Research On Interpretation And Hazard Assessment Of Geohazards In Strong Earthquake Area Using 3S Technology

At 2:28 p.m, on May 12, 2008, theYingxiu town of Wenchuan County in Sichuan Province occurred 8.0 magnitude earthquake, which affected half of China, with an area of 100,000 square kilometers. The earthquake triggers the collapse of a large number of landslides. According to incomplete statistics, the earthquake-triggered geological disasters accounted to over two thousand cases, with the total estimated amount of 50,000 cases or more. The four common geological disasters, that is, rockfall, landslides, debris flow and unstable slope, take up more than 97% of the total amount. Earthquake-induced landslide is one of the most important causes of secondary disasters, since whenever a strong earthquake occurs, slope will be deformed, leading to a large number of landslides, which are called "earthquake landslide". Strong earthquake will affect the long-term stability of slopes, especially in the rainy season with continuous geological disasters and strong debris, mainly due to heavy rain which also causes a large number of landslides, that is, "storm landslide". Therefore, storm is one of the factors inducing Geologic Hazards.Current research on"earthquake landslide"is mainly focused on its identification and characteristics, while fewer attentions are paid to dynamic analysis of characteristics of landslides induced by storm after the earthquake. Moreover, even much less researches are carried out to study the number, area, characteristics of landslides between "earthquake landslide" and" storm landslide". Given no research result is reached on the dynamic comparative analysis between "earthquake landslide" and" storm landslide" in strong earthquake zones, this paper uses multi-temporal, high-resolution aerial photos, P5, SPOT5 satellite image data to carry out point-shape remote sensing interpretation of geological hazards in Beichuan county and face-shape remote sensing interpretation of geological hazards in the typical area, with geology, geomorphology, 3S technology and other related theories and corresponding research trends home and abroad as theoretic background, and a large number of geological disasters caused by " 5.12 "Wenchuan earthquake, one strong earthquake in Beichuan County as field survey. This paper establishes remote sensing identification features of strong earthquake areas, carries out dynamic analysis of typical geological disasters in Beichuan County, and focuses on comparative analysis of number, kinds and features of "earthquake landslide" and" storm landslide". At the same time, on the basis of point-shape interpretation of all geological hazard points in Beichuan County, the present paper studies geological hazard assessment methods and systems in strong earthquake areas in Beichuan County, and establishes geological earthquake disaster risk assessment model to quickly and effectively launch assessment of geological hazards in strong earthquake areas.Main findings of the present thesis are listed as follows:(1) A more systematic method system of applying high precision remote sensing technology in studying geological hazards is initially established. Combined with the causes and image morphology characteristics ( shape, color, shadow, texture, etc.) of geological disasters, identification mark and interpretation method of geological disaster remote sending interpretation are amended and improved. Strengths and limitations of remote sensing technology used in geological disaster study are also elaborated.(2) Multi-temporal, high-resolution aerial photos, P5, SPOT5 satellite images are used to dynamically analyze the amount and area of monomer landslides, collapses, landslides and regional geological disaster before the 5.12earthquake, after the 5.12 earthquake, after 9.24torrential rain in typical areas in Beichuan County. The results are: earthquake-induced landslide is one of the major causes of secondary disasters. After strong earthquake breaking out, slopes are deformed, leading to large-area landslide; rain-induced landslide is another major causes of secondary disasters, and the storm-induced geological disasters are often regional, group-occurring, simultaneous, and large disaster-causing. On the basis of two images comparison, rain storm-inducing geological disaster area is in 9.24 rainstorm is only 1/4 times of earthquake directly induced geological disaster area in 5.12 earthquake. With the passage of time and the occurrence of rainfall, rainfall induced landslide area will continue to increase; storm not only induces new landslides, but promote the revival and expansion of earthquake landslide, which expands by 1/8 of its original area. By the same token, with the passage of time and the occurrence of rainfall, earthquake landslide area continues to expand.(3) The temporal and spatial probability concepts of geological disasters are introduced. The concept of geological hazard is perfected. Spatial distribution quantitative relationship and intrinsic relationship between the distribution and evaluation factors of earthquake-induced geological hazards are focused. Geological hazard evaluation system is established combined with storm-induced geological disaster factors. Results show that: generally, the high risk zone has a good correlation with geological hazard distribution density. Evaluation shows that despite of the area of high risk zones, which only take 52.6% of the total number of disaster areas, 1682 geological disaster points are distributed in high risk zones, accounting for 95.9% of the total number of disasters point; geological hazard assessment map of Beichuan County shows that high risk zones often distributed along fault lines or rivers, indicating that the earthquake-induced geological disasters have their own characteristics, subject to such landform controls as earthquake faults, valleys, terrain conditions, etc.(4) Quantitative indicators of the sensitivity of statistical models are established to achieve quantitative evaluation of factors. In this paper, based on mathematical statistics, a quantitative sensitivity index statistical model is established, which calculate the combination frequency between geological disaster point density of each index factors and geological disaster point average density in the whole evaluation area. Combination frequency determines the sensitivity and sensitivity value assignment.(5) Geological hazard assessment model in strong earthquake is established. The basis process is: data acquisition and pretreatment→interpretation of geological disaster remote sensing images→establishment of geological disaster sensitivity evaluation model→analysis of quantitative indicators of the sensitivity statistical models→establishment of geological disaster risk evaluation system (introducing induced factor)→geological hazard assessment→results of geological hazard assessment zoning→validation of geological hazard assessment.