Fang Li

China Geological Survey

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Xiaohong Meng

China University of Geosciences (Beijing)

Jun Wang

China University of Geosciences (Beijing)

Bo Liang

China National Petroleum Corporation (China)

Fusen Xiao

China National Petroleum Corporation (China)

Ting Yang

Southern University of Science and Technology

Qinglin Liu

Sichuan Agricultural University

Meng Zhang

Chinese Academy of Fishery Sciences

Jian Wu

Southern Medical University

Hailong Liu

Tsinghua University

Haofei Yan

China Geological Survey

Cooperative Institutions

China University of Geosciences (Beijing)

Chinese Academy of Sciences

China Geological Survey

Research Institute of Petroleum Exploration and Development

China University of Geosciences

China University of Petroleum, Beijing

Schlumberger (British Virgin Islands)

Peking University

China National Petroleum Corporation (China)

China Earthquake Administration

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Robust joint adaptive multiparameter waveform inversion with attenuation compensation in viscoacoustic media

Geophysics (2024)

Chao Li Guochang Liu Fang Li Zhiyong Wang

Full-waveform inversion (FWI) has been proven as an effective method to estimate subsurface parameters by iteratively reducing the data residual between the predictions and the observations. Nevertheless, FWI is greatly dependent on the initial model, and a poor initial model will lead to an incorrect solution. Furthermore, owing to the anelasticity of the earth, seismic waves will attenuate during propagation, which results in an attenuated gradient and makes the convergence rate of FWI even worse in viscoacoustic medium. Commonly, multiparameter (e.g. velocity and Q) waveform inversion can be used to mitigate these problems. Benefiting from the theory of Q-compensated wavefield propagation, we develop a Q-compensated joint multiparameter waveform inversion method to weaken the nonlinearity of the FWI objective function, which enables it to cope with challenges related with attenuation-induced gradient energy loss and cycle skipping simultaneously. We refer to our Q-compensated joint multiparameter FWI scheme as QJMFWI. The main contributions of QJMFWI are as follows: (1) given the difficulty associated with the estimation of velocity and Q simultaneously in viscoacoustic media, QJMFWI provides a straightforward waveform inversion method for velocity and Q model construction, by which we can obtain velocity and Q information with improved accuracy and resolution; and (2) compared with conventional FWI methods, QJMFWI relaxes the requirement for a good initial velocity and Q model, which can avoid trapping into local minima. Numerical and field data examples demonstrate that QJMFWI is an effective method to invert for accurate subsurface parameters in viscoacoustic media.

10.1190/geo2022-0663.1

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Citations (4)

The crustal structure of the Lomgmenshan fault zone and its implications for seismogenesis: New insight from aeromagnetic and gravity data

Hai Yang Shengqing Xiong Qiankun Liu Fang Li Zhiye Jia

Abstract. Although many geophysical models have been proposed in the Longmenshan fault zone (LFZ) and its surrounding areas, the deep structure of the seismic gap and its constraint of the Wenchuan and Lushan earthquakes remain uncertain. Based on the compiled aeromagnetic data and Bouguer gravity data, we have tried to create a more detailed and visible magnetic and density model beneath the LFZ using 2D forward modeling and 3D inversion. The research shows that structure heterogeneities are widely distributed beneath the LFZ. The earthquake epicenters show high magnetic anomalies and the edge of high Bouguer gravity anomalies that consist of rigid blocks where apt to accumulate stress. However, the seismic gap shows low magnetic anomalies and transition of Bouguer gravity anomalies related to a weak zone. The Sichuan Basin has two NE-trending banded high magnetic blocks extending beneath the LFZ that firmly support the crust of the Sichuan Basin was downward subduction toward the LFZ. More importantly, the basement subducts to approximately 33 km west of the Wenchuan-Maoxian fault with a low dip angle beneath the middle segment of the LFZ, whereas the distance decreases to approximately 17 and 19 km under the southern segment. Thus, the crust of the Sichuan Basin beneath the middle segment extends farther than that beneath the southern segment with the seismic gap as the transition zone. Therefore, we propose that the structural heterogeneity of the basement on the western margin of the Sichuan Basin may be the main reason for the different focal mechanisms and geodynamics of the Wenchuan and Lushan earthquakes.

Basement

10.5194/egusphere-2023-1119

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Swin Transformer for Seismic Denoising

IEEE Geoscience and Remote Sensing Letters (2024)

Fang Li Hailong Liu 伟王 Jianwei Ma

Seismic noise suppression is an important preprocessing stage for obtaining high-quality seismic signals, which are crucial for seismic exploration. Deep learning methods have achieved excellent results in the field of seismic signal processing. Currently, many researchers have used convolutional neural networks for seismic signal denoising, but few have used Transformer model for related research. We apply the swin transformer model, an improved version of transformer model based on the self-attention mechanism, to denoise two-dimensional seismic data. The swin transformer calculates self-attention within shifted windows, effectively improving information exchange within the different windows. It performs well in suppressing random seismic noise to improve the signal-to-noise ratio.

Seismic Noise

10.1109/lgrs.2024.3358234

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The longitudinal characters of the wave propagating through random media

Lianlin Li Fang Li

The longitudinal characteristics of a wave propagating through random media have been studied by the Huygens principle and generalizing a transform proposed by T.H. Legg (see Proc.IEEE AP, vol.6, p.1230-5, 2003). It is found that the coherence between the double frequencies and the moment of the random field of any order can be obtained by the longitudinal measurement.

Longitudinal field

10.1109/aprasc.2004.1422400

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Computer Application in Geosciences: Imaging of the Subsurface by Structural Coupled Inversion of Potential Field Data

Applied Mechanics and Materials (2014)

Jun Wang Xiao Hong Meng Fang Li Jun Zhou

With the continuing growth in influence of near surface geophysics, the research of the subsurface structure is of great significance. Geophysical imaging is one of the efficient computer tools that can be applied. This paper utilize the inversion of potential field data to do the subsurface imaging. Here, gravity data and magnetic data are inverted together with structural coupled inversion algorithm. The subspace (model space) is divided into a set of rectangular cells by an orthogonal 2D mesh and assume a constant property (density and magnetic susceptibility) value within each cell. The inversion matrix equation is solved as an unconstrained optimization problem with conjugate gradient method (CG). This imaging method is applied to synthetic data for typical models of gravity and magnetic anomalies and is tested on field data.

Synthetic data

Potential field

10.4028/www.scientific.net/amm.644-650.2670

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Constraint

Springer eBooks (2004)

Alain Connes Bernard de Wit Antoine Van Proeyen Sergey Gukov Rafael Hernandez

Derivative (finance)

Covariant derivative

10.1007/1-4020-4522-0_132

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Improved curvature gravity gradient tensor with principal component analysis and its application in edge detection of gravity data

Journal of Applied Geophysics (2015)

Jun Wang Xiaohong Meng Fang Li

10.1016/j.jappgeo.2015.04.013

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Citations (22)

Time‐shift Angle Domain Common Image Gathers for Multiwave

Qizhen Du Fang Li Jianmeng Sun

On the vector wavefields imaging problem, the elastic imaging condition can be extended to non‐zero time and space shifts. Through the introduction of space‐time‐shift imaging condition to elastic Kirchhoff migration, the P‐waves and PS converted waves time‐shift offset domain common image gathers (TSODCIGs) and time‐shift angle domain common image gathers (TSADCIGs) can be quickly extracted. These new gathers contain more useful seismic wavefields information than the angle gathers produced by space‐shift or time‐ shift imaging condition. Based on the multiwave TSODCIGs and TSADCIGs, the accuracy of migration velocity analysis (MVA) for multiwave will be improved. Furthermore, this paper operates directly on vector wavefields which removes a requirement for wavefields separation in the preprocessing, and the method can realize joint MVA for multiwave. The superiority of the time‐shift angle domain common image gathers is shown by comparing the results of TSODCIGs and TSADCIGs.

Seismic migration

Time shifting

10.1190/1.3513167

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Citations (1)

Land seismic in difficult terrain and complex geology: a case study from the Jungar Basin, northwest China

First Break (2015)

Lv Huantong Xianmin Li Jiang Zaichao Long Zhang Lixin Xiao

Huantong Lv, Xianmin Li, Zaichao Jiang, Long Zhang, Lixin Xiao, Jian Wu, Yan Liang, Bo Liang, Meng Zhang, Rong Li, Fang Li, Sherman Yang, Peter van Baaren, Thomas Heesom and Hongping Xiao describe how a high-density, point-source, point-receiver approach can address statics and noise challenges of rough mountain thrust-zone topography and deliver high-quality imaging results. High-density, single-component, point-receiver land acquisition geometries are increasingly displacing ‘conventional’ acquisition designs that are based on long-standing practices of sparse sampling, low channel counts and an analog approach to noise attenuation via multi-sensor arrays. Over the past decade, dense point-receiver – often complemented by point vibroseis or dynamite source – geometries have been proven in diverse locations including Australia, the Middle East, North and South America, Russia and China. Two case histories from China have recently been published that demonstrate the success of the approach in solving geological challenges encountered in the exploration and development phases of challenging oilfield environments in the Sichuan Basin (Xiao et al., 2014) and the Ordos Basin (Wang et al., 2014).

Seismic vibrator

Dynamite

Environmental geology

Economic geology

Gemology

Statics

10.3997/1365-2397.33.1.79053

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Citations (2)

Aseismic slip and cascade triggering process of foreshocks leading to the 2021 Mw 6.1 Yangbi Earthquake

Xiao Ge Liu Wen Bin Xu Zi Long He Fang Li Z. Chen

<p>Understanding the nature of foreshock evolution is important for earthquake nucleation and hazard evaluation. Aseismic slip and cascade triggering processes are considered to be two end-member precursors in earthquake nucleation processes. However, to perceive the physical mechanisms of these precursors leading to the occurrence of large events is challenging. In this study, the relocated 2021 Yangbi earthquake sequences are observed to be aligned along the NW-SE direction and exhibit several evident spatial migration fronts towards the hypocenters of large events including the mainshock. An apparent static Coulomb stress increase on the mainshock hypocenter was detected, owing to the precursors. This suggests that the foreshocks are manifestations of aseismic transients that promote the cascade triggering of both the foreshocks and the eventual mainshock. The temporal depth of the brittle-ductile transition exhibit deepening, followed by shallowing during the foreshock-mainshock-aftershock sequence. By jointly inverting both InSAR and GNSS data, we observe that the mainshock ruptured on a blind vertical fault with a peak slip of 0.8 m. Our results demonstrate that the lateral crustal extrusion and lower crustal flow are probably the major driving&#160; mechanisms of mainshock. Additionally, the potential seismic hazards on the Weixi-Weishan and Red River faults deserve further attention</p>

Hypocenter

10.5194/egusphere-egu22-6917

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Citations (1)