On five occasions in the past century, a 25-30% increase in the annual number of earthquakes Mw≥7 has coincided with a decrease in the average rotation speed of the Earth, with a corresponding decrease at times when the duration of day (LoD) is short. The correlation between Earth's angular deceleration (d [LoD] / dt) and global seismic productivity is even more striking, and can be shown to precede seismicity in 5-6 years, allowing societies at risk from earthquakes an unexpected glimpse of future seismic hazard. The cause of the Earth's variable rotation is the angular momentum exchange between the solid and fluid Earth (atmospheres, oceans, and outer core).
The maximum LoD is preceded by an angular deceleration of the Earth from 6 to 8 years corresponding to a π / 4 phase delay of the peak-to-peak period of 24-33 years of multi-decadal oscillations of the Earth's rotation. We show that lagged global seismic productivity is more pronounced at 10 ° N-30 ° S equatorial latitudes. Two mechanisms may be responsible: (1) decreased oblation (a reduction in J2) that assists in slowing down the rotation of the Earth and lithospheric overdrive, a process by which the equatorial lithosphere slowly nullifies the underlying mantle of deceleration to the west, like a loose cannon glides over the deck of a rolling ship.
The observed relationship cannot accurately indicate when and where these future earthquakes will occur, although we note that most additional Mw> 7 earthquakes have historically occurred near the equator in the West and East Indies. A striking example is that since 1900 more than 80% of all M≥7 earthquakes at the eastern Caribbean plate boundary have occurred 5 years after a maximum deceleration (including the 2010 Haiti earthquake). Calculations show that the asthenosphere has an appropriate viscosity to account for the delay between deceleration and seismicity of the subduction zone, however, a geodetic test of the anticipated overdrive to the west would be helpful. Whatever the mechanism, the 5-6-year advanced warning about increased seismic hazards offered by the first derivative of the LoD is haphazard and useful in disaster planning. The year 2017 marks six years after a slowdown episode that began in 2011, suggesting that the world has now entered a period of increased global seismic productivity lasting at least five years.
A volcano is an independent system and each one needs to be watched, monitored and studied in its own context. For his part, the director of the IGf, Hugo Delgado, stressed the importance of investing resources in volcanic research and instrumentation, in order to maintain knowledge and vigilance.
It is the best way to protect the population and the best product that the scientific community can offer, he said at a press conference. He added that the Fuego Volcano is one of the most active in Central America and on the continent. It is located 155 kilometers from Tapachula, Chiapas, relatively close to Mexican territory, but not enough to fear primary damage on this side.