Inversion of the Apollo lunar seismic data set in order to obtain information on the elastic modu... more Inversion of the Apollo lunar seismic data set in order to obtain information on the elastic moduli and the density structure of the Moon.
<p>Seismic noise recorded at the surface of Mars has been monitored... more <p>Seismic noise recorded at the surface of Mars has been monitored since February 2019, using the InSight seismometers.This noise can reach -200 dB and is 500 times lower than on Earth at night and it increases of 30 dB during the day. We analyze its polarization as a function of time and frequency in the band 0.03-1Hz. We use the degree of polarization<span>  </span>to extract signals with stable polarization independent of their amplitude and type of polarization. We detect polarized signals at all frequencies and all times. Glitches correspond to linear polarized signals which are more abundant during the night. For signals with elliptical polarization, the ellipse is in the horizontal plane below 0.3 Hz (LF). Above 0.3 Hz (HF) and except in the evening, the ellipse is in the vertical plane and the major axis is tilted. While polarization azimuths are different in the two frequency bands, they both vary as a function of local hour and season.<span>  </span>They are also correlated with wind direction, particularly during the daytime.</p><p>We investigate possible aseismic and seismic origins of the polarized signals. Lander or tether noise can be discarded. Pressure fluctuations transported by wind may explain part of the HF polarization but not the tilt of the ellipse. This tilt can be obtained if the source is an acoustic emission coming from high altitude at critical angle. Finally, in the evening when the wind is low, the polarized signals may correspond to the seismic wavefield of the Mars background noise.</p>
Let us consider the source excitation process for an impact. Following [1], we assume a simple mo... more Let us consider the source excitation process for an impact. Following [1], we assume a simple model for the seismic source function, namely, a time-dependent force acting downward on the surface of the planet during the impact: f(t)=G g(t)=G g(t)*delta(t),g(t)=1+cosomega1t for t in the interval (-pi/omega1,pi/omega1), g(t)=0 otherwise, where g(t) is the time dependence of the source, G is used
Despite 30 years of intensive observations of Mars, the structure of its interior is still largel... more Despite 30 years of intensive observations of Mars, the structure of its interior is still largely unknown. Gravity field modeling, measurements of rotational parameters, and geochemical analyses of Mars meteorites have served to bound possible models, but have produced few unambiguous results. In order to make a significant leap in our understanding of the interior of Mars, a seismic investigation is required. This has been one of the motivations for the development of the NetLander mission to Mars to be launched in 2007. This mission consists of a set of four small, low-mass landers, each of which will carry, among other instruments, an ultra-broad-band seismometer system which will operate on the surface for at least one Martian year. Despite severe constraints on mass, volume and power, the seismometers will have a sensitivity comparable to the best terrestrial seismometers (4-5 orders of magnitude better than the Viking instrument) over a wide frequency band, from DC to 50 Hz. The lander itself is designed to allow direct coupling of the seismometer to the ground, while providing protection from the wind and temperature extremes. This global seismic network will record the full range of seismic and gravity signals, from the body waves, surface waves and free oscillations generated by quakes induced by tectonics (driven by the thermoelastic contraction of the lithosphere and convective stresses), to meteoroid impacts and possible volcanic tremors, to the continuous excitation of planetary normal modes (by turbulence in the atmosphere) and tidal perturbations induced by Phobos. The comprehensive analysis of these seismic signals will enable us to determine the seismicity of the planet and the present-day meteoroid flux, and to constrain the thickness of the Martian crust, the composition and structure of Mars' mantle, including its phase transitions, as well as the state and size of the Martian core.
The objective of the Mars SEIS experiment is the determination of the deep internal structure of ... more The objective of the Mars SEIS experiment is the determination of the deep internal structure of Mars. In particular, geophysical parameters of first importance, such as the state (liquid/solid) and size of the core, as far as structure of the mantle and shape of discontinuities will be determined by the experience. The experiment integrates a Very Broad Band (2 axis) seismometer, a (3 axis) short period seismometer and environmental sensors for pressure, infrasounds and temperature. The sensors measure signals in an ultra-broad band, from the tidal frequencies (0.05 mHz) up to the short period frequencies (50 Hz). Long term VBB bias will be actively decorrelated from temperature and pressure variations, allowing the sensor to operate in a thermal environment with daily variations of about 40°K Infrasounds, which might be associated to dust devils and atmospheric discharge, will be also monitored. The overall mass of the SEIS experiment is 2.3 kg, including all sensors, data control...
The Apollo Passive Seismic Network (PSN) showed the Moon was seismically active on a scale simila... more The Apollo Passive Seismic Network (PSN) showed the Moon was seismically active on a scale similar to intraplate seismicity on Earth, but the small area covered by the PSN has prevented definitive conclusions being made about the deep lunar interior. For example, increased velocities at depths >500 km have large errors associated with them so mineralogical interpretations are poorly constrained; an increased proportion of Mg-rich olivine or the presence of garnet could explain the current data. Lunar Prospector data estimated a metallic lunar core with a radius of 340 km. However, existing geophysical data are consistent with either a metal or ilmenite core. Four types of lunar seismic events were documented: 1) Thermal moonquakes (smallest magnitude event) - associated with stresses induced by surface diurnal temperature changes. 2) Deep moonquakes (magnitude 2 or less) - >7,000 having been recognized. These events occur 700-1,200 km within the Moon and are associated with Ea...
Inversion of the Apollo lunar seismic data set in order to obtain information on the elastic modu... more Inversion of the Apollo lunar seismic data set in order to obtain information on the elastic moduli and the density structure of the Moon.
<p>Seismic noise recorded at the surface of Mars has been monitored... more <p>Seismic noise recorded at the surface of Mars has been monitored since February 2019, using the InSight seismometers.This noise can reach -200 dB and is 500 times lower than on Earth at night and it increases of 30 dB during the day. We analyze its polarization as a function of time and frequency in the band 0.03-1Hz. We use the degree of polarization<span>  </span>to extract signals with stable polarization independent of their amplitude and type of polarization. We detect polarized signals at all frequencies and all times. Glitches correspond to linear polarized signals which are more abundant during the night. For signals with elliptical polarization, the ellipse is in the horizontal plane below 0.3 Hz (LF). Above 0.3 Hz (HF) and except in the evening, the ellipse is in the vertical plane and the major axis is tilted. While polarization azimuths are different in the two frequency bands, they both vary as a function of local hour and season.<span>  </span>They are also correlated with wind direction, particularly during the daytime.</p><p>We investigate possible aseismic and seismic origins of the polarized signals. Lander or tether noise can be discarded. Pressure fluctuations transported by wind may explain part of the HF polarization but not the tilt of the ellipse. This tilt can be obtained if the source is an acoustic emission coming from high altitude at critical angle. Finally, in the evening when the wind is low, the polarized signals may correspond to the seismic wavefield of the Mars background noise.</p>
Let us consider the source excitation process for an impact. Following [1], we assume a simple mo... more Let us consider the source excitation process for an impact. Following [1], we assume a simple model for the seismic source function, namely, a time-dependent force acting downward on the surface of the planet during the impact: f(t)=G g(t)=G g(t)*delta(t),g(t)=1+cosomega1t for t in the interval (-pi/omega1,pi/omega1), g(t)=0 otherwise, where g(t) is the time dependence of the source, G is used
Despite 30 years of intensive observations of Mars, the structure of its interior is still largel... more Despite 30 years of intensive observations of Mars, the structure of its interior is still largely unknown. Gravity field modeling, measurements of rotational parameters, and geochemical analyses of Mars meteorites have served to bound possible models, but have produced few unambiguous results. In order to make a significant leap in our understanding of the interior of Mars, a seismic investigation is required. This has been one of the motivations for the development of the NetLander mission to Mars to be launched in 2007. This mission consists of a set of four small, low-mass landers, each of which will carry, among other instruments, an ultra-broad-band seismometer system which will operate on the surface for at least one Martian year. Despite severe constraints on mass, volume and power, the seismometers will have a sensitivity comparable to the best terrestrial seismometers (4-5 orders of magnitude better than the Viking instrument) over a wide frequency band, from DC to 50 Hz. The lander itself is designed to allow direct coupling of the seismometer to the ground, while providing protection from the wind and temperature extremes. This global seismic network will record the full range of seismic and gravity signals, from the body waves, surface waves and free oscillations generated by quakes induced by tectonics (driven by the thermoelastic contraction of the lithosphere and convective stresses), to meteoroid impacts and possible volcanic tremors, to the continuous excitation of planetary normal modes (by turbulence in the atmosphere) and tidal perturbations induced by Phobos. The comprehensive analysis of these seismic signals will enable us to determine the seismicity of the planet and the present-day meteoroid flux, and to constrain the thickness of the Martian crust, the composition and structure of Mars' mantle, including its phase transitions, as well as the state and size of the Martian core.
The objective of the Mars SEIS experiment is the determination of the deep internal structure of ... more The objective of the Mars SEIS experiment is the determination of the deep internal structure of Mars. In particular, geophysical parameters of first importance, such as the state (liquid/solid) and size of the core, as far as structure of the mantle and shape of discontinuities will be determined by the experience. The experiment integrates a Very Broad Band (2 axis) seismometer, a (3 axis) short period seismometer and environmental sensors for pressure, infrasounds and temperature. The sensors measure signals in an ultra-broad band, from the tidal frequencies (0.05 mHz) up to the short period frequencies (50 Hz). Long term VBB bias will be actively decorrelated from temperature and pressure variations, allowing the sensor to operate in a thermal environment with daily variations of about 40°K Infrasounds, which might be associated to dust devils and atmospheric discharge, will be also monitored. The overall mass of the SEIS experiment is 2.3 kg, including all sensors, data control...
The Apollo Passive Seismic Network (PSN) showed the Moon was seismically active on a scale simila... more The Apollo Passive Seismic Network (PSN) showed the Moon was seismically active on a scale similar to intraplate seismicity on Earth, but the small area covered by the PSN has prevented definitive conclusions being made about the deep lunar interior. For example, increased velocities at depths >500 km have large errors associated with them so mineralogical interpretations are poorly constrained; an increased proportion of Mg-rich olivine or the presence of garnet could explain the current data. Lunar Prospector data estimated a metallic lunar core with a radius of 340 km. However, existing geophysical data are consistent with either a metal or ilmenite core. Four types of lunar seismic events were documented: 1) Thermal moonquakes (smallest magnitude event) - associated with stresses induced by surface diurnal temperature changes. 2) Deep moonquakes (magnitude 2 or less) - >7,000 having been recognized. These events occur 700-1,200 km within the Moon and are associated with Ea...
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