EGU23-12953, updated on 23 Apr 2024
https://doi.org/10.5194/egusphere-egu23-12953
EGU General Assembly 2023
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

What Marsquakes Tell Us About Impact Rates on Mars

Géraldine Zenhäusern1, Natalia Wójcicka2, Simon Stähler1, Gareth Collins2, Ingrid Daubar3, Domenico Giardini1, Martin Knapmeyer4, John Clinton5, and Savas Ceylan1
Géraldine Zenhäusern et al.
  • 1ETH Zürich, Institute of Geophysics, Department of Earth Sciences, Switzerland (geraldine.zenhaeusern@erdw.ethz.ch)
  • 2Imperial College, Department of Earth Science and Engineering, UK
  • 3Brown University, Earth, Environmental, and Planetary Sciences, USA
  • 4DLR Institute of Planetary Research, Germany
  • 5ETH Zürich, Swiss Seismological Service, Switzerland

The current Martian cratering rate has been determined either from repeated orbital imaging (e.g.[1][2]), or using lunar rates extended to Mars in combination with crater counting [3]. Eight seismic events detected by the NASA InSight seismometer have been confirmed as impacts by orbital imaging [4]. Six of those events are part of the Very High Frequency (VF) group of marsquakes, which consists of 70 events in total. The impact signals are very similar to other VF events, suggesting that more or all VF events could be impact related. The unique characteristics of VF events, such as a long seismic coda interpreted as a result of shallow source in a strongly scattering near-surface layer [5] and their temporal and spatial distributions, are consistent with impact origin.

Assuming all high quality VF events are impacts allows us to place a novel constraint on the impact rate on Mars, independent of the formation of easy-to-spot large blast zones, necessary to identify fresh craters in orbital images. We test the compatibility with the existing cratering rate estimates by using two approaches to derive a first seismically constrained impact rate for Mars. First, we use the Gutenberg-Richter law to determine the slope of the VF event magnitude-frequency distribution. The impact rate is derived by applying a relationship between seismic moment and crater diameter [6]. We refine our estimates by extrapolating the detectability of each event using a semi-empirical relationship between crater size and seismic amplitude [6]. We find that both approaches give similar rates, varying slightly depending on the detectability conditions assumed by each method. The cumulative rates N(D≥8m) = 1-4x10-6 /km2/yr are higher than those from previous imaging studies, but consistent with isochron rates [3].

The discrepancy with imaging-based rates could indicate that there are impacts which are missed in imagery due to absent blast zones or that are located in unfavourable terrain, unaccounted for in the imaging-based area correction.

 

References:

[1] Daubar et al. (2013). doi: 10.1016/j.icarus.2013.04.009

[2] Daubar et al. (2022). doi: 10.1029/2021JE007145

[3] Hartmann (2005). doi: 10.1016/j.icarus.2004.11.023

[4] Daubar et al. (2023). InSight Seismic Events Confirmed as Impacts Thus Far. Lunar and Planetary Science Conference 2023 abstract.

[5] van Driel et al. (2021). doi: 10.1029/2020JE006670

[6] Wójcicka et al. (2023). Impact Rate on Mars Implied by Seismic Observations. Lunar and Planetary Science Conference 2023 abstract.

How to cite: Zenhäusern, G., Wójcicka, N., Stähler, S., Collins, G., Daubar, I., Giardini, D., Knapmeyer, M., Clinton, J., and Ceylan, S.: What Marsquakes Tell Us About Impact Rates on Mars, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12953, https://doi.org/10.5194/egusphere-egu23-12953, 2023.