The seismogenic structure of strong intraplate earthquakes in Shantou region, South China: Insights from upper crustal shear-wave velocity structure

Abstract

The Shantou region, one of the most seismically active zones of Guangdong Province (South China), has experienced multiple strong earthquakes, including two significant events with magnitudes greater than 7.0 that occurred in 1600 and 1918, respectively. To investigate the seismogenic structures responsible for these major earthquakes and their potential triggering mechanisms, we construct a high-resolution shear-wave velocity model from the surface to ∼15 ​km depth based on a dense nodal seismic array using ambient noise tomography. The model reveals a pronounced low-velocity zone (LVZ) at depths of 2-15 ​km, with a perturbation of −2 to −8%, coinciding with the northwestern extension of the Huanggangshui Fault previously identified in the offshore region. Integrating our results with previous field geological surveys and shallow reflection seismic exploration, we interpret the LVZ as a wide fault zone, potentially comprising multiple fault branches that possibly include two NW-trending faults (i.e., the Rongjiang Fault and the Hanjiang Fault). Notably, the interaction between the Huanggangshui Fault and NE-trending Littoral Fault is suggested to have triggered the 1918 M 7.3 Nan'ao earthquake. Additionally, the 1895 M 6.2 earthquake seems to have occurred at the edge of the LVZ near the Rongjiang Fault, a possible branch of the Huanggangshui Fault, further supporting the association between this structure and seismic activity. These findings imply that the LVZ may represent a region of concentrated tectonic stress, making it a potential site for future strong earthquakes. Consequently, this area should be prioritized in seismic hazard assessments. This study provides valuable insights into the seismogenic characteristics of the Shantou region and contributes to improving seismic hazard evaluations in South China.

Keywords

Intraplate earthquakes / Nan'ao earthquake / Shear-wave velocity / Ambient noise tomography / Dense seismic array

CRediT authorship contribution statement

Lue Yang: Writing - original draft, Data curation, Formal analysis, Investigation, Validation, Visualization. Lun Li: Writing - review & editing, Funding acquisition, Conceptualization, Data curation, Formal analysis, Investigation, Project administration, Resources, Supervision, Validation. Xiuwei Ye: Writing - review & editing, Investigation. Jinming Zhang: Data curation. Jialong He: Data curation. Yuan Gao: Data curation. Pengfei Li: Data curation. Yu He: Data curation. Ziwei Li: Data curation.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Author agreement and acknowledgment

All authors agree for this publication. The research was funded by the Pearl River Talent Program of Guangdong, China [grant number 2017ZT07Z066], the Innovation Group Project of the South Marine Science and Engineering Guangdong Laboratory (Zhuhai) [grant number 311021003]. Xiuwei Ye acknowledges the support from the Guangdong Science and Technology programmer [grant No. 2023A1111120028], the National Key Research and Development Program of China [grant No. 2023YFC3008602].

We thank Editor Prof. Baoshan Wang and two anonymous reviewers for their constructive comments and suggestions. Seismic data processing was conducted using the Seismic Analysis Code (http://ds.iris.edu/ds/nodes/dmc/software/downloads/sac/, last accessed September 2, 2024, Goldstein and Snoke, 2005). The figures were generated with the Generic Mapping Tools (GMT) (https://www.generic-mapping-tools.org/, last accessed September 2, 2024, Wessel et al., 2013). The cross-correlations were calculated with SeisNoise.jl (https://github.com/JuliaSeismo/SeisNoise.jl, last accessed September 2, 2024, Clements and Denolle, 2021). Rayleigh wave phase and group velocity dispersion curves were extracted using the AFTAN program (http://ciei.colorado.edu/Products/, last accessed September 2, 2024, IRIS DMS Product, 2012). The shear-wave velocity model was inverted using the DSurfTomo program (https://github.com/HongjianFang/DSurfTomo, last accessed September 2, 2024, Fang et al., 2015).

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