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Stimulation of damaging earthquakes by fluid motions in the Earth?s outer core: a 5 year advanced warning of global seismic hazards

Categoria
Seminario
Data
15 Marzo 2018 12:00 - 13:00
Luogo
14 - 15 IV piano St. 9
Affiliation
Universit? di Boulder, Colorado (USA)
Area di Ricerca
Geofisica

In the past 117 years, decadal variations of Earth?s angular rotation rate occur at periods of 20-90 years due to the conservation of angular momentum between the fluid core and the mantle. Approximately twice as many Mw?7 earthquakes occur during periods of slow rotation (?20/yr) as occur during periods of fast rotation (?10/yr), and effect which is also observed for Mw?6.6. In seeking a mechanism linking mantle deceleration to seismicity we invoke a low viscosity asthenosphere that weakly couples mantle rotation to lithosphere rotation. At 30-40 year forcing periods Maxwell viscosity introduces a ?5 year lag between applied stress and observed strain, similar to that observed between Earth`s angular deceleration and the length of the day. Rotation of the lithosphere thus lags ?5 years behind rotation of the mantle. In response to this differential motion seismicity is induced at subduction zones, which are effectively anchored to the mantle. The effect is most pronounced at the earth`s equator and vanishes at the poles. We propose that the timing of earthquakes with decadal seismic cycles is advanced or retarded by angular deceleration by a process known as synchronized entrainment. Since the earth started decelerating in 2013 we forecast that global seismicity will start to increase in 2018, with a peak in Mw?7 earthquakes around 2020.

 
 

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  • 15 Marzo 2018 12:00 - 13:00

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