A measure of an earthquake's intensity.
Richter Scale Details
Charles F. Richter developed the Richter Scale in 1935. The Richter scale is logarithmic. Every point on the scale represents a ten times intensity increase. A 7 Richter scale earthquake is ten times more powerful than a 6 Richter scale earthquake. Seismographs monitor earthquakes.
A seismograph is a device to record the vibrations of the earth's surface. A rod with a weighted end surrounded by magnets creates enough inertia to counteract the earth's vibration. The base of the seismograph is attached firmly to the surface of the earth. The Richter Scale takes the earthquake's maximum amplitude recorded by multiple seismographs in the area, factor in the distance, applies a formula, and then provides the final Richter Scale data.
Improving upon the first Richter scale, Thomas C. Hanks and Hiroo Kanamori defined a new scale in 1979 called "The Moment Magnitude Scale." Moment Magnitude Scale measures the total energy produced by the earthquake. When two or more tectonic plates crash into each other, they are distorted or displaced permanently. The Moment Magnitude Scale counts the work (or torque) that drives those distortions and displacements. As a result, the Moment Magnitude Scale becomes the most widely-used earthquake measurement unit today. However, sometimes the media still refer to it as the Richter scale.
Real-World Example of a Richter Scale
Friday, March 11th, 2011, 14:46 in Japan, an earthquake struck 70 kilometers east of Tohoku. The earthquake began in the sea. The earthquake registered a 9 on the Richter Scale, which is catastrophically destructive. Furniture and heavy equipment rattled loudly and fell, crushing those in their path: window and building glasses shattered because of the vibration. Buildings jerked, twisted, and rumbled, and lots crumbled to the ground. The entire nation was gripped with chaos and panic.
A few minutes later, a massive tsunami formed along the coast of Japan. The tsunami stretched over 180 kilometers with an average wave height of 6 meters and a peak height of 40 meters. The seawall was hopelessly crushed by the tsunami, breaching the city with colossal destructive force.
The tsunami waves reached the Fukushima-Daichi Nuclear Power Plant. It destroyed the main water pump, exploded three main nuclear reactors, followed by nuclear meltdowns—radioactive materials and water leaked into the open air. In the end, the 9 Richter scale earthquake caused $238 billion property damage, displaced 350,000 people, killed over 15,000 people.
The Richter Scale vs. the Mercalli Scale
While the Richter Scale, also known as the Moment Magnitude Scale, focuses on the energy produced by an earthquake, the Mercalli Scale focuses on something simpler and easier to observe: The feel and look of an earthquake's effect on the surrounding area. It's a very subjective measurement because it uses human senses as the measurement device instead of a seismograph. The Mercalli Scale uses Roman numerals to denote the scale of the earthquake.
- Scale I-II, Earthquake is not felt or barely felt.
- Scale III-IV, Earthquake is felt by some or most people. Causes some damage to buildings. Ripples form on water surfaces.
- Scale V-VII, Earthquake is felt by everyone. Causes moderate damage to buildings with weak support structures. Light furniture and household objects may vibrate and move.
- Scale VIII-IX, Earthquake causes people to lose balance. Causes moderate damage to well-built structures. Heavy furniture may rattle and fall.
- Scale X or greater, Earthquake causes people to be thrown around. Most buildings are collapsed. It likely results in a permanent change in local ground topography.
Due to its subjective nature, the Mercalli Scale is usually used hand-in-hand with the Moment Magnitude Scale. The objective is to provide a better damage assessment in the affected area right away instead of waiting for the determined Richter Scale number.