Ground view of collapsed building and burned area at Beach and Divisadero Streets in the Marina District of San Francisco after the 1989 Loma Prieta earthquake.
Credit: C.E. Meyer, U.S. Geological Survey
1. Earth has been more seismologically active in the past 15 years or so, says Stephen S. Gao, a geophysicist at Missouri University of Science & Technology. Not all seismologist agree, however.
2. San Francisco is moving toward Los Angeles at the rate of about 2 inches per year — the same pace as the growth of your fingernails — as the two sides of the San Andreas fault slip past one another. The cities will meet in several million years. However, this north-south movement also means that despite fears, California won't fall into the sea.
3. March is not earthquake month, despite what some people believe. True, on March 28, 1964, Prince William Sound, Alaska, experienced a 9.2 magnitude event — one of the biggest ever. It killed 125 people and caused $311 million in property damages. And on March 9, 1957, the Andreanof Islands, Alaska, felt a 9.1 temblor. But the next three biggest U.S. earthquakes occurred in February, November, and December. The devastating major earthquake in Chile of 2010 struck on Feb. 27. And the huge 9.3 temblor that spawned the devastating Indian Ocean tsunami in 2004 occurred on Dec. 26.
4. There are about 500,000 earthquakes a year around the world, as detected by sensitive instruments. About 100,000 of those can be felt, and 100 or so cause damage each year. Each year the southern California area alone experiences about 10,000 earthquakes, most of them not felt by people.
5. The sun and moon cause tremors. It's long been known that they create tides in the planet's crust, very minor versions of ocean tides. Now researchers say the tug of the sun and moon on the San Andreas Fault stimulates tremors deep underground.
6. A city in Chile moved 10 feet in the massive 8.8 magnitude earthquake Feb. 27, 2010. The rip in Earth's crust shifted the city of Concepción that much to the west. The quake is also thought to have changed the planet's rotation slightly and shortened Earth's day.
7. There's no such thing as "earthquake weather." Statistically, there is an equal distribution of earthquakes in cold weather, hot weather, rainy weather, and so on, according to the U.S. Geological Survey. Scientists say there is no physical way that weather could affect the forces several miles beneath the surface of the earth where quakes originate. The changes in barometric pressure in the atmosphere are very small compared to the forces in the crust, and the effect of the barometric pressure does not reach beneath the soil.
8. Earth's bulge was trimmed a little by the 2004 Indonesian earthquake, the 9.0+ temblor that generated the deadly tsunami on Dec. 26 that year. Earth's midsection bulges in relation to the measurement from pole-to-pole, and the catastrophic land displacement caused a small reduction in the bulge, making the planet more round.
9. The Pacific Ring of Fire is the most geologically active region of Earth. It circles the Pacific Ocean, touching the coasts North and South America, Japan, China and Russia. It's where the majority of Earth's major quakes occur as major plate boundaries collide.
10. Oil extraction can cause minor earthquakes. These are not the quakes you read about. Rather, because oil generally is found in soft and squishy sediment, when oil is removed other rock moves in to fill the void, creating "mini-seismic events" that are not noticeable to humans.
11. The largest earthquake ever recorded was a magnitude 9.5 in Chile on May 22, 1960.
12. Quakes on one side of Earth can shake the other side. Seismologists studying the massive 2004 earthquake that triggered killer tsunamis throughout the Indian Ocean found that the quake had weakened at least a portion of California's famed San Andreas Fault. The Chilean quake of 1960 shook the entire Earth for many days, a phenomenon called oscillation that was measured by seismic stations around the planet.
13. The deadliest earthquake ever struck January 23, 1556 in Shansi, China. Some 830,000 are estimated to have died.