Great and old earthquakes against great and old paradigms – paradoxes, historical roots, alternative answers

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.