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June 7 (UPI) – Scientists have understood why earthquakes along the mid-ocean ridges occur at low tide.
For 20 years, scientists have known the connection between earthquakes and tides. But since most of the ridges in the middle of the ocean have vertical faults or faults with strongly inclined planes, the researchers speculated that earthquake slips would be more likely to occur at high tide. Seismic data has shown the opposite.
"Low tides would reduce vertical force, which should prevent landslides and therefore earthquakes," said Christopher Scholz, a seismologist at the Lamont-Doherty Earth Observatory of Columbia University , at the UPI.
The researchers were surprised by the paradox, but Scholz and his colleagues discovered an explanation.
The earthquakes along the mid-ocean ridges are triggered by the expansion and contraction of the magma chambers below. The discovery – described this week in the journal Nature Communications – was made possible through a network of seabed instruments along the Pacific ridge of Juan de Fuca, which allowed scientists to measure the movements of the flaw and model the possible explanations of seismic activity.
"We were able to solve this paradox by including the response of the magma chamber to the tides," said Scholz.
Scholz and his colleagues understood that at low tide, less mass of water was squeezing over the soft pocket of molten rock beneath the volcanic ridge. As a result, the magma chamber develops. When this happens, the lower fault block is pushed up and slides along the upper block. The movement triggers earthquakes.
According to the new analysis, it does not take much to trigger an earthquake along the ocean ridges.
"The main reason these flaws are so sensitive to stress is that they are very shallow," Scholz told UPI. "Their average depth is about 1 kilometer, in contrast to continental earthquakes of about 10 kilometers." This makes the faults much smaller and the sensitivity is given by the ratio of the trigger stress divided by the strength of the fault. "
The researchers believe that other mechanisms could also cause small earthquakes on the oceanic backbone. The team of scientists plans to study other possible seismic schemes.
"Our next project related to this problem is to study the relationship between earthquakes and biweekly tides," said Scholz. "This could reveal a new behavior related to the flow of water into and out of faults that may occur at longer periods."
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