#TIDAL HEATING SERIES#
Here was analyzed a time series of deep moonquakes (correlating with deep earthquakes) with the number of seismic events per day, and calculated correspondent orbital parameters, such as variations in distance, angular and temporal occurrence between the Moon and the Sun-Earth orbital planes. Also, the angle relation between the lunar apse parallel to the axis of rotation of the Earth has been associated with an increase in the number of large earthquakes, due to tidal stresses. On Earth, deep quakes occur close to the transition zone in the mantle and their origin is often associated with dehydration of lithospheric slabs. However, cyclic tidal stress is not sufficient to cause rupture at confining pressures where deep moonquakes occur, since its hypocenters occur in deeper areas and may not be sensitive to tidal stress. Deep moonquakes, for example, have been associated with lunar orbital cyclicity. Previous studies suggest that these deep quakes can be triggered by gravitational variability, produced by the motion of the Moon around the Earth (such as the synodic, anomalistic, and sidereal periods/months), i.e., tidal periodicity. Although the interpretation of seismological data from the Apollo Missions has provided essential information on the composition and structure of the Moon, a relationship between this structuration and how the gravitational forces in the Earth-Moon-Sun system influence deep moonquakes is still unclear. One of them involves the casual mechanism of deep moonquakes, which are low magnitude seismic events (M ≤ 2) that ranges from 700 km to 1200 km in depth. Fifty years after the Apollo 11 mission, some questions on the geophysical characteristics of the Moon still remain unanswered. The genesis of deep quakes has been challenged scientists for decades. We also find that tidal dissipation is not evenly distributed in the lunar interior, but localized within the low-viscosity layer, which implies that this layer may act as a thermal blanket(16) on the lunar core and influence the Moon's thermal evolution. Compared with the lunar asthenosphere, the calculated viscosity is extremely low, and suggests partial melting at the lunar core-mantle boundary. In our simulations, a layer with a viscosity of about 2 x 10(16) Pa s leads to frequency-dependent tidal dissipation that matches tidal dissipation measurements at both monthly and annual periods. Here we numerically simulate the viscoelastic tidal response of a Moon that contains a low-viscosity layer at the core-mantle boundary and compare with geodetic observations(10,14,15). The attenuation of seismic waves in the deep lunar interior(11,12) is expected to be consistent with a low-viscosity layer at the core-mantle boundary, which may explain the observed frequency dependence(13). Calculations of the response of the Moon to tidal forces have considered lunar interior structure(1-5), but have not reproduced the geodetically observed dependence of dissipation on the lunar tidal period(10). Tidal heating of a solid planetary body occurs by viscous dissipation, depending on its internal structure(1-5) and thermal(5-8) and orbital(6-9) states.
0 kommentar(er)
