An evaluation approach for the terrestrial gravity measurement based on the seismic noise magnitude
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摘要: 本文选取GS-15型、gPhone型、PET型和CG-5型等4种陆地重力观测常用的相对重力仪,对比这几种仪器在不同背景观测环境下和不同测评时长的地震噪声等级计算结果。综合分析结果显示:金属弹簧(gPhone型、GS-15型、PET型)与石英弹簧型(CG-5型)重力仪对环境噪声的敏感性存在一定差异,但取测评时长中最平静5天和最平静1天数据所计算的地震噪声等级结果相近。因此,对于流动重力观测点,可以取最平静1天的数据来评价观测点的环境噪声水平和观测精度,可为流动重力测点选址提供方法支撑。Abstract: In this paper, we calculated the seismic noise magnitude (SNM) of four types of relative gravimeters (GS-15, gPhone, PET and CG-5) commonly used in terrestrial gravity measurement in different environments and time intervals, and compared the corresponding results. The results show that there is quite different in sensitivity to ambient noise for the metallic spring gravimeter (GS-15, gPhone, PET) and quartz spring gravimeter (CG-5). The SNM results are similar using the data of the quietest five-day or quietest one-day to evaluate. Therefore, it is feasible to use the quietest one-day recording to evaluate SNM value and observation precision. This result could provide a method for evaluating the conditions of the campaigned gravity survey station.
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表 1 2008—2011年南山、乌加河和琼中重力台站记录的PSD,SNM和PL
Table 1 The PSD,SNM and PL of Nanshan station,Wujiahe station and Qiongzhong station from 2008 to 2011
台站 仪器类型 数据年份 PSD/[(10−8 m·s−2)2·Hz−1] SNM/[(10−8 m·s−2)2·Hz−1] PL /[(10−8 m·s−2)2·(Hz·s)−1/3] 南山台 GS-15 2008 0.982 2.492 0.025 2009 3.938 3.095 0.073 2010 0.640 2.306 0.032 2011 0.977 2.490 0.047 2008—2011 1.126 2.551 0.037 乌加河台 gPhone 2008 10.273 3.511 0.108 2009 2.113 2.825 0.047 2010 4.274 3.130 0.030 2011 4.460 3.149 0.070 2008—2011 2.519 2.901 0.048 琼中台 PET 2008 39.686 4.098 0.275 2009 80.150 4.403 0.187 2010 153.434 4.685 0.223 2011 71.240 4.352 0.192 2008—2011 76.493 4.383 0.197 表 2 两台CG-5型重力仪2017年7月6日—8月20日期间的同址PSD,SNM和PL值
Table 2 The result of PSD,SNM and PL recording by two CG-5 gravimeters from 6 July 2017 to 20 August 2017 at the same station
仪器编号 取样天数 PSD/[(10−8 m·s−2)2·Hz−1] SNM/[(10−8 m·s−2)2·Hz−1] PL/[(10−8 m·s−2)2·(Hz·s)−1/3] No.1095 1 299.555 4.976 0.879 5 273.553 4.937 0.785 No.1098 1 45.449 4.157 0.359 5 42.705 4.130 0.335 表 3 2018年4月28日—5月8日白家疃台重力仪观测的PSD,SNM和PL
Table 3 The PSD,SNM and PL of Baijiatuan station from 28 April 2018 to 8 May 2018
仪器型号 取样天数 PSD/[(10−8 m·s−2)2·Hz−1] SNM/[(10−8 m·s−2)2·Hz−1] PL/[(10−8 m·s−2)2·(Hz·s)−1/3] CG-5 (No.1095) 1 478.755 5.180 1.747 5 523.303 5.221 1.810 CG-5 (No.1098) 1 60.117 4.279 0.317 5 45.611 4.159 0.316 gPhone 1 6.255 3.296 0.110 5 6.073 3.283 0.085 表 4 白家疃台和中国地震局地球物理研究所地下观测室重力数据的PSD,SNM和PL
Table 4 The PSD,SNM and precisionPL at the Institute of Geophysics station and the Baijiatuan station
测点 仪器 最平静
时段RMS
/[(10−8 m·s−2)2·Hz−1]SNM
/[(10−8 m·s−2)2·Hz−1]PL
/[10−8 m·s−2)2·(Hz·s)−1/3]白家疃台 gPhone 第1天 6.715 3.273 0.060 第6天 6.646 3.638 0.110 第8天 5.504 3.313 0.070 第9天 5.072 3.284 0.080 第10天 4.351 3.296 0.110 白家疃台 CG-5
(No. 1095)第4天 9.386 5.052 1.620 第7天 9.300 5.491 2.220 第8天 8.156 5.227 1.815 第9天 7.554 5.180 1.747 第10天 7.614 5.473 2.195 中国地震局地球
物理研究所CG-5
(No. 1095)第11天 5.195 5.050 0.631 第23天 6.236 5.117 0.911 第24天 5.981 5.021 0.864 第25天 6.076 4.930 0.829 第26天 4.921 4.976 0.879 表 6 弹簧重力仪的计算结果
Table 6 The result of spring type gravimeters
台站 仪器 PSD
/[(10−8 m·s−2)2·Hz−1]SNM
/[(10−8 m·s−2)2·Hz−1]d
/[10−12 m·s−2·s−1]Tobs
/minPL
/[(10−8 m·s−2)2·(Hz·s)−1/3]乌加河台 gPhone 2.511 2.9 0.442 18.1 0.04 白家疃台 CG-5 (No.1098) 45.611 4.1 6.940 7.6 0.32 白家疃台 gPhone 6.067 3.2 1.030 13.7 0.08 表 5 弹簧重力仪的精度估计(Crossley et al,2013 )
Table 5 Precision estimates of spring type gravimeters (Crossley et al,2013 )
仪器 PSD/[(10−8 m·s−2)2·Hz−1] SNM/[(10−8 m·s−2)2·Hz−1] d/[10−12 m·s−2·s−1] Tobs/min PL/[(10−8 m·s−2)2·(Hz·s)−1/3] gPhone-2 50.126 4.2 34.70 2.7 0.56 CG-5 31.584 4.0 3.47 10.7 0.22 gPhone-1 4.000 3.1 11.60 11.1 0.08 -
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