A conceptual 3D fold-and-thrust database for seismic hazard, seismotectonic and geodynamic purposes - a first release from eastern Central Italy

We present SEISC-3D, an ArcGIS geodatabase for 3D SEIsmic Source Characterization. It integrates multi-scale and multi-depth geological and seismological information in a compressional environment to build a detailed regional-scale, geometric and kinematic, 3D curvilinear fault model suitable for seismic hazard modelers and seismotectonic purposes and geodynamic modeling. This first release focuses on the late Pliocene-to-Quaternary arcuate and eastward convex fold-and-thrust belt still active along the Outer front of the Italian Apennines in eastern Central Italy. The near-surfaces, onshore, and offshore thrust faults represent the hanging-wall structures of a potentially seismogenic regional shear zone, known as Adriatic Basal Thrust, which develops from near-surface to MOHO depths (about 35 km).

Three hierarchic levels of structural maps are provided with decreasing details moving from fold-and-thrusts traces, enveloping thrust, and regional thrust alignments.

Different datasets (points, lines, surfaces) are unified, compiled, and held in a common ArcGIS file system folder and linked on the basis of relational models.

SEISC is composed of:

• one dataset consisting of fold hinges traces (syncline and anticlines)
• one dataset consisting of individual fold-related thrust
• one dataset consisting of enveloping thrusts organized in hierarchic orders
• one dataset consisting of interconnected curvilinear fault surfaces built along the down-dip projection of the enveloping thrusts, segmented along-strike and along-dip
• one structural data set containing geometric and kinematic point data (attitude, dip-angle, slip-vector, rake, sense of movement) for the node of each triangulated mesh of each fault surface.

A crucial point when dealing with compressional structures is the difficulty in adopting segmentation criteria suitable for a realistic earthquake-fault association. In our methodological approach, the along-strike segmentation is strongly driven by the en-echelon distribution of the fold-related thrusts and by sharp variation in strikes and bending of the enveloping thrusts. On the other hand, the down-dip segmentation is controlled by the mechanical crustal layering derived from earthquake distributions and the rheological investigation.