Fault fragment control in the 1997 Umbria‐Marche, central Italy, Earthquake Sequence

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Abstract
The Umbria‐Marche region in central Italy experienced a sequence of shallow earthquakes in late 1997, including three mainshocks on September 26th (Ms 5.5 and 5.9) and October 14th (Ms 5.5). This seismic sequence illustrates the relationships between small‐scale active faults and moderate‐magnitude earthquakes. We suggest that a small‐scale active fault corresponds to a “fault fragment” and that it refers to the fault area required for producing a coseismic deformation at the ground surface. The seismic activity and related three mainshocks occurred along three fault fragments which total ∼25 km in length and show a listric geometry at depth. Fault fragments are laterally controlled by pre‐existing transverse fold‐and‐thrust structures and may constitute a major component of the seismic strain release in active continental regions.