A Discussion on the Generality of Precursor Waves on Well Water Level Records

Taking five underground water level observation wells with high earthquake response capability and located in Shanxi,Hebei and Inner Mongolia as study objects,this paper studies and discusses the generality of precursor waves in well water levels before strong earthquakes. It is indicated that the precursor waves often happen before strong earthquakes,with the ratio of occurrence up to 65% ( 41 /63 ) ; the precursor waves have poor generality in different observation wells,which may be related to the different well-aquifer system of different observation wells and the different source parameters of earthquakes. Compared to the seismic water level fluctuations in a single well,the number of precursor wave times recorded in well water levels before strong earthquakes is slightly less than that of seismic water level fluctuations,with a ratio between 39. 7% and 50. 7%, respectively. The number of observation wells with precursor wave recordings before earthquakes accounts for up to 66. 7% of the total number of observation wells. The precursor wave in well water level records has a certain generality in terms of the number of times recorded and the spatial distribution,except for its manifestation characteristics.

Tidal Response Characteristics of the Well Water Level in the Sichuan-Yunnan Region

In this paper,the long time series data of the well water-level data of 12 wells in the Sichuan and Yunnan area is analyzed by the Baytap-G tidal analysis software,and well water level tidal response characteristic parameters( amplitude ratio and phase change)are extracted. We analyzed the features of the shape and stage change,and characteristic parameters of the tidal response of well water level before and after the earthquakes,which can provide a new method and approach to analyzing the response relationships between well water level and earth tide and barometric pressure. The results show that Luguhu Well and 9 other wells are affected by earth tides,and their well water level amplitude ratios and phases are relatively stable; the Nanxi Well and Dayao Well water level changes are affected by the barometric pressure combined with tide force,and their well water level amplitude ratios and phases are more discrete. The water level amplitude ratios and phases of Jiangyou Well,Luguhu Well and Dongchuan Well are significant to large earthquakes,and the relationship between seismic energy density and water level amplitude ratios and phases of M_2 wave of the three wells are presented.

A discussion on the records of water level “precursors” in Well Shuozhou, Shanxi Province

A lot of slow fluctuations of water level have been observed in the original recording maps of subsurface fluid in Well Shuozhou, Shanxi Province. Some typical recording maps of the 'precursors' are introduced in the paper and the features of the 'precursors' recorded by the well are analyzed. The results show that 38% strong earthquakes possess this kind of record, which has a fluctuation period arranging from several to tens of minutes and appear mostly two days before the earthquakes. Moreover, the mechanism, transmission and responding conditions of well water level are discussed, as well as the scientific meaning and practical value of the 'precursor' of the well water level in earthquake predictions.

Dynamic analysis of water level in the Wanquan Well and the precursory anomalies of earthquakes

According to the characteristics of frequent water level step-variation in the Wanquan Well, the step-variation frequency change on the time axis can be regarded as a sequence of step-variation. A study of the relationship between the process of development and evolution of the sequential step-variation and the regional seismicity indicated that the sequential step-variation anomalies are rather better in coincidence with the time, magnitude and frequency of regional seismic activities, which may predict the seismicity trend in months. Furthermore, on this basis, if the water level changes in a characteristic manner, the seismic regime during the time period from several days to 20 days or more may be evaluated. By using the method presented in this paper we had a prediction about the Baotou ML=6.6 earthquake on May 3, 1996. This event occurred within the predicted time span but with a less magnitude and a little location deviation.

Analysis on the Characteristics of the Coseismic Response of Water Levels Recorded in Three Wells in Hainan,China to the Two Sumatra-Andaman Strong Earthquakes

The characteristics of seismic water level fluctuations of the two Sumatra-Andaman strong earthquakes with magnitude 8.7 and 8.5 on December 26,2004 and March 29,2005 recorded at Jiaji well,Qionghai,Hainan were analyzed,the features of the infrequent "step" changes of well water level after the two earthquakes were also analyzed and the mechanism of the "step change" of well water level was discussed.Then the high-sample-rate digital observation data of seismically-induced water level fluctuations of the Sumatra-Andaman strong earthquakes with magnitude 8.7 and 8.5 recorded at Nanbin well,Sanya and Tanniu well,Wenchang were analyzed.The results suggest that the dominant period of the seismic well water level fluctuation in all three wells was comparatively accordant,the amplitudes of seismic water level fluctuation of the same earthquake in different wells were clearly different,the time duration of seismic water level fluctuations of different earthquakes at the same well was also clearly different.

Discussion on the Reproducibility of Precursor Waves in the Water Level Records of Jingle Well

Choosing the Jingle well in Shanxi as the research object, this paper discusses the reproducibility problem of well water level precursor waves. The results show that the start time and fluctuation cycle before similar earthquakes are highly reproducible,the ratio of which is up to 63. 1%. The fluctuation form and amplitude before some similar earthquakes are of certain similarity,but earthquakes with all precursor wave features being similar were not found in the research scope. The reason may be related to the origin and transmission route of the precursor wave as well as the properties of the seismic source area of similar earthquakes.

Characteristics of coseismic water level changes at Tangshan well for the Wenchuan MS_8.0 earthquake and its larger aftershocks

Coseismic water level changes which may have been induced by the Wenchuan Ms8.0 earthquake and its 15 larger aftershocks （Ms〉5.4） have been observed at Tangshan well. We analyze the correlation between coseismic parameters （maximum amplitude, duration, coseismic step and the time when the coseismic reach its maximum amplitude） and earthquake parameters （magnitude, well-epicenter distance and depth）, and then compare the time when the coseismic oscillation reaches its maximum amplitude with the seismogram from Douhe seismic station which is about 16.3 km away from Tangshan well. The analysis indicates that magnitude is the main factor influencing the induced coseismic water level changes, and that the well-epicenter distance and depth have less influence. Ms magnitude has the strongest correlation with the coseismic water level changes comparing to Mw and ML magnitudes. There exists strong correlation between the maximum amplitude, step size and the oscillation duration. The water level oscillation and step are both caused by dynamic strain sourcing from seismic waves. Most of the times when the oscillations reach their maximum amplitudes are between S and Rayleigh waves. The coseismic water level changes are due to the co-effect of seismic waves and hydro-geological environments.

Influence of the 2011 Mw9. 0 Japan earthquake on groundwater levels in Chinese mainland

This paper gives a description of the co-seismic and post-seismic groundwater level changes induced in Chinese mainland by the 2011 Mw9.0 Japan earthquake, and the corresponding stress changes calculated on the assumption of linear elasticity. The result shows that the main types of changes were oscillations and step increases. The North-South Seismic Belt and the Shanxi Seismic Belt were the main areas affected by the earthquake.

井水位气压效率计算方法的对比研究——以云南高大井为例

为了研究不同井水位气压效率计算方法的原理及差异性,基于2019年2月1日至2020年7月28日云南高大井的气压与水位数据,使用Clark方法、Rahi方法、回归反卷积法和Acworth方法计算了该井的气压效率BE值,分别为:0.4395、0.4968、0.6174和0.6654,平均值为0.5548。对比分析结果表明:Clark方法和Rahi方法的优点是计算简单方便,但是没有考虑时间滞后的影响;回归反卷积法可以获得BE值随滞后时间的变化情况,但是极易受到降水、蒸散发等信号的影响;Acworth方法考虑了固体潮信号并且避免了降水、蒸散发等信号的干扰,但是该方法仅适用于承压和半承压含水层中。最后,根据4种方法的特点和适用性,对不同目的下的井水位气压效应分析给出了相应的建议。

2023年2月6日土耳其两次7.8级地震引起的井水位同震响应对比分析

2023年2月6日,土耳其发生的两次7.8级地震引起了新疆乌鲁木齐地区新04井、新10井和新11井的同震响应,但同震变化形态各有不同。本文对比分析了这三口观测井水位的同震响应特征,探讨了地震引起的井水位同震响应机理。结果显示,本研究中的三口观测井水位的同震响应类型有振荡、同震下降和同震上升三种。其中,新10井表现为振荡,而新04井和新11井则分别表现为同震下降和上升,表明井水位同震变化机理的复杂性。两次地震在同一观测井的同震响应形态一致,不同观测井水位同震变化与井孔所在位置的渗透性结构改变有关。

介休井水位异常变化特征分析

根据山西介休井水位2007年数字化观测以来的数据变化,梳理归纳该井水位观测曲线的正常变化形态、同震变化以及影响介休井水位变化的人为干扰和自然环境干扰因素;同时对2023年7月27日介休井水位出现的突降异常,从井区构造环境、周边地震活动、地球物理观测异常变化等方面,与典型震例前的异常变化进行对比分析,认为该异常与山西中南部中等地震前的异常在时、空、强特征方面具有较高的相似性,表明山西南部区域的构造活动、应力水平在逐步增强。

基于Molchan图表法的流体监测井水位地震预测效能检验

为了探究水位异常和地震之间潜在的对应关系以及监测井水位的地震预测效能,通过差分法和水位固体潮加卸载比法对德阳井、剑川井、佐署井和门源井水位数据进行处理,并采用Molchan图表法对4口监测井水位的不同预测期和不同块体发生的地震进行预测效能检验。结果表明:两种方法处理后的Molchan图表法检测效能结果相似;4口监测井水位在180 d内均有较好的预测效能,均对不同范围中强地震有一定预测效能,并且预测效能受板块内构造分布情况影响,对构造发育的区域预测效能更好。

陕西凤翔井水位和区域应力场变化与地震活动性关系研究

陇县-宝鸡断裂带的北段闭锁程度较强,但关于其南段的闭锁性研究较少。承压含水层的观测井被认为是灵敏的“体应变计”,井水位的上升或下降变化往往能反映区域应力处于拉张或挤压状态。陕西凤翔井位于陇县-宝鸡断裂的中南段。基于对凤翔井水位在2013-2023年期间变化趋势的分析,利用气压系数和M_2波潮汐因子等滑动拟合,计算了不排水条件下,该井含水层的孔隙度、固体骨架的体积压缩系数和水的体积压缩系数。通过该井水位变化量和含水层垂向应力变化量的关系式,定量分析了该井周边地区构造应力场的时序特征。结合区域内GNSS基线和面应变变化,以及2013年以来的地震活动,综合分析认为,该区域的应力场变化分为两个阶段:(1) 2013-2017年,凤翔井水位下降,垂向应力减弱,处于拉张环境,地震频次较低;(2) 2017-2023年,凤翔井水位趋于平稳,垂向应力在零值上下波动,拉张减弱并逐渐转变为应力积累增强阶段,地震频次有所增加。综合近十年凤翔井水位、垂向应力、 GNSS基线和面应变以及地震活动性分析可知,陇县-宝鸡断裂带中南段应力积累较弱,形变量较小,处于相对稳定的状态。

雅安地区监测井水位预测效能对比研究

为提高监测井水位映震效果的判别准确度并提升预测效能,本文运用不同方法对雅安地区两条断裂附近的6口监测井水位的映震效果开展了对比判别研究。首先,使用差分法对监测井水位数据进行处理和分析。然后,将水位数据与区域地震活动性的两种参数(能级和最大震级)相结合,分析区域地震活动性与水位波动的关系。接着,在时域和频域两个层面对该组合序列进行分析处理。最后,采用Molchan图表法检验5种方法的预测效能,并选出最佳处理方法及断裂附近预测效能最优的监测井。结果表明:水位与地震活动性参数结合处理相比单独使用水位差分法具有优势,前者能够准确排除地震活动性对水位异常的干扰。6口监测井的最优预测方法各不相同,最优预测天数均在60 d内。通过比较监测井水位对地震的预测效能检验结果,确定了两条断裂区域预测效能最优的监测井。虽然水位与地震活动性两种参数结合处理并不适用于所有监测井,但该方法能够体现水位受地震活动性影响的程度。

乌什M_(S)7.1地震引起新55井、新46井水位水温同震响应分析

为研究乌什M_(S)7.1地震引起新55井、新46井水位不同程度的响应变化,对比分析观测井水位的同震响应特征,从含水层渗透性变化和地震波能量密度探讨了同震响应机理。结果表明:①伽师新55井和乌什新46井同震响应形态主要表现为井水位的大幅快速上升。②固体潮计算分析结果表明当地震波作用于新55井和新46井时,前者垂向水力交换增强,水平向水力交换减弱,含水层的水与井水进行交换,引起井水位同震上升变化;后者含水层渗透性增加,含水层水与井水进行交换,引起井水位同震上升变化。③地震能量密度计算结果显示新55井比新46井容易触发同震响应,这种差异性的响应可能与井含水层岩性有关。

云南井网水温和水位对几次典型地震的响应特征研究

基于2008—2023年云南井网中26口观测井水温和水位的同震响应资料,以对云南地区影响较显著的8次地震为例,对比分析各观测井水温和水位的同震响应特征,分别从地震波能量密度、岩性、断裂带的控制作用以及动态协调性等角度对其同震响应机理进行了探讨。结果表明,云南井网水温和水位对远场大震的响应较近震显著,响应主要集中在滇中一带,水位响应较水温显著,水位同震变化以振荡和上升为主,水温以脉冲为主。德宏法帕滇22井和丽江象山井有更好的响应能力,剑川滇06井、会泽甘沟滇01井、昆明官渡区小哨井、大姚地温井和南华震2井的同震响应能力较其余21口井弱。进一步分析表明,地震波能量密度与震中距线性拟合相关系数大于−0.9,成明显负相关,与震级成正相关,并给出了能量密度与渗透系数的对应关系。最后分别对水温和水位同震响应机理进行了探讨。

基于EEMD方法提取唐山井水位固体潮响应特征

以唐山井为研究对象,通过集合经验模态分解方法(Ensemble Empirical Mode Decomposition,EEMD)对井水位观测数据进行分解,提取井水位中固体潮引起的井水位变化特征,对重构信号和固体潮理论值进行一元线性回归分析。结果表明,井水位经过EEMD分解后,各高频分量均包含一部分固体潮信息,可通过部分信号分量重构研究相应因素引起的井水位变化特征,提取被其他因素掩盖的信息。在选定时间范围内,井水位对固体潮响应的时间滞后不明显,唐山井水位春季受其它因素的影响较大,夏季对固体潮的响应较好。EEMD方法可较好提取井水位中固体潮变化特征,对分解结果进行重构时需要根据数据实际情况进行选择。

汤加火山运动引起的井水位动态特征提取

为了对2022年1月15日汤加火山爆发引起的井水位变化特征进行识别、提取,以河北唐山地区4口观测井为研究对象,使用EEMD方法分别处理井水位和气压观测数据,将观测数据表征的信号从频率由高到低分为多个IMF分量。通过高频分量描述井水位和气压高频事件的变化特征,结合Hilbert谱分析得到两者高频事件能量波动所在频段范围一致,发生时间相近,进一步对其进行相干性分析。结果表明汤加火山地震爆发后,井水位出现了两次变化,水位波形变化趋势与气压波形同步反向变化,相干性结果表明井水位与气压显著相关,林西矿井对气压剧烈变化响应更为灵敏。在此基础上,分析EEMD方法对短时间序列井水位处理的效能,探索Hilbert谱识别井水位干扰信号的能力。

四川流体台网水位同震响应特征对比分析

本文统计分析了四川流体台网对2022年四川芦山M_(S)6.1、马尔康M_(S)6.0、泸定M_(S)6.8三次大地震的水位同震响应特征。研究结果显示,三次大地震引起了四川大范围内不同程度的水位同震响应。水位同震响应幅度受震级影响显著,受井震距影响并不显著。大区域范围内的水位同震响应幅度受含水层岩性、地质构造、井孔条件等影响。水位同震响应类型主要受井震距影响,与井孔深度关系不大。川20井、川49井和川50井在2022年泸定M_(S)6.8地震中水位同震响应幅度差异较大的原因可能是井孔承压性不同。受含水层岩性、所处断裂带位置和井孔承压性影响,位于同一断裂带且距离较近的川46井、川47井和川48井在这三次大地震中的水位同震响应幅度存在差异。在2022年芦山M_(S)6.1地震中,川46井与川47井的水位同震响应类型不同,这可能与井孔水位受动态应力与静态应力的主要控制作用不同有关。水位同震响应的统计和分析结果受仪器采样率影响,使用分钟值水位数据分析得到的水位同震响应结果可能不够准确,秒钟值水位数据可以为水位同震响应特征及机理的精细研究提供更丰富准确的水震波数据。