River flow regimes in a changing climate

Abstract

A river flow regime describes an average seasonal behaviour of flow and reflects the climatic and physiographic conditions in a basin. Differences in the regularity (stability) of the seasonal patterns reflect different dimensionality of the flow regimes, which can change subject to changes in climate conditions. The empirical orthogonal functions (EOF) approach can be used to describe the intrinsic dimension of river flow regimes and is also an adopted method for reducing the phase space in connection to climate change studies, especially in studies of nonlinear dynamic systems with preferred states. A large data set of monthly river flow for the Nordic countries has been investigated in the phase space reduced to the first few amplitude functions to trace a possible signature of climate change on the seasonal flow patterns. The probability density functions (PDF) of the weight coefficients and their possible change over time were used as an indicator of climate change. Two preferred states were identified connected to stable snowmelt-fed and rainfed flow regimes. The results indicate changes in the PDF patterns with time towards higher frequencies of rainfed regime types. The dynamics of seasonal patterns studied in terms of PDF renders it an adequate and convenient characterization, helping to avoid bias connected to flow regime classifications as well as uncertainties inferred by a modelling approach.     

地震活动性三分维的综合研究

从地震的混沌性现点出发,对地震时、空、强的分布进行分数维计算,寻找其变化规律。通过与断层维数进行对比,统计结果发现,三者同时与断层维数有关。依据简单的物理模型和假定,对这一现象进行了理论解释。同时还进行了岩石压裂实验,实验证明岩石裂隙的维数在2．5级左右,与假设条件及理论分析结果相一致。     

Fractal analysis of earthquake swarms of Vogtland/NW-Bohemia intraplate seismicity

The special type of intraplate microseismicity with swarm-like occurrence of earthquakes within the Vogtland/NW-Bohemian Region is analysed to reveal the nature and the origin of the seismogenic regime. The long-term data set of continuous seismic monitoring since 1962, including more than 26000 events within a range of about 5 units of local magnitude, provides an unique database for statistical investigations. Most earthquakes occur in narrow hypocentral volumes (clusters) within the lower part of the upper crust, but also single event occurrence outside of spatial clusters is observed. Temporal distribution of events is concentrated in clusters (swarms), which last some days until few month in dependence of intensity. Since 1962 three strong swarms occurred (1962, 1985/86, 2000), including two seismic cycles. Spatial clusters are distributed along a fault system of regional extension (Leipzig-Regensburger Störung), which is supposed to act as the joint tectonic fracture zone for the whole seismogenic region. Seismicity is analysed by fractal analysis, suggesting a unifractal behaviour of seismicity and uniform character of seismotectonic regime for the whole region. A tendency of decreasing fractal dimension values is observed for temporal distribution of earthquakes, indicating an increasing degree of temporal clustering from swarm to swarm. Following the idea of earthquake triggering by magma intrusions and related fluid and gas release into the tectonically pre-stressed parts of the crust, a steady increased intensity of intrusion and/or fluid and gas release might account for that observation. Additionally, seismic parameters for Vogtland/NW-Bohemia intraplate seismicity are compared with an adequate data set of mining-induced seismicity in a nearby mine of Lubin/Poland and with synthetic data sets to evaluate parameter estimation. Due to different seismogenic regime of tectonic and induced seismicity, significant differences between b-values and temporal dimension values are observed. Most significant for intraplate seismicity are relatively low fractal dimension values for temporal distribution. That observation reflects the strong degree of temporal earthquake clustering, which might explain the episodic character of earthquake swarms and support the idea of push-like triggering of earthquake avalanches by intruding magma.     

On the seismic regime network method

In this paper, based on the previous study of practical use of seismic regime windows and seismic regime belts, the problem of establishing a “seismic regime network” consisting of “windows” and “belts” is further posed and discussed according to the observed fact that many “windows” and “belts” make responses to one earthquake. For the convenience of usage, the “seismic regime network” is divided into two classes, the first class and the second one. The former can be used in tendency prediction for long-term seismic activity in a large area, the latter used in short-term prediction in a small area. In this paper, after briefly discussing the physical significance of “seismic regime network”, it is pointed out that this simple and easily used method can be used to observe and extract seismic precursory information from a large area before a great earthquake, thus it can provide a reliable basis for the analysis and judgement of seismic regime tendency in time and space. No doult, this method is of certain practical significance. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 161–169, 1991. The English version of this paper is improved by Prof. Shaoxie Xu.     

Evidence for gas influence on volcanic seismic signals recorded at Stromboli

The meaning of the large variety of seismic waveforms showing different frequencies associated with volcanic activity is still uncertain. No definitive model for source dynamics has been proposed yet. At present, seismic models explaining the origin of the spectral content of the seismic signal are mainly linked to geometrical features of the volcanic conduit and to resonant effects induced by pressure fluctuations in a fluid-filled conduit. Such models assume the physical system to be in a steady state over a long interval of time. At Stromboli, the seismicity produced by each of the three active vents is not stable and can suddenly change in time. Therefore, the application of stable resonator models appears to be unwarranted.On the basis of infrared image analyses, atmospheric pressure, and seismic wavefield signals, we show that different frequency contents and different explosive styles occur at Stromboli at the same time at different vents. Moreover, we give evidence to support the idea that seismicity and explosivity are both controlled by a variable gas flow regime released during explosions at the top of the magma column. We have recognized two main pressure regimes, controlling the explositivity at Stromboli: one is impulsive, short and possibly produced by a gas accumulation beneath a cap rock; the other has an intermittent regime feature, and lasts longer. We demonstrate how the first one generates a monochromatic low-frequency wavefield, while the second shows a high-frequency spectrum where the frequency content depends on pressure fluctuations and on pressure gradient. We suggest different pressure growth and gas flow in the magma as the common source for both explosive style and seismic wavefield.     

Specific features of the seismic regime in the lithosphere: Manifestations of the deep aqueous fluid action

We considered the seismic regime in the upper 70–100 km of the lithosphere and identified the layers (at depths of about 10, 20–30, and 60–80 km) characterized by relatively reduced effective strength and increased seismicity. The existence of such layers is related to changes in the regime of fluid-rock interaction, namely, to the characteristic depths of a jump-like decrease in the effective permeability of rocks and an increase in the spatial homogeneity of a fluid-rock system.     

Hausdorff分数维识别地震道初至走时

地震波初至走时的识别在地震勘探、人工地震层析成像以及全球地震层析成像方法研究中起重要作用．初至走时拾取的精度在很大的程度上影响地震层析成像及演的精度．本研究以提高地震波初至走时拾取的精度及定量化程度为目标,利用计算地震道时间序列分数维的方法,实现了地震波初至走时的自动拾取．本文以分形理论为基础,进行了地震道时间序列Hausdorff分数维的计算．计算结果表明地震道时间序列的分数维在初至到达前后具有不同的数值,其变化点能够定量指示出初至走时的位置．本文还给出了利用该方法对实测数据进行初至走时拾取的实例．     

Forecasting volcanic eruptions from seismic data

An increase in cumulative seismic strain release from volcanic earthquakes prior to eruptions of Bezymyanniy Volcano in 1955–1961 and Sheveluch Volcano in 1964 in Kamchatka, and of Tokachi-dake Volcano on Hokkaido Island in 1962 occurred in accordance with a hyperbolic law. The relationship obtained may be universal for andesite volcanoes. Knowing the law of the increase of cumulative seismic strain and carrying out continueus observations of the seismic regime of andesite voleanoes makes it possible to prediet time and energy of eruptions. By observation of volcanic earthquakes it is also possible to predict the place and time of the occurrence of lateral craters.     

用地震活动多参数扫描法探测汶川地震孕育的临界信息

采用时间扫描方法,通过能量释放率、b值、空间相关距离和广义维等多种统计参数的协同分析,研究了汶川8.0级大地震及其多次强余震之前区域地震活动性随时间的变化特征,发现大震前的地震活动表现出能量释放率增大,b值的大幅度减小,空间相关距离的下降和广义维的下降-回升等异常特征.对后续余震活动的分析,也可分辨出地震活动的临界异常特征.结果表明,多种统计参数的综合协同分析能够反映地震活动的特点,发现孕震系统激变前的临界行为.     

Some properties of the hierarchical model reproducing the stress state of the epicentral area of the 2003 Chuya earthquake

The stress state of the Earth’s crust in the region of the Chuya earthquake of 2003 (Gorny Altay) is studied using the data of long-term epicentral observations by dense networks of temporary stations. These data comprise 545 seismic events, which widely vary in energies and whose parameters are determined highly accurately. Two hierarchical levels of the stress field are revealed and their spatial structure and temporal behavior are investigated. It is shown that the subregional stress field, which is determined from the data on strong earthquakes, is predominantly stable across the studied area, where the regime of horizontal shear with submeridional orientation of principal pressure axes is observed. The local stress field calculated from the weak seismic events experiences regular variations, which are consistent with the block structure of the crust; this field is heightand time-dependent.     

Dynamics of Induced Seismicity during the Filling of the Nurek Reservoir

The seismological data in the area of induced seismicity in the region of the Nurek reservoir are analyzed. The analysis is based on the developed database for the earthquakes that occurred from 1955 to 1989 and is aimed at finding the regularities in the variations of the parameters of the transitional seismic regime caused by filling a reservoir. These parameters include the b-value—the slope of the graph of the Gutenberg–Richter frequency–magnitude relationship, the fractal dimension d of the set of the epicenters, and fracture cycle parameter q = αb ? d, where coefficient α determines the ratio between the magnitude and source size M = α log l + β. It is shown that during the filling of a reservoir, these parameters undergo statistically reliable variations: at the initial stages, the b-value increases, the fractal dimension of the set of epicenters decreases, and the fracture cycle parameter q grows and becomes positive in the middle of the time interval of reservoir filling. After a reservoir is filled, these parameters recover their background values. The aftershock sequences of the three strongest earthquakes—before, in the beginning, and in the middle of the reservoir filling period—are studied. It is confirmed that the Omori parameter p for the aftershock sequences during filling is smaller than for the earthquake before filling. Based on the dynamics of the studied parameters, it is conjectured that the relaxation time of the transitional seismic regime after the emergence of induced seismicity is about 10 years.     

瀑布沟水库区域地震的重新定位

利用双差定位方法对瀑布沟水库区域内2006-10-13~2013-07-31之间发生的3 784个地震进行了重新定位,获得了3 601个地震的重新定位结果,到时残差平均为0.12 s,E-W、N-S和U-D三个方向上平均定位误差分别为0.15 km、0.17 km和1.10 km。重新定位结果显示,在研究区域内的西南方向和水库流域,地震分布密集,这个区域处于鲜水河断裂中南段、安宁河断裂北段和大凉山断裂北段的位置,此区域内地震震源深度主要分布在5~30km间,表明该区域的地震主要是构造活动引起的,而水库库区内地震震源深度主要分布在0~5 km区间,分布比较集中,该地区的地震为水库诱发和人工爆破引起的地震。     

The effect of vibrations in the Zhigulevskii Hydropower Structure on soils in the nearby territories of Tolyatti City

The Zhigulevskii Hydropower Structure is used as an example to study the vibration impact of a dam on the soils of the coastal zone in the upper and lower pools. The effect of vibration of the hydropower structure on soils composing the shore in the nearby territory was evaluated on the qualitative level. The analysis of seismic monitoring data allowed the authors to conclude that the specific features of the seismic regime of the territory both during spring releases and in dry period are governed by the regime of hydropower structure operation.     

浙江珊溪水库地震：震源参数测定及断层结构和应力状态描述

利用遗传算法,搜索符合Brune ω^2模型的拐角频率（fc）及零频幅值（Ωc）的最佳值,测定浙江珊溪水库震区88条小震（1．5≤ML≤4．6）的地震矩（M0）、震源尺度（r）及静态应力降（△σ）。地震矩M0在10^10～10^14N·m范围内,与拐角频率fc遵循Mo∝fc^-3的规律;震源尺度和地震矩、应力降之间呈现多重标度特征,地震矩大于临界值2．3×10^12N·m（相应的震源尺度特征值约160m）时,震源尺度与地震矩的关系较强;而应力降（△σ）在震源尺度大于160m后基本趋向恒定,不随震源尺度的增大而增大。浙江珊溪水库震区自2002年7月以来,经历2次大规模的震群活动。震群释放的应力降大小与该震群的规模成正比关系,大的应力降集中在发震断层中段5～6km深度的区域,其发生时间既可以在主震之前,也可以在主震之后。     

福建测震台网震情值班信息管理系统设计与实现

采用C/S架构,系统开发语言为Visual Basic 6.0,数据库为Sql Server,设计开发了震情值班信息管理系统,并应用于震情值班的日常工作中.实际应用表明,该系统提高了日常工作效率,有效推进了震情值班的管理工作.     

Clustering of mining-induced seismic events in equivalent dimension spaces

High energy release during seismic events induced by mining operation is one of the major dangers perturbing production in underground mines. In this work, temporal changes of seismic event parameters for one of the Rudna Mine (Poland) panels are investigated. The study aim was to find whether the temporal clustering of smaller events in different parameters can be observed before and after the high energy events (M_l?≥?3) in the mining panel. The method chosen for analysis was the study of temporal variation of fractal dimension of the seismic events parameter sets composed from: the interevent epicentral distance (dr), logarithm of seismic energy (lE), and interevent energy coefficient (dlE), which is the absolute difference between logarithms of energy of two consecutive events. Temporal variations study was performed in equivalent dimension (ED) space. The transformation of the seismic source parameters into ED space allowed to estimate and compare the temporal changes of the fractal dimension of different parameter spaces using the same method—correlation fractal dimension, and then easily compare the obtained temporal changes of fractal dimension of different parameter sets. The effect of grouping is expressed by decrease of fractal dimension, which is connected with the similarity of events parameter values. The temporal changes of the fractal dimension of seismicity before the strong induced events would indicate some initiation phase of the process leading to the high energy release. In the case of the studied Rudna Mine panel, the temporal behavior of the fractal dimension values in different parameter spaces before seismic events showed significant changes before three out of four events with CLVD dominant source mechanisms.     

福建测震台网震情值班信息管理系统设计与实现

采用C/S架构,系统开发语言为Visual Basic 6.0,数据库为Sql Server,设计开发了震情值班信息管理系统,并应用于震情值班的日常工作中。实际应用表明,该系统提高了日常工作效率,有效推进了震情值班的管理工作。     

土体-结构界面接触对地下结构动力反应的影响

迄今为止,关于土体与结构交界面的接触效应对地下结构地震反应的影响尚未引起研究者们的重视,成果鲜有报道。本文基于接触面对法和非线性有限元波动分析方法,建立了考虑土体与结构界面接触效应的地下结构非线性地震反应分析模型和计算方法,并利用大型有限元软件ANSYS进行了求解。分析结果表明：土体与结构界面的接触效应对地下结构地震反应有明显影响,可能增大地下结构节点的峰值加速度、峰值位移和峰值应力反应;随着接触摩擦系数的增大,接触点的相对滑移逐渐减小,而接触应力的变化则无明显规律。     

1997年伽师地震临震预报的经验与启示

１９９７年１￣４月新疆伽师发生罕见的强震群活动。几个月内在十分狭小的区域内发生７次６级强震,是新疆几十年来从未遇到过的。概述了伽师地震３次准确和较为准确的临震预报;总结了地点已知的后续强震临震预报的科学和实践问题;论述了震例总结与现实预报的差异,以及地震孕育的复杂性和地震预报的现实做法。