American geologists have noticed a connection between an increase in the number of large earthquakes with a periodic slowdown in the Earth's rotation. This regularity makes it possible to calculate years especially dangerous for residents of seismically active regions.
Earthquake forecasting is challenging; modern forecasting systems correctly predict earthquakes with a magnitude of more than 5.5 in more than 50% of cases, rarely more accurately, and the cases of successful evacuation before a large seismic shock can be counted on one hand. At the American Geological Society conference, geologists Roger Bilham of the University of Colorado and Rebecca Bendick of the University of Montana presented a new methodology for predicting seismic peaks that follow the maximums in the duration of the earth's day.
Over the past 100 years, each of the five serious (25-30%) jumps in the number of earthquakes with a magnitude greater than 7.0 coincided with a slowdown in the Earth's rotation around its axis and, accordingly, an increase in the duration of the Earth's day. It takes 5–6 years between the beginning of the Earth's deceleration and a burst of seismic activity, so measuring the planet's rotation speed can become an effective tool for predicting earthquakes.
Changes in the Earth's orbital period are explained by friction between the liquid and solid parts of the planet (liquid - the oceans and the core and solid crust). The peak of the length of the day is preceded by a gradual decrease in the torque of rotation lasting from 6 to 8 years. It takes 23-24 years from peak to peak. Global seismic activity increases in the intervals between them; the closer to the equator, the more noticeable the connection.
Why there is a connection between rotation speed and earthquakes at all, scientists do not yet know. There are two hypotheses: the first explains the frequent strong earthquakes by a decrease in the flattening of the Earth as a result of slowing rotation, the second - by lithospheric overshoot, a phenomenon in which the speed of the crust becomes much greater than the speed of rotation of the liquid core below it.
The new technique does not allow predicting where and when exactly a new major earthquake will occur, although it is known that most often earthquakes with a magnitude greater than 7 during periods of global seismic intensification occur in India, the countries of Southeast Asia, Central America and the Caribbean. Since 1900, 80% of all major earthquakes at the edge of the Caribbean lithospheric plate have occurred 5 years after each slowdown maximum. The destructive earthquake of 2010 in Haiti, which killed 222,570 people, also coincided with such a peak in activity.
Ksenia Malysheva
