中美两国全球6级以上地震目录对比分析

中国地震台网中心(CENC)和美国国家地震信息中心(NEIC)提供的全球地震目录经常出现较大偏差.CENC发震时刻较早,CENC震源深度较深.2001年至2010年全球6.0级以上地震约11.67％存在明显目录偏差,印度洋板块北侧集中约70％有各类偏差地震.印度洋板块北侧各项误差统计占全世界同类地震约70％,表现出较好的一致性.这种现象应与震源过程有关,与该地区S波走时异常问题耦合,而不是算法或随机误差造成的.     

Soil loss rates due to piping erosion

Compared with surface soil erosion by water, subsurface erosion (piping) is generally less studied and harder to quantify. However, wherever piping occurs, it is often a significant or even the main sediment source. In this study, the significance of soil loss due to piping is demonstrated through an estimation of soil volume lost from pipes and pipe collapses (n = 560) in 137 parcels under pasture on loess‐derived soils in a temperate humid climate (Belgium). Assuming a period of 5 to 10 years for pipe collapse to occur, mean soil loss rates of 2.3 and 4.6 t ha^?1 yr^?1 are obtained, which are at least one order of magnitude higher than surface erosion rates (0.01–0.29 t ha^?1 yr^?1) by sheet and rill erosion under a similar land use. The results obtained for the study area in the Flemish Ardennes correspond well to other measurements in temperate environments; they are, however, considerably smaller than soil loss rates due to subsurface erosion in semi‐arid environments. Although local slope gradient and drainage area largely control the location of collapsed pipes in the study area, these topographic parameters do not explain differences in eroded volumes by piping. Hence, incorporation of subsurface erosion in erosion models is not straightforward. Copyright © 2011 John Wiley & Sons, Ltd.     

Uncertainty in index flood modelling due to calibration data sizes

Regional frequency analysis is an important tool in estimating design flood for ungauged catchments. Index flood is an important component in regionalized flood formulas. In the past, many formulas have been developed based on various numbers of calibration catchments (e.g. from less than 20 to several hundred). However, there is a lack of systematic research on the model uncertainties caused by the number of calibration catchments (i.e. what is the minimum number of calibration catchment? and how should we choose the calibration catchments?). This study uses the statistical resampling technique to explore the impact of calibration catchment numbers on the index flood estimation. The study is based on 182 catchments in England and an index flood formula has been developed using the input variable selection technique in the data mining field. The formula has been used to explore the model uncertainty due to a range of calibration catchment numbers (from 15 to 130). It is found that (1) as expected, the more catchments are used in the calibration, the more reliable of the models developed are (i.e. with a narrower band of uncertainty); (2) however, poor models are still possible with a large number of calibration catchments (e.g. 130). In contrast, good models with a small number of calibration catchments are also achievable (with as low as 15 calibration catchments). This indicates that the number of calibration catchments is only one of the factors influencing the model performance. The hydrological community should explore why a smaller calibration data set could produce a better model than a large calibration data set. It is clear from this study that the information content in the calibration data set is equally if not more important than the number of calibration data. Copyright © 2011 John Wiley & Sons, Ltd.     

Uncertainty analysis in statistical modeling of extreme hydrological events

With the increase of both magnitude and frequency of hydrological extreme events such as drought and flooding, the significance of adequately modeling hydrological extreme events is fully recognized. Estimation of extreme rainfall/flood for various return periods is of prime importance for hydrological design or risk assessment. However, due to knowledge and data limitation, uncertainty involved in extrapolating beyond available data is huge. In this paper, different sources of uncertainty in statistical modeling of extreme hydrological events are studied in a systematic way. This is done by focusing on several key uncertainty sources using three different case studies. The chosen case studies highlight a number of projects where there have been questions regarding the uncertainty in extreme rainfall/flood estimation. The results show that the uncertainty originated from the methodology is the largest and could be >40% for a return period of 200 years, while the uncertainty caused by ignoring the dependence among multiple hydrological variables seems the smallest. In the end, it is highly recommended that uncertainty in modeling extreme hydrological events be fully recognized and incorporated into a formal hydrological extreme analysis.     

Uncertainty in high and low flows due to model structure and parameter errors

This paper aims to investigate the uncertainty in simulated extreme low and high flows originating from hydrological model structure and parameters. To this end, three different rainfall-runoff models, namely GR4J, HBV and Xinanjiang, are applied to two subbasins of Qiantang River basin, eastern China. The Generalised Likelihood Uncertainty Estimation approach is used for estimating the uncertainty of the three models due to parameter values, henceforth referred as parameter uncertainty. Uncertainty in simulated extreme flows is evaluated by means of the annual maximum discharge and mean annual 7-day minimum discharge. The results show that although the models have good performance for the daily flows, the uncertainty in the extreme flows could not be neglected. The uncertainty originating from parameters is larger than uncertainty due to model structure. The parameter uncertainty of the extreme flows increases with the observed discharge. The parameter uncertainty in both the extreme high flows and the extreme low flows is the largest for the HBV model and the smallest for the Xinanjiang model. It is noted that the extreme low flows are mostly underestimated by all models with optimum parameter sets for both subbasins. The largest underestimation is from Xinanjiang model. Therefore it is not reliable enough to use only one set of the parameters to make the prediction and carrying out the uncertainty study in the extreme discharge simulation could give an overall picture for the planners.     

Probability estimation of rare extreme events in the case of small samples: Technique and examples of analysis of earthquake catalogs

The most general approach to studying the recurrence law in the area of the rare largest events is associated with the use of limit law theorems of the theory of extreme values. In this paper, we use the Generalized Pareto Distribution (GPD). The unknown GPD parameters are typically determined by the method of maximal likelihood (ML). However, the ML estimation is only optimal for the case of fairly large samples (>200–300), whereas in many practical important cases, there are only dozens of large events. It is shown that in the case of a small number of events, the highest accuracy in the case of using the GPD is provided by the method of quantiles (MQs). In order to illustrate the obtained methodical results, we have formed the compiled data sets characterizing the tails of the distributions for typical subduction zones, regions of intracontinental seismicity, and for the zones of midoceanic (MO) ridges. This approach paves the way for designing a new method for seismic risk assessment. Here, instead of the unstable characteristics—the uppermost possible magnitude M_max—it is recommended to use the quantiles of the distribution of random maxima for a future time interval. The results of calculating such quantiles are presented.     

地震危险性分析中潜在震源区范围与震级上限的不确定性分析

目前进行的地震危险性分析计算中, 潜在震源区范围和震级上限的确定过程中存在很大的不确定性。 采用二级划分和三级划分潜在震源区的方法, 对潜在震源区范围不确定性进行了研究; 用震级上限的单边正态分布模型代替固定的震级上限模型, 分析了这种改进对地震危险性分析结果的影响及其工程意义。 结果表明, 用三级划分潜源的方法代替二级划分潜在震源方法可降低局部地区的地震危险性, 对于在潜在震源区附近选址和降低工程成本有重要意义。 震级上限的改进, 使得地震危险性降低, 这对百年使用年限的工程更具有实用性。     

Increasing transmission losses from flood events due to groundwater extraction

This study continues the examination of the influence of groundwater exploitation upon the process of aquifer recharge by flood events. In the course of the developing an earlier hydrological model for the Hazeva Formation aquifer (the Wadi Paran watershed, southern Israel), it became apparent that groundwater extraction influenced absorption capacity of sub‐aquifers and regulated the distribution of percolating surface water between units. The present study lends numerical proof regarding the influence of Hazeva aquifer exploitation upon the regime of runoff and enhancement of transmission losses from flood events in Wadi Paran, and, as a result, upon increased recharge to the aquifer. Copyright © 2002 John Wiley & Sons, Ltd.     

A European digital accelerometric database:statistical analysis of engineering parameters of small to moderate magnitude events

During the NERIES Project, an accelerometric database containing European digital information was developed. Besides event and station metadata, ground motion parameters, computed in a homogeneous manner, were assembled:PGA, PGV, AI, TD, CAV, HI and PSV(f,5%)(19,961 components, 2629 events, 547 stations). Merging small and moderate magnitude events produced a unique database capable of providing important information such as:(i) Correlations between several ground motion parameters follow analogous trends as in previous worldwide datasets, with slight corrections.(ii) Although PGA attenuations with distance show great uncertainties, four recent GMPEs recommended for Europe fit quite well the central 50% data interval for the distance range 10 R 200 km; outside these distances, they do not fit.(iii) Soil amplification ratios indicate that weak motion(low magnitudes and larger distances) shows larger amplification than strong motion(short distances and large magnitudes) as represented in UBC97 for the USA, but not in EC8 for Europe.(iv) Average spectral shapes are smaller than in the EC8.(v) Differences in amplification factors for PGA, PGV and HI for EC8 soil classes B and C, and differences in spectral shapes for these soil classes, indicate that EC8, Type 2 S-coefficient should be frequency dependent, as in UBC97.     

Coupled deformation-diffusion effects on water-level changes due to propagating creep events

Water-well-level fluctuations associated with episodic creep are studied using a coupled deformation-diffusion solution for the pore pressure produced by a plane-strain shear dislocation moving steadily at a speedV in a linear elastic, saturated porous medium. For largeVr/2c, wherer is distance from the dislocation andc is diffusivity, the solution approaches the form of the uncoupled elastic solution used by Wesson (1981) to analyze water-level changes due to creep events. The differences between the two solutions are significant within 10 diffusion lengths (20c/V) from the fault plane. More specifically, the pore pressure predicted by the coupled solution reverses sign behind the dislocation and is much smaller in magnitude than that predicted by the uncoupled solution. For an undrained Poisson ratio of 0.3, Skempton's coefficient of 0.8 and a shear modulus of 30 GPa, the coupled solution predicts a peak pore-pressure change of 13.7 kPa (137 mbar) per millimeter of slip forV=1 km/day andc=1.0 m²/sec. The spectrum of the coupled solution is limited to a band of frequencies, centered at a value proportional toV and approximately inversely proportional to the distance from the observation point to the fault plant. Thus, close to the fault plane the frequency band occupied by the coupled solution may lie above the range at which water wells can respond. The coupled solution is used in interpreting the same creep-associated water-level change observed by Johnson (1973) and modeled by Wesson (1981) using the uncoupled solution. Although there are uncertainties in properties of the rock material and in the speed of the creep event, the coupled solution predicts a water-level change comparable in magnitude to the observed change.     

On the propagation of spherical waves due to large underground explosion

Summary When a high explosive pressure acts on the boundary of a spherical cavity in an elastic medium, the material in a region around the charge behaves plastically and thereafter an elastic wave is propagated. Not only that but the elastic plastic boundary moves also with a certain velocity which is less than the elastic wave velocitySabodash [3]²). In this paper, firstly the case when the elastic plastic boundary moves with a velocityV ₀. (V ₀<c) has been dealth with. The pressure in the elastic medium on this boundary has been assumed to be constant and equal toP ₀. Secondly the case when the elastic plastic boundary moves with an exponentially decaying velocity has been considered. The pressure in the elastic medium on this boundary has also been assumed to be of exponential character.     

Moment magnitude determination of local seismic events recorded at selected Polish seismic stations

The paper presents the method of local magnitude determination used at Polish seismic stations to report events originating in one of the four regions of induced seismicity in Poland or its immediate vicinity. The method is based on recalculation of the seismic moment into magnitude, whereas the seismic moment is obtained from spectral analysis. The method has been introduced at Polish seismic stations in the late 1990s but as of yet had not been described in full because magnitude discrepancies have been found between the results of the individual stations. The authors have performed statistics of these differences, provide their explanation and calculate station corrections for each station and each event source region. The limitations of the method are also discussed. The method is found to be a good and reliable method of local magnitude determination provided the limitations are observed and station correction applied.     

Incorporating space,time, and magnitude measures in a network characterization of earthquake events

We investigate the structural properties of a spatio-temporal network of earthquake events that incorporates magnitude information between the connected events. The network creates temporally directed links from an origin event towards a later event if it breaks the record closest distance from the origin among all the events in the catalog so far. Additionally, the links are conditionally classified based on the magnitude difference between connected events: “up” (“down”) connections point from a weaker (stronger) to a stronger (weaker) event. Using earthquake records from the Philippines from 1973 to 2012 and southern California from 1982 to 2012, we observe that the out-degree distributions show slight deviations from the corresponding Poisson distribution of the same mean. The space and time separations of connected earthquakes both show power-law regimes, suggesting spatio-temporal (self-)organization. More importantly, the conditional distributions of “up” and “down” connections in space, time, and network structure point to a higher likelihood of a stronger event triggering a nearby weaker event for the first few connections, as in the case of aftershocks. The results are captured by a sandpile-based model where a small but finite probability of preferentially targeting the most susceptible grid site is introduced. Our analysis, coupled with the discrete model analog, provides a quantitative picture of the spatio-temporal and magnitude organization of seismicity beyond just the successive events. The technique may be extended to further characterize similar long-period earthquake records to yield a more complete picture of the underlying processes involved in seismicity.     

Whiting events: biogenic origin due to the photosynthetic activity of cyanobacterial picoplankton

An annual whiting event occurs each year in late May to early June in Fayetteville Green Lake, New York. The initiation of this event correlates with exponential growth of the Synechococcus population within the lake. Synechococcus is the dominant (by approximately 4 orders of magnitude) autotrophic organism owing to the oligotrophic condition of the lake. The delta 13C values of the dissolved inorganic C range seasonally from -9.5% in winter to -6.2% in summer due to photosynthetic activity. Calcite precipitates principally in the microenvironment surrounding Synechococcus because of a photosynthetically driven alkalization process and the availability of the cells as nucleation sites. This calcite has a heavier delta 13C value (>4%) than does the dissolved inorganic C of the lake water owing to the cells' preferential uptake of 12C. A conceptual model suggests that photosynthetic activity and cell surface chemistry, together with the substantial surface area that arises from the great abundance of micron-sized cells, allow Synechococcus to dominate the annual whiting events in Fayetteville Green Lake.     

Entropy inference of recurrence models for variability analysis of extreme events

A complete methodology is developed to analyze the recurrence of extreme environmental events and its variability as time without further events elapses. Firstly we investigate the conditioned recurrence inference problem consisting in the selection of a probability model for the interarrival time between extreme events, given a contexto-factual evidence conditioned by the time elapsed since the last of such events. Two ways to include this condition can be considered, which yield alternative conditioned evidences and convert the former problem into two distinct ones, thus giving rise to a possible consistency violation. These problems are formalized within the logical probability framework, in a plausible logic language that allows a suitable expression of the available observational data. They are solved using the REF relative entropy method with fractile constraints, and their solutions are compared at all inference levels. It is concluded that the two conditioning ways are not really mutually exclusive and that a unique global solution to the conditioned inference can be obtained using this procedure. An example illustrates an application of the methodology to the variability analysis of the recurrence time between historical inundations of the Guadalquivir river in Spain, as time elapses with no new floods.Acknowledgments. Support for this work was provided by DGI of Spain as the grant REN2000-2988-E/CLI and the research project REN2002-01337/CLI.     

Runoff modifications due to the conversion of natural grasslands to forests in a large basin in Uruguay

Uruguay has encouraged the development of the forestry sector since 1989. As a member of the Montreal Process, the country has followed a set of criteria and indicators for the Sustainable Forest Management. The aim of this paper is to describe the studies carried out in a large basin of 2097 km², located in an area of humid subtropical climate and 1300 mm of long‐term mean annual rainfall, where the conversion of natural grasslands to forests increased up to 540 km² during the last 15 years. Using data from daily rainfall and streamflow, the study analyses the effects of afforestation on the runoff and water loss. The analysis comprises hydrographs resulting from comparable rainfall events and annual and seasonal streamflow and water loss behaviour, both before afforestation (1975–1993) and during the afforestation period (1994–2008). A statistically significant reduction of runoff volumes (33–43%) and peak flows (59–65%) were identified on storm hydrographs. The annual and seasonal streamflow also showed diminishing tendencies due to the forestry development, whereas the water loss increases. The annual streamflow decreased between 8·2 and 36·5% depending on the annual rainfall totals. The streamflow reduction was higher during spring and summer (25·2–38·4%) and smaller during autumn and winter (15–20·3%). The water loss is expected to increase by 98 mm for the long‐term mean annual rainfall. The resulting information is a valuable input for the Integrated Water Resources Management of the Negro river basin located downstream, where hydroelectric power, rice irrigation and forestry development are supported. Copyright © 2008 John Wiley & Sons, Ltd.     

Probability of earthquake recurrence with nonuniform stress rates and time-dependent failure

Current methods for calculation of long-term probabilities for the recurrence of large earthquakes on specific fault segments are based upon models of the faulting process that implicitly assume constant stress rates during the interval separating earthquakes and instantaneous failure at a critical stress threshold. However, observations indicate that the process of stress recovery following an earthquake involves rate variations at all time scales in addition to stress steps caused by nearby earthquakes. Additionally, the existence of foreshocks, aftershocks and possible precursory processes suggest that there may be significant time dependence of the earthquake nucleation process. A method for determining the conditional probabilities for earthquake occurrence under conditions of irregular stressing is developed that could be useful at all time scales including those pertinent to short-and intermediate-term prediction. Used with models for earthquake occurrence at a stress threshold, the addition of variable stressing introduces a simple scaling of the conditional probabilities by stress level and stress rate. A model for the time-dependent nucleation of earthquake slip has been proposed recently that is based upon laboratory observations of fault strength. This failure criterion results in large but relatively short duration changes in the probability of earthquake recurrence particularly following stress steps. Applied to populations of earthquakes the models predicts a 1/t decay of seismicity following stress steps as observed for aftershocks and for frequency of foreshock-mainshock pairs. The model suggests that variations of seismicity rates of small earthquakes in the nucleation zone of the expected earthquake directly indicate variations in probability of recurrence of the large earthquake.     

Applicability of P/S amplitude ratios for the discrimination of low magnitude seismic events

Applicability of regional P/S amplitude ratios for the discrimination of low-magnitude seismic events was tested and proved using earthquakes and explosions in Central Asia. Results obtained show that regional P/S amplitude ratios which may discriminate medium or large magnitude events well, are also applicable to low magnitude events. Their performances for low magnitude events are almost as good as that for medium or large events. Statistical comparisons based on 25 P/S discriminate from the four seismic stations WMQ, BLK, MUL and MAK showed that the average misclassification rate for low-magnitude seismic events averagely was only 2 percent higher than that for medium and large magnitude seismic events.     

On the large scale motion in the tropics with latent heat due to condensation

Summary A scale analysis for the large scale tropical motions with diabatic heating due to the latent heat of condensation is given. The analysis shows that the diabatic heating term in the thermodynamic energy equation becomes important when the rainfall rate is equal or greater than 2 mm per day.