Different Martian Crustal Seismic Velocities Across the Dichotomy Boundary From Multi‐Orbiting Surface Waves

Geophysical Research Letters

Weidner

et al. 2022

Self Cite

The largest seismic event ever detected on Mars occurred on 4 May 2022, and was recorded by the Seismic Experiment for Interior Structure (SEIS) Very Broadband (VBB) seismometer ) of NASA's InSight mission (Banerdt et al., 2020). The event, labeled S1222a, occurred at 23:23:06.57 UTC (sol 1222) and has a moment magnitude M w estimated at 4.7 ± 0.2 (Kawamura et al., 2022). This event is thus five times larger than the second largest event recorded (Horleston et al., 2022) and had enough energy to allow for the first direct observation of multi-orbiting Rayleigh waves on Mars (Panning et al., 2022). Based on their calculated back azimuth of 101° (with a range of 96°-112°) and epicentral distance (37° ± 1.6°), the Mars Quake Service (MQS) determined that this quality A (InSight Marsquake Service, 2020) event originated at 7.63°S, 170.67°E, near the North-South dichotomy, east of the landing site, and south of Cerberus Fossae (Figure 1).Most remarkably, S1222a generated surface waves clearly observable on all three components of the ground motion (Figure 2). While Rayleigh waves have been previously detected on Mars with impact events S1000a and S1094b (Kim et al., 2022), no Love waves had been seen before. Since Rayleigh and Love waves are predominantly sensitive to different elastic parameters (governing the speed of vertically and horizontally polarized shear waves traveling horizontally, respectively), this gives us an opportunity to study the presence of large-scale radial seismic anisotropy on Mars between the lander and the event epicenter. Radial anisotropy, which is a type of transverse isotropy with a vertical symmetry axis, manifests as a difference in the velocities of vertically (V SV

Section: Discussionsupporting

confidence: 90%

Crustal Anisotropy in the Martian Lowlands From Surface Waves

Geophysical Research Letters

Weidner

et al. 2022

Self Cite

“…The narrowness of the correlation peak, however, was strongly dependent on the presence or absence of Love wave energy in the measurement window (Panning et al, 2015). While Love wave energy is seen for this event (Beghein et al, 2022;Kawamura et al, 2022;Kim, Stähler, et al, 2022;Li et al, 2022), it arrives in a non-overlapping time window with the Rayleigh energy, and so estimated correlation peaks are generally broad (Figure 2). In Figure 2e, we show three backazimuths from this correlation-based method (Methods Ia-Ic), which correspond to the correlation computed over broadband data, the average over all narrow-band data, and only over "high-quality" data.…”

Section: Rayleigh Wave Ellipticity and Backazimuth Estimationmentioning

confidence: 95%

Locating the Largest Event Observed on Mars With Multi‐Orbit Surface Waves

Panning

Banerdt

Geophysical Research Letters

et al. 2023

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Prior to the 2018 landing of the InSight mission, the InSight science team proposed locating Marsquakes using multiple orbit surface waves, independent of seismic velocity models, for events larger than MW4.6. The S1222a MW4.7 of 4 May 2022 is the largest Marsquake recorded and the first large enough for this method. Group arrivals of the first three orbits of Rayleigh waves are determined to derive the group velocity, epicentral distance, and origin time. The mean distance of 36.9 ± 0.3° agrees with the Marsquake Service (MQS) distance based on body wave measurements of 37.0 ± 1.6°. The origin time from surface waves is systematically later than the MQS origin time by 20 s. Backazimuth estimation is similar to body wave estimations from MQS although suggesting a shift to the south. Backazimuth estimates from R2 and R3 are more scattered, but do show clear elliptical motion.

“…Constraining the crustal structure at other locations is, however, crucial to fully understand the formation and evolution of the crust, and to improve global models of crustal thickness based on gravity data 17 . Although surface waves have been recently detected for the first time from two meteorite impacts 18 , 19 and the largest marsquake ever recorded 20 , surface waves constrain the average structures along the event-lander path 19 , 21 , 22 and are less sensitive to subsurface discontinuities. The present work aims at providing seismic constraints on the crustal structure at a location far from the InSight lander.…”

Section: Introductionmentioning

confidence: 99%

“…Although surface waves have been recently detected for the first time from two meteorite impacts 18,19 and the largest marsquake ever recorded 20 , surface waves constrain the average structures along the event-lander path 19,21,22 and are less sensitive to subsurface discontinuities. The present work aims at providing seismic constraints on the crustal structure at a location far from the InSight lander.…”

mentioning

confidence: 99%

Constraints on the martian crust away from the InSight landing site

McLennan

et al. 2022

Nat Commun

The most distant marsquake recorded so far by the InSight seismometer occurred at an epicentral distance of 146.3 ± 6.9o, close to the western end of Valles Marineris. On the seismogram of this event, we have identified seismic wave precursors, i.e., underside reflections off a subsurface discontinuity halfway between the marsquake and the instrument, which directly constrain the crustal structure away (about 4100−4500 km) from the InSight landing site. Here we show that the Martian crust at the bounce point between the lander and the marsquake is characterized by a discontinuity at about 20 km depth, similar to the second (deeper) intra-crustal interface seen beneath the InSight landing site. We propose that this 20-km interface, first discovered beneath the lander, is not a local geological structure but likely a regional or global feature, and is consistent with a transition from porous to non-porous Martian crustal materials.