5:15 PM - 7:15 PM
[SSS12-P18] Leap Second and Penetrate of Pacific Slab into upper surface of Lower Mantle
Keywords:Leap Second, Deep Seismic Plane, Pacific Slab, Lower Mantle, Earth's Rotation, Megaquake of Trench Area
Deep Seismic Plane exists under Japanese Island Arcs descending along Chishima, Japan and Izu Trenches (Wadati,1935).
Japan Meteorological Agency has developed seismological network to determine hypocenters since 1922 and CMT solution for the focal mechanism since 1994. The Deep Seismic Plane is interpreting as Pacific Slab.
The magnitude of deep earthquakes increases with depth toward upper surface of Lower Mantle of 660km and the presence of hypocenters below the surface suggests the Pacific Slab penetrates into Lower Mantle.
2002 April8 610km M7.1, 2002June29 M7,2 617km, and 2010Feburuary18 M6.9 631km at the tip of Pacific Slab just above the upper surface of the Lower Mantle released strain as buckling with 2m shortening, however it was not enough and the ten days later,2010Feburuary28 M5.3 broke Pacific Ocean floor outside of Japan Trench, and finally 2011March11 M9.0 released the strain of relative Plate motion with 25m along Japan Trench has stuck with the friction on plate boundary for several hundred years.
Because the Pacific Slab of Chishima Trench Area has also already released strain around the upper surface of the Lower Mantle, as 2012August14 M7.5 728km, 2013May24 M8.3 600km, 2021Sept3 M5.8 580km, and 2024Jun6 M5.9 593km, warning on raid of Megaquake has been presented (Niitsuma, 2024).
The penetration of tip of vast Pacific Slab with high density and phase transitions into Lower Mantle should change the mass distribution in the Earth, and influence on Earth's Rotation. Time is fundamental unit defined on Earth's Rotation. The velocity of the Rotation is reduced by the tidal friction, and global timekeepers periodically have added a negative leap second to keep atomic clocks since 1972. The interval of leap second was about one year in 1970s, but increased to several years and to need positive leap second recently (Fischetti, 2024).
The intervals of leap second increase after the Earthquake deeper than 300km and larger than M7.0 from 1972 to 2024(refer Text Figure), especially from 1999 to 2006 without of leap second can be correlate clearly with the earthquakes of Pacific Slab from Japan Trench.
Such as figure skate players accelerate their spins to shorten of extended arms, the centroid of Slab of which tip should had moved toward the Earth's Rotational axis to accelerate.
Deep Earthquakes around upper surface of Lower Mantle before Megaquake along trench is important for Earthquake Forecast, however, information on the dynamics of Mantle Transition Zone is poor and the limitation by changes in Earth's Rotation might be useful.
References:
Fischetti,M. (2025) Should we abandon leap second?, Scientific American, 2024Nov.
Niitsuma, N.(2024) 2011Mar11M9.0 off Northeast Arc Heisei with break of Pacific Slab into upper surface of Lower Mantle, and Megaquake in Chishima Trench Area. Geol. Soc. Japan, Annual Meeting Yamagata,T7-O-8.
Wadati, K. (1935) On the activity of deep-focus earthquakes in the Japan Islands and neighborhoods. Geophysical Magazine, 8, 305-325.
Japan Meteorological Agency has developed seismological network to determine hypocenters since 1922 and CMT solution for the focal mechanism since 1994. The Deep Seismic Plane is interpreting as Pacific Slab.
The magnitude of deep earthquakes increases with depth toward upper surface of Lower Mantle of 660km and the presence of hypocenters below the surface suggests the Pacific Slab penetrates into Lower Mantle.
2002 April8 610km M7.1, 2002June29 M7,2 617km, and 2010Feburuary18 M6.9 631km at the tip of Pacific Slab just above the upper surface of the Lower Mantle released strain as buckling with 2m shortening, however it was not enough and the ten days later,2010Feburuary28 M5.3 broke Pacific Ocean floor outside of Japan Trench, and finally 2011March11 M9.0 released the strain of relative Plate motion with 25m along Japan Trench has stuck with the friction on plate boundary for several hundred years.
Because the Pacific Slab of Chishima Trench Area has also already released strain around the upper surface of the Lower Mantle, as 2012August14 M7.5 728km, 2013May24 M8.3 600km, 2021Sept3 M5.8 580km, and 2024Jun6 M5.9 593km, warning on raid of Megaquake has been presented (Niitsuma, 2024).
The penetration of tip of vast Pacific Slab with high density and phase transitions into Lower Mantle should change the mass distribution in the Earth, and influence on Earth's Rotation. Time is fundamental unit defined on Earth's Rotation. The velocity of the Rotation is reduced by the tidal friction, and global timekeepers periodically have added a negative leap second to keep atomic clocks since 1972. The interval of leap second was about one year in 1970s, but increased to several years and to need positive leap second recently (Fischetti, 2024).
The intervals of leap second increase after the Earthquake deeper than 300km and larger than M7.0 from 1972 to 2024(refer Text Figure), especially from 1999 to 2006 without of leap second can be correlate clearly with the earthquakes of Pacific Slab from Japan Trench.
Such as figure skate players accelerate their spins to shorten of extended arms, the centroid of Slab of which tip should had moved toward the Earth's Rotational axis to accelerate.
Deep Earthquakes around upper surface of Lower Mantle before Megaquake along trench is important for Earthquake Forecast, however, information on the dynamics of Mantle Transition Zone is poor and the limitation by changes in Earth's Rotation might be useful.
References:
Fischetti,M. (2025) Should we abandon leap second?, Scientific American, 2024Nov.
Niitsuma, N.(2024) 2011Mar11M9.0 off Northeast Arc Heisei with break of Pacific Slab into upper surface of Lower Mantle, and Megaquake in Chishima Trench Area. Geol. Soc. Japan, Annual Meeting Yamagata,T7-O-8.
Wadati, K. (1935) On the activity of deep-focus earthquakes in the Japan Islands and neighborhoods. Geophysical Magazine, 8, 305-325.