How the Cross-Faults Influence the Dynamic Rupture Process: Insights from the Littoral Fault Zone, China

ABSTRACT The Littoral fault zone (LFZ), located on the northern continental margin of the South China Sea, is a seismogenic structure controlling seismic hazard, having experienced multiple earthquakes with moment magnitudes of 7.5 along its eastern and western segments. However, despite sharing a similar tectonic environment, the central section of the LFZ at the Pearl River Estuary (PRE) is a seismic gap capable of large earthquakes. Therefore, the central section of LFZ (PRE) is considered to be a potential location for strong earthquakes. This fault segment is adjacent to the densely populated and economically developed Guangdong–Hong Kong–Macao Greater Bay area (GBA). Despite this, research on the seismic rupture process in the PRE section of LFZ is still scarce. This study utilizes dynamic rupture modeling to simulate Mw 7.5–8.0 scenario earthquakes of LFZ in the PRE and two northwest-trending cross-faults, the Xijiang fault and Qi’ao Guishan fault. By varying background stress, friction, and nucleation location assumptions, we simulate an earthquake rupture scenario and the associated ground motions. The results indicate that the Xijiang fault is more susceptible to being dynamically triggered than the Qi’ao Guishan fault. Among the six nucleation locations tested, three promote rupture on the Xijiang fault, with rupture patterns and trigger times varying with location. Other locations tend to rupture only the main northeast-strike faults of the LFZ without activating the cross-faults. Notably, the northwest-trending cross-faults extend onto land, potentially exacerbating the seismic hazard and risk to the neighboring regions compared to a rupture of the LFZ alone. This study provides a solid and reliable scientific basis for evaluating the regional seismic hazard and disaster reduction efforts.