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Joint inversion of ambient noise and gravity to investigate crustal structure and dynamic processes in the southern Sichuan Basin

Li Zhang1 ,  Guiju Wu1* ,  Rugang Xu2 ,  Yufei Xi3 ,  Jiapei Wang1 ,  Fan Wang1
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1 Key Laboratory of Earthquake Geodesy, Institute of Seismology, China Earthquake Administration, Wuhan, Hubei, China
2 Anhui Earthquake Agency, Hefei, Anhui, China
3 Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences, Shijiazhuang, Hebei, China
JSE, 025010143 https://doi.org/10.36922/JSE025010143
Received: 31 December 2025 | Revised: 23 March 2026 | Accepted: 27 March 2026 | Published online: 12 May 2026
© 2026 by the Author(s). This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution 4.0 International License ( https://creativecommons.org/licenses/by/4.0/ )
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Abstract

The southern Sichuan Basin, particularly the Changning area, is characterized by intense tectonic activity and frequent earthquakes. However, crustal structure models derived from different geophysical methods exhibit significant discrepancies, which impede an in-depth understanding of the tectonic evolution and earthquake genesis in this region. In this study, a joint inversion integrating surface-wave dispersion and Bouguer gravity anomaly data is adopted. By employing empirical velocity–density relations, the two datasets are coupled into a unified linearized least-squares inversion framework, in which local optimization is achieved through iterative solving. This approach is utilized to obtain the crustal density structure of the southern Sichuan Basin. The joint inversion results reveal an intracrustal low-density layer in the southern Sichuan Basin, inferred to originate from plastic deformation or partial melting of felsic components at relatively high temperatures. Driven by the topographic pressure gradient, this low-density layer undergoes ductile flow toward the Sichuan Basin. Obstructed by the rigid crust of the Sichuan Basin, the material migrates along both the eastern and western margins of the basin, with a broader eastward migration range. The leading edge of the low-density layer shows a distinct special correspondence with the seismic activity concentration zone in the Changning area, a stress concentration zone jointly shaped by deep material migration and tectonic blocking. This stress accumulation serves as the key controlling factor for the frequent earthquakes in the Changning area.

Keywords
Joint inversion
Seismic tomography
Crustal structure
Changning earthquakes
Funding
This research was supported by the Deep Earth Probe and Mineral Resources Exploration-National Science and Technology Major Project (2025ZD1010201), the National Natural Science Foundation of China (42574074), the Hubei Provincial Natural Science Foundation of China (2025AFB854), and the Scientific Research Fund of the Institute of Seismology, China Earthquake Administration (IS202456377).
Conflict of interest
The authors declare that they have no competing interests.
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