Physics
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja......238z&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #238
Physics
Scientific paper
Current broad band seismometers can measure accelerations (Lognonn/'e et al., 1996) aN,E=- ω^2 uN,E ≈ 10-8 cm/s^2, where aN,E is the ground acceleration and uN,E is the ground displacement in the North and East direction. Now let's clarify why it is impossible to pick out spheroidal modes of low order in Apollo seismograms. We have calculated the amplitudes of displacements u_N, u_E and u_R (along the radius) excited by a lithospheric moonquake if the seimic moment is taken to be unity. For one of the strongest moonquakes (1975 year, the 3d day) the seismic moment is ≈ 1.6 × 1022 dyn cm, the seismic energy is > 6.9 × 1019 erg. If we take ω ≈ 0.02 s-1, u_R ≈ 6 × 10-30 × 1.6 × 1022, then a_R=10-10 cm/s^2, that two orders lower than the value of the upper mentioned condition. Thus, the best current seismometers couldn't record spheroidal oscillations of low order. Seismometers installed on the Moon recorded large meteoroid impacts. The kinetic energy released during the largest meteoroid impacts detected by the Apollo lunar seismic station network is estimated to be 1018-1019 erg. However, the coefficient of seismic efficiency is very small, ˜ 10-3-10-5. Taking this coefficient to be 10-4, we obtain the value of seismic energy generated by such impacts equal to ˜ 1015 erg. The equivalent seismic moment is several orders lower than the moment of a large moonquake. These estimates show why spheroidal modes of low order were not detected on the Moon.
Gudkova T. V.
Zharkov Vladimir Naumovich
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