Abstract
We analyse the Mw 6.5, 2016 Amatrice-Norcia (Central Italy) seismic sequence by means of InSAR, GPS, seismological and geologic data. The >1000 km2 area affected by deformation is involving a volume of about 6000 km3 and the relocated seismicity is widely distributed in the hangingwall of the master fault system and the conjugate antithetic faults. Noteworthy, the coseismically subsided hangingwall volume is about 0.12 km3, whereas the uplifted adjacent volumes uplifted only 0.016 km3. Therefore, the subsided volume was about 7.5 times larger than the uplifted one. The coseismic motion requires equivalent volume at depth absorbing the hangingwall downward movement. This unbalance regularly occurs in normal fault-related earthquakes and can be inferred as a significant contribution to coseismic strain accomodated by a stress-drop driven collapse of precursory dilatancy. The vertical coseismic displacement is in fact larger than the horizontal component, consistent with the vertical orientation of the maximum lithostatic stress tensor.
Highlights
Coseismic horizontal elastic rebound or more suitable with the hangingwall gravitational collapse? We address the question whether the rock volume dilated in the brittle layer during the interseismic preparatory period was only elastically stretched[1] or alternatively fractured and permeated by a population of thousands of microfractures[8]
On August 24th 2016, an Mw 6.0 earthquake started a seismic sequence in Central Italy that had its apex with a Mw 6.5 on October 30th
These motions sum up the effects of the Amatrice-Norcia 2016 part of the seismic sequence
Summary
The Apennines are in the hangingwall of a ‘westerly’-directed and ‘easterly’-retreating subduction zone. Contraction occurs in their eastern margin where the accretionary prism involves the shallow layers of the Adriatic plate. The 2016 Amatrice-Norcia seismic sequence fits the extensional tectonics affecting the central Apennines fold-thrust belt since at least Pliocene time[18,19] that generated a system of active NW-trending normal faults[20,21,22]. 30th Mw 6.5 earthquake is characterized by rupture velocity of 2.7 km/s and by a large slip patch located ~5 km up-dip from the hypocenter with average slip of 130 cm and maximum slip of 260 cm[12].
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