A Comparison Of Earthquake Strength

Learn how the Richter Scale measures energy released during earthquakes and how this tool is used with computers to target locations and epicenters.

Earthquakes have a dual nature. On the one hand, they're a terrifying force, destroying everything they touch. On the other, their gentle rocking can barely be felt. Thousands of quakes occur each year. It's important for scientists and city officials to identify and categorize each quake's strength and potential for destruction.

Today, seismologists using computers can locate and pinpoint quake epicenter and determine the magnitude of earthquakes in minutes. But this wasn't always possible. Until 1935, when Charles Richter of the California Institute of Technology invented the Richter Scale, quake measurements, or seismic wave vibrations traveling through the planet, were recorded on seismographs. A seismograph is a machine that records a wiggly trace displaying the varying strengths of these waves.

Richter assigned a mathematical variable, called a logarithm, to a scale of whole numbers and decimals starting at one, with no top end. The magnitude of a quake is recorded on a seismograph and the scale assigns an intensity of 2.0, 2.3, 3.0 and so on to a particular magnitude. But the amount of energy released in a quake on this scale is not a direct proportional measurement. For axample, the strength of a quake measuring 6.7 is not just 42% stronger than a quake measuring 4.7. Each number is a logarithm, which means that each whole number represents a 30-fold increase in energy released. The 6.7 quake is 900 times stronger or 30 x 30 for two whole number measurement increases. This means it would take 900 quakes measuring 4.7 to equal the energy released in one 6.7 earthquake!

Before the development of the scale, reports of quake magnitude were mostly anecdotal--what people felt and observed in a particular location. For the most part, unless you were standing on or near an adjacent fault, quakes below magnitudes of 2.5 were not even felt, which is a good thing, considering the US Geological Survey (USGS) records 1,300,000 of these quakes a year. Intensity or magnitude, measures the effects of a quake at one place on people, structures and land. How strong this experience depends upon strength of the quake, distance from its origin and the type of geology you're standing on or upon which buildings are built.

Anecdotal reports are not always accurate and cannot pinpoint a quake's origin that disaster preparedness authorities need to know in order to effectively assign manpower and resources. Emergency 911 calls can quickly flood and overwhelm a system. Instead of relying upon such calls, city and county officials need accurate and timely information before committing resources.

This is why the Richter Scale is not only an important scientific device, but a valuable tool that helps authorities quickly respond to affected areas. Seismograph readings combined with computer technology can quickly pinpoint locations and epicenters. With this information. officials can identify and evacuate areas containing hazardous structures or materials, repair damaged water supplies and communication lines, shut down or reroute gas, electric utilities and nuclear power generating plants or reroute traffic to avoid compromised freeway overpasses. The faster and more accurate their response to a quake damaged area, the quicker injuries can be treated, fatalities reduced and fires controlled.

Even information for the public is readily available, although not as detailed. The USGS provides information on worldwide quake events on their website. Anyone can log on and get information concerning amplitude and locations of quakes.

Earthquake reports were once anecdotal but not very accurate. Today the Richter Scale and computers help to locate quake epicenters and determine magnitudes with a speed not considered possible a decade ago. The information generated not only helps authorities plan for responses to current quake events, but track even the smallest quakes, gathering data helpful in quake prediction.

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