Modeling Seismic Recordings of High‐Frequency Guided Infrasound on Mars

Abstract

IntroductionNASA's InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission landed on the Martian surface in November 2018 and has since been conducting geophysical and meteorological observation (Banerdt et al., 2020). To achieve its objectives, InSight is equipped with a Very Broad Band (VBB) and a Short Period (SP) seismometer, which together constitute the SEIS (Seismic Experiment for Internal Structure) instrument (Lognonné et al., 2019). SEIS is operated in combination with a weather station, Auxiliary Payload Sensor Suite (APSS) including an atmospheric pressure sensor and wind and temperature sensors, to perform meteorological observation (Banfield et al., 2019). Due to power issues appearing in the second Martian year of the mission, SP and APSS have become temporarily unavailable, and VBB has been kept on most of the time. Thus only the VBB seismic data is available for analyzing the seismic events in this study.The ground motion recorded by InSight originates from different types of sources, most of which are marsquakes (e.g., Giardini et al., 2020) or atmospheric seismic events like pressure drops (e.g., Lognonné et al., 2020). The recent seismic recordings provides a new type of seismic events, a dispersive wave train following a typical very-high-frequency marsquake (Clinton et al., 2021), where a dispersive wave train means that the wave velocity, Abstract NASA's Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) mission records several high-frequency (>0.5 Hz) dispersive seismic signals on Mars. These signals are due to the acoustic-to-seismic coupling of infrasound generated by the entry and impact of meteorites. This dispersion property is due to infrasound propagating in a structured atmosphere, and we refer to this dispersive infrasound as guided infrasound. We propose to model the propagation of guided infrasound and the seismic coupling to the ground analytically; we use a 1D layered atmosphere on a three-layer solid subsurface medium. The synthetic ground movements fit the observed dispersive seismic signals well and the fitting indicates that the regolith beneath InSight is about 40-m in thickness. We also examine and validate the previously-published subsurface models derived from InSight ambient seismic vibration data.Plain Language Summary Under particular weather conditions, the Martian atmosphere displays a special sound-wave velocity profile, where the wave velocity becomes larger with increasing altitude within a few hundred meters. When an infrasound signal-a low-frequency (<20 Hz) sound wave inaudible to humanspropagates through such a structure, the infrasound exhibits dispersion: its propagation velocity depends on its frequency. We refer to such infrasound as guided infrasound. Guided infrasound can deform the ground, and have been recorded by the seismometer of NASA's Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) mission on the Martian surface. We propose to mo...

Evaluation of S1222a Source Parameters Based on Site Effect Simulation and Implication for the Event Origin

“…We set up our simulation model as a number of shallow layers over a half‐space following previous studies. The shallow layers are set to be the subsurface models proposed by previous studies obtained from different approaches (Carrasco et al., 2023a; Hobiger et al., 2021; Onodera, 2022; Xu et al., 2022). For the half‐space, the S‐wave velocity is set to 1.5 km/s based on the reference value from receiver function analyses (1.2–2.1 km/s, Carrasco et al., 2023b; Knapmeyer‐Endrun et al., 2021; Lognonné et al., 2020) and the P‐wave velocity is set to 2.6 km/s assuming a V p / V s ratio of 1.73 for a Poisson solid (Giardini et al., 2020; Stähler et al., 2022).…”

“…In such a geological condition, ground motions are likely influenced by the site effect from these shallow layers. Subsurface models of the landing site have been proposed in previous studies using different approaches (Carrasco et al., 2023a; Hobiger et al., 2021; Onodera, 2022; Xu et al., 2022). These models all include the surface regolith layer but differ with regard to deeper layers.…”

“…These models all include the surface regolith layer but differ with regard to deeper layers. Onodera (2022) and Xu et al (2022) both showed models where seismic-wave velocity increases with depth. Hobiger et al (2021) proposed a subsurface structure with a low-velocity layer sandwiched between layers of higher velocities, while Carrasco et al (2023a) presented models characterized by a high-velocity layer over a low-velocity layer with shallower depths than the models of Hobiger et al (2021) (see Text S2 in Supporting Information S1 for more details).…”

Investigation of Martian Regional Crustal Structure Near the Dichotomy Using S1222a Surface‐Wave Group Velocities

“…The seismic observation conducted through InSight's seismometer (Lognonné et al., 2019) provided new insight into Martian seismicity and interior (e.g., Banerdt et al., 2020; Giardini et al., 2020; Lognonné et al., 2020). This revealed a first view of the subsurface/crustal structure at the InSight landing site (Lognonné et al., 2020), later improved using various methods such as ambient‐vibration H / V (Hobiger et al., 2021), marsquake‐coda H / V (Carrasco et al., 2022), compliance (Kenda et al., 2020; Onodera, 2022; Xu et al., 2022), receiver function (e.g., Kim et al., 2021; Knapmeyer‐Endrun et al., 2021; Shi et al., 2022), and autocorrelation (e.g., Compaire et al., 2021; Deng & Levander, 2020; Schimmel et al., 2021).…”

Two Seismic Events from InSight Confirmed as New Impacts on Mars

“…The first of these impact identifications was made based on analyses of an unusual seismic waveform in the coda of the very high frequency (VF; for definitions of seismic event types, see Clinton et al 2021) event S0986c (naming convention: the third seismic event occurring on Martian sol 0986 of InSight's mission): a chirp produced by normal dispersion of acoustic waves that were generated by the impact, propagated through the atmosphere, and then coupled to the ground near InSight (Garcia et al 2022). These chirps can be modeled as guided infrasound waves (Xu et al 2022). Hereafter we refer to these as impact-acoustic chirp signals.…”