关键词: 3维地震, 城市活断层, 芦花台断层, 观测系统, 资料解释

Abstract:

To test the effect of three-dimensional seismic reflection methods used in active fault survey, we have done a three-dimensional shallow seismic reflection exploration experiment around the Luhuatai Fault in the west of Yinchuan Basin. The experiment uses swath geometry of 8 lines and 10 shots. Every two adjacent swaths overlap 3 survey lines, thus 5 swaths and 28 survey lines are laid in total. The ground sampling grid is 5m×20m and the CMP grid is 2.5m×5m. The data volume that reflects the three-dimensional spatial structure of the Luhuatai Fault is obtained.In data processing, we select the suitable three-dimensional seismic data process modules. The main processes are composed of raw data input, three-dimensional geometry defining and checking, anomalous trace edit and first arrival mute, spherical divergence compensation, surgical filtering to eliminate surface waves, surface-consistent amplitude compensation, surface-consistent deconvolution, velocity analysis and residual static correction(twice iteration), DMO and the third time velocity analysis, final stacking, three-dimensional post-stack de-noising and horizontally interpolating, one-pass 3-D migration.
3-D seismic data interpretation uses the way of human-computer interaction. Through a variety of methods such as multi-line profiles contrasting, time slicing, three-dimensional visualization, and 3-D coherence cube technology, the reflection horizons are discerned and tracked, and the three-dimensional data volume reflecting the spatial variation of strata and faults is obtained. The results after fine processing and synthetical interpretation show that the Luhuatai Fault consists of two normal faults that incline to each other. The major fault inclines to SE, and the minor fault inclines to NW. The distance between them gradually increases from north to south. In addition, the minor fault merges into the major fault at the depth of approximately 780~800m. The up-breakpoint of the major fault has a tendency of deepening from north to south. The up-breakpoint depth is about 25~30m in the northern part of experimental area, and about 35~40m in the southern part of experimental area.
The experimental results show that the three-dimensional seismic data has the advantages of large volume of data, information-rich, high accuracy of migration, and high precision of tomography. It can reflect the three-dimensional spatial distribution of strata and faults in different aspects, and it is beneficial for the imaging of complex structures and faults.

Key words: three-dimensional seismic, urban active fault, Luhuatai Fault, observation system, data interpretation