摘要
西华夏块体深地震测深资料观测长度超过250 km或更远的地震记录截面中,远炮检距的PmP'波组具有几何形态平坦、视速度较低、位于折合走时零线以上的显著特征.由于其与PmP反射波组相连且波形相似,常规的波组识别常常当作PmP波组的一部分.把这个波组作为PmP波组部分进行理论地震图模拟,其走时和振幅均难以同时获得满意的拟合.以2021年粤东地区连平—河源—海丰地震宽角反射/折射剖面SP3炮远炮检距PmP'波组为例,计算得到该波组最远端的视速度为6.04 km/s,小于用临界区域PmP波组走时算出的地壳平均P波速度6.27 km/s,表明该波组不具有PmP波组属性.用新的下地壳和莫霍界面模型对PmP'波组进行二维理论地震图拟合,结果显示,这一波组是来自下地壳的回折波,表明西华夏块体下地壳普遍具有正速度梯度结构特征,反映了华南地区东南缘中生代以来岩浆底侵的结果,可能是新生地壳的证据.
The PmP' wave group with long offset has the characteristics of flat geometry, low apparent velocity and above the zero line of travel time in the seismic record section with the observation length of more than 250 km or more in the deep seismic sounding data of the western Cathaysia block. Because it is connected to the PmP reflected wave group and the waveform is similar, the conventional wave group identification is often used as a part of the PmP wave group. Using this wave group as part of the PmP wave group for theoretical seismogram simulation, it is difficult to obtain satisfactory fitting of travel time and amplitude at the same time. Taking the far-offset PmP' wave group of the wide-angle reflection/refraction profile SP3 of the Lianping—Heyuan—Haifeng earthquake in eastern Guangdong in 2021 as an example, the apparent velocity at the farthest end of the wave group is calculated to be 6.04 km/s, which is less than the average P wave velocity of the crust calculated by the travel time of the PmP wave group in the critical region of 6.27 km/s, indicating that the wave does not have the property of PmP wave. A new lower crust and Moho interface model is used to fit the two-dimensional theoretical seismograms of the PmP' wave group. The results show that this wave is a refracted wave from the lower crust, indicating that the lower crust of the Western Cathaysia block generally has a positive velocity gradient structure. This reflects the result of magma intrusion since the Mesozoic era in the southeastern margin of South China, which may be the direct evidence of newly crust.
作者
刘汉奇
王夫运
宋佳佳
王帅军
宋向辉
张雪莹
LIU HanQi;WANG FuYun;SONG JiaJia;WANG ShuaiJun;SONG XiangHui;ZHANG XueYing(Geophysical Exploration Center,China Earthquake Administration,Zhengzhou 450002,China)
出处
《地球物理学进展》
北大核心
2025年第2期432-439,共8页
Progress in Geophysics
基金
中国地震局地球物理勘探中心青年基金(YFGEC2022001)资助。
