| Earthquake is a process of strain accumulating and instant releasing in seismogenic fault, according to time, the fault movement can be divided into different stages, such as interseismic, coseismic and postseismic stage; the deformation characteristics at different activity stages reflect different stress state and mechanical properties of the fault. Earthquake preparation and occurrence are closely associated with the fault movement; study of fault movement is of great theoretical significance and practical value in understanding earthquake preparation and analyzing the risk of large earthquake. With the rapid development of space geodetic techniques and their wide application in crustal deformation, especially GPS and InSAR, it is possible to obtain the rich high-quality surface deformation observation data. Analysis of the fault movement characteristics based on deformation data has gradually become one of the main means in research of earthquake preparative activity and seismic risk. Research of earthquake examples show that, analysis of the fault movement characteristics based on deformation observation data has very important practical significance in determining fault seismogenic ability and assessing recurrence period of historical large earthquake.Located in the suture zone between Eurasian Plate and Philippine Sea Plate, the Longitudinal Valley in eastern Taiwan, China is an area of active plate tectonics and crustal deformation, which accounts for about 30 mm/yr of the 80 mm/yr of the continuous convergence of these two plates. However, since 1951 Hualien-Taitung ML 7.3 earthquake sequence, the Longitudinal Valley has not experienced earthquakes with magnitude greater than 7. Its fault movement characteristic and the risk degree of large earthquakes have been concerned by scholars. Taking the Longitudinal Valley as the research area, based on the deformation observation data obtained by GPS and InSAR technology, this paper inverted and analyzed the movement characteristics of the Longitudinal Valley fault, then based on the inversion results, this paper discussed fault seismogenic ability in the future and assessed recurrence period of historical large earthquake.The main contents and understanding in the paper are as follows:1. Interseismic movement inversion of the Longitudinal Valley fault in 1992-1999: Based on constraints from interseismic GPS velocity field data between 1992 and 1999, this paper inverted the locking fraction and slip deficit rate of the Longitudinal Valley Fault.From the fitness analysis, considering the internal strain model fitted the overall movement tendency of the longitudinal valley region is better. The slip deficit distribution of Longitudinal Valley fault by the optimal model inversion shows that, the slip deficit rate of Longitudinal Valley fault decreases gradually from north to south.2. Coseismic slip inversion of the 2003 Chengkung MW 6.8 earthquake: Based on constraints from the GPS observed surface displacements data, this paper inverted the coseismic slip distribution of the 2003 Chengkung MW 6.8 earthquake.The results show that the fault model has a significant influence on the coseismic slip inversion results, and according to the relevant information to establish the actual fault model is very important before inversion. There is a certain difference in maximum coseismic slip of the 2003 Chengkung MW 6.8 earthquake by different scholar, but the coseismic slip distribution has similar result, that is the coseismic slip extreme area occurred mainly in the vicinity of the source region, and the coseismic slip near surface is very small.3. Fault movement inversion of the southern Longitudinal Valley in 2007-2010: Based on constraints from the InSAR deformation data between 2007 and 2010, this paper inverted the slip rate of the southern Longitudinal Valley Fault in 4 years after the 2003 Chengkung MW 6.8 earthquake.From 2007 to 2010, the southern Longitudinal Valley fault movement is dominant thrust with less left-lateral component. The slip rate of the southern Longitudinal Valley Fault has a non-uniform spatial distribution, and it can be subdivided into two extremes.4. Analysis of large earthquake risk on fault based on interseismic movement and coseismic slip: based on the inversion results of interseismic fault movement and coseismic slip, as well as the rupture distribution characteristics of historical large earthquakes, using the empirical formula analyzed the large earthquake risk of Longitudinal Valley fault. In addition, according to the spatial distribution of fault movement at different activity stages, this paper analyzed the relationship between the large earthquakes and the fault movement in southern region of Longitudinal Valley.Since the 1951 Hualian-Taitung ML 7.3 earthquake sequence, according to the inversion of the slip deficit rate accumulated to 2016, the northern, the central and the southern of Longitudinal Valley Fault have become capable of releasing stored strain in a future MW 6.4, MW 7.0 and MW 7.4 earthquake, respectively. In case of cascading rupture, the entire Longitudinal Valley Fault has become capable of releasing accumulated strain in a future MW 7.5 earthquake. The microscopic epicenter of 2003 Chengkung MW 6.8 earthquake was near the transition zone between the interseismic creeping zone and the locked zone. Coseismic slip extreme area and postseismic slip concentration area are complementary to each other in the 2003 Chengkung MW 6.8 earthquake.The space-time evolution of fault movement characteristics may reflect the large earthquakes preparation, occurrence and adjustment. Analysis of the fault movement characteristics based on deformation data from different stages of large earthquake helps to understand earthquake preparation and occurrence, and establishes fault movement model in the process of large earthquakes, so as to provide a scientific basis for the analysis of seismic risk and the determination of fault seismogenic ability. |
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