Deserts, Earthquakes, and Other Things
The Sahara is the largest, covering 25% of Africa, and larger than all the other deserts combined, which include: Kalahari, Namib, Red, Great Indian, Mojave - which is the largest in the US.
"Desertification" is the term representing a desert which is enlarging secondary to human activity, which is the case for most of them.
The Sahara has been green in times past, the most recent being about 90,000 years ago.
The Richter Scale is the method used to measure the energy intensity of an earthquake. This scale, devised in 1935, runs from 2 to 9 and is not linear but exponential. That is, a value of 8 is not "twice as intense as 4" but 10 times the intensity of 7! A 3 is 10 times as intense as 2, and so on. Values below 5 are considered minor as the potential for damage is slight, whereas those of magnitude 7 produce considerable damage, and death when they occur in populated areas. The energy released by a quake of 8 is a 100,000 times greater than the atomic bomb that erased Hiroshima.
The largest earthquake reported, 8.9, occurred twice, in the Pacific near Ecuador in 1906, and again in Japan in 1933. The one known by most Americans by history is the San Francisco 8.3, also in 1906. The more recent one there, in 1989, was 7.1. A quake in Alaska in 1964 measured 8.4.
Whereas close to a million earthquakes may occur worldwide every year, about a dozen, on average, occur worldwide with a value of 7 or higher, and those above 9 occur once or twice every century.
In terms of people killed, the estimates are as follows:
China, 1556: 830,000 dead.
China, 1976: 600,000 dead.
China, 1920: 200,000 dead.
Japan, 1923: 140,000 dead.
Italy, 1908: 85,000 dead.
There are many more with high numbers, but as regards some well reported quakes, these numbers are given:
Lisbon, Portugal, 1755: 20 - 60,000 dead. Probably an 8.
Mexico City, 1985: 10,000 dead. (2 quakes: 8.1 and 7.6)
San Francisco, 1989: 67 dead. (7.1 Richter)