The allegation: global warming is melting ice caps and glaciers, thereby unloading weight. This causes an isostatic readjustment of the Earth’s crust which results in earthquakes.
The reality according to the U.S. Geological Survey:
We continue to be asked by many people throughout the world if earthquakes are on the increase. Although it may seem that we are having more earthquakes, earthquakes of magnitude 7.0 or greater have remained fairly constant.
A partial explanation may lie in the fact that in the last twenty years, we have definitely had an increase in the number of earthquakes we have been able to locate each year. This is because of the tremendous increase in the number of seismograph stations in the world and the many improvements in global communications. In 1931, there were about 350 stations operating in the world; today, there are more than 8,000 stations and the data now comes in rapidly from these stations by electronic mail, internet and satellite. This increase in the number of stations and the more timely receipt of data has allowed us and other seismological centers to locate earthquakes more rapidly and to locate many small earthquakes which were undetected in earlier years. The NEIC now locates about 20,000 earthquakes each year or approximately 50 per day. Also, because of the improvements in communications and the increased interest in the environment and natural disasters, the public now learns about more earthquakes.
According to long-term records (since about 1900), we expect about 17 major earthquakes (7.0 – 7.9) and one great earthquake (8.0 or above) in any given year.
See a video of the apparent increase of earthquakes in Arizona due to the increase in number of seismic stations: Arizona earthquakes, 1852-2011, a video time line