Mark Petersen is a seismologist with United States Geological Survey.
In this Q5, he talks about the threat of earthquakes and how people can prepare to stay safe.

Mark Petersen is a seismologist with United States Geological Survey.
In this Q5, he talks about the threat of earthquakes and how people can prepare to stay safe.

1. Mark, what have the new USGS maps published in Seismological Research Letter identify?
They identify potential ground-shaking hazards in 2017 from both human-induced and natural earthquakes in the central and eastern U.S.
Approximately 3.5 million people live and work in areas of the central and eastern U.S. with significant potential for damaging shaking from induced seismicity in 2017. The majority of this population is in Oklahoma and southern Kansas.
Research also shows that an additional half million people in the CEUS face a significant chance of damage from natural earthquakes in 2017, which brings the total number of people at high risk from both natural and human-induced earthquakes to about four million.
The good news is that the overall seismic hazard for this year is lower than in the 2016 forecast, but despite this decrease, there is still a significant likelihood for damaging ground shaking in the central and eastern U.S. in the year ahead.
The 2017 forecast decreased compared to last year because fewer felt earthquakes occurred in 2016 than in 2015. This may be due to a decrease in wastewater injection resulting from regulatory actions and/or from a decrease in oil and gas production due to lower prices.

2. What causes induced earthquakes?
Induced earthquakes  are triggered by human activities, with wastewater disposal being the primary cause in many areas of the central and eastern U.S. Wastewater from oil and gas operations can be disposed of by injecting it into deep underground wells. Injected fluids cause pressure changes that can weaken a fault and therefore bring it closer to failure. Most injection wells do not trigger felt earthquakes, suggesting that  a combination of many factors contribute to such events.
By understanding the relationship between earthquakes and wastewater injection, informed decisions can be made on processes such as controlling the volumes and rates of wastewater injected and determining which wells are most susceptible to inducing earthquakes.

3. How does the USGS distinguish between induced and natural earthquakes?
To determine whether particular clusters of earthquakes were natural or induced, the USGS relied on published literature and discussions with state officials and the scientific and earthquake engineering community. Scientists looked at factors such as whether an earthquake occurred near a wastewater disposal well and whether the well was active during the time the earthquakes occurred. If so, it was classified as an induced event.

4. What are the states that are considered ‘high hazard?’
The maps indicate an especially high ground-shaking hazard in five areas of the central and easter U.S. in 2017. These same areas were identified in the 2016 forecast.
Induced seismicity poses the highest hazard in two areas, which are Oklahoma/southern Kansas and the Colorado/New Mexico area known as the Raton Basin. In those areas, there is a significant chance that damaging levels of ground motion will occur in 2017.
Enhanced hazard from induced seismicity was also found in Texas and north Arkansas, but the levels are significantly lower in these regions than that forecasted for 2016. While earthquakes are still a concern, scientists did not observe significant activity in the past year, so the forecasted hazard is lower in 2017.
There is also a high hazard for natural earthquakes in the New Madrid Seismic Zone. The NMSZ is the only one of the five identified areas that has not experienced induced earthquake activity.
The NMSZ had a higher rate of natural earthquakes in the past three years, leading to a slightly higher hazard potential compared to previous years in portions of Arkansas, Missouri, Illinois, Kentucky and Tennessee.
There is specific concern in parts of the central U.S. since the forecasted hazard levels are higher than what is considered in current building codes, which only incorporate natural earthquakes.

5. What’s the best place for the public to find safety information?
Guidance can be found through FEMA’s Ready Campaign.
The new report is valuable for making informed decisions to reduce the nation’s vulnerability and providing safety information to those who may be at risk from strong shaking.
For example, the 2016 forecast has been used by engineers to evaluate earthquake safety of buildings, bridges, pipelines and other important structures.
Risk modelers have used data in developing new risk assessments, which can be used to better understand potential impacts on insurance premiums. The U.S. Army Corps of Engineers has used the information to provide guidance on updating their safety assessments of selected facilities.
Continuing collaborations between regulators, industry, and scientists will be important toward reducing hazard, improving future forecasts, and enhancing preparedness.

— Rimsie McConiga