木兰山重力基线场的初值测定及重力变化分析

doi:10.3969/j.issn.0253-4967.2023.02.015

摘要/Abstract

摘要：

文中基于绝对重力控制下的木兰山基线场2018年和2022年的重力观测资料, 研究了一次项系数在不同读数段的分布规律、木兰山基线场的重力场分布和近期重力变化特征。结果表明: 相对重力仪不同读数段的一次项系数存在差异, 武汉-宜昌测段(子测段)的一次项系数与武汉-绿葱坡测段(总测段)的差异可达4.809‰, CG-6型与CG-5型重力仪的结果较为一致, 2类重力仪间无系统偏差; 总测段的一次项系数是各子测段一次项系数的加权平均结果, 其相应的权因子为子测段与总测段的重力段差比值; 木兰山基线场的最大重力段差(G01-G03)为102.176mGal, 各测点的重力值平均精度为4.8μGal; 2018-2022年木兰山基线场测点的重力变化区间为5.9~12.8μGal, 重力场整体呈正变化, 测段重力变化区间为-4.8~6.9μGal。测点周边环境变化、地表垂直运动、地表水储量变化对地表实测重力变化均产生了一定影响。综合上述各项改正后的测点和测段重力变化均值较实测值相应减小了38.2%和50.8%, 改正后的重力变化结果更为精准, 但其不确定度相应增加了2.5%和2.8%。综合分析测点和测段的重力场动态变化可有效提取异常信息, 为地震重力监测提供更精确的数据支持。

关键词: 木兰山基线场, 重力变化, 一次项系数, 地表重力观测

Abstract:

Using the gravity observation data of Mulanshan short gravity baseline field in 2018 and 2022, we established a high-precision short gravity baseline field of Mulanshan based on the relative gravity joint measurement method under the control of absolute gravity. We also analyzed and discussed the accurate calibration of the monomial coefficient of the relative gravimeter during the construction of the gravity short baseline field, the distribution of gravity values in the gravity baseline field of Mulanshan and the contribution of various environmental factors in the gravity variation results, these results show that:

(1)Maximum gravity segment difference of Mulanshan calibration baseline is 102.176mGal from G01 to G03 stations, and the average accuracy of gravity value of each measuring station reaches 4.8μGal. The geological structure of the Mulanshan baseline is stable, and the gravity change of measuring stations is not obvious. From 2018 to 2022, the gravity variation range of measuring stations was 5.9~12.8μGal, with an average of 9.5μGal, and the average uncertainty was ±5.7μGal. The gravity field mainly showed a positive change. The variation range of gravity in each measurement section is -4.8~6.9μGal, with an average of(1.8±8.6)μGal. The change of the surrounding environment has a certain impact on the gravity field, and the contribution of the new buildings near the G01 and G02 to the gravity change is 3.6μGal and -0.51μGal, respectively. These gravity changes of measuring stations in the IOS and Mulanshan baseline caused by vertical surface movement are(2.17±0.44)μGal and(1.67±0.45)μGal. The gravity effect caused by the change of surface water storage is(1.07±0.84)μGal, which cannot be ignored. Compared with observation results, the gravity change of each measuring station and section after correction is reduced, and the average gravity change values are reduced by 38.2% and 50.8%, respectively. The corrected gravity change results are more accurate. Due to the cumulative effect of errors in the correction process, the uncertainty of gravity change results after correction increases accordingly, and the uncertainty of gravity change results of measuring station and measuring section increases by 2.5% and 2.8%compared with observation results, respectively. Combined with the gravity change results of the measuring station and the measuring section, we can effectively extract abnormal information in gravity dynamic change results.

(2)There are differences in monomial coefficients of different gravity sections of the relative gravimeter. The results of CG-6 and CG-5 relative gravimeters are relatively consistent, and there is no systematic deviation between the two gravimeters. The difference in the monomial coefficient between the Wuhan-Yichang section(sub-section)and the Wuhan-Lücongpo section(total section)is 4.809‰, which has a great influence on the gravity observation results. The monomial coefficient needs to be accurately measured. The difference of the monomial coefficient in the sub-section is negatively correlated with the proportion of the gravity segment difference in the sub-section to the total section; the monomial coefficient of the total section is a weighted average result of each sub-section, and the proportion of gravity segment difference in sub-section to total section is the corresponding weight factor. Accurate calibration of the monomial coefficient of the relative gravimeter is a technical guarantee to obtaining high-precision gravity observation results. The gravity segment difference of sub-segments cannot cover the gravity range of the measurement area due to smaller segment difference, which will lead to the extrapolation of the monomial coefficient, so it cannot effectively calibrate the monomial coefficient of the relative gravimeter applicable to the whole measurement area. The total section can cover the gravity range of the measurement area, and the monomial coefficient is the ratio between the segment difference measured by the relative gravimeter and the known segment difference, and its calibration accuracy is inversely proportional to the gravity segment difference, so when using the total section as a reference for calibration of the monomial coefficient of the relative gravimeter, accuracy of the calibration can be guaranteed and precision of the calibration can be improved, so calibration result of the monomial coefficient using the total section is more accurate. The existing widely used relative gravimeters(such as LCR, CG-5, BURRIS, CG-6, and so on)have time-varying characteristics of the monomial coefficient, weakening the errors caused by changes of the monomial coefficient is essential to improve the accuracy of observations, and corresponding calibration is required before each period of gravity observation. The monomial coefficient of the relative gravimeters needs to be calibrated using a large segment difference, and the segment difference(or the accumulated segment difference)should be greater than 300mGal.

Key words: Mulanshan gravity baseline, gravity change, monomial coefficients, Surface gravity observation

中图分类号:

P315.72

汪健, 张新林, 谈洪波, 胡敏章, 吴桂桔, 李忠亚, 张明辉. 木兰山重力基线场的初值测定及重力变化分析[J]. 地震地质, 2023, 45(2): 553-569.

WANG Jian, ZHANG Xin-lin, TAN Hong-bo, HU Min-zhang, WU Gui-ju, LI Zhong-ya, ZHANG Ming-hui. DETERMINATION OF GRAVITY VALUES FOR MULANSHAN CALIBRATION BASELINE AND ANALYSIS OF GRAVITY CHANGE[J]. SEISMOLOGY AND GEOLOGY, 2023, 45(2): 553-569.

图/表 14

图1 木兰山重力基线场的点位分布高程据ASTER DEM V003模型绘制, 分辨率为30m

Fig. 1 Map of gravity stations of the Mulanshan baseline.

表1 绝对重力和垂直梯度观测结果

Table1 Results of absolute gravity and vertical gradient observation

点名	北纬 /(°)	东经 /(°)	高程 /m	观测日期	观测组数	使用组数	垂直梯度 /μGal·cm^-1	垂直梯度段差精度/μGal	地面重力值 /μGal	标准差 /μGal
IOS	30.53	114.35	34	2018-01-07	30	30	-3.1374	2.56	979350956.17	±1.12
IOS	30.53	114.35	34	2022-03-12	25	25	-3.1562	1.76	979350962.05	±1.99

表2 相对重力仪一次项系数标定结果

Table2 Results of absolute gravity and vertical gradient observation

仪器类型	仪器号	一次项因子	标定区间	标定日期
LCR-G	G829	1.000 675	JZ01-JZ04	2018-01-10
	G1003	1.000 332	JZ01-JZ04	2018-01-10
CG-5	C1056	0.999 806	JZ01-JZ04	2018-01-11
	C216	1.000 679	JZ01-JZ04	2018-01-11
	C509	0.998 899	JZ01-JZ04	2018-01-11
	C1333	1.000 377	JZ01-JZ04	2018-01-11
	C1121	0.999 835	JZ01-JZ04	2018-01-11
	C509	0.998 717	武汉-绿葱坡	2022-03-22
	C207	0.990 269	武汉-绿葱坡	2022-03-22
	C217	0.999 226	武汉-绿葱坡	2022-03-22
	C221	0.999 839	武汉-绿葱坡	2022-03-22
	C231	1.000 372	武汉-绿葱坡	2022-03-22
CG-6	C090	1.000 186	武汉-绿葱坡	2022-03-22
	C092	0.999 862	武汉-绿葱坡	2022-03-22
	C236	1.000 247	武汉-绿葱坡	2022-03-22
	C238	1.001 667	武汉-绿葱坡	2022-03-22

表3 木兰山基线场各测点的重力值结果

Table3 Results of gravity value of observations sites of the Mulanshan gravity baseline

点号	2018年1月重力值 /m·s²	点值精度 /μGal	2022年3月重力值 /m·s²	点值精度 /μGal	2018-2022年重力变化 /μGal
木兰山G01	366.5048×10^-5	4.8	366.5176×10^-5	4.3	12.8
木兰山G02	313.8634×10^-5	4.8	313.8713×10^-5	4.4	7.9
木兰山G03	264.3284×10^-5	4.9	264.3398×10^-5	4.6	11.4
木兰山G04	未观测		280.1167×10^-5	4.7

图2 不同读数段的一次项系数结果

Fig. 2 Monomial coefficient in different measure segment.

图3 CG-5型、CG-6型重力仪的一次项系数差异结果

Fig. 3 Results of monomial coefficient variance between CG-5 and CG-6 gravimeter.

表4 子测段的一次项系数变化结果

Table4 Results of monomial coefficient variance in sub-segment

测段	段差值占比 /%	CG6-090	CG6-092	CG6-236	CG6-238	CG5-207	CG5-217	CG5-221	CG5-231	CG5-509
武汉-宜昌	11.23	3.469‰	4.131‰	4.809‰	4.712‰	4.351‰	3.483‰	4.351‰	4.05‰	4.015‰
宜昌-绿葱坡	88.77	-0.650‰	-0.650‰	-0.640‰	-0.649‰	-0.650‰	-0.651‰	-0.650‰	-0.631‰	-0.641‰

图4 一次项系数差异结果

Fig. 4 Results of monomial coefficient variance.

图5 木兰山基线场2018-2022年重力变化结果

Fig. 5 Results of gravity change in the Mulanshan baseline from 2018 to 2022.

图6 a 木兰山G01测点周边新建的停车场模型; b 新建停车场引起的重力效应(单位: μGal)

Fig. 6 Model of newly constructed parking lot(a) and its gravity effect(b) nearby G01 station.

图7 a 木兰山G02测点周边新建的建筑物模型; b 新建建筑物引起的重力效应(单位: μGal)

Fig. 7 Model of newly constructed building(a)and its gravity effect(b)nearby G02 station.

图8 武汉(a)、黄陂GNSS站(b)的地表垂向运动时序图

Fig. 8 Observed time series of daily vertical movement at Wuhan(a), and Huangpi(b) stations.

图9 武汉地表水储量变化引起的重力效应

Fig. 9 Gravity effect caused by surface water storage change in Wuhan.

图10 木兰山基线场2018-2022年各项重力效应改正前、后的重力变化结果

Fig. 10 Gravity change results before and after gravity effect correction in Mulanshan baseline from 2018 to 2022.

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