earthquake disaster reliefEarthquake questions are raised whenever an event has happened, or one predicted.

Earthquakes have enthralled both young and old, from the “great San Francisco” earthquake of 1906, or the tsunami of 2007, to the latest headlines from Haiti and Chile.

The word “earthquake” is generally used to refer to any event caused naturally or by man that creates seismic (shaking) waves generated at geological fault lines but also by volcanic activity and man-made mine blasts and nuclear experiments.

This initial rupture is called the hypocenter. If you throw a rock into a lake, the waves ripple outwards from where the rock entered the water, getting weaker and weaker the farther from the center. This ground level center, in earthquake terms, is called the epicenter which is directly about the hypocenter.

During an earthquake, typically the first seismic wave is a compression wave, which is fast moving and hits with a sudden thump. They are followed a few seconds later by a second kind of seismic wave, a transverse wave, and cause the rocking, swaying, and shaking motions. Quakes are often preceded by foreshocks, or followed by aftershocks, which can be quite damaging and dangerous. They can occur hours or even days before or after the actual earthquake itself.

The size of earthquakes is usually measured using the “Richter” scale (Charles Richter developed this in the 1920s at the California Institute of Technology). It compares the heights of the seismic waves out from the epicenter and quantifies the amount of seismic energy by assigning a single number.

Following is a list of Richter scale numbers with related explanations of their power and an estimate of occurrence (source Wikipedia):

  • 2.0 Richter Magnitude: Micro earthquakes, not felt. Approximately 8,000 a day.
  • 2.0-2.9 Richter Magnitude: Usually not felt, but recorded. About 1,000 a day
  • 3.0-3.9 Richter Magnitude: Often felt, but infrequently cause damage. 49,000 a year.
  • 4.0-4.9 Richter Magnitude: Noticeable shaking of indoor items, rattling noises but little likelihood of significant damage. 6,200 a year.
  • 5.0-5.9 Richter Magnitude: Can cause major damage to poorly-constructed buildings over restricted regions (unlikely to cause more than slight damage to well-designed buildings). 800 a year.
  • 6.0-6.9 Richter Magnitude: Destructive in areas up to about 100 miles across in populated areas. 120 a year.
  • 7.0-7.9 Richter Magnitude: Usually cause serious damage over larger areas. 18 a year.
  • 8.0-8.9 Richter Magnitude: Can cause very serious damage in areas several hundred miles across. 1 a year.
  • 9.0-9.9 Richter Magnitude: Devastating in areas several thousand miles across. 1 per 20 years.
  • 10.0+ Richter Magnitude: Of epic proportions. Never recorded.

Here are some well-known earthquakes, and their approximate Richter scale magnitudes:

  • 0.5 Magnitude Equals The Power Of A Large Hand Grenade (approx.)
  • 3.5 Magnitude Chernobyl Nuclear Disaster, 1986
  • 6.9 Magnitude San Francisco Bay Area Earthquake (CA, USA), 1989
  • 8.0 Magnitude San Francisco Earthquake (CA, USA), 1906
  • 8.5 Magnitude Sumatra Earthquake (Indonesia), 2007
  • 9.5 Magnitude Valdivia Earthquake (Chile), 1960 (251 ZJ in this case)
  • 10.0 Magnitude Never Recorded

This site will address other questions and answers about earthquakes.

Like this post? Subscribe to my RSS feed and get loads more!