PROS Supriyadi, Wahyu H, Agus S Chance of time fulltext
Proceedings of the IConSSE FSM SWCU (2015), pp. SC.130–135
SC.130
ISBN: 978-602-1047-21-7
Chance of time lapse microgravity method survey
for subsidence monitoring
Supriyadi†a, Wahyu Hardyantoa, Agus Setyawanb
a
Universitas Negeri Semarang, Sekaran Gunungpati, Semarang 50229, Indonesia
b
Universitas Diponegoro, Tembalang, Semarang 50239, Indonesia
Abstract
Times lapse microgravity method is a development method style. Technically that is
developing is looping gravity measurements at the same point by a certain time interval,
usually taking the measurements performed in the dry season and rainy season. Based
on mathematical modeling is known that micro-gravity anomaly between the time
rooted in subsidence and subsurface density changes associated with the dynamics of
groundwater and pollution due to human activities, seawater intrusion. This fact can be
observed by means of looping gravity by using Gravimeter with precision μGal.
Gravimeter with the use of precision is necessary given the gravity anomaly due to
pollution (seawater intrusion) small. Modeling of micro gravity anomaly between the
time due to sea water intrusion by using software Grav3D The results showed that
during the period of September 2002, November 2005, and October 2013 showed that
a large subsidence that occurred in Semarang, especially in the port of Tanjung Mas and
surrounding 16 cm/year.
Keywords microgravity, time lapse, anomaly, μGal
1.
Introduction
Gravity method is one of the oldest methods in geophysics, but its application to the
source of the anomaly near the surface and are connected with the environment has not
been as intensive as the application for geodynamics studies or exploration in the estimation
of the geological structure is relatively large. This is caused by the level of accuracy is still in
order mGal anomaly or 103 μGal. In terms of tools gravimeter, 10 μGal accuracy has been
achieved in early 1970, but the accuracy of readings is totally dependent on the accuracy of
the operator because the gravimeter still use mechanical reading device.
Time lapse Microgravity method is the development of the gravity method with the
fourth dimension is time. The principle of the method is the measurement of repeated gravity
either daily, weekly, monthly or yearly using a rigorous Gravimeter in order μGal and
elevation measurements carefully (Allis and Hunt, 1986). Any changes or differences in the
results of the gravity observations in the first period to the next period is called the anomaly
microgravity. Observation of gravity changes can be caused by the dynamics around point
very, such as changes in the depth of groundwater levels and soil subsidence.
An increase in accuracy gravimeter and the development of digital systems, the
application of gravity methods to source anomalies near the surface and are connected with
the environment and for the purpose of monitoring is increasingly used, including for
†
Corresponding author. Tel.: + 62 085 226 233 319; E-mail address: pryfis@yahoo.com
SWUP
Supriyadi, W. Hardyanto, A. Setyawan
SC.131
monitoring geothermal reservoirs, oil and gas (Allis & Hunt, 1986; Andres & Pedersen , 1993;
Kamah et al., 2001; Galderen et al., 1999; Eiken et al., 2000; Akasaka & Nakanishi, 2000;
Mariita, 2000; Nishijima, et al., 2005).
The case study of subsidence in Semarang has been done by previous researchers, such
as by Marsudi (1996) have predict subsidence due to a decrease in ground water level using
a one-dimensional consolidation. Muhrozi et al., (1996) identify subsidence in Semarang
northern research subsidence in many countries is that the more subsidence research
conducted by the method Sipat Datar, including in Houston Texas 1973–1987 (Holdahl &
Zilkoski, 1991), Flat Sipat method. Wahyudi (1999) Evaluation and Analysis of subsidence in
the port of Tanjung Mas Semarang, and Sutanto (2002) with GPS (Global Positioning System)
large measure subsidence in Semarang, it appears that the studies that have been conducted
using the approach of geology and geodesy.
Research subsidence by using GPS, for example in Western Venezuela (Chrzanowski et
al., 1991). Monitoring of subsidence in Salto Caxias Brazil by Santos et al., (2001). In addition,
Abidin et al., (2005) using methods Leveling, GPS and techniques INSAR (Interferometric
Synthetic Aperture Radar) to monitor subsidence in Jakarta. Based on the research that has
been done is given the opportunity to perform subsidence measurements using other
methods, one of which is a method of microgravity across time. This method has advantages
compared with the method that has been done, for example, enables the measurement of
the distribution of the measuring point more and a relatively short time for the measurement
period.
2. Materials and methods
Time lapse microgravity anomaly the difference in value between the time of each
measurement point Bouguer anomaly at specific time intervals as follows.
∆g ( x, y, z , ∆t ) = ∆g ( x, y, z , t 2 ) − ∆g ( x, y, z , t1 )
(1)
If the very point elevation changes at two of the measurement period, then Eq. (1) can be
written as
∆g ( x, y, z , ∆t ) = ( g obs ( 2) − g obs (1) ) − ( g (ϕ 2 ) − g (ϕ1) ) − (c1 + c 2 ρ )(h2 − h1 ) + c3 ( ∆h2 − ∆h 1 ) . (2)
During interval measurements on t1 and t2 so relatively fixed position point, where ϕ1 = ϕ2,
then Eq. (2) can be simplified to
(3)
∆g ( x, y, z, ∆t ) = ( g obs ( 2) − g 0bs (1) ) − (c1 + c 2 ρ )(h2 − h1 ) + c3 (∆h2 − ∆h1 )
(4)
( g obs ( 2) − g obs (1) ) = ∆g ( x, y, z , ∆t ) + (c1 + c 2 ρ )(h2 − h1 ) − c3 (∆h2 − ∆h1 )
Kadir (1999) states that for 3-dimensional objects with mass density distribution, time lapse
microgravity at the point P (x, y, z) on the surface is expressed by the following equation.
∞ ∞ ∞
∆ρ (α , β , γ , ∆t )( z − γ )
(5)
∆g ( x, y , z , ∆t ) = G
dα dβ dγ
∫ ∫ ∫ [( x − α )
0 − ∞− ∞
2
+ ( y − β )2 + (z − γ )2
]
3/ 2
From Eqs. (4) and (5), we obtain
∞∞∞
∆ρ (α , β , γ , ∆t )( z − γ )
( g obs ( 2) − g obs (1) ) = G ∫ ∫ ∫
dα dβ dγ +
3
/
2
0 − ∞− ∞ ( x − α ) 2 + ( y − β ) 2 + ( z − γ ) 2
(6)
(c1 + c 2 ρ )(h2 − h1 ) − c3 (∆h2 − ∆h1 )
Based on mathematical modeling and simulation of synthetic data show that the effect
of topography does not affect the time lapse microgravity anomalies. Time lapse microgravity
anomaly is affected by changes in elevation (subsidence) very point. Consolidation is causing
[
SWUP
]
Chance of time lapse microgravity method survey for subsidence monitoring
SC.132
subsidence did not cause the soil mass lost so Bouguer correction is not performed. Thus Eq.
(6) can be simplified to
∞∞∞
∆ρ (α , β , γ , ∆t )( z − γ )
( g obs ( 2 ) − g obs (1) ) = G ∫ ∫ ∫
0 −∞−∞ ( x − α ) 2 + ( y − β ) 2 + ( z − γ ) 2
[
]
3/ 2
dαdβ dγ + c1 ( h2 − h1 ) .
(7)
Eq. (7) shows that the difference between the value of the gravity measurement results
caused by changes in the subsurface density associated with groundwater level changes and
subsidence.
For survey purposes based on subsidence, the source of the anomaly associated with
changes in the depth of the ground water level must be reduced. For the purposes of the
reduction can be done in two ways, namely (1) using a specially designed filter adapted to
the conditions in the field, and (2) using real data the results of measurements in the field.
Especially for (2) in Semarang is not available the data in question. This is due to the
measurement of changes in the depth of the ground water level was done continuously for
a certain period. To overcome these problems, in this study used a filet MBF (Model Based
Filter)
As the study used data from gravity measurements in Semarang September 2002, June
2003, December 2003, June 2004, February 2005, November 2005, in May 20012, October
2012, May 2013, and October 2013 by using gravimeter Scintrex Autograv CG 5 at 110 points
scattered in Semarang below.
3. Results and discussion
In accordance with the above theory, obtained micro gravity anomaly between the
time the initial condition September 2002. Data in the period September 2012 into the data
a deduction from the next period to obtain a micro-gravity anomaly over time. Furthermore,
this anomaly data corrected by the data reduction in groundwater that occur during periods
of measurements to obtain a micro-gravity anomaly between the time due to subsidence.
Examples of measurement results period September 2002, November 2005, and October
2013 hereinafter in qualitative analysis with software surfer to get subsidence contour map
(see Figure 1).
In general, the value of gravity during the measurement period in Semarang
(September 2002, November 2005, and October 2013) indicates that the value of gravity in
the northern part is greater than in the south. Results resulting in the northern part of
Semarang is lowlands and southern highlands and in accordance with the theory that the
value of gravity at a point depends on elevation, where the higher of the surface gravity value
decreases and vice versa.
Based on the gravity of each subsequent period calculated micro gravity anomaly
between the time that represents the difference between the gravity of the period
November 2005 to September 2002 and the period October 2013 to September 2002.
Contour micro gravity anomaly between the time as in Figure (2). In the period between the
time (September 2002–November 2005) and (September 2002–October 2013) showed three
anomalies, namely the positive anomalies that indicate an increase in groundwater levels
and subsidence, negative anomalies that indicate a decrease in ground water level, and zero
indicates no there is a change.
Time lapse microgravity anomaly value according to the Eq. (7) consists of two sources,
namely subsidence and changes in the subsurface density associated with groundwater level
changes. To obtain the source of the anomaly due to subsidence, the other anomaly sources
SWUP
Supriyadi, W. Hardyanto, A. Setyawan
SC.133
must be reduced by using MBF (Model Based Filter) a filter that was built for that purpose.
Time lapse microgravity anomaly (see Figure 3(a)). Furthermore, value of this anomaly value
is converted to the value of subsidence. Contour subsidence based micro gravity anomaly
data across time as in Figure 3(b).
(a)
(b)
(c)
Figure 1. Gravity contour for each measurement period, (a) September 2002, November 2005,
and (c) October 2013.
(a)
(b)
Figure 2. Time lapse microgravity anomaly, (a) September 2002–November 2005, (b)
September 2002–October 2013.
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Chance of time lapse microgravity method survey for subsidence monitoring
SC.134
(a)
(b)
Figure 3. (a) Time lapse microgravity anomaly due to subsidence, (b) and subsidence
that occurred during the measurement period based on time lapse microgravity
anomaly.
In that period the subsidence that occurred in North Semarang growing which is 20 to
48 cm in some places, for example: the port of Tanjung Mas, Marina beach area, PRPP,
housing Puri Anjasmoro, Lor village Stage and Stage Kidul, Terboyo Kulon, Terboyo Wetan,
and housing Tanah Mas. Kaligawe area, Mlatiharjo, Simpang Lima, Miroto, Gabahan, Jagalan,
Kauman, Bangunharjo, Karangturi, Pendrikan, Mugas, Pleburan, Lempongsari, Gayamsari,
relative Pedurungan not experienced subsidence compared to the previous period. The new
zone of subsidence that appeared in the previous period coverage is more widespread.
Area of subsidence that occurred north Semarang more dominant layer of soil
compaction caused by naturally. This is attributed to the fact that the layer of soil in the
region is the result of sedimentation and human activity in the form of reclamation.
4. Conclusion and remarks
Time Lapse Microgravity methods can be used for monitoring subsidence. For this
purpose, the data processing time lapse micro gravity anomaly must be corrected with the
data of decreased water level. For the purposes of correction can be done by using a MBF
(Model Based Filter) or by the results of measurements in wells monitored in the study site.
For example, a case study in Semarang which indicates that the maximum subsidence during
the period 16 cm/year occurred in Tanjung Mas port and its surroundings.
Acknowledgment
Thank To DP2M-DIKTI which funded this research through grants Hibah Pascasarjana (2002,
2003, 2004, 2005) and Hibah Kompetensi (2012, 2013). Thanks to the support BMKG Jakarta
for gravimeter Scintrex Autograv CG 5
References
Abidin, H.Z., Andreas, H., Gamal M., Djaja, R., Subarya, C., Hirose, K., Maruyama, Y., Murdohardono,
D., & Rajiyowiryono, H. (2005). Monitoring land subsidence of Jakarta (Indonesia) using leveling,
GPS survey and InSAR techniques. Retrieved from http://www.springerlink.com/content/
l36836464m5283jh/fulltext.pdf
SWUP
Supriyadi, W. Hardyanto, A. Setyawan
SC.135
Akasaka, C., & Nakanishi, S. (2000). An evaluation of the background noise for microgravity monitoring
in the Oguni field, Japan. Proceedings of 25th Stanford Geothermal Workshop, 24 – 26 January
2000.
Allis, R.G., & Hunt, T.M. (1986). Analysis of exploration induced gravity changes at Wairakei
geothermal field. Geophysics, 51, 1647–1660.
Andres, R.B.S., & Pedersen, J.R. (1993). Monitoring the bulalo geothermal reservoir, Philippines, using
precision gravity data. Geothermics, 22(5/6), 395–402.
Eiken, O., Zumberge, M., & Sasagawa, G. (2000). Gravity monitoring of offshore gas reservoir. SEG
Expanded Abstract, 19, 431.
Galderen, V.M., Haagmans, R., & Bilker, M. (1999). Gravity changes and natural gas extraction in
Groningen. Geophysical Prospecting, 47, 979–993.
Holdahl, S.R., & Zilkoski, D.B. (1991). Subsidence at Houston, Texas 1973–1989. Proceedings of The
Fourth International Symposium on Land Subsidence, May 1991, IAHS Publ.200, 3–14.
Kamah, M.Y., Negara, C., Pulungan, I., & Budiardjo (2001). Application of microgravity method on
monitoring geothermal reservoir changes during production of steam in the Kamojang
geothermal field, West Java Indonesia. 5th SEGJ International Symposium – Imaging Technology,
Tokyo, Japan, 24-26 January 2001.
Mariita, N.O. (2000). Application of precision gravity measurement to reservoir monitoring of Olkaria
geothermal field, Kenya. Proceedings World Geothermal Congress 2000, Kyushu – Tohoku, Japan,
May 28–Jun 10, 2000.
Marsudi (2000). Prediksi laju amblesan Tanah di dataran alluvial Semarang – Jawa Tengah
(unpublished dissertation), Institut Teknologi Bandung.
Nishijima, J., Fujimitsu, Y., Ehara, S., & Yamauchi, M.(2005). Microgravity monitoring and repeated GPS
survey at Hatchobaru geothermal field, Central Kyushu, Japan. Proceeding World Geothermal
Congress 2005.
Santos, M., Gemael, C., Blake, B., Faggion, P., Krueger, C.P., Ferreira, L.D.D., Soares, M., & Chrzanowski,
S. (2002). Stage 1 of subsidence monitoring of the area surrounding Salto Caxias Power Dam in
Brazil. Proceedings The 10th FIG International Symposium on Deformation Measurement, 19–22
March Orange, California, USA.
Sutanto, H. (2002). Spatial modelling of land subsidence and sea level rise in a coastal urban setting,
case study: Semarang, Central Java, Indonesia (Unpublished Master’s Thesis). International
Institute for Geo-information Science and Earth Observation (ITC), the Netherlands.
Wahyudi (1999). Evaluation an analysis of land subsidence iin Tanjung Emas Harbour are in Semarang.
Proceedings of sixth. AEESEAP Triennial conference, Kuta Bali, August, 23–25.
SWUP
SC.130
ISBN: 978-602-1047-21-7
Chance of time lapse microgravity method survey
for subsidence monitoring
Supriyadi†a, Wahyu Hardyantoa, Agus Setyawanb
a
Universitas Negeri Semarang, Sekaran Gunungpati, Semarang 50229, Indonesia
b
Universitas Diponegoro, Tembalang, Semarang 50239, Indonesia
Abstract
Times lapse microgravity method is a development method style. Technically that is
developing is looping gravity measurements at the same point by a certain time interval,
usually taking the measurements performed in the dry season and rainy season. Based
on mathematical modeling is known that micro-gravity anomaly between the time
rooted in subsidence and subsurface density changes associated with the dynamics of
groundwater and pollution due to human activities, seawater intrusion. This fact can be
observed by means of looping gravity by using Gravimeter with precision μGal.
Gravimeter with the use of precision is necessary given the gravity anomaly due to
pollution (seawater intrusion) small. Modeling of micro gravity anomaly between the
time due to sea water intrusion by using software Grav3D The results showed that
during the period of September 2002, November 2005, and October 2013 showed that
a large subsidence that occurred in Semarang, especially in the port of Tanjung Mas and
surrounding 16 cm/year.
Keywords microgravity, time lapse, anomaly, μGal
1.
Introduction
Gravity method is one of the oldest methods in geophysics, but its application to the
source of the anomaly near the surface and are connected with the environment has not
been as intensive as the application for geodynamics studies or exploration in the estimation
of the geological structure is relatively large. This is caused by the level of accuracy is still in
order mGal anomaly or 103 μGal. In terms of tools gravimeter, 10 μGal accuracy has been
achieved in early 1970, but the accuracy of readings is totally dependent on the accuracy of
the operator because the gravimeter still use mechanical reading device.
Time lapse Microgravity method is the development of the gravity method with the
fourth dimension is time. The principle of the method is the measurement of repeated gravity
either daily, weekly, monthly or yearly using a rigorous Gravimeter in order μGal and
elevation measurements carefully (Allis and Hunt, 1986). Any changes or differences in the
results of the gravity observations in the first period to the next period is called the anomaly
microgravity. Observation of gravity changes can be caused by the dynamics around point
very, such as changes in the depth of groundwater levels and soil subsidence.
An increase in accuracy gravimeter and the development of digital systems, the
application of gravity methods to source anomalies near the surface and are connected with
the environment and for the purpose of monitoring is increasingly used, including for
†
Corresponding author. Tel.: + 62 085 226 233 319; E-mail address: pryfis@yahoo.com
SWUP
Supriyadi, W. Hardyanto, A. Setyawan
SC.131
monitoring geothermal reservoirs, oil and gas (Allis & Hunt, 1986; Andres & Pedersen , 1993;
Kamah et al., 2001; Galderen et al., 1999; Eiken et al., 2000; Akasaka & Nakanishi, 2000;
Mariita, 2000; Nishijima, et al., 2005).
The case study of subsidence in Semarang has been done by previous researchers, such
as by Marsudi (1996) have predict subsidence due to a decrease in ground water level using
a one-dimensional consolidation. Muhrozi et al., (1996) identify subsidence in Semarang
northern research subsidence in many countries is that the more subsidence research
conducted by the method Sipat Datar, including in Houston Texas 1973–1987 (Holdahl &
Zilkoski, 1991), Flat Sipat method. Wahyudi (1999) Evaluation and Analysis of subsidence in
the port of Tanjung Mas Semarang, and Sutanto (2002) with GPS (Global Positioning System)
large measure subsidence in Semarang, it appears that the studies that have been conducted
using the approach of geology and geodesy.
Research subsidence by using GPS, for example in Western Venezuela (Chrzanowski et
al., 1991). Monitoring of subsidence in Salto Caxias Brazil by Santos et al., (2001). In addition,
Abidin et al., (2005) using methods Leveling, GPS and techniques INSAR (Interferometric
Synthetic Aperture Radar) to monitor subsidence in Jakarta. Based on the research that has
been done is given the opportunity to perform subsidence measurements using other
methods, one of which is a method of microgravity across time. This method has advantages
compared with the method that has been done, for example, enables the measurement of
the distribution of the measuring point more and a relatively short time for the measurement
period.
2. Materials and methods
Time lapse microgravity anomaly the difference in value between the time of each
measurement point Bouguer anomaly at specific time intervals as follows.
∆g ( x, y, z , ∆t ) = ∆g ( x, y, z , t 2 ) − ∆g ( x, y, z , t1 )
(1)
If the very point elevation changes at two of the measurement period, then Eq. (1) can be
written as
∆g ( x, y, z , ∆t ) = ( g obs ( 2) − g obs (1) ) − ( g (ϕ 2 ) − g (ϕ1) ) − (c1 + c 2 ρ )(h2 − h1 ) + c3 ( ∆h2 − ∆h 1 ) . (2)
During interval measurements on t1 and t2 so relatively fixed position point, where ϕ1 = ϕ2,
then Eq. (2) can be simplified to
(3)
∆g ( x, y, z, ∆t ) = ( g obs ( 2) − g 0bs (1) ) − (c1 + c 2 ρ )(h2 − h1 ) + c3 (∆h2 − ∆h1 )
(4)
( g obs ( 2) − g obs (1) ) = ∆g ( x, y, z , ∆t ) + (c1 + c 2 ρ )(h2 − h1 ) − c3 (∆h2 − ∆h1 )
Kadir (1999) states that for 3-dimensional objects with mass density distribution, time lapse
microgravity at the point P (x, y, z) on the surface is expressed by the following equation.
∞ ∞ ∞
∆ρ (α , β , γ , ∆t )( z − γ )
(5)
∆g ( x, y , z , ∆t ) = G
dα dβ dγ
∫ ∫ ∫ [( x − α )
0 − ∞− ∞
2
+ ( y − β )2 + (z − γ )2
]
3/ 2
From Eqs. (4) and (5), we obtain
∞∞∞
∆ρ (α , β , γ , ∆t )( z − γ )
( g obs ( 2) − g obs (1) ) = G ∫ ∫ ∫
dα dβ dγ +
3
/
2
0 − ∞− ∞ ( x − α ) 2 + ( y − β ) 2 + ( z − γ ) 2
(6)
(c1 + c 2 ρ )(h2 − h1 ) − c3 (∆h2 − ∆h1 )
Based on mathematical modeling and simulation of synthetic data show that the effect
of topography does not affect the time lapse microgravity anomalies. Time lapse microgravity
anomaly is affected by changes in elevation (subsidence) very point. Consolidation is causing
[
SWUP
]
Chance of time lapse microgravity method survey for subsidence monitoring
SC.132
subsidence did not cause the soil mass lost so Bouguer correction is not performed. Thus Eq.
(6) can be simplified to
∞∞∞
∆ρ (α , β , γ , ∆t )( z − γ )
( g obs ( 2 ) − g obs (1) ) = G ∫ ∫ ∫
0 −∞−∞ ( x − α ) 2 + ( y − β ) 2 + ( z − γ ) 2
[
]
3/ 2
dαdβ dγ + c1 ( h2 − h1 ) .
(7)
Eq. (7) shows that the difference between the value of the gravity measurement results
caused by changes in the subsurface density associated with groundwater level changes and
subsidence.
For survey purposes based on subsidence, the source of the anomaly associated with
changes in the depth of the ground water level must be reduced. For the purposes of the
reduction can be done in two ways, namely (1) using a specially designed filter adapted to
the conditions in the field, and (2) using real data the results of measurements in the field.
Especially for (2) in Semarang is not available the data in question. This is due to the
measurement of changes in the depth of the ground water level was done continuously for
a certain period. To overcome these problems, in this study used a filet MBF (Model Based
Filter)
As the study used data from gravity measurements in Semarang September 2002, June
2003, December 2003, June 2004, February 2005, November 2005, in May 20012, October
2012, May 2013, and October 2013 by using gravimeter Scintrex Autograv CG 5 at 110 points
scattered in Semarang below.
3. Results and discussion
In accordance with the above theory, obtained micro gravity anomaly between the
time the initial condition September 2002. Data in the period September 2012 into the data
a deduction from the next period to obtain a micro-gravity anomaly over time. Furthermore,
this anomaly data corrected by the data reduction in groundwater that occur during periods
of measurements to obtain a micro-gravity anomaly between the time due to subsidence.
Examples of measurement results period September 2002, November 2005, and October
2013 hereinafter in qualitative analysis with software surfer to get subsidence contour map
(see Figure 1).
In general, the value of gravity during the measurement period in Semarang
(September 2002, November 2005, and October 2013) indicates that the value of gravity in
the northern part is greater than in the south. Results resulting in the northern part of
Semarang is lowlands and southern highlands and in accordance with the theory that the
value of gravity at a point depends on elevation, where the higher of the surface gravity value
decreases and vice versa.
Based on the gravity of each subsequent period calculated micro gravity anomaly
between the time that represents the difference between the gravity of the period
November 2005 to September 2002 and the period October 2013 to September 2002.
Contour micro gravity anomaly between the time as in Figure (2). In the period between the
time (September 2002–November 2005) and (September 2002–October 2013) showed three
anomalies, namely the positive anomalies that indicate an increase in groundwater levels
and subsidence, negative anomalies that indicate a decrease in ground water level, and zero
indicates no there is a change.
Time lapse microgravity anomaly value according to the Eq. (7) consists of two sources,
namely subsidence and changes in the subsurface density associated with groundwater level
changes. To obtain the source of the anomaly due to subsidence, the other anomaly sources
SWUP
Supriyadi, W. Hardyanto, A. Setyawan
SC.133
must be reduced by using MBF (Model Based Filter) a filter that was built for that purpose.
Time lapse microgravity anomaly (see Figure 3(a)). Furthermore, value of this anomaly value
is converted to the value of subsidence. Contour subsidence based micro gravity anomaly
data across time as in Figure 3(b).
(a)
(b)
(c)
Figure 1. Gravity contour for each measurement period, (a) September 2002, November 2005,
and (c) October 2013.
(a)
(b)
Figure 2. Time lapse microgravity anomaly, (a) September 2002–November 2005, (b)
September 2002–October 2013.
SWUP
Chance of time lapse microgravity method survey for subsidence monitoring
SC.134
(a)
(b)
Figure 3. (a) Time lapse microgravity anomaly due to subsidence, (b) and subsidence
that occurred during the measurement period based on time lapse microgravity
anomaly.
In that period the subsidence that occurred in North Semarang growing which is 20 to
48 cm in some places, for example: the port of Tanjung Mas, Marina beach area, PRPP,
housing Puri Anjasmoro, Lor village Stage and Stage Kidul, Terboyo Kulon, Terboyo Wetan,
and housing Tanah Mas. Kaligawe area, Mlatiharjo, Simpang Lima, Miroto, Gabahan, Jagalan,
Kauman, Bangunharjo, Karangturi, Pendrikan, Mugas, Pleburan, Lempongsari, Gayamsari,
relative Pedurungan not experienced subsidence compared to the previous period. The new
zone of subsidence that appeared in the previous period coverage is more widespread.
Area of subsidence that occurred north Semarang more dominant layer of soil
compaction caused by naturally. This is attributed to the fact that the layer of soil in the
region is the result of sedimentation and human activity in the form of reclamation.
4. Conclusion and remarks
Time Lapse Microgravity methods can be used for monitoring subsidence. For this
purpose, the data processing time lapse micro gravity anomaly must be corrected with the
data of decreased water level. For the purposes of correction can be done by using a MBF
(Model Based Filter) or by the results of measurements in wells monitored in the study site.
For example, a case study in Semarang which indicates that the maximum subsidence during
the period 16 cm/year occurred in Tanjung Mas port and its surroundings.
Acknowledgment
Thank To DP2M-DIKTI which funded this research through grants Hibah Pascasarjana (2002,
2003, 2004, 2005) and Hibah Kompetensi (2012, 2013). Thanks to the support BMKG Jakarta
for gravimeter Scintrex Autograv CG 5
References
Abidin, H.Z., Andreas, H., Gamal M., Djaja, R., Subarya, C., Hirose, K., Maruyama, Y., Murdohardono,
D., & Rajiyowiryono, H. (2005). Monitoring land subsidence of Jakarta (Indonesia) using leveling,
GPS survey and InSAR techniques. Retrieved from http://www.springerlink.com/content/
l36836464m5283jh/fulltext.pdf
SWUP
Supriyadi, W. Hardyanto, A. Setyawan
SC.135
Akasaka, C., & Nakanishi, S. (2000). An evaluation of the background noise for microgravity monitoring
in the Oguni field, Japan. Proceedings of 25th Stanford Geothermal Workshop, 24 – 26 January
2000.
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