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

doi:10.3969/j.issn.0253-4967.2024.02.014

摘要/Abstract

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

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

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.

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.

图/表 13

图1 区域构造及5.5级以上历史震例分布图

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

图2 普洱大寨井孔柱状图

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

表1 滇西南地区5.5级以上地震前普洱大寨井水化学离子浓度变化特征

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

图3 普洱大寨井离子浓度时序曲线(五日值)

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

表2 滇西南地区5.5级以上地震前普洱大寨井-含水层渗透性变化特征

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

图4 普洱大寨井水位相位滞后时间进程曲线(月值)

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

表3 普洱大寨井2017年以来的水化学组分测试结果

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

图5 普洱大寨井水离子浓度特征图(2017—2021年) a 地下水Piper图; b 观测井不同时期的水化学组分对比图

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

图6 氢氧同位素组成

Fig. 6 Hydrogen and oxygen isotope composition.

图7 通关、普洱测点的重力时序图

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

图8 2017年氦同位素相对2016年背景变化量①

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

图9 2016—2019年云南地区GPS面应变场分布

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

图10 GNSS 24号格网的面应变、剪应变时间序列

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

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