If the crust of the earth were not pretty solid, it would be shaking about and moving up and down constantly. But there are places in the rocks of the earth’s crust where it isn’t strongly held together-where faults exist. Along this break one rock mass might rub against another with very great force and friction. The energy of this rubbing is changed to vibration in the rocks-and we have an earthquake.
There are two ways we can describe an earthquake in terms of size:one is in the force of the earthquake itself, and the other is in the damage it does. Since the loss of human lives and the destruction of property worry people more than technical measurements, the great earthquakes people remember are those in which many lives were lost.
The most famous one in north America was the san Francisco earthquake of 1906. A great fire followed this quake. Seven hundred people died and property damage amounted to about $425,000,000. More recently, in February, 1971, a heavy quake in the los angeles area caused many million dollars in damage to homes, businesses and roadways.
One of the most famous earthquakes in Europe took place in Lisbon, Portugal, in 1755. The city was destroyed and at least thirty thousand people were killed. In 1908, in Calabria and sicily, a quake killed about seventy-five thousand people; and in 1915, in central Italy, hundreds of towns and villages were damaged and thirty thousand people were killed.
Two great earthquakes that caused enormous damage took place in Tokyo, japan, and in the kansu province in china. The Tokyo quake of 1923 killed more than one hundred thousand persons and destroyed this city and the city of yokohama, too. The chinese quake in 1920 covered more than three hundred square miles and killed about two hundred thousand people.
An earthquake may be a great earthquake and do very little damage. For example, the greatest earthquake on record in the united states is hardly known to most people. It took place near the town of new Madrid, Missouri, in 1811 and 1812. There were 1,874 separate earthquake shocks felt and some of the shocks were felt four hundred miles away. But this area was sparsely settled, so not much damage was done.
Other well-known earthquakes that people remember are:
2004, Sumatra, 227,898 deaths were recorded
2005, Pakistan, 86,000 deaths were recorded
2008, eastern Sichuan china, 87,587 deaths were recorded
2010, Haiti, 316,000 deaths were recorded.