COMMENTS

In the past the 1887 earthquake has been believed to have occurred 10-20 km off the coast 
of Imperia. The Catalogue of Strong Earthquakes in Italy (Boschi et al., 1997) and the 
Parametrical Catalogue of Italian Earthquakes (Gruppo di Lavoro CPTI, 1999) first locate 
the event beneath the coast a few km E of Imperia. This is partially due to the fact that 
higher intensities in fact concentrate in a relatively small area around Imperia, and 
partially to the fact that the automatic location procedure used in both catalogues tends 
to force offshore earthquakes towards inland.

An inland source is also suggested by the comparison of the size and intensity level of 
the highest degree isoseismal (intensity IX)  with the size of lower degree isoseismals. 
An offshore source would require a larger magnitude than that calculated for CPTI (Me 
6.3), which in turn should be reflected in a larger propagation of the intermediate level 
intensities. An offshore source would also require that all intensity IX data points be 
interpreted as site amplification effects, which is unlikely given their number and 
diversity of the associated site conditions.

Little is known about the kinematics of this source, except for the substantial dip-slip 
component required by he occurrence of a sizeable tsunami. Eva and Rabinovich (1997) 
model the tsunami data with a normal fault located offshore but do not discuss the 
reasons for this choice. As shown by several of the works described in the Previous 
Studies section, the regional stress field that can be inferred from background seismicity 
is purely compressional with a largest principal stress oriented N-S to NW-SE (e.g. the 21 
April 1995, Ventimiglia earthquake). A similar trend is also suggested by the general 
plate motions in this reach of the Alps/Apennines system.

Evidence for cumulative tectonic deformation is also very limited. No evident uplift is 
reported along the coast. Given the magnitude of the 1887 earthquake, however, and the 
fact that similar events must be rare (recurrence interval > 1,000 y), the inferable rate of 
coseismic uplift would be extremely low and possibly unresolvable.


OPEN QUESTIONS

1) All the hypotheses made about the essential parameters of this source remain 
essentially unwarranted. Is the source really inland? Is the causative fault of the 1887 
earthquake purely reverse?

2) Is there any geological evidence of sustained activity along this fault? 

3) Does the fault terminate against one of the many roughly N-S transverse features that 
cut the western Ligurian coast at nearly right angles?

4) Does this source coincide with an especially strong fault zone (asperity), or are similar 
events likely to occur all along western Liguria and across the border with France?
