When it comes to earthquakes, size matters but so does the terrain

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By Allison Chinchar | CNN Meteorologist

Earthquakes can be like Jell-O. A simple, yet often used analogy is that if you’re sitting in a valley or basin, it acts like a bowl of gelatin and it will shake more than surrounding rock.

But not all earthquakes are created equal and the ground you walk on can make all the difference.

“The local geology definitely matters — what you’re sitting on,” said Dr. Susan Hough, a geophysicist with the US Geological Survey. “What the topography is, it definitely matters.”

Earthquakes are broken down into two basic wave types: body waves (often called P-waves or S-waves which travel through the Earth) and surface waves (which travel along the Earth’s surface).

The surface of the Earth is made up of a variety of soil types – from sand to clay to rock and many others, so the damage resulting from those basic wave types can vary as an earthquake travels through these varying types of terrain.

Hough explains further that while the waves themselves travel the same way, in the sense that a P wave is still a P wave, and a S wave is still a S wave, however, their speeds and amplitudes will change depending on the rock type.

Whether it is sedimental rock or a young sandy soil, it makes a difference.

Because the particle motion of surface waves is larger than that of body waves, surface waves tend to cause more damage.

Earthquakes occur on every continent in the world — from the highest peaks in the Himalayan Mountains to the lowest valleys like the Dead Sea to the bitter cold regions in Antarctica. However, the distribution of these quakes is not random.

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Size matters, and so does the type of terrain

When it comes to earthquakes, the size is very important. The physical size of an earthquake is measured in magnitude. For example, a 5.5 is a moderate earthquake, and a 6.5 is a strong earthquake. Because the scale is logarithmically based, each whole number increase in magnitude represents a tenfold increase. So, a 6.5 magnitude quake is 10 times bigger than a 5.5 magnitude, not one times bigger like the number implies.

But just because the magnitude of an earthquake is bigger does not always mean the resulting damage is worse.

For example, in January 2010, a magnitude 7.0 quake struck Haiti. More than 200,000 people lost their lives during that event with estimated damages between $7.8 and $8.5 billion.

In 2019 a 7.1 magnitude quake struck near Ridgecrest, California. For this stronger quake only one person lost their life, with an estimated $5 billion in damages.

Besides the magnitude being similar, the depths were also similar. The Haiti quake was 8 miles (13 km) deep, and the California quake was 5 miles (8 km) deep. While 8 miles may not sound shallow, it is in terms of earthquakes. Geologically speaking, any earthquake that is less than 43 …read more

Source:: The Mercury News – Entertainment

      

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