Regional geological disaster risk assessment takes regional geological disasters as the research object, and the spatial distribution law of regional geological disasters and vulnerability evaluation of disaster-bearing bodies as the main research contents. It is a necessary link to establish a regional geological disaster spatial early warning system project, which is mainly used to formulate reasonable disaster prevention and mitigation decisions and regional land planning policies to serve disaster prevention and management.

Since the late 1960s or early 1970s, the study on risk zoning of geological disasters with landslides as the main body has been started. For example, the landslide sensitivity prediction zoning in California, a landslide-prone city in the western United States in the late 1960 s, and the legislative research on slope land utilization at county administrative level; In 1970s, France put forward the danger zoning system of slope geological disasters (ZERMOS). In 1980s, many countries and regions in the world began to study regional geological hazard zoning and prediction, such as Italy, Switzerland, the United States, France, Australia, Spain, New Zealand and India. Since 1990s, in order to promote extensive international coordination and cooperation, the United Nations has adopted resolution 1987, and decided to launch the International Decade for Natural Disaster Reduction in the last decade of the 20th century. 199 1 year, the science and technology committee of the United Nations International Decade for Natural Disaster Reduction (IDNDR) put forward the program and objectives of disaster prevention, mitigation, mitigation and environmental protection of the International Decade for Natural Disaster Reduction (PREEMPT). The first of the three planned tasks is to carry out disaster assessment and put forward: "All countries assess natural disasters, that is, assess their risks and vulnerabilities. It mainly includes: ① which natural disasters are generally fragile; ② Assess the geographical distribution, occurrence interval and influence degree of various disaster threats; 3 estimate and evaluate the vulnerability of the most important population and resource concentration points. " Incorporate natural disaster assessment into important measures to achieve disaster reduction goals. Around the International Decade for Disaster Reduction, many countries in North America and Europe have carried out geological disaster risk assessment research and land use legislation on the basis of existing geological disaster risk zoning research, expanding the original simple geological disaster risk research to comprehensive disaster reduction system research.

From 1970, the United States conducted a risk assessment of California earthquake, landslides and other natural disasters 10, which was completed in 1973. The results show that the possible losses caused by California 1970 ~ 2000 natural disasters are 55 billion dollars. At the same time, the US Geological Survey and the Policy Development and Research Office of the Ministry of Housing and Urban Development jointly supported the prediction and evaluation of nine natural disasters, including floods, earthquakes, typhoons, storm surges, tsunamis, tornadoes, landslides, strong winds and expansive soil, and established a set of disaster prediction models for counties in the United States to estimate the expected losses of nine disasters by the year 2000. The United States has set up a special committee composed of 10 members, and formulated a ten-year plan for disaster reduction, which takes natural disaster assessment as an important part of research and requires individual or comprehensive disaster risk assessment. In recent years, Japan, Britain and other countries have also carried out disaster risk analysis or disaster assessment on earthquakes, floods, tsunamis, mudslides, landslides and other disasters, and taken the relevant results as an important basis for determining the responsibility for disaster reduction and implementing relief.

Switzerland is one of the most successful countries in the world to study the risk zoning of geological disasters. In order to ensure the safety of agricultural land and construction land and prevent losses caused by natural disasters, the Swiss federal government put forward "to realize the rational use of land on the premise of ensuring the integrity and coordinated development of the country" from the legislative height of 1979, and promulgated the Federal Territorial Management Law. Article 22 of the law stipulates: "Each state shall investigate and determine that it is affected by nature. On the basis of federal government laws, state governments have formulated corresponding state government laws. For example, Article 89 of the Land Management Law promulgated by Wozhou (1987) stipulates: "Land threatened by natural disasters such as avalanches, landslides, collapses, floods, etc. is prohibited from carrying out any construction activities in disaster risk areas before being evaluated, fully demonstrated or eliminated by experts. "Then, the plan was made, and the risk zoning map of slope geological disasters with the scale of1:25000 and the risk zoning map with the scale of1:10000 were compiled and studied. Switzerland has formed a disaster risk assessment and prevention system under the guidance of the national constitution, which is formulated by the state and must be implemented by the county government. On the one hand, buildings in high-risk areas are illegal. On the other hand, as high-risk property, insurance companies absolutely refuse to accept property insurance business in high-risk areas, thus ensuring the most effective control of natural disasters in Switzerland. Disaster risk zoning in Switzerland not only directly serves architectural planning and government decision-making, but also indirectly serves the social security system. Although Switzerland is one of the countries with the most serious geological disasters such as landslides and collapses in the world, from the last glaciation to the last one or two hundred years, Switzerland has experienced major landslides (such as Flims, Elm and Handa), but thanks to the national disaster risk zoning system, its disaster losses in the last two or three decades are one of the few countries in the world.

France is one of the countries with serious disasters such as floods, landslides, collapses and avalanches. As early as the 1970s, we began to study the risk zoning of natural disasters nationwide, and the zoning map directly served the disaster reduction and prevention work, minimizing the loss of natural disasters. France's Code del'Urbanisme, promulgated in 1977, stipulates that buildings in disaster-prone areas such as floods, soil erosion, landslides and avalanches must be strictly restricted. 198 1, the planning law has made specific restrictions on the land use in areas prone to natural disasters. For example, landslide danger zones are divided into two categories, one is a serious danger zone where construction activities must be prohibited, and the other is a more dangerous zone where construction activities must be fully demonstrated. 1982, France promulgated the Law on the Prevention and Control of Natural Disasters, and formulated four prevention and control plans for natural disasters: floods, avalanches, landslides and earthquakes. In order to further predict and minimize the losses caused by disasters, according to the prevention and control plan, the risk zoning map of disaster-prone areas is compiled, including red areas (high-risk areas), white areas (dangerous areas dominated by one disaster) and blue areas (although there are disasters, they can be prevented). In the red area, all new construction activities are absolutely forbidden, while in the blue area, it is necessary to provide sufficient demonstration and reliability evaluation report of the consequences of building disasters. If the relevant preventive measures are not taken within five years, the property insurance company may not compensate for the casualties and property losses caused by natural disasters. By 1989, according to the results of disaster risk zoning in France, there were 15600 towns and villages in France threatened by four natural disasters, namely floods, avalanches, landslides and earthquakes, accounting for about one third of the total number of towns and villages in China. Due to the adoption of disaster zoning and corresponding preventive measures, the disaster losses in France have been effectively controlled.

Second, an overview of domestic geological disaster risk research

In the past 20 years, the state has attached great importance to disaster reduction. For example, China Agenda 2 1 century pointed out that "the risk analysis of natural disasters in China should be carried out, including risk identification, risk estimation and risk assessment". This shows that China has taken disaster risk assessment as an important part of disaster prevention and mitigation construction and brought it into the national sustainable development system. 2 1 Century Agenda takes disaster prevention and mitigation as one of the important tasks of sustainable development capacity building in most places, and puts forward disaster risk assessment action plans. In China, the systematic and in-depth disaster risk assessment is earthquake disaster. Its representative work achievement is the three generations of China's seismic intensity zoning map and its use regulations completed by the State Seismological Bureau. Based on the national regional seismic risk assessment, the figure determines the intensity value of the future probability exceeding 10% under the general site conditions in different regions, that is, the basic earthquake intensity. Comprehensive natural disaster risk research has also achieved some research results. For example, Huang Chongfu and others established the mathematical model of urban earthquake disaster risk assessment by fuzzy set method. Some experts in water conservancy, agriculture, forestry, meteorology and other departments have carried out some regional risk analysis or disaster prediction and evaluation studies on floods, forest fires, typhoon disasters, etc., compiled risk maps, and put forward disaster evaluation or risk evaluation methods and technologies. Although these works are not deep and systematic, they have played a positive guiding role in reducing disasters and improving disaster risk management level in the industry.

Since 1999, the Ministry of Land and Resources issued the Administrative Measures for the Prevention and Control of Geological Disasters, which indicates that the prevention and control of geological disasters in China has gradually moved towards the legal track. In order to further implement the Administrative Measures for the Prevention and Control of Geological Disasters and do a good job in the prevention and control of geological disasters from the source, the Ministry of Land and Resources issued the Notice on Implementing the Risk Assessment of Geological Disasters in Construction Land. Through several years of management practice, and to meet the needs of disaster reduction and prevention in the whole society, on March 6, 2004, the State Council officially issued the Regulations on the Prevention and Control of Geological Disasters, which provided legal protection for the prevention and control of geological disasters in China. The "Regulations" stipulate that in engineering construction in areas prone to geological disasters, the risk assessment of geological disasters should be carried out at the feasibility study stage, and the assessment results should be taken as an integral part of the feasibility study report; It is clearly required that "when compiling the overall urban planning, village and market town planning in geological disaster-prone areas, the risk assessment of geological disasters should be carried out in the planning area". The main types of geological disasters are determined, including collapse, landslide, debris flow, ground collapse, ground fissure and ground subsidence. With the development of geological disaster risk assessment and disaster prevention management in China towards scientific and legal direction, the rational and safe utilization of land resources in China has been further optimized, which has played an important role in controlling and reducing man-made geological disasters.

The research of geological hazard risk assessment (price) in China began in 1990s, and it has made rich achievements in this field and played an important role in disaster reduction management. For example, Su Jingyu (1993) put forward the signs and methods to judge the risk distribution of debris flow. Liu Xilin et al. (1988) studied the regional debris flow risk assessment, gave eight indicators of regional debris flow risk assessment and the formula for calculating the vulnerability of people and property, put forward a statistical model for judging the degree of debris flow risk and evaluating the debris flow accumulation range, and evaluated the debris flow disaster risk in Yunnan and Sichuan provinces. According to the theory of environmental economics, Sean (1994) preliminarily demonstrated the attribute characteristics of geological disasters and the economic analysis method of risk assessment. Zhang Yecheng (1995) Risk Analysis of Debris Flow Disaster in Dongchuan City, Yunnan Province. , Zhang Yecheng, Luo, Yin Kunlong and Yan systematically studied the spatial prediction and zoning of landslide disaster and slope instability, and successively put forward the information analysis model, multiple regression analysis model and discriminant analysis model for quantitative evaluation, and carried out the risk analysis and zoning of landslide disaster in Qinba Mountain area and Three Gorges reservoir area. Zhu Liangfeng (2002) and others developed a regional geological disaster risk analysis system based on GIS, and carried out the risk analysis, vulnerability analysis and final risk analysis of landslide and debris flow disasters nationwide. After years of research, Yin Kunlong and others developed MapGIS landslide hazard risk analysis system (IASLH). In this system, the information model of landslide disaster analysis is put forward. According to the relationship between landslide distribution information and landslide influencing factors, the model calculates the landslide information, carries out landslide risk zoning accordingly, and evaluates the landslide disasters in Xunyang area of Hanjiang River basin in China and China by using IASLH system.

At present, the study of geological disaster risk is in the ascendant, and it will develop more rapidly in the future, with more extensive research contents and richer and more advanced theoretical methods. It can be predicted that in the near future, it will become a new field with perfect theory and technical methods. Its basic trend is to develop towards quantitative evaluation, comprehensive evaluation and spatial management. Mainly as follows:

(1) From the historical and current analysis, the trend is the combination of prediction and research;

(2) From individual analysis to the combination of individual and regional research;

(3) From qualitative analysis to quantitative evaluation;

(4) From single factor analysis to comprehensive factor evaluation;

(5) From the pure theoretical study of risk assessment to the combination of risk assessment and disaster reduction management, and the combination of risk assessment and prevention, the purpose of risk assessment is to serve social and economic construction and disaster reduction management;

(Multi-factor information modeling, evaluation and spatial management supported by GIS spatial technology are developing unprecedentedly, which will gradually replace the traditional survey statistics and manual mapping and develop into network technology;

(7) Research theories and methods tend to be rich in content, forming the integration and intersection of multiple disciplines, especially closely combined with sociology.

Although after more than 20 years of development, the research and evaluation of geological disaster risk at home and abroad have made rich achievements in theory and practice, but there is no systematic and perfect theory and method system, and there is no unified evaluation standard. The domestic research in this field is still very weak, and the professional disaster assessment of geological disasters is still in the process of increasingly in-depth discussion and summary. The main problems include:

(1) At present, only direct economic losses are considered in landslide and debris flow disasters, and there is little research on the evaluation method of indirect economic losses.

(2) The objective and composition of the existing risk assessment framework and index system of landslide and debris flow disasters are not clear enough, and the index system is not complete enough. Different scholars have different expressions on the logical relationship between analytical levels, lacking a general evaluation framework system;

(3) The research on the acceptable risk level of landslide and debris flow disaster is very weak, and there is no convincing standard system;

(4) The theory and method of landslide and debris flow disaster risk assessment are not perfect;

(5) Vulnerability analysis in landslide and debris flow hazard risk assessment is still a rather weak link. In vulnerability analysis, only casualties in historical disasters such as landslides and mudslides are generally considered, while economic and property losses and resource and environmental losses in historical disasters are rarely considered.