Evidence for Surface Faulting Earthquakes on the Montereale Fault System (Abruzzi Apennines, Central Italy)

Abstract

We conducted paleoseismic studies along the Montereale fault system (MFS; central Italy). The MFS shows geomorphological evidence of Late Quaternary activity and falls within the highest seismic hazard zone of central Apennines, between the epicentral areas of two recent earthquake sequences: 2009 L'Aquila and 2016–2017 central Italy. We excavated two trenches along the San Giovanni fault splay of the system, one intercepting the N140° striking bedrock main fault plane and the other cutting two subparallel fault scarps on the colluvial/alluvial deposits on the fault hanging wall. Excavations revealed repeated fault reactivation with surface faulting in prehistorical and historical times. We recognized and dated seven events in the last 26 kyr. The most recent ground‐rupturing event (evb1) possibly occurred 650–1,820 AD, consistent with one of the three main shocks that struck the area in 1,703 AD. A previous event (evb2) occurred between 5,330 bc and 730 bc, while older events occurred at 6,590–5,440 bc (evb3), 9,770–6,630 bc (evb4), and 16,860–13,480 bc (evb5). We documented two older displacement events (evb7 and evb6) between 23,780 bc and 16,850 bc. The minimum vertical slip rate at the trench site in the last 28–24 kyr is 0.3–0.4 mm/year. The inferred average recurrence interval for surface‐faulting events along the MFS is no longer than ~4 kyr. Based on the surface fault length ranging between 12 and 20 km, earthquakes with ≥M 6.0 are possible for the MFS. The MFS is an independent earthquake source, and its paleoseismic data are fully comparable with those known for faults in central Apennines.

Seismicity Rate Changes and Geodetic Transients in Central Apennines

“…Furthermore, we argue that the geometry and the frictional properties of the segmented system affects the degree of interseismic coupling. This likely leads to differences in recurrence intervals and maximum magnitude between mature listric faults and younger high-angle normal faults as exhibited by the historical seismicity and paleoseismology across Central Apennines (e.g., Cinti et al, 2018;Falcucci et al, 2018;Galadini & Galli, 2003;Galli et al, 2019;Guidoboni et al, 2018).…”

22‐kyr‐Long Record of Surface Faulting Along the Source of the 30 October 2016 Earthquake (Central Apennines, Italy), From Integrated Paleoseismic Data Sets

“…The overall average recurrence interval of surface faulting along the investigated portions of the VBFS is in the range 3360–3640 years (seven events since 19820–18180 BCE; Table ). Recurrence intervals of thousands of years for surface faulting events are typical of the major normal faults in the central Apennines (e.g., Cinti et al, ; Galadini & Galli, ; Galli et al, ; Pantosti et al, ). However, using the time window of the last ~4,000 years, the average interval is 1,220–1,970 years (three events since 1930–415 BCE), which is substantially shorter (Table ).…”

“…Vettore fault (~1 mm/year in the last 30 kyr; Di Donato et al, 2018;Galli et al, 2019). The slip rate evaluations belonging to the same splay of the system are within the same order of magnitude and are comparable to those of other active fault systems in the central Apennines, which are generally around 0.3-0.4 mm/year in the Holocene (e.g., Cinti et al, 2018;Galli et al, 2018;Michetti et al, 1996;Moro et al, 2016;Pantosti et al, 1996;Salvi et al, 2003). In order to obtain a value representative for the activity of the VBFS, these estimates should be considered within a reference frame reconciling both the coseismic slip and the long-term deformation.…”

Surface Faulting of the 30 October 2016 Mw 6.5 Central Italy Earthquake: Detailed Analysis of a Complex Coseismic Rupture

“…The long‐term extension originated a compound network of normal fault systems up to ~25–30 km in length, partially coaxial with the Neogene thrusts, mostly NW trending and SW dipping (Figure ; Barchi et al, ; Boncio & Lavecchia, ; Cowie & Roberts, ; Lavecchia et al, ; Roberts et al, ). Most of these faults show clear hints of late Pleistocene to recent tectonic activity (offset postglacial deposits and landforms, compound fault scarps affecting both continental deposits and pre‐Quaternary bedrock), while geologic and paleoseismic data provide values of individual fault slip rates in the 0.2–1.3 mm/year range (Barchi et al, ; Benedetti et al, ; Cinti et al, ; Cowie et al, ; Galadini & Galli, ; Galli et al, ; Giraudi, ).…”