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Report on the application of geodetic measurements to the determination of recent crustal movements in Finland
Tectonophysics, 29 (1975) 345-347 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
345
REPORT ON THE APPLICATION OF GEODETIC MEASUREMENTS TO THE DETERMINATION OF RECENT CRUSTAL MOVEMENTS IN FINLAND
TAWNO HONKASALO The Finnish Geodetic Institute, Helsinki (Finland) (Accepted for publication June 17, 1975)
ABSTRACT Honkasalo, T., 1975. Report on the application of geodetic measurements to the determination of recent crustal movements in Finland. In: N. Pavoni and R. Green (Editors), Recent Crustal Movements. Tectonophysics, 29 (l-4): 345-347. The use of repeated precise Ievellings, a high-precision traverse, the measurement of secular gravity variation, a long water tiltmeter and a satellite laser for studying the crustal movement are described.
An exact study about vertical crustal movement during this century was made when the network of the First Precise Levell~ng of Finlund (18921910) was relevelled by the Finnish Geodetic Institute (1935-1955). These levellings cover southern and central Finland up to the latitude of 65”N. The Second Precise Levelling (KB&%inen, 1966) was extended to the northern part of Finland. Some selected lines are being relevelled in 1973-1975. This will enable the crustal movement in Lapland to be computed. To determine the scale for the stellar triangulation network with balloonborne flashers and for satellite triangulation, (1 long precise traverse (Parm, 1974) through Finland along the first-order triangulation was planned. This measurement is going on now and will be completed this year. An accuracy of + 10 cm is estimated for this 900 km long traverse, i.e. 1 : 10 000 000. At the Second Symposium of Recent Crustal Movements at Aulanko, Finland, in 1965, a proposal was made to measure a precise gravity line across
Finland to study the changes brought about by the Fennoscandian land uplift. In 1966 a line of three stations with gravity differences smaller than 1 mGal was measured. In cooperation with the Geographical Survey Office of Sweden the line was extended in 1967 over the Gulf of Bothnia and then the measurements were continued over Sweden and Norway to the Atlantic coast. Thus the line is composed of eight stations. The line was remeasured in 1971-1972. One interval has been measured five times in five years. An
346
_20L
---~--I
+_2
____3
l“-f-
Fig. 1. Observed changes of gravity. 1 = observed changes of gravity and their standard errors (Petterson, 1975), 2 = observed changes of gravity and their standard errors (Kiviniemi, 1974), 3 = estimated gravity changes computed on the basis of the Fennoscandian land uplift.
accuracy of +2-3 PGal has been obtained. The results are somewhat surprising, because no correlation with land uplift can be found. The changes are at most 34 + 8 ~Gal/5 yr (Kiviniemi, 1974). These changes seem to be real since all the possible systematic errors have been investigated. This work will be repeated at 5-year intervals and in addition two more similar lines have been planned. To study the tilting of the earth’s crust caused by the Fennoscandian land uplift, a water tiltmeter, long pipe level (K&%inen, 1973) has been constructed. The prototype instrument was 50 m long. The recording is being carried out photographically using Newton light interference fringes. An accuracy of *0’10002 was obtained with this prototype instrument. Two new instruments are being installed 200 m under the earth’s surface in a mine 50 km west of Helsinki. The E-W pipe is 180 m long and the N-S pipe is 60 m. The pipe levels will be used for recording earth tides and if the stability proves good enough, for studying the secular tilting of the earth’s crust. The Finnish Geodetic Institute is participating in cooperation with other European countries in the study of earth tides (Honkasalo, 1973). Five vertical-component stations have been measured using a Geodynamics recording gravimeter and observations are at present being made at the sixth station. The stations form a five-station line at 200-km intervals in the N-S direction across Finland. This is a part of the European profile. The other line is in the E-W direction and is along the above-mentioned Fennoscandian land uplift gravity line, where an accurate knowledge of earth tides is needed in order to enable the computation of earth-tide corrections for gravity values. In this work we again have cooperation with North European countries. The E-W line will be extended to Sweden and Norway. A third line has been planned from Helsinki to Copenhagen. The observations using Verbaandert-Melchior horizontal pendulums to
347
measure the Finland. A satellite operational vation with
variation
in the deviation
of the vertical will be continued
in
laser (Halme et al., 1973) is under construction and it will be in 1975. The use of this instrument can be combined with obserthe Helsinki University of Technology’s 14-m radiotelescope.
REFERENCES Halme, S.J., Paunonen, M., Sharma, A., Kakkuri, J. and Kalliomlki, K., 1973. Development of a Satellite Laser System. Reports 8th Natl. Conv. on Radio Science, Otaniemi, Finland. Honkasalo, T., 1973. Fennoscandinavian Tidal Gravity Profile. Preliminary Experimental Results. 78me Symp. Int. sur les Marees Terrestres, Sopron, Hongrie, 1973. Kaarilinen, E., 1966. The Second Levelling of Finland. Publ. Finn. Geod. Inst. Helsinki, No. 61. Kaariainen, J., 1973. Uber die 50 m lange Rohrlibelle zur Untersuchung der Neigung der Erdkruste. Rep. Finn. Geod. Inst. Helsinki, 73 : 1. Kiviniemi, A., 1974. High Precision Measurements for Studying the Secular Variation in Gravity in Finland. Publ. Finn. Geod. Inst. Helsinki, No. 78. Parm, T., 1974. A High Precision Traverse for Scale Determination of Stellar Triangulation and for Controlling the First-Order Triangulation. Int. Symp. on Terrestrial Electromagnetic Distance Measurements and Atmospheric Effects on Angular Measurements, Stockholm. Pettersson, L., 1975. Studium av sekular dndring i tyngdkraften utefter latitud 63’ mellan Atlanten och Bottenhavet. Nordiska Kommissionen for Geodesi, Referat af det syvende nordiske geodaetmode i K$benhavn, 1974. Kdbenhavn 1975.
345
REPORT ON THE APPLICATION OF GEODETIC MEASUREMENTS TO THE DETERMINATION OF RECENT CRUSTAL MOVEMENTS IN FINLAND
TAWNO HONKASALO The Finnish Geodetic Institute, Helsinki (Finland) (Accepted for publication June 17, 1975)
ABSTRACT Honkasalo, T., 1975. Report on the application of geodetic measurements to the determination of recent crustal movements in Finland. In: N. Pavoni and R. Green (Editors), Recent Crustal Movements. Tectonophysics, 29 (l-4): 345-347. The use of repeated precise Ievellings, a high-precision traverse, the measurement of secular gravity variation, a long water tiltmeter and a satellite laser for studying the crustal movement are described.
An exact study about vertical crustal movement during this century was made when the network of the First Precise Levell~ng of Finlund (18921910) was relevelled by the Finnish Geodetic Institute (1935-1955). These levellings cover southern and central Finland up to the latitude of 65”N. The Second Precise Levelling (KB&%inen, 1966) was extended to the northern part of Finland. Some selected lines are being relevelled in 1973-1975. This will enable the crustal movement in Lapland to be computed. To determine the scale for the stellar triangulation network with balloonborne flashers and for satellite triangulation, (1 long precise traverse (Parm, 1974) through Finland along the first-order triangulation was planned. This measurement is going on now and will be completed this year. An accuracy of + 10 cm is estimated for this 900 km long traverse, i.e. 1 : 10 000 000. At the Second Symposium of Recent Crustal Movements at Aulanko, Finland, in 1965, a proposal was made to measure a precise gravity line across
Finland to study the changes brought about by the Fennoscandian land uplift. In 1966 a line of three stations with gravity differences smaller than 1 mGal was measured. In cooperation with the Geographical Survey Office of Sweden the line was extended in 1967 over the Gulf of Bothnia and then the measurements were continued over Sweden and Norway to the Atlantic coast. Thus the line is composed of eight stations. The line was remeasured in 1971-1972. One interval has been measured five times in five years. An
346
_20L
---~--I
+_2
____3
l“-f-
Fig. 1. Observed changes of gravity. 1 = observed changes of gravity and their standard errors (Petterson, 1975), 2 = observed changes of gravity and their standard errors (Kiviniemi, 1974), 3 = estimated gravity changes computed on the basis of the Fennoscandian land uplift.
accuracy of +2-3 PGal has been obtained. The results are somewhat surprising, because no correlation with land uplift can be found. The changes are at most 34 + 8 ~Gal/5 yr (Kiviniemi, 1974). These changes seem to be real since all the possible systematic errors have been investigated. This work will be repeated at 5-year intervals and in addition two more similar lines have been planned. To study the tilting of the earth’s crust caused by the Fennoscandian land uplift, a water tiltmeter, long pipe level (K&%inen, 1973) has been constructed. The prototype instrument was 50 m long. The recording is being carried out photographically using Newton light interference fringes. An accuracy of *0’10002 was obtained with this prototype instrument. Two new instruments are being installed 200 m under the earth’s surface in a mine 50 km west of Helsinki. The E-W pipe is 180 m long and the N-S pipe is 60 m. The pipe levels will be used for recording earth tides and if the stability proves good enough, for studying the secular tilting of the earth’s crust. The Finnish Geodetic Institute is participating in cooperation with other European countries in the study of earth tides (Honkasalo, 1973). Five vertical-component stations have been measured using a Geodynamics recording gravimeter and observations are at present being made at the sixth station. The stations form a five-station line at 200-km intervals in the N-S direction across Finland. This is a part of the European profile. The other line is in the E-W direction and is along the above-mentioned Fennoscandian land uplift gravity line, where an accurate knowledge of earth tides is needed in order to enable the computation of earth-tide corrections for gravity values. In this work we again have cooperation with North European countries. The E-W line will be extended to Sweden and Norway. A third line has been planned from Helsinki to Copenhagen. The observations using Verbaandert-Melchior horizontal pendulums to
347
measure the Finland. A satellite operational vation with
variation
in the deviation
of the vertical will be continued
in
laser (Halme et al., 1973) is under construction and it will be in 1975. The use of this instrument can be combined with obserthe Helsinki University of Technology’s 14-m radiotelescope.
REFERENCES Halme, S.J., Paunonen, M., Sharma, A., Kakkuri, J. and Kalliomlki, K., 1973. Development of a Satellite Laser System. Reports 8th Natl. Conv. on Radio Science, Otaniemi, Finland. Honkasalo, T., 1973. Fennoscandinavian Tidal Gravity Profile. Preliminary Experimental Results. 78me Symp. Int. sur les Marees Terrestres, Sopron, Hongrie, 1973. Kaarilinen, E., 1966. The Second Levelling of Finland. Publ. Finn. Geod. Inst. Helsinki, No. 61. Kaariainen, J., 1973. Uber die 50 m lange Rohrlibelle zur Untersuchung der Neigung der Erdkruste. Rep. Finn. Geod. Inst. Helsinki, 73 : 1. Kiviniemi, A., 1974. High Precision Measurements for Studying the Secular Variation in Gravity in Finland. Publ. Finn. Geod. Inst. Helsinki, No. 78. Parm, T., 1974. A High Precision Traverse for Scale Determination of Stellar Triangulation and for Controlling the First-Order Triangulation. Int. Symp. on Terrestrial Electromagnetic Distance Measurements and Atmospheric Effects on Angular Measurements, Stockholm. Pettersson, L., 1975. Studium av sekular dndring i tyngdkraften utefter latitud 63’ mellan Atlanten och Bottenhavet. Nordiska Kommissionen for Geodesi, Referat af det syvende nordiske geodaetmode i K$benhavn, 1974. Kdbenhavn 1975.