Early Estimation of Strong Aftershock Duration Time

In order to solve the problem of early estimation of moderately strong aftershock duration time in an earthquake sequence,this study has been conducted.First,the definition of the strong aftershock has been given.It is pointed out that there is a difference in the strong aftershock duration time between the main shock type sequence and the strong earthquake swarm sequence.After dividing the three cases,i.e.,a strong aftershock duration time larger than 1 day,smaller than 1 day,and no strong aftershock occurred in a main shock type sequence by using the pattern recognition method,we gave the rough correlation relation between strong aftershock duration time and first large shock magnitude for two types of sequences.Finally,the judgment index and method of estimating strong aftershock duration times for different sequence types have been given.     

Comparison of the return period for landslide-triggering rainfall events in Japan based on standardization of the rainfall period

The intensity of rainfall events with potential to cause landslides has varying temporal characteristics. In this study, the time at which the 72-h accumulated rainfall reached its maximum was used to standardize the period of rainfall measurement. The proposed standardization of the rainfall period was used in conjunction with the return level of rainfall intensity, obtained from intensity–duration–frequency curves, to investigate rainfall intensity anomalies associated with 10 hazardous rainfall events that triggered numerous landslides at the regional scale in Japan. These landslides included shallow landslides in volcanic and non-volcanic areas, as well as deep-seated landslides. The rainfall events that triggered the shallow landslides were divided into two types: downpours that repeatedly reached close to the 100-year return level within approximately 3–4 h, and accumulated rainfall that reached close to 200–400 mm over longer time intervals but within 72 h. Lithological differences seemed unrelated to the differences between the two types of shallow-landslide-triggering rainfall; however, precipitation >1000 mm was necessary to trigger deep-seated landslides. Although the characteristics of the hyetographs differed markedly among the landslide-triggering rainfall events, all the landslides could have been triggered when the mean rainfall intensity reached the 100-year rainfall level during the standardized period. Thus, the landslide trigger can be evaluated indirectly based on the increase in the return level of the mean rainfall intensity, which could provide a means for estimating the time of landslide occurrence.     

Impact of the sampling duration on the uncertainty of averaged velocity measurements with acoustic instruments

Average velocity in streams is a key variable for the analysis and modelling of hydrological and hydraulic processes underpinning water resources science and practice. The present study evaluates the impact of the sampling duration on the quality of average velocity measurements acquired with contemporary instruments such as Acoustic Doppler Velocimeters (ADV) an Acoustic Doppler Current Profilers (ADCP). The evaluation combines considerations on turbulent flows and principles and configurations of acoustic instruments with practical experience in conducting customized analysis for uncertainty analysis purposes. The study sheds new insights on the spatial and temporal variability of the uncertainty in the measurement of average velocities due to variable sampling durations acting in isolation from other sources of uncertainties. Sampling durations of 90 and 150 s are found sufficient for ADV and ADCP, respectively, to obtain reliable average velocities in a flow affected only by natural turbulence and instrument noise. Larger sampling durations are needed for measurements in most of the natural streams exposed to additional sources of data variability.     

Drying increases organic colloidal mobilization in the karst vadose zone: Evidence from a 15-year cave-monitoring study

Understanding the hydrological processes of colloids within the karst vadose zone is vital to the security of karst groundwater and providing appropriate paleohydrological explanations of colloid-facilitated metals in speleothem. This study addresses the mobilization mechanisms driving colloidal organic matter (COM) transport in the karst vadose zone using a 15-year long monthly monitoring dataset from a cave drip point (HS4) in Heshang Cave, Qingjiang Valley, China. Variations in COM concentrations were reported as the fluorescence difference values of raw and filtered (<0.22 μm) samples at an excitation wavelength of 320 nm and emission wavelength of ~400 nm. A fluorescence humification index (HIX) lower than 0.8 and an autochthonous index (BIX) higher than 1.2 indicated that the origin of COM was mainly from the karst vadose zone, rather than the soil zone. The COM concentration varied from 0.001 to 0.038 Raman Unit (RU), with evident seasonal fluctuations. Rising limbs for COM values occurred prior to rising limbs within a dripwater hydrograph; moreover, the COM peak values corresponding to the beginning of the increasing hydrograph generally suggested that the mobilization of COM reflected the movement of the air–water interface (AWI) in the karst vadose zone rather than rainfall intensity or flow velocity. COM peak values were positively correlated with the antecedent drying duration and negatively correlated with HIX values. These phenomena may be explained by the increased amount of organic matter that was aggregated and absorbed on the surface of carbonate in the karst vadose zone during a longer drying duration. Moreover, the longer drying duration was also beneficial to autochthonous biological activity, which subsequently decreased the HIX value of the organic matter in the karst vadose zone. The movement of AWI and the drying duration are both controlled by the outside weather conditions. This study is therefore conducive to evaluating the security of karst groundwater in response to climate change, and challenges prevailing paleoclimate interpretations of colloid-facilitated metal abundance timeseries reported from speleothems.     

Analysis of the impact of conservation measures on stream flow regime in catchments of the Loess Plateau,China

Catchments in the Loess Plateau have been under the influence of human activities for centuries. In the last four decades, soil conservation measures have accelerated and intensified. These measures were designed to reduce soil erosion, improve agricultural productivity, and enhance environmental quality. It is important to evaluate the effects of these measures on hydrology in order to develop sustainable catchment management plans in the region. This study evaluated changes in stream flow data for four selected catchments in the Loess Plateau following large‐scale soil conservation measures. The non‐parametric Mann–Kendall test was used to identify trends in annual stream flow and the results showed significant downward trends in three of the four catchments. The Pettitt test indicated that a change point occurred in 1978 in these three catchments. Annual precipitation in all the catchments showed no significant trend during the period of record. Comparison of daily flow duration curves for two 20‐year periods (1957–1978) and (1979–2003) showed significant changes in stream flow regime. Reduction in most percentile flows varied between 20 and 45%, and the reduction in low flows was greatest. Overall, the reductions in daily flow were increasing with time, with significant changes occurring in the 1990s. However, it is not clear whether these catchments have seen the full effects of the soil conservation measures, so the results of this study might underestimate the final impact of soil conservation on stream flow regime. Copyright © 2007 John Wiley & Sons, Ltd.     

汶川8.0级地震序列及相关问题讨论

汶川8.0级地震序列具有明显的分段特性,较强余震分布于茂县、绵竹以南及平武以北。主破裂过程在中南段以逆冲为主,序列逐渐衰减,呈主余型的序列衰减特征;北段是汶川地震破裂过程的终止区域,主破裂过程在该区域以走滑为主,形成多震型的序列特征,也成为汶川序列较大余震的主体活动区域。序列较强余震活动明显受引潮力调制,大多数较强余震发生在固体潮大、小潮时段,并且16时前后是较强余震的优势发震时段。序列衰减系数p值随时间增加而逐渐增大,最终基本稳定在1附近变化。结合以往的研究,对序列类型及最大强余震震级、强余震活动持续时间等进行了初步讨论。初步的统计结果还显示,8级左右强震序列中主震与最大余震之间的震级差正比于主震破裂尺度,这意味着当震级大体接近时,较大的破裂尺度与较为充分的能量释放相对应     

Mediating stream baseflow response to climate change: The role of basin storage

Inter‐basin differences in streamflow response to changes in regional hydroclimatology may reflect variations in storage characteristics that control the retention and release of water inputs. These aspects of storage could mediate a basin's sensitivity to climate change. The hypothesis that temporal trends in stream baseflow exhibit a more muted reaction to changes in precipitation and evapotranspiration for basins with greater storage was tested on the Oak Ridges Moraine (ORM) in Southern Ontario, Canada. Long‐term (>25 years) baseflow trends for 16 basins were compared to corresponding trends in precipitation amount and type and in potential evapotranspiration as well as shorter trends in groundwater levels for monitoring wells on the ORM. Inter‐basin differences in storage properties were characterized using physiographic, hydrogeologic, land use/land cover, and streamflow metrics. The latter included the slope of the basin's flow duration curve and basin dynamic storage. Most basins showed temporal increases in baseflow, consistent with limited evidence of increases and decreases in regional precipitation and snowfall: precipitation ratio, respectively, and recent increases in groundwater recharge along the crest of the ORM. Baseflow trend magnitude was uncorrelated to basin physiographic, hydrogeologic, land use/land cover, or flow duration curve characteristics. However, it was positively related to a basin's dynamic storage, particularly for basins with limited coverage of open water and wetlands. The dynamic storage approach assumes that a basin behaves as a first‐order dynamical system, and extensive open water and wetland areas in a basin may invalidate this assumption. Previous work suggested that smaller dynamic storage was linked to greater damping of temporal variations in water inputs and reduced interannual variability in streamflow regime. Storage and release of water inputs to a basin may assist in mediating baseflow response to temporal changes in regional hydroclimatology and may partly account for inter‐basin differences in that response. Such storage characteristics should be considered when forecasting the impacts of climate change on regional streamflow.     

近震信号检测参数设置研究

地震信号检测是进行各种地震数据分析和处理的首要任务,STA/LTA方法具有算法简单、便于实时处理等特点,被广泛应用于地震信号检测.结合实际震例数据研究STA/LTA方法进行地震信号检测的各种影响因素,得到该方法进行检测时最合理的参数设置范围.     

2016年8月24日意大利中部MW6.2地震强地面运动特征分析

对意大利国家强震台网在2016年8月24日获得的其中部拉齐奥大区阿库莫利市发生的M_W6.2地震强震动三分向记录进行处理和分析。完成原始数据基线校正、滤波等基本数据处理,回归此次地震动幅值衰减规律,发现其整体与ITA08及BA08的衰减趋势一致,但远场实际值低于预测值,不同场地条件下的衰减特性与ITA10一致,近震源幅值较大,且方向性明显;计算并回归分析几种持时,与全球经验预测方程均基本吻合;比较4个幅值较大的近震源台站的反应谱,发现其明显高于欧洲抗震设计规范中的设计反应谱。结合此次震害特点,该地区在实际建设中仍需提高抗震设防能力,以确保安全性等级。     

Model and parameter uncertainty in IDF relationships under climate change

Quantifying distributional behavior of extreme events is crucial in hydrologic designs. Intensity Duration Frequency (IDF) relationships are used extensively in engineering especially in urban hydrology, to obtain return level of extreme rainfall event for a specified return period and duration. Major sources of uncertainty in the IDF relationships are due to insufficient quantity and quality of data leading to parameter uncertainty due to the distribution fitted to the data and uncertainty as a result of using multiple GCMs. It is important to study these uncertainties and propagate them to future for accurate assessment of return levels for future. The objective of this study is to quantify the uncertainties arising from parameters of the distribution fitted to data and the multiple GCM models using Bayesian approach. Posterior distribution of parameters is obtained from Bayes rule and the parameters are transformed to obtain return levels for a specified return period. Markov Chain Monte Carlo (MCMC) method using Metropolis Hastings algorithm is used to obtain the posterior distribution of parameters. Twenty six CMIP5 GCMs along with four RCP scenarios are considered for studying the effects of climate change and to obtain projected IDF relationships for the case study of Bangalore city in India. GCM uncertainty due to the use of multiple GCMs is treated using Reliability Ensemble Averaging (REA) technique along with the parameter uncertainty. Scale invariance theory is employed for obtaining short duration return levels from daily data. It is observed that the uncertainty in short duration rainfall return levels is high when compared to the longer durations. Further it is observed that parameter uncertainty is large compared to the model uncertainty.