地电场日变幅与地电暴分析

利用昌黎台地电场资料分析地电场日变幅季节变化特征,显示有季节效应,EW、SN测向夏季日变幅地震最大,而出现最小值的季节两测向表现不一。分析认为,与地电场观测信号的复杂多样性有关。地电暴可以记录到磁暴急始变幅、初相、主相的变化形态,但由于电场和磁场之间存在一阶差分的关系,并不是所有地电暴都和地磁暴变化一致,甚至有些地电暴没有变化形态,而是出现高频上下起伏的脉冲形式。利用多台地电场资料,对同一个K指数为7的磁暴进行急始变幅、扰动最大变幅分析,结果显示,各台不尽相同,可能与台址介质的电性结构有关。     

A new seasonal design flood method based on bivariate joint distribution of flood magnitude and date of occurrence

Abstract

Seasonal design floods which consider information on seasonal variation are very important for reservoir operation and management. The seasonal design flood method currently used in China is based on seasonal maximum (SM) samples and assumes that the seasonal design frequency is equal to the annual design frequency. Since the return period associated with annual maximum floods is taken as the standard in China, the current seasonal design flood cannot satisfy flood prevention standards. A new seasonal design flood method, which considers dates of flood occurrence and magnitudes of the peaks (runoff), was proposed and established based on copula function. The mixed von Mises distribution was selected as marginal distribution of flood occurrence dates. The Pearson Type III and exponential distributions were selected as the marginal distribution of flood magnitude for annual maximum flood series and peak-over-threshold samples, respectively. The proposed method was applied at the Geheyan Reservoir, China, and then compared with the currently used seasonal design flood methods. The case study results show that the proposed method can satisfy the flood prevention standard, and provide more information about the flood occurrence probabilities in each sub-season. The results of economic analysis show that the proposed design flood method can enhance the floodwater utilization rate and give economic benefits without lowering the annual flood protection standard.

Citation Chen, L., Guo, S. L., Yan, B. W., Liu, P. & Fang, B. (2010) A new seasonal design flood method based on bivariate joint distribution of flood magnitude and date of occurrence. Hydrol. Sci. J. 55(8), 1264–1280.     

Thresholds in the storm response of a lake chain system and the occurrence and magnitude of lake overflows: Implications for flood frequency

The aim of this paper is to illustrate the effects of spatial organization of lake chains and associated storage thresholds upon lake-overflow behaviour, and specifically their impact upon large scale flow connectivity and the flood frequency of lake overflows. The analysis was carried out with the use of a multiple bucket model of the lake chain system, consisting of a network of both lakes and associated catchment areas, which explicitly incorporated within it three storage thresholds: a catchment field capacity threshold that governs catchment subsurface stormflow, a total storage capacity threshold that governs catchment surface runoff, and a lake storage capacity threshold that determines lake overflow. The model is driven by rainfall inputs generated by a stochastic rainfall model that is able to capture rainfall variability at a wide range of time scales. The study is used to gain insights into the process controls of lake-overflow generation, and in particular, to explore the crucial role of factors relating to lake organization, such as the average catchment area to lake area (A_C/A_L) ratio and the distribution of A_C/A_L with distance in the downstream direction (increasing or decreasing). The study showed that the average A_C/A_L value was the most important factor determining the frequency of occurrence and magnitude of floods from a landscape consisting of lake chains. The larger the average A_C/A_L value the more runoff is generated from catchments thus increasing both the occurrence and magnitude of lake overflows. In this case the flood frequency curve reflects that of the catchment area, and lake organization does not play an important role. When A_C/A_L is small the landscape is lake dominated, the spatial organization of lakes has a significant impact on lake connectivity, and consequently on flood frequency. One of the aspects of lake organization that may have a significant influence on lake connectivity is the spatial distribution of A_C/A_L from upstream to downstream (increasing or decreasing). In a landscape in which A_C/A_L increases downstream, lake overflow will occur more frequently relative to a similar landscape (i.e. identical A_C/A_L) with a constant value of A_C/A_L. When A_C/A_L decreases downstream, however, runoff inputs from the upstream parts will trigger lake overflow in the downstream parts, and consequently, full connectivity may be achieved leading to increased flood frequencies.     

Patterns in the daily periodicity of low magnitude seismicity in Kamchatka

A daily periodicity in small (K ≤ 8. 0) Kamchatka earthquakes has been detected, with the maximum occurring during the nighttime. The effect was not observed throughout the area of study, but only in several zones. We show that the results are not affected by human and weather factors. A hypothesis is put forward to explain the physical causes of the effect, viz., that the daily periodicity of small earthquakes could be due to natural VLF electromagnetic radiation acting on the geologic medium. It is pointed out that the effect is related to the previously identified effect of natural electromagnetic radiation modulating the intensity of geoacoustic emission from rocks.     

江苏地区地电暴特征及差异性

利用FFT方法对江苏区域地电场、地磁以及有关台站的钻孔应变数据进行处理,提取频谱特征,对该区各地电台站的地电暴特征进行分析,研究结果表明：①江苏区域地电场各测项地电暴数据与地磁H分量变化趋势接近,但各台地电场不同测项的突跳方向存在各向异性,4个地电台站EW向数据具有一致同向现象,NS向数据有差异性;②由各分量优势周期对应性可知,江苏地区地电场NS向含有的地磁场H分量高于体应变成分,地电场EW向倾向于地磁场H分量与体应变叠加抵消的结果;③当磁暴发生时,地磁H分量变化幅度相同的台站,地电场变化幅度不同,地电台站的地电暴变化特征与其地下结构有关,地下深层阻抗越大,感应电场越大,地电场日变化幅度越大。     

The time of occurrence and the magnitude of the largest aftershock over India

Summary The time of occurrence and the magnitude of the largest aftershock in relation to the main shock have been studied for India and its neighbourhood based on the USCGS data during the years 1963–1971. It is found that the largest aftershock occurs within 2 hours after the main shock in about 50% of the cases and frequency of occurrencen(t) of the largest aftershocks decreases hyper-bolically with the intervalt after the main event and could be represented by a law of the formn(t)=At ^–h whereA andh are constants. The probability of occurrence of the largest aftershock within 2 hours of the main shock is found to be higher over island are regions of the world. The difference (M ₀–M ₁) of the magnitude of the largest aftershockM ₁ to that of the main shockM ₀ as a measure of aftershock activity does not show any marked regional variation over India and its neighbourhood, as was reported by Mogifor Japan. Examination of the values ofM ₁/M ₀ and the constantb in Gutenberg-Richter's frequency magnitude relationship reveals a range of variation in both; high values ofM ₁/M ₀ have been found to be associated with high values ofb in many tectonic earthquakes and thus not, restricted to reservoir associated seismic activity.     

川滇地区烈度计台站测定震级校正分析

烈度计台与测震台的布设环境、仪器类型不同,所测定的震级值存在一定差异。收集2017—2019年川滇地区301个烈度计台站记录的46次M_L 3.0以上地震,进行震级校正。统计烈度计实测震级值与测震台网平均震级值的偏差,对原量规函数进行修正,进而做台站校正。综合修正后,利用量规函数和台站校正值重新计算烈度计震级,结果表明:在震中100 km范围内,烈度计测定震级偏差平均值由校正前的0.145降低至0.033,标准差由0.382降低至0.295,离散度减小;校正后的烈度计震级结果较优,说明本研究获得的量规函数和台站校正值更加适用于川滇地区烈度计台站的震级计算。     

Probability of earthquake occurrence and magnitude estimation in the post shut-in phase of geothermal projects

Induced seismicity in geothermal projects is observed to continue after shut-in of the fluid injection. Recent experiments show that the largest events tend to occur after the termination of injection. We use a probabilistic approach based on Omori??s law and the Gutenberg?CRichter magnitude?Cfrequency distribution to demonstrate that the probability of exceeding a certain maximum magnitude still increases after shut-in. This increase is governed by the exponent of Omori??s law q and the Gutenberg?CRichter b value. For a reduced b value in the post-injection phase, the probability of occurrence directly after shut-in can be even higher than the corresponding probability for an ongoing injection. For the reference case of q?=?2 and a 10% probability at shut-in time t _S to exceed a given maximum magnitude, we obtain an increase to 14.6% for t?=?2t _S at a constant Gutenberg?CRichter b value after shut-in. A reduction of the b value by one quarter leads to a probability of 20.5%. If we consider a constant probability level of occurrence for an event larger than a given magnitude at shut-in time, this maximum magnitude increases by 0.12?units for t?=?2t _S (0.26?units for a reduced b value). For the Soultz-sous-Forêts (France) injection experiment in 2000, recent studies reveal q?=?9.5 and a b value reduction by 14%. A magnitude 2.3 event 9?h after shut-in falls in the phase with a probability higher than for the continued injection. The probability of exceeding the magnitude of this post-injection event is determined to 97.1%.     

Expected magnitude and distance of potential source area and the estimating method

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河南地区地震目录最小完整性震级探讨

以河南地区(31°-37°N,110°-117°E)1970-2020年11月地震目录作为研究资料,采用G—R关系法、震级—序号法和最大曲率法测定不同时段最小完整性震级Mc.结果 显示,1970-1979年由于研究区内台站数量少,Mc约为ML2.5;1980-2001年为稳定的模拟观测时期,地震监测能力有所提升,Mc约...     

Model of earthquake occurrence in the European area

Summary The time distribution of earthquake occurrence in the European area is investigated by statistical laws. The original data of shallow-focus earthquakes are taken from the European catalogue 1901–1967. Evidence is given that the process with the negative binomial entries as a model describing the occurrence of shallow-focus earthquakes is better than the Poisson process. Further, the influence of magnitude classes and magnitude threshold value on the time distribution of earthquake occurrence is examined.Communication presented at the XIII General Assembly of the European Seismological Commission in Brasov in 1972.     

渤海湾地区壳幔结构重磁综合研究

渤海湾盆地是华北克拉通破坏的中心,其东部渤海海域深部结构研究对认识华北克拉通破坏范围及动力学过程具有重要意义.为此,本文选取自河北新城经天津静海沿东南方向进入渤海海域的剖面进行重磁反演,研究其地壳结构特征.通过对该地区文献调研及2010年渤海海陆联测初步结果建立初始模型,结合本地区密度、磁化率特征进行二度半体重磁异常反...     

Long-term earthquake prediction in the Aegean area based on a time and magnitude predictable model

The Aegean and surrounding area (34°N–43°N, 18°E–30°E) is separated into 76 shallow and intermediate depth seismogenic sources. For 74 of these sources intervent times for strong mainshocks have been determined by the use of instrumental and historical data. These times have been used to determine the following empirical relations: $$\begin{gathered} \log T_t = 0.24M_{\min } + 0.25M_p - 0.36\log \dot M_0 + 7.36 \hfill \\ M_f = 1.04M_{\min } - 0.31M_p + 0.28\log \dot M_0 - 4.85 \hfill \\ \end{gathered} $$ whereT ₁ is the interevent time, measured in years,M _min the surface wave magnitude of the smallest mainshock considered,M _p the magnitude of the preceding mainshock,M _f the magnitude of the following mainshock, \(\dot M_0 \) the moment rate in each source per year. A multiple correlation coefficient equal to 0.74 and a standard deviation equal to 0.18 for the first of these relations were calculated. The corresponding quantities for the second of these relations are 0.91 and 0.22. On the basis of the first of these relations and taking into consideration the time of occurence and the magnitude of the last mainshock, the probabilities for the occurrence of mainshocks in each seismogenic source of this region during the decade 1993–2002 are determined. The second of these relations has been used to estimate the magnitude of the expected mainshock.     

不同量级磁暴对新沂地震台地电阻率的影响

探讨强烈磁暴对新沂地震台地电阻率测最的影响.根据磁暴效应,得出对地电阻率的影响,从而进行不同量级磁暴对江苏省新沂地震台地电阻率的影响分析.同时分析各测向产生的差异性及原因.由于新沂地震台地电阻率测量采用正反向双向供电,磁暴对地电阻率的影响量很小,其形态仍存在同步变化.如果采取减少每次测量的供电时间、供电次数,加大供电电...     

Comparison of local and global approximators in multivariate chaotic forecasting of daily streamflow

ABSTRACT

Although it is conceptually assumed that global models are relatively ineffective in modelling the highly unstable structure of chaotic hydrologic dynamics, there is not a detailed study of comparing the performances of local and global models in a hydrological context, especially with new emerging machine learning models. In this study, the performance of a local model (k-nearest neighbour, k-nn) and, as global models, several recent machine learning models – artificial neural network (ANN), least square-support vector regression (LS-SVR), random forest (RF), M5 model tree (M5), multivariate adaptive regression splines (MARS) – was analysed in multivariate chaotic forecasting of streamflow. The models were developed for Australia’s largest river, the River Murray. The results indicate that the k-nn model was more successful than the global models in capturing the streamflow dynamics. Furthermore, coupled with the multivariate phase-space, it was shown that the global models can be successfully used for obtaining reliable uncertainty estimates for streamflow.     

Simulation of eutrophication and associated occurrence of hypoxic and anoxic condition in a coastal bay in Japan

A probabilistic method of calculating the occurrence of oxygen-depleted water within a combined hydrothermal and water quality model was presented in this paper to investigate the environmental impact of eutrophication on the living resources. The method was applied to an eutrophicated shallow coastal bay in western Japan, where the occurrence of red tides at the water surface and the onset of bottom hypoxic waters are observed every summer. Both meteorology and freshwater inflow contribute to the development of stratification of the bay, thus limiting the dissolved oxygen supply to bottom waters. The resulting hydrodynamics enhances the development of oxygen-depleted bottom waters by transporting organic matter produced by algal blooms to the inner bay, where it decomposes and exerts high SOD. During August, about 60% of the inner bay is hypoxic for prolonged durations and as a result most of the benthic biota and fish die. The method used here is a very useful and informative way to evaluate the spatial and temporal damage and severity caused by hypoxia on living resources. Moreover, the model results agreed very well with the observed hydrodynamics, thermal structure and water quality data of the stratified bay. The model can be used for other lakes and bays where knowledge of temperature and density stratification is important for assessing water quality.     

Effect of an earthquake occurrence on the flow intensity of the subsequent events

Aftershocks or swarms indicate increase of the flow intensity in the vicinity of the initial earthquakes. By normalizing their number according to the dynamic range of the standard frequency magnitude distribution the increase or positive aftereffect property of the initial earthquakes can be compared for different magnitude intervals, periods of time or regions. After applying accurate formal algorithm of aftershock identification it is possible to study negative aftereffect of the main events (nonaftershocks) in the catalog.Negative aftereffect means decrease of the probability of successive events in a time-space vicinity of the main event, when the aftershocks are over. The negative effect is the most important part of the seismic cycle and seismic gaps approach. Global statistical test give high confidence level for the relative decrease in intensity of the flow of the events withM7 in the first 20–25 years after the events withM8 in their 1^o-vicinities in the total time period under study of approximately 60 years. The decrease approximates 32% of the undisturbed intensity of the flow ofM>7 events in the vicinities.Self-similar negative aftereffect was observed 3–7 years after 6M<7 events, it totals approximately 18% of the undisturbed intensity. Another type of self-similarity of seismic regime, with respect to the negative aftereffect, is the decrease of probabilities of aftershocks with large magnitudes in aftershock sequences. When we have adequate dynamic range in the catalog for the study of this property, for example, for main events withM7 in the catalog with low cut-off limitM=4, the statistical significance of the negative aftereffect is clear. However, the absolute value of the effect is also rather small, about 10%, which means that in 90% of the cases the aftershock sequences do not experience lack of energy due to the main shock energy release and follow a standard magnitude distribution for earthquakes in the entire catalog.The small values of the negative aftereffect apparently indicate partial stress relase by earthquakes and may explain short recurrence time intervals after major earthquakes observed periodically in different places.     

Reconstructing historic Glacial Lake Outburst Floods through numerical modelling and geomorphological assessment: Extreme events in the Himalaya

Recession of high‐mountain glaciers in response to climatic change frequently results in the development of moraine‐dammed glacial lakes. Moraine dam failure is often accompanied by the release of large volumes of water and sediment, termed a Glacial Lake Outburst Flood (GLOF). Chukhung Glacier is a small (~3 km²) receding valley glacier in Mt. Everest (Sagarmatha) National Park, Nepal. Unlike many Himalayan glaciers, which possess a thick mantle of supraglacial debris, its surface is relatively clean. The glacier terminus has receded 1.3 km from its maximum Holocene position, and in doing so provided the space for an ice‐contact moraine‐dammed lake to develop. The lake had a maximum volume of 5.5 × 10⁵ m³ and drained as a result of breaching of the terminal moraine. An estimated 1.3 × 10⁵ m³ of material was removed from the terminal moraine during breach development. Numerical dam‐breach modelling, implemented within a Generalised Likelihood Uncertainty Estimation (GLUE) framework, was used to investigate a range of moraine‐dam failure scenarios. Reconstructed outflow peak discharges, including failure via overtopping and piping mechanisms, are in the range 146–2200 m³ s^‐1. Results from two‐dimensional hydrodynamic GLOF modelling indicate that maximum local flow depths may have exceeded 9 m, with maximum flow velocities exceeding 20 m s^‐1 within 700 m of the breach. The floodwaters mobilised a significant amount of material, sourced mostly from the expanding breach, forming a 300 m long and 100 m wide debris fan originating at the breach exit. moraine‐dam. These results also suggest that inundation of the entire floodplain may have been achieved within ten minutes of initial breach development, suggesting that debris fan development was rapid. We discuss the key glaciological and geomorphological factors that have determined the evolution of a hazardous moraine‐dammed lake complex and the subsequent generation of a GLOF and its geomorphological impact. © 2014 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.