Visualisation of active normal fault scarps in the Apennines, Italy: a key to assessment of tectonic strain release and earthquake rupture.

Gerald P. Roberts

Active normal fault scarps that offset 12-18 ka landforms in the Apennines, Italy, have been mapped into Google Earth to provide precise locations for structures responsible for tectonic strain release and earthquake rupture. Climate change at the end of the last glacial maximum (12-18 ka) reduced erosion and sedimentation rates below a critical threshold allowing preservation of displacements produced by surface ruptures to palaeoearthquakes. The resultant fault scarps, which record the surface displacements from multiple earthquakes, allow determination of the spatial variation in the rates of fault slip, a parameter critical to assessment of how long-term strain release recorded in the geomorphology (104 years) relates to short-term strain release recorded by earthquake catalogues and geodesy (102-3 years). Spatial variation in fault slip occurs at a scale of tens of kilometres, whilst fault scarps have offsets of <20-40 metres and a geomorphic expression that can only be visualised on topographic images with spatial resolution approaching the metre-scale. Thus, until now, debate has surrounded the exact positions of scarps at least in part due to problems of visualising both the detailed geomorphic features and their regional variation. Provision of complete SPOT image coverage and topography within Google Earth allows individual scarps visited during fieldwork to be visualised at a regional scale within an easily-accessible interface. The resultant maps are used to comment on tectonic strain release and earthquake rupture.