From: USGS
For the first time, new USGS maps
identify potential ground-shaking hazards from both human-induced and
natural earthquakes. In the past, USGS maps only identified natural
earthquake hazards.
This is also the first one-year outlook for the nation’s earthquake
hazards, and is a supplement to existing USGS assessments that provide a
50-year forecast
The report shows that approximately 7 million people live and work in
areas of the central and eastern U.S. (CEUS) with potential for
damaging shaking from induced seismicity. Within a few portions of the
CEUS, the chance of damage from all types of earthquakes is similar to
that of natural earthquakes in high-hazard areas of California.
“By including human-induced events, our assessment of earthquake
hazards has significantly increased in parts of the U.S.,” said Mark
Petersen, Chief of the USGS National Seismic Hazard Mapping Project.
“This research also shows that much more of the nation faces a
significant chance of having damaging earthquakes over the next year,
whether natural or human-induced.”
Induced earthquakes
are triggered by human activities, with wastewater disposal being the
primary cause for recent events in many areas of the CEUS. Wastewater
from oil and gas production operations can be disposed of by injecting
it into deep underground wells, below aquifers that provide drinking
water.
Important Note: USGS scientists only distinguished between
human-induced and natural seismicity in the CEUS. In the west,
scientists categorized all earthquakes as natural. Scientists also used a
different methodology in looking at the CEUS compared to the west.
USGS
map displaying potential to experience damage from a natural or
human-induced earthquake in 2016. Chances range from less than one
percent to 12 percent.
Six States Face the Highest Hazards
The most significant hazards from induced seismicity are in six
states, listed in order from highest to lowest potential hazard:
Oklahoma, Kansas, Texas, Colorado, New Mexico and Arkansas. Oklahoma and
Texas have the largest populations exposed to induced earthquakes.
“In the past five years, the USGS has documented high shaking and
damage in areas of these six states, mostly from induced earthquakes,”
said Petersen. “Furthermore, the USGS Did You Feel It?
website has archived tens of thousands of reports from the public who
experienced shaking in those states, including about 1,500 reports of
strong shaking or damage.”
In developing this new product, USGS scientists identified 21 areas
with increased rates of induced seismicity. Induced earthquakes have
occurred within small areas of Alabama and Ohio but a recent decrease in
induced earthquake activity has resulted in a lower hazard forecast in
these states for the next year. In other areas of Alabama and small
parts of Mississippi, there has been an increase in activity, and
scientists are still investigating whether those events were induced or
natural.
People living in areas of higher earthquake hazard should learn how
to be prepared for earthquakes, and guidance can be found through FEMA’s Ready Campaign.
USGS
map displaying 21 areas where scientists have observed rapid changes in
seismicity that have been associated with wastewater injection. The map
also shows earthquakes—both natural and induced—recorded from 1980 to
2015 in the central and eastern U.S. with a magnitude greater than or
equal to 2.5.
One-Year Outlook: The Nation’s Shortest Forecast Yet
The new hazard model estimates where, how often and how strongly
earthquake ground shaking could occur in the United States during
calendar year 2016. The USGS chose this short timeframe of one year
because induced earthquake activity can increase or decrease with time
and is subject to commercial and policy decisions that could change
rapidly.
The USGS National Seismic Hazard Map
uses a 50-year forecast because that is the average lifetime of a
building, and such information is essential to engineering design and
the development of building codes. Building code committees are still
determining whether it is appropriate to treat induced earthquakes in
building code revisions, in part because induced seismicity changes on
short time scales compared to the years it takes for building codes to
be updated, reviewed and adopted.
How Will This Help Protect Communities?
The new report can be used by both government officials to make more
informed decisions and by emergency response personnel to assess
vulnerability and provide safety information to those who are in
potential danger. Engineers can use this product to evaluate earthquake
safety of buildings, bridges, pipelines and other important structures.
Dramatic Change in the Central U.S.
The central U.S. has undergone the most dramatic increase in
seismicity over the past six years. From 1973 to 2008, there was an
average of 24 earthquakes of magnitude 3.0 and larger per year. From
2009 to 2015, the rate steadily increased, averaging 318 per year and
peaking in 2015 with 1,010 earthquakes. Through mid-March in 2016, there
have been 226 earthquakes of magnitude 3.0 and larger in the central
U.S. region. To date, the largest earthquake located near several active
injection wells was a magnitude 5.6 in 2011 near Prague, Oklahoma.
Research in the Western U.S.
The CEUS has experienced the most significant U.S. increase in
seismic activity due to induced earthquakes in recent years. Therefore,
in the 2016 forecast, scientists distinguish between human-induced and
natural seismicity only for the CEUS. Scientists also used a historical
catalog of seismic events leading back to the 1700s, putting a strong
emphasis on earthquakes in 2015.
While there are some areas of induced earthquakes in the western
U.S., they don’t significantly change the regional hazard level compared
to the much more abundant natural earthquakes. Therefore scientists
just considered the historical catalog in the western U.S. and did not
separate natural from induced earthquakes. Future research could take a
more detailed look at induced seismicity in the west, including in
California at The Geysers, Brawley or the Los Angeles Basin.
Explanation of Updates — Mostly, But Not All, Are Induced
The USGS published a study
in 2014 that only considered natural earthquakes. The largest changes
in this new report are primarily due to hazards from induced
earthquakes, but the calculations also consider updated forecasts for
natural earthquakes since the previous hazard map was released. For
example, the New Madrid Seismic Zone near Memphis has experienced a
higher rate of natural earthquakes in the past two years, leading to a
slightly higher hazard potential in small portions of Arkansas,
Missouri, Illinois, Kentucky and Tennessee.
Wastewater disposal is thought to be the primary reason for the
recent increase in earthquakes in the CEUS. While most injection wells
are not associated with earthquakes, some other wells have been
implicated in published scientific studies, and many states are now
regulating wastewater injection in order to limit earthquake hazards.
Many questions have been raised about hydraulic fracturing—commonly referred to as “fracking”—and USGS studies suggest that this process is only rarely the cause of felt earthquakes.
Learn more by reading six facts and common questions about human-caused earthquakes.
Distinguishing 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
at the time these earthquakes occurred. If so, it was classified as an
induced event.
Current research indicates that the maximum magnitudes of induced
earthquakes may be lower than for natural earthquakes, but many
scientists suggest that induced earthquakes can trigger larger
earthquakes on known or unknown faults. In the CEUS, there may be
thousands of faults that could rupture in a large earthquake. Induced
earthquakes also tend to exhibit swarm-like behavior with more numerous
and smaller earthquakes at shallower depths. These factors were taken
into account in the analysis.
Testing and Future Research
“We are using the best available data and
principles to determine when, where and how strong the ground could
shake from induced earthquakes,” said Petersen. “Of course there is a
level of uncertainty associated with this and all hazard maps, as we are
still learning about their behavior and can only forecast with
probability—instead of predict with certainty—where earthquakes are
likely to occur in the future. Testing these maps after a year will be
important in validating and improving the models.”
USGS Science
The USGS is the only federal agency
with responsibility for recording and reporting earthquake activity
nationwide and assessing seismic hazard. These maps are part of USGS
contributions to the National Earthquake Hazards Reduction Program,
which is a congressionally established partnership of four federal
agencies with the purpose of reducing risks to life and property in the
United States that result from earthquakes.
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