新疆乌苏5.1级地震前波速比异常震例研究

Study of the Abnormity of Wave-velocity Ratio before M_S5.1 Wusu Earthquake in Xinjiang

利用天山中段数字化地震波资料,采用多台和达法,计算2006年11月23日新疆乌苏5.1级地震前后波速比的变化情况,得到如下结果:(1)在空间分布上,乌苏5.1级地震前,波速比形成一个近似椭圆形低值异常区,且椭圆长半轴约为70km,短半轴约为55km,椭圆走向NW,地震就发生在该椭圆区域的西北部边缘;(2)在时间进程上,乌苏5.1级地震前出现近9个月的波速比低值异常,震前未出现明显的高值突跳点。波速比呈现正常—降低—发震的模式。而乌苏地震后,波速比值出现一段时间的低值,2007年以后,波速比值出现高、低值起伏变化。

We use the digital wave form data of earthquakes in middle part of the Tianshan Mountains and apply the Multi-station Method to calculate the wave-velocity ratio before and after the MS5.1 Wusu earthquake on Nov.23,2006.We obtain the following results：（1）In the aspect of spatial distribution,the wave-velocity ratio formed a low-value oval area before the MS5.1 Wusu earthquake.The long axis is approximately 70 km in radius,while the short axis is approximately 55 km in radius.And the ellipse is in NW direction.The MS5.1 Wusu earthquake occured in the northeast part of the ellipse.After the earthquake,the values of the wave-velocity ratio of this region returned to be normal.（2）In the time course,the wave-velocity ratio appeared to be low-value abnormity for nearly 9 months before the earthquake.And no obvious high value.The wave-velocity ratio formed a pattern of normality,fall,earthquake occurrance.However,in 2007 after the Wusu earthquake,the time-sequence curve fluctuated.