Measuring Earthquakes

Earthquakes ronment/environment-natural- disasters/earthquakes/earthquake-101/ ronment/environment-natural- disasters/earthquakes/earthquake-101/

How do we measure an earthquake? There are two main scales with which we can measure an earthquake. ▫Mercalli ▫Richter

The Mercalli Scale In 1902 Guiseppe Mercalli made a scale for measuring the intensity of an earthquake by relating it to the amount of damage it caused. We can use Mercalli’s modified scale to find the epicenter of an earthquake.

IBarely felt IIFelt by a few sensitive people, some suspended objects may swing IIISlightly felt indoors as though a large truck were passing IVFelt indoors by many people, most suspended objects swing, windows and dishes rattle, standing autos rock VFelt by almost everyone, sleeping people are awakened, dishes and windows break VIFelt by everyone, some are frightened and run outside, some chimneys break, some furniture moves, slight damage VIIConsiderable damage in poorly built structures, felt by people driving, most are frightened and run outside VIIISlight damage to well built structures, poorly built structures are heavily damaged, walls, chimneys, monuments fall IXUnderground pipes break, foundations of buildings are damaged and buildings shift off foundations, considerable damage to well built structures XFew structures survive, most foundations destroyed, water moved out of banks of rivers and lakes, avalanches and rockslides, railroads are bent XIFew structures remain standing, total panic, large cracks in the ground XIITotal destruction, objects thrown into the air, the land appears to be liquid and is visibly rolling like waves

The Richter Scale Prior to 1935 earthquakes were measured by using the Mercalli Scale. Charles Richter (1935) created a numerical method based on a logarithmic scale from one to ten used to express the energy released by an earthquake

Richter Scale Richter magnitudes are based on a logarithmic scale, base 10 This means that for each whole number you go up on the Richter scale the strength of the earthquake goes up ten times.

Magnitude Examples A magnitude of 3 is ____ times ____________ than a magnitude of 2 A magnitude of 5 is ____ times ____________ than a magnitude of 7 A magnitude of 6 is ____ times ____________ than a magnitude of 2

M1 M2 M3

Magnitude Scale mlhttp:// ml Historic Earthquakes events/1960_05_22.phphttp://earthquake.usgs.gov/earthquakes/world/ events/1960_05_22.php

So, what does it mean? Think of it in terms of energy released by explosives: ▫A magnitude 1 earthquake releases as much energy as blowing up 6 ounces of TNT ▫A magnitude 8 earthquake releases as much energy as blowing up 6 million tons of TNT! ▫That is roughly 6 nuclear bombs!

Measuring Via Richter Scale What do we need to determine the size of the earthquake? ▫Seismograph  Determine the lag time (P-S)  Determine distance from epicenter  Determine the amplitude (height) of largest wave ▫Nomogram  Find the S-P interval  Find the amplitude  Draw a line that connects the above points to find magnitude

Example