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摘要:
冰盖厚度是研究南极冰盖质量、建立冰盖动力学模型的基本参数，对于冰川均衡调整、冰盖物质平衡及全球气候变化研究具有重要意义.基于地震学的远震接收函数和H-Kappa格网搜索方法可以用于地震台站下方冰盖厚度的可靠探测，不仅能与冰雷达获得的冰盖厚度进行独立对比，还可以与冰雷达方法相互补充，进一步填补南极大陆冰盖厚度探测空白区.本文利用布设于南极大陆冰盖上方的流动地震台阵记录到的远震波形数据，基于接收函数方法对台阵下方的冰盖厚度进行了研究.结果显示：基于远震接收函数方法的冰盖厚度与Bedmap2冰厚格网模型相比，二者差别大多在200 m以内；少数台站差值达到600 m左右，这一差别可能与Bedmap2测线分布空区、冰雷达测深不确定性以及冰盖内部复杂波速结构等因素有关.本文研究结果表明：利用南极大陆冰盖上方的流动地震台阵，基于远震接收函数方法可以获得比较可靠的南极冰盖厚度，为独立验证冰雷达的探测结果并弥补冰雷达探测空白区提供了有效方法.同时，部分台站接收函数波形的复杂性可能暗示了南极大陆数千米厚的冰盖内部结构不是均一的，仍然存在比较复杂的内部结构变化.因此，有必要进一步利用包括接收函数波形拟合、地震面波反演等方法对南极大陆冰盖厚度及其内部精细结构进行更为深入的研究.
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关键词:
- 南极 /
- 冰盖厚度 /
- 远震接收函数 /
- H-Kappa格网搜索
Abstract:Ice sheet thickness is a fundamental parameter in research on Antarctic ice sheet mass and ice sheet dynamic model construction, which has great significance for glacial isostatic adjustment, ice sheet mass balance and global climate change studies. Accurate ice thickness acquired utilizing the seismological receiver function and H-Kappa grid search method can not only be an independent comparison and verification for the ice thickness obtained by radio echo sounding method, but also fill the gap of radio echo sounding measurement in Antarctica. In this paper, P-receiver functions (PRFs) are extracted from teleseismic events waveform data recorded by the temporary seismic arrays deployed on the ice sheet, then the ice thickness beneath the stations is calculated using the H-Kappa method. Compared the ice thickness derived from PRFs with Bedmap2 ice sheet thickness database, the results show that most of the differences are within 200 meters, and only a few reach 600 meters, which may be attributed to the vacancy of Bedmap2 survey lines and the uncertainty of radio echo sounding, as well as the inherit complexity of the inner ice structure beneath some stations. It can be concluded that the ice thickness obtained from the teleseismic receiver function method is reliable, thus it can not only be an independent verification for radio echo sounding results, but also provide an effective method for making up the limitations of radio echo sounding measurements. At the same time, the complexity of the receiver function waveforms beneath several stations may also indicate that the inner velocity structure of the Antarctic ice sheet is not homogeneous. There may be complex velocity structure in the ice sheet, and it is necessary to use some other methods such as receiver function waveform inversion and surface wave inversion for further study.
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Key words:
- Antarctica /
- Ice sheet thickness /
- Teleseismic receiver function /
- H-Kappa grid search
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图 1
南极Bedmap2冰厚及本文使用冰上台站位置
Figure 1.
Antarctic ice thickness from Bedmap2 database and the location of seismic stations used in this study
图 2
内陆中山站-Dome A断面冰雷达测量反射空白区(崔祥斌等，2009)
Figure 2.
Echo free zone of radio echo sounding along Zhongshan station-Dome A transect (after Cui et al., 2009)
图 3
远震事件的震中分布
Figure 3.
Epicenter distribution of teleseismic events used in this study
图 4
理论模型合成接收函数波形对比(高斯因子4.5)
Figure 4.
Comparison of synthetic P-wave receiver functions (PRFs) for theoretical model
图 5
GM01、ST01、N076台接收函数随反方位角(a)、射线参数(b)分布.可以看出来自冰岩界面的Ps转换波和多次波比较清晰
Figure 5.
Receiver function waveforms arranged by (a) back-azimuth and (b) ray parameter for station GM01, ST01 and N076. The converted and mutiple phases from the ice-rock interface can be indentified clearly
图 6
沿测线接收函数波形与下方冰盖厚度
Figure 6.
Profiles showing PRFs and the ice sheet thickness beneath the stations
图 7
示例台站H-Kappa叠加扫描结果
Figure 7.
H-Kappa stacking results for station GM01, N076, ST01 and E018
图 9
本文接收函数与Bedmap2冰厚结果差值
Figure 9.
Differences of ice thickness between Bedmap2 and PRFs obtained in this study
图 8
7组冰厚模型合成接收函数H-Kappa搜索结果
Figure 8.
H-Kappa stacking results for synthetic PRFs of the seven ice sheet models
图 10
直接计算法(PpPs)、H-Kappa(本文)、Bedmap2冰厚格网冰厚结果比较
Figure 10.
Comparison of ice thickness obtained from direct method (PpPs arrival time), H-Kappa (this study) and Bedmap2
图 11
沉积层对冰岩界面震相的干扰
Figure 11.
Effect of the sediment on converted phases of interest at the ice-bedrock interface
表 1
接收函数正演理论模型参数
Table 1.
Parameters of forward modeling models for P-wave receiver functions
介质层 深度
(km)密度
(g·cm-3)VS
(km·s-1)VP/VS 冰层 3.15 0.92 1.94 1.96 地壳 33 2.77 3.64 1.74 半无限空间 - 3.77 4.55 1.80 
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表 2
55个台站H-Kappa结果
Table 2.
H-Kappa results of 55 stations
台站名 经度(°) 纬度(°) 冰厚(km) VP/VS PRFs个数 冰厚(km)Hansen E018 157.22 -76.82 1.70±0.21 2.27±0.09 46 - E020 156.55 -76.73 1.98±0.31 2.58±0.06 21 - E030 153.38 -76.25 2.02±0.25 2.38±0.05 36 - N028 153.65 -78.03 1.95±0.21 2.43±0.05 31 - N036 151.28 -78.55 2.54±0.23 2.32±0.07 61 - N044 148.62 -79.07 2.84±0.32 2.29±0.03 25 - N060 142.6 -80 3.14±0.36 2.29±0.06 22 - N068 138.92 -80.39 2.92±0.23 2.15±0.03 25 - N076 135.43 -80.81 2.45±0.18 2.05±0.06 58 - N084 131.47 -81.16 2.38±0.19 2.08±0.06 28 - N092 126.98 -81.46 2.51±0.22 2.11±0.07 19 - N100 122.59 -81.65 2.49±0.21 2.06±0.08 337 - N108 117.61 -81.88 2.46±0.17 2.12±0.07 47 - N116 112.57 -82.01 1.98±0.17 2.12±0.06 20 - TIMW 135.27 -80.39 2.54±0.28 2.04±0.09 67 - GM01 104.73 -83.99 2.95±0.21 2.12±0.05 203 3.05 GM02 97.58 -79.43 2.90±0.24 2.06±0.08 206 2.90 GM03 85.94 -80.22 3.08±0.27 2.02±0.05 120 3.10 GM04 61.11 -83 2.96±0.29 2.18±0.07 142 2.95 GM05 51.16 -81.18 2.57±0.19 2.23±0.08 253 2.80 GM06 44.31 -79.33 2.88±0.30 2.21±0.10 25 3.15 GM07 39.61 -77.31 3.08±0.31 2.03±0.05 36 3.00 N124 107.64 -82.07 2.16±0.15 2.34±0.08 202 2.50 N132 101.95 -82.07 3.09±0.19 2.21±0.06 135 3.35 N140 96.77 -82.01 2.17±0.24 2.14±0.08 504 2.40 N148 91.51 -81.86 3.00±0.27 2.14±0.04 71 3.20 N156 86.5 -81.67 2.28±0.26 2.15±0.10 137 2.35 N165 81.76 -81.41 2.52±0.31 2.11±0.06 75 2.80 N173 77.47 -81.11 2.55±0.28 2.04±0.10 103 2.45 N182 73.19 -80.74 2.52±0.21 2.12±0.06 42 2.60 N190 69.43 -80.33 3.14±0.34 2.12±0.03 84 3.25 N198 65.96 -79.86 2.67±0.26 2.07±0.06 145 2.85 N206 62.86 -79.39 2.25±0.23 2.07±0.08 66 2.40 N215 59.99 -78.9 2.79±0.17 2.11±0.10 221 2.75 P061 77.22 -84.5 2.92±0.21 2.03±0.07 165 2.90 P071 77.33 -83.65 2.14±0.28 2.0±0.09 53 2.10 P080 77.36 -82.81 2.36±0.22 2.17±0.07 138 2.35 P116 77.05 -79.57 1.78±0.19 2.16±0.05 47 2.00 P124 77.66 -78.87 1.53±0.21 2.07±0.04 16 1.30 SWEI 129.36 -86.99 3.54±0.24 2.50±0.04 73 - BENN -117.39 -84.57 1.30±0.18 2.50±0.09 88 - BYRD -119.47 -80.02 2.05±0.19 2.23±0.05 103 - ST01 -98.74 -83.23 2.75±0.20. 2.14±0.06 49 - ST02 -109.12 -82.07 2.18±0.22 2.37±0.05 46 - ST03 -113.15 -81.41 1.82±0.21 2.13±0.08 53 - ST04 -116.58 -80.72 3.58±0.31 2.42±0.03 45 - ST06 -121.82 -79.33 3.04±0.26 2.41±0.05 78 - ST07 -123.8 -78.64 2.52±0.26 2.53±0.08 82 - ST08 -125.53 -77.95 2.26±0.22 2.53±0.07 55 - ST09 -128.47 -76.53 2.91±0.37 2.46±0.07 61 - ST10 -129.75 -75.81 1.81±0.17 2.03±0.08 22 - ST13 -130.51 -77.56 2.15±0.21 2.25±0, 07 69 - ST14 -134.08 -77.84 1.28±0.16 2.25±0.07 76 - UPTW -109.04 -77.58 3.21±0.27 2.22±0.04 95 - WAIS -111.78 -79.42 3.05±0.26 2.17±0.06 180 -
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表 3
7个接收函数正演冰层模型
Table 3.
Seven ice sheet models for synthetic receiver functions
模型 模型1 模型2 模型3 模型4 模型5 模型6 模型7 理论厚度(km) 2.80 2.90 3.00 3.01 3.02 3.05 3.10 搜索厚度(km) 2.79±0.15 2.90±0.15 3.00±0.15 3.01±0.15 3.02±0.15 3.10±0.15 3.10±0.15
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