What Causes Earthquakes?

Find out more about what causes earthquakes and other earthquake facts for the San Francisco Bay Area.

First, it's important to note that earthquakes happen many miles below the earth's surface. This means that geologists have to study them from a distance.

They use a number of different tools that help them pin point the location of a certain earthquake. These tools are also used to better understand what causes earthquakes.

The depth of earthquakes also makes it challenging to predict them. Geologists study the ground near major faults to look for changes in the earth. They also have a number of labs set up to help them study earthquakes. The labs replicate the environment of earthquakes including temperature, depths and other factors.

So, what causes earthquakes? The basic description of an earthquake is when rock on a fault line crumbles, explodes or moves based on extreme tension. Of course, this is an overly simplified explanation, but is a quick overview of what happens during an earthquake.

To understand what causes earthquakes a little better, let me give you a little more information about fault lines, the types of waves that occur when an earthquake strikes and a quick overview of the Richter Scale. These sections will help explain the 'why do earthquakes happen' in a little more detail.

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Fault Lines

One of the ways a fault is created is when two different types of rocks butt up against each other. The other way a fault is created is when the strata of the same type of rock are displaced either vertically or horizontally. Earthquakes typically happen along fault lines since the rock is weaker along a fault vs. along a non-faulted rocky area.

There are three different types of faults that create earthquakes: the normal fault, the reverse fault and the strike slip fault. Each moves in a unique way, which allows geologists to track the type of earthquake that has occurred.

The San Andreas Fault is one of the most well known faults in the San Francisco area. It is a strike slip fault. This is also the fault that is believed to have caused both the 1906 San Francisco Earthquake and the 1989 Loma Prieta San Francisco Earthquake.

It's also important to know a little about the types of earthquake waves to better understand what causes earthquakes.

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Types of Earthquake Waves

When the rock along a fault ruptures, explodes or moves dramatically, it creates waves. This is typically what people feel when they talk about feeling an earthquake. The waves from the earthquake also usually create the most damage.

There are three different types of earthquake waves: the P wave, the S wave and the Surface Waves. Both the P and S waves travel through the earth and are called body waves. The P wave is the faster of the two. The S wave travels a little slower.

Surface waves are the ones that do the most damage in an earthquake. They travel along the surface of the earth and these are the waves that people feel after the earthquake occurs.

Geologists track all three waves to determine when and where the earthquake originated. Since all three travel at different speeds, the geologists are able to quickly determine the originating location of the earthquake.

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Measuring and Understanding the Magnitude of an Earthquake

Now that we've covered some basics on what causes earthquakes, let's talk a little about how they are measured. The most popular type of measurement of an earthquake is a measurement called the Richter Scale.

The Richter Scale is an internationally recognized way of measuring the magnitude of an earthquake. It was created by Charles Richter in 1935.

Richter created the scale as a simple way to compare different types of earthquakes in different areas. The scale has no top limit, although the largest measured earthquakes are in the mid to upper 8.0 range.

Each full point on the scale is an increase in magnitude of 10 times. This means that a 4.0 earthquake is 10 times more powerful than a 3.0 earthquake, a 5.0 earthquake is 10 times more powerful than a 4.0 earthquake and so on.

Most earthquakes under 3.0 are rarely felt by people in and around the epicenter of the earthquake. Once an earthquake reaches the 3.0 mark that is when the earthquake waves are strong enough to be felt from a distance away.

The Richter Scale was not in existence during the 1906 San Francisco earthquake. However, based on research and measuring the damage that occurred, it's documented the earthquake was around an 8.3. The 1989 Loma Prieta earthquake was a 6.9 on the Richter Scale.

Find even more San Francisco earthquake facts from these earthquake books including first hand accounts, historical pictures and more details on how they happened.