# New Impacts on Mars: Unraveling Seismic Propagation Paths Through a Cerberus Fossae Impact Detection

Constantinos Charalambous, W. Thomas Pike, Benjamin Fernando, Natalia Wójcicka, Doyeon Kim, Marouchka Froment, Philippe Lognonné, Savana Woodley, Lujendra Ojha, Valentin Bickel, et al.

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## To cite this version:

Constantinos Charalambous, W. Thomas Pike, Benjamin Fernando, Natalia Wójcicka, Doyeon Kim, et al. New Impacts on Mars: Unraveling Seismic Propagation Paths Through a Cerberus Fossae Impact Detection. Geophysical Research Letters, 2025, 52 (3), pp.044061. 10.1029/2024GL110159. hal-05070598

HAL Id: hal-05070598

https://hal.science/hal-05070598v1

Submitted on 17 May 2025

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# Geophysical Research Letters®

## RESEARCH LETTER

10.1029/2024GL110159

**Key Points:**

* We associate a new 21.5-m Mars impact crater in the tectonically active Cerberus Fossae region with InSight's seismic event, S0794a

* The location derived seismically and via orbital imaging implies the impact's energy traveled significant distances through the mantle

* This challenges previous assumptions of a crustal waveguide, resulting in more distant locations for many high-frequency marsquakes

**Supporting Information:**

Supporting Information may be found in the online version of this article.

**Correspondence to:**

C. Charalambous,  
constantinos.charalambous@imperial.ac.uk

**Citation:**

Charalambous, C., Pike, W. T., Fernando, B., Wójcicka, N., Kim, D., Froment, M., et al. (2025). New impacts on Mars: Unraveling seismic propagation paths through a Cerberus Fossae impact detection. *Geophysical Research Letters*, 52, e2024GL110159. https://doi.org/10.1029/2024GL110159

Received 9 MAY 2024

Accepted 5 DEC 2024

© 2025. The Author(s). This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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## New Impacts on Mars: Unraveling Seismic Propagation Paths Through a Cerberus Fossae Impact Detection

Constantinos Charalambous¹ ID, W. Thomas Pike¹ ID, Benjamin Fernando² ID, Natalia Wójcicka³ ID, Doyeon Kim³ ID, Marouchka Froment⁴ ID, Philippe Lognonné⁵ ID, Savana Woodley⁶ ID, Lujendra Ojha⁷ ID, Valentin T. Bickel⁸ ID, Joseph McNeil⁹ ID, Gareth S. Collins³ ID, Ingrid J. Daubar¹⁰ ID, Anna Horleston¹¹ ID, and Bruce Banerdt¹² ID

¹Department of Electrical and Electronic Engineering, Imperial College, London, UK, ²Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, USA, ³Department of Earth Science and Engineering, Imperial College, London, UK, ⁴NORSAR, Solutions Department, Kjeller, Norway, ⁵Université Paris Cité, Institut de physique du globe de Paris, CNRS, Paris, France, ⁶Open University, Milton Keynes, UK, ⁷Department of Earth and Planetary Sciences, Rutgers, The State University of New Jersey, Piscataway, NJ, USA, ⁸Center for Space and Habitability, University of Bern, Bern, Switzerland, ⁹Natural History Museum, London, UK, ¹⁰Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, RI, USA, ¹¹School of Earth Sciences, University of Bristol, Bristol, UK, ¹²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

**Abstract** To date, eight meteoroid impacts have been identified in the seismic record of NASA's InSight mission on Mars, occurring either within 300 km or beyond 3,500 km. We report the association of a high-frequency marsquake, S0794a, with a new 21.5-m-diameter impact crater discovered at an intermediate distance of 1,640 km in the tectonically active Cerberus-Fossae graben system. This impact enables the direct comparison between surface and subsurface sources, as well as providing the first data point in the critical gap between previous impacts, both in distance and crater size. Additionally, the location of this event necessitates a reassessment of assumed seismic raypaths that were thought to propagate along a slow crustal waveguide. We find that the raypaths instead penetrate and travel through the faster mantle, implying numerous identified marsquake epicenters should be relocated up to two times farther from InSight, with implications for seismically derived impact rates and regional seismicity.

**Plain Language Summary** We have used global and high-resolution orbital imaging to discover a fresh crater that appeared at the same time as one of the quakes detected by NASA's InSight lander. This means the seismometer detected a meteoroid strike rather than geological activity within the planet. We know the location of this impact as well as the timing of seismic energy arriving by different types of vibrations which traveled through Mars at different speeds. With this information, we can work out that these waves penetrated below the crust and into the mantle rather than being confined to the crust as previously thought. This new path of propagation leads us to question how far away other marsquakes were from the InSight lander. This has implications for both how often marsquakes occur as well as how frequently meteoroids hit Mars.

## 1. Introduction

The primary objective of the InSight mission (Banerdt et al., 2020) was to reveal the internal structure of Mars through seismic analysis (Lognonné et al., 2019, 2020). Accurately locating the sources of seismic waves is required to allow inversion of the seismic signals to construct a detailed model of Mars' interior; however, seismic data from InSight's single station is insufficient to provide a location without prior assumptions for the model (Drilleau et al., 2020), unless multi-orbital surface waves are detected (Panning et al., 2015). Hence, alternative model-independent approaches to locating seismic sources, such as orbital imaging of fresh impact craters, are of critical importance.

To date, the sources of only two teleseismic signals, originating from distances further than 3,500 km (59°) from InSight, have been precisely located. These signals were generated by impacts with blast zones exceeding 20 km across, observable via the low-resolution orbital Mars Color Imager (MARCI, Malin et al. (2001)), thereby constraining their formation time to within a day (Posiolova et al., 2022). These two seismic events, designated by their mission sol (Martian day) as S1000a and S1094b, with raypaths penetrating deep into the mantle, have been
pivotal in the seismic analysis of Mars' interior (e.g., Durán et al., 2022; Irving et al., 2023; Kim et al., 2022; Samuel et al., 2023).

In addition, six nearby events have been matched with craters up to 9.2 m in diameter (I. Daubar et al., 2023) within 300 km (5°) of InSight, offering an opportunity to probe the crustal structure beneath the lander (Drilleau et al., 2023). For each of these events, the seismic arrival was followed by an acoustic “chirp” produced by the meteoroid's hypersonic atmospheric entry and impact, allowing estimation of crater azimuth and distance based on polarization and the better-constrained speed of sound, without any prior seismic model (Garcia et al., 2022). Crater location estimates were subsequently confirmed by high-resolution imaging.

However, for the overwhelming majority (>90%) of events cataloged within distances ranging from 5° to 59° (InSight Marsquake Service, 2023), there is ambiguity in both their source mechanisms and propagation paths. Prior to the observation of S1000a, the absence of identifiable low-frequency energy in many events suggested that energy from shallow sources was trapped within a slow crustal waveguide (Giardini et al., 2020). These events, characterized by high-frequency energy (>1 Hz), were classified as HF-family events. Conversely, events exhibiting predominantly low-frequency energy (<1 Hz), were classified as LF-family events, and attributed to deeper sources beneath the crust with energy propagating mainly through the mantle at higher velocities (Clinton et al., 2021). While both HF- and LF-family events have a similar range of differential S-P travel times, the assumed lower crustal velocity of HF-family events implied they were distributed only up to 45° (2,700 km) (Ceylan et al., 2022), halfway to the inferred core shadow, the cutoff distance of direct P- and S-wave phases (Stähler et al., 2021).

The distinction between the HF- and LF-event families was subsequently blurred by the detection of the two teleseismic impact events, which featured the simultaneous arrival of broadband energy propagating through both the crust and the mantle, from ~0.1–10 Hz. Additionally, a recent machine-learning analysis revealed similar broadband signatures for numerous HF events located beyond ~5° (Stott et al., 2023). This raises the question as to whether the raypaths of HF-family events have also traversed more quickly across the mantle, rather than guided through the crust. This would relocate their sources farther from InSight, spreading them out up to the core shadow, with implications for their distribution across the planet, and hence seismicity and impact rates.

To address the ambiguity in seismic-wave propagation pathways, we aim to identify a seismic event resulting from a meteoroid impact located within the critical distance gap between known impact-seismic matches to date. Upon identifying a unique match, we quantitatively assess the implications.

## 2. Methodology

In our companion paper (Bickel et al., 2024) we use machine learning to identify craters in high-resolution orbital images within 50° (~3,000 km) of InSight with time windows set by before-and-after images of crater formation. However, the low cadence of high-resolution orbital imagery presents a challenge, with repeat times ranging from months to more than 10 years (Bickel et al., 2024; I. Daubar et al., 2022), precluding a unique seismic match (e.g., I. Daubar et al., 2020; Fernando et al., 2023). In contrast, InSight seismic events provide precise timing of energy arrival from a potential impact but only offer an estimate of the source location.

Taking this into account, our resulting workflow is shown in Figure 1f. We first consider the three largest fresh impact craters, which are the most likely to have been both detectable seismically and resolvable at MARCI's highest resolution (~0.6 km/pixel, Malin et al. (2001)), given their extended blast zones. After constraining the time of impact, where possible, to a shorter window through MARCI images, we identify the best match among all seismic events within that window by comparing various seismic characteristics with those expected from the crater-forming impact. Our assessment includes location estimates using the suite of existing Mars interior models, seismic moment, profile and source duration. In addition to distance-magnitude criteria used for potential matches by our companion paper, to claim positive association we also require that the match is unique with little possibility that the impact-generated seismic signal was obscured by ambient noise.

The three largest craters in our companion paper (Bickel et al., 2024), all single craters above 15 m in diameter and located at distances from 19° to 40°, are listed in Figure 1f:
<figure><img src="image_4.png" /><figcaption>**Figure 1.** (a) Constraining MARCI images of CF crater (here upsampled for visualization) before (top, 2021-02-10) and after formation (bottom, 2021-02-20). (b) Constraining Context camera (CTX; Malin et al. (2007)) images showing before (top, 2019-07-03) and after (bottom, 2021-11-02). (c) High-resolution image by Color and Stereo Surface Imaging System (CaSSIS; Thomas et al. (2017)). Inset square denotes possible nearby contemporaneous dark slope-streak formations (see Text S3 in Supporting Information S1). (d) High Resolution Imaging Science Experiment (HiRISE; A. S. McEwen et al. (2007)) close-up of the newly formed crater over older, cratered terrain. (e) Timeline of imaging constraints and albedo change over time at the crater location in MARCI images. (f) Workflow of the matching of a crater to a seismic event.</figcaption></figure>
ID24 is a 22.5-m-diameter crater formed between 2019-05-25 and 2020-12-16. It resides in an area of pronounced topographic variation (Figure S1 in Supporting Information S1) where shadowing confounds MARCI's identification of the blast zone, ~1–2 km across, hence preventing tighter date constraints.

ID79 is an 18-m-diameter crater formed between 2010-12-12 and 2021-04-13. It features a limited central region of the blast zone (~500 m) characterized by faint linear rays and weak contrast (Figure S2 in Supporting Information S1), placing it possibly earlier in the 11-year time window, pre-dating InSight.

ID106 is a 21.5-m-diameter crater formed between 2019-07-03 and 2021-11-02 (Figure 1). It is located in the Cerberus Fossae (CF) region, and has a central region of the blast zone 1 km across, surrounded by a linear-to-arcuate ray system extending up to 2 km (Figure 1).

We therefore used MARCI images to better constrain the time of impact for ID79 and ID106 (henceforth the CF crater).

## 2.1. MARCI Image Processing

Both ID79 and the CF crater, at diameters of 18 and 21.5 m respectively, are considerably smaller than the two smallest previously identified by MARCI, measuring 49 m (I. Daubar et al., 2022) and 35 m (McEwen, 2023). Therefore, to enhance detection, we focused our search on MARCI's highest-resolution images, requiring the crater to be located near the center of the field of view to minimize distortions from the camera's fish-eye lens (Robbins, 2022). Unlike MARCI's higher-cadence, low-resolution images (>1–4 km/pixel), the acquisition interval for its high-resolution images (0.6 km/pixel) varies from days to months.

To better quantify subsequent surface change after an impact, we minimized the effect of solar illumination and atmospheric conditions by normalizing all images within a 101-pixel box around each pixel, removing the box mean and dividing by the box variance. To further compensate for local changes, this normalized albedo was compared to that of the four nearest pixels. To exclude artifacts, we only accept a consistent change seen in all five visible bands (Bell et al., 2009).

# 3. Results

## 3.1. Orbital Image Analysis

For ID79, we identified significant darkening at the crater site in the MARCI image from 2016-07-16. Since the crater formation predates the InSight mission and cannot be matched to a seismic event, it is excluded from further analysis.

For the CF crater we searched MARCI images spanning the 28-month CTX window of our target crater (Figure 1b). At the impact location, a significant initial darkening is seen between MARCI images taken on sols 785 and 795 (Figure 1a; Figure S3 in Supporting Information S1) followed by a gradual brightening over the subsequent 14 high-resolution images spanning more than 700 sols (Figure 1e; Figure S3 in Supporting Information S1). No other pixel within 400 km of this location shows such a significant shift followed by a subsequent exponential decay. The best fit ($r = 0.95$) to the temporal albedo evolution is achieved with an RGB weighting of [0.8 1.0 0.4] and an exponential recovery time $\tau = 670 \pm 140$ sols (Figure 1e). This is consistent with the impact removing high-albedo surface dust, followed by dust settling (Figure 1e) (I. Daubar et al., 2016).

Therefore, only the CF crater remains as a robust candidate to identify an impact-seismic match and is the focus of our subsequent analysis.

## 3.2. Seismic Analysis

For crater ID24, without tighter constraints from MARCI, 477 possible seismic events fall in the time window defined by CTX (Figure 1f) (InSight Marsquake Service, 2023). Hence, a unique match for ID24 is not possible. In contrast, for the CF crater, just four seismic events fall within the 10-sol MARCI window: S0786a, S0792a, S0793a, and S0794a (InSight Marsquake Service, 2023). The epicentral distance uncertainties of these events rely on phase-arrival timing and velocity estimation, the latter determined by the propagation pathway based on event classification (Ceylan et al., 2022). Crustal-waveguided events are assigned a P-wave velocity of $v_p = 4$ km/s, with $v_p/v_s = \sqrt{3}$, while mantle-going event velocities rely on a set of prior Mars interior models (see Clinton
et al., 2021; Lognonné et al., 2023 review). Given uncertainty regarding propagation paths, we compare the observed S-P travel times (InSight Marsquake Service, 2023) to those of both crustal-guided and mantle-going waves as possibilities when assessing potential seismic-event matches, assuming the CF crater is the impact source 1,640 km away (epicentral distance of 27.65°).

S0793a has previously been positively associated with a 3.9 m crater ~90 km west of InSight through analysis of the impact-generated seismoacoustic signal and an S-P travel time of only ~13 s (Garcia et al., 2022), too close to be considered. S0792a cannot be a match based on its S-P travel time; it is too short by more than 110 s for mantle-going waves and by 220 s for crustal-guided waves. This precludes its match regardless of propagation pathway. S0786a also cannot be matched based on its S-P travel time, which exceeds by 60 s the expected differential for mantle-going waves and falls short by more than 60 s for crustal-guided waves.

Only S0794a remains as a potential match, further supported by the following seismic analysis and subsequent evidence.

### 3.2.1. Spectral Signature and Seismic Location

Among the four candidate events, only S0794a exhibits an excess of low-frequency energy above the atmosphere-induced noise, as determined by comodulation (Figure 3a; Text S4 in Supporting Information S1; Charalambous et al., 2021). Although classified as an HF-family event, S0794a shares this broadband characteristic with the mantle-traversing seismic waves of the two distant impact events (Kim et al., 2022; Posiolova et al., 2022), contrasting with the high-frequency-only energy of nearby impacts propagating in the crust (e.g., Figure 3b). Further, the production and survival of significant high-frequency energy for S0794a, as observed for the distant impact events (e.g., Figure 3b), suggests an impact source and considerable propagation through a weakly attenuating mantle (Menina et al., 2023; Samuel et al., 2023).

Seismic-location estimates depend on this low-frequency energy to provide azimuthal information (Ceylan et al., 2022; Drilleau et al., 2022; Zenhäusern et al., 2022) as the depolarization of high-frequency body waves from scattering precludes such determination (Menina et al., 2021). S0794a's low-frequency energy provides estimated P- and S-wave azimuths of 74° and 80° respectively (see Text S5 and Figure S7 in Supporting Information S1), with a mean of 77 ± 4°, in close agreement to the CF crater's back azimuth of 78.1° (Figure 2a). Assuming mantle-going seismic propagation from the CF impact, the current suite of velocity models predicts an S-P travel time on average only 10 s shorter than the observed 175 ± 5 s, comparable to two nearby major LF events already located in CF; S0173a at 175 ± 3 s, and S0235b at 167 ± 3 s (Figure 2c).

Finally, we note that at a distance of 1,640 km, S0794a is not expected to produce the seismo-acoustic “chirp” detected for nearer impacts due to the atmospheric attenuation at such distance (I. J. Daubar et al., 2024).

### 3.2.2. Noise Levels During Search Window

During the 10-sol MARCI window, InSight fortunately experienced some of the lowest seismic-noise levels throughout the mission (see Figure 9 of Lognonné et al. (2023)). The low-frequency energy of S0794a lies above the 90th-noise percentile for this window (Figure 4c), making it unlikely for this event to go undetected (<10%). The likelihood of a second impact within S0794a's uncertainty ellipse within 10 sols is highly improbable (<≈3E-3), given the current crater-production rate (Hartmann & Daubar, 2017). Such a strong signal for a comparatively large crater in such a short window within the seismic uncertainty ellipse therefore makes it highly unlikely (<≈3E-4) that S0794a represents detection of a second impact near the CF crater, while the CF impact went undetected seismically.

### 3.2.3. Seismic Moment

Seismic moments calculated from marsquake amplitudes assume energy release deep within the subsurface, and therefore do not accurately reflect the seismic moment of a surface impact (Posiolova et al., 2022). However, we can still validly compare the equivalent deep-crustal seismic moment as proxy values of our candidate events to the empirical scaling relationship inferred from other known impacts on the same basis (Zenhäusern et al., 2024). Only S0794a is consistent with these previous values, extending the validity of these seismic-crater scaling-law relationships proposed by Wójcicka et al. (2020) and Zenhäusern et al. (2024). The seismic moment of the two
<figure><img src="image_5.png" /><figcaption>**Figure 2.** (a) Previous estimated location of impact S0794a by MQS (red, 17.6°, unknown BAZ), assuming crustal waveguiding, juxtaposed with this study's new seismically estimated location (yellow ellipse and yellow dot) relative to the nearest and largest-magnitude LF events in CF (black diamonds), S0173a ($M_w$ = 3.7), and S0235b ($M_w$ = 3.7). Yellow ellipse encompasses the combined uncertainties in back-azimuth and epicentral distance estimations of S0794a, determined from this study assuming a source at 0-km depth. Impact is located at 9.48°N, 163.03°E (yellow star, 27.65°N, 300.00E epicentral distance). (b) Schematic of wave-guided crustal propagation (modified after Giardini et al. (2020)) against P-wave raypath at the impact source of S0794a propagating through the lithosphere. (c) Comparison of band-pass filtered envelopes of seismic-power excess (Charalambous et al., 2021, 2022) between S0794a (red) and nearby LF marsquakes, S0173a (green) and S0235b (light blue), time-aligned on the S-wave arrival.</figcaption></figure>

other small-magnitude events, S0786a and S0792a, is inconsistent with an origin from a 21.5-m crater with estimated diameters less than 9 m (Figures 4a–4c).

Finally, the relationships proposed by Zenhäusern et al. (2024) enable us to infer seismic detectability compared to other confirmed impacts, suggesting that an impact of this size could be detected up to distances of at least 45° away at any time during the mission (Figure 4a) with an expected amplitude exceeding the 90th-noise percentile for the 10-sol window (Figure 4c), thus supporting the likelihood estimates presented above.
### 3.2.4. Seismic-Cutoff Frequency

To further corroborate the impact-seismic match of S0794a, we compare seismically derived source durations ($\tau$), the inverse of cutoff frequency, with those of confirmed Martian impacts (see Text S6 in Supporting Information S1). This comparison excludes S0786a and S0792a as the noise hinders estimation of their cutoff frequencies.

S0794a displays an unusually high cutoff frequency (~4.5 Hz) in the P-wave displacement spectrum, as observed in other Mars impacts (Garcia et al., 2022; Posiolova et al., 2022), contrasting with tectonic events on the planet that feature slower rupture processes (Stähler et al., 2022). Above the cutoff, its cubic roll-off in frequency (Figure S8 in Supporting Information S1) is also consistent with an impact source mechanism, likely attributed to the volumetric nature of the shock wave in porous regolith (e.g. Ford et al., 2011), as observed on Mars (Garcia et al., 2022; Posiolova et al., 2022), the Moon (Gudkova et al., 2015) and shallow explosions on Earth (Ford et al., 2011; Walter & Priestley, 1991).

A power-law relationship between source duration and crater diameter, $D$, is observed for previously confirmed impacts, $\tau \sim D^{0.36 \pm 0.04}$ (Figure 4d). No model assumptions come into this scaling, which is based on direct observables. With a cutoff frequency of 4.5 Hz and a 21.5-m crater, S0794a lies between the nearby and distant impact groups, consistent with this scaling.

## 4. Discussion

Our identification of the CF impact in MARCI and its association with the S0794a event provides insights into surface changes, source identification, impact dynamics, and possible seismic models for Mars. Moreover, the resulting relocation of this event and its analogs holds implications for the planet's seismic activity and impact rates.

### 4.1. Surface Changes After Impact

This result provides the first observations of an impact identified by a single pixel in MARCI, as well as the first high-frequency tracking of the subsequent fading over many orbital images, not possible with high-resolution imaging. The step-wise reduction in albedo observed in the time window of impact, followed by a gradual recovery (Figure 1e; Figure S3 in Supporting Information S1), is consistent with previous observations of comparable small craters and blast zones on Mars in high-resolution images (I. Daubar et al., 2016) attributed to the removal of higher albedo surface dust by the atmospheric-impact shock wave with dust airfall providing an expected non-linear rate of recovery.

The best-fit exponential recovery time of 670 ± 140 sols for this impact is considerably lower than the median lifetimes of at least ~5,300 sols derived from these previous orbital observations based on a linear recovery (I. Daubar et al., 2016). However, this reflects in part the difference between weighting recovery time by observation from orbital imaging, which favors the longest-lasting (I. Daubar et al., 2016), compared to weighting by production from seismically detected impacts. The recovery time is comparable to the time constants derived from power loss due to dust settling on InSight's and Pathfinder's solar panels (500 and 350 sols, Lorenz et al. (2021)).

An exponential recovery in albedo at the pixel level with comparable time constants in MARCI imaging should provide a signature to identify more candidate impact locations for targeted, high-resolution orbital imaging, thereby providing formation times beyond the five impacts previously identified due to their extended blast zones (I. Daubar et al., 2022).

### 4.2. Source Discrimination

Nearby confirmed impacts are all classified as very-high frequency (VF) events within the HF family due to their energy bandwidth extending up to 35 Hz (Ceylan et al., 2022); this provided an initial basis for considering VF events as impacts (Zenhäusern et al., 2024). The association of S0794a with a new crater provides the first direct evidence that at least one VF-type event without an acoustic “chirp” signature is an impact, supporting the hypothesis that numerous (or all) VF events share this origin (Zenhäusern et al., 2024).

Furthermore, positive identification of an impact event in CF, a region of high seismic activity from a range of marsquakes, allows comparison of signals of events with different depths, focal mechanisms (e.g., Brinkman et al., 2021; Jacob et al., 2022) and tectonic contexts (e.g., Stähler et al., 2021). Figure 2c compares the scaled low-
<figure><img src="image_6.png" /><figcaption>**Figure 3.** (a) S0794a (top) Velocity spectrogram of the power summed over all axes. (bottom) Comodulation analysis applied to the total seismic-signal power (color) and atmospheric-pressure envelopes (black) calculated in half-octave windows centered from 1/4 to 2 Hz, and measured wind speed (gray). Amplitudes of traces and envelopes are normalized by their maxima. Where the seismic envelope is above that of atmospheric noise, the residual can be attributed to seismic energy. See Figure S5 in Supporting Information S1 for an extended version of this plot. (b) Filtered seismograms aligned at P-wave arrival and rotated to radial (R), transverse (T), and vertical (Z) directions for the smaller, nearby S0981c (epicentral distance, Δ: 4.2°, diameter, *D*: 7.2 m), the largest S1094b (distance: 58.5°, diameter: 150 m), and the newly discovered S0794a impact (distance: 27.6°, diameter: 21.5 m).</figcaption></figure>

frequency energy envelopes between the S0794a impact and the highest-magnitude LF events in CF. The similarity of the S-coda decay and duration is consistent with attenuation averaged along a similar propagation path (Aki & Chouet, 1975). However, despite S0794a's explosive source, its less impulsive, more emergent body-wave arrivals indicate additional scattering within the crust (e.g., Menina et al., 2023), as observed for other impact events (Figure 3), providing a possible discriminator for source depths associated with different families of marsquakes.

### 4.3. Impact Dynamics and Source Duration Time

The identification of S0794a allows consideration of how impact dynamics are represented in the seismic signal. Using the scaling between measured crater diameter, *D*, and impactor momentum, *I* (see I. Daubar et al., 2018; Gudkova et al., 2015; Lognonné et al., 2023), our observed relationship in Figure 4d between crater diameter and source duration $\tau$, becomes $\tau = \tau_0(I/I_0)^\beta$, where $I_0 = 10^7$ Ns is the reference momentum, $\tau_0 \approx 0.21$ s is the reference source duration and $\beta \approx 0.14$ is the scaling exponent for Mars, determined using the Gudkova et al. (2015) model for impact momentum. Our Mars scaling exhibits a similar power-law relationship to that observed for lunar impacts, where $\tau_0 = 0.65$ (Gudkova et al., 2015). Both power laws closely align with that proposed by Froment et al. (2024), $v_s \tau \propto (I/I_0)^{0.13}$, calibrated for lunar and Martian impacts as well as numerical simulations, based on the shear velocity $v_s$ in the source region, approximately 300 m/s on Mars and 100 m/s on the Moon. As the source duration scales with the energy and propagation velocity of the shock waves, this ratio of 3 in $v_s$ closely corresponds to the ratio between our derived $\tau_0$ prefactors, 0.21 for Mars and 0.65 observed for the less-mature regolith on the Moon, underscoring the pivotal role of target properties in determining source kinematics. This reflects the correlation between impact-source duration and regolith porosity reported by Gudkova et al. (2015) on the Moon.

We can also obtain an independent estimate of impactor momentum by comparison with Apollo-SIVB artificial impacts on the Moon, which generated 33-m-diameter craters (Rajšić et al., 2021). $\pi$-group crater scaling suggests that impactors with a certain momentum form craters larger by the ratio $\alpha = (\frac{8\text{Moon}}{8\text{Mars}})^{\frac{-\mu}{\frac{\pi}{2}+\mu}}$, about 15% in the lower
<figure><img src="image_7.png" /><figcaption>**Figure 4.** Seismic-moment/crater-diameter and amplitude/distance scaling relationships proposed by Zenhäusern et al. (2022) (a and b): (a) The black line, with uncertainties indicated by dashed lines, represents overall mission detectability thresholds. The dark gray region delineates crater diameters not expected to be detectable at a given distance. Transparent markers are predictions of crater sizes based on seismic moment; filled markers are actual diameter measurements made from orbital images. (b) Light-shaded area represents the entire uncertainty in expected impact seismic moment for a range of target materials, from cohesive soil to cohesionless sand. In both (a) and (b), the corresponding values for S0786a and S0792a are shown with gray markers, highlighting their inconsistency with the scaling relationships, in contrast to S0794a. Diamond markers represent effective crater diameters for impact clusters. The largest craters are excluded due to the unknown attenuation structure of the Martian mantle, precluding refined magnitude estimation, and the limited validity of seismic-moment comparison due to their deeper-probing sources (Posiolova et al., 2022). (c) Noise percentiles over the 10-sol window. Left axis represents the mean S-wave displacement power spectral density of received seismic energy in the low-frequency range, observed predominantly in S0794a and other HF-family events (Stott et al., 2023). This energy largely determines the long-period plateau for magnitude calibration assuming mantle-going waves for HF events (Böse et al., 2021), and hence their seismic moment (Zenhäusern et al., 2024) from which the expected crater diameter can be inferred (Zenhäusern et al., 2024), assuming an impact source 1,640 km away (right axis). For S0786c and S0792a this is an absolute upper bound as no seismic energy is detected below 2 Hz. (d) Source duration, τ, estimated from seismic-cutoff frequencies against observed crater diameter (main axis) and impact momentum (secondary upper axes) estimated using Gudkova et al. (2015)'s model and independently with a calibration to the known Apollo-SIVB momentum (Equation 1).</figcaption></figure>

gravity of the Moon (where μ = 0.4, Holsapple (1993)). This implies that the S0794a and Apollo-SIVB impacts had a comparable vertical momentum. Using the γ = 0.32 power-law exponent between crater diameter D and I proposed by I. Daubar et al. (2018), we can write:

$$I_{\text{Mars}} = \left( \frac{D_{\text{Mars}}}{\alpha D_{\text{SIV B}}} \right)^{1/\gamma} I_{\text{SIV B}}, \quad (1)$$
Equation 1 allows an independent comparison between momentum and cutoff frequency of Martian impacts. The momentum of InSight's nearby impact S0986c, observed with an 8 Hz cutoff, can be estimated at $1.1 \times 10^5$ Ns based on its 6.1 m effective crater-cluster diameter (Garcia et al., 2022). The exponent $\beta \sim 0.13-0.14$ in the above source-duration models thus predicts a theoretical cutoff frequency ratio between S0794a and S0986c impacts of 1.7-1.8, aligning with the observed values at 4.5 and 8 Hz, respectively. Notably, S0794a lies midway between the much smaller S0793a impact and significantly larger S1094b, as shown in Figure 4d. The variability in this scaling depends on source parameters (cluster or single-crater impacts), target geology, and attenuation and scattering effects that obscure source characteristics (Gudkova et al., 2015; Lognonné et al., 2009).

Finally, we note that the seismic moment measured for S0794a and the other impacts, along with the momentum estimated above remain in excellent agreement with their known relation of proportionality (Froment et al., 2024; Wójcicka et al., 2020); thus, the source-duration relationships above can be readily extrapolated in this context.

## 4.4. Velocity Models of Mars' Interior

The impact origin of S0794a offers an opportunity to refine our current 1-D models of Mars' interior (Drilleau et al., 2022; Duran et al., 2022; Irving et al., 2023; Stähler et al., 2021). Notably, there exists a discrepancy of up to 5% in seismic wavespeeds across these models, particularly evident in the uppermost mantle depths between 70 and 120 km, which originates from assumptions about the major element composition (e.g., Khan et al., 2022; Wänke & Dreibus, 1994; Yoshizaki & McDonough, 2020). At these depths, the observed multiply orbiting Rayleigh waves (R2-R7) of S1222a travel with a group velocity of 3.8 km/s (Kim, Duran, et al., 2023), aligning with faster models with a lower-mantle FeO content (e.g., Duran et al., 2022; Irving et al., 2023) over those that are based on Wänke-Dreibus or Taylor compositions (e.g., Stähler et al., 2021). However, until now, differences among published velocity models have had a negligible effect on predictions of body-wave travel times from the predominant LF-marsquake cluster in CF, partly because of trade-offs with epicentral distance. This trade-off is removed by the association of the S0794a waveforms with an impact. As mentioned previously, there is, on average, a 10-s discrepancy between our distance estimates and the impact crater location at 27.65° epicentral distance, which falls within the predicted uncertainty ellipse of 25 – 34°, as reflected in Figure 2b, based on the suite of Mars' 1-D (Khan et al., 2021; Knapmeyer-Endrun et al., 2021; Stähler et al., 2021) and 3-D interior models (Drilleau et al., 2023; Kim, Stähler, et al., 2023). This discrepancy allows a re-evaluation of the seismic wavespeeds in the uppermost mantle of Mars (up to 120 km depth), potentially excluding certain cosmochemical constraints previously prescribed as priors for inversion.

## 4.5. Event Localization and Relocation

Following the relocation of S0794a, many previously published marsquake distances within the HF-event family will likely need to be revised. Assuming a zero source depth and average crustal thicknesses of 30–60 km (Kim, Duran, et al., 2023), the current suite of interior models imply the seismic raypaths of HF-family events increasingly traverse the faster mantle beyond a transition distance of 5 ± 3° at a $2\sigma$ level, relocating them up to two times farther away. For the most distant events, this would fill the gap right up to the expected core shadow.

Relocating events to a greater distance also affects the source-magnitude estimates. This is further complicated when a different frequency band is used to determine the magnitude. Following Böse et al. (2021), calibrated MQS magnitudes for crustal-waveguided events used the peak amplitude of the 2.4 Hz resonance, a hypothesized local subsurface seismic amplifier (Hobiger et al., 2021). The previous MQS magnitude for S0794a was $M_w = 3.1 \pm 0.2$, derived from this resonance, which had been used for magnitude calibration of all HF-family events so far. However, using the low-frequency energy plateau band for LF-family events with mantle-going waves, as appropriate to this event's revised raypath, reduces its estimated magnitude to $M_w \approx 2.8 \pm 0.2$.

The low-frequency energy component also offers the possibility of azimuth determinations for some events within the HF family, as demonstrated here for the first time with S0794a (Text S5 in Supporting Information S1). Coupled with revised distances, this provides new locations for future crater-seismic matching.

## 4.6. Implications for Seismicity and Impact Rates

We make an initial assessment of how the measured tectonic-seismic and impact-seismic rates will change as a result of this relocation. Further work will focus on magnitude recalibration and the consequences of the shift in
the best-fit models of Mars' interior structure. The majority of HF-family events, but not all previously assumed to be wave-guided in the crust, will likely need to be relocated. This has several significant effects:

1. Relocation of many of the HF-family events which were previously clustered around Cerberus Fossae indicates that this region is less seismically active than was previously thought. This is significant, given that the CF region was previously calculated to be responsible for the release of around half the observed global seismic moment Stähler et al. (2022).

2. The relocation of the majority of VF events, assumed to be impacts (e.g., Zenhäusern et al., 2024), up to twice as far away from InSight will reduce their corresponding areal flux contribution to the impact rate by the square of the increase in distance, or by up to a factor of four.

3. The subsequent shift in source magnitude also causes a shift in the corresponding estimated crater diameter.

Using S0794a as an example, the scaling laws (Zenhäusern et al., 2024) predicted an estimated crater size of ~29 m, based on a magnitude that assumed crustal-guided propagation. With mantle propagation, its distance is increased by 1.6 times, reducing its areal flux contribution by 2.6, while the crater is now imaged and measured at 21.5 m. For this event only, its contribution to the impact rate is reduced significantly because it is associated with a smaller crater farther from InSight.

While the cumulative shift in impact rates from the last two effects listed above will be complicated, these do not change the overall estimate of the total seismic energy received at InSight's location. Rather, this energy now arrives from spatially more distributed larger impacts associated with the revised estimates of their corresponding crater size.

## 5. Conclusions

The seismic detection of an impact crater formation in Cerberus Fossae fills a crucial gap in distance and crater size, fundamentally reshaping our understanding of seismic-wave propagation on Mars. The seismic signature of S0794a strengthens the argument that other VF events without acoustic-signature chirps are also of impact origin, with implications for independent determinations of the contemporaneous impact rate. The evidence for mantle-going waves from S0794a implies that the location of this event is considerably farther away from InSight than previously published; the same is likely true for HF-family events farther away from the lander than a critical distance of around 5±3°, assuming surface sources. As such, the majority of previously published marsquake locations across various event categories necessitate revised distances using updated interior models. Future work will seek to refine these estimates, and place tighter constraints on interior structure and velocity of Mars, refining the planet's seismicity and the contemporaneous impact rate by potentially identifying additional seismic events associated with other fresh impacts in the catalog of our companion paper (Bickel et al., 2024).

## Data Availability Statement

SEIS data are available from the InSight Mars SEIS Data Service at IPGP, IRIS-DMC and NASA PDS (InSight Mars SEIS Data Service, 2019). The InSight seismic catalogue is available at (InSight Marsquake Service, 2023). Orbital imagery data are available online using the links given below. MRO CTX and MARCI image data are openly available on the NASA Planetary Data System: https://pds-imaging.jpl.nasa.gov/volumes/mro.html. CaSSIS image data are openly available here: https://observations.cassis.unibe.ch/ HiRISE data are openly available here: https://www.uahirise.org/anazitisi.php. The used USGS map product (MOLA topography) is openly available here: https://astrogeology.usgs.gov/search/map/mars_mgs_molaDem_463m.

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## Acknowledgments

The authors would like to thank Prof. Quentin Williams, the editor, as well as Dr. Jiaqi Li and an anonymous reviewer for their thorough and constructive reviews, which have helped strengthen this manuscript. We acknowledge NASA, CNES, their partner agencies and Institutions (UKSA, SSO, DLR, JPL, IPGP-CNRS, ETHZ, IC, MPS-MPG) and the flight operations team at JPL, SISMOC, MSDS, IRIS-DMC and PDS for providing SEED SEIS data. We also express our thanks to the HiRISE and CaSSIS imaging operations teams, who made special efforts to target and acquire these data. CC is funded by the UK Space Agency Fellowship in Mars Exploration Science under ST/Y005600/1. IJD was supported by NASA Grant 80NSSC20K0971. N.W. and G.S.C. were supported by UK Space Agency Grants ST/S001514/1, ST/T002026/1, and ST/Y000102/1. M.F. received support from the Research Council of Norway (FRIPRO project 335903, AIR). A.H. is funded by a UK Space Agency Fellowship in Mars Exploration Science under ST/Y005597/1 and under Grant ST/W002523/1. This manuscript constitutes InSight Contribution Number 338.
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