Magnitude 4.0 - OKLAHOMA

Earthquake Summary

Tectonic Summary

EARTHQUAKES IN THE STABLE CONTINENTAL REGION
Most of North America east of the Rocky Mountains has infrequent earthquakes. Here and there earthquakes are more numerous, for example in the New Madrid seismic zone centered on southeastern Missouri, in the Charlevoix-Kamouraska seismic zone of eastern Quebec, in New England, in the New York - Philadelphia - Wilmington urban corridor, and elsewhere. However, most of the enormous region from the Rockies to the Atlantic can go years without an earthquake large enough to be felt, and several U.S. states have never reported a damaging earthquake. The earthquakes that do occur strike anywhere at irregular intervals.

Earthquakes east of the Rocky Mountains, although less frequent than in the West, are typically felt over a much broader region. East of the Rockies, an earthquake can be felt over an area as much as ten times larger than a similar magnitude earthquake on the west coast. A magnitude 4.0 eastern U.S. earthquake typically can be felt at many places as far as 100 km (60 mi) from where it occurred, and it infrequently causes damage near its source. A magnitude 5.5 eastern U.S. earthquake usually can be felt as far as 500 km (300 mi) from where it occurred, and sometimes causes damage as far away as 40 km (25 mi).

FAULTS
Earthquakes everywhere occur on faults within bedrock, usually miles deep. Most of the region's bedrock was formed as several generations of mountains rose and were eroded down again over the last billion or so years.

At well-studied plate boundaries like the San Andreas fault system in California, often scientists can determine the name of the specific fault that is responsible for an earthquake. In contrast, east of the Rocky Mountains this is rarely the case. All parts of this vast region are far from the nearest plate boundaries, which, for the U.S., are to the east in the center of the Atlantic Ocean, to the south in the Caribbean Sea, and to the west in California and offshore from Washington and Oregon. The region is laced with known faults but numerous smaller or deeply buried faults remain undetected. Even most of the known faults are poorly located at earthquake depths. Accordingly, few earthquakes east of the Rockies can be linked to named faults. It is difficult to determine if a known fault is still active and could slip and cause an earthquake. In most areas east of the Rockies, the best guide to earthquake hazards is the earthquakes themselves.

COMMON QUESTIONS and ANSWERS

Why are there suddenly so many earthquakes?

Oklahoma has had small earthquakes for as long as there have been records of them. The number of earthquakes varies from year to year. Most of the earthquakes are too small for people to feel. Earthquakes large enough to cause damage are rare.

Is there a fault there?

Probably. Although some earthquakes result from the breaking of previously unfaulted rock, most earthquakes occur when the two sides of an existing fault slide past each other. Most faults form and grow by making earthquakes. However, there are many faults in the Earth almost everywhere, and most of the faults have no evidence of causing earthquakes recently. Probably those faults formed by making earthquakes in the past, but they might not be making earthquakes now.

Which fault caused the recent earthquake(s)?

Are the earthquakes man-made?

We don’t know. Most earthquakes are natural, but in a few places scientists have shown that small or medium-sized earthquakes were caused by nearby human activities. A definite answer would require installing more earthquake instruments where the earthquakes are occurring and perhaps getting additional information from other types of instruments.

Is something bigger coming?

There’s no way to tell with present-day understanding of earthquakes. Usually, though, small earthquakes are not followed by big ones. East of the Rockies, it’s common for swarms of small earthquakes to occur in an area over a few days to a few years without producing a strong earthquake. Then the swarm stops. We usually don’t know why an earthquake swarm starts or why it stops. We have seen earthquake swarms in many places, and we are likely to see other swarms in the future.

When’s the next big earthquake?

As far as we know, no one anywhere in the world can predict earthquakes reliably. It’s easy to make an earthquake prediction. Enough people do it every year that, once in a while, someone’s prediction is correct. Probably that’s by chance, in the same way that a blindfolded person who throws enough darts is likely to make one or two bulls-eyes by chance. It’s one thing to predict an earthquake, but it’s another thing entirely to get it right many times in a row, so that people can actually use the results. Reliable earthquake prediction is a long-term goal of earthquake science. That goal is a long time off.

Earthquake Information for Oklahoma

Earthquake Maps

• 
  Recent Activity At This Location
• 
  Location Maps
• 
  Did You Feel It? Tell Us
• 
  ShakeMap
• 
  PAGER Earthquake Impact
• 
  Historical Seismicity
• 
  Seismic Hazard Map
• 
  EQ Density Map
• 
  Google Map
• 
  Google Earth KML
  (Requires Google Earth)

Scientific & Technical Information

• USGS/SLU Regional Moment Tensor Solution
• Phase Data
• Theoretical P-Wave Travel Times

Additional Information

• Oklahoma Geological Survey