What Causes Strong Earthquakes?

Flickr/UN Photo/Logan Abassi United Nations Development Programme

Diking has been determined to be a new cause of strong earthquakes. This geologic event has been known to scientists but has only been found to cause earthquakes with a magnitude between six and seven recently.

Diking happens when the Earth’s tectonic plates move apart that causes the magma to surface the Earth, forming vertical magma. Scientists say that this event can occur anywhere but is usually observed in Iceland, Hawaii and regions of Africa in the East African Rift System, where the plates are spreading apart.

“Diking is a known phenomenon, but it has not been observed by geophysical techniques often,” lead researcher Christelle Wauthier, an assistant professor of geosciences at Penn State, says in a statement. “We know it’s linked with rift opening and it has implications on plate tectonics. Here, we see that it also could pose hazards to nearby communities.”

The researchers studied the changes in the Earth’s surface before and after the Nyiragongo volcano eruption in the Democratic Republic of Congo in 2002 that left 100 people dead and 100,000 homeless. An earthquake which was measured at a 6.2 magnitude then happened eight months after in the town of Kalehe, 12 miles from the volcano, killing several people.

Flickr/MONUSCO / Neil WetmoreDonald Acosta | Australia Network News

Flickr/MONUSCO / Neil Wetmore

The researchers wanted to discover the link between two natural disasters using the Interferometric Synthetic Aperture Radar, a remote sensing technique that measures the changes in the Earth’s surface.

“This technique produces ground surface deformation maps. Then, you can invert those deformation maps to find a source that could explain the observed deformation,” Wauthier explains. “For the deformation observed in January 2002, we found that the most likely explanation, or best-fitting model, was a 12-mile diking intrusion in between Nyiragongo and Kalehe.”

The research team discovered that the fault that slipped in the East African Rift System caused the earthquake. They were able to come up with this conclusion after performing a Coulomb stress-change analysis, which is a modelling technique that quantifies the stress caused by the faults. A positive result means that the receiver fault is closer to slipping and generating an earthquake.

According to the researchers, the dike opening pushed outward the rocks, straining and stressing them. The dike caused the fault to fail, consequently causing the earthquake eight months later.


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