全文转自 http://earthquake.usgs.gov/learn/topics/increase_in_earthquakes.php
我大致翻译一下，造福懒人。
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.
不断地有人问起，世界各地的地震是不是越来越多。虽然看上去地震越来越多，但 7 级及 7 级以上的地震数量仍然持平。
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.
近 20 年来，我们每年得以记载的地震数量的确在增加。但这是因为世界上地震监测站的极剧增多以及全球通讯的不断发展。1931 年时，全球仅有约 350 个地震监测站；如今，该数量已经超过 8,000，且通过电子邮件、互联网及卫星快速地传递着数据。监测站数量的增长以及更加频繁的数据接收使得我们及其他地震监测站能够更快地对地震进行定位，并发现更多早年无法检测到的小地震。NEIC（美国国家地震信息中心）现在每年可以定位约 20,000 个地震（大约每天 50 个）。而且，由于通讯的发展以及人们对环境自然灾害的关注增加，如今的公众更容易了解更多地地震情况。
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.
根据长期记录（自 1900 年起）显示，任意一年都有大约 17 次大规模地震（7.0 - 7.9 级）和一次超大规模地震（8.0 及以上）。