COMMENTS

Based on preliminary observations we propose for the Cividale Source the following 
geometrical characteristics:

- the length (25 km) is based on scaling with width, constrained  by geomorphological 
observations and empirical relationship  between magnitude and rupture area.

- the down-dip width (10.6 km) is based on the assumptions  made concerning the 
minimum and maximum faulting depth,  constrained by empirical relationship of 
rupture area with respect to  the magnitude;

- the strike is chosen according with the general orientation of  mapped tectonic 
structures (N313) belonging to the Dinaric  system;

- the fault dips 70 towards the northeast;

- the rake is assumed to be 180 (pure right strike-slip) based on  strike and on general 
geodynamic considerations;

- the minimum and maximum depth (1.3 and 10 km  respectively) are constrained by 
subsurface geology and by the lack of  evidence of coseismic surface faulting;

The 26 March 1511 earthquake is the only event reported in the current catalogues 
(CPTI, 1999) that can be associated with the Cividale Source based on damage 
distribution.

The area of the strongest effects of this event falls in the Tagliamento valley (very 
close to the macroseismic epicentre of the 1976 Gemona earthquake) and in western 
Slovenjia. To explain the strong damage in Slovenjia we may hypothesise that 
during the 1511 sequenceinvolved two or more major shocks, one on the Cividale 
Fault proper and the other on another tectonic structure found more to the east.

This source belongs to the Dinaric fault system, which is characterised by NW-SE 
orientations and right-lateral reverse movement.

Despite the large magnitude there is no evidence of coseismic surface ruptures along 
the surface trace of the Cividale Fault.


OPEN QUESTIONS

1) What is the average return time of the Cividale Source? Current catalogues (CPTI, 
1999), which cover reliably a time span of less than 1,000 years, report only a large 
event in 1511 that can be associated with it.

2) Is the equivalent Magnitude of the 1511 earthquake over-estimated?

3) How can we explain the presence of two zones with the strongest effect in western 
Slovenjia and in the Tagliamento valley?

4) What are the relationships between the Cividale Source and the Gemona East 
Source?

5) Is the Cividale Fault characterised mainly by strike-slip movements? Or is it rather 
an oblique fault?
