Dormant Fault Lines More Dangerous Than Active Fault Lines

Oct 19, 2011
Shannon Webster

Active faults like San Andreas are less dangerous. - By Image courtesy of the NASA Jet Propulsion Labor

Dormant fault lines are more dangerous than active fault lines in the event of an earthquake. A dormant fault is one with no quake in over 100 years.

The conventional thinking regarding earthquakes has been that the faults that are the most active are the most dangerous to humans. The thinking goes that since the faults shake more frequently, the opportunities for destruction and death are greater. This logic was the standard thinking for decades when it came to planning and preparing for earthquakes.

Recently, scientists have been looking at areas where faults have been staying dormant for long periods of time, then coming back for a few rounds of quakes. Their findings show these quakes cause more damage and greater loss of life, even at lower Richter Scale readings than their more active counterparts. There are three main thoughts on why this change in understanding is occurring.

Expectation

When earthquakes are regular, they become expected. People are aware that an earthquake could happen at any time, and are generally better prepared than people living along dormant fault lines. The emergency responders are trained in how to handle earthquake responses, and the local people are able to find safe zones more rapidly.

Practice drills are taught in schools in areas of high quake activity, allowing people to know what to do without having to spend time thinking or remembering a lesson from years ago. Radio and television programs air commercial reminders of what to do during an earthquake, further instilling the knowledge into the citizens of the area. This increased expectation leads to the second aspect of why dormant faults are more dangerous: preparation.

Preparation

Cities in active earthquake zones tend to be better prepared. The residents are trained in how to help their neighbors, through work and school. The occurrence frequency helps individuals to remain calmer when the earth begins shaking.

Additionally, this preparation extends to building codes and standards. Roads and buildings are built to tougher standards, able to withstand the strongest earthquakes possible. Areas that are dormant do not have these same standards, leading to more building collapses, ruptured gas and power lines, and bridge collapses. These events drive the death toll higher in areas where a fault line does not erupt frequently. A look at Haiti will show a recent example of an area that was not prepared for a major earthquake along a dormant fault line.

Population

While large populations of people all live in the Ring of Fire along the Pacific Rim, there are also large groups of people living in areas that are not frequented by earthquakes. The population on the United States is very concentrated. A Virginia earthquake, which was felt up into Canada, could have had more catastrophic results if it had been as big as the Haitian quake. The number of people living in the New Madrid Fault Line has increased significantly in the 200 years since its last quake. The building standards are not as tough in these areas as they are along the Ring of Fire.

Since the faults aren't active, people think they are in a "safe zone" from earthquakes. As the Virginia and Haitian quake both show, there is no place that is completely free from a tremor. They have a sense of complacency because the fault is not erupting over the course of a decade or longer. They relax and don't take the preparation seriously. When these quakes happen, they tend to destroy more infrastructure and take more lives than the larger tremors in California or Japan.

These three factors have led scientists to rethink which earthquakes are the most important to study, and which will really be the most dangerous quakes around the world. It is nearly universally agreed upon that dormant faults, when they awake, are more dangerous and costly than active fault lines.