A 4.1 magnitude earthquake was felt by the Baltimore community last Thursday. Many were surprised because it is unusual to have earthquakes of this size in this area.
Earthquakes occur when sections of the Earth slip past each other, releasing stored energy. The sections of the slip are called fault planes.
When planes reach the surface they shake the ground, and in some cases they are violent enough to harm structures and people.
The direct cause of earthquakes is the movement of tectonic plates, roughly 100-kilometer-thick sections of Earth’s crust consisting of many fault planes.
Geologists believe that earthquake slips are related to accumulated strain or stress near a fault plane from previous earthquakes. The accumulation of strain varies with time, making it difficult for geologists to predict when an earthquake will occur.
Historically, geologists have studied seismic records to identify patterns.
They have successfully recorded the earthquake history from the past hundreds or thousands of years for different fault planes. By identifying active fault zones and determining how recent the previous earthquake was, geologists can map the likelihood of an earthquake occurrence at particular zones.
Geologists Roger Bilham of the University of Colorado Boulder and Rebecca Bendick of the University of Montana studied the patterns of earthquakes and came up with a new way to analyze earthquakes.
They recently published a paper that theorizes there is some degree of global synchronization of earthquakes due to weak global stresses.
The geologists believe earthquake occurrences resemble repeating systems known as integrate-and-fire-oscillators that synchronize with external or self-organized forces. Past researchers found fault slip rates and recurrences of earthquakes to be key factors in determining synchronization.
In their search for synchronization, the geologists studied earthquakes of magnitude seven (scaled logarithmically from zero to 10) and higher from 1900 to present, looking at dates, interevent intervals between two earthquakes and renewal interval, which are dependent on the fault slip and the rate of strain accumulation. Patterns were quantified and statistically tested.
Their findings showed periods with significantly higher occurrences of magnitude seven or higher earthquakes — as much as 30 compared to the average of 15 annually.
Due to Earth’s elastic properties, both dynamic and static strains relate to the earthquake cycles. Sources of global strain include the Earth’s rotation which has slowed slightly. This change in rotation was present in each period with an increased number of earthquakes.
“The correlation between Earth’s rotation and earthquake activity is strong and suggests there is going to be an increase in numbers of intense earthquakes next year,” Bilham said in a press release.
For every period when the Earth’s rotation is slowed, which is approximate every five to six years, there was a noticeable increase in earthquakes.
“It is straightforward. The Earth is offering us a five-year heads-up on future earthquakes,” Bilham said.
The last period the Earth’s rotation was shorter and an increase in earthquakes occurred was 2011. By the pattern, the next period should begin in 2016 or 2017.
However, 2017 has not yet had many major earthquakes.
“The inference is clear. Next year we should see a significant increase in numbers of severe earthquakes,” Bilham said. “We have had it easy this year [2017]. So far we have only had about six severe earthquakes. We could easily have 20 a year starting in 2018.”
Bilham’s study also approximated the probable location of the earthquakes. That location is the region 30 degrees north or south of the equator, which is Earth’s widest point. A slowdown in Earth’s rotation at those points will be more powerful.
Geologists are far from predicting the occurrence of earthquakes, but if there is an increase in major earthquakes next year, this research may be a big step in earthquake prediction.
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