zhiming bai - Academia.edu (original) (raw)

Papers by zhiming bai

Earthquake research advances, Jul 1, 2023

Frontiers in Earth Science, Feb 24, 2023

Altaids in the Central Asian Orogenic Belt (CAOB) is one of the world's largest orogenic belts co... more Altaids in the Central Asian Orogenic Belt (CAOB) is one of the world's largest orogenic belts containing mineral deposits. Together with the Junggar terrain they open an important window to study the Paleozoic tectonic evolution of the CAOB. In this paper, we analyze a 637-km-long wide-angle refraction/reflection seismic profile across the Altai-Eastern Tianshan orogenic belt in the southern Altaids, conducted in September 2018 using 10 large explosive charges fired in drilled holes. We use a traveltime inversion method to reconstruct the lithospheric P-wave velocity structure along the profile. The lithosphere is composed of a 43-55-km-thick crust, a~10-km-thick crust-mantle transition layer beneath the Altai Mountain, and a~25-km-thick layer of lithospheric mantle. The results clearly reveal: a prominent Moho uplift beneath the Yemaquan Island Arc, two major crustal-scale low-velocity anomalies (LVAs) beneath the Yemaquan Arc and Bogda Mountain, and three high-velocity anomalies (HVAs) near the surface around the Kalatongke, Yemaquan and Kalatage mining areas. We hypothesize that the subduction of the Paleo-Asian Ocean occurred with strong mantle upwelling. We suggest that continued compression of the Paleo-Asian Ocean causes the delamination of lithosphere, as well as asthenospheric material upwelling and magma underplating into the crust. Consistently, Paleozoic mafic-ultramafic rocks and mantle-derived minerals related to gold, copper and nickel deposits, are widely extended in the area. Our results show that the P-wave velocity-depth curves for deeper depths (>30 km) in the southern Altai and Junggar Basin are close to those of the continental arcs and global continent average. Despite powerful Paleozoic subduction activity, orogeny and volcanism strongly modified the lower crust in the region, part of ancient continental crust was still preserved below the southern Altai and Junggar Basin. In addition, the upper part (depth 5-30 km) of the velocity-depth curve for the Junggar Basin is close to that of the Costa Rica volcanic front and the British Columbia accreted terrain, suggesting that Paleozoic orogenic activity has intensively reconstructed the upper-middle crust beneath the Junggar Basin.

Earthquake Science, Nov 16, 2017

Seismic ray tracing in anisotropic media with irregular surface is crucial for the exploration of... more Seismic ray tracing in anisotropic media with irregular surface is crucial for the exploration of the fine crustal structure. Elliptically anisotropic medium is the type of anisotropic media with only four independent elastic parameters. Usually, this medium can be described by only the vertical phase velocity and the horizontal phase velocity for seismic wave propagation. Model parameterization in this study is described by flexible triangular grids, which is beneficial for the description of irregular surface with high degree of approximation. Both the vertical and horizontal phase velocities are defined in the triangular grids, respectively, which are used for the description of phase velocity distribution everywhere in the model by linear interpolation. We develop a shooting ray tracing method of turning wave in the elliptically anisotropic media with irregular surface. Runge-Kutta method is applied to solve the partial differential equation of seismic ray in elliptically anisotropic media. Linearly modified method is used for adjusting emergent phase angles in the shooting scheme. Numerical tests demonstrate that ray paths coincide well with analytical trajectories in transversely homogeneous elliptically anisotropic media. Seismic ray tracing results in transversely inhomogeneous elliptically anisotropic media demonstrate that our method is effective for further first-arrival tomography in elliptically anisotropic media with an irregular surface.

Bulletin of the Seismological Society of America, 2019

Remarkable V‐shaped conjugate strike‐slip faults extend along the Bangong–Nujiang suture in centr... more Remarkable V‐shaped conjugate strike‐slip faults extend along the Bangong–Nujiang suture in central Tibet. Motions of these faults are considered to accommodate ongoing east–west extension and north–south contraction. Fabrics within the fault zone that are anisotropic to seismic waves can provide clues as to the unusual scale and style of lithospheric deformation. With the goal of determining the upper‐crustal anisotropy pattern in central Tibet, we measured shear‐wave splitting parameters (fast wave polarization direction and delay time) using waveforms generated by 194 local earthquakes recorded by 49 stations of the SANDWICH network. Stations located in eastern and western zones of the study area show anisotropy directions that agree well with the maximum horizontal compressive stress direction. The fast polarization directions at stations near active strike‐slip faults generally run parallel to the strikes of these faults. Pervasive inactive thrust faults caused by Cretaceous–Te...

Applied Mathematics and Mechanics, 2009

ABSTRACT In this paper, we introduce a flexible model for the control and measurement of NAMRs (n... more ABSTRACT In this paper, we introduce a flexible model for the control and measurement of NAMRs (nanomechanical resonators). We obtain the free Hamiltonian of the dc-SQUID (direct current superconducting quantum interference device) and the interaction Hamiltonian between these two NAMRs and the dc-SQUID by introducing the annihilation and creation operators under the rotating wave approximation. We can treat the mode of the dc-SQUID as a classical field. In the Heisenberg picture, the generation of two-mode squeezed states of two nanomechanical resonators is shown by their collective coordinate and momentum operators.

Earth and Planetary Science Letters, 2021

The Tibetan plateau is bounded in part by cratonic blocks, and in part by tectonothermally younge... more The Tibetan plateau is bounded in part by cratonic blocks, and in part by tectonothermally younger and weaker crust. How the Tibetan plateau interacts with bordering non-cratonic crust is a continuing debate, whether the plateau is currently enlarging its area, and if so, whether by thrusting or by lowercrustal flow, or both. The gently sloping northeastern margin of Tibet has been inferred to incorporate a lower-crustal channel flow outward towards the Ordos block that is a part of the North China Craton. We calculated receiver functions using teleseismic waveforms recorded by a dense nodal seismic array crossing from the Longxi basin of northeastern Tibet across a transition zone marked by the Liupan Shan (mountains) into the Ordos block. Our image shows the Longxi upper crust overthrusts onto the Ordos block building the Liupan Shan, and the Longxi lower crust underthrusts beneath the Ordos forming a 10-km thick crustal root. The Ordos crust forms a crustal-scale wedge inserted into the Longxi crust, and deformation is limited to a narrow zone of <50 km either side of the Liupan Shan. Convergence between the Longxi Basin and Ordos block is producing a narrow mountain range rather than broadening the plateau. The larger-scale gentle topography is likely an expression of negligible crustal deformation of the Longxi basin. Even if the Longxi basin of NE Tibet, between the Qaidam and Sichuan basins, is underlain by a weak lower crust, tunneling channel flow does not extend beyond the Liupan Shan, and the Tibetan Plateau has not grown outward beneath the Ordos block.

Science China Earth Sciences, 2020

Geological studies show that the southern part of Ailaoshan-Red River shear zone (ALSRRSZ) has ex... more Geological studies show that the southern part of Ailaoshan-Red River shear zone (ALSRRSZ) has experienced complex metallogenic processes and multi-stage non-uniform uplifting, called oblique uplifting since the Cenozoic. To detect the deep structure and geodynamic background beneath Daping, Chang'an and other gold and polymetallic deposits in this area, we carried out a high-density short-period seismic array survey in southern Yunnan province. The array used is approximately 240 km long with an interval of 500 m between two adjacent stations. Based on the data collected by the array, we used H-κ stacking and common conversion point (CCP) methods of receiver functions to reveal the fine crustal structure beneath this array, which was located from Lvchun (western end) to the east and ended in Maguan. The three main conclusions are as follows. (1) The average crustal thickness is approximately 37 km and the V p /V s ratio is 1.75. However, the thickness and V p /V s ratio of the Ailao Mountain are rather greater or higher than those of the western Lanping-Simao Basin and eastern South-China block. These results may indicate that the crust is rich in ferromagnesian minerals or has a thermal fluid anomaly after orogenic movement. (2) There are two obvious inclined interfaces beneath the Ailao Mountain in the mid-upper crust, which suggests that strong deformation occurred there during the orogenic period. Some evidences, such as the weak converted-wave Pms phase from the Moho, low P-wave velocities of the upper mantle, high surface heat flow values, and generally developed hot springs, indicate that a strong crust-mantle interaction exists in the southern segments of the Ailaoshan-Red River shear zone. These interactions include a diapir of mantle-sourced magma (stronger in the east than that in the west), lateral collision from the Indian Plate, and the differential uplift caused by the strike-slip movement of the Red River Fault. All of above deep processes led to the Cenozoic oblique uplifting of Ailao Mountain. (3) By combining the location of the deposits on the surface, characteristics of the average crustal V p /V s ratio, hypocenters of the small earthquakes along the research profile, Moho shape, and horizontal variations of the Pms phase amplitudes, we speculate that the Ailaoshan Fault was the upgoing conduit for metallogenic magma and played a significant role in the Cenozoic development of the multiform metal deposits around the Ailao Mountain area.

Solid Earth Sciences, 2019

The East China Continental Margin (ECCM) is an exemplified natural laboratory not only for studyi... more The East China Continental Margin (ECCM) is an exemplified natural laboratory not only for studying the origin and evolution of trench-arcbasin system, but also for investigating the deformation mechanism within continent and its margins. For a better understanding on the structure and evolution of the ECCM, a NWeSE trending onshore-offshore seismic profile was recently carried out there using controlled source wideangle and passive broadband seismic experiments in combination. This 1050-km-long seismic profile transects the East China Sea Continental Shelf Basin (CSB), Zhemin Volcanic Belt, Lower Yangtze Block, and southern North China Craton from East China Sea to continental East China. Preliminary results, such as crustal reflected and refracted phases and P-wave receiver functions, show a good quality of the seismic data and tentatively delineate some first-order characteristics of the crustal structure of the ECCM. Expectably, more detailed crustal seismic velocity and geometric structures along the profile can be constructed by a further processing of the seismic data, and enable continuous and detailed comparisons of the crustal structure and inherent nature among different blocks, combined with other existing seismic profiles in the study region. And these further studies will provide reliable constraints on some controversial geologic issues, such as the origin of CSB, the contacting boundaries and collisional processes among Cathaysian Block, Yangtze and North China cratons.

Acta Geologica Sinica - English Edition, 2019

Seismological Research Letters, 2016

The tectonic processes that formed the Tibetan plateau have been a significant topic in earth sci... more The tectonic processes that formed the Tibetan plateau have been a significant topic in earth science, but images of the subducting Indian continental lithosphere (ICL) are still not clear enough to reveal detailed continental collision processes. Seismological methods are the primary ways to obtain images of deep crust and upper-mantle structures. However, previous temporary seismic stations have been unevenly distributed over central Tibet. The Institute of Geology and Geophysics, Chinese Academy of Sciences, has initiated a 2D broadband seismic network in central Tibet across the Bangong-Nujiang suture to fill in gaps among earlier north-south linear profiles for the purpose of detecting the lateral variation of the northern end of the subducting ICL. The health status for each station has been checked at each scheduled service trip. The noise level analysis shows a quiet background in central Tibet, with low cultural noise. Preliminary earthquake locations indicate that they are crustal and broadly distributed rather than only occurring along major faults, suggesting a diffused deformation in the conjugated strike-slip fault zone. Preliminary receiver function analysis shows a complicated crust with significant east-west lateral variations.

Earth and Planetary Science Letters, 2015

West-east extension is a prominent tectonic feature of southern and central Tibet despite ongoing... more West-east extension is a prominent tectonic feature of southern and central Tibet despite ongoing northsouth (N-S) convergence between India and Eurasia. Knowledge of deep structure beneath the N-S trending rifts is key to evaluating models proposed for their origin, including gravitational collapse, oblique convergence along the arcuate plate boundary, and mantle upwelling. We model direct S and Moho-reflected SsPmp phases at teleseismic distances to constrain variations in crustal thickness across the major rifts crossed by a ∼900-km long, WE broadband array in the Lhasa Terrane. Crustal thicknesses are ∼70-80 km. However, Moho depth decreases by ∼10 km within a horizontal distance of 100 km west of the Yadong-Gulu rift (YGR) and Nyainquentanghla mountains (NQTL). This Moho uplift, taken with deep, extensional focal mechanisms and reduced seismic velocity in the upper mantle, suggests that asthenospheric upwelling has significantly contributed to the pattern of extension across the YGR and NQTL. The ∼100-km separation between surface rift and Moho uplift is likely enabled by partial decoupling across a ductile middle crust.

Earth and Planetary Science Letters, 2014

The Tibetan Plateau is formed by continuing convergence between Indian and Asian plates since ∼50... more The Tibetan Plateau is formed by continuing convergence between Indian and Asian plates since ∼50 Ma, involving more than 1400 km of crustal shortening. New seismic data from western Tibet (the TW-80 experiment at 80 • E) reveal segmentation of lower crustal structure by the major sutures, contradicting the idea of a mobile lower crust that flows laterally in response to stress variations. Significant changes in crustal structure and Moho depth occur at the mapped major tectonic boundaries, suggesting that zones of localized shear on sub-vertical planes extend through the crust and into the upper mantle. Converted waves originating at the Moho and at a shallower discontinuity are interpreted to define a partially eclogitized layer that extends 200 km north of the Indus-Yarlung Suture Zone, beneath the entire Lhasa block at depths of between 50 and 70 km. This layer is thinner and shallower to the north of the Shiquanhe Fault which separates the northern Lhasa block from the southern part, and the degree of eclogitization is interpreted to increase northward. The segmentation of the Tibetan crust is compatible with a shortening deformation rather than shear on horizontal planes. Unless the Indianplate mantle lithosphere plunges steeply into the mantle beneath the Indus-Yarlung suture, leaving Indian-plate crust accreted to the southern margin of Tibet, then it too must have experienced a similar shortening deformation.

Chinese Journal of Geophysics, 2004

Based on the finite difference inversion and ray inversion method, the crust and upper mantle str... more Based on the finite difference inversion and ray inversion method, the crust and upper mantle structure along the Zhefang-Binchuan and Menglian-Malong wide-angle seismic profiles, both of which are located in Yunnan province, are imaged using the geophysical data of travel-time, amplitude ratio and Bouguer gravity anomalies. Thus some new recognitions about the geodynamics and the seismotectonic environment are derived. The crust thickness along the Zhefang-Binchuan profile is 35∼46km, and that of the Menglian-Malong profile is 33∼44.5km. The geometry of the Moho interface looks like that given by Hu H X et al. The P wave velocity on the top of the mantle beneath some places is relatively low and the variation range of the velocity is very large, which may indicates that the Yunnan region is a typical area of active tectonics. Moreover, there exits a prominent consistency between the shallow and deep structures, which implies that the activity of shallow material always has a deep background. The velocity structure of Zhefang-Binchuan profile indicates that there exists a large low velocity anomaly which penetrates the whole crust to the east of the Nujiang fault exposed on the ground, and this possibly associated with the upwelling of the deep material. The characteristic of the large faults which are the borders between some first order tectonic units can also be derived from the both velocity structure profiles: the Red River fault is a hyper-fault that cuts the lithosphere, the Nujiang fault cuts deeply in the crust and even stretches downward into the top of the upper mantle, yet the Changning-Shuangjiang fault has a listric shape with a small dip angle, which may suggest that its incision depth is not very deep. The large earthquakes took place in Yunnan province always have a relationship with the large and deep faults that stretches into the upper mantle. Some earthquakes with shallow focal depths are generally located at the converge positions of different faults within the upper-middle crust or the places where the velocity contours on the belt between the high and low velocity anomaly blocks are crooked. It is estimated that these locations are favorable to the accumulation of energy and regional stress.

$Research paper thumbnail of Crustal structure across the Three Gorges area of the Yangtze platform, central China, from seismic refraction/wide-angle reflection data$

Tectonophysics, 2009

We present active-source seismic data recorded along a 300 km-long profile across the Three Gorge... more We present active-source seismic data recorded along a 300 km-long profile across the Three Gorges area of the western Yangtze platform, central China. From west to east, the profile crosses the Zigui basin, Huangling dome and Jianghan basin. The derived crustal P-wave velocity structure changes significantly across the Tongchenghe fault that lies at the transition from the Huangling dome to the Jianghan basin. West of the Tongchenghe fault, beneath the Zigui basin and the Huangling dome, we observe a~42 km thick crust of relatively low average velocity (6.3-6.4 km/s). In contrast, east of the Tongchenghe fault, beneath the Jianghan basin, the crust is only 30 km thick and has a high average velocity (6.6-6.7 km/s). A west-east variation in crustal composition along the Tongchenghe fault is also inferred. West of the fault, P-wave velocities suggest a felsic composition with an intermediate layer at the base of the crust, whilst, east of the fault, felsic, intermediate, and mafic crustal layers are apparent. Our results suggest that the crust beneath the Jianghan basin has been thinned by rifting, accompanied by intrusion of the lower crust by mafic dikes and sills. The west-to-east division of the crust in the Three Gorges area coincides with first-order geophysical contrasts in gravity, topography, crustal and lithospheric thickness.