Crustal P-wave velocity structure in Lower Yangtze region: Reinterpretation of Fuliji-Fengxian deep seismic sounding profile

Abstract

The finite-difference inversion method and RayInvr technique had been employed to interpret the wide-angle seismic reflection/refraction data of the Fuliji-Fengxian deep seismic sounding (DSS) profile in Lower Yangtze region, hence the velocity structure was acquired and conclusions were summarized as follows: (1) The velocity model along this profile can be divided into three large layers vertically (upper, middle and lower crusts) and six blocks laterally, and this velocity distribution agrees with the feature of stable platform. (2) The depth of Moho discontinuity is 30-36 km. The thickness of the upper crust is 10.5-13.0 km, where the lateral velocity varies strongly, and the velocity increases to 6.2 km/s −1 at bottom. Besides, the velocity distributions in the bottom layer of middle crust and lower crust have an apparent inhomogeneity. The velocity in upper layer of middle crust, lower layer of middle crust, lower crust and uppermost mantle is 5.9-6.2, 6.3-6.4, 6.6-7.0 and 8.06-8.29 km/s −1 , respectively. (3) On two sides of the Tanlu fault belt (TFB), the mid-crustal velocity structure is quite different, nevertheless no apparent discrimination in velocity distribution and boundary topography exhibits in lower crust, hence it is inferred that the Jiashan segment of TFB had probably cut through whole crust in the Mesozoic, and the fault behaviour in lower crust had disappeared due to the low viscosity produced by the orogenic extension or crustal balance, while the fault features in the rigid middle-upper crust have been preserved up to the present. (4) The moderate earthquakes with Ms > 5.0 nearby Zhenjiang are related to the deep faults extending into the lower crust, and the earthquakes were probably induced by the energy been transferred from mantle lithosphere to upper-mid crust along the deep faults, and aggregated at some preferable tectonic positions.

The deep background of large-scale, Mesozoic Cu-Au-W metallogenesis in northeastern South China: Constraints from Yingshan-Changshan wide-angle seismic reflection/refraction data

“…The Moho depth (33-35 km) of the Yingshan-Changshan profile is consistent with previous results (Wang et al, 2000;Bai and Wang, 2006;Xu et al, 2014b;Zheng et al, 2014;Zhang et al, 2015).…”

Azimuthally Anisotropic Structure in the Crust and Uppermost Mantle in Central East China and Its Significance to Regional Deformation Around the Tan‐Lu Fault Zone

“…They speculated that the fault might have cut through the entire crust into the uppermost mantle because of the tensile stress field that arose from the regional Moho uplift. But while the fault geometry is preserved in the brittle upper‐middle crust, extension during orogenic processes that characterize the south‐central segment and crustal adjustment to accommodate the various instability actions must have eroded the fault features in the lower crust (Bai & Wang, 2006). Our observations support the deep penetration of the TLF zone with the direction of the anisotropy preserved in the crust to the uppermost mantle favoring the fault' strike.…”

“…One crucial implication of our observation and interpretation of anisotropic pattern in the TLF zone and adjacent regions in the crust and uppermost mantle is that the TLF zone is a deep lithospheric structure; a piece of information that is vital in resolving the age-long debate about the depth extent of the TLF zone in the south. For instance, Bai and Wang (2006) interpret the lack of apparent velocity anomaly in the fault zone beyond the middle crust as the lack of fault geometry. They speculated that the fault might have cut through the entire crust into the uppermost mantle because of the tensile stress field that arose from the regional Moho uplift.…”

Continent‐Continent Collision Between the South and North China Plates Revealed by Seismic Refraction and Reflection at the Southern Segment of the Tanlu Fault Zone

“…Moreover, due to the westward subduction and the subsequent retreat of the Pacific/Paleo‐Pacific Plate beneath the Eurasian continent in the Early Cretaceous (Zhu et al., 2009), the eastern China lithosphere switched from a compressional regime to a regional extensional deformation. Under the extensional regime, erosion of the magma possibly took place, resulting in the migration of the injected magmatic materials in the fault zone to regions in the subsurface with low‐pressure gradients (Bai & Wang, 2006; Lü et al., 2013). Still, the cooled magma materials were preserved in the crust of the TFZ, which is characterized as the reflection‐free zone in the crust and the high‐velocity anomaly near the surface (Figure 10).…”