2018年浙江梅雨降水异常偏少的大尺度环流特征及前兆信号分析

2018年浙江梅雨降水异常偏少,梅雨期平均环流特征欧亚中高纬度为“两槽一脊型”,西太平洋副热带高压(以下简称西太副高)偏东偏北,东亚高空急流偏北,浙江以南缺少低空急流的支持,不利于形成持续降水。6月上、中旬水汽输送不足、南北气流辐合较弱、东亚高空急流偏南、南海夏季风偏强、印度季风偏弱是梅雨开始偏晚的重要原因。梅汛期主要形成了三次降水过程(过程Ⅰ、过程Ⅱ和过程Ⅲ)和一次降水间歇过程,过程Ⅰ和过程Ⅱ表现为南北气流辐合型降水,过程Ⅲ为台风降水。系统分析了与不同过程相对应的大尺度环流及其演变特征,发现由于冷空气活动偏弱、南海夏季风偏强、西南水汽输送偏弱,过程Ⅰ的强度强于过程Ⅱ。在环流分析基础上,进一步挖掘与浙江梅雨有密切关联的海洋、大气和陆面信号,发现对该年梅雨异常偏弱有重要指示意义的前兆信号为冬、春季Ni?o关键区海温指数为正异常且北太平洋中部海温呈现负异常、冬季西南印度洋海温为正异常、春季喀拉海-巴伦支海海冰偏少、4-5月南半球环状模指数和北极涛动指数分别处于正位相和负位相。基于浙江梅雨序列,依托相关系数和同号率两个指标筛选出从前冬到春季稳定维持或有所增强的气候信号,利用多元线性回归、多因子综合判别、联合诊断三种方法分别构造可冬季发布和春季发布的梅雨预测模型,发现线性模型整体上能够较好地预测梅雨降水距平,特别是对降水偏少情形指示意义突出。

钻孔应变数据的环境响应去除与震前异常提取

基于四川省姑咱台的钻孔应变观测数据,研究了2013年4月芦山MS7.0地震的应变异常。首先通过时间序列分解法去除芦山地震前后(2011年1月至2014年1月)观测数据的长期背景趋势和周期趋势,其次采用多通道奇异谱分析法分解数据,去除水位和气压引起的应变响应,最后提取应变数据中的震前负熵异常。结果表明:水位与水位应变响应的相关系数为-0.97;有96.1%天的日气压与其应变响应的相关系数的绝对值大于0.9,验证了本文环境响应去除算法的有效性;负熵异常累积与贝尼奥夫应变累积的一致性表明,震前4—6个月出现的负熵异常可能是地震前兆异常。以上结论充分表明本文试验的方法对于钻孔应变数据环境响应的去除及地震前兆异常的提取是有效的。

2013年岷县漳县M_(S)6.6地震和2017年九寨沟M_(S)7.0地震震前地球物理观测异常空间分布机理分析

对甘东南地区2013年岷县漳县M_(S)6.6地震和2017年九寨沟M_(S)7.0地震震前地球物理观测异常特征进行总结梳理。根据活动构造单元对地球物理观测台站进行区域划分,统计了相关构造单元上异常的数量和百分比,以及不同学科震前异常数量、百分比、异常持续时间等特征,并对异常的空间分布和机理进行分析,讨论了活动构造对异常分布的影响、异常强度与震源机制及断层应力之间的关系。结果表明:①2013年岷县漳县M_(S)6.6地震比2017年九寨沟M_(S)7.0地震震前地球物理观测异常百分比高,两次地震的震前电磁异常和跨断层水准测量异常均较为显著,而流体异常不明显;②震前地球物理观测异常分布与活动构造相关,2013年岷县漳县M_(S)6.6地震震前异常主要集中在东昆仑-西秦岭断裂带和六盘山-海原断裂带,2017年九寨沟M_(S)7.0地震震前异常则主要集中在龙门山断裂带和东昆仑-西秦岭断裂带;③两次地震震前地球物理观测异常分布均与GNSS速度场分布特征有较好的对应关系;④安德森断层应力模式解释了2013年岷县漳县M_(S)6.6地震(逆冲型)比2017年九寨沟M_(S)7.0地震(走滑型)的形成需要更多的应力积累,因此2013年岷县漳县M_(S)6.6地震虽然震级较小但震前异常更显著。

闪长岩破裂的声发射前兆现象及其裂纹路径演化规律

为了研究岩石破裂过程中裂纹扩展路径演化规律,基于声发射监测数据,结合矩张量反演、裂纹尺度量化及裂纹拓扑关系量化建立了裂纹扩展路径分析方法,并基于室内声发射试验分析了闪长岩单轴压缩破坏过程。研究结果表明:闪长岩在受载过程中产生微裂纹的特征尺度为1.06 mm,明显高于矿物颗粒的平均尺度;随着应力的增加,闪长岩试件内部的微裂纹由离散状态逐渐过渡为相互贯通状态,微裂纹相对集中区域更容易演化为宏观裂纹。

聚丙烯纤维再生混凝土主破裂前兆特征研究

为研究聚丙烯纤维再生混凝土的破裂尺度和主破裂前兆特征,设计制作了20组粗骨料替代率为25%和50%的试件,通过开展单轴压缩声发射试验,提取聚丙烯纤维再生混凝土破裂过程声发射能量和主频。以能量为媒介,探讨破裂尺度和声发射信号特征之间的对应关系。采用K-means聚类方法将大尺度破裂和小尺度破裂进行二维聚类分析,然后运用支持向量机得到大尺度破裂和小尺度破裂两类聚类的分界线。分析了聚丙烯纤维再生混凝土破裂过程声发射信号演化规律,发现存在声发射事件率减少,大尺度破裂信号增加,低能量小尺度破裂信号消失等特征。引入前兆响应系数概念,计算结果表明低能量小尺度破裂信号消失特征的前兆响应系数最大,前兆响应时间最早。

基于微震多参数的大规模岩体垮塌前兆特征研究

微震监测技术能进行工程岩体失稳垮塌前兆特征的辨识和分析,对于地质灾害预警防控具有重要意义。本文基于已有室内岩石受压损伤破坏声发射实验规律,通过开展现场微震多参数定量分析,探究了柿竹园矿山6·21大爆破诱发山体滑移垮塌的前兆特征。大爆破诱发微震事件的b值和空间分形维数表现出下降趋势,b值急剧下降和分形维数降到最低可作为工程岩体失稳垮塌的前兆特征。此外,能量指数和累计视体积的变化可以分别表征应力和应变的变化。能量指数快速下降和累计视体积持续增加的组合特征反映了岩体的失稳状态。经过多个失稳破坏阶段后岩体发生最终的失稳垮塌。该案例表明微震监测能为工程岩体失稳垮塌的预警和防控提供重要信息,也为涉及爆破作业的诸多地质工程活动的安全监测提供了参考。

门源M_(S)6.9地震前前兆吸引子的特征提取

以非线性动力系统为理论依据类比地震孕育过程,以非线性动力系统的吸引子理论类比研究地震前兆吸引子,将高台台钻孔倾斜定点形变观测作为孕震系统的状态变量,借助G-P算法从宏观观测数据入手推演前兆动力学特征。在验证了以钻孔倾斜作为状态变量时非线性动力系统前兆吸引子存在的基础上,通过研究以NS、EW分量作为状态变量时吸引子维数的变化特征,归纳总结出门源M_(S)6.9地震前出现异常的NS分量对应的前兆吸引子存在降维特性,即在震前随着时间推移和三维重构相空间数据分布变得集中而有序,相应的地震前兆吸引子的分形维数也更低;而在震前未出现异常的EW分量对应的前兆吸引子的分形维数则保持不变,且其三维重构相空间中点的分布也无明显差异。

油页岩单轴压缩声发射演化规律及其破坏前兆特征

为研究油页岩受载破坏过程中有效前兆特征,利用TP耦合气体逸出试验系统对油页岩开展单轴压缩声发射试验,采集岩样破坏全过程产生的声发射信号,分析岩样变形破坏声发射随时间变化规律,对岩样加载破坏过程中声发射特征方差与自相关系数进行深入分析。试验结果表明:试验过程中有明显声发射现象产生,声发射特征变化与岩样变形破坏过程有着良好的对应关系;通过分析声发射RA(上升时间/峰值幅度)与AF(平均频率)特征,岩样在试验过程中以张拉破裂为主,后期剪切破裂逐渐增多;声发射特征在临近峰值强度时快速增大,表现出明显的临界慢化现象,方差与自相关系数的突然增大可以作为岩石破坏的前兆特征,且方差的前兆特征信息的捕捉相较于自相关系数更加容易且更为可靠;将声发射b值与声发射特征参数方差结合分析,可以有效剔除试验过程产生的伪信号,方差斜率快速上升阶段出现的b值突降点,可以确定为岩石破坏前兆特征点。研究成果可为岩土工程灾害预警提供可靠依据。

2022年1月2日宁蒗M_(s)5.5地震异常特征分析

选取2022年1月2日宁蒗5.5级地震前距离震中250 km范围内的前兆资料,总结本次地震活动异常特征,并对比分析了距震中50 km范围内的两次历史5级地震前的异常特征,为今后该地区地震异常的判定及震情跟踪提供了参考。结果表明:宁蒗M_(S)5.5地震前共存在16项异常,其中测震学异常5条,微观前兆异常9条,宏观前兆异常2条,并在时间和空间上存在一定的特征。时间上,微观前兆异常以短期异常为主,震前3个月异常数量明显增加,表现为破年变和转折异常,地震活动性异常以中强地震长时间平静为主;空间上,微观前兆异常主要集中在震中200 km范围内,地震活动性异常主要为中小地震的有序条带分布。且与历史地震相比,此次地震与两次历史地震前的共有的异常特征有:宁蒗-木里-盐源多震区长时间中强震显著平静,在形变长趋势破年变异常背景下,流体短临异常较为突出。

Experimental investigation on predicting precursory changes in entropy for dominant frequency of rockburst

Rockburst is a dynamic phenomenon accompanied by acoustic emission(AE)activities.It is difficult to predict rockburst accurately.Based on the fast Fourier transform(FFT)method and the information entropy theory,the evolution model of dominant frequency entropy was established.The AE energy,frequency and stress were synthetically considered to predict rockburst.Under the triaxial and the single-face unloading tests,the relationship between AE energy and the development of internal cracks was analyzed.Using the FFT method,the distribution characteristics of AE dominant frequency values were obtained.Based on the information entropy theory,the dominant frequencies evolved patterns were ascertained.It was observed that the evolution models of the dominant frequency entropy were nearly the same and shared a characteristic“undulation-decrease-rise-sharp decrease”pattern.Results show that AE energy will be released suddenly before rockburst.The density of intermediate frequency increased prior to rockburst.The dominant frequency entropy reached a relative maximum value before rockburst,and then decreased sharply.These features could be used as a precursory information for predicting rockburst.The proposed relative maximum value could be as a key point to predict rockburst.This is a meaningful attempt on predicting rockburst.

Distinctive Precursory Air–Sea Signals between Regular and Super El Ni os

Statistically different precursory air–sea signals between a super and a regular El Ni no group are investigated, using observed SST and rainfall data, and oceanic and atmospheric reanalysis data. The El Ni no events during 1958–2008 are first separated into two groups： a super El Ni no group（S-group） and a regular El Ni no group（R-group）. Composite analysis shows that a significantly larger SST anomaly（SSTA） tendency appears in S-group than in R-group during the onset phase[April–May（0）], when the positive SSTA is very small. A mixed-layer heat budget analysis indicates that the tendency difference arises primarily from the difference in zonal advective feedback and the associated zonal current anomaly（u）.This is attributed to the difference in the thermocline depth anomaly（D） over the off-equatorial western Pacific prior to the onset phase, as revealed by three ocean assimilation products. Such a difference in D is caused by the difference in the wind stress curl anomaly in situ, which is mainly regulated by the anomalous SST and precipitation over the Maritime Continent and equatorial Pacific.

Precursory Signals of Extensive and Persistent Extreme Cold Events in China

The distinct precursory signals of countrywide extensive and persistent extreme cold events (CECs) were investigated and contrasted with those of countrywide cold wave events (CCWs). It is shown that most CECs were accompanied by a CCW in the initial stages. From the comparison between the CECs and the CCWs that were independent of any CEC, it is found that a south- west-northeast-oriented tilted ridge at 500 hPa was present around the Europe-Barents Sea regions approximately 10 days prior to the start of the CEC. Consistent with this feature, a high sea level pressure and strong cold air accumulation occurred over a broad extent of northern Eurasia one week prior to the start of the CEC. The tilted ridge and the strong cold air accumulation were the precursory signals that were absent for the CCW, and they provide important clues for the early prediction of whether a CCW event might evolve into a CEC.

Certainty factors of earthquake precursory anomaly evidences CF(E)

In this paper, we propose the principle, methods and calculating formulas for determining the certainty factors of earthquake precursory anomaly evidences CF (E). Based on the guidebooks for earthquake prediction, we give the methods of determining the CF values of 22 evidences (including seismic gap, belt, b-value, c-value, velocity ratio, strengthen of anomalous activities, quiet of anomalous activities, seismic window, earthquake swarm,earthquake sequence, coda wave, initial motion of P wave, stress drop, geoelectricity, geomagnetism, stress,ground tilt, ground water level, radon and hydrochemistry, gravity, space environment and macroscopic anomalies), and show three examples. The purposes are to use the Expert System for Earthquake Prediction (ESEP) further.

Research on the Spatial Inhomogeneity Paramter C_v of Earthquake Precursory Group

A research method and parameter C_v which depicts the spatial inhomogeneity of earthquakeprecursory group, are developed in the paper. The influences of factors, such asinhomogeneous distribution of precursory observatory stations, the variety of observing itemnumber at each observatory station and the anomaly number of the same observing item atdifferent stations, etc., which cause the non-earthquake induced inhomogeneity, can beeliminated from C_v. The criteria of C_v to recognize particular spatial pattern of earthquakeprecursory group are also introduced. Based on the method, the spatial inhomogeneity ofradon precursory group and its relation to moderately strong earthquakes occurred in NorthChina during the same period are analyzed. The results show 5 strengthen processes of spatialinhomogeneity of radon precursory group before each of 5 earthquakes with M≥5. 0 in theregion during the period from Jan. 1, 1995 to Feb. 1, 1998. Among them 4 earthquakesoccurred within the time interval which the

Decline of groundwater table in Beijing and recognition of seismic precursory information

This paper quantitatively analyzed groundwater table fluctuations caused by groundwater overdraft, and probed into the possibility of drawing earthquake precursory information from groundwater table variations on the background of groundwater overdraft. Main effect factors of groundwater regime in Beijing region include groundwater extraction and rainfall. The decline of groundwater table was directly related to regional groundwater overdraft. Using the method of correlation analysis, the paper analyzed the relation between groundwater overdraft and groundwater level variations, with the aim of evaluating the effect of groundwater overdraft on water levels in observation wells and providing scientific basis for identifying seismic precursory information. The results indicate that the variations of groundwater level in slightly-affected zones of groundwater overdraft can contain some seismic precursory information, and it is possible to extract seismic precursory anomalies if proper mathematical methods are adopted to remove the trend component and annual period changes.

The statistical study of precursory anom alies observed in Chinese Seismological Network

By using the precursory anomalies at fixed seismological stations or observational points in China, which are obtained every year from the Assembly of National Seismologic Consideration (ANSC) from 1988 to 1996, to study the relationship between the anomalies in a certain year and the earthquakes occurring in the Chinese mainland in the next year. Based on the anomalies before 84 moderate or large earthquakes, it is concluded that except for the means of ground water level, the anomalous ratios for the other six means of earthquake forecasting in seismic regions are smaller than that in aseismic regions or that in the whole mainland of China. The means which has the maximum anomalous ratio is the means of ground water level, and the regions where the maximum ratio is observed are Xinjiang Uygur Autonomous Region, Sichuan and Yunnan provinces. The means which have the second anomalous ratios are the hydrogeochemistry and deformation and the regions where the second ratio is obtained are Xinjiang Uygur Autonomous Region, Yunnan Province. The means which has the minimum ratio is geomagnetism, the regions where the minimum ratio is observed are Inner Mongolia Autonomous Region and South China. The composite nomalous ratios for all means are 26.85% in seismic regions, 25.11% in aseismic regions. The latter also is the background level of precursory anomalies in Chinese Seismological Network. The anomalous ratios are 26.30% for the earthquakes of M S about 5.0 within the range of 200 km distant from the epicenter, 29.19% for earthquakes about 6.0 within 300 km, and 29.44% for earthquakes about 7.0 within 500 km.

Study on medium-short term earthquake forecast in Yunnan Province by precursory events

The medium-short term forecast for a certain kinds of main earthquake events might be possible with the time-to-failure method presented by Varnes (1989), Bufe and Varnes (1993), which is to simulate an accelerative releasing model of precursory earthquake energy. By fitting the observed data with the theoretical formula, a medium-short term forecast technique for the main shock events could be established, by which the location, time and magnitude of the main shock could be determined. The data used in the paper are obtained from the earthquake catalogue recorded by Yunnan Regional Seismological Network with a time coverage of 1965~2002. The statistical analyses for the past 37 years show that the data of M2.5 earthquakes were fairly complete. In the present paper, 30 main shocks occurred in Yunnan region were simulated. For 25 of them, the forecasting time and magnitude from the simulation of precursory sequence are very close to the actual values with the precision of about 0.57 (magnitude unit). Suppose that the last event of the precursory sequence is known, then the time error for the forecasting main shock is about 0.64 year. For the other 5 main shocks, the simulation cannot be made due to the insufficient precursory events for the full determination of energy accelerating curve or disturbance to the energy-release curve. The results in the paper indicate that there is no obviously linear relation in the optimal searching radius for the main shock and the precursory events because Yunnan is an active region with damage earthquakes and moderate and small earthquakes. However, there is a strong correlation between the main shock moment and the coefficient k/m. The optimal fitting range for the forecasting time and magnitude can be further reduced using the relation between the main shock moment lgM0 and the coefficient lgk/m and the value range of the restricting index m, by which the forecast precision of the simulated main shock can be improved. The time-to-failure method is used to fit 30 main shocks in the paper and more than 80% of them have acquired better results, indicating that the method is prospective for its ability to forecast the known main shock sequence. Therefore, the prospect is cheerful to make medium-short term forecast for the forthcoming main shocks by the precursory events.

Erratum to:Experimental investigation on predicting precursory changes in entropy for dominant frequency of rockburst

Because of an unfortunate mistake during the production of this article,the initial printed versions and the online PDF had incorrect DOI numbers.The DOI has now been corrected and synchronized with the correct DOIs of the HTML versions.

Anomalies of Precursory Group and Grouped Strong Earthquakes in the Sichuan-Yunnan Region

Three methods of extracting the information of anomalies of a precursory group are put forward, i.e., the mathematical analyses of the synthetic information of earthquake precursors (S), the inhomogeneous degree of precursory groups (ID) and the values of short-term and impending anomaly in near-source area (NS). Using these methods, we calculate the observational data of deformation, underground fluid and hydrochemical constituents obtained from different seismic stations in the Sichuan-Yunnan region and conclude that the synthetic precursory anomalies of a single strong earthquake with M S6.0 differ greatly from those of the grouped strong earthquakes, for the anomalous information of precursory groups are more abundant. The three methods of extracting the synthetic precursory anomaly and the related numerical results can be applied into the practice of prediction to the grouped strong earthquakes in the Sichuan-Yunnan region. Inhomogeneous degree (ID) of synthetic precursory anomaly can be identified automatically because it takes the threshold of distributive characteristics of the anomalies of precursory group as its criterion for anomaly.

Possible precursory anomalies in ground water level associated with the Wenchuan Ms 8.0 earthquake in 2008,Sichuan,China

We have examined the water level data from 16 wells in Sichuan province,China,recorded before the Wenchuan Ms8.0 earthquake occurred in 2008.We found that the data of 5 among these wells exhibit possible precursory anomalies,which are respectively named the Chuan No.08 well in Deyang,Chuan No.ll well in Pujiang,Chuan No.13 well in Luzhou,Chuan No.22 well in Qionglai and Beichuan.In time durations,these anomalies are of long-,intermediate-and short-term signals which are primarily distributed on the northeast(NE)trending Longmenshan fault zone as well as the parallel Huayingshan fault zone.It seems that the variations of the well levels on the Huayingshan fault zone imply compression while those on the Longmenshan fault zone reflect extension.These anomalies occurred first in the areas outside the epicenter region of the Wenchuan Ms8.0 earthquake,then migrated to the seismogenic fault zone.And they migrated from southwest to northeast in agreement with the rupture process of the main shock.