3. Earthquakes 3.4 Measuring Earthquakes


A seismography phone app


A seismograph


Seismograph


The instrument used to measure and record an earthquake and how long it lasted. Smart phone apps mean we can now carry a seismograph in our pockets!


Richter scale


The Richter scale was the original scale used to measure the magnitude (strength) of an earthquake. This scale goes from 1 to 8. Each one-unit increase means that the earthquake is 10 times more powerful than one at the previous unit. It may be unreliable for larger earthquakes.


Moment magnitude scale


Modified Mercalli Scale


The moment magnitude scale (MMS) is now used to measure the magnitude of earthquakes. It has replaced the Richter scale because it is more reliable for larger earthquakes. The scale goes from 1 to 10.


This scale is based on eyewitness accounts of the shaking experienced during the earthquake. The scale goes from I to X (1 to 10 in roman numerals) – the higher the number the larger the damage seen.


Question Time


1. Examine the diagram of the earthquake and explain each of the key words labelled.


2. On what type of plate boundaries do earthquakes typically occur?


3. Explain the formation of a tsunami wave using a diagram to support your answer.


4. Name the piece of equipment used to measure and record an earthquake.


5. Explain the difference between the Richter scale and the moment magnitude scale.


Focus Seismic waves Epicentre


27


FUN FACT! The 1960 Chile earthquake


was measured as 8.5 on the Richter scale. Scientists revised this using the


moment magnitude scale, and the size was updated to magnitude 9.5. This is the


largest earthquake ever recorded since seismographs were invented.


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