山东长岛地区地震波非弹性衰减Q值、场地响应及震源参数研究

利用山东台网记录的长岛震群2017年2月14日—9月1日期间的波形与震相资料研究长岛地区非弹性衰减系数,得到该地区介质平均Q值与频率f的关系式为Q(f)=363.9f1.374 1。采用Moya等1]提出的利用遗传算法联合反演得到长岛周边台站的场地响应,根据Brune模型震源参数计算公式求解长岛震群序列地震震源参数。结果显示,各个震源参数之间均存在一定的相关关系,地震矩随ML震级的增大而增加,地震矩与破裂半径R之间存在半对数关系,拐角频率fc随地震矩的增大而减少;长岛地震序列的应力降数值普遍偏小,最大不超过0.9MPa,这意味着长岛震源区整体构造应力较低,也可能指示长岛震群为低摩擦应力的断层作用;震源参数随时间的变化方面,整体而言,长岛震群地震应力降变化起伏很大,在M4.1地震发生前,拐角频率与应力降均发生快速下降后随即翻转上升的现象,证明在M4.1地震发生前震源区整体应力的挤压逐渐增强。

Inelastic Attenuation Q Value, Site Response, and Seismic Source Parameters in Changdao Region, Shandong

Based on the waveform and seismic phase data of the Changdao earthquake swarm from February 14 to September 1, 2017, the inelastic attenuation coefficient of the Changdao area is studied, and the relationship between the average Q value and the frequency f in the Changdao area is Q(f)=363.9f^{1.374 1}. The site responses of stations around Changdao are obtained using the joint conversion of genetic algorithm proposed by Moya, and the source parameters of Changdao earthquake swarm sequence are calculated by the Brune model formula. The results show that there are some correlations between the various source parameters:the seismic moment increases with the local magnitude M_L, and there is a semilogarithmic relationship between the seismic moment and the rupture radius R. The corner frequency f_c decreases with the increase of seismic moment. The stress drop values of the Changdao earthquake sequence are generally small, and the maximum does not exceed 0.9 MPa, which means the overall structural stress in Changdao focal area is low. Considering the changes of source parameters over time, the changes in stress drop of the earthquake swarm is very irregular. Before the occurrence of the M4.1 earthquake, the corner frequency and stress drop both decreased rapidly and immediately increased. This proves that the overall stress in the Changdao focal area increased before the M4.1 earthquake.