黑龙江地区背景噪声面波群速度层析成像

Crustal and uppermost mantle structure of the Heilongjiang region from ambient noise tomography

本文选取黑龙江省台网及吉林、内蒙古部分台站共44个固定地震台站连续2年的地震数据,利用两个台站间互相关方法获得瑞利面波经验格林函数,再用自适应时频分析方法提取群速度频散曲线,最后利用传统面波层析成像方法反演获得黑龙江地区周期为8～40s范围内群速度分布图像.反演结果揭示黑龙江地区地壳及上地幔群速度结构存在明显横向不均匀性.短周期群速度异常与研究区内山脉、盆地和断层带的分布有较好的对应关系:8～20s群速度显著低速异常显示松辽盆地具有较厚的沉积层.周期为16～25s的高、低速度异常区的反转反映了大兴安岭地区莫霍面深度大于松辽盆地.周期为30～40s群速度分布图像较好地体现深部构造与浅部构造的对应关系,尤其是观测到了依兰一伊通断裂带以东区域可能反映上地幔物质活动的低速异常.本研究也为进一步结合传统天然地震面波成像方法,获取该区域地壳和上地幔三维剪切波速度结构奠定基础,对研究东北地区构造活动以及探讨深源地震分布和成因具有重要科学意义.

We have inverted for the Rayleigh wave group velocity distribut province at periods of 8～40 s using ambient noise tomography. Two years e in this study are from 44 permanent seismic stations of the Heilongjian Network and adjacent stations in Jilin and Inner Mongolia provinces. Green＇s extracted from cross-correlations of data at adjacent stations and group measurements were then made using the frequency time analysis meth significa velocity nt lateral variations in crustal and uppermost mantle structures od. of ion of Heilongjiang ontinuous data used g Regional Seismic functions were first velocity dispersion Our results show the region. Group anomalies at short periods correlate well with the surface geology of basins and mountains. The strong slow velocity anomaly at periods of 8～20 s beneath the Songliao basin suggests a rather thick sediment deposit. The reverse phenomenon of the fast and slow group velocity anomalies at periods of 16～25 s indicates that the Moho beneath the Greater Higgnan Mountains is at deeper depth than that in the Songliao basin. Slow velocity anomalies at long periods of 30～40 s were observed beneath the eastern area of the northern extension of the Tanlu fault zone, indicating upper mantle activities there such as localized asthenospheric upwelling. The work reported here has completed an important step towards incorporating teleseismie surface wave inversion of the crust and mantle structures of this northeast China region which could provide important observational constraints in understanding the tectonic process at the surface and distribution and origin of deep earthquakes beneath the region.