汶川及芦山地震余震分布的空间尺度效应

基于GIS点格局方法，从余震点分布的不确定性以及烈度区与点空间距离格局的关系角度研究了汶川及芦山余震点格局．结果表明：余震在较小尺度内接近随机分布且关联效应明显； 在较大尺度内余震聚集分布，空间距离关联仍呈幂律关系，无标度区间的上下限与不同烈度区的长短轴间存在关联．汶川、 芦山余震形成东北—西南向矩形的热点、 次热点分布区，区域内最邻近指数为0.99，0.76； 映秀Ⅺ度、 芦山Ⅸ度烈度区内最邻近指数分别为1.02和0.95，显示余震点在强烈度、 高聚集区内趋向随机分布．余震点距离关联特征表明：汶川余震在13.5—20 km和30—43 km区间，芦山余震在7—14.5 km区间内关联程度显著； 汶川余震在66—82 km、 225—236 km、 317—321.5 km区间以及芦山余震在15.5—22 km、 23—32.5 km、 33.5—43.5 km区间仍呈幂律关系. 该结果与汶川地震Ⅺ—Ⅸ度、 芦山地震Ⅸ—Ⅶ度烈度分布区域的长短轴存在一定关联，321.5 km和40 km与两次地震主破裂面长度也较为吻合. 对比核密度估计与地震烈度图可以看出: 带宽越小，核密度面积与较高烈度区域的一致性越大； 随着带宽的扩大，核密度面积与烈度区的差异也越大．

Spatial location behavior of aftershocks of Wenchuan Ms8.0 and Lushan Ms7.0 earthquakes

With the method of GIS, this paper analyzes the point pattern of aftershocks of Wenchuan and Lushan earthquakes, from the perspective about the uncertainty of aftershock distribution and the relationship between seismic intensity region and spatial distance pattern. The result shows that in a smaller scale, the aftershocks are approximately in the random distribution and correlation effect is obvious; while the aftershocks present aggregated distribution in larger scale, but the spatial correlation characteristics are still in power-law relationship, and the upper and lower limits of scale-free area are associated with the major and minor axes of the different intensity seismic region. Wenchuan and Lushan aftershocks form a hot and sub hot spot regions, which is like a NE－SW rectangular, the nearest neighbor index for this two regions are 0.99 and 0.76. The nearest neighbor index of Yingxiu Ⅺ degree and Lushan Ⅸ degree was 1.02, 0.95, indicating that the aftershocks tend to distribute randomly in the region with strong intensity and high aggregation. The distance-associated features of the aftershocks indicate that, the aftershocks of Wenchuan earthquake in the intervals of 13.5—20 km, 30—43 km and the aftershocks of Lushan earthquake in the interval of 7—14.5 km are correlated significantly; the aftershocks of Wenchuan earthquake in the intervals of 66—82 km, 225—236 km and 317—321.5 km and the aftershocks of Lushan earthquake in the intervals of 15.5—22 km, 23—32.5 km and 33.5—43.5 km are also have power-law relation, which is coincident with the major and minor axes of Wenchuan earthquake Ⅺ－Ⅸ degree and Lushan earthquake Ⅸ－Ⅶ degree regions, also the 321.5 km and 40 km are consistent with the fracture plane of the two earthquakes. Comparison with the kernel density estimation and the seismic intensity map shows that the consistency between kernel density area and high intensity regions increases with the search radius decreasing; with the expansion of the search radius, the discrepancy between kernel density area and seismic intensity region is more greater.