We are all familiar with earthquakes. But why do they happen? Well, it all starts with the Earth’s crust, which is thought to be made up of 15 to 20 tectonic plates. The movements of these plates can have massive consequences for the land and people living above them. Shifting tectonic plates can build mountains, cause volcanoes to erupt, and – you guessed it – cause violent earthquakes. Areas of the world that are situated on top of the meeting point between two plates (a fault) are particularly prone to earthquakes. Want to learn more about earthquakes? Check out our roundup of intriguing facts about earthquakes, including why they happen, how they’re measured, and major historic quakes.
#1 Earthquakes Aren’t Only Measured Using the Richter Scale.
Charles Richter devised what we now call the Richter scale in 1935. His scale allows scientists to determine an earthquake’s magnitude by measuring the size of its seismic waves using a seismograph. The Richter scale goes from 1 to 10, with 10 denoting the most significant seismic activity. The scale is logarithmic, meaning that each point is 10 times greater than the point before it. However, it was originally created with short distance ranges in mind. Over the years, other measurements like body wave magnitude and surface wave magnitude were developed.
However, since seismic wave amplitude in one specific area is a limited metric that only works well for localized quakes, rather than large seismic events that often affect many regions, seismologists Hiroo Kanamori and Thomas C. Hanks came up with a measurement called a “moment” in the 1970s. A moment is found by multiplying three variables: the distance the plates moved, the length of the fault line between them, and the rigidity of the rock itself. The resulting metric tells scientists how much energy is released in an earthquake, which gives a more accurate representation of quake size than simply measuring how much the ground shakes. The metric from the moment calculation is converted to a number between 1 and 10, similar to the Richter scale, using a standard calculation. Moment magnitude is considered the most accurate measurement of earthquake's size and strength. Sometimes journalists mistakenly mention the Richter scale when they actually mean to reference the moment magnitude scale, but both scale metrics are still in use today.
#2 The Largest Earthquake Recorded in the US Happened in Alaska.
The largest recorded earthquake that happened in the United States hit Prince William Sound near Alaska on March 28, 1964. The boundary between the North American and Pacific plates runs through and around Alaska, so it is not uncommon for the area to experience earthquakes. The 1964 earthquake had a magnitude of 9.2. It damaged buildings and homes in Alaska. It also generated landslides, tsunamis, and aftershocks that had effects as far away as Oregon and California. After the megaquake, Alaskan officials took action to be better prepared for the next large earthquake, including passing new building codes. The town of Valdez, which was found to be on unstable land, was actually moved four miles east to shift it to more stable ground!
#3 The World’s Largest Earthquake Happened in Chile.
On May 22, 1960, there was a massive earthquake that originated off the coast of Valdivia, Chile. It was extremely powerful and damaging; in fact, the earthquake was a record-breaking 9.5 magnitude event (although some studies assign it a 9.4 or a 9.6). This catastrophic earthquake happened because the Nazca plate, which runs beneath the Pacific Ocean along South America’s western coast, is slowly slipping beneath the South American plate, which is located underneath the continent. On May 22, 1960, there was a massive shift, causing the megaquake. The earthquake also set off an 80-foot tsunami that hit Chile as well as a series of tsunamis that hit far-off Pacific regions, including Hawaii, Japan, and the Philippines. Following the megaquake, seismic waves traveled around the world and shook the earth for days. Whole towns were devastated as a result of the massive earthquake, tsunamis, and aftershocks. The death toll in Chile was estimated to be over 1,000 and as many as 2 million people were left homeless.
#4 There Are Tens of Thousands of Earthquakes Each Year.
You might be surprised (or even shocked!) to learn that the National Earthquake Information Center (NEIC) records an average of 20,000 earthquakes every year. These quakes happen all around the world, but while they are recorded by seismographs, they are not always strong enough to be noticed by humans. In fact, scientists estimate that there are millions of earthquakes each year that are simply too weak to be recorded. In southern California alone, there are about 10,000 earthquakes a year! However, most of them go unnoticed.
#5 Most Earthquakes Occur in a Zone Called the Ring of Fire.
The Ring of Fire refers to region that encircles the Pacific Ocean. There are 452 volcanoes located in the Ring of Fire, which accounts for over 75% of the world’s active and dormant volcanoes. The Ring of Fire is also called the Circum-Pacific Belt. It is the most seismically active region in the world. In fact, 80% to 90% of the world’s earthquakes occur there. The next most seismic region of the world is the Alpide Belt, which extends from the Mediterranean region eastward through Turkey, Iran, and northern India; about 5% – 6% of the world’s earthquakes occur there. In the United States, Alaska is the most seismically active state. Why? Alaska is located along the Ring of Fire. Because of this, it actually has more large earthquakes than California, but since the Golden State’s population is larger, quakes there often receive greater amounts of attention.
Want to learn more facts about earthquakes? Check out this educational video: