Contribution of Buckling to Coseismic Uplift and Long-Term Fold Growth in Active Fold-Thrust Belts

Academic Background

Fold-thrust belts are significant structural units at the foreland of many orogenic belts worldwide, often accompanied by intense seismic activity. Understanding the complex relationships among fault slip, fold growth, and earthquakes is crucial for assessing seismic risks and revealing the connections between long-term topographic growth and short-term coseismic uplift. Traditional research primarily relies on fault-related folding theories, suggesting that fold formation and seismic activity are mainly driven by slip along underlying faults. However, the role of buckling—a mechanism characterized by bed-parallel contraction—in fold growth and seismic activity has long been overlooked. This study, through an investigation of the M5.0 Mangya earthquake that occurred on March 28, 2019, in the Shizigou Anticline of the western Qaidam Basin, reveals for the first time the contribution of buckling to moderate earthquakes and explores its impact on long-term fold growth.

Source of the Paper

This paper was co-authored by Kai Huang, Kejie Chen, Lei Wu, and others from institutions such as the Southern University of Science and Technology, Zhejiang University, and China National Petroleum Corporation. It was published online on October 7, 2024, in the journal Geology, titled “Buckling contributes to both coseismic uplift and long-term fold growth in active fold-thrust belts.” The research was supported by the Guangdong Provincial Key Laboratory of Geophysical High-Resolution Imaging Technology and the National Natural Science Foundation of China.

Research Process and Results

1. Data and Methods

The research team conducted a detailed study of the source mechanism and surface deformation of the Mangya earthquake using 3D seismic imaging data, interferometric synthetic aperture radar (InSAR) analysis, and borehole logging data. The specific workflow is as follows:

• 3D Seismic Imaging: The subsurface structure of the Shizigou Anticline was revealed through 3D pre-stack depth migration seismic data, including the interfaces of Cenozoic strata, boundaries of salt-bearing layers, and the distribution of major faults.
• InSAR Analysis: Surface deformation caused by the earthquake was extracted using two InSAR images, and the optimal source fault geometry was estimated through an elastic inversion model.
• Borehole Data Analysis: Data from drilling rods broken during the earthquake were combined to further validate the source depth and geometric characteristics of the slip surface.

2. Main Results

• Earthquake Mechanism: The study found that the Mangya earthquake was not caused by slip along known faults but by interbed slip due to buckling in the limb of the Shizigou Anticline. This slip occurred at the interface between the salt-bearing layer (Upper Xiaganchaigou Formation) and the overlying clastic layer (Shangganchaigou Formation), with a slip surface depth of 1.8–2.2 km and a slip amount of 470 mm.
• Surface Deformation: InSAR data showed that the coseismic uplift and subsidence were located in the northeastern limb and the core of the Shizigou Anticline, respectively, significantly deviating from the location of long-term fold growth.
• Fold Geometry Changes: 3D seismic imaging revealed along-strike geometric variations in the Shizigou Anticline, transitioning from a broad and gentle anticline in the northwest to a narrow and steep anticline in the southeast. The Mangya earthquake occurred precisely at this geometric transition zone.

3. Discussion and Conclusions

• Seismic Contribution of Buckling: The study demonstrates that buckling can not only trigger moderate earthquakes but also modulate fold geometry through interbed slip. This finding challenges the limitations of traditional fault-related folding models and provides a new perspective for understanding seismic mechanisms in fold-thrust belts.
• Long-Term Fold Growth: Buckling plays a significant role in the long-term growth of the Shizigou Anticline, particularly under the mechanical contrast between the salt-bearing layer and the overlying clastic layer, significantly influencing fold geometry and seismic activity.

Research Highlights

• First Demonstration of Buckling-Induced Earthquakes: This study is the first to prove through an actual earthquake case that buckling can trigger moderate earthquakes, filling a research gap in the field.
• Multidisciplinary Data Integration: The research combines 3D seismic imaging, InSAR analysis, and borehole data, providing a comprehensive understanding of the source mechanism and surface deformation.
• Implications for Seismic Risk Assessment: The results suggest that seismic risk assessment in fold-thrust belts should not rely solely on fault slip models but also consider the contribution of buckling.

Research Value

This study not only deepens the understanding of seismic mechanisms in fold-thrust belts but also provides new theoretical foundations for seismic risk assessment. Furthermore, the importance of buckling in earthquakes and fold growth revealed by this research may apply to other similar tectonic environments globally, such as the Zagros Mountains and the Kuqa Fold-Thrust Belt.

Additional Valuable Information

The research team acknowledged the data support from multiple scholars and institutions, particularly the seismic wave data provided by the Qinghai Earthquake Agency. Additionally, the study received funding from the Guangdong Provincial Key Laboratory and the National Natural Science Foundation of China, highlighting the importance of multi-institutional collaboration in scientific research.