The scientific study of earthquakes is comparatively new. Until the 18th
century, few factual descriptions of earthquakes were recorded, and the
natural cause of earthquakes was little understood. Those who did look
for natural causes often reached conclusions that seem fanciful today;
one popular theory was that earthquakes were caused by air rushing out
of caverns deep in the Earth’s interior.
The earliest earthquake for which we have descriptive information
occurred in China in 1177 B.C. The Chinese earthquake catalog describes
several dozen large earthquakes in China during the next few thousand
years. Earthquakes in Europe are mentioned as early as 580 B.C., but the
earliest for which we have some descriptive information occurred in the
mid-16th century. The earliest known earthquakes in the Americas were in
Mexico in the late 14th century and in Peru in 1471, but descriptions of
the effects were not well documented. By the 17th century, descriptions
of the effects of earthquakes were being published around the
world—although these accounts were often exaggerated or distorted.
The most widely felt earthquakes in the recorded history of North
America were a series that occurred in 1811-12 near New Madrid, Mo. A
great earthquake, whose magnitude is estimated to be about 8, occurred
on the morning of December 16, 1811. Another great earthquake occurred
on January 23, 1812, and a third, the strongest yet, on February 7,
1812. Aftershocks were nearly continuous between these great earthquakes
and continued for months afterwards. These earthquakes were felt by
people as far away as Boston and Denver. Because the most intense
effects were in a sparsely populated region, the destruction of human
life and property was slight. If just one of these enormous earthquakes
occurred in the same area today, millions of people and buildings and
other structures worth billions of dollars would be affected.
[Illustration: _The great 1906 San Francisco earthquake and fire
destroyed most of the city and left 250,000 people homeless._]
The San Francisco earthquake of 1906 was one of the most destructive in
the recorded history of North America—the earthquake and the fire that
followed killed nearly 700 people and left the city in ruins. The Alaska
earthquake of March 27, 1964, was of greater magnitude than the San
Francisco earthquake; it released perhaps twice as much energy and was
felt over an area of almost 500,000 square miles. The ground motion near
the epicenter was so violent that the tops of some trees were snapped
off. One hundred and fourteen people (some as far away as California)
died as a result of this earthquake, but loss of life and property would
have been far greater had Alaska been more densely populated.