Earthquake Swarm in Brawley, CA- 8/26/12

 

Shakemap of the 5.5 Earthquake

The Quake

In the past few days there has been over 1791 earthquakes ranging from not felt (Intensity I) to magnitude 5.5 and 5.3 (Intensity VII and VI) near Brawley, CA. They were felt throughout Southern California and Arizona, and caused damage ranging from broken windows, to large cracks in buildings. Electricity was lost for several hours in places, but was soon returned. The earthquakes were located on the Brawley Seismic Zone near the US-Mexico Border. Footage of the earthquakes can be seen to the right.

Intensity vs. Magnitude

Ok. What is the difference between magnitude and intensity? Magnitude is measured in Movement Magnitude and Richter Scales. The Richter Scale is a base-10 logarithmic scale that measures the amplitude of an earthquake's waves.

What is base-10? Well, base ten means that a magnitude 1 is theoretically 10 times larger than a magnitude 0 and a magnitude 2 is 10 times larger than a magnitude 1 and a magnitude 3 is 10 times larger than a magnitude 2, and so on. The difference between a magnitude 5 and 9 is 10x10x10x10=10,000 times. So a magnitude 5 is nothing compared to a magnitude 9 earthquake. Magnitude is the measurement of the energy released at the epicenter.

Now, on to intensity. Intensity is the measurement of the ground motion, or the effect of the earthquake in a given location. For example, an intensity III earthquake's effects include: being felt by most people indoors, and with vibrations being similar to a large passing truck. For the recent 5.5 earthquake, which was intensity VII, effects include: difficult to stand, furniture broken, negligible damage in well built structures, and slight to moderate damage in ordinary structures.