Deformation Monitoring And Simulation Research Of Mt. Changbai Tianchi Volcano

This thesis is a study on the deformation monitoring of the Tianchi volcano in the Changbai Mountains by using the techniques of differential interferometry synthetic aperture radar (D-InSAR) and computer numerical simulation. Using D-InSAR technology the deformation field of 1995—1998 of Jianbaishan volcano which lies in the southeast of Mt. Changbai is obtained. Ten corner reflectors have beed installed around Mt. Changbai in order to carry out test research of CR-InSAR technique. Using the data of GPS and leveling surveying of 2002-2003, the Mogi's Point Source model and Okada's tensile point source model inversion is made to obtain the optimum parameters of magma chamber in the Mt. Changbai volcano; andthe inversion results are applied to forward simulation of the deformation field from D-InSAR. This work is on the basis of previous the studies, and the main results and innovation are as follows:①Investigating the means of deformation monitoring around volcano areas and the current situation of research.Deformation observation is the main means to monitor the activity of magmatic and forecast volcano eruptions. Although some tectonic activity and deformation cannot be at the peak before eruption, the majority of the volcanic eruptions did have obvious surface deformation. Accurate measurements of surface deformation can be used for the research of volcanic activity and volcanic eruption prediction. The surface deformation data can be used for numerical simulation in order to get parameters of volcanic magma chambers (size, pressure depth, etc) and important information of the underground structure of related hydrothermal systems.In this thesis, the status quo and deficiency of the means of deformation monitoring at the volcanic areas are presented and discussed, the advantage of the technology of InSAR is introduced. At the end of this part, the significance and background of this research are given. ②Investigating geological conditions and present situation of research in the Mt. Changbai volcano area.During the Ninth Five-year and Tenth Five-year Project period, comprehensive researches have been made on the activity of the Mt. Changbai volcano, including volcanic geology, geophysics, deformation, mineralogy, lithology, geochemistry, dating, environment effect and volcanic hazard prediction and monitoring-control, and so on. The results show that Mt. Changbai volcano is an active volcano with most potential eruption hazard in China, and it is being in the stage from an initial disturbance state to a roilyt stage.Analyzing these research results provides some information for following research work.③Using D-InSAR technology, the deformation in the near field of the Mt. Changbai is obtained.Because of the complex terrain and adverse climatic conditions, conventional volcanic deformation monitoring methods (such as leveling, GPS etc) are very difficult to gain volcano deformation of a larger regional. Using the technology of InSAR with its unique advantages can directly obtain the quantitative data of volcanic deformation in the large scope, with continuous coverage of the space.This work collected two scences of ENVISAT SAR data (200401104, 20051015) and five scenes of JERS-1 SAR data (19930615, 19940829, 19950816, 19980707, 19980820). These SAR data are processed using two-pass and three-pass differential interferomertry mode. But using the ENVISAT SAR data can not obtain the deformation result because of the poor coherence of the data. I obtained the perfect deformation result using the pair JERS-1 SAR data (19950816/19980820). The results show that during the three years from 1995 to 1998, there were 6-12cm LOS deformation in the area of Mt. Jianbai volcano which is located in the southeast of Mt. Changbai volcano. Although there is no other information can test this result, the frequent earthquakes can demonstrate the activity of this area.④Experimental research of CR-InSAR technology in the area of Mt. Changbai volcano. Although InSAR makes up for the lack of many previous measuring methods (such as leveling, GPS etc), and can monitor large-scale surface deformation, having immense advantages., its limition of application can not be neglected, which results in some uncertainties of results, such as temporal unrelated, spatial unrelated and delay caused by atmospheric effect. All these influential factors can bring some errors to interferometry deformation measure. The appearance of CR-InSAR (Corner Reflector InSAR) and PS-InSAR (Permanent Scatteres, InSAR) enhances effectively temporal coherence and spatial coherence of these repeat-pass image series, realizing observations of small deformation in vegetative cover areas. Moreover, accuracy of CR-InSAR monitoring is better than accuracy of conventional InSAR.After the earlier preparation, including analysis of the geological background, interpreting remote sensing images, analysis of topography and morphology, ten corner reflectors were installed around the Mt. Changbai volcano in August 2006, in order to make experimental research in the area of Mt. Changbai volcano. On April 13, 2007 the first ENVISAT SAR data after installing the corner reflectors are acquired. Based on the SAR data analysis seven feature points were found except the three points at the altitude above 1600m, the reason may be the snow has not melted.⑤Simulation calculation was carried out by means of Mogi point source model and Okada tensile point source model.In order to study the activity of the magma chamber at different periods, this work uses the JERS-1 data of 1995-1998 and the data of GPS and leveling of 2002-2003 to simulate the parameters of the magma at the Mt. Changbai volcano.In this thesis, I try to use different models and different combination models to simulating calculation, such as Mogi single point source, Mogi two-points source, Okada triaxial tensile model, the combined model of Mogi two-points source and Okada tensile model. Through comparative analysis of the errors it is found that the Mogi two-points source model is the optimum fitting methods. A point source is located at 7.9km below of the Mt. Changbai Tianchi volcano, another is located at 5.5km below of the Mt. Jianbai volcano. It is found that the inversion result of the Mogi double point source and the result of the D-InSAR are in good agreement, and the forward simulation result of the deformation field obtained by D-InSAR technology is also satisfactory. The inversion calculation result of Okada triaxial tensile model shows that the source is located at the north of the Tianchi crater and there is an obviously tensile component in the direction of NNW and NWW. This result accords well with the result of deep geophysical probing. The triaxial tensile source is considered to give the detailed parameters of the magma chamber which is located below in Mt.Changbai volcano.From these results we can infer that there may be a channel between the two magma chambers because of the direction of this two magma chamber is consistent with the strike of the hidden fault which has seismic activity in this area. Magmatic activity and migration may be the reason of activity of fault activity and seismic activity. The volcanic activity in the area of the Mt. Changbai has intermittence in time and migration in space.The activity of the volcano is likely in the stage from an initial disturbances state to a roilyt stage. In order to forecasts the eruptive risk of the volcano, the monitoring of earthquakes, deformation, hydration, especially continuous measurement at fixed station should be enhanced.