山东地区地壳P波三维速度结构及其与地震活动的关系

利用山东及周边区域地震台网1975—2014年1月期间记录到的1369个地震的13781个P波到时数据对山东地区地壳结构进行了层析成像研究.结果表明,山东地区地壳速度结构存在明显的不均匀性.沂沭断裂带介质速度结构复杂,呈现明显的分段特征,两侧块体速度存在差异,具有块体边界的构造特征.鲁西断块20km以下深度处存在大规模的低速异常区,这与该地区始新世发生的大规模滑脱拆离构造有关,可能产生于太平洋板块的西向俯冲导致地幔热物质沿沂沭断裂带向上并向西涌动.历史大震及ML4.0以上中强震大部分为走滑型地震,主要发生于高低速异常过渡带且有深大断裂穿过的地区.震群主要发生于低速体上部或周边,且震源深度优势分布在中上地壳,这与地下介质富含流体并导致应力集中有关.

3D P wave velocity structures of crust and their relationship with earthquakes in the Shandong area

A high-resolution 3D P-wave velocity structure of the crust in Shandong area was imaged by inverting 13781 arrival times from 1369 local events recorded by Shandong seismic network from 1975 to January 2014. Tomographic results reveal that the P-wave velocity structure of the crust of Shandong area has significant heterougeneities. The blocks on both sides of the Tanlu fault zone show different velocity structures, implying that the Tanlu fault may be a boundary fault. Our results also show that large-scale low velocity anomalies related to the Luxi large-scale detachment structure of Eocene exists below 20 km depth in the Luxi area, which was possibly associated with the westwards subduction of the Pacific plate that made the hot mantle material ascend along the Tanlu fault zone. The distribution of major earthquakes, most of which are of strike-slip type, spatially coincides with the transition zone between the low-velocity zone and high velocity zone, accompanied by the deep fault zone. These low-velocity anomalies may be related to the enriched fluid, which may weaken the lithospheric strength and make the tectonic stresses easier to accumulate there. The boundaries between the low-velocity and high-velocity anomalies may act as an elastic boundary along which tectonic stresses easily accumulate and transfer to the shallow depth of the crust and generate earthquakes.