Rating criteria for Sources derived from geophysical/geological data (Type A sources)

The rating of Type A sources is based on expert judgement by the compiler of each individual source. The process of rating the reliability of Type A sources is very complex because of the large number and the diverse nature of uncertainty types involved in the identification and characterisation of any individual source. For example, some of the sources carry an epistemic uncertainty associated with their mere existence, or with their attitude towards generating their maximum-size earthquake versus releasing multiple smaller events. These types of non-conventional uncertainties are difficult to be incorporated into a single rating parameter and for the time being this task has been entirely left to the expert judgement of the individual compilers. It is anticipated that a more accurate incorporation of all types of uncertainties into the source rating will be the object of future efforts based on the experience gained with FAUST.

Here we propose a simplified scheme that was followed for rating all Type A sources regardless of the country they occur in. Notice that additional information on the reliability of the proposed source parameters is generally contained in the Open Questions text associated with most sources.

Class A - Is assigned to all sources for which there exists combined instrumental, historical and geologic/geomorphic evidence. The source parameters are constrained by seismological or geodetic evidence that allow a finer resolution than that allowed by surface geology data alone.

Class B - Is assigned to all sources for which there exists satisfactory historical and geologic/geomorphic evidence. Class B typically includes the source of earthquakes that occurred in the pre-instrumental era. The source parameterisation is jointly constrained by the extent of historical rupture and by the occurrence of significant geologic features such as the size and extent of a basin, the intersection with known tectonic lineaments, the rupture terminations of Class A sources, etc.

Class C - Is assigned to all sources that were derived from geologic/geomorphic evidence but for which limited or no historical evidence exists. The source must be on-land and associated with clearly identified large-scale features belonging to known regional trends. This class and the following Class D must include sources for which there is epistemic uncertainty as to their existence as active features and to their potential as seismogenic sources.

Class D - Similarly to the rating C, it is assigned to all sources that were derived from geologic/geomorphic evidence with limited or no historical constraints. Unlike the previous class, the source may be offshore and its location constrained by reflection seismology data or other large-scale geodynamic observations used to pinpoint regional trends of homogeneous tectonic deformation.

Notice that, despite the greater reliability of sources rated A and B, the remaining two classes contain sources that were active in very remote times or were never active historically. Class C and D sources are therefore the most likely candidates for large earthquakes of the future, and for this reason they should receive special attention both by the compilers of future releases of the catalogue and by all potential end-users.
 


Rating criteria for Sources derived from intensity data (Type B and C sources)

The rating of Type B and C sources is expressed by two parameters Q1 and Q2 based exclusively on the quality of the solution supplied by Boxer. The two parameters are assigned automatically according to the following scheme:
 
Q1
Orientation uncertainty
  
Q2
Number of 
intensity data
A
<10°
  
A
>500
B
10°-24°
  
B
100-499
C
25°-49°
  
C
50-99
D
*50°
  
D
20-49
E
no orientation assessed
  
E
<20

The automatic assignment is justified by the fact that Type B and C sources that are looked at in detail are often turned into Type A sources and subsequently rated by expert judgement. Notice that for Type C sources Q1 is always set to E.

The end-user should consider that by definition all Type B and C sources were active historically and therefore are not regarded as immediate candidates for large future earthquakes. The importance of reliable Type B and C sources in conjunction with well constrained Type A sources rests essentially in their capacity to (1) delineate homogeneous tectonic trends and (2) highlight areas of historical quiescence.