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- Title
Stresses in the Lunar Interior: Insights From Slip Directions in the A01 Deep Moonquake Nest.
- Authors
Turner, A. R.; Hawthorne, J. C.; Gaddes, M.
- Abstract
We probe the present‐day stresses in the lunar interior by examining the slip directions of moonquakes in the A01 nest. In this nest, some deep moonquakes appear to slip "backwards," in the opposite direction to other events. We assess whether these changes in slip direction result from a spatial variation in the tectonic stress or from a temporal variation in the tidal stress. To test these two options, we first show that a dominant tectonic stress implies deep moonquakes can only slip in one direction: forwards and backwards, while a dominant tidal stress could allow moonquakes to slip in more directions: any combination of forwards, backwards, left, and right. Then we look for the number of slip directions; we separate the deep moonquake waveforms into slip directions using a principal component analysis technique. We find two slip directions present in the A01 deep moonquake nest. The moonquakes slip in a variety of directions as time evolves. This observation implies that the tidal stresses drive deep moonquakes. Additionally, these results place a new constraint on the magnitude of the tectonic stresses at depth; they must be smaller than the modeled tidal stress of ∼0.1 MPa. Plain Language Summary: The stresses that act in the lunar interior are not well known but are important for improving our knowledge of the interior of the Moon and its evolution. Deep inside the Moon, at depths between 700 and 1,200 km, moonquakes occur approximately every 27 days, suggesting they are influenced by Earth's time‐varying gravitational pull: by Earth‐induced tides. Are the tides responsible for generating deep moonquakes? Or is long‐term tectonic stress, in addition to the tidal stresses responsible? Using the waveforms of these deep moonquakes, we aim to determine the relative magnitudes of the tidal and tectonic stresses acting deep in the lunar interior. To do this, we look at the directions in which the moonquakes slip. We observe that deep moonquakes slip in a variety of different directions, which can only be caused by tidal stresses. Since these deep moonquakes are generated by the tides, this observation reveals that tectonic stresses in the lunar interior must be smaller than 0.1 MPa. Key Points: We examine why some moonquakes appear to slip in the opposite direction from the othersUsing moonquake waveforms, we infer that slip direction changes through time because of tidal loadingThe results indicate that the tidal stress, with magnitude 0.1 MPa, is larger than the tectonic stress
- Subjects
PRINCIPAL components analysis; TIME pressure; SPATIAL variation; ACCIDENTAL falls
- Publication
Journal of Geophysical Research. Planets, 2022, Vol 127, Issue 12, p1
- ISSN
2169-9097
- Publication type
Article
- DOI
10.1029/2022JE007364