The InSight mission landed on Mars in November 2018 and has since observed multiple convective vortices with both the high performance barometer and the low‐noise seismometer SEIS that has ...unprecedented sensitivity. Here, we present a new method that uses the simultaneous pressure and seismic measurements of convective vortices to place constraints on the elastic properties of the Martian subsurface and the Martian vortex properties, while also allowing a reconstruction of the convective vortex trajectories. From data filtered in the (0.02–0.3 Hz) frequency band, we estimate that the mean value of η (η = E/1 − ν2, where E is the Young's modulus and ν is the Poisson's ratio) of the Martian ground in the region around SEIS is 239 ± 140 MPa. In addition, we suggest that the previously reported paucity of vortex seismic observations to the west of InSight may be due to the fact that the ground is harder to the west than to the east, consistent with geomorphological surface interpretations.
Plain Language Summary
In 2018, the InSight mission placed a seismic instrument on the surface of Mars in order to measure the motion of the Martian ground. As on Earth, there are fluctuations of pressure in the Martian atmosphere caused by small local variations in the atmospheric weight. Whirlwinds, for example, have a lower pressure in their center and they pull up the ground (like a vacuum cleaner). Such changes in pressure deform the elastic Martian ground and the InSight seismic instrument is sensitive enough to measure these deformations. We present a new method that uses the InSight pressure and seismic measurements of whirlwinds in order to determine how hard or soft the Martian ground is. We are also able to estimate the path that the whirlwinds follow as they pass by InSight. We find that the surface material just under InSight has elastic properties similar to dense gravel, but that the whirlwinds detected by the seismic instrument are not in the same places as the whirlwinds tracks observed from space. Our results suggest that the ground is harder to the west and, consequently, that it is more difficult for whirlwinds to deform the ground and create a seismic signal in that region.
Key Points
Elastic properties of the Martian subsurface can be constrained using simultaneous pressure and seismic measurements of convective vortices
Our modeling can also be used to constrain Martian convective vortex properties and to reconstruct the vortex trajectories
The results indicate that the Martian ground may be harder to the west of InSight, consistent with geomorphological surface interpretations
The InSight Mission began acquiring the first seismic data on Mars in early 2019 and has detected hundreds of events. The largest events recorded to date originate at Cerberus Fossae, a young ...volcanic region characterized by high volume, low viscosity lava flows. A handful of Low Frequency (LF) quakes that share key attributes of Long Period quakes recorded on Earth's volcanoes are also traced to Cerberus Fossae. This study explores whether a traditional volcanic source model that simulates the generation of tremor as pressurized fluid makes its way through a channel at depth, can explain these atypical LF events. We consider a wide range of physical parameters including fluid viscosity, the ratio of driving pressure to lithostatic pressure, aspect ratio of the channel, and the equilibrium channel opening. We find that the model can produce the observed seismic signature, with a combination of low‐viscosity magma and high volume flux of ∼104 − 105 m3/s that are within an order‐of‐magnitude agreement with Cerberus Fossae lava flow properties deduced from analysis of lava flow dimensions. It is impossible, however, at this stage to conclude whether or not this is a likely explanation for Mars, as the model results in fluxes that are extreme for Earth yet are just within bounds of what has been inferred for Cerberus Fossae. We therefore conclude that we cannot rule out active magma flow as the mechanism responsible for the atypical LF events that likely originate from Cerberus Fossae.
Plain Language Summary
A number of Marsquakes are located at a region of Mars that hosted geologically recent volcanic eruptions. A subset of these events resemble seismic events recorded at volcanoes on Earth. We set out to study whether these events can be explained by fluid flow at depth, using a model of fluid flow through a channel. We find that low viscosities and high flow rates that are within an order‐of‐magnitude agreement with flow properties deduced from modeling of Cerberus Fossae lava flows are required to match the observed events in question. It is impossible at this stage of the InSight mission, however, to conclude whether or not this is a likely explanation for Mars.
Key Points
Low Frequency (LF) events that share attributes of volcanic quakes are traced to a young volcanic region on Mars
LF events are modeled as deep volcanic quakes caused by pressure‐driven flow across a channel at Cerberus Fossae
LF attributes are matched by fluids less viscous and of higher fluxes than terrestrial flood basalts
Convective vortices (whirlwinds) and dust devils (dust‐loaded vortices) are one of the most common phenomena on Mars. They reflect the local thermodynamical structure of the atmosphere and are the ...driving force of the dust cycle. Additionally, they cause an elastic ground deformation, which is useful for retrieving the subsurface rigidity. Therefore, investigating convective vortices with the right instrumentation can lead to a better understanding of the Martian atmospheric structures as well as the subsurface physical properties. In this study, we quantitatively characterized the convective vortices detected by NASA's InSight (∼13,000 events) using meteorological (e.g., pressure, wind speed, temperature) and seismic data. The evaluated parameters, such as the signal‐to‐noise ratio, event duration, asymmetricity of pressure drop profiles, and cross‐correlation between seismic and pressure signals, are compiled as a catalog. Using these parameters, we investigated (a) the vortex structure and (b) the subsurface physical properties. Regarding the first topic, we tried to illustrate the vertical vortex structure and its link to the shape of the pressure profiles by combining the asymmetrical features seen in the observed pressure drops and the terrestrial observations of dust devils. Our results indicate that most of the vortices move with the wall tilted in the advection direction. Concerning the second topic, selecting the highly correlated events between pressure perturbation and ground response, we estimated the subsurface rigidity at the InSight landing site down to 100 m depth. Our results indicate that the subsurface structure can be modeled with two layers having a transition at 5–15 m depth.
Plain Language Summary
As frequently observed on Earth, convective vortices or dust‐loaded vortices are also seen on Mars. They reflect the local atmospheric structure and are the main driving force to lift the fine dust from the ground. In 2018, NASA's InSight succeeded in installing the meteorological and geophysical packages on Mars. That brought us, in particular, meteorological data with an extremely high temporal resolution, contributing to resolving local phenomena such as convective vortices. In this study, using InSight's meteorological (e.g., pressure, air temperature) and seismic data, we quantitatively characterize convective vortices to understand this phenomenon from both meteorological and geophysical aspects. Especially focusing on the asymmetricity of pressure drop profiles at vortex encounters and the correlation between the pressure variations and seismic signals, we investigated (a) a link between the shape of pressure drop profiles and the vertical vortex structure and (b) the ground rigidity structure by measuring the ground responses against the vortex‐related pressure variations. Consequently, first, we found that most of the vortices move with the wall tilted in the advection direction. Second, our results indicated that the subsurface structure can be modeled with two layers down to 100 m with a transition at 5–15 m depth.
Key Points
We quantitatively characterized the Martian convective vortices observed by InSight's seismometer and meteorological instruments
Focusing on the pressure drop profiles, we inferred a link between the asymmetricity and the vertical vortex structure
With the cataloged parameters, we performed a compliance analysis and evaluated the ground rigidity at the InSight landing site
Seismic detection of the martian core Stähler, Simon C.; Khan, Amir; Banerdt, W. Bruce ...
Science (American Association for the Advancement of Science),
07/2021, Letnik:
373, Številka:
6553
Journal Article
Recenzirano
Odprti dostop
Single seismometer structure
Because of the lack of direct seismic observations, the interior structure of Mars has been a mystery. Khan
et al.
, Knapmeyer-Endrun
et al.
, and Stähler
et al.
used ...recently detected marsquakes from the seismometer deployed during the InSight mission to map the interior of Mars (see the Perspective by Cottaar and Koelemeijer). Mars likely has a 24- to 72-kilometer-thick crust with a very deep lithosphere close to 500 kilometers. Similar to the Earth, a low-velocity layer probably exists beneath the lithosphere. The crust of Mars is likely highly enriched in radioactive elements that help to heat this layer at the expense of the interior. The core of Mars is liquid and large, ∼1830 kilometers, which means that the mantle has only one rocky layer rather than two like the Earth has. These results provide a preliminary structure of Mars that helps to constrain the different theories explaining the chemistry and internal dynamics of the planet.
Science
, abf2966, abf8966, abi7730, this issue p.
434
, p.
438
, p.
443
see also abj8914, p.
388
Data from the InSight mission on Mars help constrain the structure and properties of the martian interior.
Clues to a planet’s geologic history are contained in its interior structure, particularly its core. We detected reflections of seismic waves from the core-mantle boundary of Mars using InSight seismic data and inverted these together with geodetic data to constrain the radius of the liquid metal core to 1830 ± 40 kilometers. The large core implies a martian mantle mineralogically similar to the terrestrial upper mantle and transition zone but differing from Earth by not having a bridgmanite-dominated lower mantle. We inferred a mean core density of 5.7 to 6.3 grams per cubic centimeter, which requires a substantial complement of light elements dissolved in the iron-nickel core. The seismic core shadow as seen from InSight’s location covers half the surface of Mars, including the majority of potentially active regions—e.g., Tharsis—possibly limiting the number of detectable marsquakes.
The InSight mission (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) has been collecting high-quality seismic data from Mars since February 2019, shortly after its ...landing. The Marsquake Service (MQS) is the team responsible for the prompt review of all seismic data recorded by the InSight's seismometer (SEIS), marsquake event detection, and curating seismicity catalogues. Until sol 1011 (end of September 2021), MQS have identified 951 marsquakes that we interpret to occur at regional and teleseismic distances, and 1062 very short duration events that are most likely generated by local thermal stresses nearby the SEIS package. Here, we summarize the seismic data collected until sol 1011, version 9 of the InSight seismicity catalogue. We focus on the significant seismicity that occurred after sol 478, the end date of version 3, the last catalogue described in a dedicated paper. In this new period, almost a full Martian year of new data has been collected, allowing us to observe seasonal variations in seismicity that are largely driven by strong changes in atmospheric noise that couples into the seismic signal. Further, the largest, closest and most distant events have been identified, and the number of fully located events has increased from 3 to 7. In addition to the new seismicity, we document improvements in the catalogue that include the adoption of InSight-calibrated Martian models and magnitude scales, the inclusion of additional seismic body-wave phases, and first focal mechanism solutions for three of the regional marsquakes at distances ∼30°.
We present inversions for the structure of Mars using the first Martian seismic record collected by the InSight lander. We identified and used arrival times of direct, multiples, and depth phases of ...body waves, for 17 marsquakes to constrain the quake locations and the one-dimensional average interior structure of Mars. We found the marsquake hypocenters to be shallower than 40 km depth, most of them being located in the Cerberus Fossae graben system, which could be a source of marsquakes. Our results show a significant velocity jump between the upper and the lower part of the crust, interpreted as the transition between intrusive and extrusive rocks. The lower crust makes up a significant fraction of the crust, with seismic velocities compatible with those of mafic to ultramafic rocks. Additional constraints on the crustal thickness from previous seismic analyses, combined with modeling relying on gravity and topography measurements, yield constraints on the present-day thermochemical state of Mars and on its long-term history. Our most constrained inversion results indicate a present-day surface heat flux of 22 ± 1 mW/m2, a relatively hot mantle (potential temperature: 1740 ± 90 K) and a thick lithosphere (540 ± 120 km), associated with a lithospheric thermal gradient of 1.9 ± 0.3 K/km. These results are compatible with recent seismic studies using a reduced data set and different inversion approaches, confirming that Mars' potential mantle temperature was initially relatively cold (1780 ± 50 K) compared to that of its present-day state, and that its crust contains 10-12 times more heat-producing elements than the primitive mantle.
J’examine les relations entre propriétés des failles géologiques long-termes et propriétés des forts séismes que produisent ces failles. J’ai compilé les données sismologiques disponibles sur les ...grands séismes historiques mondiaux, et cartographié, sur images satellitaires, les failles long-termes rompues par ces séismes et les traces des ruptures. L’analyse combinée des données montre que : i) les failles long-termes ont certaines propriétés génériques (organisation des réseaux, segmentation latérale, forme de distribution du glissement cumulé, etc) ; ii) les forts séismes ont également des propriétés communes (similarité de distribution du glissement cosismique, du nombre de segments rompus, de la chute de contrainte sur chaque segment majeur rompu, de la distance relative entre hypocentre et zone de glissement maximum, etc) ; iii) la maturité structurale des failles est la propriété tectonique qui impacte le plus le comportement des forts séismes. Il est probable que cette maturité diminue la friction statique et la complexité géométrique du plan de faille. Elle agit sur la localisation de la zone d’initiation du séisme, sur la localisation et l’amplitude maximum du glissement cosismique, sur la direction de décroissance de ce glissement, sur la « capacité » de la rupture à se propager et donc sur sa vitesse de propagation. Elle dicte le nombre de segments majeurs qui peuvent être rompus, et par conséquent, elle contrôle la longueur totale et la chute de contrainte globale de la rupture. Pour comprendre la physique des forts séismes, il apparaît donc indispensable d’analyser conjointement les propriétés des failles rompues et les propriétés des séismes produits.
I examine the relations between the properties of long-term geological faults and the properties of the large earthquakes these faults produce. I have gathered available seismological information on large historical earthquakes worldwide and mapped in detail, on satellite images, both the long-term fault and the rupture traces. The combined analysis of the data shows that: i) long-term faults have a number of generic properties (arrangement of overall fault networks, lateral segmentation of fault traces, form of cumulative slip distribution, etc); ii) large earthquakes also have generic properties (similarity of envelope shape of coseismic slip-length profiles, of decrease in rupture width along rupture length, of number of broken segments, of stress drop on broken segments, of relative distance between hypocenter and zone of maximum slip, etc); iii) the structural maturity of the faults is the tectonic property most impacting the behavior of large earthquakes. The maturity likely acts in reducing both the static friction and the geometric complexity of the fault plane. It partly governs the location of the earthquake initiation, the location and amplitude of the maximum coseismic slip, the direction of the coseismic slip decrease, the rupture propagation efficiency and speed, the number of major fault segments that are broken, and hence the rupture length and its overall stress drop. To understand the physics of earthquakes, it thus seems necessary to analyze jointly the tectonic properties of the broken faults and the seismological properties of the earthquakes.
The InSight mission has operated on the surface of Mars for nearly two Earth years, returning detections of the first Marsquakes. The lander also deployed a meteorological instrument package and ...cameras to monitor local surface activity. These instruments have detected boundary layer phenomena, including small-scale vortices. These vortices register as short-lived, negative pressure excursions and closely resemble those that could generate dust devils. Although our analysis shows InSight encountered more than 900 vortices and collected more than 1000 images of the martian surface, no active dust devils were imaged. In spite of the lack of dust devil detections, we can leverage the vortex detections and InSight's daily wind speed measurements to learn about the boundary layer processes that create dust devils. We discuss our analysis of InSight's meteorological data to assess the statistics of vortex and dust devil activity. We also infer encounter distances for the vortices and, therefrom, the maximum vortex wind speeds. Surveying the available imagery, we place upper limits on what fraction of vortices carry dust (i.e., how many are bonafide dust devils) and estimate threshold wind speeds for dust lifting. Comparing our results to detections of dust devil tracks seen in space-based observations of the InSight landing site, we can also infer thresholds and frequency of track formation by vortices. Comparing vortex encounters and parameters with advective wind speeds, we find evidence that high wind speeds at InSight may have suppressed the formation of dust devils, explaining the lack of imaged dust devils.
PDF
