COMMENTS

This source is responsible for the 26 September 1997, 15:23 UT event of the 
Umbria-Marche earthquake sequence. Its location and geometry are well 
constrained by several types of instrumental data. The source is represented as 
a W-dipping normal fault with the peculiarity of a low dip angle (ca. 30). The 
Summaries of the Main Studies text may also include the analysis of other 
earthquakes of the sequence and descriptions of geologic features regarding a 
much larger area than that of the source.

In the past the Colfiorito area was mainly studied from the general geological 
point of view. The first paper to analyse presumed active tectonic features in 
this area is that by Cello et al. (1997). The 1997-98 earthquake sequence 
fostered a number of in-depth studies with the main purpose of understanding 
both seismological and geological aspects. As concerns the field detection of 
surface deformations, three different papers gave three different 
interpretations. Cello et al. (1998) interpreted the surface displacements 
detected both in the Colfiorito basin and in the Cesi-Forcella basin as surface 
faulting. Basili et al. (1998) contend that the surface displacements detected 
both in the Colfiorito basin and in the Cesi-Forcella basin were the result of 
ground shaking, whereas  the ground-surface ruptures seen in the Sellano area 
were the result of tectonic deformation, and possibly of genuine surface 
faulting. Cinti et al. (1999) detected an array of three sets of parallel 
ruptures that were interpreted as a brittle response to a more distributed 
tectonic deformation.


OPEN QUESTIONS

1) Did surface faulting actually occur during the 1997-98 earthquake sequence? 
If not, was the observed deformation the response to seismic shaking or to 
tectonic warping?

2) Can the faults exposed in the Colfiorito Basin be considered truly active and 
seismogenic?

3) What are the geological observations that could be used to constrain the 
long-term behaviour of this source?
