Abstract
Two Mw 5.7 earthquakes struck a sparsely populated region of southern Italy, on October 31 and November 1, triggering a swarm-like sequence that lasted for several days. The earthquakes were caused by pure right-lateral slip between 10 and 24 km depth over a nearly vertical, previously undetected east-west fault. This mechanism is not typical for southern Italy, where normal faulting in the uppermost 12 km of the crust seems to dominate. However, east-west strike-slip faulting is kinematically consistent with the widely documented Apennines extension. The earthquake-causative fault appears to connect the Mattinata fault, a major active strike-slip feature cutting across the Gargano promontory, with east-west structures known beneath the axial part of the Apennines. The 2002 earthquakes thus highlighted a mode of earthquake release that may explain several large yet poorly understood historical earthquakes (e.g., 1361, 1456, 1731, 1930) located between the crest of the Apennines and the Adriatic coastline.
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