Abstract: In 1979 an earthquake of magnitude 6 occurred in Liyang County, Jiangshu province. The epicenter was located in the junction of a NE trending active fault, the known Maoshan fault, with a NW trending active fault, the Fangshan-Tiger Mt. fault.In this paper the focal mechanism of the major shock and several aftershocks has been studied and the strike of seismic fracture has been also determined by means of null vector data. The research results indicate that the Liyang earthquake was caused by a right lateral strike-slip dislocation with some normal dip-slip component along the east branch of the Maoshan fault belt under the action of the NEE compression stress field.From the observation of aftershocks, it can be suggested that both the source volume of the b-value of this earthquake sequence is rather small. Using Wyss method and Gibowicz empirical formula, we approximately estimated the stress-drop and the seismic moment as well as the apparent stress of the Liyang earthquake. In the mean time, on the basis of the field geological observations we pointed out tentatively that the Liyang earthquake was generated probably by the locked NE Maoshan fault associted with the left lateral shifting of the NW Fangshan-Tiger Mt. active fault. And this seemed to be a reasonable explanation for the recurrence of two destructive earthquakes being occurred there within 5 years.The authors assume that the Liyang earthquake can be regarded to be a low stress-drop event under a high stress background, implying that the south part of the North China fault block has been stepping into a active stage of high stress.

摘要： 该地震发生在北东向茅山活动断裂与北西向芳山-老虎山活动断裂的交汇部位。本文研究了主震与若干余震的震源机制解,并应用零矢量方法确定了地震破裂面的走向。研究结果表明,该地震是在北东东向挤压应力作用下,沿着茅山断裂带东支发生了右行走滑错动兼有正断层性质的倾滑分量。根据对余震的观测可知,溧阳地震的震源体积与b值均偏小。运用Wyss方法及Gibo Wicz经验公式粗略估算了溧阳地震的应力降、地震矩与视应力。同时,根据野外地质观察指出,该地区之所以在最近五年来重复发生两次破坏性地震,可能与北西向芳山-老虎山断裂带的左行错动引起北东向茅山断裂带闭锁有关。