As you may have heard, a 7.9 magnitude earthquake struck about 170 miles off the coast of Alaska around 12:30am this morning. For many people, myself included, the next question that pops into your head is well, "what does 7.9 mean?" While many news reports of the quake will continue to circulate throughout the day, the goal of this post is to help the average Joe (or Jane) gain a basic understanding of how to interpret the magnitude of these earthquakes.
Ok, ok. Well what the heck is magnitude?
Magnitude is simply the energy that is released when an earthquake occurs. Without going into calculations, its based on the amount of rock movement below the surface. The more movement, the higher magnitude of the quake.
That's all fine and dandy, but what's the difference between a 7.9 versus say, a 6.9?
Each time the magnitude increases by one whole number, the amount of energy released is about 32 times greater. This means that a magnitude 7.9 is 32 times more powerful than a 6.9.
Which ones should I be worried about?
While many small, unnoticeable earthquakes happen every day, ones that are generally 5.5 or higher have potential danger. Below you can see a magnitude to intensity comparison to get a feel for what can happen with different magnitudes.
Thankfully, this higher 7.9 magnitude quake hit quite away off shore. But what would a 7.9 look like if it were to hit directly offshore along the San Andreas fault line? What type of shaking and intensity would a California resident like myself potentially feel?
As you can see, the effects would be extreme, with very heavy damage spanning hundreds of kilometers along the coastline and sever to strong damage reaching inland almost as far as Sacramento! Although this is a hypothetical situation, it is possible to say the least.
You see, the California and Alaska coast are part of whats called the "Ring of Fire" where over 80% of the world's earthquakes occur.
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The other ring of fire...
I hope this post was helpful in getting a better understanding of earthquakes and what their magnitudes mean. If you enjoyed the post, don't forget drop a quick upvote, thanks!