大华北地区地震灾害与风险评估

Seismic Hazard and Risk Assessments in North China Based on the Historical Intensity Observations

摘要:

地震灾害与风险是两个本质不同的概念：地震灾害是指由地震所引起的自然现象，而地震风险是指由地震灾害所导致人类及其环境破坏的可能性。在考虑抗震设防时，地震风险是更为重要的因素。本文首先对地震灾害与风险这两个概念进行探讨，然后利用500年的历史地震烈度资料对大华北地区的地震灾害和风险进行评估。研究结果表明，大华北地区具有较高的地震灾害和地震风险，尤其是鄂尔多斯周缘和京津唐地区；研究区内很多城市现行的抗震设防要求可能偏低。

Abstract:

Seismic hazard and risk are two important concepts in engineering design and other policy considerations.Although seismic hazard and risk have often been used interchangeably，they are fundamentally different.Furthermore，seismic risk is more important in engineering design and other policy considerations.Seismic hazard describes the natural phenomenon or property of an earthquake，whereas seismic risk describes the probability of loss or damage that could be caused by a seismic hazard.Seismic hazard assessment is an effort by earth scientists to quantify seismic hazard and its associated uncertainty in time and space from instrumental，historical，and geological observations.Seismic risk quantification is complicated and somewhat subjective because it depends on the desired measurement of consequence（i.e.，outcome of physical interaction between the seismic hazard and exposure）and how the hazard and exposure interact in time and space.Seismic risk assessment can be expressed in many different ways for different users. A model for estimating seismic risk must make assumptions to describe how the hazard and exposure interact in time.In this paper，we first discuss the basic concepts of seismic hazard and risk，and then estimated them from 500-year intensity observations for North China.The key element of this method is to establish the frequency intensity curve that describes the relationship between intensity and annual frequency （or return period）at a site.The main content and steps are described as follows.First，historical intensity observations were collected，the earthquake catalog was checked for completeness，and aftershocks were deleted.Second，the intensity database was geo-referenced in geographic information system （GIS）.Third，based on the characteristic of seismicity，the coverage，geological characteristic and population density，the region was divided into cells in which the intensity observations were digitized in GIS.Fourth，analyses were performed on the digitized intensity records to estimate seismic hazard such as the frequency （or return period）-intensity relationship for each cell.Under the assumption that the occurrences of earthquakes follow Poisson distribution，we also estimate seismic risk in terms of the exceedance probability of intensity I ≥ Ⅶ，Ⅷ，Ⅸ in 50 years，and the corresponding intensity with 10 percent probability of exceedance in 50 years.The results show that North China has high seismic hazard and seismic risk.The results also show that the current design peak ground acceleration （PGA） for many cities in North China，particularly Beijing，Tianjin，and Tangshan，might not be adequate.