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Present-Day Tectonic Stress Evolution in Southern Yunnan Based on Focal Mechanisms
Wenjie Fan1,2, Ye Zhu1,3, Yingfeng Ji1,3
1State Key Laboratory of the Tibetan Plateau Earth System, Environment and Resources (TPESER), Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China.
Sensors (Basel, Switzerland)
|September 9, 2023
Summary
Tectonic extrusion near the eastern Himalayas causes frequent earthquakes in southern Yunnan. This study reveals complex earthquake focal mechanisms and a clockwise rotation of stress axes, influenced by block interactions.
Area of Science:
- Geophysics
- Tectonics
- Seismology
Background:
- Tectonic extrusion bypassing the eastern Himalayan syntaxis increases stress instability and earthquake frequency in southern Yunnan, China.
- The precise stress field and earthquake focal mechanism evolution in this region remain poorly understood.
Purpose of the Study:
- To determine the present-day regional tectonic stress field in southern Yunnan.
- To analyze the relationship between earthquake focal mechanisms and stress evolution in the region.
Main Methods:
- Calculated focal mechanisms for earthquakes (Magnitude Local 2.5 or greater) using a modified grid point test method (January 2009–June 2023).
- Inverted historical earthquake focal mechanism solutions to obtain the regional tectonic stress field.
Main Results:
- Observed complex and diverse seismic focal mechanisms, predominantly strike-slip, followed by normal and reverse fault events.
- Identified a clockwise rotation of maximum and minimum principal stress axes from northeast to southwest.
- Found stress deflection at block boundaries, indicating influence from inter-block interactions.
Conclusions:
- The stress field in southern Yunnan is shaped by the interaction of tectonic blocks, particularly the Sichuan-Yunnan block and the South China block.
- A decreasing northward-to-southward trend in block movement speed and increasing R-value in the Lamping-Simao block suggest reduced compressive stress.
- Higher compressive stress and smaller R-values in the South China block indicate stronger extrusion, potentially due to resistance from the Sichuan-Yunnan block.
Keywords:
focal mechanism solutiongrid point test methodsouthern Yunnan regionstress fieldstress shape ratio (R-value)More Related Videos
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