How do we Measure Earthquake Strength?

The clip above is real footage from several different Earthquakes from all over the world.  We think of them as rare events, but actually an earthquake occurs somewhere on Earth every 30 seconds!  Why don't we feel them all?  Why don't they all cause so much destruction?  

The obvious answers to these questions is that not all earthquakes are equal, some are stronger than others, but how do we measure the strength of an earthquake? 

The Richter Scale

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The Richter Scale is the older of the two systems we have for measuring and describing earthquake strength.  THE RICHTER SCALE MEASURES EARTHQUAKE MAGNITUDE.

MAGNITUDE IS THE AMOUNT OF ENERGY RELEASED BY AN EARTHQUAKE BASED ON THE SIZE OF THE LARGEST SEISMIC WAVES.

THE RICHTER SCALE IS ALOG SCALE RANGING FROM 0 TO 10.  THIS MEANS THAT EACH NUMBER ON THE SCALE IS 10X LARGER THAN THE NUMBER BEFORE IT.

For example, a 4.0 is 10 times larger than a 3.0, and 100 times larger than a 2.0.  In addition, each successive number represents a 32 fold increase in the size of the waves released. 

The problem with the Richter Scale is that discussing an earthquakes power based on the size of the waves isn't that useful for the general public.  In other words, knowing a earthquakes Richter Scale number doesn't tell us how much damage was done by the earthquake

The Modified Mercalli Scale

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The Modified Mercalli Scale was developed in response to the problems of the Richter Scale.  THE MODIFIED MERCALLI SCALE MEASURES EARTHQUAKE INTENSITY.

INTENSITY IS A MEASURE OF THE AMOUNT OF DAMAGE DONE TO HUMAN STRUCTURES AS REPORTED BY OBSERVERS. 

THE MERCALLI SCALE GOES FROM I TO XII.  EACH NUMBER ON THE SCALE GOES WITH SPECIFIC, OBSERVABLE DAMAGE. This way, a reported number paints a clear picture of what happened as a result of the quake. 

The intensity of an earthquake is effected by two factors.  The depth of the earthquake effects intensity. A very deep earthquake does less damage than a shallow one, so it is less intense.  The other factor is distance to the epicenter.  An earthquake that occurs very close to a city will do much more damage, and therefore be more intense than one that occurs in the middle of nowhere. 

Earthquake Safety

If you are indoors

  • Drop down to the floor
  • Get under something sturdy (table, desk, doorway)
  • Stay away from windows, fireplaces, and heavy furniture that could fall over
  • Cover your eyes with one hand
  • Hold onto whatever you’re under
  • When the shaking stops look for fires or gas leaks to stop them immediately

 Be Prepared

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Prepare a survival kit including

  • Flashlights
  • canned food and a can opener
  • first aid kit
  • radio and batteries
  • water