Starting from the 1980's of last century, China has launched the national plan of constructing nuclear power plants along the coastline region in eastern China. Currently, in some of these candidate sites, nuclear facilities have been installed and are in operation, but some other nuclear power plants are still under construction or in site evaluation. In 2012 the Atomic Energy Commission issued the specific guide for volcanic hazards in site evaluation for nuclear installations(IAEA Safety Standards Series No. SSG-21), which was prepared under the IAEA's program for safety standards. It supplements and provides recommendations for meeting the requirements for nuclear installations established in the safety requirements publication on site evaluation for nuclear installations in relation to volcanic hazards. To satisfy the safety standards for volcanic hazard, we follow the IAEA SSG-21 guidelines and develop a simple and practical diffusion program in order to evaluate the potential volcanic hazard caused by tephra fallout from the explosive eruptions.
In this practice, we carried out a case study of the active volcanoes in north Hainan Province so as to conduct the probabilistic analysis of the potential volcanic hazard in the surrounding region. The Quaternary volcanism in north Hainan Island, so-called Qiongbei volcanic field is characterized by multi periodic activity, in which the most recent eruption is dated at about 4 000a BP. According to IAEA SSG-21, a capable volcano is one for which both 1)a future eruption or related volcanic event is credible; and 2)such an event has the potential to produce phenomena that may affect a site. Therefore, the Qiongbei volcanic field is capable of producing hazardous phenomena that may reach the potential nuclear power plants around. The input parameters for the simulation of tephra fallout from the future eruption of the Qiongbei volcanic field, such as the size, density and shape of the tephra, the bulk volume and column height, the diffusion parameter P(z), wind direction and intensity, were obtained by field investigation and laboratory analysis. We carried out more than 10000 tephra fallout simulations using a statistical dataset of wind profiles which are obtained from China Meteorological Data Sharing Service System(CMDSSS). Tephra fallout hazard probability maps were constructed for tephra thickness threshold of 1cm. Our results show that the tephra produced by the future large-scale explosive eruption from the Qiongbei volcanic field can affect the area in a range about 250km away from the eruption center.
In summary, the current key technical parameters related to volcanic activity and potential hazards in IAEA/SSG-21 guidelines, such as 10Ma volcanic life cycle and 1×10^-7 volcanic disaster screening probability threshold, etc. are based on the volcanic activity characteristics in the volcanic island arc system. In consideration of the relatively low level of volcanic activity compared with volcanic island arc system due to the different tectonic background of volcanism in mainland China, the time scale of volcanic disaster assessment in IAEA SSG-21 guideline is relatively high for volcanoes in mainland China. We suggest that the study of "conceptual model" of volcanic activity should be strengthened in future work to prove that there is no credible potential for future eruptions, so that these volcanoes should be screened out at early stage instead of further evaluation by probabilistic model.

A destructive earthquake occurred around Changde,Hunan Province,south-central China in 1631.The previous research of this earthquake yielded 4 different epicenter locations and isoseismal intensity maps.The authors replotted the isoseismals of this event based on checking historical earthquake records,in which the intensity value of the innermost isoseismal is Ⅷ.We concluded that the depth of this earthquake is from 15km to 18km.The basic considerations of our conclusion are as follows:a.This earthquake occurred in an area of lacustrine and fluvial deposits,with the magnitude of M 6¹/2;b.The geometrical center of the innermost isoseismal is the epicenter;c.The depth of epicenter is about 15 to 18km,which is based on the statistical relation between magnitude,depth of the earthquake source and epicenter intensity as well as Xie's statistical result.Finally,the authors discussed the influences of different ground conditions on the textual research and identification of historical data.

Combined with the consideration of relative codes,this paper mainly presents a preliminary analysis on the engineering application of Yuwangshan Fault zone based on the results achieved in the project of active fault exploration and seismic hazard assessment in the city of Ningbo. The conclusions we get from it are as follows. We don't have to take safety distance into account as to the west section of Yuwangshan Fault in engineering and construction because it has not been active since mid-Pleistocene,whereas,as to the east section of this fault,there's no need to consider the safety distance about Ⅲ-type and Ⅳ-type buildings,nevertheless,the case is different for Ⅰ-type and Ⅱ-type buildings because the potential surface deformation to some extent will occur with the scenario earthquake of 6.0,even if no direct surface offset. Due to the existence of about 6km² area where near-fault peak ground accelerations lightly exceeds the present-day standard,the authors put forward a package of aseismatic solutions which consist of the identification of aseismatic capability to buildings in the area and consideration of this factor in new buildings' construction.There's a potential area of seismic settlement of 30km² which may sink 5 cm or above according to the characteristics of distribution of soft soil as well as the assessment of near-fault strong ground motion in the east of the west section of Yuwangshan Fault. We should not ignore this important result.Given the importance of the results to the policy-decision for the mitigation of seismic disasters,we should seek for the trade-off between the safety and economic rationality in engineering application analysis.