Waveform modeling of historical seismograms of the 1930 Irpinia earthquake provides insight on “blind” faulting in Southern Apennines (Italy)

Abstract

The Southern Apennines chain is related to the west‐dipping subduction of the Apulian lithosphere. The strongest seismic events mostly occurred in correspondence of the chain axis along normal NW–SE striking faults parallel to the chain axis. These structures are related to mantle wedge upwelling beneath the chain. In the foreland, faulting develops along E–W strike‐slip to oblique‐slip faults related to the roll‐back of the foreland. Similarly to other historical events in Southern Apennines, the I0 = XI (MCS intensity scale) 23 July 1930 earthquake occurred between the chain axis and the thrust front without surface faulting. This event produced more than 1400 casualties and extensive damage elongated approximately E‐W. The analysis of the historical waveforms provides the chance to study the fault geometry of this “anomalous” event and allow us to clarify its geodynamic significance. Our results indicate that the MS = 6.6 1930 event nucleated at 14.6 ± 3.06 km depth and ruptured a north dipping, N100°E striking plane with an oblique motion. The fault propagated along the fault strike 32 km to the east at about 2 km/s. The eastern fault tip is located in proximity of the Vulture volcano. The 1930 hypocenter, similarly to the 1990 (MW = 5.8) Southern Apennines event, is within the Mesozoic carbonates of the Apulian foredeep and the rupture developed along a “blind” fault. The 1930 fault kinematics significantly differs from that typical of large Southern Apennines earthquakes, which occur in a distinct seismotectonic domain on late Pleistocene to Holocene outcropping faults. These results stress the role played by pre‐existing, “blind” faults in the Apennines subduction setting.

High-resolution seismic imaging of theMw5.7, 2002 Molise, southern Italy, earthquake area: Evidence of deep fault reactivation

“…Moving toward the foreland domain, geophysical ad geological data indicate a transition from normal to strike‐slip faulting stress regime without significant changes of the maximum horizontal extension direction [ Montone et al , 2004]. In the external Apennines and Apulian foreland, active deformation is mainly accommodated along right‐lateral strike‐slip faults, roughly oriented east–west, as for recent moderate magnitude events (e.g., the M w 5.7, 1990 Potenza earthquake [ Di Luccio et al , 2005b] and the M w 5.7, 2002 Molise earthquake [ Chiarabba et al , 2005a]), and probably for large historical earthquakes (e.g., the M 6.7, 1627 Capitanata earthquake [ Gruppo di Lavoro CPTI , 2004] and the M 6.7, 1930 Irpinia earthquake [ Pino et al , 2008, and references therein]).…”

The Source of the 30 October 1930Mw 5.8 Senigallia (Central Italy) Earthquake: A Convergent Solution from Instrumental, Macroseismic, and Geological Data

“…More recently, several investigators attempted to derive their essential source parameters, including the earthquake location, magnitude, and focal mechanism, by carefully retrieving, processing, and analyzing all available seismograms (e.g., Baroux et al, 2003, for the 1909 Lambesc earthquake, southern France; Stich et al, 2005, for the 1909 Benavente earthquake, central Portugal; Pino et al, 2008, for the 1930 Irpinia earthquake, southern Italy; Pino et al, 2009, for the 1908. In all cases the intensity and instrumentally derived parameters were compared with available tectonic, stress field, and Global Positioning System (GPS) evidence.…”

Moment Tensor Resolution: Case Study of the Irpinia Seismic Network, Southern Italy

“…Our modeling indicates normal faulting with a strong strike-slip component. A notable strike-slip component was also observed in previous earthquakes in the region, such as the 1930 event (Pino et al, 2008) and two events in 1962 (Westaway, 1987). In particular, the latter occurred very close to the 2012 earthquake.…”