Home GeoForum Forums Geologia & Professione Vulcani & Terremoti Terremoto Amatrice: thread non tecnico

Ciao michela,
giusto pour parler,
questo mi ricorda un articolo che lessi tempo fa, al quale ti rimando http://www.dst.uniroma1.it/sciterra/sezioni/doglioni/Publ_download/2009RiguzzietalTectonophysics.pdf
e del quale ti allego uno stralcio del paragrafo 8 (la figura 10 è molto didattica)

“A statistically significant correlation has been shown between seismicity (M>5.5 global shallow thrust earthquakes) and higher peak tidal stresses at continent–ocean margins, where there is a large ocean-loading component of tidal stress (Ray, 2001). However, compressive earthquakes occur more frequently during the high tide (Cochran et al., 2004) whereas extensional earthquakes are more frequent during low tides (Wilcock, 2001). In compressional tectonic settings the vertical load is expressed by &3, whereas it is given by &1 in extensional tectonic settings. During a high tide (both solid and fluid) we could expect a thicker section of rocks and water and therefore an increase of the lithostatic load. However, during the high tide, the gravity is at the minimum, opposite to the sign of the tide. Therefore, the lithostatic load (&gz, where & is density, g, gravity, and z, thickness) becomes smaller during the high tide, and larger during the low tide. This oscillating wave determines a decrease of &3 during the high tide, and an increase of &1 during the low tide. In the first case the Mohr circle enlarges to the left, while in the second case it enlarges to the right. Both opposite cases facilitate rupture in compressional and extensional settings respectively (Fig. 10). In this view, the oscillating horizontal component of the tides load and pump the tectonic system, drop by drop, slowly but steadily, whereas the vertical component of the tides might be the unloading mechanism when enough energy has accumulated along fault zones. As an example, during the recent Apennines L'Aquila earthquake sequence (April 6, 2009), the main event (Mw= 6.3, extensional focal mechanism, NEIC) occurred very near to a gravity maximum (low solid tide), thus suggesting that the larger the lithostatic load, the larger is σ1 and the activation of extensional stresses. Since the lithosphere has been documented to be in a critical state, small variations of the lithostatic load even of few Pascal may trigger the rupture or the slow viscous flow of rocks (e.g., Twiss and Moores, 1992).”
andrebbe magari verificata a posteriori la situazione per la scossa del 24
ciao