The Gravitational Signature of Earthquakes

The static displacement field generated by an earthquake redistributes the Earth’s mass and consequently causes the Earth’s rotation and global gravitational field to change. Although the coseismic effect of earthquakes on the Earth’s rotation and global gravitational field has been modeled in the past, no unambiguous observations of this effect have yet been made. However, the Gravity Recovery And Climate Experiment (GRACE) satellite, which is scheduled to be launched in 2001, will measure time variations of the Earth’s gravitational field to high degree and order with unprecedented accuracy. Here, the coseismic effect of earthquakes on the Earth’s global gravitational field will be modeled and compared with the expected accuracy of the GRACE measurements. It is shown that the coseismic effects of great earthquakes such as the 1960 Chilean or 1964 Alaskan events can cause global gravitational field changes that are large enough to be detected by GRACE. However, the coseismic effects of the largest earthquakes that have occurred during the past 35 years cause global gravitational field changes that are probably too small to be detected by GRACE.