Deep moonquake properties: deciphering stresses and deformation patterns

在1969至1972年间，作为阿波罗太空任务的一部分，五个地震仪被放置在月球的近侧。其中四个台站运行到1977年，形成了月球地震台网。这些月球地震数据为了解月球内部的结构和动力学提供了独特的见解。在地震台网7年的运行期间，记录了一系列地震信号，包括流星体撞击、人为撞击、浅层月震和深部月震。这个项目的重点是深部月震。深部月震与中级地震有显著相似之处。两者都被认为是在抑制脆性破坏的条件下发生的。同样，这两次地震都会在同一小块区域反复发生，也就是所谓的鸟巢。最后，这两起事件的物理机制仍不清楚。了解深部月球地震的震源特性可能有助于洞察地球上发生的过程。深月震还表现出在中级地震中没有观察到的更神秘的行为，包括与固体月球潮汐有关的强烈周期性。然而，潮汐应力和月震发生之间的关系并不简单，月震对一系列不同的轨道特征做出了反应。目前尚不清楚这种周期性是否表明是潮汐应力还是构造应力驱动了月球地震。尽管深月震占了月球地震目录的近一半，但其震源机制仍未得到很好的解释，也很少有研究集中在破裂的性质上。该项目的重点将是研究同震应力降与潮位相之间的关系。已经有一系列研究评估了作用于深部地震的潮汐应力，但它们不能充分描述震源的应力下降。进一步分析深月震巢的来源特性，可以深入了解月球内部的破裂过程，以及破裂与潮汐应力之间的关系。通常应用于地面数据的一系列地震技术将进行适当修改，并应用于阿波罗数据。这将包括光谱拟合、经验格林函数和台间相干性分析，以确定以前未研究过的深部月亮地震的破裂程度、应力降和辐射能量。该项目属于天文学和空间科学研究领域的月球科学主题。

Between 1969 and 1972, five seismometers were placed on the near side of the moon as part of the Apollo space missions. Four of these stations operated until 1977, forming the lunar seismic network. This lunar seismic data provides unique insights into the structure and dynamics of the lunar interior. A range of seismic signals were recorded during the 7-year operation of the seismic network, including meteoroid impacts, artificial impacts, shallow moonquakes and deep moonquakes. This project will focus on deep moonquakes. There are notable similarities between deep moonquakes and intermediate earthquakes. Both are thought to occur at conditions that inhibit brittle failure. Likewise, both quakes repeatedly arise in the same small area, referred to as nests. Finally, the physical mechanism of both events remains unclear. Understanding the source properties of deep moonquakes may provide insight into the processes occurring on Earth. Deep moonquakes also exhibit more enigmatic behaviours that are not observed in intermediate earthquakes, including a strong periodicity linked to the solid Moon tides. However, the relationship between tidal stress and moonquake occurrence is not simple, and moonquakes respond to a range of different orbital characteristics. It is still unclear if this periodicity indicates whether tidal or tectonic stresses drive moonquakes. Despite deep moonquakes making up nearly half of the moonquake catalogue, their source mechanisms are still poorly explained, and few studies have focused on the properties of rupture. The focus of this project will be to investigate the relationship between coseismic stress drop and tidal phase. There has been a range of studies evaluating the tidal stress acting on deep earthquakes, but they do not adequately describe the stress drop of the seismic source. Further analysis of the source properties of deep moonquake nests could provide insight into the rupture processes in the moon's interior and the relationship between rupture and tidal stresses. A range of seismic techniques commonly applied to terrestrial data will be modified appropriately and applied to the Apollo data. This will include spectral fitting, empirical Green's Functions and inter-station phase coherence analysis to determine the rupture extent, stress drop and radiated energy of previously unstudied deep moonquakes. This project falls within the Lunar Science topic of the Astronomy and Space Science research area.