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Recent crustal movements of the travale geothermal area measured by classical geodetic control network
Pergamon
0x4-3707KwooO28-x
1. Geodynamics Vol. 20, No. 1, pp. 77-84, 1995 Copyright @ 1995 Elsevier Science Ltd Printed in Great Britain. All rights resewed 0264-37u7/95 $9.50 + 0.00
RECENT CRUSTAL MOVEMENTS OF THE TRAVALE GEOTHERMAL AREA MEASURED BY CLASSICAL GEODETIC CONTROL NETWORK
A. BEINAT,’
C. MARCHESINI,’
A. ROSSI,’ and I. DINI
’ Dipartimento di Georisorse e Territorio, Universith di Udine, Via Cotonificio 114, 33100 Udine, * Istituto Internazionale per le Ricerche Geotermiche, Pisa and 3 ENEL-DPT, VDAG, Pisa, Italy (Received for publication 16 March 1993; accepted in revised form 25 October 1994)
Abstract-In order to support and integrate an existing precise levelling control network, in the Travale geothermal area (Tuscany, Italy), a geodetic network was set up in 1973 to monitor the ground displacements occurring as natural neotectonic activity and induced by steam production in the geothermal field. This network consists of 7 benchmarks located across the main distensive fault system at the SW boundary of a regional graben-shaped tectonic feature that trends in Apenninic direction. The area is also affected by intensive geothermal exploitation. The net was measured several times with different types of geodetic methods: geometric and trigonometric levelling, distances and GPS. In the years 1988, 1990 and 1991 the distances were measured with the Mekometer ME 5000. The use of this very high precision distance meter allows to evidence a constant displacement trend also within a short period of measures.
1. INTRODUCTION
The Travale area is located a few kilometres to the E-SE of the Larderello geothermal basin (Fig. 1). The first drilling in this area, for the exploitation of H3B03 present in the existing thermal manifestations, dates back to 1860. Until 1940 interest was concentrated on the production of boric acid, but in the post-war period the Travale area was included in the development programmes for the production of geothermal power (Cataldi et al., 1970). In 1951 the five productive wells in this area were together delivering some tens of m3/h of hot water and about 50 t/h of steam, at an average pressure of 3.2 ata. In the same year a small exhausting-to-atmosphere generating plant (with two 3500 kW units) was brought into service. As a consequence of the progressive decrease in economically utilizable steam, in early 1962 it became necessary to dismantle the generating plant. After 1969 a research program, set up to cover a larger area than the one previously investigated, led to the discovery of a new productive area located several kilometres north-east of the old field. The first exploratory well drilled in this area (T22) produced 314 t/h of steam, with a delivery pressure of 8.07 ata, a 77
78
. . . . . . . . . . . . .
. . . . . . . . . . .
. . . . . . . .
. . . .
Marine, lagoonal and lacustrine deposits: mainly clays. (Pliocene - U. Miocene)
Flysh facies formations: mainly shales. (Eocene - Jurassic)
Terrigenous upper complex: sandstones (“macigno”) and shales (“scaglia”). (L. Miocene - U. Cretaceous)
Pravalently
carbonate complex. (Jurassic - U. Trias)
Main fault system. Bases of geodetic network (EDM and GPS equipment) Fig. 1. Travale
Radicondoli
area (Tuscany, Italy).
Schematic geological map and geodetic network
Geodetic measurementsin the Travale geothermal area
79
wellhead temperature of 185°C. The shut-in pressure was 60 ata. Since July 1973 this well has been feeding a 15 MW exhausting-to-atmosphere power plant (Burgassi et al., 1975). During recent years, the exploration of the new Travale-Radicondoli area has continued with the drilling and exploitation of several other wells. At present 4 geothermal power plants are active in the area, with a total installed capacity of 80 MW.
2. THE TRAVALE
NETWORK
A geodetic network was set up to monitor the horizontal ground displacements occurring as natural neotectonic activity and induced by steam production in the gheothermal field. This network consists of 7 benchmarks located across the main distensive fault system at the SW boundary of a regional graben-shaped tectonic feature that trends in Apenninic direction. The 7 points are located as follows (Fig. 1). -C
and D are on the uplifted side of the main tectonic feature, where the Mesozoic carbonatic formation is exposed; -F, G and E are located in the zone where considerable to maximum subsidence values and geothermal fluid production are observed; -A and B are in the area corresponding to the main tectonic depression. From the point of view of the foundation
terrains:
-A, C and D are buried pillar in soft terrains; -E and F are made by benchmarks installed on exposed rocks; -G is on a specially constructed monument on the top of a wooded hill made of Gabro rocks; -B is on the top of a medieval tower built on cemented conglomerates.
3. CLASSICAL MEASUREMENTS
3.1. Geometric levelling From 1973 onward, the study of some geodetic parameters on the Travale-Radicondoli area has provided a useful monitoring tool of the exploitation induced field evolution. A network of elevation benchmarks was established in the Travale geothermal area and the first measurements were made in June 1973 using precision geometric levelling. The local geothermal power-plant began operations 1 month later (Burgassi et al., 1975). Vertical changes in the area throughout the various phases of development and exploitation of this field were monitored by 15 different surveys of the network over a period of 15 years. At present the levelling network of 180 benchmarks covers about 40 km; 60% of the lines run along rough country roads.
80
A. Beinat
pi al.
This network includes the geothermal field with producing and re-injection wells. The results of these observations reveal a maximum subsidence in the central part of this area at an average rate of 20-25 mm/year (Geri et al., 1984; Di Filippo et al., 1985). In Fig. 2 the topographic elevation changes measured in the period 1988-1991 are shown. A precision gravity network was set up in 1979 to acquire information on any density variations or (fluid) mass movements within the reservoir. Gravity
. A
/ ,yO
Elevation
benchmarks
(Levelling
. . . .
Bases of geodetic network (EDM and GPS equipment) Lines of ground vertical
movement
500
N
.
(in mm)
holding the reference benchmark *stable during the relevant period (1988-1991) 0
’ Casalone
.
network)
6
t .
. .
1000 m
. l
0
4
. .
I I
4
-‘, Q7
Travale
l
* AD Pod. Aquarello
Fig.
2. Elevation
changes
in the ‘I‘ravale-Radicondoli
area during
the 3-year
period
1988-1993
Geodetic measurements
in the Travale geothermal area
81
measurements were repeated several times. The g variation observed reached a maximum of 40 ugal (Geri et al., 1985). 3.2. Trigonometric levelling The geometric levelling connects the points A, B, E, F, G of the geodetic network. In order to connect the points C and D, located on top of hills, the trigonometric levelling is necessary. The contemporaneous reciprocal zenith angles measurements was performed in order to minimize the effect of the refraction coefficient. Two Kern theodolites DKM2 were used from points C, F and G and afterwards from points D, G and E; in this way we have two height determinations for every point on the hills (C and D). 3.3. Distance measurements (from 1988) The distance measurements were peformed by the most precise distance meter currently available: the Kern Mekometer ME 5000. Because of its high intrinsic precision (0.1 mm + 0.1 mm/km) the fluctuations of the air refraction index along the path of measurements constitute the most important part of the measurement error. For this reason special care was taken with the temperature and pressure detection near both the Mekometer and the prisms. Beside the usual mechanical thermo-hygrographs we used an electronic device for temperature tele-detection consisting of electronic temperature probes that continuously transmit the detected data by radio to a receiving unit. For the pressure, mechanical measuring devices were used. For longer distances (up to 8 km) we used special prism holders equipped with 7 prisms, specially made for this purpose. For shorter distances the holders can support only 3 prisms set close to each other on a straight line. The distances between the centres of the cube corners are smaller than the Kern holders permitting a better reflection of the laser beam.
4. NETWORK ADJUSTMENT
For the three measurement campaigns (1988, 1990 and 1991) up to now performed, 2D and 3D network adjustments were executed by the least squares method and with the further requirement of a minimum norm for the vector of the unknowns. Operating in this way, i.e. considering a completely free network adjustment, we used the same arbitrary local reference system (the Y-axis is directed approximately toward North and X-axis toward East) for all epochs of measurement (Beinat et al., 1991). Distances, zenith angles and levelling height differences were adjusted at the same time using scientific software (Crosilla and Marchesini, 1983) that also corrects the distance measurements for the atmospheric effect. The a priori mean standard errors (or,) used in the adjustment were calculated with the
A. Beinat
82 Table
I. Horizontal
et al.
displacements
and error ellipses
1991-1990
Point
1991-1988
Aa
A>
(1
(mm)
(mm)
(mm)
-18.57 - IS.21 -3.13 - IO.25 IS.24 13.46 18.47
~ 15.04 -1x.34 5.92 7.54 31.11 ~ 10.00 - 1.20
14.30 19.28 19.13 14.62 12.31 14.13 10.80
-4.03 -6.98 -7.60 6.85 14.60 -1.16 -1.67
-7.57 5.88 -11.78 - 1.27 12.73 -2.x7 4.x7
6.91 8.35 8.32 x.22 6.36 9.50 8.95
-27.11 1.30 97.87 15.99 143.28 13.72 135.26
non-linear formula described in Marchesini (1990). The a posterior? sigma zero (o,J resulted in 0.97, 0.74 and 0.66 respectively. The differences between the adjusted horizontal co-ordinates of the three campaigns are reported in Table 1 with the parameters of the error ellipses TBAVALENETWORK B 9km
Legenda:
8 -
6
A 19BB 0 1990 x 1991
7-
A 6 F 5 -
B
3 E
G *I 3
C
@
2Ellisses and defwmallens scale 0 1Omm
I
1 Fig. 3. Horizontal
II
u
1 -
1
2
displacements
I
3
I
4
I
5
from 1988 to 1991 and error
1
6
1
7
I
8 km
ellipses in the Travale
network.
Geodetic measurements in the Travale geothermal area
calculated on the basis of the sum of the campaigns; the values of a and p are three y is the angle between the major semi-axis the ellipses represent a probablity greater the displacements and their error ellipses.
83
variance-covariance matrices of both times the major and minor semi-axis, and the X-axis, in this case the area of than 99%. Figure 3 shows graphically
5. CONCLUSIONS
Despite the short period (3 years) of monitoring horizontal displacements in the area with the type of EDM equipment (Kern ME 5000), we can forward some meaningful conclusions from the results. Considering that exploitation of the geothermal field mainly took place in the central part of the area, including benchmarks E, F and G, the data shown in Figs 2 and 3 reveal that the displacement vectors of A, E, F and G trend towards the part of the area with the highest values of subsidence. The vectors of benchmarks B and D, quite far from the exploited area, are less affected by the induced stress: their trends, although less direct, run towards the nearest peripheral parts of the subsiding area. Benchmark C, sited in a relatively remote position, seems practically unaffected by the stress induced by the subsiding area, both with regard to the direction and magnitude of the displacement. On the whole the impact of the geothermal area is evident, producing a stress field that runs roughly towards the centre of the subsiding area. It is worth remarking that: l
l
the displacement trends remain almost constant during the reference period (1988-1991); and: their absolute values sum up to considerable total values, with an average rate per year comparable with the subsidence rate (l-2 cm/year).
It is not easy to recognise any particular behaviour connected with local geological features, although the hypothesis of a component of a pre-existing stress field of tectonic origin, would be plausible.
REFERENCES Beinat A., Capra A., Gubellini A., Kogoj D., Marchesini C., Postpischl D., Rossi A., Vittuari L. and Vodopivec F. (1991) Travale geothermal area: crustal deformations detected by geodetic control network. IUGG XX Genera1 Assembly, Vienna, 11.8-24.8. Burgassi P. D., Stefani G. C., Cataldi R., Rossi A., Squarci P. and Taffi L. (1975) Recent development of geothermal exploration in the Travale-Radicondoli area. 2nd U. N. Symp. Development Use Geothermal Resources, Vol. 3, pp. 1571-1581. Cataldi R., Rossi A., Squarci P., Stefani G. C. and Taffi L. (1970) Contribution to the knowledge of the Larderello geothermal region. Remarks on the Travale field. Geothermics 2, 587402. Crosilla F. and Marchesini C. (1983) Geodetic network optimization for the detection of crustal movements using a mekometer. Boll. Geodesia Scienze Afini XLII, 301-315. Di Filippo M., Geri G., Marson I., Palmieri F., Perusini P., Rossi A. and Toro B. (1985) Exploitation, subsidence and gravity changes in the Travale-Radicondoli Geothermal field. Znt. Symp. on Geothermal Energy, Vol. 9-1, pp. 273-278, August 1985, Kailua Kona, Hawaii. Geothermal Resources Council Transaction.
x4
A. Beinat
CI al.
Geri G., Perusini P. and Rossi A. (1984) Topographic changes in the Travale-Radicondoli geothermal tield during the first ten years of exploitation. 3rd Znf. Symp. on Land Subsidence, Venice, 19-25 March. Geri G., Marson I., Rossi A. and Toro B. (1985) Crustal deformation and gravity changes during the first ten years of exploitation of the new Travale-Radiocondoli geothermal field, Italy. Geofhermics 14(2/3), 273285. Marchesini C. (1990) Zum Fehlermodell bei Streckenmessungen. Zeifschr. Verm. (ZfV), 115, 481-488.
0x4-3707KwooO28-x
1. Geodynamics Vol. 20, No. 1, pp. 77-84, 1995 Copyright @ 1995 Elsevier Science Ltd Printed in Great Britain. All rights resewed 0264-37u7/95 $9.50 + 0.00
RECENT CRUSTAL MOVEMENTS OF THE TRAVALE GEOTHERMAL AREA MEASURED BY CLASSICAL GEODETIC CONTROL NETWORK
A. BEINAT,’
C. MARCHESINI,’
A. ROSSI,’ and I. DINI
’ Dipartimento di Georisorse e Territorio, Universith di Udine, Via Cotonificio 114, 33100 Udine, * Istituto Internazionale per le Ricerche Geotermiche, Pisa and 3 ENEL-DPT, VDAG, Pisa, Italy (Received for publication 16 March 1993; accepted in revised form 25 October 1994)
Abstract-In order to support and integrate an existing precise levelling control network, in the Travale geothermal area (Tuscany, Italy), a geodetic network was set up in 1973 to monitor the ground displacements occurring as natural neotectonic activity and induced by steam production in the geothermal field. This network consists of 7 benchmarks located across the main distensive fault system at the SW boundary of a regional graben-shaped tectonic feature that trends in Apenninic direction. The area is also affected by intensive geothermal exploitation. The net was measured several times with different types of geodetic methods: geometric and trigonometric levelling, distances and GPS. In the years 1988, 1990 and 1991 the distances were measured with the Mekometer ME 5000. The use of this very high precision distance meter allows to evidence a constant displacement trend also within a short period of measures.
1. INTRODUCTION
The Travale area is located a few kilometres to the E-SE of the Larderello geothermal basin (Fig. 1). The first drilling in this area, for the exploitation of H3B03 present in the existing thermal manifestations, dates back to 1860. Until 1940 interest was concentrated on the production of boric acid, but in the post-war period the Travale area was included in the development programmes for the production of geothermal power (Cataldi et al., 1970). In 1951 the five productive wells in this area were together delivering some tens of m3/h of hot water and about 50 t/h of steam, at an average pressure of 3.2 ata. In the same year a small exhausting-to-atmosphere generating plant (with two 3500 kW units) was brought into service. As a consequence of the progressive decrease in economically utilizable steam, in early 1962 it became necessary to dismantle the generating plant. After 1969 a research program, set up to cover a larger area than the one previously investigated, led to the discovery of a new productive area located several kilometres north-east of the old field. The first exploratory well drilled in this area (T22) produced 314 t/h of steam, with a delivery pressure of 8.07 ata, a 77
78
. . . . . . . . . . . . .
. . . . . . . . . . .
. . . . . . . .
. . . .
Marine, lagoonal and lacustrine deposits: mainly clays. (Pliocene - U. Miocene)
Flysh facies formations: mainly shales. (Eocene - Jurassic)
Terrigenous upper complex: sandstones (“macigno”) and shales (“scaglia”). (L. Miocene - U. Cretaceous)
Pravalently
carbonate complex. (Jurassic - U. Trias)
Main fault system. Bases of geodetic network (EDM and GPS equipment) Fig. 1. Travale
Radicondoli
area (Tuscany, Italy).
Schematic geological map and geodetic network
Geodetic measurementsin the Travale geothermal area
79
wellhead temperature of 185°C. The shut-in pressure was 60 ata. Since July 1973 this well has been feeding a 15 MW exhausting-to-atmosphere power plant (Burgassi et al., 1975). During recent years, the exploration of the new Travale-Radicondoli area has continued with the drilling and exploitation of several other wells. At present 4 geothermal power plants are active in the area, with a total installed capacity of 80 MW.
2. THE TRAVALE
NETWORK
A geodetic network was set up to monitor the horizontal ground displacements occurring as natural neotectonic activity and induced by steam production in the gheothermal field. This network consists of 7 benchmarks located across the main distensive fault system at the SW boundary of a regional graben-shaped tectonic feature that trends in Apenninic direction. The 7 points are located as follows (Fig. 1). -C
and D are on the uplifted side of the main tectonic feature, where the Mesozoic carbonatic formation is exposed; -F, G and E are located in the zone where considerable to maximum subsidence values and geothermal fluid production are observed; -A and B are in the area corresponding to the main tectonic depression. From the point of view of the foundation
terrains:
-A, C and D are buried pillar in soft terrains; -E and F are made by benchmarks installed on exposed rocks; -G is on a specially constructed monument on the top of a wooded hill made of Gabro rocks; -B is on the top of a medieval tower built on cemented conglomerates.
3. CLASSICAL MEASUREMENTS
3.1. Geometric levelling From 1973 onward, the study of some geodetic parameters on the Travale-Radicondoli area has provided a useful monitoring tool of the exploitation induced field evolution. A network of elevation benchmarks was established in the Travale geothermal area and the first measurements were made in June 1973 using precision geometric levelling. The local geothermal power-plant began operations 1 month later (Burgassi et al., 1975). Vertical changes in the area throughout the various phases of development and exploitation of this field were monitored by 15 different surveys of the network over a period of 15 years. At present the levelling network of 180 benchmarks covers about 40 km; 60% of the lines run along rough country roads.
80
A. Beinat
pi al.
This network includes the geothermal field with producing and re-injection wells. The results of these observations reveal a maximum subsidence in the central part of this area at an average rate of 20-25 mm/year (Geri et al., 1984; Di Filippo et al., 1985). In Fig. 2 the topographic elevation changes measured in the period 1988-1991 are shown. A precision gravity network was set up in 1979 to acquire information on any density variations or (fluid) mass movements within the reservoir. Gravity
. A
/ ,yO
Elevation
benchmarks
(Levelling
. . . .
Bases of geodetic network (EDM and GPS equipment) Lines of ground vertical
movement
500
N
.
(in mm)
holding the reference benchmark *stable during the relevant period (1988-1991) 0
’ Casalone
.
network)
6
t .
. .
1000 m
. l
0
4
. .
I I
4
-‘, Q7
Travale
l
* AD Pod. Aquarello
Fig.
2. Elevation
changes
in the ‘I‘ravale-Radicondoli
area during
the 3-year
period
1988-1993
Geodetic measurements
in the Travale geothermal area
81
measurements were repeated several times. The g variation observed reached a maximum of 40 ugal (Geri et al., 1985). 3.2. Trigonometric levelling The geometric levelling connects the points A, B, E, F, G of the geodetic network. In order to connect the points C and D, located on top of hills, the trigonometric levelling is necessary. The contemporaneous reciprocal zenith angles measurements was performed in order to minimize the effect of the refraction coefficient. Two Kern theodolites DKM2 were used from points C, F and G and afterwards from points D, G and E; in this way we have two height determinations for every point on the hills (C and D). 3.3. Distance measurements (from 1988) The distance measurements were peformed by the most precise distance meter currently available: the Kern Mekometer ME 5000. Because of its high intrinsic precision (0.1 mm + 0.1 mm/km) the fluctuations of the air refraction index along the path of measurements constitute the most important part of the measurement error. For this reason special care was taken with the temperature and pressure detection near both the Mekometer and the prisms. Beside the usual mechanical thermo-hygrographs we used an electronic device for temperature tele-detection consisting of electronic temperature probes that continuously transmit the detected data by radio to a receiving unit. For the pressure, mechanical measuring devices were used. For longer distances (up to 8 km) we used special prism holders equipped with 7 prisms, specially made for this purpose. For shorter distances the holders can support only 3 prisms set close to each other on a straight line. The distances between the centres of the cube corners are smaller than the Kern holders permitting a better reflection of the laser beam.
4. NETWORK ADJUSTMENT
For the three measurement campaigns (1988, 1990 and 1991) up to now performed, 2D and 3D network adjustments were executed by the least squares method and with the further requirement of a minimum norm for the vector of the unknowns. Operating in this way, i.e. considering a completely free network adjustment, we used the same arbitrary local reference system (the Y-axis is directed approximately toward North and X-axis toward East) for all epochs of measurement (Beinat et al., 1991). Distances, zenith angles and levelling height differences were adjusted at the same time using scientific software (Crosilla and Marchesini, 1983) that also corrects the distance measurements for the atmospheric effect. The a priori mean standard errors (or,) used in the adjustment were calculated with the
A. Beinat
82 Table
I. Horizontal
et al.
displacements
and error ellipses
1991-1990
Point
1991-1988
Aa
A>
(1
(mm)
(mm)
(mm)
-18.57 - IS.21 -3.13 - IO.25 IS.24 13.46 18.47
~ 15.04 -1x.34 5.92 7.54 31.11 ~ 10.00 - 1.20
14.30 19.28 19.13 14.62 12.31 14.13 10.80
-4.03 -6.98 -7.60 6.85 14.60 -1.16 -1.67
-7.57 5.88 -11.78 - 1.27 12.73 -2.x7 4.x7
6.91 8.35 8.32 x.22 6.36 9.50 8.95
-27.11 1.30 97.87 15.99 143.28 13.72 135.26
non-linear formula described in Marchesini (1990). The a posterior? sigma zero (o,J resulted in 0.97, 0.74 and 0.66 respectively. The differences between the adjusted horizontal co-ordinates of the three campaigns are reported in Table 1 with the parameters of the error ellipses TBAVALENETWORK B 9km
Legenda:
8 -
6
A 19BB 0 1990 x 1991
7-
A 6 F 5 -
B
3 E
G *I 3
C
@
2Ellisses and defwmallens scale 0 1Omm
I
1 Fig. 3. Horizontal
II
u
1 -
1
2
displacements
I
3
I
4
I
5
from 1988 to 1991 and error
1
6
1
7
I
8 km
ellipses in the Travale
network.
Geodetic measurements in the Travale geothermal area
calculated on the basis of the sum of the campaigns; the values of a and p are three y is the angle between the major semi-axis the ellipses represent a probablity greater the displacements and their error ellipses.
83
variance-covariance matrices of both times the major and minor semi-axis, and the X-axis, in this case the area of than 99%. Figure 3 shows graphically
5. CONCLUSIONS
Despite the short period (3 years) of monitoring horizontal displacements in the area with the type of EDM equipment (Kern ME 5000), we can forward some meaningful conclusions from the results. Considering that exploitation of the geothermal field mainly took place in the central part of the area, including benchmarks E, F and G, the data shown in Figs 2 and 3 reveal that the displacement vectors of A, E, F and G trend towards the part of the area with the highest values of subsidence. The vectors of benchmarks B and D, quite far from the exploited area, are less affected by the induced stress: their trends, although less direct, run towards the nearest peripheral parts of the subsiding area. Benchmark C, sited in a relatively remote position, seems practically unaffected by the stress induced by the subsiding area, both with regard to the direction and magnitude of the displacement. On the whole the impact of the geothermal area is evident, producing a stress field that runs roughly towards the centre of the subsiding area. It is worth remarking that: l
l
the displacement trends remain almost constant during the reference period (1988-1991); and: their absolute values sum up to considerable total values, with an average rate per year comparable with the subsidence rate (l-2 cm/year).
It is not easy to recognise any particular behaviour connected with local geological features, although the hypothesis of a component of a pre-existing stress field of tectonic origin, would be plausible.
REFERENCES Beinat A., Capra A., Gubellini A., Kogoj D., Marchesini C., Postpischl D., Rossi A., Vittuari L. and Vodopivec F. (1991) Travale geothermal area: crustal deformations detected by geodetic control network. IUGG XX Genera1 Assembly, Vienna, 11.8-24.8. Burgassi P. D., Stefani G. C., Cataldi R., Rossi A., Squarci P. and Taffi L. (1975) Recent development of geothermal exploration in the Travale-Radicondoli area. 2nd U. N. Symp. Development Use Geothermal Resources, Vol. 3, pp. 1571-1581. Cataldi R., Rossi A., Squarci P., Stefani G. C. and Taffi L. (1970) Contribution to the knowledge of the Larderello geothermal region. Remarks on the Travale field. Geothermics 2, 587402. Crosilla F. and Marchesini C. (1983) Geodetic network optimization for the detection of crustal movements using a mekometer. Boll. Geodesia Scienze Afini XLII, 301-315. Di Filippo M., Geri G., Marson I., Palmieri F., Perusini P., Rossi A. and Toro B. (1985) Exploitation, subsidence and gravity changes in the Travale-Radicondoli Geothermal field. Znt. Symp. on Geothermal Energy, Vol. 9-1, pp. 273-278, August 1985, Kailua Kona, Hawaii. Geothermal Resources Council Transaction.
x4
A. Beinat
CI al.
Geri G., Perusini P. and Rossi A. (1984) Topographic changes in the Travale-Radicondoli geothermal tield during the first ten years of exploitation. 3rd Znf. Symp. on Land Subsidence, Venice, 19-25 March. Geri G., Marson I., Rossi A. and Toro B. (1985) Crustal deformation and gravity changes during the first ten years of exploitation of the new Travale-Radiocondoli geothermal field, Italy. Geofhermics 14(2/3), 273285. Marchesini C. (1990) Zum Fehlermodell bei Streckenmessungen. Zeifschr. Verm. (ZfV), 115, 481-488.