Ultra broad band seismology on InterMarsNet
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文摘
Very broad band seismometers, which are included in the baseline of the InterMarsNet payload cover the whole frequency band from tidal frequencies up to 50 Hz. By using the results of field tests performed on Earth with the deployment scenario of the InterMarsNet seismic experiment, it is shown that it should probably be possible to reach very low micro-seismic noise level, possibly less than a spectral amplitude of 10−9 m s−2 Hz− on the vertical component. Despite the fact that only three stations will be available for the network, sufficient information should be available in the three-component short period records to determine the location of Marsquake foci and the origin time to a level that will enable studies of the seismicity, interior velocity structure, and tectonic activity of the planet. Despite the fact that the most current signals will be recorded in the frequency band 10 mHz-10 Hz, it is shown that the detection of a quake of moment 1018 N m, or the stack of the InterMarsNet records of quakes with a moment greater than 1017 N m will allow normal mode frequency measurement in the range 5-20 mHz for a noise amplitude of 10−9 m s−2 Hz−. Observation in the range 3-5 mHz cannot also be ruled out. These normal mode frequencies will have a high scientific return for determining the deep Mars structure. At longer periods, the detection of the tides of Phobos will provide information on the deep internal structure even if no strong quakes are recorded. It is shown that the amplitude of the Phobos tide fundamental after the analysis of a 2 year time series from a single station, for a realistic and conservative estimate of the long period noise may be measured with a precision of 1 % . For less noise scenario, and/or by using the stack of all the records, information from the higher Phobos tidal harmonics will also be obtained.