Evidence of both M2 and O1Earth tide waves in radon‐222 air concentration measured in a subglacial laboratory
Evidence of both M2 and O1Earth tide waves in radon‐222 air concentration measured in a subglacial laboratory
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DOI：
10.1029/2011jb009111
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发表时间：
2012-12
影响因子：
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通讯作者：
P. Richon;L. Moreau;J. Sabroux;E. Pili;A. Salaün
中科院分区：
文献类型：
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作者：
P. Richon;L. Moreau;J. Sabroux;E. Pili;A. Salaün
[1]自1960年代以来，记录了许多与地震有关的氡-222的时间变化，并经常被讨论，有时引发了一场关于氡-222作为地震前兆信号的相关性的争论。氡信号中的全日S_1-O_1和半日S_2-M_2固体潮特征是在自然环境下获得的。这可以用来校准震中区附近应变积累下的氡变化，这一点经常被讨论，但很少被实验数据证明。对法国阿尔卑斯山勃朗峰Argentiere冰川下实验室采集的10个月时间序列的分析表明，M2-O1波在氡信号中有明确的幕式出现，显著幅度分别为36和50Bq m−3。从而证明了在自然环境中，M2波和O1波引起的氡变化是可以探测到的。在这个特殊的地方，在实验室钻探的天然岩坝上游一侧施加的循环应力变化可能放大了氡的响应。氡信号的放大是由这种特殊的机械作用力下的孔弹性变形引起的。这可以解释为什么大多数先例研究未能在其他地下实验室记录的氡信号中检测到M2-O1特征。
[1] Many earthquake-related radon-222 temporal changes have been recorded since the 1960s and are frequently discussed, sometimes initiating a controversial debate on the relevance of radon-222 as an earthquake precursory signal. The diurnal S1–O1 and semidiurnal S2–M2 Earth tide signatures in radon signals are acquired in a natural context. This can be used to calibrate the radon changes under strain accumulation close to epicentral areas, which are often discussed but are rarely evidenced by experimental data. The analysis of a 10 month time series acquired in the subglacial laboratory of the Argentiere glacier, Mont Blanc Massif, French Alps, demonstrates here the unambiguous episodic appearance of the M2–O1 waves in the radon signal with significant amplitudes of 36 and 50 Bq m−3, respectively. We thus prove that radon variations induced by gravitational M2 and O1 waves are detectable in a natural environment. In this particular place, the radon response is probably amplified by cyclic stress variations applied on the upstream side of the natural rock dam into which the laboratory is drilled. The amplification of the radon signal is induced by poroelastic deformation under this particular mechanical forcing. This can elucidate why most precedent studies failed to detect M2–O1 signatures in radon signals recorded in other underground laboratories.