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1.
文中根据南北地震带中段及附近区域1973年以来86次5.0级以上的地震序列统计结果,对地震序列类型和空间分布进行分析,结果表明:1)研究区域内的地震序列以主余型为主(51%),多震型次之(29%),孤立型最少(20%);同一序列类型中,随着地震震级增大,主余型地震所占的比例增加,多震型、孤立型逐渐减少,7.0级以上地震以主余型为主,无孤立型地震;对于不同破裂类型,逆冲型地震中主余型最多,多震型地震更可能为走滑和正断性质的地震。2)主余型和多震型地震序列的主震与最大余震震级的线性关系相对较好;绝大多数地震的最大余震多发生在震后20d内,主余型最大余震集中在震后3d内发生,多震型地震中次大地震集中在震后12d内发生,孤立型地震的最大余震多发生在地震当天。3)地震序列空间分布显示,主余型地震分布相对较广,多震型地震主要集中在川西巴塘—理塘、川东马边—昭通一带、川北松潘和滇西北云龙、姚安、龙陵及附近区域,甘孜-玉树断裂带、鲜水河断裂带NW段及四川盆地等地更易发生孤立型地震。4)地震序列类型的空间分布可能与本区域的地质构造和历史地震活动存在一定的关系。 相似文献
2.
陕西地区震源参数和平均应力场的研究 总被引：2，自引：0，他引：2
利用陕西地区地震台网记录的小震垂直分量最大振幅比测定了陕西地区的震源参数，并用其小震断层面解反演了平均应力场。结果表明，陕西地区最大主压应力方向为北东东向，倾角中等，相对中等主压应力较大，小震断层面呈北西和北东向优势分布。分区试验表明，关中地区与全省基本一致，陕南似乎存在较大差异，其最大主压应力方向为北北西一南南东方向，中等主压应力也相对较小。 相似文献
3.
利用1958~2001年共44年的ECMWF资料及参数化方法,计算了对流层顶上、下3 km气层间的臭氧含量及其吸收太阳辐射加热率的时空分布.结果表明: (1) 臭氧分布的空间梯度从赤道指向两极,而加热率则是分别由高纬和低纬指向副热带,这样的经向梯度可能是驱动对流层顶结构变化的一种重要因素;两者空间分布的季节变化显著,但其对应关系并不完全一致,1月和4月的空间结构与7月和10月的相反,随季节调整具有突变现象;东亚及青藏高原是季节变化相对稳定的区域.(2) 在热带对流层顶控制区加热率与臭氧含量呈正相关,而极地对流层顶控制区各季节有所不同,还与太阳赤纬变化相关联;各纬度间加热率季节变化的位相和变率都存在差异,但南半球相对较为一致,最大距平为±2×10-4 K·d-1,北半球则较复杂,最大正距平为4×1010-4 K·d-1;两半球的季节周期位相趋于相反.(3) 除赤道外,臭氧距平的季节变化位相超前于加热率距平2~3月,并且发生在季节变化的调整期;最大距平出现在南极的8月大于0.4 DU,3~4月则小于-0.2 DU,而北极为±0.2 DU.(4) 臭氧含量和加热率的年际与年代际演变关系对应一致,并具有多尺度的结构特征;但两半球及赤道的时空演变差异明显,30° S~30° N间副热带控制区的加热率变幅剧烈,最大距平为±2.5×10-4 K·d-1,高纬和两极的变幅在不同演变期各不相同;臭氧的变幅结构与之相反,北极的最大距平分别大于0.25 DU和小于-0.35 DU.(5) 20世纪70年代以前及70年代中期,两半球的正负距平具有相反的演变结构,而90年代是负距平演变最剧烈的时期. 相似文献
4.
2001年昆仑山口西MS8.1地震经历了一个复杂的破裂过程,其破裂长、幅度大、破裂速度多变,成为大陆型地震研究的典型地震。本文融合近场高精度大地测量观测（4幅InSAR影像,34个GPS点位同震位移）和高信噪比远震波形记录,基于有限断层反演理论,联合反演得到该地震同震破裂时空过程的统一模型;同时,基于欧洲区域台网波形数据,利用反投影方法获得高频破裂的时空展布。联合反演结果表明,破裂自西向东传播的过程中走向有所变化,破裂尺度达400km,最大滑移量达8m,地震矩大小为6.1×1020Nm,对应的矩震级MW为7.78。主断层破裂经历了3个阶段,其中,超剪切破裂阶段对应最大位错区域,破裂到达西大滩段与昆仑山口断层交叉处时,破裂速度与尺度迅速下降。反投影结果同样显示破裂的3个阶段空间上对应大地测量反演的3个最大破裂区,最大破裂区的扩展速度达6km/s,但超剪切破裂终止在断层交叉口东部约30km处断层走向发生转变的位置。 相似文献
5.
《水文科学杂志》2013,58(2):367-386
Abstract Extremes of streamflow are usually modelled using heavy tailed distributions. While scrutinising annual flow maxima or the peaks over threshold, the largest elements in a sample are often suspected to be low quality data, outliers or values corresponding to much longer return periods than the observation period. In the case of floods, since the interest is focused mainly on the estimation of the right-hand tail of a distribution function, sensitivity of large quantiles to extreme elements of a series becomes the problem of special concern. This study investigated the sensitivity problem using the log-Gumbel distribution by generating samples of different sizes and different values of the coefficient of L-variation by means of Monte Carlo experiments. Parameters of the log-Gumbel distribution were estimated by the probability weighted moments (PWM) method, both for complete samples and the samples deprived of their largest element. In the latter case Hosking's concept of the “A” type PWM with Type II censoring was employed. The largest value was censored above the random threshold T corresponding to the non-exceedence probability F T. The effect of the F T value on the performance of the quantile estimates was then examined. Experimental results show that omission of the largest sample element need not result in a decrease in the accuracy of large quantile estimates obtained from the log-Gumbel model by the PWM method. 相似文献
6.
Two kinds of seismic gaps 总被引：11，自引：0，他引：11
Kiyoo Mogi 《Pure and Applied Geophysics》1979,117(6):1172-1186
The same term seismic gaps has been used for different kinds of seismic gaps, resulting in some confusion. It is shown that there are two kinds of seismic gaps which are defined by two different features of seismic activity. One is a gap in the spatial distribution of rupture zones of the largest earthquakes in a seismic belt. This is termed a seismic gap of the first kind. A seismic gap of the first kind could be identified not only for great shallow earthquakes along plate boundaries, but also probably for smaller intra-plate earthquakes. The other is a gap in seismicity of smaller-magnitude earthquakes before larger earthquakes. This premonitory phenomenon is termed a seismic gap of the second kind. Focal regions of the largest earthquakes in an active seismic belt are frequently seismic gaps of both the first and the second kind. Some earthquakes, however, are not preceded by any appreciable premonitory gap (the second kind). This different feature in different cases may depend on the structural states of the earth's crust, such as heterogeneity. 相似文献
7.
GEORGE A. GRIFFITHS 《水文科学杂志》2013,58(3):231-248
Abstract The exact distribution of the ratio of any magnitude to the sum of all magnitudes in an annual flood series satisfying the usual distribution-free assumptions of independence and identical distribution, and the additional parametric assumption of exponential tail behaviour with truncation, is shown to be a beta distribution of the first kind. A two-parameter linear transformation of the beta distribution completes the derivation and yields a Wakeby distribution which has the number of members in a series as a given parameter. The Wakeby distribution is developed to illustrate how, in principle, some perceived deficiencies in current flood frequency analysis may be met: more complex parametric assumptions should lead to distributions of wider application. In particular, the distribution has a secure theoretical basis and is hydrologically more realistic because it bounds the variate and requires the definition of a temporally finite annual series. Analytical expressions are obtained for estimating the two distribution parameters; the quantite standard error and a plotting rule. An example is given of the application of the distribution to the design flood problem and an annual flood series is modelled. It is further suggested that a suitable design value for the largest flood to be withstood by a protection work is a statistic of the largest flood occurring during its lifetime. For the derived Wakeby distribution this criterion specifies risk and probability of non-exceedance of the design flood once a lifetime is selected. 相似文献
8.
2004年12月26日印度尼西亚西北近海8.7级大地震,是一次浅源的海沟俯冲型板间地震。震中位于印尼-美拉尼西亚板块边界构造带的西北端,2004年沿该带发生的8次M≥7地震显示总体由东向西迁移的特征,表明它们具有相互联系的统一动力过程。这些板间地震的发生与该地处于几个板块汇聚地带和较大的板块运动速率有关,它们导致了强烈而复杂的构造变形和构造活动。印度洋-澳大利亚板块向东南亚陆块的低角度俯冲,在俯冲带浅部形成积累应变能的巨大闭锁区,它的突然破裂和大尺度滑动是造成印尼8.7级大地震的直接原因 相似文献
9.
The apparent magnitude of an earthquakey is defined as the observed magnitude value and differs from the true magnitudem because of the experimental noisen. Iff(m) is the density distribution of the magnitudem, and ifg(n) is the density distribution of the errorn, then the density distribution ofy is simply computed by convolvingf andg, i.e.h(y)=f*g.If the distinction betweeny andm is not realized, any statistical analysis based on the frequency-magnitude relation of the earthquake is bound to produce questionable results. In this paper we investigate the impact of the apparent magnitude idea on the statistical methods that study the earthquake distribution by taking into account only the largest (or extremal) earthquakes. We use two approaches: the Gumbel method based on Gumbel theory (Gumbel, 1958), and the Poisson method introduced byEpstein andLomnitz (1966). Both methods are concerned with the asymptotic properties of the magnitude distributions. Therefore, we study and compare the asymptotic behaviour of the distributionsh(y) andf(m) under suitable hypotheses on the nature of the experimental noise. We investigate in detail two dinstinct cases: first, the two-side limited symmetrical noise, i.e. the noise that is bound to assume values inside a limited region, and second, the normal noise, i.e. the noise that is distributed according to a normal symmetric distribution.We further show that disregarding the noise generally leads to biased results and that, in the framework of the apparent magnitude, the Poisson approach preserves its usefulness, while the Gumbel method gives rise to a curious paradox. 相似文献
10.
针对九寨沟MS7.0地震之后不同时间段的余震序列目录,利用推定最大余震震级,给出了实际最大余震震级的估计值。结果表明,推定最大余震震级随主震后时间尺度的延长而趋于稳定,且该值与实际发生的最大余震的震级一致。需要强调的是,就九寨沟地震序列而言,当余震数据较为完备时,采用主震后较短时间段内（1～2天）的余震目录就可以较准确地估算出主震区域内可能发生的最大余震震级。实际上,主震后12h（0.5天）的余震数据已完全可以给出最大余震震级的有效下限。此外,计算中我们采用了里氏震级ML和面波震级MS的余震目录,结果显示,2种震级类型目录的估算结果完全一致,表明利用推定最大余震震级估算实际最大余震震级的方法不受震级类型的影响。据此,该最大余震震级快速评估方法可进一步推广应用于我国大陆地区中强震后强余震灾害分析评估中。目前的拟合技术也显示出随着测震技术的不断进步以及余震识别能力的提高,快速评估方法可以在主震后短时间（<1天）内准确地预测可能发生的最大余震震级。 相似文献
11.
On robustness of large quantile estimates to largest elements of the observation series 总被引：1，自引：0，他引：1
The robustness of large quantile estimates of largest elements in a small sample by the methods of moments (MOM), L‐moments (LMM) and maximum likelihood (MLM) was evaluated and compared. Bias (B) and mean square error (MSE) were used to measure the estimation methods performance. Quantiles were estimated by eight two‐parameter probability distributions with the variation coefficient being the shape parameter. The effect of dropping largest elements of the series on large quantile values was assessed for various variation coefficient (CV)/sample size (n) ‘combinations’ with n = 30 as the basic value. To that end, both the Monte Carlo sampling experiments and an asymptotic approach consisting in distribution truncation were applied. In general, both sampling and asymptotic approaches point to MLM as the most robust method of the three considered, with respect to bias of large quantiles. Comparing the performance of two other methods, the MOM estimates were found to be more robust for small and moderate hydrological samples drawn from distributions with zero lower‐bound than were the LMM estimates. Extending the evaluation to outliers, it was shown that all the above findings remain valid. However, using the MSE variation as a measure of performance, the LMM was found to be the best for most distribution/variation coefficient combinations, whereas MOM was found to be the worst. Moreover, removal of the largest sample element need not result in a loss of estimation efficiency. The gain in accuracy is observed for the heavy‐tailed and log‐normal distributions, being particularly distinctive for LMM. In practice, while dealing with a single sample deprived of its largest element, one should choose the estimation method giving the lowest MSE of large quantiles. For n = 30 and several distribution/variation coefficient combinations, the MLM outperformed the two other methods in this respect and its supremacy grew with sample size, while MOM was usually the worst. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
12.
On June 15, 1995 at 00:15 GMT a devastating earthquake (6.2M
L
) occurred in the western end of the Gulf of Corinth. This was followed 15 min later by the largest aftershock (5.4M
L
). The main event was located by the University of Patras Seismological Network (PATNET) at the northern side of the Gulf of Corinth graben. The second event (5.4M
L
) was located also by PATNET near the city of Egion, on a fault parallel to the Eliki major fault that defines the south bound of the Gulf of Corinth graben. A seismogenic volume that spans the villages of Akrata (SE) and Rodini (NW) and extends to Eratini (NE) was defined by the aftershock sequence, which includes 858 aftershocks of magnitude greater than 2M
L
that occurred the first seventeen days. The distribution of hypocentres in cross section does not immediately suggest a planar distribution but rather defines a volume about 15 km (depth) by 35 km (NW-SE) and by 20 km (NE-SW). 相似文献
13.
The Donzurubo subaqueous pyroclastic flow deposits deposited in subaqueous environments maintaining high temperatures (about 500°C). Each flow unit of these pyroclastic flow deposits shows some characteristic size distributions in its stratigraphic column. The concentration of pumice at the top clearly defines the top facies of a flow unit. Median diameter (Md Ø) and the averages of the largest ten essential dense debris increase gradually starting from both the top and the bottom of the flow unit. The maximum points of Md Ø and the averages of the largest ten essential dense debris are usually found in the middle zone of each flow unit, but the Md Ø maximum points are generally in a lower position than the averages. Mechanical analyses show that the deposits consist of polymodal populations. They show, on the whole, an asymmetrical distribution, which is mainly due to the absence of the coarser fractions of the main population. The size distribution characteristics and the C-M pattern of the deposits suggest that these subaqueous pyroclastic flow deposits were not originated by homogeneously suspended turbulent flows but by incandescent turbulent flows with layered suspension. 相似文献
14.
Extremes of stream flow and precipitation are commonly modeled by heavytailed distributions. While scrutinizing annual flow
maxima or the peaks over threshold, the largest sample elements are quite often suspected to be low quality data, outliers
or values corresponding to much longer return periods than the observation period. Since the interest is primarily in the
estimation of the right tail (in the case of floods or heavy rainfalls), sensitivity of upper quantiles to largest elements
of a series constitutes a problem of special concern. This study investigated the sensitivity problem using the log-Gumbel
distribution by generating samples of different sizes (n) and different values of the coefficient of variation by Monte Carlo experiments. Parameters of the log-Gumbel distribution
were estimated by the probability weighted moments (PWMs) method, method of moments (MOMs) and maximum likelihood method (MLM),
both for complete samples and the samples deprived of their largest elements. In the latter case, the distribution censored
by the non-exceedance probability threshold, F
T
, was considered. Using F
T
instead of the censored threshold T creates possibility of controlling estimator property. The effect of the F
T
value on the performance of the quantile estimates was then examined. It is shown that right censoring of data need not reduce
an accuracy of large quantile estimates if the method of PWMs or MOMs is employed. Moreover allowing bias of estimates one
can get the gain in variance and in mean square error of large quantiles even if ML method is used. 相似文献
15.
Rakesh K. Goel 《地震工程与结构动力学》2000,29(4):461-480
This paper investigates the response of asymmetric‐plan buildings with supplemental viscous damping to harmonic ground motion using modal analysis techniques. It is shown that most modal parameters, except dynamic amplification factors (DAFs), are affected very little by the plan‐wise distribution of supplemental damping in the practical range of system parameters. Plan‐wise distribution of supplemental damping significantly influences the DAFs, which, in turn, influence the modal deformations. These trends are directly related to the apparent modal damping ratios; the first modal damping ratio increases while the second decreases as CSD moves from right to left of the system plan, and their values increase with larger plan‐wise spread of the supplemental damping. The largest reduction in the flexible edge deformation occurs when damping in the first mode is maximized by distributing the supplemental damping such that the damping eccentricity takes on the largest value with algebraic sign opposite to the structural eccentricity. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
16.
An analysis based on the L-moments theory suggests of adopting the generalized Pareto distribution to interpret daily rainfall depths recorded by the rain-gauge network of the Hydrological Survey of the Sardinia Region. Nevertheless, a big problem, not yet completely resolved, arises in the estimation of a left-censoring threshold able to assure a good fitting of rainfall data with the generalized Pareto distribution. In order to detect an optimal threshold, keeping the largest possible number of data, we chose to apply a “failure-to-reject” method based on goodness-of-fit tests, as it was proposed by Choulakian and Stephens [Choulakian, V., Stephens, M.A., 2001. Goodness-of-fit tests for the generalized Pareto distribution. Technometrics 43, 478-484]. Unfortunately, the application of the test, using percentage points provided by Choulakian and Stephens (2001), did not succeed in detecting a useful threshold value in most analyzed time series. A deeper analysis revealed that these failures are mainly due to the presence of large quantities of rounding off values among sample data, affecting the distribution of goodness-of-fit statistics and leading to significant departures from percentage points expected for continuous random variables. A procedure based on Monte Carlo simulations is thus proposed to overcome these problems. 相似文献
17.
Peter R. Wilcock 《地球表面变化过程与地形》1992,17(3):289-298
The largest grains found in samples of transported sediment are commonly used to estimate flow competence. With samples from a range of flows, a relationship between the flow and the largest mobile grain can be derived and used to estimate the critical shear stress for incipient motion of the different grain sizes in the bed sediment or, inversely, to estimate the magnitude of the flow from the largest grain found in a transport sample. Because these estimates are based on an extreme value of the transport grain-size distribution, however, they are subject to large errors and are sensitive to the effect of sample size, which tends to vary widely in sediment transport samples from natural flows. Furthermore, estimates of the critical shear stress based on the largest sampled moving grain cannot be scaled in a manner that permits reasonable comparison between fractions. The degree to which sample size and scaling problems make largest-grain estimates of fractional critical shear stress deviate from a true relationship cannot be predicted exactly, although the direction of such a deviation can be demonstrated. The large errors and unknown bias suggest that the largest sampled mobile grain is not a reliable predictor of either critical shear stress or flow magnitude. It is possible to define a single flow competence for the entire mixture, based on a central value of the transport grain-size distribution. Such a measure is relatively stable, does not require between-fraction scaling, and appears to be well supported by observation. 相似文献
18.
针对2010年4月14日玉树发生MS7.1地震,本文利用InSAR数据给出同震视线向位移确定出的发震断层空间展布,并以该同震位移为约束反演得到主震和最大余震的同震位错分布.结果表明,主震同震位错发生在东玉树断裂,最大余震同震位错发生在西玉树断裂东端;基于位错分布计算了同震库仑应力变化与西部余震集中区地震活动之间的关系,结果反映玉树主震后最为活跃的余震活动可能受控于近东西向的次级断层(走向约为85°),而非玉树主干断裂;玉树断裂带整体呈现为左旋走滑运动,但其具体断层运动形式表现出主干断裂典型走滑运动、走滑断裂间的拉张和逆冲性质的次级运动、次级断裂与主干断裂相互作用下更为复杂的多方向次级断层活动等等不同变形特征,而主震同震破裂与余震空间分布均与这些不同断层变形方式有着密切关系. 相似文献
19.
20.
Aerial surveys were conducted in the north-central Gulf of Mexico from June 1988 to May 1989. Sightings of marine debris and specifically large floating plastics were recorded during these surveys. Five study areas off the Louisiana coast were monitored and seasonal distribution and densities were estimated. Each study area contained plastic throughout the year. The estimated densities of plastic were largest in the offshore areas (4 & 5) and smallest in the inshore areas (1 & 3). Seasonally, density of plastic was smallest in the summer and largest in the fall. The reasons for the differences in seasons and study areas are not apparent but the amount of plastic in each area and season could be affected by variations in currents, winds, discharge from rivers, and human activity. 相似文献