THE CHARACTERISTICS AND MECHANISM OF FLUID ANOMALIES IN THE DAZHAI OBSERVATION WELL OF PU’ER, YUNNAN PROVINCE BEFORE THE M5.9 MOJIANG EARTHQUAKE ON SEPTEMBER 8, 2018

doi:10.3969/j.issn.0253-4967.2024.02.014

Abstract

Abstract:

The precursors before earthquakes are very useful to earthquake prediction, and fluid anomalies before earthquakes are very important to precursory observations. This paper reviews the characteristics of hydrochemical ions and well-aquifer permeability anomalies of the Dazhai observation Well in Pu’er, which is in the Yunnan-Southwestern region of China, for all M≥5.5 earthquakes since 2004. We find that both the chemical ions and physical parameters before the Mojiang M5.9 earthquake exhibited the largest magnitude of changes since observation, and the abnormal state was much stronger than that of previous historical earthquakes, but the magnitude of the earthquake was below 6. About 1.5-2a before the M5.9 Mojiang earthquake, the composition of hydrogen and oxygen isotopes of the water samples in the Dazhai observation Well showed a significant deviation, accompanied by a continuously increasing concentration of fluoride ions from sources at deeper depths. This might suggest that the deep material in the earthquake source area began to be active. At the same time, starting one year before the earthquake, the phase lag of the water level in the wellhole changed from negative to positive, indicating that the source and pathway of well water recharge have been changed. In addition, around half a year before the earthquake, the continuously observed water chemical ions at shallow depths in the wellhole began to show a dramatic change. Moreover, macroscopic anomalies of hot spring water volume increased sharply before the earthquake, showing a remarkable evolution process from deep to shallow, from background to short-term, and from micro anomalies to macro anomalies before the earthquake. To investigate the causes and mechanisms of this phenomenon, we attempt to discuss the abnormal evolution process before the M5.9 Mojiang earthquake from the aspects of regional deep material activity and regional stress level. The abnormal concentration of the hydrochemical ions and the change of aquifer permeability observed continuously at the Dazhai observation well before the M5.9 Mojiang earthquake were caused by the continuous increase in shear stress in the region, which caused the aquifer to be compressed, resulting in a vertical fluid recharge and ultimately the alternation and mixing of different aquifer water bodies. In addition to being controlled by the continuous increase in regional vertical shear stress, the abnormal formation process was also accompanied by the intense activity of deep-sourced chemical elements such as helium isotope and fluoride ion. The abnormal evolution process showed a remarkably coupled process of migration from deep to shallow, which may be the reason why the shallow ion anomaly before the M5.9 Mojiang earthquake was the most significant among all the observed cases. Therefore, the evolution process of fluid activity starting from the deep and continuously transmitting to the surface with the accumulation of regional stress is essential to the abnormal evolution of the hydrological phenomenon before the M5.9 Mojiang earthquake. The regional stress and the process of deep material activity are the biggest differences between the M5.9 Mojiang earthquake and other historical earthquake cases in the study area, which will be the two main factors to be considered when similar ion changes occur again in the future. Our study provides insight into a comprehensive understanding of the predictive significance of underground fluid anomalies in the Dazhai well and the coupled evolution process of deep-shallow fluid anomalies before the earthquake.

Key words: characteristics of fluid anomalies, deep-shallow coupling, Dazhai observation well of Pu’er, M5.9 Mojiang earthquake

摘要：

文中梳理了2004年以来普洱大寨井连续观测的水化学离子和井-含水层渗透性异常特征。研究发现, 在观测井周边250km范围内5.5级以上地震发生前, 多次出现过可重复、可类比的异常变化, 对地震具有较好的异常指示和预测意义。但相比以往震例, 墨江5.9级地震发生前, 无论是化学离子还是物理参数均出现了观测以来幅度最大的变化, 异常状态较以往强烈很多, 但发震的震级只有5.9级。为了研究这一现象产生的原因和机理, 文中尝试从区域深部物质活动和区域应力水平2个方面对墨江5.9级地震前的异常演化过程开展讨论, 得到以下认识: 墨江5.9级地震前, 流体异常整体呈现出较为显著的从深部到浅部、从背景到短期微观异常再到临震宏观异常的演化过程; 墨江5.9级地震前, 普洱大寨连续观测的水化学离子浓度异常和井-含水层渗透性的改变是由于区域内垂向剪切应力持续增强引起的含水层受挤压, 从而形成了垂向的流体补给, 最终引起不同含水层水体发生交替混合而产生的结果; 本次异常形成初期还伴随深部物质剧烈活动的现象, 较为显著的由深部到浅部的耦合作用过程可能是导致墨江5.9级地震前出现自观测以来地下流体异常幅度最显著的原因。因此, 流体活动从深部开始, 随着区域应力不断积累, 不断向地表传递的演变过程是墨江5.9级地震前流体异常演化的本质特征; 区域应力的作用方式和深部物质活动程度不同, 是引起墨江5.9级地震前异常特征与研究区其他历史震例前明显不同的根本原因。文中研究为全面认识普洱大寨井地下流体异常的预测意义和地震前流体异常的深浅耦合演化过程提供了一定参考。

关键词: 地下流体异常, 深浅耦合, 普洱大寨井, 墨江5.9级地震

HU Xiao-jing, FU Hong, ZHANG Xiang, LI Li-bo, HUANG Jiang-pei, LI Qiong, GAO Wen-fei. THE CHARACTERISTICS AND MECHANISM OF FLUID ANOMALIES IN THE DAZHAI OBSERVATION WELL OF PU’ER, YUNNAN PROVINCE BEFORE THE M5.9 MOJIANG EARTHQUAKE ON SEPTEMBER 8, 2018[J]. SEISMOLOGY AND GEOLOGY, 2024, 46(2): 477-491.

胡小静, 付虹, 张翔, 李利波, 黄江培, 李琼, 高文斐. 2018年9月8日墨江5.9级地震云南普洱大寨流体异常特征及机理[J]. 地震地质, 2024, 46(2): 477-491.

Figures/Tables 13

Fig. 1 The Geological location and the M≥5.5 earthquakes around the Dazhai observation well.

Fig. 2 The Schematic diagram of the Dazhai observation well borehole.

Table1 Variation characteristics of chemical ion concentration in the water of Dazhai observation well in Pu’er before the M≥5.5 earthquake in southwest Yunnan

Fig. 3 Time series of ions concentration of Dazhai observation well(5-day value).

Table2 Variation characteristics of permeability between Dazhai observation well and aquifer before the M≥5.5 earthquakes in Southwest Yunnan

序号	震例	变化形态	开始时间	持续时间	震时变化	震中距/km
1	2007-06-03,宁洱M6.4	持续减小—转折—发震	震前13个月	8个月	瞬时增大	28
2	2011-03-24,缅甸M7.2	持续减小—突升—发震	震前16个月	13个月	瞬时减小	252
3	2014-10-07,景谷M6.6	持续增大—转折—发震	震前13个月	4个月	瞬时增大	91
4	2015-03-01,沧源M5.5	无变化				235
5	2018-09-08,墨江M5.9	持续增大—转折—发震	震前15个月	10个月	瞬时增大	79

Fig. 4 Phase lag time process of water level in Dazhai observation well(monthly value).

Table3 Test results of water chemical components in Dazhai observation well since 2017

取样日期	Na⁺	K⁺	Ca²⁺	Mg²⁺	Cl^-	F^-	SO₄^2-	HCO₃^-	NO₃^-	δ¹⁸O	δD
取样日期	mg/L									‰
2017-05-21	45.93	1.472	37.248	7.492	3.457	0.658	3.958	257.46	0.441	-10.1	-72.8
2018-05-29	51.52	2.26	10.81	6.66	0.49	0.51	9.56	280.07	1.64	-11.06	-78.72
2019-06-30	46.52	1.52	37.55	6.93	0.48	0.19	9.38	268.47	1.08	-11.01	-78.71
2020-06-15	45.74	1.60	31.14	5.81	0.52	0.21	4.46	250.17	0.41	-10.72	-78.17
2021-06-20	43.32	1.87	45.99	6.79	1.57	0.00	3.88	311.84	0.10	-11.32	-80.13

Fig. 5 Characteristics of water ion concentration in Dazhai observation well(2017—2021).

Fig. 6 Hydrogen and oxygen isotope composition.

Fig. 7 Time sequence diagram of gravity at Tongguan and Pu’er measuring points.

Fig. 8 Background changes of Helium isotopes in 2017 relative to 2016.

Fig. 9 Distribution of GPS surface strain field in Yunnan during 2016—2019.

Fig. 10 Time series of surface strain and shear strain on GNSS No.24 grid.

References 21

[1]	曹颖, 钱佳威, 黄江培, 等. 2021. 利用时移层析成像方法分析2014年云南景谷 M_S6.6 地震震源区的P波速度变化[J]. 地震地质, 43(6): 1563—1585. doi: 10.3969/j.issn.0253-4967.2021.06.012.
	CAO Ying, QIAN Jia-wei, HUANG Jiang-pei, et al. 2021. P-wave velocity changes in hypocenter region of the 2014 Jinggu M_S6.6 earthquake using time-lapse tomography based on double-difference tomography[J]. Seismology and Geology, 43(6): 1563—1585(in Chinese). DOI
[2]	胡小静, 付虹, 李涛, 等. 2020. 云南普洱大寨井水位同震响应研究及预测意义[J]. 地震研究, 43(2): 340—347.
	HU Xiao-jing, FU Hong, LI Tao, et al. 2020. Study on co-seismic response and prediction significance of groundwater level in the Dazhai Well[J]. Journal of Seismological Research, 43(2): 340—347(in Chinese).
[3]	李营, 陈志, 胡乐, 等. 2022. 流体地球化学进展及其在地震预测研究中的应用[J]. 科学通报, 67(13): 1404—1420. doi: 10.1360/TB-2021-0955.
	LI Ying, CHEN Zhi, HU Le, et al. 2022. Advances in seismic fluid geochemistry and its application in earthquake forecasting[J]. Chinese Science Bulletion, 67(13): 1404—1420(in Chinese). doi: 10.1360/TB-2021-0955.
[4]	刘耀炜, 任宏微, 张磊, 等. 2015. 鲁甸6.5级地震地下流体典型异常与前兆机理分析[J]. 地震地质, 37(1): 307—317. doi: 10.3969/j.issn.0253-4967.2015.01.024.
	LIU Yao-wei, REN Hong-wei, ZHANG Lei, et al. 2020. Underground fluid anomalies and the precursor mechanisms of the Ludian M_S6.5 earthquake[J]. Seismology and Geology, 37(1): 307—317(in Chinese).
[5]	刘耀炜, 孙小龙, 王世芹, 等. 2008. 井孔水温异常与2007年宁洱6.4级地震关系分析[J]. 地震研究, 31(4): 347—353.
	LIU Yao-wei, SUN Xiao-long, WANG Shi-qin, et al. 2008. Relationship of bore-hole water temperature anomaly and the 2007 Ning’er M6.4 earthquake[J]. Journal of Seismological Research, 31(4): 347—353(in Chinese).
[6]	路畅, 周晓成, 李营, 等. 2021. 玛多 M_S7.4 地震地表破裂带与东昆仑断裂温泉的水文地球化学特征[J]. 地震地质, 43(5): 1101—1126. doi: 10.3969/j.issn.0253-4967.2021.05.005.
	LU Chang, ZHOU Xiao-cheng, LI Ying, et al. 2021. Hydrogeochemical characteristics of groundwater in the surface rupture zone of Madoi M_S7. 4 earthquake and hot springs in the east Kunlun Fault[J]. Seismology and Geology, 43(5): 1101—1126(in Chinese). DOI
[7]	彭关灵, 孔德育, 孙楠, 等. 2020. 2014年景谷 M_S6.6 和2018年墨江 M_S5.9 地震前视应力、视体积异常特征研究[J]. 地震研究, 43(2): 355—362.
	PENG Guan-ling, KONG De-yu, SUN Nan, et al. 2020. Characterization of apparent stress and apparent volume before the 2014 Jinggu M_S6.6 and 2018 Mojiang M_S5.9 earthquake, Yunnan[J]. Journal of Seismological Research, 43(2): 355—362(in Chinese).
[8]	孙小龙, 向阳. 2018. 基于同震水震波的水文地质参数求取方法探讨[J]. 水文地质工程地质, 45(3): 22—29.
	SUN Xiao-long, XIANG Yang. 2018. A discussion of the method of estimating hydraulic parameters based on ground-water responses to seismic waves[J]. Hydrogeology & Engineering Geology, 45(3): 22—29(in Chinese).
[9]	易立新, 刘香, 侯建伟, 等. 2007. 地震研究中的断层流体动力学问题[J]. 地震, 27(1): 1—8.
	YI Li-xin, LIU Xiang, HOU Jian-wei, et al. 2007. The problems of fault fluids dynamics in seismological research[J]. Earthquake, 27(1): 1—8(in Chinese).
[10]	张彧齐. 2020. 云南思茅盆地泉水水文地球化学特征及成因研究[D]. 北京: 中国地质大学: 27—29.
	ZHANG Yu-qi. 2020. Hydrogeochemical characteristics and genesis of the springs in the Simao Basin of Yunnan[D]. China University of Geosciences, Beijing: 27—29(in Chinese).
[11]	Chen Z, Li Y, Liu F, et al. 2022. Geochemical and geophysical effects of tectonic activity in faulted areas of the North China Craton[J]. Chemical Geology, 609: 121048. doi.org/10.1016/j.chemgeo.2022.121048.
[12]	Kinoshita C, Kano Y, Ito H. 2015. Shallow crustal permeability enhancement in central Japan due to the 2011 Tohoku earthquake[J]. Geophysical Research Letters, 42(3): 773—780.
[13]	Montgomery D R, Manga M. 2003. Streamflow and water well responses to earthquakes[J]. Science, 300(5628): 2047—2049. PMID
[14]	Shi Z, Wang G. 2016. Aquifers switched from confined to semiconfined by earthquakes[J]. Geophysical Research Letters, 43(21): 11166—11172.
[15]	Skelton A, Andrén M, Kristmannsdóttir H, et al. 2014. Changes in groundwater chemistry before two consecutive earthquakes in Iceland[J]. Nature Geoscience, 7(10): 752—756.
[16]	Tian J, Zhou X, Yan Y, et al. 2023. Earthquake-induced impulsive release of water in the fractured aquifer system: Insights from the long-term hydrochemical monitoring of hot springs in the Southeast Tibetan Plateau[J]. Applied Geochemistry, 148:105553. https://doi.org/10.1016/j.apgeochem.2022.105553.
[17]	Wang C Y, Wang L P, Manga M, et al. 2013. Basin-scale transport of heat and fluid induced by earthquakes[J]. Geophysical Research Letters, 40(15): 3893—3897.
[18]	Woith H, Wang R, Maiwald U, et al. 2013. On the origin of geochemical anomalies in groundwaters induced by the Adana 1998 earthquake[J]. Chemical Geology, 339: 177—186.
[19]	Yan R, Wang G, Ma Y, et al. 2020. Local groundwater and tidal changes induced by large earthquakes in the Taiyuan Basin, North China from well monitoring[J]. Journal of Hydrology, 582:124479.
[20]	Zhou Z, Tian L, Zhao J, et al. 2020. Stress-related pre-seismic water radon concentration variations in the Panjin observation well, China(1994—2020)[J]. Frontiers in Earth Science, 8:596283. doi: 10.3389/feart.2020.596283.
[21]	Zhou Z, Zhong J, Zhao J, et al. 2021. Two mechanisms of earthquake-induced hydrochemical variations in an observation well[J]. Water, 13(17): 2385. doi: 10.3390/w13172385.