1984年5月21日南黄海地震的震源参数——用IDA记录测定浅震震源参数

SOURCE PARAMETERS OF THE SOUTH YELLOW SEA EARTHQUAKE OF MAY 21, 1984——USE OF IDA RECORD FOR THE DETERMINATION OF VERY SHALLOW EARTHQUAKE-SOURCE PARAMETERS

本文讨论了利用国际部署加速度仪台网(IDA)的超长周期瑞雷波记录,反演震源参数的有关理论和方法.对于震源深度大于30km的地震,地震矩张量的五个元素都可以测定;对于浅源(h≤30km)地震,其中两个元素变为无解.本文以1984年5月21日南黄海浅源地震为例,研究了在浅震难题的情况下,如何更多地提取震源信息的问题,测定了主震的断层机制为:走向北35°西,倾角52°,滑动方向54°,地震矩为1.2×10^(18)N·m,压应力主轴方向为北74.4°东,是一个走向北北西的左旋逆断层.本文还阐述了分布源模型问题。结果表明,采用分布源与采用点源模型对南黄海这种中强地震反演结果的影响不大.分析了震源有限性问题,提出了进行修正的一种明确表达式.

In this paper, the method and theory relevant to inversion for source parameters by using long-period Rayleigh waves on IDA accelerograms (International Deployment of Accelerograph) are discussed. For earthquake sources deeper than 30 km, all of the five elements of the momemt tensor can be retrieved. For shallow (h≤30 km) earthquakes, two of the five elements become unresolvable. Taking the Nan Huang Hai (South Yellow Sea) shallow earthquake of May 21, 1984 as an example, the difficult problem of how to extract more source information from shallow earthquakes is studied. The main shock fault mechanism is determined as following: strike N35°W, dip 52°, slip 54°, seismic moment 1.2×1025 dyne. cm. The compression axes is in the direction of N74.4°E. It turns out to be a reverse fault striking NNW with left-lateral slip. The distributed source model problem is also discussed. The results indicate that it does not make large difference for inversion results of moderate earthquakes, such as the South Yellow Sea earthquake, by utilizing the model of distributed source or point source. Analysing the finiteness of the source, an explicit expression for performing correction is presented.