According to the US Geological Survey (USGS), approximately 500,000 detectable earthquakes occur every year – which means at least some will be affected by the time you read this article. Of that gigantic number, however, only about 100,000 are intense enough for humans to feel the effects, and only about 100 of those actually cause destruction. In other words, the earth is shaking a lot whether we realize it or not. Why do earthquakes happen, when do they happen, and can you avoid them by moving to the moon? These and other questions are discussed below.
1. You can trace earthquakes back to the inner core of the earth.
Understanding earthquakes requires a short trip to the center of the earth, a solid sphere made of iron and other metals that can reach temperatures as high as 1
The crust consists of a patchwork of huge, discrete slabs of rock called tectonic plates. Sometimes when two plates slide against each other, the friction between their jagged edges causes them to temporarily get stuck. The pressure builds until it can finally overcome the friction and the plates eventually go their separate ways. At this point, all of the pent-up energy is released in waves – or seismic waves – that literally shake the land on the earth’s crust.
2. Scientists cannot predict earthquakes, but they can predict them occasionally.
Unfortunately, there is no fancy device that warns us when an earthquake is coming. Although scientists can’t predict exactly when or where an earthquake will occur, they can occasionally predict the likelihood of hitting a certain area soon (and if that sounds a bit vague, it’s because it is). For one thing, we know where the tectonic plates adjoin each other, and that’s where the high-strength earthquakes occur. The Ring of Fire, for example, is an area on the edge of the Pacific Ocean where about 81 percent of the world’s largest earthquakes occur. We also know that especially large earthquakes are sometimes preceded by tiny quakes known as foreshocks (although they cannot be identified as foreshocks unless a larger earthquake actually hits – if it doesn’t, they are just regular, small earthquakes). When small quakes near a plate boundary coincide with other geological changes, it can indicate that a major earthquake is imminent.
In February 1975, for example, the Chinese city of Haicheng experienced possible foreshocks after months of shifting land height and water level. As a result, officials ordered its millions of residents to evacuate immediately. The next day, a 7.0 magnitude earthquake struck the region. Although there were 2,000 victims, an estimated 150,000 people could have been killed or injured if no one had escaped.
3. There is a very slim chance that “The Big One” will perform in the next year.
However, successful predictions like Haicheng’s are rare, and scientists spend a lot of time monitoring known lines of error – the boundaries between plates – to see how much pressure is building and when it can cause problems. It’s not an exact science.
One fluctuating forecast is for “The Big One,” a massive earthquake expected to hit the San Andreas Fault Zone, an 800-mile network of fault lines that will run from northern to southern California at some point in the future. Currently, the USGS predicts a 31 percent chance that a magnitude 7.5 quake will hit Los Angeles in the next 30 years and a 20 percent chance that such a quake will hit the Bay Area of San Francisco.
The likelihood of “The Big One” depends in part on other earthquakes in this fault zone. After two consecutive quakes in Ridgecrest, California, in 2019, seismologists observed changes in pressure in the surrounding fault lines, and a study published in July 2020 suggested that the odds for “The Big One” might be next year rose to 1.15 Percent – three to five times more likely than previously assumed.
4. Underwater earthquakes can cause tsunamis.
Because so much of the earth’s surface is covered with water, many earthquakes don’t touch the land at all, but that doesn’t mean they don’t affect people. When plates shift on the ocean floor, the energy displaces the water above them, causing it to rise dramatically. Then gravity pulls the water back down, causing the surrounding water to form a massive wave or tsunami.
Earthquakes can also cause tsunamis indirectly by changing the landscape. On July 9, 1958, a 7.8 magnitude earthquake struck Lituya Bay in northeast Alaska, causing a rock fall on an adjacent cliff. As an estimated 40 million cubic meters of rock rushed into the bay, the force generated an estimated 1,720-foot wave – the largest tsunami of all time.
5. Alaska also holds the record for the largest earthquake in the United States
The boundary between the North American and Pacific plates runs through and around Alaska, which means Alaskan earthquakes are no stranger to earthquakes. One is discovered in the state about every 15 minutes, according to the Alaska Earthquake Center.
On March 28, 1964, a 9.2 magnitude earthquake – the largest ever in the United States – struck Prince William Sound, a body of water bordering the Gulf of Alaska. The first buildings and houses at the armed forces level not only caused a series of landslides, tsunamis, and other earthquakes (so-called aftershocks) that affected communities as far as Oregon and California.
Scientists discovered that the earthquake happened because the Pacific plate not only rubbed the North American plate – it actually slid under it. The area where these plates converge is called the “subduction zone”. Occasionally the pressure builds up and causes a great movement or megathrust when it finally releases. Although experts still couldn’t predict these movements, investigating the damage helped the Alaskans strengthen their defenses against future earthquakes. Officials passed better building codes, and the town of Valdez, on unstable land, was actually moved four miles east.
6. The world’s largest recorded earthquake occurred in Chile.
The 1960 earthquake near Valdivia, Chile, was larger than the Alaska earthquake four years later, but the conditions that caused it were similar. The Nazca Plate, which runs under the Pacific Ocean along the west coast of South America, slides under the South American Plate (which is under the continent itself). On May 22, 1960, there was a large displacement along a length of 560 to 620 miles of the Nazca Plate that caused a catastrophic, record breaking earthquake measuring 9.5 in magnitude. Just like in Alaska, this quake triggered a series of tsunamis and aftershocks that decimated entire cities. The damage is difficult to quantify, but it is estimated that at least 1,655 people died and an additional 2 million people were made homeless.
7. An earthquake can leave genetic scars on one species.
About 800 years ago, an earthquake near Dunedin, New Zealand pushed up part of its coastline, wiping out the bull kelp that lived there. Soon new bull kelp began to settle in the area, and their offspring are now indistinguishable from the neighboring sea kelp, which was never evicted. In July 2020, scientists published a study in the journal Royal Society procedure B. This shows that the two kelp populations actually have different genetic makeup. Their results suggest that earthquakes – and similar geological disasters – can have an extremely long-term impact on the biodiversity of the affected area.
8. The Richter scale for measuring earthquakes is not always accurate.
In 1935, Charles Richter developed a scale for determining the strength of an earthquake by measuring the size of its seismic waves with a seismograph. Basically, a seismograph is an instrument with a mass attached to a solid base. The base moves during an earthquake, the mass doesn’t. The movement is converted into an electrical voltage, which is recorded on paper in a wave pattern by a moving needle. The different height of the waves is called the amplitude. The higher the amplitude, the higher the score of an earthquake on the Richter scale (from one to ten). Since the scale is logarithmic, each point is ten times larger than the one below.
However, the amplitude of seismic waves in a given area is a limited metric, especially for larger earthquakes that affect fairly large regions. In the 1970s, seismologists Hiroo Kanamori and Thomas C. Hanks developed a measurement called “moment” that was obtained by multiplying three variables: distance the plates moved; Length of fault line between them; and stiffness of the rock itself. At this moment it is essentially indicated how much energy is released in an earthquake. This is a bigger metric than just how bad the ground is shaking.
To put it in terms that the general public could grasp, they created the Moment Size Scale, which converts moment to a number between one and 10. Values increase logarithmically, just like on the Richter scale, which is not uncommon for news channels or journalists who mistakenly mention the Richter scale when they are actually talking about the moment magnitude scale.
9. The moon also has earthquakes.
These seismic shifts are aptly referred to as moonquakes and can occur for several reasons (which we know so far). Deep moonquakes are usually due to the earth’s gravitational pull manipulating the internal structures of the moon. A surface-level quake is sometimes the result of a meteor strike or the sharp change in temperature between day and night. In May 2019, scientists suggested a possible fourth reason for shallower tremors: the moon shrinks as its core cools, and this process causes shifts in its crust. When the crust shifts, the drop offs – or ridges – we see on the lunar surface can shift too.