Moonquakes and lunar interior
JIANG Ming-ming and AI Yin-shuang(Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China)
The Apollo Seismic Network deployed by the astronauts of the Apollo grogram provided us with the excellent seismic data for revealing the lunar interior. Here we review studies of the moonquakes and seismic structure of the Moon based on the seismic data. Generally,the signals recorded by the seismometers are of three kinds:impacts,moonquakes,and local events. Impacts are classified as meteoroids and artificial impacts,and moonquakes are classified as shallow and deep moonquakes by focal depth. Shallow moonquakes are located at depth of about 50-220 km,they are strong but rare,and with high-frequency. Deep moonquakes are located at the depth of about 700-1150 km,and occur as clusters related with the tidal stress between the Earth and the Moon. Local events occur after sunrise or sunsets,probably generated by near surface thermal cracks and deformations. The studies of the lunar interior mainly focused on determination of the thickness of the lunar crust and the 1-D structure of the lunar upper mantle beneath the network. The available data suggest that the crust is on average about 40 km differing from the previous estimations (about 60 km). However,structure of the lower mantle,the core,and the deep discontinuities of the Moon are still ambiguous. Prospects on lunar seismology are discussed.