Crustal Deformation And Seismic Hazard of Longmenshan Fault Zone With Limited Observations

The Longmenshan Fault Zone forms the eastern boundary of the Bayan Har Block in China and results from the block’s eastward movement being strongly resisted by the South China Block. In 2008, the Wenchuan earthquake ruptured the central-northern segment of the fault zone. Five years later, the Lushan earthquake struck the southern segment. The epicenters of these two events were approximately 90 km apart, with an unruptured section, known as the Dayi Gap, located between the two fault zones.

Previous research has explored the pre-earthquake deformation characteristics of the Longmenshan Fault Zone. However, due to sparse observational data prior to the Wenchuan earthquake, the resolution of fault locking state models was limited. This study addresses the issue of data sparsity by using the Least Squares Collocation (LSC) method to enhance the existing dataset, enabling a more detailed inversion of the fault’s pre-earthquake locking state. The results provide partial explanations for the co-seismic rupture patterns of the Wenchuan earthquake and show good agreement with the distribution of pre-Wenchuan earthquakes of magnitude 3 and above in the region. 

Based on the findings, future earthquakes are more likely to occur south of the Dayi Gap, with the fault potentially rupturing into the gap itself. Additionally, the results demonstrate that the LSC method can effectively densify sparse surface deformation data. While the resolution may not match that of inversions based on dense, high-quality observations, the method successfully identifies the main locked zones of the fault.