6th Colloquium on historical earthquakes & paleoseismology studies

30 October 2016-type earthquakes rupturing the Mt. Vettore-mt. Bove fault system (Central Italy) during the Holocene

25 Oct 2018, 09:00

20m

Han-sur-Lesse

Oral Preference Session 2.2

Speaker

Dr Daniela Pantosti (Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, Rome, Italy)

Description

A campaign of paleoseismological investigations was performed on the nearly 22 km-long coseismic surface rupture of the 30 October 2016 Mw 6.5 normal-faulting earthquake in Central Apennines. The main goal was the definition of the maximum magnitude, the average rate of displacement and the frequency of seismic events on the Mt. Vettore-Mt. Bove fault system (VBFS hereinafter). We show the results from the analysis of three trenches at different sites, one dug across a synthetic rupture strand and two across antithetic strands, as well as the integration of other paleoseismic data collected along the VBFS at different time. A major finding of our field campaign is the recognition of slip events associated with individual earthquakes affecting deposits of Holocene age based on radiocarbon dating. The paleoevents are very similar in geometry and size of deformation (up to 0.5 m of throw) to the 30 October 2016 event and re-ruptured the same fault portions within thousands time-windows. Then, paleoseismicity confirms that the VBFS growth develops during large seismic events where surface slip tends to concentrate on the same splays involved in the 2016 October earthquake rupture process, including minor antithetic faults. Moreover, the 30 October rupture traces overprinted and magnified those produced by two previous spatially and temporally clustered mainshocks of lower magnitudes, like the 24 August Mw6.0 to the south and partially the 26 October Mw5.9 to the north (Villani et al. 2018 Tectonics and references therein), involving previously activated faults as well as additional strands of the VBFS. This proves that surface ruptures can re-occur on the same portion of a fault system even within a few days/months, a scenario that has been seldom documented so far. From a paleoseismic perspective, this extreme case of very short lapses of time between surface faulting events and the observed complexity of rupture traces highlight how critical can be the reconstruction of discrete slip events in trenches stratigraphy.