Role of environmental factors in seismic-noise excitation on Mars

Seismic noises are excited by various factors including human activity and natural forces such as winds, river flows, and ocean tides. In addition to anthropogenic noises, seismic noises from natural phenomena are also recorded at frequencies higher than 1 Hz. We analyze the diurnal fluctuation in spectral amplitudes of seismic noises in rural as well as urban regions for three years on Korea Peninsula. We assess correlations between ambient seismic noises and meteorological factors such as wind speed, temperature and atmospheric pressure, which allows us to infer the main sources of high-frequency noises. We analyze seismic noises in mountain regions. Seismic noises at mountain regions present diurnal variation in spectral amplitudes at frequencies of 30-40 Hz. High-speed wind appears to be the main source to develop daily-varying seismic noises. We further analyze ambient seismic noises in 8 pm to 5 am local time to minimize the influence of human activities. The noise amplitude increases with wind speed. The observation is apparent in mountain regions with complex terrain and obstacles. We analyze the seismic records from the seismometers of the Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) mission that started in late 2018 on Mars. The seismic instruments of InSight mission consist of very broad band and short-period seismometers. We also collect meteorological information including wind speed, temperature and atmospheric pressure. We observe diurnal periodicity in spectral amplitudes at frequencies greater than 0.2 Hz. We find dominant energy varying between 3.8 and 4.2 Hz. We observe weak coherent energy in 2.5-3.3 Hz and 5.6-6.7 Hz. Also, we find strong energy that fluctuates with time in 20-30 Hz. The sources of these noises may be wind, temperature, atmospheric pressure, and instrumental self noises. We analyze the spectral contents of Mars considering the effective natural sources for seismic noises in the Earth. The seismic data may allow us to infer the natural phenomena on Mars.