- Email: [email protected]
Determination of mantle upwelling rate beneath Taiyuan basin by using absolute gravity, GPS, groundwater and GLDAS data
Determination of mantle upwelling rate beneath Taiyuan basin by using absolute gravity, GPS, groundwater and GLDAS data Lelin Xing, Linhai Wang, Minzhang Hu PII: DOI: Reference:
S0926-9851(17)30093-9 doi:10.1016/j.jappgeo.2017.01.026 APPGEO 3196
To appear in:
Journal of Applied Geophysics
Received date: Revised date: Accepted date:
15 January 2016 6 January 2017 20 January 2017
Please cite this article as: Xing, Lelin, Wang, Linhai, Hu, Minzhang, Determination of mantle upwelling rate beneath Taiyuan basin by using absolute gravity, GPS, groundwater and GLDAS data, Journal of Applied Geophysics (2017), doi:10.1016/j.jappgeo.2017.01.026
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Determination of mantle upwelling rate beneath Taiyuan basin by using absolute gravity, GPS, groundwater and GLDAS data
D
MA
NU
SC R
IP
T
Lelin Xing, Linhai Wang, Minzhang Hu Key Laboratory of Earthquake Geodesy, Institute of Seismology, China Earthquake Administration, Wuhan 430071, China Abstract: The taiyuan basin is in the Shanxi rift system of China. Results of tectonic studies indicate that the Moho is uplifted by 2-3 km under the Taiyuan basin. However, there is no quantitative evidence shows whether the rift is still in the status of mantle upwelling. Herein, we estimated mantle upwelling rate of Taiyuan basin by using absolute gravity, GPS , groundwater and GLDAS data in this paper. In order to utilize the absolute gravity measurements in terms of tectonic study it is necessary to reduce all disturbing environmental effects. Many of those can be modeled, such as tide, polar motion, ocean tidal loading and atmospheric mass components. The Taiyuan station located in the Taiyuan basin, and absolute gravity measurements with a FG5 instrument were performed from 2009 to 2014, a secular trend was obtained. In-situ GPS data was used to estimate the vertical motion rate since 2011, and the result indicated a land subsidence. In-situ groundwater level was collected with daily surveys from 2009 to 2015, and local hydrology impact on effect was made. The global terrestrial water storage loading effect on gravity at Taiyuan station was computed by using GLDAS global hydrology model. Furthermore there is a good agreement between GRACE results and GLDAS hydrological model results. Subtracting the gravity change rate attributable to the land subsidence, groundwater level and global hydrology from the absolute gravity change
CE P
TE
rate, the residual gravity change rate was obtained. It reflects mantle upwelling about 2.1 2.6 cm/yr beneath Taiyuan basin. Keywords: Absolute gravimetry, Gravity variations, Gravity change rate, Hydrological model, Groundwater
1. Introduction
AC
Temporal gravimetry is an efficient tool to monitor mass transfer, such as those implied by crustal uplifting and crustal thickening (Sun et al. 2009), volcanic reservoir charge (Battaglia et al. 2004), ground water movements (Longuevergne et al., 2010; Jacob et al. 2010),. The physical principle is that changes in the gravity value are due to changes in mass distribution and vertical displacement. As every geodetic quantity, gravity vatiations integrate different processes. The challenge therefore relies in separating the contribution of each process in the measured signal. The method of removing unwanted signals is to model each source individually: Earthtide, airpressure changes, polar motion, global and local hydrology, and others. What remain are residuals, typically the focus of a particular study. Absolute gravimeters reached a precision about of 2.0μGal (Niebauer et al., 1995). The feature makes AG the very important tool in geophysical and geodynamics studies. The impact of environmental effects on gravity measurements is needed to be took into account. Tainyuan basin is in the central part of the Shanxi Rift system which located in the east margin of the Ordos block. It is well known for its intense neotectonics and strong earthquakes, standing between longitudes 111.5º-113ºE and latitude 37º-38ºN, is a typical Cenozoic fault basin and bounded by two major faults named Jiaocheng and Taigu located on the northwest and southeast, as showed in Fig.1. The two faults are formed by a series of NE-striking high-angle normal faults which control the formation and development of the basin (Guo et al., 2007). GPS, leveling and SAR measurements indicate the land extent and subsidence in the Taiyuan basin (Wang et al., 2001; Ma et al., 2006; Zhu et al., 2013). Evolution of the Shanxi Rift system of northern China is thought to have been governed by regional stress fields which
ACCEPTED MANUSCRIPT
TE
D
MA
NU
SC R
IP
T
developed in conjunction with the collisional interaction of the Indian and Eurasian plates. The most likely mechanism for explaining rifting is flexural bending of the lithosphere due to an isostatic load resulting from necking of the lithosphere. The lower part of the crust is plastically attenuated, and faults are formed only in the upper layer of the crust. The Cenozoic mantle upwelling might control the formation and evolution of the Shanxi rift (Xu et al.,1992).
Fig.1. Topography and tectonic sketch maps of study region. The Taiyuan station is marked as black circle. The purple lines are
CE P
active faults. The red circle denotes the gravity profile.
AC
Slant-stacking and migration images of receiver functions reveal uplift about 4-6km of the Moho in the Shanxi rift. The Moho is uplifted by 2-3 km under the Taiyuan basin (Tang et al.,2010). The Taiyuan basin region might have experienced mantle upwelling since the Cenozoic time. The hot mantle heated the upper mantle and the crust, which caused the large-scale mid and lower crust slow velocity and negative gravity anomaly (Guo et al., 2015). The Bouguer gravity anomaly of the profile used here, derived from the EGM2008 spherical harmonic coefficients(Pavlis et al., 2012), were downloaded from the webpage of BGI(http://big.omp.obs-mip.fr). The gravity profile, given in Fig.2, crosses the Taiyuan basin in the Shanxi rift. The sourtheast-ward positive gravity trend is about 0.2mGal/km. Broad residual positive anomalies are associated with the Luliangshan uplift and Taihangshan uplift. A sharp negative anomaly in the Taiyuan basin reveals the thinning of the lithosperic plate and upward expansion of the asthenosphere.
ACCEPTED MANUSCRIPT Fig.2. Bouguer and topographic profiles crossing the Taiyuan basin and extending across the Shanxi rift.
MA
2. Absolute gravity measurements
NU
SC R
IP
T
For the interpretation of the gravity profile, we can use modern geodesy method to determine the upward expansion of Moho surface/mantle upwelling in quantity, and this is the primary goal of this paper. A research project was undertaken from 2009 by China Earthquake Administration. The project, including one absolute gravity station performed every year from 2009 to 2015, with in-situ continuous GPS and groundwater level measurements. This study presents geodetic evidence of the decreasing crustal thickness by gravity observation at the Taiyuan station: a gravity change can reflect material transport accompanying vertical movements at the surface and on the crustal bottom. The vertical displacement, local and global hydrology changes add additional gravity changes at the surface to isolate the signal from mass change. As the bottom of crust is uplifting, the mass beneath the station is increasing because crust is displaced by mantle, causing a reduction in gravity. In-situ continuous GPS and groundwater measurements reveal land subsidence and rise of groundwater level, and a positive absolute gravity change rate is shown. Removing the contribution of surface vertical displacement and hydrology, including groundwater and terrestrial water storage, residual gravity change rate reflects the interior mass distribution.
AC
CE P
TE
D
Each absolute gravity measurement was performed by using the FG5-232 gravimeter. Each survey consisted of 25 hours of repeated measurements. Each measurement included 25 sets, and each set included 100 free-fall drops. A single drop was made at interval of 10 S. In total, 2500 drops were collected. To minimize computational biases, a common processing scheme for the data analysis has been adopted, ensuring consistency with respect to model and setup parameters. All raw gravity observations were reprocessed using the g9 software (Micro-g LaCoste, 2012). Some physical corrections were made to compensate for tide, polar motion, ocean tidal loading and atmospheric mass components. Vertical transfer of the measured gravity value was done using the vertical gravity gradient, which was determined by using two CG-5 relative gravimeters at least six return measurements. All absolute gravity observations in this work are given at a reference height of 130cm, close to a point where the influence of the gradient uncertainty on the FG5 is almost zero (Timmen, 2010). The absolute gravity values were listed in Table 1. The standard deviation of the final gravity sets is less than 3.0 μGal. The time series of the absolute gravity value is depicted in Fig.3. The result shows an obvious positive gravity change rate. For the trend calculation, a least squares adjustment was performed assigning equal weights to the epoch results. The gravity change rate inferred from absolute gravity time-series for the site Taiyuan is 10.05 0.87 μGal/yr. The standard deviation following the gravity rate of change number indicates one sigma level, with reliability of 67%. For the effect of hydrology on the observed gravity value is not treated in g9 when processing absolute gravity data, having reduced the gravity value for the time-variable tidal, polar motion, and atmospheric mass components, it may remain strongly influenced by hydrological variations (Mikolaj et al.,2015). So, the linear gravity change rate reveals the physical processes underlying crustal deformation and mass distribution. In order to obtain the residual gravity change rate related with mantle upwelling, the contributions of hydrology and vertical displacement should be eliminated from the absolute gravity change rate. Table 1 Compilation of gravity values as measured with the FG5 gravimeter at the Taiyuan station. Date(mean)
sets
g-value(Gal)
Set scatter(Gal)
21.05.2009
25
979659021.2
1.6
01.11.2009
25
979659023.2
2.8
ACCEPTED MANUSCRIPT 25
979659028.0
0.9
03.09.2010
25
979659330.0
0.7
28.04.2011
25
979659342.3
0.8
17.10.2011
25
979659334.0
1.1
01.05.2012
25
979659333.2
1.0
07.08.2013
25
979659349.7
0.7
27.09.2013
25
979659370.9
17.07.2014
25
979659369.1
26.10.2014
25
979659366.4
1.1
15.04.2015
25
979659376.6
1.0
14.09.2015
25
979659375.4
1.6
IP
T
28.07.2010
0.9
MA
NU
SC R
2.3
D
Fig.3. Gravity variations at the Taiyuan station as obtained with the FG5 gravimeter since 2009.
3. GPS measurements
AC
CE P
TE
The continuous GPS data were used to estimate the vertical motion rate at Taiyuan station. The gravity station is located near the GPS station. The GPS data were processed using the GIPSY software to remove phase and pseudorange data (http://www.cgps.ac.cn/index.action). The vertical motion rate, derived by fitting displacement of the entire observed period is -8.50±0.59 mm/yr, is depicted in Fig.4.
Fig.4. Time series of daily solution of vertical displacements at the Taiyuan station from continuous GPS recording. The red line is linear fit to the time series.
Here we used the Bouguer model for correcting the effect of elevation change (Ekman et al., 1996), the gravity change rate g z is given by
g z 2g / a hz 2 Gc hz 0.19 hz Gal / yr (1) where G is the gravitational constant, g is the gravitational acceleration, hz is the vertical motion rate, a is the radius of the Earth and c is the density of crust. The gravity change rate of 1.62 ± 0.11μGal /yr due to elevation change is computed which is
ACCEPTED MANUSCRIPT consistent with the increasing trend monitored by absolute gravity measurements.
4. Groundwater measurements
MA
NU
SC R
IP
T
The level of the water table beneath the Taiyuan station is monitored by a water gauge in a well. Water level was collected with daily surveys from 2009 to 2015. The water level change rate, estimated by fitting level of the entire observed period is 1.82±0.03 m/yr, is depicted in Fig.5. Long-term trends in water level at the Taiyuan station highlight a local rise of the water table during the period 2009-2015. The water level records of absolute gravity measurement time series were also selected, and the change rate is 1.82±0.03 m/yr. The trend is consistent with the daily solution, but with a larger accuracy.
Fig.5. Groundwater level records at the Taiyuan station. Black line is the linear fit for daily level, and blue dash line for AG measurements time series.
D
A change in gravity is related to a change in mass, which is attributed to the change in the volume of water occupying pore space in the unconfined aquifer and can be calculated by(Jacob et al., 2008)
TE
gw =2 GPe hw 42Pe hw Gal / yr (2)
CE P
in which Pe is effective porosity.
AC
Although we didn’t make an experiment to determine the porosity of rocks beneath Taiyuan station, we know exactly the composition of the rocks based on the arrangement of borehole data, the typical porosity of 0.1 for the aquifer in the study area (Guo, 2005; Chen et al., 2011). Due to the change of groundwater level is the main effect for gravity change, the porosity can be estimated. The porosity Pe g / (42* hw ) is 0.11 ±0.02 with considering the vertical motion effect. Hence, the gravity change
rate due to groundwater table change is 8.010.09 μGal/yr. The trend of gravity variation due to water level change is consistent with the increasing trend monitored by absolute gravity measurements.
5. Global Hydrology effects 5.1 GLDAS model As discussed by Llubes et al. (2004), the gravity variations due to hydrology can be separated into two major scales: local and regional. The local scale is dominated by the Newtonian attraction of the underlying water masses. At the regional scale, surface and shallow water induces a global elastic deformation of the Earth which has an effect on the gravity field through both mass redistribution and vertical movement. For the computation of the global hydrology effect, we used the Global Land Data Assimilation System (GLDAS) NOAH hydrological data (Rodell et al., 2004). The GLDAS/NOAH described global soil moisture (0-10cm, 10-40cm, 4—100cm, and 100-200cm) and snow (snow water equivalent) content variations and has a 0.25 grid and daily temporal sampling; hence, it does not consider groundwater. The regional effect was obtained by considering the effects of loading and of Newtonian attraction at distances greater than 0.25 for convolution between the surface mass distribution and the Green’s functions.
ACCEPTED MANUSCRIPT
TE
D
MA
NU
SC R
IP
T
Water within 0.25 has a dominantly Newtonian effect, we multiplied the local value of the soil moisture by the coefficient -4.2μGal/cm due to the absolute gravity station is below the ground only about 12m. The equivalent water heights at Taiyuan station were extracted from hydrological models by bilinear interpolation in terms of the four nearby grid values (Mikolaj et al.,2016). The water loading effect on gravity at Taiyuan station was computed by using GLDAS global hydrology model by mGlobal (Mikolaj et al.,2016), as showed in Fig.6. The modeled gravity changes due to continental water storage can reach as much as a 3-4 μGals of peak-to-peak amplitude. The gravity change rate is about -0.30±0.06 μGal/yr, which reveals the decreasing of the equivalent water height in this regional area.
Fig.6. The time series of global hydrology effects on gravity for the Taiyuan station.
GM R2
60
l
W l 2 m0
lm
(l +1-
2hl' )(Clm cos(m ) Slm sin(m ))Plm (cos ) (3) 1 kl'
AC
g s ( R, , )
CE P
5.2 GRACE results The gravity change on the Earth’s surface can be derived from GRACE products according to (Zhou et al., 2009; Van Camp et al., 2014)
where M is the mass of the Earth, Clm and Slm are the fully normalized spherical harmonic coefficients, and are co-latitude and longitude, R is Earth’s radius, Plm (cos ) is the fully normalized associated Legendre function,
l
and m are, the harmonic degree and order,
respectively. hl and kl are the load Love numbers of degree l for vertical displacement and potential, respectively. Due to the large errors filter in the high-degree Stokes coefficients provided by GRACE products, a filter is usually applied, for example Gaussian filter (Whar, et al., 1998), to obtain a reliable result. For the space-based gravimetry, we used RL05 monthly data released by CSR (Bettadpur, 2007) and applied the 350 km fan filter(Zhang et al., 2009). The gravity change due to global hydrology effect at Taiyuan station was computed according to Eq.(3). The water loading effect on monthly gravity change was also computed by using the GLDAS hydrological model for comparison. From Fig.7, the hydrological-effect-induced seasonal variations is also obvious, the peak-to-peak amplitude is about 3 μGal, and the gravity change rate is about -0.28±0.07 μGal/yr from GRACE. Furthermore there is a good agreement between GRACE and GLDAS in amplitude,
ACCEPTED MANUSCRIPT
MA
NU
SC R
IP
T
but not in phase. The GLDAS hydrological model has spatial resolutions of 0.25°×0.25°, which means that the water distribution at Taiyuan station is averaged in a grid with a certain size of 28km×22km. Similary, the gravity change from GRACE is smoothed with a radius of 350km. As a result, both GRACE and GLDAS hydrological models give a spatial mean of the regional water storage changes. This may be the reason why the gravity change rate of GRACE agrees well with the GLDAS hydrological model.
D
Fig.7. Comparison of gravity changes derived from GRACE and GLDAS hydrological model. The blue circles show the gravity change derived from GRACE; the purple circles show the water loading effect on gravity derived from GLDAS.
TE
6. Residual gravity change rate and mantle upwelling The observed gravity change rate g1 of 10.05 0.87 μGal/yr at the Taiyuan station described
CE P
above is presented in Table 1. The gravity change rate is obtained on the deformed earth surface which can be decomposed into two contributions associated with crustal vertical displacement and internal mass change. To obtain the bottom of crust deformation, we must separately to interpret the gravity changes. We first eliminate the contribution from the surface movement as determined by continuous GPS, and the
AC
Bouguer gradient of -1.9 μGal/cm must be used based on the local crustal density 2.7 2.9 g / cm3 . Multiplying the Bouguer gradient by the corresponding land subsidence inferred from GPS measurements as shown in Fig.4, we obtained the Bouguer gravity change rate g 2 is 1.62 ± 0.11μGal /yr. For the contribution of the local groundwater level change, we linked gravity variations using an infinite slab hypothesis shown in Eq.(2). The groundwater change rate of 1.82±0.02 m/yr induces a gravity change rate
g3 of about 8.010.09 μGal/yr. The water loading effect on gravity at Taiyuan station was also computed by using GLDAS global hydrology model, and the associated gravity change rate g 4 is about
-0.30
0.06 μGal/yr. Subtracting the gravity change rate attributable to the land subsidence, groundwater level and global hydrology from the observed gravity change rate, i.e., g5 g1 g2 g3 g4 , the residual gravity change rate is 0.72 0.88 μGal/yr as listed in Table 2. The positive gravity change suggests that the mass under the Taiyuan station is increasing gradually coincide with the mantle upwelling, as presented in Fig.8.
ACCEPTED MANUSCRIPT With density contrast of 0.8 0.2 g / cm3 between crustal and mantle(Chen et al.,2004), the gravity change related to this Bouguer layer can be expressed simply as 2 G h 0.72 μGal. The crustal
Table2 Gravity change rates at the Taiyuan station
g2
g3
10.05 0.87
1.62 ± 0.11
8.010.09
g4
g5
-0.300.06
0.720.88
AC
CE P
TE
D
MA
NU
g1
SC R
IP
T
thinning rate is inferred as 2.1 2.6 cm/yr , i.e., the change rate of the crustal expansion upword or mantle upwelling from -0.5 to 4.7 cm/yr with a reliability of 67%. Compared to the mean surface land subsidence of -8.5 mm/yr, as determined by GPS, the 2.1 cm/yr of mantle upwelling on the Moho surface seems reasonable in light of the mean elevation of 1.0 km of the Taiyuan basin and the crustal thickness of 35 km below it (Tang et al., 2010).
Fig.8 The mechanism of land subsidence and mantle upwelling for Taiyuan basin inferred from absolute gravity, GPS, groundwater and GLDAS data.
7. Conclusions The aim of this paper was to determine the change rate of mantle upwelling quantitatively by using absolute gravity, GPS and groundwater level data at Taiyuan station. To successfully eliminate the impact of water mass variation on gravity measurements, it is necessary to monitor local groundwater level change combined with global hydrology models. The absolute gravity change rate of 10.05 0.87 μGal/yr reflects the vertical movement and mass distribution. To analyze the deep mass transfer, we used in-situ GPS, groundwater level data to eliminate the vertical movement and local hydrology effects on gravity change rate. The contributions of vertical movement, groundwater level and global hydrology effect are 1.62 ± 0.11μGal /yr, 8.010.09 μGal/yr and -0.30 0.06 μGal/yr. Subtracting the gravity change rate attributable to the land subsidence, groundwater level and global
ACCEPTED MANUSCRIPT hydrology from the observed gravity change rate, the residual gravity change rate is about 0.72 0.88 μGal/yr. It reflects mantle upwelling about 2.1 2.6 cm/yr beneath Taiyuan basin.
AC
CE P
TE
D
MA
NU
SC R
IP
T
Acknowledgements We are grateful to the editor and the two reviewers for their constructive comments and suggestions, which helped to improve the manuscript significantly. This work was financially supported by the Key Foundation of Institute of Seismology, China Earthquake Administration (Grant No. IS201326130) and the “973” project (Grant No. 2013CB733304). References Battaglia, M., Segall, P.,2004. The interpretation of gravity changes and crustal deformation in active volcanic areas. Pure appl. Geophys. 161,1453-1467. Bettadpur, S., 2007. UTCSR Level-2 gravity field product user handbook. GRACE 327-734 Rep.Center for Space Research, The University of Texas at Austin, Austin. Chen, Y.L., Li, Z.F., Qin, Y., 2011. The mechanism of secondary porosity in Taiyuan sandstone, at Shuangshan Region, Ordos basin. Coal Geology and Exporation,39(1),11-15(in Chinese). Ekman, M., Makinen, J., 1996. Recent postglacial reboud, gravity change and mantle flow in Fennoscandia. Geophys.J.Int.,126, 229-234. Guo, Q.H., Wang, Y.X., Ma, T., Ma, R.,2007. Geochemical processes controlling the elevated fluoride concentrations in groundwater of the Taiyuan Basin, Northern China. J. Geochem. Explor. 93(1),1-12. Guo, Q.H.,2009. Groundwater system evolution and genesis of relevant environmental problems: a case study at Taiyuan basin, Shanxi Province, China (PhD thesis), China University of Geosciences, Wuhan(in Chinese). Guo, Z., Chen, Y.S., Yin, W.W., 2015. Three-dimensional crustal model of Shanxi gaben from 3D joint inversion of ambient noise surface wave and Bouguer gravity anomalies. Chin. J. Geophysics.(in Chinese),58(3),821-831. Jacob, T., Bayer, R., Chery, J., Jourde, H., Le Moigne, N., Boy, J., Hinder, J., Luck, B., Brunet, P., 2008. Absolute gravity monitoring of water storage variation in a karst aquifer on the larzac plateau(Southern France). J. Hydrol.359,105-117. Jacob, T., Bayer, R., Chery, J., Moigne, N., 2010. Time-lapse microgravity surveys reveal water storage heterogeneity of a karst aquifer. J. Geophys. Res. 115, B06402. Llubes, M., Florsch, N., Hinderer, J., Longuevergne, L., Amalvict, M., 2004. Local hydrology, the Global Geodynamics Project and CHAMP/GRACE perspective: some case studies. J. Geodyn. 38:355-374. Longuevergne, L., Scanlon, B.R., Wilson, C.R., 2010. GRACE hydrological estimates for small basins: evaluating processing approaches on the high plains aquifer, USA. Water Resour. Res. 46,W11517. Ma, R., Wang, Y.X., Ma, T., Sun, Z.Y., Yan, S.L., 2006. The effect of stratigraphic het-erogeneity on areal distribution of land subsidence at Taiyuan, Northern China. Env. Geol. 50, 551–586. Micro-g LaCoste, 2012. g9 user’s manual, April 2012 version. Micro-g LaCoste, Lafavette, Colorado, USA. Mikolaj, M., Meurers, B., Guntner, A.,2016. Modelling of global mass effects in hydrology, atmosphere and oceans on surface gravity. Comp. Geosci.93,12-20. Mikolaj, M., Meurers, B., Mojzes, M.,2015. The reduction of hydrology-induced gravity variations at sites with insufficient hydrological instrumentation. Stud. Geophys. Geod.59(3),424-437. Niebauer, T.M., Sasagawa, G.S., Faller, J.E., Hilt, R., Klopping, F., 1995. A new generation of absolute gravimeter. Metrologia. 32:159-180. Pavlis, N.K., Holmes, S.A., Kenyon, S.C., Factor, J.K., 2012. The development and evaluation of the Earth
ACCEPTED MANUSCRIPT
AC
CE P
TE
D
MA
NU
SC R
IP
T
Gravitational Model 2008(EGM2008). J Geophys. Res. 117:B04406. Rodell, M., Houser, P. R., Jambor, U., Gottshalck, J., Mitchell, K., Meng, C., Arsenault, K., Cosgrove, B., Radakovich, J., Bosilovich, M., Entin, J.K., Walker, J.P., Lohmann, D., Toll, D., 2004. The global land data assimilation system. Bullet. Am. Meteorol. Soc. 85,381-394. Sun, W., Wang, Q., Wang, Y., Li, H., Okubo, S., Shao, D.S., Liu, D.Z., Fu, G.Y., 2009. Gravity and GPS measurements reveal mass loss beneath the Tibetan Plateau: Geodetic evidence of increasing crustal thichness. Geophys. Res. Lett. 36,L02303. Tang, Y.C., Feng, Y.G., Chen, Y.S., Zhou, S.Y., Ning, J.Y., Wei, S.Q., Li, P., Yu, C.Q., Fan, W.Y., Wang, H.Y., 2010. Receiver function analysis at Shanxi Rift. Chin. J. Geophys. 53(9), 2102–2109(in Chinese). Timmen, L., 2010. Absolute and relative gravimetry. In:Sciences of Geodesy –I: Advances and future directions. Springer, Berlin, Heidelberg, 1-48. Van Camp, M., de Viron, O., Metivier, L., Meurers., B., Francis, O., 2014. The quest for a consistent signal in ground and GRACE gravity time-series. Geophys. J. Int.197(1):192-201. Wang, X.W., Guo, Y.H., Fan, X.F., 2001. Analysis of recent vertical deformation in Shanxi area. Crust. Deformation Earthq. 21 (2), 64–69(In Chinese). Whar, J., Molenaar, M., Bryan, F.,1998. Time variability of the earth’s gravity field: hydrological and oceanic effects and their possible detection using GRACE. J.Geophys.Res.103(B12),32005-30229. Xu, X.W., Ma, X.Y.,1992. Geodynamics of the Shanxi Rift system, China. In: P.A. Ziegler (Editor), Geodynamics of Rifting, Volume I. Case history studies on rifts: Europe and Asia. Tectonophysics. 208:325-340. Zhang, Z. Z., Chao, B. F., Lu, Y., Hsu, H.T., 2009. An effective filtering for GRACE time-variable gravity: Fan filter. Geophys. Res. Lett. 36,L17311. Zhou, J.C., Sun, H.,P., Xu, J.Q.,2009. Validating global hydrological models by ground and space gravimetry. Chin. Sci. Bull. 54(9),1534-1542. Zhu, W., Zhang, Q., Ding, X.L., Zhao, C.Y., Yang, C.S., Qu, W., 2013. Recent ground deformation of Taiyuan basin (China) investigated with C-, L- and X-bands SARimages. J. Geodyn.70:28-35.
ACCEPTED MANUSCRIPT
AC
CE P
TE
D
MA
NU
SC R
IP
T
Highlights We present the preliminary FG5, GPS, and groundwater measurement results at the Taiyuan station. Absolute gravimetry at the Taiyuan station showed a clear gravity increase since 2009. Continuous GPS measurements in the Taiyuan station showed a land subsidence since 2010. Regional gravity changes computed from the GLDAS hydrological model are in agreement with the results derived from GRACE. Residual gravity change rate reflects the mantle upwelling due to tectonic activity beneath the Taiyuan basin.
S0926-9851(17)30093-9 doi:10.1016/j.jappgeo.2017.01.026 APPGEO 3196
To appear in:
Journal of Applied Geophysics
Received date: Revised date: Accepted date:
15 January 2016 6 January 2017 20 January 2017
Please cite this article as: Xing, Lelin, Wang, Linhai, Hu, Minzhang, Determination of mantle upwelling rate beneath Taiyuan basin by using absolute gravity, GPS, groundwater and GLDAS data, Journal of Applied Geophysics (2017), doi:10.1016/j.jappgeo.2017.01.026
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Determination of mantle upwelling rate beneath Taiyuan basin by using absolute gravity, GPS, groundwater and GLDAS data
D
MA
NU
SC R
IP
T
Lelin Xing, Linhai Wang, Minzhang Hu Key Laboratory of Earthquake Geodesy, Institute of Seismology, China Earthquake Administration, Wuhan 430071, China Abstract: The taiyuan basin is in the Shanxi rift system of China. Results of tectonic studies indicate that the Moho is uplifted by 2-3 km under the Taiyuan basin. However, there is no quantitative evidence shows whether the rift is still in the status of mantle upwelling. Herein, we estimated mantle upwelling rate of Taiyuan basin by using absolute gravity, GPS , groundwater and GLDAS data in this paper. In order to utilize the absolute gravity measurements in terms of tectonic study it is necessary to reduce all disturbing environmental effects. Many of those can be modeled, such as tide, polar motion, ocean tidal loading and atmospheric mass components. The Taiyuan station located in the Taiyuan basin, and absolute gravity measurements with a FG5 instrument were performed from 2009 to 2014, a secular trend was obtained. In-situ GPS data was used to estimate the vertical motion rate since 2011, and the result indicated a land subsidence. In-situ groundwater level was collected with daily surveys from 2009 to 2015, and local hydrology impact on effect was made. The global terrestrial water storage loading effect on gravity at Taiyuan station was computed by using GLDAS global hydrology model. Furthermore there is a good agreement between GRACE results and GLDAS hydrological model results. Subtracting the gravity change rate attributable to the land subsidence, groundwater level and global hydrology from the absolute gravity change
CE P
TE
rate, the residual gravity change rate was obtained. It reflects mantle upwelling about 2.1 2.6 cm/yr beneath Taiyuan basin. Keywords: Absolute gravimetry, Gravity variations, Gravity change rate, Hydrological model, Groundwater
1. Introduction
AC
Temporal gravimetry is an efficient tool to monitor mass transfer, such as those implied by crustal uplifting and crustal thickening (Sun et al. 2009), volcanic reservoir charge (Battaglia et al. 2004), ground water movements (Longuevergne et al., 2010; Jacob et al. 2010),. The physical principle is that changes in the gravity value are due to changes in mass distribution and vertical displacement. As every geodetic quantity, gravity vatiations integrate different processes. The challenge therefore relies in separating the contribution of each process in the measured signal. The method of removing unwanted signals is to model each source individually: Earthtide, airpressure changes, polar motion, global and local hydrology, and others. What remain are residuals, typically the focus of a particular study. Absolute gravimeters reached a precision about of 2.0μGal (Niebauer et al., 1995). The feature makes AG the very important tool in geophysical and geodynamics studies. The impact of environmental effects on gravity measurements is needed to be took into account. Tainyuan basin is in the central part of the Shanxi Rift system which located in the east margin of the Ordos block. It is well known for its intense neotectonics and strong earthquakes, standing between longitudes 111.5º-113ºE and latitude 37º-38ºN, is a typical Cenozoic fault basin and bounded by two major faults named Jiaocheng and Taigu located on the northwest and southeast, as showed in Fig.1. The two faults are formed by a series of NE-striking high-angle normal faults which control the formation and development of the basin (Guo et al., 2007). GPS, leveling and SAR measurements indicate the land extent and subsidence in the Taiyuan basin (Wang et al., 2001; Ma et al., 2006; Zhu et al., 2013). Evolution of the Shanxi Rift system of northern China is thought to have been governed by regional stress fields which
ACCEPTED MANUSCRIPT
TE
D
MA
NU
SC R
IP
T
developed in conjunction with the collisional interaction of the Indian and Eurasian plates. The most likely mechanism for explaining rifting is flexural bending of the lithosphere due to an isostatic load resulting from necking of the lithosphere. The lower part of the crust is plastically attenuated, and faults are formed only in the upper layer of the crust. The Cenozoic mantle upwelling might control the formation and evolution of the Shanxi rift (Xu et al.,1992).
Fig.1. Topography and tectonic sketch maps of study region. The Taiyuan station is marked as black circle. The purple lines are
CE P
active faults. The red circle denotes the gravity profile.
AC
Slant-stacking and migration images of receiver functions reveal uplift about 4-6km of the Moho in the Shanxi rift. The Moho is uplifted by 2-3 km under the Taiyuan basin (Tang et al.,2010). The Taiyuan basin region might have experienced mantle upwelling since the Cenozoic time. The hot mantle heated the upper mantle and the crust, which caused the large-scale mid and lower crust slow velocity and negative gravity anomaly (Guo et al., 2015). The Bouguer gravity anomaly of the profile used here, derived from the EGM2008 spherical harmonic coefficients(Pavlis et al., 2012), were downloaded from the webpage of BGI(http://big.omp.obs-mip.fr). The gravity profile, given in Fig.2, crosses the Taiyuan basin in the Shanxi rift. The sourtheast-ward positive gravity trend is about 0.2mGal/km. Broad residual positive anomalies are associated with the Luliangshan uplift and Taihangshan uplift. A sharp negative anomaly in the Taiyuan basin reveals the thinning of the lithosperic plate and upward expansion of the asthenosphere.
ACCEPTED MANUSCRIPT Fig.2. Bouguer and topographic profiles crossing the Taiyuan basin and extending across the Shanxi rift.
MA
2. Absolute gravity measurements
NU
SC R
IP
T
For the interpretation of the gravity profile, we can use modern geodesy method to determine the upward expansion of Moho surface/mantle upwelling in quantity, and this is the primary goal of this paper. A research project was undertaken from 2009 by China Earthquake Administration. The project, including one absolute gravity station performed every year from 2009 to 2015, with in-situ continuous GPS and groundwater level measurements. This study presents geodetic evidence of the decreasing crustal thickness by gravity observation at the Taiyuan station: a gravity change can reflect material transport accompanying vertical movements at the surface and on the crustal bottom. The vertical displacement, local and global hydrology changes add additional gravity changes at the surface to isolate the signal from mass change. As the bottom of crust is uplifting, the mass beneath the station is increasing because crust is displaced by mantle, causing a reduction in gravity. In-situ continuous GPS and groundwater measurements reveal land subsidence and rise of groundwater level, and a positive absolute gravity change rate is shown. Removing the contribution of surface vertical displacement and hydrology, including groundwater and terrestrial water storage, residual gravity change rate reflects the interior mass distribution.
AC
CE P
TE
D
Each absolute gravity measurement was performed by using the FG5-232 gravimeter. Each survey consisted of 25 hours of repeated measurements. Each measurement included 25 sets, and each set included 100 free-fall drops. A single drop was made at interval of 10 S. In total, 2500 drops were collected. To minimize computational biases, a common processing scheme for the data analysis has been adopted, ensuring consistency with respect to model and setup parameters. All raw gravity observations were reprocessed using the g9 software (Micro-g LaCoste, 2012). Some physical corrections were made to compensate for tide, polar motion, ocean tidal loading and atmospheric mass components. Vertical transfer of the measured gravity value was done using the vertical gravity gradient, which was determined by using two CG-5 relative gravimeters at least six return measurements. All absolute gravity observations in this work are given at a reference height of 130cm, close to a point where the influence of the gradient uncertainty on the FG5 is almost zero (Timmen, 2010). The absolute gravity values were listed in Table 1. The standard deviation of the final gravity sets is less than 3.0 μGal. The time series of the absolute gravity value is depicted in Fig.3. The result shows an obvious positive gravity change rate. For the trend calculation, a least squares adjustment was performed assigning equal weights to the epoch results. The gravity change rate inferred from absolute gravity time-series for the site Taiyuan is 10.05 0.87 μGal/yr. The standard deviation following the gravity rate of change number indicates one sigma level, with reliability of 67%. For the effect of hydrology on the observed gravity value is not treated in g9 when processing absolute gravity data, having reduced the gravity value for the time-variable tidal, polar motion, and atmospheric mass components, it may remain strongly influenced by hydrological variations (Mikolaj et al.,2015). So, the linear gravity change rate reveals the physical processes underlying crustal deformation and mass distribution. In order to obtain the residual gravity change rate related with mantle upwelling, the contributions of hydrology and vertical displacement should be eliminated from the absolute gravity change rate. Table 1 Compilation of gravity values as measured with the FG5 gravimeter at the Taiyuan station. Date(mean)
sets
g-value(Gal)
Set scatter(Gal)
21.05.2009
25
979659021.2
1.6
01.11.2009
25
979659023.2
2.8
ACCEPTED MANUSCRIPT 25
979659028.0
0.9
03.09.2010
25
979659330.0
0.7
28.04.2011
25
979659342.3
0.8
17.10.2011
25
979659334.0
1.1
01.05.2012
25
979659333.2
1.0
07.08.2013
25
979659349.7
0.7
27.09.2013
25
979659370.9
17.07.2014
25
979659369.1
26.10.2014
25
979659366.4
1.1
15.04.2015
25
979659376.6
1.0
14.09.2015
25
979659375.4
1.6
IP
T
28.07.2010
0.9
MA
NU
SC R
2.3
D
Fig.3. Gravity variations at the Taiyuan station as obtained with the FG5 gravimeter since 2009.
3. GPS measurements
AC
CE P
TE
The continuous GPS data were used to estimate the vertical motion rate at Taiyuan station. The gravity station is located near the GPS station. The GPS data were processed using the GIPSY software to remove phase and pseudorange data (http://www.cgps.ac.cn/index.action). The vertical motion rate, derived by fitting displacement of the entire observed period is -8.50±0.59 mm/yr, is depicted in Fig.4.
Fig.4. Time series of daily solution of vertical displacements at the Taiyuan station from continuous GPS recording. The red line is linear fit to the time series.
Here we used the Bouguer model for correcting the effect of elevation change (Ekman et al., 1996), the gravity change rate g z is given by
g z 2g / a hz 2 Gc hz 0.19 hz Gal / yr (1) where G is the gravitational constant, g is the gravitational acceleration, hz is the vertical motion rate, a is the radius of the Earth and c is the density of crust. The gravity change rate of 1.62 ± 0.11μGal /yr due to elevation change is computed which is
ACCEPTED MANUSCRIPT consistent with the increasing trend monitored by absolute gravity measurements.
4. Groundwater measurements
MA
NU
SC R
IP
T
The level of the water table beneath the Taiyuan station is monitored by a water gauge in a well. Water level was collected with daily surveys from 2009 to 2015. The water level change rate, estimated by fitting level of the entire observed period is 1.82±0.03 m/yr, is depicted in Fig.5. Long-term trends in water level at the Taiyuan station highlight a local rise of the water table during the period 2009-2015. The water level records of absolute gravity measurement time series were also selected, and the change rate is 1.82±0.03 m/yr. The trend is consistent with the daily solution, but with a larger accuracy.
Fig.5. Groundwater level records at the Taiyuan station. Black line is the linear fit for daily level, and blue dash line for AG measurements time series.
D
A change in gravity is related to a change in mass, which is attributed to the change in the volume of water occupying pore space in the unconfined aquifer and can be calculated by(Jacob et al., 2008)
TE
gw =2 GPe hw 42Pe hw Gal / yr (2)
CE P
in which Pe is effective porosity.
AC
Although we didn’t make an experiment to determine the porosity of rocks beneath Taiyuan station, we know exactly the composition of the rocks based on the arrangement of borehole data, the typical porosity of 0.1 for the aquifer in the study area (Guo, 2005; Chen et al., 2011). Due to the change of groundwater level is the main effect for gravity change, the porosity can be estimated. The porosity Pe g / (42* hw ) is 0.11 ±0.02 with considering the vertical motion effect. Hence, the gravity change
rate due to groundwater table change is 8.010.09 μGal/yr. The trend of gravity variation due to water level change is consistent with the increasing trend monitored by absolute gravity measurements.
5. Global Hydrology effects 5.1 GLDAS model As discussed by Llubes et al. (2004), the gravity variations due to hydrology can be separated into two major scales: local and regional. The local scale is dominated by the Newtonian attraction of the underlying water masses. At the regional scale, surface and shallow water induces a global elastic deformation of the Earth which has an effect on the gravity field through both mass redistribution and vertical movement. For the computation of the global hydrology effect, we used the Global Land Data Assimilation System (GLDAS) NOAH hydrological data (Rodell et al., 2004). The GLDAS/NOAH described global soil moisture (0-10cm, 10-40cm, 4—100cm, and 100-200cm) and snow (snow water equivalent) content variations and has a 0.25 grid and daily temporal sampling; hence, it does not consider groundwater. The regional effect was obtained by considering the effects of loading and of Newtonian attraction at distances greater than 0.25 for convolution between the surface mass distribution and the Green’s functions.
ACCEPTED MANUSCRIPT
TE
D
MA
NU
SC R
IP
T
Water within 0.25 has a dominantly Newtonian effect, we multiplied the local value of the soil moisture by the coefficient -4.2μGal/cm due to the absolute gravity station is below the ground only about 12m. The equivalent water heights at Taiyuan station were extracted from hydrological models by bilinear interpolation in terms of the four nearby grid values (Mikolaj et al.,2016). The water loading effect on gravity at Taiyuan station was computed by using GLDAS global hydrology model by mGlobal (Mikolaj et al.,2016), as showed in Fig.6. The modeled gravity changes due to continental water storage can reach as much as a 3-4 μGals of peak-to-peak amplitude. The gravity change rate is about -0.30±0.06 μGal/yr, which reveals the decreasing of the equivalent water height in this regional area.
Fig.6. The time series of global hydrology effects on gravity for the Taiyuan station.
GM R2
60
l
W l 2 m0
lm
(l +1-
2hl' )(Clm cos(m ) Slm sin(m ))Plm (cos ) (3) 1 kl'
AC
g s ( R, , )
CE P
5.2 GRACE results The gravity change on the Earth’s surface can be derived from GRACE products according to (Zhou et al., 2009; Van Camp et al., 2014)
where M is the mass of the Earth, Clm and Slm are the fully normalized spherical harmonic coefficients, and are co-latitude and longitude, R is Earth’s radius, Plm (cos ) is the fully normalized associated Legendre function,
l
and m are, the harmonic degree and order,
respectively. hl and kl are the load Love numbers of degree l for vertical displacement and potential, respectively. Due to the large errors filter in the high-degree Stokes coefficients provided by GRACE products, a filter is usually applied, for example Gaussian filter (Whar, et al., 1998), to obtain a reliable result. For the space-based gravimetry, we used RL05 monthly data released by CSR (Bettadpur, 2007) and applied the 350 km fan filter(Zhang et al., 2009). The gravity change due to global hydrology effect at Taiyuan station was computed according to Eq.(3). The water loading effect on monthly gravity change was also computed by using the GLDAS hydrological model for comparison. From Fig.7, the hydrological-effect-induced seasonal variations is also obvious, the peak-to-peak amplitude is about 3 μGal, and the gravity change rate is about -0.28±0.07 μGal/yr from GRACE. Furthermore there is a good agreement between GRACE and GLDAS in amplitude,
ACCEPTED MANUSCRIPT
MA
NU
SC R
IP
T
but not in phase. The GLDAS hydrological model has spatial resolutions of 0.25°×0.25°, which means that the water distribution at Taiyuan station is averaged in a grid with a certain size of 28km×22km. Similary, the gravity change from GRACE is smoothed with a radius of 350km. As a result, both GRACE and GLDAS hydrological models give a spatial mean of the regional water storage changes. This may be the reason why the gravity change rate of GRACE agrees well with the GLDAS hydrological model.
D
Fig.7. Comparison of gravity changes derived from GRACE and GLDAS hydrological model. The blue circles show the gravity change derived from GRACE; the purple circles show the water loading effect on gravity derived from GLDAS.
TE
6. Residual gravity change rate and mantle upwelling The observed gravity change rate g1 of 10.05 0.87 μGal/yr at the Taiyuan station described
CE P
above is presented in Table 1. The gravity change rate is obtained on the deformed earth surface which can be decomposed into two contributions associated with crustal vertical displacement and internal mass change. To obtain the bottom of crust deformation, we must separately to interpret the gravity changes. We first eliminate the contribution from the surface movement as determined by continuous GPS, and the
AC
Bouguer gradient of -1.9 μGal/cm must be used based on the local crustal density 2.7 2.9 g / cm3 . Multiplying the Bouguer gradient by the corresponding land subsidence inferred from GPS measurements as shown in Fig.4, we obtained the Bouguer gravity change rate g 2 is 1.62 ± 0.11μGal /yr. For the contribution of the local groundwater level change, we linked gravity variations using an infinite slab hypothesis shown in Eq.(2). The groundwater change rate of 1.82±0.02 m/yr induces a gravity change rate
g3 of about 8.010.09 μGal/yr. The water loading effect on gravity at Taiyuan station was also computed by using GLDAS global hydrology model, and the associated gravity change rate g 4 is about
-0.30
0.06 μGal/yr. Subtracting the gravity change rate attributable to the land subsidence, groundwater level and global hydrology from the observed gravity change rate, i.e., g5 g1 g2 g3 g4 , the residual gravity change rate is 0.72 0.88 μGal/yr as listed in Table 2. The positive gravity change suggests that the mass under the Taiyuan station is increasing gradually coincide with the mantle upwelling, as presented in Fig.8.
ACCEPTED MANUSCRIPT With density contrast of 0.8 0.2 g / cm3 between crustal and mantle(Chen et al.,2004), the gravity change related to this Bouguer layer can be expressed simply as 2 G h 0.72 μGal. The crustal
Table2 Gravity change rates at the Taiyuan station
g2
g3
10.05 0.87
1.62 ± 0.11
8.010.09
g4
g5
-0.300.06
0.720.88
AC
CE P
TE
D
MA
NU
g1
SC R
IP
T
thinning rate is inferred as 2.1 2.6 cm/yr , i.e., the change rate of the crustal expansion upword or mantle upwelling from -0.5 to 4.7 cm/yr with a reliability of 67%. Compared to the mean surface land subsidence of -8.5 mm/yr, as determined by GPS, the 2.1 cm/yr of mantle upwelling on the Moho surface seems reasonable in light of the mean elevation of 1.0 km of the Taiyuan basin and the crustal thickness of 35 km below it (Tang et al., 2010).
Fig.8 The mechanism of land subsidence and mantle upwelling for Taiyuan basin inferred from absolute gravity, GPS, groundwater and GLDAS data.
7. Conclusions The aim of this paper was to determine the change rate of mantle upwelling quantitatively by using absolute gravity, GPS and groundwater level data at Taiyuan station. To successfully eliminate the impact of water mass variation on gravity measurements, it is necessary to monitor local groundwater level change combined with global hydrology models. The absolute gravity change rate of 10.05 0.87 μGal/yr reflects the vertical movement and mass distribution. To analyze the deep mass transfer, we used in-situ GPS, groundwater level data to eliminate the vertical movement and local hydrology effects on gravity change rate. The contributions of vertical movement, groundwater level and global hydrology effect are 1.62 ± 0.11μGal /yr, 8.010.09 μGal/yr and -0.30 0.06 μGal/yr. Subtracting the gravity change rate attributable to the land subsidence, groundwater level and global
ACCEPTED MANUSCRIPT hydrology from the observed gravity change rate, the residual gravity change rate is about 0.72 0.88 μGal/yr. It reflects mantle upwelling about 2.1 2.6 cm/yr beneath Taiyuan basin.
AC
CE P
TE
D
MA
NU
SC R
IP
T
Acknowledgements We are grateful to the editor and the two reviewers for their constructive comments and suggestions, which helped to improve the manuscript significantly. This work was financially supported by the Key Foundation of Institute of Seismology, China Earthquake Administration (Grant No. IS201326130) and the “973” project (Grant No. 2013CB733304). References Battaglia, M., Segall, P.,2004. The interpretation of gravity changes and crustal deformation in active volcanic areas. Pure appl. Geophys. 161,1453-1467. Bettadpur, S., 2007. UTCSR Level-2 gravity field product user handbook. GRACE 327-734 Rep.Center for Space Research, The University of Texas at Austin, Austin. Chen, Y.L., Li, Z.F., Qin, Y., 2011. The mechanism of secondary porosity in Taiyuan sandstone, at Shuangshan Region, Ordos basin. Coal Geology and Exporation,39(1),11-15(in Chinese). Ekman, M., Makinen, J., 1996. Recent postglacial reboud, gravity change and mantle flow in Fennoscandia. Geophys.J.Int.,126, 229-234. Guo, Q.H., Wang, Y.X., Ma, T., Ma, R.,2007. Geochemical processes controlling the elevated fluoride concentrations in groundwater of the Taiyuan Basin, Northern China. J. Geochem. Explor. 93(1),1-12. Guo, Q.H.,2009. Groundwater system evolution and genesis of relevant environmental problems: a case study at Taiyuan basin, Shanxi Province, China (PhD thesis), China University of Geosciences, Wuhan(in Chinese). Guo, Z., Chen, Y.S., Yin, W.W., 2015. Three-dimensional crustal model of Shanxi gaben from 3D joint inversion of ambient noise surface wave and Bouguer gravity anomalies. Chin. J. Geophysics.(in Chinese),58(3),821-831. Jacob, T., Bayer, R., Chery, J., Jourde, H., Le Moigne, N., Boy, J., Hinder, J., Luck, B., Brunet, P., 2008. Absolute gravity monitoring of water storage variation in a karst aquifer on the larzac plateau(Southern France). J. Hydrol.359,105-117. Jacob, T., Bayer, R., Chery, J., Moigne, N., 2010. Time-lapse microgravity surveys reveal water storage heterogeneity of a karst aquifer. J. Geophys. Res. 115, B06402. Llubes, M., Florsch, N., Hinderer, J., Longuevergne, L., Amalvict, M., 2004. Local hydrology, the Global Geodynamics Project and CHAMP/GRACE perspective: some case studies. J. Geodyn. 38:355-374. Longuevergne, L., Scanlon, B.R., Wilson, C.R., 2010. GRACE hydrological estimates for small basins: evaluating processing approaches on the high plains aquifer, USA. Water Resour. Res. 46,W11517. Ma, R., Wang, Y.X., Ma, T., Sun, Z.Y., Yan, S.L., 2006. The effect of stratigraphic het-erogeneity on areal distribution of land subsidence at Taiyuan, Northern China. Env. Geol. 50, 551–586. Micro-g LaCoste, 2012. g9 user’s manual, April 2012 version. Micro-g LaCoste, Lafavette, Colorado, USA. Mikolaj, M., Meurers, B., Guntner, A.,2016. Modelling of global mass effects in hydrology, atmosphere and oceans on surface gravity. Comp. Geosci.93,12-20. Mikolaj, M., Meurers, B., Mojzes, M.,2015. The reduction of hydrology-induced gravity variations at sites with insufficient hydrological instrumentation. Stud. Geophys. Geod.59(3),424-437. Niebauer, T.M., Sasagawa, G.S., Faller, J.E., Hilt, R., Klopping, F., 1995. A new generation of absolute gravimeter. Metrologia. 32:159-180. Pavlis, N.K., Holmes, S.A., Kenyon, S.C., Factor, J.K., 2012. The development and evaluation of the Earth
ACCEPTED MANUSCRIPT
AC
CE P
TE
D
MA
NU
SC R
IP
T
Gravitational Model 2008(EGM2008). J Geophys. Res. 117:B04406. Rodell, M., Houser, P. R., Jambor, U., Gottshalck, J., Mitchell, K., Meng, C., Arsenault, K., Cosgrove, B., Radakovich, J., Bosilovich, M., Entin, J.K., Walker, J.P., Lohmann, D., Toll, D., 2004. The global land data assimilation system. Bullet. Am. Meteorol. Soc. 85,381-394. Sun, W., Wang, Q., Wang, Y., Li, H., Okubo, S., Shao, D.S., Liu, D.Z., Fu, G.Y., 2009. Gravity and GPS measurements reveal mass loss beneath the Tibetan Plateau: Geodetic evidence of increasing crustal thichness. Geophys. Res. Lett. 36,L02303. Tang, Y.C., Feng, Y.G., Chen, Y.S., Zhou, S.Y., Ning, J.Y., Wei, S.Q., Li, P., Yu, C.Q., Fan, W.Y., Wang, H.Y., 2010. Receiver function analysis at Shanxi Rift. Chin. J. Geophys. 53(9), 2102–2109(in Chinese). Timmen, L., 2010. Absolute and relative gravimetry. In:Sciences of Geodesy –I: Advances and future directions. Springer, Berlin, Heidelberg, 1-48. Van Camp, M., de Viron, O., Metivier, L., Meurers., B., Francis, O., 2014. The quest for a consistent signal in ground and GRACE gravity time-series. Geophys. J. Int.197(1):192-201. Wang, X.W., Guo, Y.H., Fan, X.F., 2001. Analysis of recent vertical deformation in Shanxi area. Crust. Deformation Earthq. 21 (2), 64–69(In Chinese). Whar, J., Molenaar, M., Bryan, F.,1998. Time variability of the earth’s gravity field: hydrological and oceanic effects and their possible detection using GRACE. J.Geophys.Res.103(B12),32005-30229. Xu, X.W., Ma, X.Y.,1992. Geodynamics of the Shanxi Rift system, China. In: P.A. Ziegler (Editor), Geodynamics of Rifting, Volume I. Case history studies on rifts: Europe and Asia. Tectonophysics. 208:325-340. Zhang, Z. Z., Chao, B. F., Lu, Y., Hsu, H.T., 2009. An effective filtering for GRACE time-variable gravity: Fan filter. Geophys. Res. Lett. 36,L17311. Zhou, J.C., Sun, H.,P., Xu, J.Q.,2009. Validating global hydrological models by ground and space gravimetry. Chin. Sci. Bull. 54(9),1534-1542. Zhu, W., Zhang, Q., Ding, X.L., Zhao, C.Y., Yang, C.S., Qu, W., 2013. Recent ground deformation of Taiyuan basin (China) investigated with C-, L- and X-bands SARimages. J. Geodyn.70:28-35.
ACCEPTED MANUSCRIPT
AC
CE P
TE
D
MA
NU
SC R
IP
T
Highlights We present the preliminary FG5, GPS, and groundwater measurement results at the Taiyuan station. Absolute gravimetry at the Taiyuan station showed a clear gravity increase since 2009. Continuous GPS measurements in the Taiyuan station showed a land subsidence since 2010. Regional gravity changes computed from the GLDAS hydrological model are in agreement with the results derived from GRACE. Residual gravity change rate reflects the mantle upwelling due to tectonic activity beneath the Taiyuan basin.