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Urban structure imaging using noise-based techniques has rapidly developed in recent years. Given the complexity of the cross-correlation function in high-frequency signals, here, the beamforming (BF) method was used to analyze one data set taken from a dense array in the Jizhong Depression and obtain multi-mode dispersion curves. Multi-mode surface waves improved inversion stability, reduced non-uniqueness, and yielded a one-dimensional shear wave (S-wave) velocity model. Interpolation yielded a high-resolution three-dimensional (3D) S-wave velocity model for the study area. The model shows that velocity gradually changed in the horizontal direction and greatly increased in the vertical direction, which is largely consistent with changes in the sedimentary environment related to the continuous subsidence of the Jizhong Depression since the Quaternary. A low-velocity anomaly at a depth of ~300–400 m was revealed and determined to be caused by either a deep-buried ancient river course or low-lying area. This study demonstrates the potential of the BF method for processing dense array data sets of urban exploration. The high-resolution 3D S-wave velocity model provides a new reference for studying the Quaternary structure of the Jizhong Depression, as well as groundwater resources, urban infrastructure, and underground spaces. [ABSTRACT FROM AUTHOR]

As interference waves in deep reflection data processing, surface waves are often suppressed as noise, but surface waves carry considerable underground media information, including structural information and the physical properties of rocks. Reasonable extraction and use of surface wave signals are of great significance when studying shallow characteristics. Deep reflection data are collected using large offsets, trail spacing, and explosive sources. The surface wave energy tends to be stronger, and the high-frequency surface wave signal is abundant. After extraction and inversion, the shallow shear wave velocity structure can be obtained. Near the Cuonadong dome in the southern Tibetan detachment system (STDS), a large number of leucogranites are developed in the core, containing important rare metal minerals and high metallogenic potential. However, studies regarding the shallow structure in this region are rare. In this paper, we use deep reflection data from a profile through the Cuonadong dome to obtain the S-wave velocity structure of the study area by extracting the surface wave fundamental-mode dispersion curve and inversion. Combined with regional geological and magnetotelluric data, we supposed that the thickness of the Cuonadong dome sediment layer (< 1.4 km/s) varies greatly from east to west, the thickness of the sediment layer is the deepest near the Cuona fault and Jisong fault (more than 1 km), and the core of the dome is the thinnest. Under the Cuonadong dome, there are obvious high-velocity anomalies (> 2.2 km/s), and the horizontal S-wave velocity changes greatly, which is mainly related to the destruction of magmatic activity since the Miocene. These understandings of the structure and velocity field of the Cuonadong dome can provide a powerful geophysical basis for establishing the dome structure model and searching for hidden ore bodies. [ABSTRACT FROM AUTHOR]

The high topography of the Tibetan Plateau was generated by the Cenozoic India‐Eurasia collision. A high‐resolution shear wave velocity model can provide improved understanding of the Tibetan structure and crustal deformation with complicated tectonic evolution. Based on continuous seismic observations at approximately 400 stations, we collected over 10,000 Rayleigh wave phase velocity dispersion curves extracted from ambient noise cross‐correlation functions. A direct surface wave inversion method was applied to obtain an S wave velocity model of the Tibetan crust. A heterogeneous structure including several prominent low‐velocity zones (LVZs) and relatively narrow low‐velocity bands connecting the LVZs is revealed. Our model shows significant crustal low‐velocity structures with lateral variations along the Himalayan front. In the eastern segment of the Lhasa terrane, the LVZ is spatially correlated with Miocene porphyry Cu deposits, which are probably related to strong tearing of the Indian lithosphere, while preexisting weak zones contribute to the LVZs in the western segment. Meanwhile, the LVZ along the Bangong‐Nujiang suture could be considered as a channel for eastward extrusion of ductile material, that is, crustal flow on geological timescales. This "flow" in the middle‐lower crust probably contributed to the formation of the V‐shaped conjugate strike‐slip fault system in central Tibet. The development of conjugate strike‐slip faults, however, ceased near 90°E, since the eastward "flow" was blocked by an intracrustal high‐velocity block in Amdo. This preexisting rigid zone (containing the Amdo microcontinent) hence influences the pattern of material transport inside the Tibetan crust and the deformation of the plateau. Key Points: Three‐dimensional architecture of crustal low‐velocity zones of the Tibetan Plateau is obtained by dense array ambient noise tomographyLow‐velocity zones along southern Tibet and the Miocene porphyry Cu deposit formation are related to Indian lithosphere tearingEastward crustal flow blocked by a rigid block in Amdo contributed to the formation of conjugate strike‐slip faults in central Tibet [ABSTRACT FROM AUTHOR]

The Central Yunnan block (CYB) plays a key role in accommodating the crustal tectonic deformation of the southeastern Tibet, but its exact mechanism is poorly understood. Here we obtained a fine S-wave velocity structure of the upper crust across the Xiaojiang fault system in CYB, using the ambient noise tomography with a linear dense short-period array. The result shows a strong S-wave velocity variation along the profile, which is consistent with geomorphology and hypocenters occurred in this area. The velocity variations along the profile correspond well to the major faults seen on the surface and are consistent with the transition from surface erosion, to ductile basement and to rigid basement in the greater depth. Combining the upper crustal structure from our image with the location of hypocenters, we propose that most faults of Xiaojiang fault system cut through the upper crust steeply and control the tectonic deformation of the upper crust in the CYB. • Ambient noise tomography shows a fine S-wave velocity structure of the upper crust across Xiaojiang fault system. • The velocity variations along the profile correspond well to the major faults seen on the surface and are consistent with geomorphology and hypocenters occurred in this area. • Most faults of Xiaojiang fault system cut through the upper crust steeply and control the tectonic deformation of the upper crust in the Central Yunnan Block. [ABSTRACT FROM AUTHOR]

The Xiaojiang Fault Zone (XJF) is an important boundary fault on the southeast border of the Tibetan Plateau, with a complex subterranean structure and strong tectonic activity. In the present study, 252 seismograph stations were deployed in the northern section of the XJF to collect ambient noise data in a span of 35 days. The minimum resolution attained was 2 km × 2 km to develop a high-precision underground velocity structure model. The velocity model helped in revealing that the low-velocity distribution originated below the XJF. It was also found that the fault, which is the primary channel for magma to rise, might be the cause of the upper crustal deformation of the XJF. The Dongchuan mining area is located to the west of the XJF, which has a low-velocity structure. However, the high-velocity structure appeared on both sides of the ore body. It is speculated that the ore was formed by magma intrusion. The intrusion serves as a heat source for the mining area and promotes deposit formation. [Display omitted] • A short-period dense array based ambient noise tomography for Xiaojiang fault. • High and low velocity 3D structure under Xiaojiang fault. • Deep ore metallogenesis constraints beneath the Dongchuan ore field. [ABSTRACT FROM AUTHOR]

Deep reflection seismic data contain abundant surface wave information for which the velocity structure in the near-surface shallow underground can be obtained using multichannel analysis of surface waves (MASW). This paper uses the MASW method to process deep reflection data in the Yuanmou area in Yunnan province, China. The MASW method uses the phase velocity spectral transformation of Rayleigh waves to obtain its dispersion curve. The initial model for different lithology classifications is established to invert the underground velocity structure. This study obtains a two-dimensional shear wave velocity structure profile to investigate the shear wave velocity structure. Generally, the study results have shown that the shear wave velocity structure obtained by the MASW method corresponds well with the surface conditions and accurately reflects faults' changes, folds, and lithology. Moreover, the formation sand content calculation shows a large difference in Dongshan sag's formation sand content. The sand contents of Cretaceous and Middle Jurassic strata are over 30% similar, and the sandstone content of underlying Early Jurassic strata is mostly 30% lower. The stratum buried depth of Early Jurassic strata is between 0– 800 m. The dip angle of LZJF at this location is 90°. The west side of the LZJF is based on Proterozoic uplift, and the Quaternary sedimentary thickness exceeds 300 m above the uplift stratum. Whereas on the east side of the LZJF, the stratum of the Dongshan sag section is mainly a synclinal structure. • Multichannel analysis of surface waves method is applicable to surface wave data in deep reflection profile. • The interlayer velocity difference method can be used to distinguish strata by shear wave velocity. • Shallow velocity structure can distinguish shallow geological structure with high resolution. [ABSTRACT FROM AUTHOR]