On the Incorporation of the Effect of Crustal Structure into Empirical Strong Ground Motion Estimation

This article has two purposes. Firstly, a validation exercise of the modal summation technique for the computation of synthetic strong-motion records is performed for two regions of Europe (Umbria-Marche and south Iceland), using a variety of region specific crustal structure models, by comparing the predicted ground motion amplitudes with observed motions. It is found that the rate of decay of ground motions is well predicted by the theoretical decay curves but that the absolute size of the ground motions is underpredicted by the synthetic time-histories. This is thought to be due to the presence of low-velocity surface layers that amplify the ground motions but are not included in the crustal structure models used to compute the synthetic time-histories. Secondly, a new distance metric based on the computed theoretical decay curves is introduced which should have the ability to model the complex decay of strong ground motions. The ability of this new distance metric to reduce the associated scatter in empirically derived equations for the estimation of strong ground motions is tested. It is found that it does not lead to a reduction in the scatter but this is thought to be due to the use of crustal structure models that are not accurate or detailed enough for the regions studied. This revised version was published online in July 2006 with corrections to the Cover Date.     

Detecting Changes in Ground Water Quality at Regulated Facilities

The Resource Conservation and Recovery Act (PL 94–580) and related federal and state legislation have mandated routine monitoring of ground water quality at regulated facilities. The objective of the required monitoring activities is detection of adverse changes in ground water quality caused by the facilities.
Both failure to detect pollution and an incorrect determination of pollution can be very expensive. It is crucial, therefore, that monitoring programs be designed and operated to provide statistically sound information. It is equally important that users of ground water quality data understand the nature and limitations of information from monitoring.
To address the preceding issues, the authors present a general approach to analyzing ground water quality data in light of the stated monitoring objective. The suggested approach accounts for "natural" variation in background water quality through pairing of observations. The limitations of quarterly sampling for detecting small changes in quality over a short time frame are discussed.     

地电阻率与水位关系的机理分析

从地电阻率的观测理论出发,指出地电阻率场地的电性结构、岩石的饱和度和孔隙度决定了地电阻率和水位的关系。在长期的观测资料基础上,通过实例系统地分析了地电阻率和水位的关系,给出了不同层位的水位变化和不同方式的水位变化对地电阻率观测结果的影响,认为非构造水位变化与地电阻率的关系主要取决于表层土壤或岩石的水饱和度,构造水位变化与地电阻率变化存在明确的相关关系,从而进一步探讨了与前兆异常有关的水位和地电阻率变化。