ered very severe. a less-known scale, the mercalli scale (麦氏震级), was devised by italian seismologist giuseppe mercalli to measure the severity of an earthquake in terms of its impact on a particular area and its inhabitants and buildings.
some earthquakes are too small to be felt but can cause movement of the earth, opening up holes and displacing rocks. shock waves from a very powerful earthquake can trigger smaller quakes hundreds of miles away from the epicenter. approximately 1,000 earthquakes measuring 5.0 and above occur yearly. earthquakes of the greatest intensity happen about once a year and major earthquakes (7.0-7.9) occur about 18 times a year. strong earthquakes (6.0-6.9) occur about 10 times a month and moderate earthquakes (5.0-5.9) happen more than twice daily. most earthquakes are not even noticed by the general public, since they happen either under the ocean or in unpopulated areas. sometimes an earthquake under the ocean can be so severe, it will cause