While we let our beloved fellowmen in Bohol to recover from the tragic 7.2 magnitude earthquake that hit the island, let us differentiate what are the difference between a magnitude and an intensity.
According to British Geological Survey, magnitude is the earthquake size and is determined from the logarithm of the maximum displacement or amplitude of the earthquake signal as seen on the seismogram, with a correction for the distance between the focus and the seismometer. Thus, it is the amount of force released from the source of the quake which in effect is recorded by an equipment called Richter scale through wave presentation. The longest gap of the wave determines the magnitude of the quake.
An example is the recent quake in Bohol, Philippines. The earthquake is a 7.2 magnitude earthquake with a tectonic origin.
Note, there is no limit on measuring magnitude. It can even reach unexperienced earthquake magnitude. However, it can have negative values.
Intensity, therefore, is the effect of magnitude. Intensity by means how it affected the infrastructures, people, and environment. Using the Mercalli scale, intensity ranges from intensity I – VIII or higher. For example, an intensity I quake is not felt by most people. However, intensity VI is felt by all people and when damage is slight.
As a summary, magnitude is the force of the quake while intensity is the effect of the force.
Until now, there is still no known device to predict quakes. All we can do is be prepared and know what to do during disasters like this.