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Authors: Scalera, G. 
Title: Great and old earthquakes against great and old paradigms – paradoxes, historical roots, alternative answers
Issue Date: 2-Jan-2008
Series/Report no.: /14 (2008)
Keywords: Wadati-Benioff zones
Earthquakes and volcanoes correlations
Geodynamics of active margins
Expanding Earth
Subject Classification04. Solid Earth::04.01. Earth Interior::04.01.02. Geological and geophysical evidences of deep processes 
04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics 
04. Solid Earth::04.07. Tectonophysics::04.07.04. Plate boundaries, motion, and tectonics 
04. Solid Earth::04.07. Tectonophysics::04.07.08. Volcanic arcs 
Abstract: The similarity of the vertical displacements shown by case-history extreme-magnitude earthquakes are scrutinised (Chile 1960, Alaska 1964, Sumatra 2004, . . . ). A common interpretation – an uprising of lithospheric material – can be found, which is supported by the irregularities of the hypocentres distribution along the Wadati-Benioff zones. In the case of major South American earthquakes, a volcanic eruptions-earthquakes correlation is recognisable. Further support to this interpretation is the displacement of the Earth’s instantaneous rotation pole – 3.0 mas (10 cm), observed at ASI of Matera, Italy – the seismic data (USGS)in the two days following the main shock, the geomorphologic data, and the satellite data of uplift/subsidence of the coasts (IGG) make possible a new interpretation of the Great Sumatran earthquake (26 December 2004) based on the second conjugate – nearly vertical – CMT fault plane solution. All this converges toward different causes of seismogenetic processes, strongly supporting a deep origin of disturbances, fluxes of materials leading to more or less sudden movements of masses, and phase changes, which lead to either earthquakes or silent-slow events in Wadati-Benioff zones. A reinterpretation of the geodynamics of the active margins and mountain building is proposed with a heuristic model that does not resort to large-scale subduction, but only to isostatic uplift of deep material intruding between two decoupling plates in a tensional environment. Concomitant phase changes toward less-packed lattice and buoyancy effect caused by the Clapeyron slope can help the extrusion of material over the m.s.l., constituting an orogenic process. The phenomena expected to occur in the model directly and harmoniously contribute to the building up of the surface geophysical and geomorphological features of the orogenic zones.
Description: This paper is an innovative interpretation of the geodynamics of the active margins in a framework different from the plate tectonics one. Large scale subduction do not appears a necessary concept, if the detected new phenomena and correlations are considered. South American Pacific margin is found to be the key region to investigate in greater detail the active margins geodynamics.
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