Sharon Begley (2006) explained how melting glaciers could trigger earthquakes and volcanos:
"One cubic meter of ice weighs just over a ton, and glaciers can be hundreds of meters thick. When they melt and the water runs off, it is literally a weight off Earth's crust. The crust and mantle therefore bounce back, immediately as well as over thousands of years. That 'isostatic rebound,' according to studies of prehistoric and recent earthquakes and volcanoes, can make the planet's seismic plates slip catastrophically."
Add the fact that earthquakes often occur in clusters - principles of chaos theory - and we might expect that, once again, centuries of positivist experiences might disappoint. U.S. Geological Surveys have, since the 1900's, recorded a yearly average of nearly 1.5 million earthquakes. Consequently their expectations seem to remain (despite the "slight" ongoing changes...) the same (much as the market experts, throughout the years... even when confronted with crisis); they expect about 18 major earthquakes (7.0-7.9) and one great earthquake (8.0 or higher) per year.