts of lateral variations m signal penetration have been studied, for 10-kg charges, by calculating amplitudes at fixed-offset channels for different shot positions. Although there are some variations in these amplitudes, we argue that this is not the only explanation l~ar satiations in apparent deep retlectivity and that the lower crustal rellectivit~, is ~eaker below the "l'ransscandmavian Granite Porph~r', Belt than below the Southern Svecofennian Province. From earlier studies, the meteor impact that has ~ccurred in this area is interpreted not to have affected the lower on.st.
Place, publisher, year, edition, pages
Elsevier, 1998. Vol. 288, no 1-4, 17-30 p.
Moho; seismic reflectivity; signal penetration; seismic amplitude; seismic profiles; Siljan; BALTIC SHIELD; REFRACTION; BASIN; VIBROSEIS; EVOLUTION
Earth and Related Environmental Sciences
IdentifiersURN: urn:nbn:se:uu:diva-28017OAI: oai:DiVA.org:uu-28017DiVA: diva2:55913