How Do Earthquakes Affect Bridges

Have you ever wondered how earthquakes affect bridges.

I must admit that I had not thought about that subject until quite recently. Now I do.

In the last few years in the North Texas area, we have been experiencing a significant

increase in the frequency and magnitude of earthquakes.

There are many who say that this is the result of the exploration for underground

gas reserves, which has become widespread in this area.

No matter the root cause, the subject of how earthquakes affect bridges is now on

the minds of many.

How Earthquakes Affect Bridges Has Many Factors

When evaluating the affects of earthquakes the most important factors to take into account are the magnitude of the earthquake, the distance from the epicenter of the earthquake and the

geologic conditions at the site of the earthquake itself.

When it comes to how earthquakes can affect bridges, the main concern is the

damage that can be caused by the ground motion that the earthquake creates.

Going deeper into this subject, one must take a look at the local geology and type of

soil that the bridge has been built upon.

When soft soil lies on top of hard bedrock the ground motion is amplified, this is known

as ground-motion amplification.

This type of amplification can result in much greater damage, even from bridges that are

quit a distance from the epicenter of the earthquake itself.

In fact, soft sandy soils can actually be liquefied by strong ground motion in a

process call liquefaction.

When liquefaction occurs, the foundation of structures, like bridges, can be completely

compromised.

Whether Earthquakes Affect Bridges Depends Greatly On the Magnitude

The general rule of thumb is that earthquakes below a magnitude of 4.0 do

not cause infrastructure damage.

Since 2013 there have been over fifty reported earthquakes in a two mile area

alone just west of the Dallas city limit.

None of these earthquakes have been recorded to be above 4.0.

But there have been earthquakes in the North Texas area in the past that have been

above 4.0.

The largest recorded earthquake in the State of Texas occurred in 1931, when a

magnitude 5.8 earthquake was recorded in far West Texas near the town of Valentine.

Highway engineers have devised standards in an attempt to earthquake-proof bridges that have been built since the early 1990's.

Most bridges that we drive on daily were built before these higher standards were

implemented however.

Today, the subject of how earthquakes affect bridges is something that all of us must pay attention to avoid a potential catastrophe.