Experimental Study On Urban Underground Geological Anomalies Detected Of Reflected Wave Method

At present, our country is facing the great strategic task of integration of urban and rural construction with quicker step of urbanization, rapidly increasing urban population and continuously expansion of city scale. During the new city construction and the old city reconstruction, the problems of urban ecological environment protection and geological disasters have been increasingly prominent. Earthquakes, landslides, land subsidence are common geological disasters types in the city. In order to eliminate the risk of geological disasters and ensure safer in the city construction and reconstruction, it need to provide solid urban geological data. Therefore, urban geological survey work should take the antecedence objectively. Based on previous studies and the method principle of shallow reflection seismic exploration, the paper made research on exploration test of common city geological anomaly-faults and landslides.By preliminary reconnaissance of the workspace and data collection, the paper firstly analyzed the influencing factors of urban underground geological anomalies exploration, made field test on the source conditions and observation system and also analyzed the key problems during the treatment process of shallow reflection method. Constructing three different types of fault models based on fault geophysical exploration, and then the paper made numerical simulation by staggered grid approximation seismic numerical simulation technology based on the finite difference calculation to study the propagation characteristics and wave field response characteristics of reflective wave in the fault geological anomalies for providing scientific guidance on the shallow seismic reflection exploration in the practical field detection; In addition, the paper constructed landslide model similar to the field with the dynamic elastic modulus parameters of rock and soil layers obtained by wave velocity testing in the field to do numerical simulation. By simulating it found the optimal acquisition parameters and observation systems to provide theoretical basis for subsequent field data collection.According to the land seismic exploration specification, the field detection of Putian city underground fault and the exploration of Tianshui landslide showed the result that selecting appropriate observation system and acquisition parameters, shallow reflection seismic exploration could accurately reflect the buried depth and the spatial distribution characteristic of Putian underground faults; and it could reflect the landslide depth and direction through the difference of wave groups, energy and frequency. Through the comparison analysis with the results of electrical method, it showed that the shallow seismic reflection prospecting has better resolution and exploration accuracy and the results achieved by shallow seismic reflection prospecting could provide some basic geological information for local urban construction and reconstruction.The paper only made research on faults and landslide due to many interference factors and complicated situations. It achieved some results, but there still existed some problems such as the use of artificial hammering source, it could not get the geological conditions of deeper portion because of its limited exploration depth; on the other hand, the resolution of exploration results is not high in particular field; and it could not provide wave field separation technology suitable for shallow seismic reflection exploration.