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Earthquakes

With most disasters, there is some warning that trouble is coming. You have time to prepare, hide or run. That's generally not the case with earthquakes. When the initial shaking starts, you only have a few seconds to get yourself to a safe place.

What happens after can often be worse than the quake. It could trigger a volcanic eruption, fires, landslides or a catastrophic tsunami like the one that struck Indonesia in 2004, killing an estimated 230,000 people.

To properly prepare for an earthquake, you first need to understand the basics. Start with this five minute video from National Geographic.

Earthquakes 101 | National Geographic

These are the different types of quakes, the different intensity levels, and how to prepare before, protect yourself during, and survive after the big one hits.

Faut Types

Earthquakes generally happen along a fault line. The three main types are normal, reverse (thrust) and strike-slip.

From Wikipedia:

“Normal faults occur mainly in areas where the crust is being extended such as a divergent boundary. Reverse faults occur in areas where the crust is being shortened such as at a convergent boundary. Strike-slip faults are steep structures where the two sides of the fault slip horizontally past each other; transform boundaries are a particular type of strike-slip fault. Many earthquakes are caused by movement on faults that have components of both dip-slip and strike-slip; this is known as oblique slip.”

The most powerful earthquakes, called megathrust earthquakes, are of magnitude 8 or more. Those typically strike reverse faults, especially ones along convergent plate boundaries. Smaller earthquakes less than magnitude 7 are usually associated with normal faults.

Plate Movement

How Strong is that Eartquake?

There are many different ways to measure different aspects of an earthquake:

Magnitude is the most common measure of an earthquake's size. It is a measure of the size of the earthquake source and is the same number no matter where you are or what the shaking feels like. The Richter scale is an outdated method for measuring magnitude that is no longer used by the USGS for large, teleseismic earthquakes. The Richter scale measures the largest wiggle (amplitude) on the recording, but other magnitude scales measure different parts of the earthquake. The USGS currently reports earthquake magnitudes using the Moment Magnitude scale, though many other magnitudes are calculated for research and comparison purposes.

Intensity is a measure of the shaking and damage caused by the earthquake; this value changes from location to location.

Types of Magnitudes

Magnitude is expressed in whole numbers and decimal fractions. For example, a magnitude 5.3 is a moderate earthquake, and a 6.3 is a strong earthquake. Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude as measured on a seismogram.

Click Here for a Calculator by the USGS to figure out how much bigger one earthquake is compared to another.

When initially developed, all magnitude scales based on measurements of the recorded waveform amplitudes were thought to be equivalent. But for very large earthquakes, some magnitudes underestimate true earthquake size, and some underestimate the size. Thus, we now use measurements that describe the physical effects of an earthquake rather than measurements based only on the amplitude of a waveform recording.

Seismic Scale

Seismic Scale

Soil Liquefaction

When an earthquake shakes water-saturated loose ground, it can start to act like a liquid. What was solid, can give way and allow buildings and vehicles to sink. Below is a video showing what it looks like.

Aftershocks

Whenever a major earthquake hits, you've got to stay alert for aftershocks. That's an earthquake that happens after the main earthquake or mainshock. They are always smaller than the mainshock, but they can still be extremely dangerous.


Preparation - Survival

Click Here for information on what to do from the United States government website, Ready.gov.

Click Here for the Earthquake Safety Video Series

Click Here for Earthquake Information Poster

How to Prepare for an Earthquake - America's Prepareathon

Click Here for the Red Cross Earthquake Safety Information.

Click Here to download a PDF file with information on what to do from the United States government website, Ready.gov.

PDF Information from Ready.gov

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This information is presented to make people aware of the larger world around them. If you can prepare for something as devastating as this, you're much more likely to be ready for smaller disruptions. Be aware and prepare.

6/6/2020
Updated 4/15/2021
Updated 6/3/2021