基于地震活动性资料估计海原断裂倾角

本文以海原断裂带区域活动构造为基础，将海原断裂划分为西、中、东3段.基于1999年12月26日至2010年7月26日间的精定位小震目录，估计了海原断裂带各段的倾角.考虑海原断裂沿走向可能存在南倾与北倾两种情况，将倾角的范围设置为.首先运用网格搜索法确定了平面断层模型，其次以特征深度节点为基础数据运用多项式构建了曲面断层模型.结果表明：当进行平面拟合时，海原断裂西段与中段、东段的倾向不同，西段为南倾，其倾角值为71°，而中段、东段为北倾，其倾角值分别为72°、65°，各段的倾角值均由地表以下8 km地震资料确定.当进行曲面拟合时，在8 km深度以内海原断裂西段、中段、东段的倾角均处于80°左右，即接近陡立.西段的倾角在深度为9 km处出现转换，之后倾角接近陡立；中段的倾角在深度为16 km处出现转换，之后倾角逐渐减小，当深度为18 km时倾角为30°；东段的倾角在深度为11 km处出现转换，倾角为42°，在深度为16 km处出现第二次转换，倾角为55°，之后倾角逐渐减小.结合震源机制解和大地测量观测资料反演拟合的合理性，验证了本文所估计倾角的可靠性.

Estimation of dip angle of Haiyuan faults based on seismic data

The Haiyuan faults is divided into three sections, based on the regional activity structure, which are the western section, the middle section and the eastern section. The dip angles of the Haiyuan faults are estimated by fitting the fault surface with the accurate location of small earthquakes from December 26, 1999 to July 26, 2010. The dip tendency of the fault along the strike may be divided into south and north dipping. Thus, we set the dip angle in the range of. The plane fault model is determined by grid search method and the curved surface fault model is constructed by polynomials with the characteristic depth node. The results show that the dip angle of the western fault is different from that of the middle and eastern segments. The west section is south dipping with the dip value of 71°. On the contrary, the middle section and the east section are north dipping with the dip values of 72° and 65°, respectively. The dip value of each section is determined by the seismic data 8 km below the surface. The dip angle of the western, middle and eastern sections of the Haiyuan faults is about 80°, which is close to an upright fault. The western section has a conversion at the depth of 9 km, and then the dip angle is close to vertical. The middle section has a conversion at the depth of 16 km. Afterwards, the dip angle is decreasing. The dip angle is 30° as the depth is 18 km. There are two conversions in the eastern section:the first being at depth of 11 km with the dip angle 42° and the second at the depth of 16 km with the dip angle 55°. Then, the dip angle decreases gradually. The reliability of the dip angle is verified by the focal mechanism solution and the inversion results of geodetic observation data.