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Meteoroid impacts shape planetary surfaces by forming new craters and alter atmospheric composition. During atmospheric entry and impact on the ground, meteoroids excite transient acoustic and seismic waves. However, new crater formation and the associated impact-induced mechanical waves have yet to be observed jointly beyond Earth. Here we report observations of seismic and acoustic waves from the NASA InSight lander’s seismometer that we link to four meteoroid impact events on Mars observed in spacecraft imagery. We analysed arrival times and polarization of seismic and acoustic waves to estimate impact locations, which were subsequently confirmed by orbital imaging of the associated craters. Crater dimensions and estimates of meteoroid trajectories are consistent with waveform modelling of the recorded seismograms. With identified seismic sources, the seismic waves can be used to constrain the structure of the Martian interior, corroborating previous crustal structure models, and constrain scaling relationships between the distance and amplitude of impact-generated seismic waves on Mars, supporting a link between the seismic moment of impacts and the vertical impactor momentum. Our findings demonstrate the capability of planetary seismology to identify impact-generated seismic sources and constrain both impact processes and planetary interiors.

NASA’s InSight (Interior exploration using Seismic Investigations, Geodesy and Heat Transport) mission landed in Elysium Planitia on Mars on 26 November 2018. It aims to determine the interior structure, composition and thermal state of Mars, as well as constrain present-day seismicity and impact cratering rates. Such information is key to understanding the differentiation and subsequent thermal evolution of Mars, and thus the forces that shape the planet’s surface geology and volatile processes. Here we report an overview of the first ten months of geophysical observations by InSight. As of 30 September 2019, 174 seismic events have been recorded by the lander’s seismometer, including over 20 events of moment magnitude Mw= 3–4. The detections thus far are consistent with tectonic origins, with no impact-induced seismicity yet observed, and indicate a seismically active planet. An assessment of these detections suggests that the frequency of global seismic events below approximately Mw= 3 is similar to that of terrestrial intraplate seismic activity, but there are fewer larger quakes; no quakes exceeding Mw= 4 have been observed. The lander’s other instruments—two cameras, atmospheric pressure, temperature and wind sensors, a magnetometer and a radiometer—have yielded much more than the intended supporting data for seismometer noise characterization: magnetic field measurements indicate a local magnetic field that is ten-times stronger than orbital estimates and meteorological measurements reveal a more dynamic atmosphere than expected, hosting baroclinic and gravity waves and convective vortices. With the mission due to last for an entire Martian year or longer, these results will be built on by further measurements by the InSight lander.

For the first time, we measured the ellipticity of direct Rayleigh waves at intermediate periods (15–35 s) on Mars using the recordings of three large seismic Martian events, including S1222a, the largest event recorded by the InSight mission. These measurements, together with P‐to‐s receiver functions and P‐wave reflection times, were utilized for performing a joint inversion of the local crustal structure at the InSight landing site. Our inversion results are compatible with previously reported intra‐crustal discontinuities around 10 and 20 km depths, whereas the preferred models show a strong discontinuity at ∼37 km, which is interpreted as the crust‐mantle interface. Additionally, we support the presence of a shallow low‐velocity layer of 2–3 km thickness. Compared to nearby regions, lower seismic wave velocities are derived for the crust, suggesting a higher porosity or alteration of the whole local crust. As never before on Mars, we measured the characteristics of seismic waves traveling along the Martian surface that carry information about the crustal structure at the InSight site. We combined these measurements with two other local‐scale independent observations to derive a consolidated model for the crust underneath the InSight lander. Our results suggest a Martian crust with 4 layers and, particularly, one thin layer of about 2 km thickness close to the surface. The crust‐mantle discontinuity was found at ∼37 km depth, where the sharpest change in seismic wave velocity is observed. Overall, the seismic wave velocities of the local Martian crust at the InSight site are lower than those derived in other regions on Mars, which suggests a higher porosity or local alteration. Rayleigh waves ellipticity was measured between periods 15–35 s at the InSight landing site using large seismic events, including S1222aA 4‐layer crust, including a shallow low‐velocity layer, is required to explain the ellipticity, receiver functions and P‐wave lag timesLow crustal velocities are derived for the InSight site, which may be due to high porosity or heavy alteration at local scale Rayleigh waves ellipticity was measured between periods 15–35 s at the InSight landing site using large seismic events, including S1222a A 4‐layer crust, including a shallow low‐velocity layer, is required to explain the ellipticity, receiver functions and P‐wave lag times Low crustal velocities are derived for the InSight site, which may be due to high porosity or heavy alteration at local scale

On 4 May 2022, the seismometer on Mars observed the largest marsquake (S1222a) during its operation. One of the most specific features of S1222a is the long event duration lasting more than 8 hr, in addition to the clear appearance of body and surface waves. As demonstrated on Earth, by modeling a long‐lasting and scattered surface wave with the radiative transfer theory under the isotropic scattering condition, we estimated the scattering and intrinsic quality factors of Mars (Qsand Qi). This study especially focused on the frequency range between 0.05–0.09 Hz, where Qsand Qihave not been constrained yet. Our results revealed that Qi= 1,000–1,500 and Qs= 30–500. By summarizing the Martian Qiand Qsestimated so far and by comparing them with those of other celestial bodies, we found that, overall, the Martian scattering and absorption properties showed Earth‐like values. Since February 2019, NASA's InSight (Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport) has been conducting quasi‐continuous seismic observation for more than three years. The seismic data from Mars has contributed significantly to a better understanding of the interior structure and the seismicity of the red planet. On 4 May 2022 (1222 Martian days after landing), another key event occurred, called S1222a. The event showed the largest seismic moment release (magnitude 4.7) and extremely long duration (>8 hr) with intense seismic scattering. As demonstrated on Earth, the long‐lasting scattered waves are useful for retrieving information about the structural heterogeneity within a planet. In this study, by applying the radiative transfer theory—which considers the energy transportation from the seismic source to the observation point—to Mars, we evaluated the energy decay rate due to seismic scattering and energy absorption by a medium. By comparing our results with those of other solid bodies, we found that the Martian scattering and absorption features were closer to the terrestrial ones than to the lunar ones. We modeled the scattering effect of the largest marsquake (S1222a) using radiative transfer theory on a spherical MarsThe inversion revealed that the intrinsic and scattering quality factors below 0.1 Hz are 1,000–1,500 and 30–500, respectivelyWe summarized the Martian quality factors derived so far and found that they are relatively Earth‐like rather than Moon‐like We modeled the scattering effect of the largest marsquake (S1222a) using radiative transfer theory on a spherical Mars The inversion revealed that the intrinsic and scattering quality factors below 0.1 Hz are 1,000–1,500 and 30–500, respectively We summarized the Martian quality factors derived so far and found that they are relatively Earth‐like rather than Moon‐like

Attenuation and phase velocity of seismic waves propagating in cubic polycrystalline aggregates with elongated grains are computed from the Rayleigh (low-frequency) to the geometrical optics (high-frequency) regime using a spectral function approach. In this study, we consider the case of perfectly aligned ellipsoidal grains with randomly oriented crystallographic axes. Such anisometric medium exhibits transverse isotropy. The frequency dependence of both phase velocity and scattering attenuation for quasi-compressional (q- P ), quasi-shear vertical (q- S V ) and quasi-shear horizontal (q- S H ) waves are examined in detail. The attenuation depends on the effective volume of the grain in the Rayleigh regime, on the grain dimension in the direction of propagation in the stochastic regime, and is inversely proportional to the grain size in the direction of propagation in the geometrical optics regime. The phase velocity exhibits a much more complex pattern depending on the grain shape and frequency. In particular, the fast/slow direction of propagation is not systematically aligned with the direction of low/high attenuation. The anisotropy in velocity typically varies from 1% in the Rayleigh regime to a few percents at the transition from the stochastic to the geometrical optics regime. Even for a highly anisotropic cubic iron crystals, q- S V and q- S H attenuations differ by at most 12% in the Rayleigh-to-stochastic transition regime but are equal in other frequency ranges. The q- S V and q- S H phase velocities, from the Rayleigh to the stochastic regime, differ by at most 1%. Anisotropy induced by geometrical effects should therefore be detectable in laboratory or seismological data. [ABSTRACT FROM AUTHOR]

Abstract: Imagining a medium composed of an arbitrary distribution of point-like heterogeneities, we study the reconstruction of scattered waves in Green''s function derived from the cross-correlation function of waves excited by random noise sources of which the distribution is stationary and homogeneous. We show that the reconstruction process is intimately related to generalized forms of the optical theorem. The role of absorption in the formulation of the theorem is discussed. The reconstruction of multiply-scattered arrivals from the cross-correlation of two random wavefields is demonstrated to all orders of scattering for the simple case of two point scatterers, through application of the optical theorem for a single scatterer. In the case of N point scatterers, the cross-correlation of two Green''s functions is expressed in the form of Feynman-like diagrams. The wavepaths that contribute to the reconstruction of an arbitrary multiply-scattered arrival of Green''s function are identified. Repeated application of the generalized optical theorem, formulated as a diagrammatic rule, demonstrates the destructive interference between all spurious multiply-scattered arrivals. [Copyright &y& Elsevier]

Monitoring changes of seismic properties at depth can provide a first‐order insight into Earth’s dynamic evolution. Coda wave interferometry is the primary tool for this purpose. This technique exploits small changes of waveforms in the seismic coda and relates them to temporal variations of attenuation or velocity at depth. While most existing studies assume statistically homogeneous scattering strength in the lithosphere, geological observations suggest that this hypothesis may not be fulfilled in active tectonic or volcanic areas. In a numerical study we explore the impact of a non‐uniform distribution of scattering strength on the spatio‐temporal sensitivity of coda waves. Based on Monte Carlo simulation of the radiative transfer process, we calculate sensitivity kernels for three different observables, namely travel‐time, decorrelation, and intensity. Our results demonstrate that laterally varying scattering properties can have a profound impact on the sensitivities of coda waves. Furthermore, we demonstrate that the knowledge of the mean intensity, specific intensity, and energy flux, governed by spatial variation of scattering strength, is key to understanding the decorrelation, travel‐time, and scattering kernels, respectively. A number of previous works on coda wave sensitivity kernels neglect the directivity of energy fluxes by employing formulas extrapolated from the diffusion approximation. In this work, we demonstrate and visually illustrate the importance of the use of specific intensity for the travel‐time and scattering kernels, in the context of volcanic and fault zone setting models. Our results let us foresee new applications of coda wave monitoring in environments of high scattering contrast. To monitor the evolution of the dynamic Earth, seismologists use a part of the seismic record called “coda,” which is composed of waves that have bounced multiple times off heterogeneities of the crust. The coda is extremely sensitive to weak perturbations of propagation properties induced by Earth’s tectonic and volcanic activity. The correct physical modeling of coda waves is therefore key to unravel the rich information encoded in their waveforms. A limitation of current seismological monitoring techniques is the neglect of strong lateral variations of coda waves propagation properties documented by geological observations. Our work focuses specifically on this aspect. We provide a complete theoretical and numerical framework to model and understand the spatial and temporal sensitivity of coda waves to medium perturbations in complex geological settings. Using simple but realistic models of a fault zone and a volcano, we illustrate the profound impact of non‐uniform scattering properties on the coda wave sensitivity, which in turn determines the ability of seismologists to correctly retrieve the magnitude and location of physical changes in the crust. Our results let us foresee new applications of coda wave monitoring in environments of high scattering contrast, such as volcanic and fault zone settings. A non‐uniform distribution of scattering strength can have a profound impact on the spatio‐temporal sensitivity of coda wavesWe illustrate this using Monte Carlo simulations for models with either a volcanic, fault zone, or two half‐spaces settingThe mean intensity, specific intensity, and energy flux, is key to understanding the decorrelation, travel‐time, and scattering kernels, respectively A non‐uniform distribution of scattering strength can have a profound impact on the spatio‐temporal sensitivity of coda waves We illustrate this using Monte Carlo simulations for models with either a volcanic, fault zone, or two half‐spaces setting The mean intensity, specific intensity, and energy flux, is key to understanding the decorrelation, travel‐time, and scattering kernels, respectively

The seismometer deployed on the surface of Mars as part of the InSight mission (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) has recorded several hundreds of marsquakes in the first 478 sols after landing. The majority of these are classified as high‐frequency (HF) events in the frequency range from approximately 1 to 10 Hz on Mars' surface. All the HF events excite a resonance around 2.4 Hz and show two distinct but broad arrivals of seismic energy that are separated by up to 450 s. Based on the frequency content and vertical‐to‐horizontal energy ratio, the HF event family has been subdivided into three event types, two of which we show to be identical and only appear separated due to the signal‐to‐noise ratio. We show here that the envelope shape of the HF events is explained by guided Pg and Sg phases in the Martian crust using simple layered models with scattering. Furthermore, the relative travel times between these two arrivals can be related to the epicentral distance, which shows distinct clustering. The rate at which HF events are observed varies by an order of magnitude over the course of one year and cannot be explained by changes of the background noise only. The HF content and the absence of additional seismic phases constrain crustal attenuation and layering, and the coda shape constrains the diffusivity in the uppermost shallow layers of Mars. The high‐frequency events are the most commonly observed class of marsquakes by the InSight mission. As the frequency content and signal shape over time is different from seismic events (i.e., events that excite elastic waves traveling in the subsurface such as earthquakes, impacts, or explosions) observed both on Earth and the Moon, these were not immediately recognized as signals of seismic origin. This paper shows that these signals can be explained by distant shallow small quakes together with wave propagation effects in the Martian crust. This interpretation opens the possibility to use these signals to probe the material properties of the crust and raises the question which physical process causes these events. InSight’s seismometers have recorded several hundreds of events at frequencies between 1 and 10 HzThe envelopes of these events can be explained by seismic waves guided in the crust over significant distancesThis observation helps to constrain the elastic properties of the shallow structure InSight’s seismometers have recorded several hundreds of events at frequencies between 1 and 10 Hz The envelopes of these events can be explained by seismic waves guided in the crust over significant distances This observation helps to constrain the elastic properties of the shallow structure

Abstract: This erratum corrects typographical errors in the paper “Reconstruction of multiply-scattered arrivals from the cross-correlation of waves excited by random noise sources in a heterogeneous dissipative medium” by L. Margerin and H. Sato [Copyright &y& Elsevier]