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Some results concerning crustal movements in Finland
Tectonophysics, 71 (1981) 65--71
65
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
SOME RESULTS CONCERNING CRUSTAL MOVEMENTS IN F I N L A N D
AIMO KIVINIEMI
Finnish Geodetic Institute, Helsinki (Finland) (Received July 1, 1980)
ABSTRACT
Kiviniemi, A., 1981. Some results concerning crustal movements in Finland. In: P. Vysko~il, R. Green and H. M~/lzer (Editors), Recent Crustal Movements, 1979. Tectonophysics, 71: 65--71. Land uplift isobases determined by two precise levellings cover the whole country. High-precision gravity measurements on the land uplift gravity line running along an approximate latitude of 63°N were repeated nine times in thirteen years. No secular variation in gravity was observed. Records have been made with a long water-tube tilt meter since 1978. The tidal parameters were determined and the drifts of the instrument were studied.
PRECISE LEVELLING
The First Precise Levelling was carried o u t in 1892--1910 in southern and central Finland or between the approximate latitudes of 60°--65°N. In 1935 the Second Precise Levelling was started, and in 1955 the loops were extended to an approximate latitude of 66.5°N. This net was adjusted. On the basis of these two precise levellings the land uplift isobases were determined up to the latitude mentioned. The land uplift isobases in Lapland, between the latitudes of 66.5°--70°N were estimated, mainly using the hypothesis of the isostatic after-effect of the ice period. The form of the isobases was estimated to be elliptical. In order to determine the land uplift isobases in Lapland more accurately, the Second Precise Levelling was extended there. The land uplift isobases were determined b y a repeated precise levelling in 1953--1975. First, in 1953--1962, t w o loops and six junction lines to Sweden and Norway were levelled. This network covers most of Lapland. In 1973--1975, the measurement 9 f a north--south line through Lapland was repeated. The land uplift isobases in Lapland were determined b y comparing the results of these two levellings. These isobases are no longer regular concentric elliptical curves. The isobases show that the area of maximal land uplift is large and extends further north than was assumed earlier. The isobases determined by two precise levellings (Fig. 1) indicate only 0040-1951/81/0000--0000/$ 02.50 © 1981 Elsevier Scientific Publishing Company
66 51 "
~2~
~o ,
(
%...
SUOMI-FINLAND 5 5O0 000
F.
Levelling of High Precision and Land Uplift LevelledLmes IntemationaiJunc~or~s ..~ •
0,8 Is~aS~S ol LanU Upiih in rnm per Yea,
Tide Gaug~
~,,
i
i:'~:i~;~~
¸
2°
Fig. 1. Levelling of high precision and land uplift in Finland.
J
,
7O:
67
the average uplifting velocity during a given time interval. However, more detailed information will be obtained when the results of the Third Precise Levelling, begun in 1978, are available. HIGH-PRECISION GRAVITY MEASUREMENTS
It is anticipated that the land-uplift p h e n o m e n o n described above will cause a variation in gravity. All known explanations assume that land uplift decreases gravity. A land uplift of 10 mm should cause a decrease of 1.71-3.08 pGal, depending on the theory accepted. These approximations are based on the theories of the isostatic land-uplift mechanism or of variation in the geoid. If the yearly land uplift is not equal in the different areas, it is possible to study this phenomenon by repeated measurements of the gravity differences. In Finland such research was begun in 1966. The main techniques of this study are: (1) The differences in the yearly land uplift between the observation stations are as great as possible, while the gravity differences to be measured are smaller than 1 mGal. (2) The measuring instruments are tested and calibrated carefully. (3) The measurements are carried out as symmetrically as possible. Due to the above, the test fields take the form of the line running along a latitude (Fig. 2). The measurements on a line running along latitude 63°N have been repeated nine times in thirteen years by different international teams, as shown in Table I. The published results in Table II do n o t show any variation in the gravity in spite of the fact that this variation should be, on the basis of the theories mentioned above, from --10.3 to --18.3 pGal. The discrepancies between the observed and expected variations in gravity cannot be explained by the measuring errors (ref. Table II). In the opinion of the author, the above theories do n o t explain the land-uplift mechanism. The mechanism is in fact more complicated than the isostatic hypothesis or variation in the geoid would suggest. MEASUREMENTS WITH A LONG WATER-TUBE TILT METER
The tilt observations with the 177 m long tube, oriented in an E--W direction, have been carried out almost continuously since 1978. An interferometric m e t h o d is used at both ends of the tube in the recording. The recording accuracy at one end has been +0.02 #m, which corresponds to a tilt of +0.05 mseca between two successive hourly readings between the ends of the tube. This accuracy is relatively high, e.g. the tide can cause a tilt of up to some 35 mseca at the latitude ~)f the recording site. This is about 700 times greater than the recording accuracy m e n t i o n e d . On the basis of the recordings mentioned above, the tidal parameters were determined at the recording site (~ = 60 ° 15.8'N, ~ = 24°04.8'E, h =--117.6 m). The results obtained are given in the Table III.
68
i' 69
t
~
}
('x
~ ~ . , j
1%
.......
\
,
~,-
J
I
%
L
(
/'~
,
g&r / ~
/) ~,alajOKi . HaapavesL
fJ /
__._____.~------'-'~
~Meldal
/
\
o
z
H afslo
\
Kramf~
da 0
Aanekoskl
Joensuu I / / t /
i
a.
"~ Alvdalen
(
\
Gievik
/
_.~
~. .~mib
/
V,rolah
S*untio
-'~Osth~
f I
M
A
G,5 k-
R
Fig. 2. The Fennoscandian land uplift gravity lines.
In addition to the tilt caused by the tide, anomalies were also found in the recording data. These are drifts which consist of a linear and a nonlinear part. The greatest linear drift has been 30 mseca/month, with a different
69 TABLE I List of measurements carried out on the line of 63°N Year
Gravimeter No.
Observer
Section of line
Number of single measurem.
Standard error (if published)
1966 1967 1967 1967 1971
55, 62, 67, 69 24, 55, 69 24, 55, 69 24, 55, 69, 115 55, 62, 100 258,142 55, 62, 100 142, 258 45, 54, 55, 62 195,258 100, 142, 290 55, 62 55, 62 380 55, 69A 5 4 , 1 2 0 , 139, 290
SE, AK AK LP AK AK CG AK CG CG, BH, LH AM, LP
F j 1) j 1) F F F J J J
9 10 10 4 9 9 8 8 8
-+3.1 -+3.1 +4.5 +3.2 -+2.9 -+9.3 +4.0 -+11.8 -+2.0
AK AK RB AK LP, LH ~I EK AK RH EG, AK LP, EG
F 2) F 2) F F, J F, J F,J F, J F 2)1) F 2)1) F, J F, J
12 12 4--6 6 6 6 4 9 9 5 4
1971 1972
1972 1973 1975 1977 1977 1977 1977 1978 1978 1979 1979
-- 3) 55 275 258, 38 3), 55 258, 38 3), 54, 290
-+1.0 -+4.9 -+2.0 -+3.7 -+2.4
-+3.4
The abbreviations above are: F = Finnish section of the line. J = the junction between Sweden and Finland. RB = Dr. Rudolf Brein, Institut fiir Angewandte Geod~isie in Frankfurt/Main. SE = Mr. Sven Ernberg, Defense Mapping Agency Topographic Center. CG = Prof. Carl Gerstenecker, Technical University of Darmstadt. EG = Prof. Erwin Groten, Technical University of Darmstadt. LH = Mr. Lars-Ake Haller, Geographical Survey Office of Sweden. BH = Mr. B.G. Harsson, Geographical Survey of Norway. RH = Mr. Roger Hipkin, University of Edinburgh. AK = Prof. Aimo Kiviniemi, Finnish Geodetic Institute. EK = Dr. Erik Klingel~, Swiss Federal Institute of Technology, Ziirich. A_M = Mr. Age Midtsundstad, Geographical Survey of Norway. LP = Dr. Lennart Pettersson, Geographical Survey of Sweden. 1) = transported together. 2) = only the difference between Vaasa and A~/nekoski was measured. 3) = D-gravimeter. -- = not yet published.
sign. U n t i l n o w , t h e r e a s o n f o r t h e s e d r i f t s h a s b e e n l a r g e l y u n k n o w n . T h e s e drifts cannot be explained by instrumental errors in the tilt meter. Tilting of t h e c r u s t is o n e p o s s i b l e r e a s o n , as are d i f f e r e n t k i n d s o f l o a d i n g e f f e c t s .
70 ' F A B L E Ii
Gravity differences between J o e n s u u , A ~ i n e k o s k i , Vaasa and Kramfors (in p G a l ) Year
Observer
1966 1967 1967 1971 1972 1972 1973 1975
A K , SE AK LP AK LP AK AK RB
1977 1977 1978 1979 1979
AK LP, LH AK EG, AK EG, LP
Mean and standard error with equal weights Standard error o f a weight unit Expected variation o v e r 11 years Computed land uplift difference in m m o v e r 11 years
Joensuu-:~//nekoski
A~/nekoski Vaasa
+ 3 5 6 . 7 _+ 4 . 7 + 3 5 1 . 6 _+ 1.9
....4 9 2 . 1 _+ 2 . 4 - - 4 8 8 . 4 -+ 4.1
+ 3 5 5 . 1 _+ 3 . 3
- - 4 7 4 . 9 + 1.3
3 5 3 . 8 ,+ 1.9
- - 4 8 8 . 4 ,+ 1.0 - - 4 8 1 . 6 -+ 4 . 9 - - 4 8 6 . 7 _+ 2.2
357.4 _+ 2.0 356.3 _+ 2.6
V a a s a ..... Kramfors
--374.5 --374.5 --371.5 --368.3
_+ 3.1 ,+ 4 . 6 + 4.0 ,+ 2.7
--489.3 _+ 0.2 --492.2 +_ 1.9 --487.5 ,+ 3.4
--372.8 _+ 3.5 --372.0 ,+
3 5 5 . 2 _+ 0 . 9
- - 4 8 6 . 8 -+ 1.8
--372.3 + 0.9
_+ 2 . 2
,+ 5.4
_+ 2.3
--5.5 to --9.8
--4.0 to --7.1
--0.8 to --1.4
+31.9
+23.1
+4.4
not yet computed not yet computed
Only the non-linear part of the drift has been studied until now. It seems probable that it is caused at least partly by elastic deformation of the earth's crust due to barometric loading. In fact, the correlation between the nonlinear drift and the horizontal air pressure gradient studied with a 1100 km long base line in the E--W direction was found to be clear. Further, no correlation between the non-linear drift and hydrological loading effect was found. Some discussion of the cause of the linear part of the drift is also pos-
T A B L E III T i d a l parameters O1
P1S1K1
M2
$2K2
N2
7
0.710 + 9
0.725 + 6
0.701 + 2
0 . 7 0 4 -+ 3
0.694 + 9
A~
--2°.4 + 0.7
--3°.0 -+ 0.5
--2°.26 -+ 0.12
--1°.18 + 0.25
--2°.8 -+ 0.7
71
sible. It seems very probable that land uplift plays no role, because the tilt meter is parallel to the land uplift isobases. Another horizontal tube tilt meter is under construction. It will be in the same underground mine, the length being 60 m and in a N--S direction. As the observation accuracy of the 177 m long tilt meter is +0.05 mseca and the weekly tilt due to the Fennoscandian land uplift can reach 0.2 mseca, the long water-tube tilt meter is sufficient for a continuous study of the Fennoscandian land uplift. Therefore installation of a water-tube tilt meter in a tunnel with a large land-uplift gradient has been planned. REFERENCES Hyt6nen, E., 1979. Geodetic Operations in Finland 1975--1978. Levellings and Land Uplift. Helsinki 1979, 4 pp. K~/Sri~nen, E., 1966. The Second Levelling of Finland in 1935--1955. Helsinki, 313 pp. K~/~/ri~/nen, E., 1975. Land uplift in Finland on the basis of sea level recordings. Reports of the Finnish Geodetic Institute, 75 (5): 14 pp. K~/~ri~nen, J., 1979. Observing the Earth Tides with a Long Water-Tube Tiltmeter. Helsinki, 74 pp. Kiviniemi, A., 1974. High Precision Measurements for Studying the Secular Variation in Gravity in Finland. Helsinki, 64 pp. Kivinierni, A., 1979. Geodetic Operations in Finland 1975--1978. Helsinki, 6 pp.
65
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
SOME RESULTS CONCERNING CRUSTAL MOVEMENTS IN F I N L A N D
AIMO KIVINIEMI
Finnish Geodetic Institute, Helsinki (Finland) (Received July 1, 1980)
ABSTRACT
Kiviniemi, A., 1981. Some results concerning crustal movements in Finland. In: P. Vysko~il, R. Green and H. M~/lzer (Editors), Recent Crustal Movements, 1979. Tectonophysics, 71: 65--71. Land uplift isobases determined by two precise levellings cover the whole country. High-precision gravity measurements on the land uplift gravity line running along an approximate latitude of 63°N were repeated nine times in thirteen years. No secular variation in gravity was observed. Records have been made with a long water-tube tilt meter since 1978. The tidal parameters were determined and the drifts of the instrument were studied.
PRECISE LEVELLING
The First Precise Levelling was carried o u t in 1892--1910 in southern and central Finland or between the approximate latitudes of 60°--65°N. In 1935 the Second Precise Levelling was started, and in 1955 the loops were extended to an approximate latitude of 66.5°N. This net was adjusted. On the basis of these two precise levellings the land uplift isobases were determined up to the latitude mentioned. The land uplift isobases in Lapland, between the latitudes of 66.5°--70°N were estimated, mainly using the hypothesis of the isostatic after-effect of the ice period. The form of the isobases was estimated to be elliptical. In order to determine the land uplift isobases in Lapland more accurately, the Second Precise Levelling was extended there. The land uplift isobases were determined b y a repeated precise levelling in 1953--1975. First, in 1953--1962, t w o loops and six junction lines to Sweden and Norway were levelled. This network covers most of Lapland. In 1973--1975, the measurement 9 f a north--south line through Lapland was repeated. The land uplift isobases in Lapland were determined b y comparing the results of these two levellings. These isobases are no longer regular concentric elliptical curves. The isobases show that the area of maximal land uplift is large and extends further north than was assumed earlier. The isobases determined by two precise levellings (Fig. 1) indicate only 0040-1951/81/0000--0000/$ 02.50 © 1981 Elsevier Scientific Publishing Company
66 51 "
~2~
~o ,
(
%...
SUOMI-FINLAND 5 5O0 000
F.
Levelling of High Precision and Land Uplift LevelledLmes IntemationaiJunc~or~s ..~ •
0,8 Is~aS~S ol LanU Upiih in rnm per Yea,
Tide Gaug~
~,,
i
i:'~:i~;~~
¸
2°
Fig. 1. Levelling of high precision and land uplift in Finland.
J
,
7O:
67
the average uplifting velocity during a given time interval. However, more detailed information will be obtained when the results of the Third Precise Levelling, begun in 1978, are available. HIGH-PRECISION GRAVITY MEASUREMENTS
It is anticipated that the land-uplift p h e n o m e n o n described above will cause a variation in gravity. All known explanations assume that land uplift decreases gravity. A land uplift of 10 mm should cause a decrease of 1.71-3.08 pGal, depending on the theory accepted. These approximations are based on the theories of the isostatic land-uplift mechanism or of variation in the geoid. If the yearly land uplift is not equal in the different areas, it is possible to study this phenomenon by repeated measurements of the gravity differences. In Finland such research was begun in 1966. The main techniques of this study are: (1) The differences in the yearly land uplift between the observation stations are as great as possible, while the gravity differences to be measured are smaller than 1 mGal. (2) The measuring instruments are tested and calibrated carefully. (3) The measurements are carried out as symmetrically as possible. Due to the above, the test fields take the form of the line running along a latitude (Fig. 2). The measurements on a line running along latitude 63°N have been repeated nine times in thirteen years by different international teams, as shown in Table I. The published results in Table II do n o t show any variation in the gravity in spite of the fact that this variation should be, on the basis of the theories mentioned above, from --10.3 to --18.3 pGal. The discrepancies between the observed and expected variations in gravity cannot be explained by the measuring errors (ref. Table II). In the opinion of the author, the above theories do n o t explain the land-uplift mechanism. The mechanism is in fact more complicated than the isostatic hypothesis or variation in the geoid would suggest. MEASUREMENTS WITH A LONG WATER-TUBE TILT METER
The tilt observations with the 177 m long tube, oriented in an E--W direction, have been carried out almost continuously since 1978. An interferometric m e t h o d is used at both ends of the tube in the recording. The recording accuracy at one end has been +0.02 #m, which corresponds to a tilt of +0.05 mseca between two successive hourly readings between the ends of the tube. This accuracy is relatively high, e.g. the tide can cause a tilt of up to some 35 mseca at the latitude ~)f the recording site. This is about 700 times greater than the recording accuracy m e n t i o n e d . On the basis of the recordings mentioned above, the tidal parameters were determined at the recording site (~ = 60 ° 15.8'N, ~ = 24°04.8'E, h =--117.6 m). The results obtained are given in the Table III.
68
i' 69
t
~
}
('x
~ ~ . , j
1%
.......
\
,
~,-
J
I
%
L
(
/'~
,
g&r / ~
/) ~,alajOKi . HaapavesL
fJ /
__._____.~------'-'~
~Meldal
/
\
o
z
H afslo
\
Kramf~
da 0
Aanekoskl
Joensuu I / / t /
i
a.
"~ Alvdalen
(
\
Gievik
/
_.~
~. .~mib
/
V,rolah
S*untio
-'~Osth~
f I
M
A
G,5 k-
R
Fig. 2. The Fennoscandian land uplift gravity lines.
In addition to the tilt caused by the tide, anomalies were also found in the recording data. These are drifts which consist of a linear and a nonlinear part. The greatest linear drift has been 30 mseca/month, with a different
69 TABLE I List of measurements carried out on the line of 63°N Year
Gravimeter No.
Observer
Section of line
Number of single measurem.
Standard error (if published)
1966 1967 1967 1967 1971
55, 62, 67, 69 24, 55, 69 24, 55, 69 24, 55, 69, 115 55, 62, 100 258,142 55, 62, 100 142, 258 45, 54, 55, 62 195,258 100, 142, 290 55, 62 55, 62 380 55, 69A 5 4 , 1 2 0 , 139, 290
SE, AK AK LP AK AK CG AK CG CG, BH, LH AM, LP
F j 1) j 1) F F F J J J
9 10 10 4 9 9 8 8 8
-+3.1 -+3.1 +4.5 +3.2 -+2.9 -+9.3 +4.0 -+11.8 -+2.0
AK AK RB AK LP, LH ~I EK AK RH EG, AK LP, EG
F 2) F 2) F F, J F, J F,J F, J F 2)1) F 2)1) F, J F, J
12 12 4--6 6 6 6 4 9 9 5 4
1971 1972
1972 1973 1975 1977 1977 1977 1977 1978 1978 1979 1979
-- 3) 55 275 258, 38 3), 55 258, 38 3), 54, 290
-+1.0 -+4.9 -+2.0 -+3.7 -+2.4
-+3.4
The abbreviations above are: F = Finnish section of the line. J = the junction between Sweden and Finland. RB = Dr. Rudolf Brein, Institut fiir Angewandte Geod~isie in Frankfurt/Main. SE = Mr. Sven Ernberg, Defense Mapping Agency Topographic Center. CG = Prof. Carl Gerstenecker, Technical University of Darmstadt. EG = Prof. Erwin Groten, Technical University of Darmstadt. LH = Mr. Lars-Ake Haller, Geographical Survey Office of Sweden. BH = Mr. B.G. Harsson, Geographical Survey of Norway. RH = Mr. Roger Hipkin, University of Edinburgh. AK = Prof. Aimo Kiviniemi, Finnish Geodetic Institute. EK = Dr. Erik Klingel~, Swiss Federal Institute of Technology, Ziirich. A_M = Mr. Age Midtsundstad, Geographical Survey of Norway. LP = Dr. Lennart Pettersson, Geographical Survey of Sweden. 1) = transported together. 2) = only the difference between Vaasa and A~/nekoski was measured. 3) = D-gravimeter. -- = not yet published.
sign. U n t i l n o w , t h e r e a s o n f o r t h e s e d r i f t s h a s b e e n l a r g e l y u n k n o w n . T h e s e drifts cannot be explained by instrumental errors in the tilt meter. Tilting of t h e c r u s t is o n e p o s s i b l e r e a s o n , as are d i f f e r e n t k i n d s o f l o a d i n g e f f e c t s .
70 ' F A B L E Ii
Gravity differences between J o e n s u u , A ~ i n e k o s k i , Vaasa and Kramfors (in p G a l ) Year
Observer
1966 1967 1967 1971 1972 1972 1973 1975
A K , SE AK LP AK LP AK AK RB
1977 1977 1978 1979 1979
AK LP, LH AK EG, AK EG, LP
Mean and standard error with equal weights Standard error o f a weight unit Expected variation o v e r 11 years Computed land uplift difference in m m o v e r 11 years
Joensuu-:~//nekoski
A~/nekoski Vaasa
+ 3 5 6 . 7 _+ 4 . 7 + 3 5 1 . 6 _+ 1.9
....4 9 2 . 1 _+ 2 . 4 - - 4 8 8 . 4 -+ 4.1
+ 3 5 5 . 1 _+ 3 . 3
- - 4 7 4 . 9 + 1.3
3 5 3 . 8 ,+ 1.9
- - 4 8 8 . 4 ,+ 1.0 - - 4 8 1 . 6 -+ 4 . 9 - - 4 8 6 . 7 _+ 2.2
357.4 _+ 2.0 356.3 _+ 2.6
V a a s a ..... Kramfors
--374.5 --374.5 --371.5 --368.3
_+ 3.1 ,+ 4 . 6 + 4.0 ,+ 2.7
--489.3 _+ 0.2 --492.2 +_ 1.9 --487.5 ,+ 3.4
--372.8 _+ 3.5 --372.0 ,+
3 5 5 . 2 _+ 0 . 9
- - 4 8 6 . 8 -+ 1.8
--372.3 + 0.9
_+ 2 . 2
,+ 5.4
_+ 2.3
--5.5 to --9.8
--4.0 to --7.1
--0.8 to --1.4
+31.9
+23.1
+4.4
not yet computed not yet computed
Only the non-linear part of the drift has been studied until now. It seems probable that it is caused at least partly by elastic deformation of the earth's crust due to barometric loading. In fact, the correlation between the nonlinear drift and the horizontal air pressure gradient studied with a 1100 km long base line in the E--W direction was found to be clear. Further, no correlation between the non-linear drift and hydrological loading effect was found. Some discussion of the cause of the linear part of the drift is also pos-
T A B L E III T i d a l parameters O1
P1S1K1
M2
$2K2
N2
7
0.710 + 9
0.725 + 6
0.701 + 2
0 . 7 0 4 -+ 3
0.694 + 9
A~
--2°.4 + 0.7
--3°.0 -+ 0.5
--2°.26 -+ 0.12
--1°.18 + 0.25
--2°.8 -+ 0.7
71
sible. It seems very probable that land uplift plays no role, because the tilt meter is parallel to the land uplift isobases. Another horizontal tube tilt meter is under construction. It will be in the same underground mine, the length being 60 m and in a N--S direction. As the observation accuracy of the 177 m long tilt meter is +0.05 mseca and the weekly tilt due to the Fennoscandian land uplift can reach 0.2 mseca, the long water-tube tilt meter is sufficient for a continuous study of the Fennoscandian land uplift. Therefore installation of a water-tube tilt meter in a tunnel with a large land-uplift gradient has been planned. REFERENCES Hyt6nen, E., 1979. Geodetic Operations in Finland 1975--1978. Levellings and Land Uplift. Helsinki 1979, 4 pp. K~/Sri~nen, E., 1966. The Second Levelling of Finland in 1935--1955. Helsinki, 313 pp. K~/~/ri~/nen, E., 1975. Land uplift in Finland on the basis of sea level recordings. Reports of the Finnish Geodetic Institute, 75 (5): 14 pp. K~/~ri~nen, J., 1979. Observing the Earth Tides with a Long Water-Tube Tiltmeter. Helsinki, 74 pp. Kiviniemi, A., 1974. High Precision Measurements for Studying the Secular Variation in Gravity in Finland. Helsinki, 64 pp. Kivinierni, A., 1979. Geodetic Operations in Finland 1975--1978. Helsinki, 6 pp.