Seismology on Mars

Abstract

A three‐axis short‐period seismometer has been operating on the surface of Mars in the Utopia Planitia region since September 4, 1976. During the first 5 months of operation, approximately 640 hours of high‐quality data, uncontaminated by lander or wind noise, have been obtained. The detection threshold is estimated to be magnitude 3 to about 200 km and about 6.5 for the planet as a whole. No large events have been seen during this period, a result indicating that Mars is less seismically active than earth. Wind is the major source of noise during the day, although the noise level was at or below the sensitivity threshold of the seismometer for most of the night during the early part of the mission. Winds and therefore the seismic background started to intrude into the nighttime hours starting on sol 119 (a sol is a Martian day). The seismic background correlates well with wind velocity and is proportional to the square of the wind velocity, as is appropriate for turbulent flow. The seismic envelope power spectral density is proportional to frequency to the −0.66 to −0.90 power during windy periods. A possible local seismic event was detected on sol 80. No wind data were obtained at the time, so a wind disturbance cannot be ruled out. However, this event has some unusual characteristics and is similar to local events recorded on earth through a Viking seismometer system. If it is interpreted as a natural seismic event, it has a magnitude of 3 and a distance of 110 km. Preliminary interpretation of later arrivals in the signal suggest a crustal thickness of 15 km at the Utopia Planitia site which is within the range of crustal models derived from the gravity field. More events must be recorded before a firm interpretation can be made of seismicity or crustal structure. One firm conclusion is that the natural background noise on Mars is low and that the wind is the prime noise source. It will be possible to reduce this noise by a factor of 103 on future missions by removing the seismometer from the lander, operation of an extremely sensitive seismometer thus being possible on the surface.

Mars and its magnetic field— Some new aspects

“…Densities in linear approximation are taken from Anderson et al (1977) and a resulting pressure distribution is obtained assuming hydrostatic equilibrium. Application of (3) yields under appropriate suppositions for the melting temperature the rough estimation L -3.5 x lo5 J kg-'.…”

The Noise Model of the SEIS Seismometer of the InSight Mission to Mars

“…First, the VBBs and the SPs are each protected by three layers of insulation: the WTS, the RWEB and a gold coated evacuated container (the "sphere") for the VBBs, and the WTS, the RWEB and the SP-box for the SPs. Note that this concept of wind shielded protection, already suggested by Anderson et al (1977) following the Experience Return of Viking, was very rapidly tested (e.g. Lognonné et al (1996) for wind shield tests made for InterMarsnet).…”

“…The seismic noise induced by the wind on a lander has been the main source of noise witnessed by the Viking seismic experiment-see Anderson et al (1977), Nakamura and Anderson (1979). As the Viking seismometers were located on the top of the Viking lander platform, it appears-e.g.…”

Evaluating the Wind-Induced Mechanical Noise on the InSight Seismometers

“…Wind induced noise has been directly detected by the Viking seismic experiment (Anderson et al 1977;Nakamura and Anderson 1979). In fact, significant periods of time during the Viking lander missions were dominated by the wind-induced lander vibration (Goins and Lazarewicz 1979).…”