Earthquake synchrony and clustering on Fucino faults (Central Italy) as revealed from in situ³⁶Cl exposure dating

Abstract

[1] We recover the Holocene earthquake history of seven seismogenic normal faults in the Fucino system, central Italy. We collected 800 samples from the well-preserved limestone scarps of the faults and modeled their 36 Cl concentrations to derive their seismic exhumation history. We found that > 30 large earthquakes broke the faults in synchrony over the last 12 ka. The seven faults released strain at the same periods of time, 12-9 ka, 5-3 ka, and 1.5-1 ka. On all faults, the strain accumulation and release occurred in 3-6 ka supercycles, each included a 3-5 ka phase of slow (≤ 0.5-2 mm/yr) strain accumulation in relative quiescence, followed by a cluster of three to four large earthquakes or earthquake sequences that released most of the strain in < 1-2 ka. The large earthquakes repeated every 0.5 ± 0.3 ka during the paroxysmal phases and every 4.3 ± 0.9 ka between those phases. Earthquakes on the northern faults produced twice larger surface slips (~2 m) and had larger magnitudes (Mw 6.2-6.7) than those on the southern faults. On most faults, the relative strain level was found to control the amount of slip and the time of occurrence of the next large earthquake. Faults entered a phase of clustered activity once they had reached a specific relative strain threshold. The Tre Monti fault is identified as the most prone to break over the next century. Our data document earthquake synchrony and clustering at a broader space and time scale than has been reported to date.

Complete seismic release of tectonic strain and earthquake recurrence in the Apennines (Italy)

“…In particular, it is not clear if the distribution of recurrence intervals is best described by a renewal model with a strong central tendency [Matthews et al, 2002], by the view that repeated large earthquakes can happen in rapid succession without requiring time for stress regeneration [Jackson and Kagan, 2006] or that strain is released by clustered events in a time span considerably shorter than their mean recurrence interval [Wallace, 1987]. A recent 36 Cl exposure dating study of the fault scarps of the Fucino fault system [Benedetti et al, 2013] suggests that over the last 12,000 kyr, >30 large earthquakes broke the faults in synchrony in 3-6 kyr spaced clusters of large events releasing most of the strain in <1-2 kyr long episodes. If these results are generalized, there emerges a general scenario where migrating pulses of activity are temporarily focused for a timescale of few thousand years, similarly to what is proposed for the Basin and Range province [Wallace, 1987].…”

Pulsed strain release on the Altyn Tagh fault, northwest China

“…In contrast to long-term temporal changes in slip rate that have been inferred (Goldfinger et al, 2013;Wallace, 1987;Weldon et al, 2004) or shown elsewhere (Benedetti et al, 2013;, the present study uses direct measurements of both age and offset to document a discrete, short pulse of accelerated slip along a major, long-lived strike-slip fault. Based on its duration and magnitude, we conclude that the mid-Holocene slip pulse resulted from either a spatiotemporal cluster of events or a single great earthquake.…”

“…Stress changes between interacting faults Stein, 1999;Stein et al, 1994) can synchronize slip behavior (Benedetti et al, 2013;Scholz, 2010). The North Altyn fault (NAF) is a candidate structure with which the ATF may interact (Figs.…”

Integrating faults and past earthquakes into a probabilistic seismic hazard model for peninsular Italy

“…Moreover, long-term observations of faults in various tectonic contexts have shown that slip rates vary in space and time (e.g. Bull et al, 2006;Nicol et al, 2006Nicol et al, , 2010 , 2009a, b;Gunderson et al, 2013;Benedetti et al, 2013;D'Amato et al, 2016), and numerical simulations (e.g. Robinson et al, 2009;Cowie et al, 2012;Visini and Pace, 2014) suggest that variability mainly occurs in response to interactions between adjacent faults.…”