| Citation: |
Kong H D，Liu R F，Bian Y J，Liu W. 2024. Determination of the radiated seismic energy for M≥6.0 earthquakes in the Qinghai-Xizang Plateau. Acta Seismologica Sinica，46（3）：442−457. DOI: 10.11939/jass.20220174
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This study focuses on the radiated seismic energy of earthquakes with a magnitude of 6.0 or greater in Qinghai-Xizang Plateau of China, a region known for its seismic activity due to its unique tectonic setting. Radiated seismic energy, predominantly carried by highfrequency body waves, is a critical parameter that reflects the dynamic rupture process of an earthquake and complements the static characteristics described by seismic moment and moment magnitude. The accurate measurement of the radiated seismic energy is essential for a comprehensive understanding of earthquake dynamics, emergency response, and disaster assessment. The research utilized self-developed software to measure the radiated seismic energy of shallow earthquakes with a moment magnitude （MW） above 6.0 that occurred in QinghaiXizang Plateau since 1990. The study involved 34 earthquakes and aimed to analyze the energy release patterns in the region. It will help us to enhance our understanding of energy release patterns and their implications for seismic hazard assessment.
Introduction
The Qinghai-Xizang Plateau, often referred to as the “Roof of the World”, is not only a significant geographical feature but also a critical area for the study of seismic activity due to its location at the convergence of multiple tectonic plates. The region’s seismicity is influenced by the ongoing collision and compression of the Indian Plate with the Eurasian Plate, leading to a high potentiality for earthquake occurrences. The accurate measurement and analysis of radiated seismic energy are crucial for the potential hazards assessment posed by earthquakes, emergency response strategies forewarning, and guidance on the development of resilient infrastructure.
Methodology
The study employed a self-developed software to measure the radiated seismic energy of shallow earthquakes with a moment magnitude （MW） above 6.0. The software operates on the principles of point-source modeling and integrates the seismic moment rate spectrum over a specific frequency range to calculate the radiated energy. The methodology incorporates corrections for geometric spreading and frequency-dependent attenuation, ensuring the reliability and accuracy of the measurements. Data from the Incorporated Research Institutions for Seismology （IRIS） and the Global Seismic Network （GSN） were utilized to provide a robust dataset for the analysis.
Results
The research findings reveal several key insights into the radiated seismic energy and energy release patterns in the Qinghai-Xizang Plateau:
1） Stability and reliability of measurements: The radiated energy measurements for the 34 selected earthquakes were found to be stable and reliable, showing a high degree of consistency with that of the IRIS database. This validation confirms the effectiveness of the self-developed software in accurately determining radiated seismic energy.
2） Diversity in energy release: A significant variation in the energy release was observed between earthquakes, even those with similar MW and epicentral locations. For instance, the Garze and Nyima earthquakes, both with a moment magnitude of 6.4, exhibited substantial differences in their radiated energy and energy magnitude （Me）, underscoring the importance of considering both static and dynamic characteristics of seismic sources.
3） Regional characteristics of energy-to-moment ratio: The study identified distinct regional characteristics in the energy-to-moment ratio, with an average ratio （1.90×10−5） for Qinghai-Xizang Plateau which is 1.6 times higher than the global average. This suggests that earthquakes in this region are more energetically efficient, potentially leading to greater seismic hazards. A regional characteristic in the distribution of the energy-to-moment ratio was identified, with the eastern part of Qinghai-Xizang Plateau exhibiting a higher average ratio （2.25×10−5） than the western part （1.62×10−5）. This regional variation is believed to be linked to the geological structure background, indicating that radiated seismic energy can reflect the regioral geological state.
4） Mechanism-dependent energy release: The energy-to-moment ratio was found to be dependent on the focal mechanism of the earthquake, with strike-slip earthquakes exhibiting higher ratios compared to dip-slip earthquakes. This relationship provides valuable insights into the tectonic processes underlying seismic activity in the region. The study also found that within the same region, there is a significant range in the energy-to-moment ratio （from 5.03×10−6 to 4.80×10−5）, reflecting differences in energy release processes on various faults. The research concludes that the measurement of both energy magnitude and moment magnitude is necessary for fully understanding the source characteristics of an earthquake. The findings contribute to a better understanding of the potential destructiveness of earthquakes in Qinghai-Xizang Plateau and provide valuable insights for earthquake emergency response and disaster mitigation efforts in the region.
5） Geological significance: The regional variation in the energy-to-moment ratio appears to correlate with the underlying geological structure, indicating that the radiated seismic energy can serve as an indicator of the geological state and stress accumulation levels in the region.
Discussion
The research findings underscore the complexity of seismic energy release in Qinghai-Xizang Plateau and the need for a comprehensive assessment of earthquake hazards. The identification of regional characteristics in the energy-to-moment ratio provides valuable insights into the potentiality for seismic risk and the underlying tectonic processes. The research also highlights the importance of considering both the static （seismic moment and moment magnitude） and dynamic （radiated energy and energy magnitude） aspects of earthquakes for a more thorough understanding of their hazards.
The energy release patterns observed in this study have significant implications for the development of seismic hazard maps and the implementation of risk mitigation strategies. The higher energy release efficiency observed in Qinghai-Xizang Plateau suggests that earthquakes in this region may pose a greater threat to human settlements and infrastructure, necessitating enhanced preparedness and response capabilities.
Conclusion
The comprehensive analysis of radiated seismic energy in Qinghai-Xizang Plateau presented in this study contributes to a more nuanced understanding of earthquake dynamics in this seismically active region. The findings have significant implications for seismic hazard assessment and disaster mitigation strategies. By revealing the regional variations in energy release and their relationship with geological structures, this research aids in the development of targeted approaches to earthquake risk management in Qinghai-Xizang Plateau.
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