Application of WebGIS in seismological study

Introduction Earthquake is a destructive natural disaster. Earthquake studies are very complex, which not only involves space and time of large size, but also requires vast amount of spatially referenced data, such as historical records, modern instrument data, scientific experiment data and a lot of other data coming from related subjects. GIS, as an integrating tool processing multi-source data, has become a key technology in earthquake studies. In recent years, many GIS application system…     

利用GIS组件建立工程地震WebGIS系统

利用GIS软件组件建立了工程地震WebGIS系统。该系统采用浏览器 /服务器体系结构 ,实现了工程地震空间信息的网络共享和初步的协同工作。用户可以直接从网上通过浏览器来浏览、查询、分析和使用工程地震研究中的各类空间数据及GIS应用 ,同时还可以将需要的数据下载到本地机上使用或将自己的研究成果提交到远程服务器上发布 ,以实现共享。对地图在网上的传输显示速度问题和系统的安全性问题也采取适当的措施给以解     

Direct measurement of crustalP-velocities in the norsar area

Using simulated data, it is demonstrated that one may estimate the body wave velocity in the crust by measuring the angle of incidence ofP-waves provided only the very first part of the signal is used. This angle has been measured for a set ofP-waves at the NORSAR long period instrument sites. Combining these observations with measurements of apparent velocities, we find that the data indicates a crust velocity of 6.1±0.4 km/sec. While it is somewhat uncertain to what depth the value is representative, the observations are in obvious disagreement with previous authors who concluded that long periodP-waves were not affected by the earth's crust. Because of difficulties in separating the effects of real velocity variations from measurement errors, the details of the observedP-wave variation across the array are difficult to interpret. The consistent behavior of the data does, however, indicate that variations of approximately 3% must exist in the crustalP-wave velocity across the array.     

论历史地震研究在工程地震中的作用

本文通过回顾，展望及对现行《工程场地地震安全性评价工作规范》有关条文的理解，论述了历史地震研究在工程地震中的重要作用。历史地震研究，不仅在甄别历史地震参数、评定场地的地震基本烈度、编制地震烈度区划图、分析地震资料的时空不均匀性和历史地震对场地的方面是主要的手段和方法，而且在提供具有概率含义的抗震设防参数、编制综合性的设防区划图、确定背景地震强度等方面，也可能成为重要的方法。     

Fractal velocity models in refraction seismology

The introduction of noise components to a simple crustal velocity model is shown to markedly affect the appearance of synthetic seismograms calculated according to ray theory applied to refraction experiments. Here we simulate noise by a self-similar process with a power spectral density which falls off as inverse wavenumber to a simple power (0–2). The major effect is to destroy the coherency of the arrival branches normally expected from deterministic velocity models; the arrival amplitudes also show large trace-to-trace variations and considerable sensitivity to shot position. Some of these differences can be ascribed to the variety of noise model chosen (i.e., white noise, flicker noise and brown noise). It is argued that there is no clear distinction between coherent noise and geological structure.