Philosophy & Terms
The HeDBAF constitutes a multi-purpose, upgradable and updatable tool which not only aims at providing crucial information to the scientific community, engineers, the state and common people, but at contributing to various implementations and applications, such as numerical modelling either for seismic hazard analysis (SHA), tsunami propagation, crustal deformation, etc.
Following the steps of the Database of Individual Seismogenic Sources (DISS) and the Quaternary active faults database of Iberia (QAFI), HeDBAF not only is the source of information, for most of the parametric information, clearly given (whether it is literature data, original data, empirical relationship, or expert judgement, all abbreviated as source-keys), but the methodology followed to extract this information is stated. This means that the end-user has at his/her disposal the origin of the parametric information and the distinction between real data or any other kind of estimation. In this way, the scientific and highly specialized working group of the geodatabase ensures that most of the parametric information will be filled in, leaving as few blank fields as possible.
To that end, the core of the geodatabase, i.e. the tectonic information, will be separated into two distinct, but interrelated, datasets: i) the Fault Traces (FT), and ii) the Fault Zones (FZ). The purpose of each dataset is to provide a different level of information covering different needs.
Fault Traces (FT) dataset
The FT dataset includes fault traces mapped at the highest possible accuracy which means that it is scale sensitive. The accuracy depends on the source of information: it can be derived from research papers, technical reports, dedicated thematic maps, etc. The optimized scale of visualization is below 1:100,000. However, as a layer of the final published product, it is visible by choice on any scale. Each fault trace can be part of a fault segment or represent a fault segment by itself, or be part of a larger fault zone.
This dataset includes faults with geomorphic marks, such as free faces, (coseismic) ruptures, fault scarps, triangular facets (flat-irons), or sometimes inferred faults based on geomorphological evidence, such as river deflections, linear mountain-fronts, etc. It should be mentioned that the geomorphological evidence is a complementary element for the more accurate geographical positioning of the fault trace and not for the existence of the fault. In the case of earthquake – actually related faults (seismic faults), the traces can correspond to primary ground ruptures.
The main purpose of this dataset is to provide information necessary for Surface Faulting Hazard or Surface Fault-Rupture Hazard. This type of hazard assessment is crucial for building and infrastructure design considering that a possible fault displacement could damage the foundations of any technical construction. From a more scientific point of view, the detailed mapping of fault traces can contribute to fault linkage/segmentation scenarios. Such scenarios are also important for SHA since they can help determine whether a possible rupture can be constrained or interfere with neighbouring faults, increasing, thus, the magnitude potential.
Fault Zones (FZ) dataset
The FZ dataset represents one or more fault segments of similar geometric and kinematic characteristics, and, consequently, one or more Fault Traces (FT). It is optimally viewed in small-scale maps. As a result, there is no need for very detailed mapping.
The distinctive difference between Fault Zones and Fault Traces is that the former involves earthquake rupturing scenarios (or hazard scenarios) and can be divided into one or more fault segments. Concerning hazard scenarios and consequently SHA, an important feature to be estimated is the Maximum Credible Earthquake (MCE).
Terminology & Glossary
Seismic fault is defined as an active fault if its activation has been confirmed by a strong earthquake during the instrumental or historical period, by an observed surface seismic rupture or by a palaeoseismological investigation.
It should be mentioned that the above definition does not exclude the existence of seismic faults identified by seismological, geophysical, geodetic or other instrumental observations.
A fault is characterized as Active when it documents displacement at least once during the Upper Pleistocene (in the last 126,000 years or so) and can therefore be the source of a future earthquake.
A fault is characterized as active when:
- it has produced a surface rupture associated with a historical or modern earthquake
- it has yielded soil ruptures dated during the Upper Pleistocene-Holocene period, as has been determined by excavating palaeoseismological trenches perpendicular to its trace
- it displaces or affects (e.g. folds) Upper Pleistocene-Holocene geological formations
- free faces with sclickenlines observed along the fault’s length have not been eroded at places
- characteristic escarpments and tectonic scarps can be recognized along its length
- debris or talus cones develop at the base of the fault scarp
- morphotectonic structures (e.g. triangular facets, etc.) are shown along its length
- it cuts or displaces river or stream beds in a systematic way
- it demonstrates aseismic slip (proven by geodetic measurements or other indications)
- it is associated with seismic epicentres of the instrumental period or with the alignment of microearthquakes
- it has a structural relationship with another known active fault (it is subparallel, it branches, it has en echelon geometry, etc.)
- it is associated with active volcanism or hot springs
- the stress field of its last activation is roughly the same as the one given by the focal mechanisms in the same area.
A fault is characterized as Potentially Active when it documents displacement at least once during the Quaternary (in the last 2.600.000 years).
The Potentially Active faults:
- displace or affect (e.g. folds) quaternary geological formations but they have not been reactivated during the last 126.000 years
- there is no available geological data indicating their direct relation to strong earthquakes
- they show a small degree of correlation with the distribution of major earthquake epicenters of the instrumental period.
- geomorphological features (eg fault surfaces) along the fault traces are significantly eroded
- they have been identified on the basis of geophysical surveys in areas covered by recent deposits
- their direction is compatible with the active tectonic stresses prevailing in the area.
Non active faults (Inactive or Faults of Undetermined activity) are those for which there are no geological or other (seismological, historical, paleoseismological, geophysical) indications for their activation at least during the Quaternary period (last 2.600.000 years).