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Passive seismic analyses are a key technology for the exploration and monitoring of subsurface reservoirs. Searching for alternative resources in the framework of the energy transition is creating a surge for identifying as many potential sites as possible suitable for geothermal exploitation. The Lower Rhine Embayment, at the western border of North Rhine-Westphalia in Germany, is an extensional system with a very high potential for geothermal exploitation. The area experiences moderate but continuous natural seismicity. Here, we report on a passive seismic dataset recorded with 48 seismic stations centred at and around Eschweiler–Weisweiler (https://doi.org/10.14470/MO7576467356, Finger et al., 2022). Background seismic noise levels are high at this site due to high levels of anthropogenic noise and thick unconsolidated sedimentary layers. The final station layout is a compromise between targeted network design and suitably quiet locations. We show that the network design allows for the application of state-of-the-art methods including waveform-based source location methods and ambient-noise velocity imaging methods.

Abstract We report observations of Rayleigh waves that orbit around Mars up to three times following the S1222a marsquake. Averaging these signals, we find the largest amplitude signals at 30 and 85 s central period, propagating with distinctly different group velocities of 2.9 and 3.8 km/s, respectively. The group velocities constraining the average crustal thickness beneath the great circle path rule out the majority of previous crustal models of Mars that have a >200 kg/m3 density contrast across the equatorial dichotomy between northern lowlands and southern highlands. We find that the thickness of the Martian crust is 42–56 km on average, and thus thicker than the crusts of the Earth and Moon. Considered with the context of thermal evolution models, a thick Martian crust suggests that the crust must contain 50%–70% of the total heat production to explain present‐day local melt zones in the interior of Mars.

Abstract We have modeled the high‐frequency seismogram envelopes of the large event S1222a and four recently identified near impacts recorded by the InSight mission by introducing a stratification of velocity and attenuation into a multiple‐scattering approach. We show that a simple conceptual model composed of a strongly diffusive, weakly attenuating layer overlying a transparent medium captures the essential features of the observed envelopes. The attenuation profiles reveal that the minimal extension of heterogeneities at depth is of the order of 20 km in the vicinity of InSight and 60 km on the path to S1222a. We interpret this result as an indication that the Martian crust as a whole is at the origin of the strong scattering. Our heterogeneity model suggests that the sources of a number of distant Very‐high‐Frequency seismic events are shallow and located to the south or in close vicinity of the Martian dichotomy.

Abstract The shallow crustal structure of Mars records the evolutionary history of the planet, which is crucial for understanding the early Martian geological environment. Until now, seismic constraints on the Martian crust have come primarily from the receiver functions (RFs). However, analysis of the Mars RFs did not focus on the shallow structure (1–5 km) so far due to the limitation of the signal‐to‐noise ratio at high frequencies for most events. Here, we take advantage of the S1222a and six other marsquakes, which exhibit high signal‐to‐noise ratios, to probe the shallow structure of Mars. We observe a converted S‐wave at approximately 1 s after the direct P‐wave in the high‐frequency P‐wave RFs. This suggests a discontinutity at 2‐km depth between highly fractured and more coherent crustal materials.

Abstract Prior to the 2018 landing of the InSight mission, the InSight science team proposed locating Marsquakes using multiple orbit surface waves, independent of seismic velocity models, for events larger than MW4.6. The S1222a MW4.7 of 4 May 2022 is the largest Marsquake recorded and the first large enough for this method. Group arrivals of the first three orbits of Rayleigh waves are determined to derive the group velocity, epicentral distance, and origin time. The mean distance of 36.9 ± 0.3° agrees with the Marsquake Service (MQS) distance based on body wave measurements of 37.0 ± 1.6°. The origin time from surface waves is systematically later than the MQS origin time by 20 s. Backazimuth estimation is similar to body wave estimations from MQS although suggesting a shift to the south. Backazimuth estimates from R2 and R3 are more scattered, but do show clear elliptical motion.

We invert Rayleigh wave ellipticity curves extracted from ambient seismic vibrations at the InSight landing site to resolve, for the first time on Mars, the shallow subsurface to around 200 m depth. While our seismic velocity model is largely consistent with the expected stacks of lava flows, we find a seismic low velocity zone at about 30 to 75 m depth that we interpret as a sedimentary layer sandwiched between layers of basalt flows.

Using a novel pattern recognition algorithm, up to 50,000 new seismic events have been detected on the Moon over an 8-month period from newly rediscovered Apollo 17 seismic data. These events occur periodically, with a sharp double-peak at sunrise and a broad single-peak at sunset. Due to the proximity of the events to the Apollo 17 site, and the diurnal timing of the peaks, we interpret these events to be thermally-driven – caused by rapid heating and cooling of materials at the surface of the Moon as the sun passes overhead. Locating the source of these detected events is ongoing, and could be valuable for identifying which surface features are the source of the events. This will lead to a better understanding of the conditions under which they occur. This body of work is particularly relevant to studies of lunar regolith breakdown, because thermal seismic events at the surface of the Moon are an expression of an active degradational process. Keywords: Apollo, Thermal moonquake, Moonquake catalog, Regolith production

Seismological constraints obtained from receiver function (RF) analysis provide important information about the crust and mantle structure. Here, we explore the utility of the free-surface multiple of the P-wave (PP) and the corresponding conversions in RF analysis. Using earthquake records, we demonstrate the efficacy of PPs-RFs before illustrating how they become especially useful when limited data is available in typical planetary missions. Using a transdimensional hierarchical Bayesian deconvolution approach, we compute robust P-to-S (Ps)- and PPs-RFs with InSight recordings of five marsquakes. Our Ps-RF results verify the direct Ps converted phases reported by previous RF analyses with increased coherence and reveal other phases including the primary multiple reverberating within the uppermost layer of the Martian crust. Unlike the Ps-RFs, our PPs-RFs lack an arrival at 7.2 s lag time. Whereas Ps-RFs on Mars could be equally well fit by a two- or three-layer crust, synthetic modeling shows that the disappearance of the 7.2 s phase requires a three-layer crust, and is highly sensitive to velocity and thickness of intra-crustal layers. We show that a three-layer crust is also preferred by S-to-P (Sp)-RFs. While the deepest interface of the three-layer crust represents the crust-mantle interface beneath the InSight landing site, the other two interfaces at shallower depths could represent a sharp transition between either fractured and unfractured materials or thick basaltic flows and pre-existing crustal materials. PPs-RFs can provide complementary constraints and maximize the extraction of information about crustal structure in data-constrained circumstances such as planetary missions., (© 2021. The Authors.)

A planet's crust bears witness to the history of planetary formation and evolution, but for Mars, no absolute measurement of crustal thickness has been available. Here, we determine the structure of the crust beneath the InSight landing site on Mars using both marsquake recordings and the ambient wavefield. By analyzing seismic phases that are reflected and converted at subsurface interfaces, we find that the observations are consistent with models with at least two and possibly three interfaces. If the second interface is the boundary of the crust, the thickness is 20 ± 5 kilometers, whereas if the third interface is the boundary, the thickness is 39 ± 8 kilometers. Global maps of gravity and topography allow extrapolation of this point measurement to the whole planet, showing that the average thickness of the martian crust lies between 24 and 72 kilometers. Independent bulk composition and geodynamic constraints show that the thicker model is consistent with the abundances of crustal heat-producing elements observed for the shallow surface, whereas the thinner model requires greater concentration at depth., (Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

The Seismic Experiment for Interior Structure (SEIS) of the InSight mission to Mars, has been providing direct information on Martian interior structure and dynamics of that planet since it landed. Compared to seismic recordings on Earth, ground motion measurements acquired by SEIS on Mars are made under dramatically different ambient noise conditions, but include idiosyncratic signals that arise from coupling between different InSight sensors and spacecraft components. This work is to synthesize what is known about these signal types, illustrate how they can manifest in waveforms and noise correlations, and present pitfalls in structural interpretations based on standard seismic analysis methods. We show that glitches, a type of prominent transient signal, can produce artifacts in ambient noise correlations. Sustained signals that vary in frequency, such as lander modes which are affected by variations in temperature and wind conditions over the course of the Martian Sol, can also contaminate ambient noise results. Therefore, both types of signals have the potential to bias interpretation in terms of subsurface layering. We illustrate that signal processing in the presence of identified nonseismic signals must be informed by an understanding of the underlying physical processes in order for high fidelity waveforms of ground motion to be extracted. While the origins of most idiosyncratic signals are well understood, the 2.4 Hz resonance remains debated and the literature does not contain an explanation of its fine spectral structure. Even though the selection of idiosyncratic signal types discussed in this paper may not be exhaustive, we provide guidance on best practices for enhancing the robustness of structural interpretations., Competing Interests: Conflict of interest The authors acknowledge there are no conflicts of interested recorded.