Ocean waves interact with the solid Earth, generating two dominant signals called microseisms, which carry information about energy exchange between different Earth systems. Here, we show that 6C (three-component translation and three-component rotation) observations are able to resolve their seasonal azimuthal variations. We employ the rotational motions retrieved by a small seismic array at the Pinon Flat Observatory (PFO) to investigate the two dominant microseismic sources: primary (10-20s) and secondary (3-10s) microseisms. The primary microseismic Rayleigh waves show strong seasonal variations as expected, whereas the secondary microseismic Rayleigh waves show slight seasonal changes. In contrast, we find that secondary microseismic Love waves exhibit considerable seasonality. This discrepancy from the secondary microseismic Rayleigh waves provides us with new insights into the generation mechanism of Love waves. In addition, the results suggest that rotational motions of primary microseisms retrieved by the seismic array are more sensitive to atmospheric pressure-induced ground deformation.

A document by Le Tang. Click on the document to view its contents.

In the past few years, the remarkable progress of commercially operated spacecrafts, the success with reusable rocket engines, as well as the international competition to explore space, has led to a substantial acceleration of activities in the design and preparation of ambitious future lunar missions. In the search for ice and/or cavities imaging the shallow subsurface structure is of vital importance. Hereby, previous studies have shown that seismic interferometry is a promising method to investigate the subsurface properties from passive lunar data. In this study, we want to evaluate the potential of this method further by examining the required duration of seismic measurements and the influence of scattering on the Green´s function retrieval. Therefore, we applied seismic interferometry to both measured Apollo 17 data and synthetic data. Our findings indicate that, under optimal conditions, a few hours of data are sufficient when using the method of time-scaled phase-weighted stack (ts-PWS). However, this strongly depends on the inter-station distance, the orientation towards the principal noise sources, and the timing of the measurement during the lunar cycle. Additionally, we were able to reproduce the measured data using numerical simulations in 2D. The synthetic results show that scattering effects clearly influence the Green´s function extraction, especially for larger station distances.

The estimation of crustal structure and thickness is instrumental in understanding the formation and evolution of terrestrial planets. Initial planetary missions with seismic instrumentation on board face the additional challenge of dealing with seismic activity levels that are only poorly constrained a priori. For example, the lack of plate tectonics on Mars leads to low seismicity which could in turn hinder the application of many terrestrial data analysis techniques. Here we propose using a joint inversion of receiver functions and apparent incidence angles, which contain information on absolute S-wave velocities of the subsurface. Since receiver function inversions suffer from a velocity depth trade-off, we in addition exploit a simple relation which defines apparent S-wave velocity as a function of observed apparent P-wave incidence angles to constrain the parameter space. We then use the Neighbourhood Algorithm for the inversion of a suitable joint objective function. The resulting ensemble of models is then used to derive uncertainty estimates for each model parameter. In preparation for analysis of data from the InSight mission, we show the application of our proposed method on Mars synthetics and sparse terrestrial data sets from different geological settings using both single and multiple events. We use information theoretic statistical tests as a model selection criteria and discuss their relevance and implications in a seismological framework.