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.