EAR-PF: Are large earthquakes like small earthquakes? Using synthetic earthquakes to resolve discrepancies in observations of earthquake stress drop magnitude-invariance

詹姆斯·尼利博士被授予NSF EAR博士后奖学金，以评估小地震和大地震是否以同样的方式释放能量。这项工作将在芝加哥大学与美国地质调查局的Sunny Park博士和Annemarie Baltay博士合作进行。较大的地震比较小的地震释放更多的能量，但地震如何释放能量还没有被很好地理解，尽管对地震学家理解地震过程以及至关重要的地震造成的地震危险有着重要的影响。具体地说，给定地震释放能量的方式至少在一定程度上决定了震动的强度(这反过来应该告知建筑安全标准等)。利用计算机模拟，尼利博士将检验有关地震如何释放能量的假设，并评估从小地震中获得的见解是否能帮助我们更好地理解较罕见的大地震带来的危险。此外，尼利博士将致力于一项倡议，以促进伊利诺伊州议员和该州研究人员之间的知识共享关系。在这个项目中，尼利博士将研究地震应力下降--地震导致断层上的应力下降--是否具有震级不变性的问题。地震应力降被认为可以控制破坏建筑物的高频震动的水平，并可能提供对地震破裂动力学的洞察。一些研究表明，地震应力降随震级的变化是恒定的，而另一些研究则表明，地震应力降随震级而有系统地变化。由于地震学家无法直接测量应力降，他们无法将估计值与真实值进行比较，因此不知道哪种方法最准确。尼利博士将通过生成一个具有已知应力降的合成地震的大型数据集来解决这个问题，然后将四种常用的应力降估计方法应用于该数据集。为了模拟真实的地震数据，尼利博士将产生不同于应力降方法假设的简单地震模型的地震，并检查应力降估计值与真实值的匹配程度。尼利博士将确定哪种应力降方法最准确，然后检查真实地震的大型数据集，以确定应力降是否为震级不变。如果应力降震级不变是真的，地震学家可以测量一个地区过去小地震的应力降，以洞察未来大地震的应力降和潜在的震动水平。但如果应力降震级不变性是错误的，那么地震学模型--因此，包括建筑规范在内的政策准备--可能是错误的，需要进行重大修改。除了这一压力下降分析，尼利博士还将致力于扩大科学单页倡议(SOPI)，这是一个位于伊利诺伊州的项目，研究生和博士后研究人员向州立法者提供对科学主题的简短分析。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Dr. James Neely has been awarded an NSF EAR Postdoctoral Fellowship to assess whether small and large earthquakes release energy in the same way. This work will be conducted at the University of Chicago in collaboration with Dr. Sunny Park and Dr. Annemarie Baltay of the U.S. Geological Survey. Larger earthquakes release more energy than smaller earthquakes, but how earthquakes release that energy is not as well understood, despite having important implications for seismologists’ understanding of earthquake processes and, crucially, the seismic hazards that earthquakes pose. Specifically, the way that a given earthquake releases energy determines, at least in part, how strong the shaking will be (which should, in turn, inform building safety standards, etc.). Using computer simulations, Dr. Neely will examine assumptions about how earthquakes release energy and assess whether insights from small earthquakes can help us better understand the hazards posed by rarer, large earthquakes. Additionally, Dr. Neely will work on an initiative to foster knowledge-sharing relationships between Illinois state legislators and researchers within the state.In this project, Dr. Neely will examine the question of whether earthquake stress drop—the decrease in stress along a fault due to an earthquake—is magnitude-invariant. Earthquake stress drop is thought to control the levels of high-frequency shaking that damages buildings, and it may provide insight into earthquake rupture dynamics. Some studies suggest that earthquake stress drop is constant with earthquake magnitude, while others indicate that it varies systematically with magnitude. Because seismologists cannot directly measure stress drop, they cannot compare estimates to the true value, so it is not known which methods are most accurate. Dr. Neely will overcome this issue by generating a large dataset of synthetic earthquakes with known stress drops and then apply four commonly used stress drop estimation methods to this dataset. To simulate real earthquake data, Dr. Neely will generate earthquakes that differ from the simple earthquake models assumed by the stress drop methods and examine how well the stress drop estimates match the true values. Dr. Neely will identity which stress drop method is most accurate and then examine a large dataset of real earthquakes to determine whether stress drop is or is not magnitude-invariant. If stress drop magnitude-invariance is true, seismologists can measure the stress drops of a region’s past small earthquakes to gain insight into the stress drops, and potential shaking levels, of future large earthquakes. But if stress drop magnitude-invariance is false, then seismological models—and as a result policy preparations, including building codes—for this future shaking may be wrong and need major revisions. In addition to this stress drop analysis, Dr. Neely will work to expand the Science One-Pager Initiative (SOPI), an Illinois-based program where graduate students and post-doctoral researchers provide short analyses of scientific topics to state legislators.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.