Measuring Earthquakes
There are two measurements scientists can use to describe the size of an earthquake:
- Intensity – a measure of the degree of earthquake shaking at a given locale based on the amount of damage
- Magnitude – estimates the amount of energy released at the source of the earthquake
Intensity Scales
The Modified Mercalli Intensity Scale was developed using CA buildings as its standard. The scale uses rates from I (not felt) to XII (total damage). There are many factors that contribute to the intensity of the earthquake, and the destruction caused at a locale may not be a true measure of the earthquakes actual severity
Mercali Intensity Map for the 1994 Northridge earthquake. This map was created using data gathered from the earthquake. Image from Wikipedia Community Internet Intensity Map for the 1994 Northridge earthquake. This map was made by people logging into the USGS's Did You Feel It? website and recording what they felt during the earthquake. Note that the intensity patterns for both earthquakes are similar. Image from https://pubs.usgs.gov/fs/fs030-01/
Magnitude Scales
The Richter magnitude is a concept introduced by Charles Richter in 1935 and is based on the amplitude of the largest seismic wave recorded and accounts for the decrease in wave amplitude with increased distance. This scale is used primarily for local/nearby earthquakes (ML)
The Moment magnitude scale was developed to more adequately estimate the size of very large earthquakes. The earthquake's magnitude is derived from the amount of displacement that occurs along a fault. This is the scale most often used by seismologists (MW)
