重力水平梯度及其在地震重力前兆中的研究初探

doi:10.3969/j.issn.0253-4967.2015.04.007

摘要/Abstract

摘要：

首先根据水平无限长圆柱形地质体的理论重力异常, 在频率域使用余弦变换法, 通过位场变换计算了水平方向的重力梯度, 并与理论重力梯度做比较, 发现余弦变换法计算得到的水平重力梯度是可靠的。其次, 使用频率域中的余弦变换法计算了2010年9月至2012年10月芦山地震前的累积重力水平梯度, 并求得沿龙门山断裂带走向和垂向的重力水平梯度。结果表明: 沿断裂带走向和垂向的重力梯度能够以明显的条带状更好地显现出重力在断裂两侧的相对变化, 并且芦山震中位于重力梯度高值区的中间地带; 重力水平总梯度变化显示, 在理县—芦山一带、康定—石棉一带为重力梯度高值区, 且高值区位置及走向与区域断裂构造基本重合, 并在理县、康定以及石棉附近重力水平梯度值为极值区。

关键词: 位场变换, 重力异常, 芦山M_S7.0地震, 重力梯度, 方向导数

Abstract:

In this paper, according to the synthetic gravity anomaly of a horizontally infinite cylindrical geologic body, gravity gradient in horizontal direction was calculated by potential field discrete cosine transformation in frequency domain. In the calculation, the minimum curvature method was used to extend edge lines. We found that the gravity gradient field from the potential field transformation was dependable by comparison with synthetic gravity gradient, except the data in the edges. Then, the accumulative horizontal gravity gradients before Lushan M_S7.0 earthquake were calculated for the accumulative gravity anomaly from September 2010 to October 2012. In the north-south direction, gravity gradient in Daofu-Kangding-Shimian and Markang-Lixian-Lushan exhibited a positive high value, and the strike of the high value zone was in line with the strike of Xianshuihe Faults and Markang Faults. In the east-west direction, high value zone was not as obvious as that in the north-south direction. Gravity gradients in the direction along and vertical to the strike of Longmenshan Faults were calculated by the definition of directional derivative. In the along-strike direction, high gravity gradient values appeared in Markang-Lixian areas along Markang Faults and Daofu-Kangding-Shimian areas along Xianshuihe Faults, and extremum appeared in Kangding-Shimian and the area nearby Lixian. In the direction vertical to the strike of Longmenshan fault zone, high gravity gradient values appeared in Lixian-Lushan-Kangding-Shimian areas, and the extremum appeared in the area nearby Kangding. The results indicate that gravity gradient in the direction along and vertical to the strike of faults can better show the relative gravity change on the two sides of faults. Lushan M_S7.0 earthquake is located at the transition zone between the two high value zones of gravity gradient. The total horizontal gravity gradient shows that the location and strike of the high value zone are basically consistent with regional faults, and the extremums of total horizontal gravity gradient appeared nearby Lixian, Kangding and Shimian.

Key words: field potential transformation, gravity anomaly, Lushan M_S7.0 earthquake, gravity gradient, directional derivative

中图分类号:

P315.72⁺6

赵云峰, 祝意青, 刘芳. 重力水平梯度及其在地震重力前兆中的研究初探[J]. 地震地质, 2015, 37(4): 1020-1029.

ZHAO Yun-feng, ZHU Yi-qing, LIU Fang. preliminary discussion on horizontal gravity gradient and its application to seismic gravity precursor research[J]. SEISMOLOGY AND GEOLOGY, 2015, 37(4): 1020-1029.

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