Characterizing variations in magnitude-frequency distribution and b-value using relative magnitudes

使用相对幅度表征幅度频率分布和 b 值的变化

• 批准号: 2315814
• 负责人: Yihe Huang
• 金额: $ 25.92万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-09-01 至 2026-08-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2315814&HistoricalAwards=false
• 关键词: Characterizing; variations; magnitude; frequency; distribution

The “magnitude-frequency distribution” (MFD) of earthquakes describes how often earthquakes of different magnitudes occur in a particular region, with large earthquakes being far less frequent than small ones. The proportion of small to large earthquakes, which scientists obtain from the MFD, is represented using the “b-value”. This quantity is used to infer from recordings of frequent, small earthquakes how often rarer, large earthquakes are expected, and to flag regions that may be at risk for major earthquakes. Robust estimates of b-value require enormous collections (or ‘catalogues’) of earthquake data, in which all magnitudes were estimated the same way. Dr. Huang and her team will characterize the variations in MFD and b-value by recalculating earthquake magnitudes for two catalogs: one from southern California (where most earthquakes occur naturally) and one from Oklahoma (where most earthquakes are triggered by injection of wastewater from oil and gas production). Using the new MFDs, she and her team will assess how b-values may vary in these two regions during foreshocks, large earthquakes, and aftershocks; and (where applicable) operation of nearby wastewater injection wells. This project will provide vital information for quantitative seismic hazard analysis, which is required for updating building codes and other public safety measures; and will advance scientific understanding of earthquake physics. The PI and her group will also develop and share a free online educational tool that will enable students, teachers, and the general public to access and analyze seismograph data, and estimate earthquake magnitudes.Current MFD and b-value analyses are strongly affected by magnitude uncertainties of small earthquakes and mixed magnitude types in earthquake catalogs. Recent studies have shown that MFDs can deviate from exponential distribution at low-magnitude ranges and b-value can vary considerably with the magnitude of completeness due to the discontinuity of MFDs in high-resolution catalogs. The project will produce earthquake catalogs with consistent magnitudes for small and large earthquakes using recalculated magnitude differences, which will enable a systematic analysis of the spatial-temporal variations in MFDs and b-value in Southern California and Oklahoma. After the magnitudes are recalculated, the project will investigate the possible deviations of MFDs from exponential distribution and their effects on the estimation of b-value. The project will also quantify whether there are significant changes of b-values during foreshocks, mainshocks, and aftershocks as well as the operation of injection wells for induced seismicity. The systematic MFD and b-value analysis together will produce more robust parameters for seismic hazard analysis and unveil whether b-value variations manifest changes in fault stress state.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

地震的“震级-频率分布”（MFD）描述了不同震级的地震在特定地区发生的频率，大地震的频率远远低于小地震。科学家从MFD中获得的小地震到大地震的比例使用“b值”表示。这个数量被用来从频繁的小地震的记录中推断出预计发生更罕见的大地震的频率，并标记可能有大地震风险的地区。b值的稳健估计需要大量的地震数据集合（或“目录”），其中所有震级都以相同的方式估计。黄博士和她的团队将通过重新计算两个目录的地震震级来表征MFD和b值的变化：一个来自南加州（大多数地震自然发生），另一个来自俄克拉荷马州（大多数地震是由石油和天然气生产的废水注入引发的）。使用新的MFD，她和她的团队将评估在前震，大地震和余震期间，这两个地区的b值如何变化;以及（在适用的情况下）附近废水注入威尔斯井的操作。该项目将为定量地震危险分析提供重要信息，这是更新建筑法规和其他公共安全措施所必需的;并将促进对地震物理学的科学认识。PI和她的小组还将开发和共享一个免费的在线教育工具，使学生、教师和公众能够访问和分析地震仪数据，并估计地震震级。目前的MFD和b值分析受到小地震震级不确定性和地震目录中混合震级类型的强烈影响。最近的研究表明，MFD可以偏离指数分布在低震级范围和b值可以有很大的变化，由于在高分辨率目录的MFD的不连续性的完整性的大小。该项目将使用重新计算的震级差为小地震和大地震产生具有一致震级的地震目录，这将使系统分析南加州和俄克拉荷马州的MFD和b值的时空变化成为可能。在重新计算量值后，该项目将调查MFD与指数分布的可能偏差及其对b值估计的影响。该项目还将量化前震、主震和余震期间b值是否有显著变化，以及诱发地震活动的注入威尔斯井的操作。系统的MFD和b值分析将为地震危险性分析提供更可靠的参数，并揭示b值变化是否表明断层应力状态的变化。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。