Abstract

This paper analyzes static surface displacements associated with the Avezzano, Italy, earthquake (Ms = 6.9) of 13 January 1915. The Avezzano event locates on a shallow normal fault centered in the Apennine mountains near a Quaternary tectonic depression named “Conca del Fucino.” The 1915 earthquake is the only sizable event to have occurred in the area for at least a millennium, although many Holocene and Quaternary faults can be recognized in the field. Awareness of the seismic potential of the Fucino region has heightened in recent years with the outward expansion of metropolitan Rome (80 km southwest). Because of a fortuitous pre-earthquake leveling survey near the fault in the mid 19th century, good quality geodetic data exist that illuminate details of the 1915 rupture. We modeled the faulting using both uniform (USP) and variable (VSP) slip planar dislocations. The best fitting focal mechanism includes pure dip slip on a plane striking 135° and plunging 63° to the southwest. This fault geometry is consistent with surface scarps and the broad scale tectonics of the region and is common to several large earthquakes of the south-central Apennines. The USP analysis estimates fault length, width, slip and moment to be 24 km, 15 km, 83 cm, and 9.7 × 1018 N-m, respectively. Numerical simulations indicate that residuals left in the uniform slip model are not entirely random and represent systematically unmodeled features of fault slip. VSP models of the earthquake significantly reduce the USP variance and reveal a broad two-lobed slip pattern, separating a central region of low moment release. New formulations detailing the relationships between VSP and minimum model norm solutions to underdetermined inverse problems are presented as well as concise statements dealing with the intrinsic and combined resolving power of a geodetic network.

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