小江断裂带北段地震活动与构造运动的观测与研究

Insight into earthquake process and deduction of natural disaster is an important direction of seismological devlopment. Xiao-Jiang fault belt locates along eastern boundary of the Chuan-Dian rhombic block, which is one of the places where strong earthquakes often take place. Especially, its northern segment has been regarded as one where an earthquake with magnitude more than 7 will take place very probably in the near future. Therefore, 24 broadband instruments, 18 strong-motion instruments and 12 recording-continuous GPSs will be kept in operation there in order to capture possible signals coming from underground; a new method for absolute location of earthquakes will be developed in order to clearly and accurately know tempo-spacial characteristics of the seismicity; a non-linear inversion method for determing focal mechanisms of the events as small as possible will be developed in order to understand mechanism of the earthquakes; and creep or stick-slip which will probably occurre and stress-stain characteristics in the observation area will be quantitatively anlayzed with combined information on seismicity, focal mechanisms and the recording-continuous GPSs in order to build a characterized image of the seismicity, faulting and stress-strain change. Finally, the rupure process would be imaged by jointly inversting far-field and near-field data, and the whole process of nucleation, occurrence and healing will be analyzed and discussed if there occured a destructive earthquake at the observation area.

探究地震过程,减轻自然灾害,是地震学发展的重要方向。小江断裂带是川滇菱形块体的东边界，是我国强震多发地之一；尤其是其北段，被认为是未来发生7级以上地震可能性极高的地段。因此，拟在小江断裂带北段运行24套微震仪、18套强震仪和12套连续GPS仪，以捕捉可能的"地动"信号；拟发展针对小台网的非线性绝对定位方法，以准确把握地震活动的时空特征；拟发展针对小震甚至微震的震源机制非线性反演方法，以准确了解地震活动的性质；拟综合利用地震活动、震源机制以及GPS直接观测信息，定量分析观测区可能发生的断层粘滑或蠕滑以及应力应变特征，构建较详细的地震活动、断层运动以及应力应变特征图像；若在观测期间发生破获性地震，拟利用远场和近场资料联合反演其破裂过程，并探讨其孕育、发生和愈合过程。

(1)利用小江断裂带北段架设的18个强震台、24个宽频带台和12个连续GPS观测站构成的台阵，获取了观测区的强地面运动记录、宽频带地震记录和观测点位置的时间序列。(2)发展了基于小孔径台阵或台网的非线性地震定位方法-逆时成像方法，并将这种方法应用于实际地震定位。(3)发展了利用地震记录的极性和振幅反演小微地震的震源机制的方法-广义极性振幅技术，并将这种技术应用于实际地震的震源机制反演。基于小微地震的震源机制，初步反演了当地的应力场特征。(4)基于24个台站记录的3181次地震事件的P波走时残差，计算分析了P波的快波方向或慢波方向。(5)利用云南省地震台网、昭通防震减灾局局域台网、巧家台阵所有台站以及应急流动台站震后约210天的原始记录，对发生在观测区附近的2014年鲁甸Ms6.5地震序列的发震构造进行了再研究。(6)基于巧家GPS台阵观测资料计算了当地的速度场。在欧亚框架下，观测区整体以11.0mm/yr的速度朝方位角约140º方向运动，在华南框架下，观测区整体运动的平均速度为6.0mm/yr，方位角约为180º。（7）基于巧家GPS台阵观测数据分析了当地的地表形变。观测区北区、南区和整个区域主压应变率轴方位分别约为102º、130º和114º。无论是主应变率的大小，或是最大切应变率的大小，或是面应变率的大小，均呈现北大南小的特征。（8）采用反正切函数拟合法，利用巧家台阵近断层观测和陆态网络远场观测分别估算了小江断裂带北段滑移速率。（9）利用位错理论拟合观测数据估算了断裂带的闭锁深度。