On December 29, 2015 there was a swarm of earthquakes near Devore, California. The largest was a 4.3 on the Richter scale. The epicenter was seven miles from Fontana. There was a small earth movement then a banging noise and sharp shaking when the 4.3 hit. During events like this, you automatically think about the Big One. How do we measure quakes? There are two scales that register the effects of earthquakes. The Modified Mercalli scale refers to what people feel at the time of the earthquake and the damage. For example, the 4.3 Devore quake would register as a moderate quake, that was felt by people walking, that included the rocking of free-standing objects – which is a fairly accurate description of the events. The most commonly referred to scale is the Richter scale, which measures quakes by the intensity of the earth’s movement on a scale from 1 to 10. Both scales work hand-in-hand to describe the earthquake. The Richter scale measures the speed of the ground movement and the Modified Mercalli scale details the affect and damage of the quake. For example, the 1964 Great Alaskan Earthquake registered 9.2 on the Richter scale (it was the largest earthquake in the United States to date), and the Modified Mercalli scale would describe it as total destruction; objects thrown in the air, shaking and distortion of the ground. What caused such a powerful action? Two large tectonic plates were involved – the North American plate and the Pacific plate. These plates came in contact with one another from Japan to Baja, California, and across to the Gulf of Alaska. The Pacific plate is denser then the North American plate, so as the denser plate grinded against the lighter plate, it caused the North American plate to bulge. When you mix intense friction and pressure over centuries, something has got to give. That is what happened on March 27, 1964. The denser Pacific plate dove downward under the North American plate causing the coast of Alaska to instantly move forward approximately 64 feet. The geography was forever changed – many buildings collapsed due to liquefaction (the wet clay soil they were built upon virtually liquefied). Under the ocean, massive landslides took place, causing tremendous energy and displacements of tons of water, which sent massive tsunami waves over 100 feet tall racing to the Alaskan coast and across the ocean. The Great Alaskan quake occurred about 16 miles beneath the earth’s surface and lasted over four minutes. The demolition and rebuilding was a nightmare due to the changes in elevations and massive destruction. When Mother Nature shows her wrath, it makes humans feel like ants on an orange. So, now we understand about the scales, but the question still remains – when the next big quake hits Southern California, will it be the dreaded Big One? It is just a matter of time!
SharLeigh has an inquisitive nature – she is interested in current events, history, science and many more subjects, including things that go bump in the night! Since 1997, SharLeigh has scoured the internet, looking for interesting, fun and timely topics covering all sorts of human-interest subjects for her articles from her home in Fontana, CA.