Earthquakes definitely alter the Earth's gravity field, because they change the Earth's mass distribution. These changes have been routinely noticed by people

Earthquakes definitely alter the Earth's gravity field, because they change the Earth's mass distribution. These changes have been routinely noticed by people who track satellites. In the early 2000s there was a mission called GRACE to precisely measure the gravity field and its temporal variation. It's important to know it exactly for all sorts of purposes. Here's some nice results from GRACE: http://www.nasa.gov/vision/earth/lookingatearth/grace-images-20051220.html http://www.nasa.gov/vision/earth/lookingatearth/grace-images... The second item there shows a change in the acceleration due to gravity that was caused by the Sumatra earthquake of December 2004. It is measured in nano m/s^2. The movie above that item shows the changes in gravity due (mostly) to sloshing water on a global scale.