Tomographic imaging of P wave velocity structure beneath the region around Beijing

Abstract

The three-dimension crustal and upper mantle structures in the region around Beijing were studied by seismic tomography. We used the P wave arrival times from local and teleseismic events. These events were recorded by 250 stations of the North China Seismic Array and 108 stations of the Beijing Telemetry Seismic Network. 118 869 P wave arrivals from 10 285 local events and 12 189 P wave arrivals from 107 teleseismic events were used in the inversion. We obtained the 3-D P wave velocity structure of the crust and upper mantle with the horizontal resolution of 0.3° in the studied region. The tomographic imaging shows the remarkably heterogeneous velocity variation. The velocity anomalies are in well agreement with the geological structure in the shallow crust. The different relationships between seismic activities and velocity anomalies may imply the different seismogenic structure and mechanism. Beneath the Moho under Taihangshan mountain and Yanshan mountain, we found the high velocity anomalies deep to 120 km and 200 km, respectively. The deep high velocity zone may be explained by the existence of the mountain root under Yanshan mountain. The high velocity anomalies in the upper mantle of North China basin may be the relics of the de-rooting from the former craton mantle lithosphere.

Study on surface-wave tomography in Abaga volcanic area, Inner Mongolia

“…The results of previous studies show that the Ordos block is a high velocity anomaly within the depth range of 100-150 km Li et al, 2006;Tian et al, 2009;Obrebski et al, 2012), thus forming a clear contrast with the large-scale low velocity anomaly in the western part. In addition, body-wave imaging shows that the low velocity anomaly beneath the Datong volcano tends to extend westward (Ding et al, 2009;Tian et al, 2009;Lei, 2012). Therefore, the inversion results in this paper still do not rule out the conclusion obtained by using the NM array data previously (Hou et al, 2019), that is, the low velocity anomaly under South Gobi of the Mongolian Plateau and the deep material of Honggeertu volcano and even Datong volcano may have connectivity or interaction, or both may come from the upwelling of the same thermal region.…”