In the bustling waters off the coast of South China, a silent dance of tectonic plates has been unfolding, one that could reshape our understanding of seismic activity and its implications for the energy sector. Researchers, led by Hu Yi from the Key Laboratory of Ocean and Marginal Sea Geology at the South China Sea Institute of Oceanology, Chinese Academy of Sciences, have uncovered a fascinating story of fault activity and its potential link to a historic earthquake.
Using high-resolution seismic reflection profiles, the team delved into the offshore segment of the Littoral Fault Zone (LFZ) near Nan’ao Island. What they found was a ~19 km-wide graben, a depressed block of land bordered by seaward- and landward-dipping normal faults. These faults, along with fault-propagation folds and growth faults reaching the seafloor, paint a picture of a region that is far from geologically dormant.
“Despite the regional NW–SE compressional stress regime, we observed active normal faulting,” explains Hu Yi. This finding is significant as it implies that vertical stress, rather than the expected horizontal stress, is the dominant driving force in this region. The team’s forward modeling of the fault-propagation fold revealed three discrete episodes of normal dip-slip displacement, each around 20 meters, separated by prolonged quiescent periods. This suggests episodic fault activity and seismic-scale strain accumulation, a potential recipe for significant seismic events.
The implications for the energy sector are profound. Understanding the mechanisms behind intraplate seismicity can help in assessing seismic hazards and mitigating risks for offshore energy exploration and production. The study proposes a gravitational seismic model driven by upper crustal loading to explain both the fault motion and the down-draw tsunami observed during the 1918 M7.3 earthquake. This model could provide valuable insights for designing safer and more resilient offshore structures.
The research, published in the journal *Remote Sensing* (translated from Chinese as “遥感”), offers new insights into intraplate seismogenic mechanisms and associated hazards along the South China coast. As Hu Yi puts it, “Our findings challenge the traditional views and open up new avenues for research in this field.”
This study not only sheds light on the complex interplay of geological forces but also underscores the importance of continuous monitoring and research in understanding and mitigating seismic risks. For the energy sector, this means a more informed approach to offshore operations, potentially leading to safer and more sustainable energy exploration and production. As we continue to push the boundaries of our understanding, the dance of the tectonic plates off the South China coast serves as a reminder of the dynamic and ever-changing nature of our planet.