It encompasses not only studies of the solid Earth but also of the oceans and atmosphere, the outer atmosphere, fields, particles, and planets within the solar system, and the relationship of the Sun and the planets. Geodesy is concerned with the shape of the Earth, its gravity field, and its orbital parameters, and with changes in the shape of the Earth brought about by tidal and tectonic forces. Studies of this shape and the gravity field lead to an understanding of the distribution of mass within the Earth. Variations of orbital parameters, such as changes in the pole of rotation and the length of the day, are measured at International Latitude Observatories established in a number of countries. The gravity field is studied by direct surface measurements and by analyses of the effect of the field on satellite trajectories.
Seismology is the study of earthquakes and related phenomena.
Central to the field is the study of seismic waves generated by earthquakes and other disturbances, such as underground nuclear explosions. Earthquakes generate these waves. By carefully timing the arrival of the waves, seismologists are able to study the physical properties of the deep interior of the Earth. Similarly, by locally monitoring seismic waves generated artificially by explosions, exploration geophysicists can determine underground structures that may indicate mineral deposits. This part of seismology overlaps with the field of tectonophysics, which is concerned with deformations in the Earth.