Doyeon Kim

We report the detection by the InSight seismometer of a long-period infrasound wave detected about 5.8 hr after the S1094b impact on Mars, on December 24th, 2021. This is the first observation of a long-period ( T > 10 sec) infrasound signal associated with an impact on Mars. This signal can be modeled by atmospheric normal mode summation and is a long-period thermospheric wave, refracted above 150 km altitude, whose low frequency reduces very strongly the expected attenuation of Martian atmosphere CO2 molecular relaxation. Waveform inversions provide an estimate of the kinetic energy of the S1094b impactor in the range of 1-3 10^13 J (2.4-7.2 kT TNT equivalent), in agreement with previous estimates based on the crater diameter. Most of the excitation is likely related to energy deposition during atmospheric entry and not to the surface explosion. The S1094b event is now associated with three different observations: seismic, infrasound and crater formation, enabling future multi-messenger inversions to better estimate the impactor velocity, mass and density.

Tectonic deformation on stagnant-lid planets reflects the interaction between long-lived lithospheric structures and evolving stress fields. Whether the ancient tectonic fabrics can localise present-day seismic failure under contemporary stress fields remains poorly tested by direct geophysical observations. Here we show that the farside seismic event, S0976a, detected by InSight in the western hemisphere is a marsquake that occurred in Valles Marineris and involved strike-slip faulting in the deep crust. The stress orientation inferred from the focal mechanism is consistent with reactivation of pre-existing fault systems under a present-day stress field shaped primarily by long-term planetary cooling, regional Tharsis-related loading, and surface erosion-related local unloading. These observations provide direct seismic evidence that inherited fault systems on Mars can remain mechanically favourable for reactivation over billion-year timescales, suggesting that slip on deeply rooted faults remains a key mechanism of long-term strain release in a cooling single-lid planet.

Reliable estimates of seismic source size on Mars are critical for interpreting tectonic activity and impact processes, constraining the planet's interior evolution, and informing the design of future Martian seismic experiments. However, because InSight observations are limited to a single station, magnitude estimates cannot rely on empirical averaging of site and path effects as on Earth, and instead depend on comparisons between observed and modeled waveform amplitudes. Consequently, inferred magnitudes are sensitive to assumptions about interior structure, attenuation, and source parametrization. Existing Marsquake Service (MQS) magnitude‐scaling relations were calibrated using pre‐InSight interior models and tectonic source assumptions, potentially biasing magnitude estimates. Here, we reanalyze spectral amplitudes using InSight seismic data and investigate how post‐InSight interior models and source‐dependent parametrization influence inferred moment magnitudes. Using waveform simulations for a suite of 1‐D interior models, we quantify the effects of velocity structure, attenuation, three‐dimensional heterogeneity, and source physics on long‐period magnitude scaling. We introduce separate source representations and scaling relations for marsquakes and impacts. Across the tested post‐InSight models, the shallow crustal structure beneath InSight primarily controls scaling. Recalibrated marsquake magnitudes are lower by approximately 0.5 on average relative to MQS magnitudes, with the reduction varying across plausible shallow structures. Applying impact‐specific scaling brings seismic and crater‐derived estimates into closer agreement, although differences remain for large distant impacts, and the recalibrated magnitudes enable tentative matching of seismic detections to cataloged Martian impact craters. These relations provide site‐specific calibration for InSight observations and tighter constraints on Martian seismicity and impact processes.

Renewed international interest in lunar seismometer deployments requires robust single‐station location approach for the highly scattering Moon's crust. We present an event‐location strategy using major lunar event types recorded by the Apollo seismic network. Frequency‐dependent polarization analysis provides P ‐wave back‐azimuth and incidence, which, combined with S – P differential times, enables event localization despite strong scattering. Artificial impacts with known source locations show that epicenter and depth are recovered within 1‐ uncertainty when signal‐to‐noise ratio (SNR) exceeds 2. Natural events with SNR >2 are likewise consistent with previously reported multi‐station locations, demonstrating robust performance across event types. For all events, azimuthal misfit strongly correlates with SNR and shows no systematic dependence on crustal path length. P ‐wave inclination separates deep moonquake nests from shallow events and provides complementary sensitivity to Apollo‐site regolith thickness and seismic wavespeed. This approach is directly applicable to forthcoming lunar missions.

Mantle plumes beneath major oceanic hot spots appear to be rooted in unusually large structures near the core-mantle boundary, which have markedly reduced seismic wave speeds. The origin of these large ultralow-velocity zones (ULVZs), referred to as mega-ULVZs, remains uncertain partly because of lack of constraints on the relative reduction in shear versus compressional wave speeds ( R _S/P ). This ratio can give clues into the compositional makeup of the mega-ULVZs. Through joint seismic analysis of core-diffracted P and S waves beneath Hawai’i, we constrain the R _S/P of its mega-ULVZ to 1 to 1.3. Mineralogical modeling reveals that iron enrichment via solid iron-rich magnesiowüstite [(Mg,Fe)O] matches this seismic constraint, independent of modeled ULVZ thickness. Enrichment of metallic iron-rich magnesiowüstite likely enhances the thermal conductivity of mega-ULVZs and provides a mechanism to drive localized plume upwelling. Higher reported R _S/P values for smaller ULVZs near subduction zones may therefore indicate different processes at play controlling ULVZ formation across the diverse core-mantle boundary landscape.

China's Chang'E‐4 probe successfully soft‐landed on the lunar far side at Von Kármán crater in January 2019. Onboard, the Lunar Penetrating Radar (LPR) detected subsurface structures and properties such as dielectric permittivity, aiding in our understanding of regolith composition and origin. This study introduces an automatic method for estimating dielectric permittivity using radar diffraction focusing analysis. While developed from traditional seismic analysis, the method is tailored for LPR data by incorporating random noise removal, entropy‐based focusing, and lunar‐specific parameter optimization to address the challenges of noise interference, complex diffraction overlapping and applicability to LPR data. Applied to Chang'E‐4's first 42 lunar‐day data, this method revealed subsurface structure and permittivity distributions. Combined with instantaneous amplitudes, centroid frequencies, and geological features, we present a preferred geological interpretation. Our findings suggest that, after experiencing the latest basaltic magma intrusion and subsequent weathering, the region underwent multiple episodes of high ilmenite content ejecta deposition at a depth of 20–33 m. This was followed by several impacts, leaving craters visible today. Subsequently, the area was overlain by at least two ejecta layers with low ilmenite content at a depth of 13–25 m. Later, two meteoroids struck the paleo‐surface; the larger one created the most prominent irregular crater on the current surface. Thereafter, ejecta from nearby craters such as Finsen and Von Kármán L covered the area, weathering into the current lunar regolith. Our inversion results demonstrate high reliability, align with previous studies and geological context, and can offer methodological and empirical insights for future planetary missions.

A planet’s interior is a time capsule, preserving clues to its early history. We report the discovery of kilometer-scale heterogeneities throughout Mars’ mantle, detected seismically through pronounced wavefront distortion of energy arriving from deeply probing marsquakes. These heterogeneities, likely remnants of the planet’s formation, imply a mantle that has undergone limited mixing driven by sluggish convection. Their size and survival constrain Mars’ poorly known mantle rheology, indicating a high viscosity of 10 ^21.3 to 10 ^21.9 pascal-seconds and low temperature dependence, with an effective activation energy of 70 to 90 kilojoules per mole, suggesting a mantle deforming by dislocation creep. The limited mixing, coupled with ubiquitous, scale-invariant heterogeneities, reflects a highly disordered mantle, characteristic of the more primitive interior evolution of a single-plate planet, contrasting sharply with the tectonically active Earth.

The upper few kilometers of subducting plates govern subduction zones. Direct seismic imaging shows a variety of features there depending on the imaging method used. We compare P‐to‐S mode conversions from the subducting plate interface from teleseismic earthquakes to those from local earthquakes. Seismic signals are examined from 33 seismometers in the Alaska Peninsula region, including several permanent and temporary stations. The timing of the P‐to‐S conversions from local arrivals (local PS; 1–20 Hz signals) convert off an interface on average 8 km shallower than the equivalent teleseismic mode conversion, (teleseismic Ps; 0.05–1 Hz signals). The consistent positive teleseismic conversion is interpreted as the oceanic Moho, placing the local‐PS conversions near the slab surface. Using 2D full waveform modeling, we find that models with a thin low‐velocity layer at the top of the subducting plate containing elongated scatterers are required to reconcile observations at both frequencies. Scattering at high frequencies can be explained by anastomosing shear zones juxtaposing highly variable lithologies along foliation that parallels the plate surface. Local PS timing shows that a low‐velocity layer exists across most of the array with velocities increasing as depth increases, in a manner resembling progressive metamorphism; the base of this layer generates the most prominent teleseismic Ps conversion. What constitutes this layer changes with depth; the layer is likely the metamorphosing oceanic crust at >40 km depth but shallower is better explained as a shear zone comprised of fluids, hydrous minerals, and/or metasediment.

Analysis of conversions between compressional and shear waves is a workhorse method for constraining crustal and lithospheric structure on Earth; yet, such converted waves have not been unequivocally identified in seismic data from the largest events on the Moon, due to the highly scattered waveforms of shallow seismic events. We reanalyze the polarization attributes of waveforms recorded by the Apollo seismic network to identify signals with rectilinear particle motion below 1 Hz, arising from conversions across the crust‐mantle boundary. Delay times of these converted waves are inverted to estimate crustal thickness and wavespeeds beneath the seismometers. Combined with gravimetric modeling, these new crustal thickness tie‐points yield an updated lunar crustal model with an average thickness of 29–47 km. Unlike previous models, ours include explicit uncertainty estimates, offering critical context for future lunar missions, geophysical studies, and predicting 15–36 km crust at Schrödinger and 29–52 km at Artemis III sites.

The properties of the Martian crust, including its thickness, composition, and porosity, provide invaluable constraints on the origin and geological evolution of Mars. Surface-wave observations from seismic events recorded by InSight’s seismometer SEIS (Seismic Experiment for Internal Structure) have provided the best direct constraints on Martian crustal structure to date. However, surface-wave signals have only been unequivocally identified in three low-frequency family events (S1000a, S1094b, and S1222a), limiting our understanding of crustal structure and its heterogeneity. In this study, we identify fundamental-mode Rayleigh-wave signals in two Cerberus Fossae marsquakes (S0235b and S1133c) and invert their group velocity dispersion measurements for shear wavespeed structure along two source–receiver paths in Elysium Planitia. Surface-wave signals are isolated using frequency-dependent polarization analysis, which allows us to filter seismic energy based on particle motion. R1 signals identified in events S0235b and S1133c exhibit retrograde elliptical particle motion, as expected for Rayleigh waves, and yield back azimuths that are compatible with the propagation direction indicated by body waves. We find that the crustal shear wavespeed structure along both minor arc paths is consistent with existing velocity profiles in the northern lowlands, suggesting a relatively uniform composition in the mid-to-lower crust. In addition, our observations of R1, together with weak or absent Rayleigh-wave overtone signals, suggests hypocentral depths of S0235b and S1133c of less than 30 km, placing them in the crust.