For a large-size faulted basin with many active faults developed, the strong ground motion in basin will be influenced by the following several factors, the fault dips, the activity modes, the expand shape of faults inside basin or along basin edges. In order to research the relations between the fault dip angles and strong ground motion characters in faulted basin, Yinchuan basin and Yinchuan buried fault are suitable for us to carry out our plans. In Yinchuan faulted basin, there are two major faults inside and two enormous faults stretching along west and east sides. Yinchuan buried fault, a Late Pleistocene epoch-Holocene active fault, is a major one of those activity faults which perhaps affect the urban planning and development and earthquake resistance of Yinchuan City seriously. In our research, according to the earthquake risk evaluation results of southern segment of Yinchuan Fault, we defined the characteristic earthquake magnitude M(w)6.5 and assume different dip angles (30 degrees, 45 degrees, 60 degrees, 66 degrees, 75 degrees, and 85 degrees) for simulations of strong ground motion. By an improved Finite-Element Method, we computed all above cases of ground motion and draw following conclusions. For a gently dipping fault, the intensive distribution of ground motion appeared in the area between the southern segment of Yinchuan buried fault and the Luhuatai fault which means that the Luhuatai fault blocks the spreading of seismic wave. With the increasing of the fault dip angle, the strong ground motion mainly distribute on the hanging-wall close to the fault which shows that the fault angle of inclination is the major factor controlling the ground motion distribution. Furthermore, along the direction of the trend of Yinchuan buried fault, several areas of weaker ground motion formed gradually. When the fault dip became larger and larger until 85 degrees, influenced by edge faults of Yinchuan basin with the occurrence of "steep in west edge and gentle in east edge", special reflection region of strong ground motion in UD component become stronger and stronger in the southwest area far away from the Yinchuan buried fault which makes the regions near Yinchuan fault and Luhuatai fault become two major possible risk zones if potential earthquake occurred. All above results remind us that it is quite necessary to consider the combined action of active fault dip angle and reflected waves from edge faults in faulted basin when we undertake the seismic safety evaluation and resistance for buildings and constructions in the near-field region.
