21 research outputs found
Autocorrelation of the Ground Vibrations Recorded by the SEIS-InSight Seismometer on Mars
Since early February 2019, the SEIS (Seismic Experiment for Interior Structure) seismometer deployed at the surface of Mars in the framework of the InSight mission has been continuously recording the ground motion at Elysium Planitia. In this study, we take advantage of this exceptional data set to put constraints on the crustal properties of Mars using seismic interferometry (SI). To carry out this task, we first examine the continuous records from the very broadband seismometer. Several deterministic sources of environmental noise are identified and specific preprocessing strategies are presented to mitigate their influence. Applying the principles of SI to the single-station configuration of InSight, we compute, for each Sol and each hour of the martian day, the diagonal elements of the time-domain correlation tensor of random ambient vibrations recorded by SEIS. A similar computation is performed on the diffuse waveforms generated by more than a hundred Marsquakes. A careful signal-to-noise ratio analysis and an inter-comparison between the two datasets suggest that the results from SI are most reliable in a narrow frequency band around 2.4 Hz, where an amplification of both ambient vibrations and seismic events is observed. The average autocorrelation functions (ACFs) contain well identifiable seismic arrivals, that are very consistent between the two datasets. Interpreting the vertical and horizontal ACFs as, respectively, the P- and S- seismic reflectivity below InSight, we propose a simple stratified velocity model of the crust, which is mostly compatible with previous results from receiver function analysis. Our results are discussed and compared to recent works from the literature.This study is InSight contribution number 164. The authors acknowledge both âUniversitĂ© FĂ©dĂ©rale de Toulouse Midi PyrĂ©nĂ©esâ and the âRĂ©gion Occitanieâ for funding the PhD grant of Nicolas Compaire. The French authors acknowledge the French Space Agency CNES and ANR (ANR-14-CE36-0012-02 and ANR-19-CE31-0008-08) for funding the InSight Science analysis
Constraining Martian Regolith and Vortex Parameters From Combined Seismic and Meteorological Measurements
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 (0.02â0.3 Hz) frequency band, we estimate that the mean value of η (η = E/[1 â Îœ2], where E is the Young's modulus and Îœ 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
Seismic Constraints on the Thickness and Structure of the Martian Crust from InSight
NASAÂżs InSight mission [1] has for
the first time placed a very broad-band seismometer on
the surface of Mars. The Seismic Experiment for
Interior Structure (SEIS) [2] has been collecting
continuous data since early February 2019. The main
focus of InSight is to enhance our understanding of the
internal structure and dynamics of Mars, which includes
the goal to better constrain the crustal thickness of the
planet [3]. Knowing the present-day crustal thickness of
Mars has important implications for its thermal
evolution [4] as well as for the partitioning of silicates
and heat-producing elements between the different
layers of Mars. Current estimates for the crustal
thickness of Mars are based on modeling the
relationship between topography and gravity [5,6], but
these studies rely on different assumptions, e.g. on the
density of the crust and upper mantle, or the bulk silicate
composition of the planet and the crust. The resulting
values for the average crustal thickness differ by more
than 100%, from 30 km to more than 100 km [7].
New independent constraints from InSight will be
based on seismically determining the crustal thickness
at the landing site. This single firm measurement of
crustal thickness at one point on the planet will allow to
constrain both the average crustal thickness of Mars as
well as thickness variations across the planet when
combined with constraints from gravity and topography
[8]. Here we describe the determination of the crustal
structure and thickness at the InSight landing site based
on seismic receiver functions for three marsquakes
compared with autocorrelations of InSight data [9].We acknowledge NASA, CNES, partner agencies and institutions (UKSA, SSO,DLR, JPL, IPGP-CNRS, ETHZ, IC, MPS-MPG) and the operators of JPL, SISMOC, MSDS, IRIS-DMC and PDS for providing SEED SEIS data. InSight data is archived in the PDS, and a full list of archives in the Geosciences, Atmospheres, and Imaging nodes is at https://pds-geosciences.wustl.edu/missions/insight/. This work was partially carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. ©2021, California Institute of Technology. Government sponsorship acknowledge
Autocorrelation of the Ground Vibrations Recorded by the SEISâInSight Seismometer on Mars
Since early February 2019, the SEIS (Seismic Experiment for Interior Structure)
seismometer deployed at the surface of Mars in the framework of the InSight mission has been
continuously recording the ground motion at Elysium Planitia. In this study, we take advantage of this
exceptional data set to put constraints on the crustal properties of Mars using seismic interferometry (SI).
To carry out this task, we first examine the continuous records from the very broadband seismometer.
Several deterministic sources of environmental noise are identified and specific preprocessing strategies
are presented to mitigate their influence. Applying the principles of SI to the single-station configuration
of InSight, we compute, for each Sol and each hour of the martian day, the diagonal elements of the
time-domain correlation tensor of random ambient vibrations recorded by SEIS. A similar computation
is performed on the diffuse waveforms generated by more than a hundred Marsquakes. A careful signal-
to-noise ratio analysis and an inter-comparison between the two datasets suggest that the results from
SI are most reliable in a narrow frequency band around 2.4 Hz, where an amplification of both ambient
vibrations and seismic events is observed. The average autocorrelation functions (ACFs) contain well
identifiable seismic arrivals, that are very consistent between the two datasets. Interpreting the vertical
and horizontal ACFs as, respectively, the P- and S- seismic reflectivity below InSight, we propose a simple
stratified velocity model of the crust, which is mostly compatible with previous results from receiver
function analysis. Our results are discussed and compared to recent works from the literature
The interior of Mars as seen by InSight (Invited)
InSight is the first planetary mission dedicated to exploring the whole interior of a planet using geophysical methods, specifically seismology and geodesy. To this end, we observed seismic waves of distant marsquakes and inverted for interior models using differential travel times of phases reflected at the surface (PP, SS...) or the core mantle-boundary (ScS), as well as those converted at crustal interfaces. Compared to previous orbital observations1-3, the seismic data added decisive new insights with consequences for the formation of Mars: The global average crustal thickness of 24-75 km is at the low end of pre-mission estimates5. Together with the the thick lithosphere of 450-600 km5, this requires an enrichment of heat-producing elements in the crust by a factor of 13-20, compared to the primitive mantle. The iron-rich liquid core is 1790-1870 km in radius6, which rules out the existence of an insulating bridgmanite-dominated lower mantle on Mars. The large, and therefore low-density core needs a high amount of light elements. Given the geochemical boundary conditions, Sulfur alone cannot explain the estimated density of ~6 g/cm3 and volatile elements, such as oxygen, carbon or hydrogen are needed in significant amounts. This observation is difficult to reconcile with classical models of late formation from the same material as Earth. We also give an overview of open questions after three years of InSight operation on the surface of Mars, such as the potential existence of an inner core or compositional layers above the CM
Constraints on the shallow elastic and anelastic structure of Mars from InSight seismic data
Marsâs seismic activity and noise have been monitored since January 2019 by the seismometer of the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) lander. At night, Mars is extremely quiet; seismic noise is about 500 times lower than Earthâs microseismic noise at periods between 4 s and 30 s. The recorded seismic noise increases during the day due to ground deformations induced by convective atmospheric vortices and ground-transferred wind-generated
lander noise. Here we constrain properties of the crust beneath InSight, using signals from atmospheric vortices and from the
hammering of InSightâs Heat Flow and Physical Properties (HP3) instrument, as well as the three largest Marsquakes detected
as of September 2019. From receiver function analysis, we infer that the uppermost 8â11 km of the crust is highly altered and/
or fractured. We measure the crustal diffusivity and intrinsic attenuation using multiscattering analysis and find that seismic
attenuation is about three times larger than on the Moon, which suggests that the crust contains small amounts of volatiles
Productivité et performance à l'exportation dans le transport : une étude sur le cas de huit pays
First seismic constraints on the Martian crust - receiver functions for InSight
EGU2020: Sharing Geoscience Online, 4-8 May, 2020NASA's InSight mission arrived on Mars in November 2018 and deployed the first very broad-band seismometer, SEIS, on the planet's surface. SEIS has been collecting data continuously since early February 2019, by now recording more than 400 events of different types. InSight aims at enhancing our understanding of the internal structure and dynamics of Mars, including better constraints on its crustal thickness. Various models based on topography and gravity observed from the orbit currently vary in average crustal thickness from 30 km to more than 100 km, with important implications for MarsÂż thermal evolution, and the partitioning of silicates and heat-producing elements between different layers of Mars.
We present P-to-S and S-to-P receiver functions, which are available for 4 and 3 marsquakes, respectively, up to now. Out of all of the marsquakes recorded to date, these are the only ones with clear enough P- or S-arrivals not dominated by scattering to make them suitable for the analysis. All of the quakes are located at comparatively small epicentral distances, between 25° and 40°. We observe three consistent phases within the first 10 seconds of the P-to-S receiver functions. The S-to-P receiver functions also show a consistent first phase. Later arrivals are harder to pinpoint, which could be due to the comparatively shallow incidence of the S-waves at the considered distances, which prevents the generation of converted waves. Identification of later multiple phases in the P-to-S receiver functions likewise remains inconclusive. To obtain better constraints on velocity, we also calculated apparent velocity curves from the P-to-S receiver functions, but these provide meaningful results for only one event so far, implying a large uncertainty. Due to difficulties in clearly identifying multiples, the receiver functions can currently be explained by either two crustal layers and a thin (25-30 km) crust or three crustal layers and a thicker (40-45 km) crust at the landing site. This model range already improves the present constraints by providing a new maximum value of less than 70 km for the average crustal thickness. Information from noise autocorrelations as a complementary method, identification of P-reverberations and S-precursors in the event recordings, and more extensive modeling, ultimately including 3D-effects, are considered to further our understanding of the waveforms and tighten the constraints on the crust
Seasonal variations of subsurface seismic velocities monitored by the SEIS-InSight seismometer on Mars
The SEIS seismometer deployed at the surface of Mars in the framework of the NASA-
InSight mission has been continuously recording the ground motion at Elysium Planitia
for more than one martian year. In this work, we investigate the seasonal variation of the
near surface properties using both background vibrations and a particular class of high-
frequency seismic events. We present measurements of relative velocity changes over one
martian year and show that they can be modeled by a thermoelastic response of the Mar-
tian regolith. Several families of high-frequency seismic multiplets have been observed at
various periods of the martian year. These events exhibit complex, repeatable waveforms
with an emergent character and a coda that is likely composed of scattered waves. Taking advantage of these properties, we use coda wave interferometry to measure relative
travel-time changes as a function of the date of occurrence of the quakes. While in some
families a stretching of the coda waveform is clearly observed, in other families we ob-
serve either no variation or a clear contraction of the waveform. These various behaviors
correspond to different conditions of illumination at the InSight landing site, depending
on the season. Measurements of velocity changes from the analysis of background vi-
brations above 5 Hz are consistent with the results from coda wave interferometry. We
identify a frequency band structure in the power spectral density that can be tracked over
hundreds of days. This band structure is the equivalent in the frequency domain of an
autocorrelogram and can be efficiently used to measure relative travel-time changes as a
function of frequency. We explain how the PSD analysis allows us to circumvent the con-
tamination of the measurements by the Lander mode excitation which is inevitable in the
time domain. The observed velocity changes can be adequately modeled by the thermoe-
lastic response of the regolith to the time-dependent incident solar flux at the seasonal
scale. In particular, the model captures the time delay between the surface temperature
variations and the velocity changes in the subsurface. Our observations could serve as
a basis for a joint inversion of the seismic and thermal properties in the first 20 meters
below InSight
Noise Autocorrelations on Mars
EGU General Assembly in Viena, Austria,7â12 April 2019InSight landed on Mars on November 26th, 2018 with several geophysical instruments including a short-period
seismometer and a broadband seismometer (SEIS, Seismic Experiment for Interior Structure). Both seismometers
are now installed directly on the Mars surface and enable to analyze the continuous seismic signal. The purpose
of this study is to analyze autocorrelations of Mars continuous seismic signal. Seismic interferometry by ambient
noise autocorrelations is a special case of Greenâs function retrieval for single-station analysis. High-frequency
noise autocorrelations can be used to extract the zero-offset reflectivity and basin resonances beneath of the landing
site while low-frequency noise autocorrelations contain mainly orbiting surface waves and are useful to extract
normal modes. We analyze the signal by using both the classical and phase autocorrelations. Correlograms are
stacked using the phase weighted stack method in order to enhance the signal to noise ratio.
The method was tested also on the two blindtest datasets provided by the Marsquake Service (MQS) and by the
Mars Structure Service (MSS). It is further applied to analyze the first data recorded on Mars by the co-located
broadband and short period seismometers