Glossary

Epicentre
The epicentre denotes the surface projection of the location of the earthquake source (hypocentre) or for larger earthquakes the point on the earthquake source area from which the rupture originates.

Hazard H
Probability of the occurrence of a (natural) phenomenon with damaging potential in a defined area and a defined time unit.

Hazard curve
Graphical illustration as a probabilistic assessment of the earthquake hazard for a point, showing the connection between the annual probability of occurrence or exceedence and a selected parameter of the ground motion. Peak ground accelerations, macroseismic intensity, spectral accelerations, etc. are used as ground motion parameters.

Hypocentre
(cf. epicentre)

Intensity I
The macroseismic intensity I represents a classification of the strength of ground motion based on observed effects in a limited area such as a town. The effects of the ground motion serve as basis for assignment of intensity degrees. Intensities are a robust measure of strength classification, subdivided in 12 intensity degrees:

   I Not felt.
   II Scarcely felt.
   III Weak.
   IV Largely observed.
   V Strong.
   VI Slightly damaging.
   VII Damaging.
   VIII Heavily damaging.
   IX Destructive.
   X Very destructive.
   XI Devastating.
   XII Completely devastating.

A detailed description of the intensity definitions according to the most recent scale development in form of the European Macroseismic Scale EMS-98 (Grünthal, 1998), which has been introduced in an mandatory way for Europe and moreover is in use on all continents, is provided by the short form of EMS-98.

Magnitude
The magnitude M, introduced by Charles Richter in 1935, is an instrumental measure to determine the strength of earthquakes. The magnitude is usually determined from the logarithm of the maximum amplitude recorded by seismographs under consideration of the distance to the earthquake source. So local magnitude 4 correlates with an earthquake, which was recorded in a distance of 100 km with a maximal 2800-fold amplifying Wood-Anderson-Seismograph and giving a maximum amplitude on the seismogram of 1 cm.
Furthermore, distiction is made between body-wave, surface-wave, moment, and other magnitudes.

Moment magnitude M_w
is a physically motivated and with the other magnitude types calibrated measure of strength founded on a mechanical model of an abruptly activated fault area as a response to stress load. The largest observed moment magnitude up to now is 9.5 at the Chile earthquake in 1960. Conversion formulae exist between magnitude types and intensity in order to transform the different strength measures to one and another and also to classify pre-instrumental historical earthquakes in form of magnitudes.

Paleoseismology
Method to search for signs of earlier earthquakes in geological sediments, including the assessment of their magnitudes and determination of the age of the geological movements. P. is normally limited to geological terrains of continuous sedimentation in the past thousands of years. It is useful for the extension in time of reports of earthquakes until the most recent geological past.

Risk R
The term risk encompasses the probability and the amount of harmful consequences or expected losses resulting from interactions between natural or human induced hazards and vulnerable conditions. The term risk is derived from insurance industry: there can be no risk if there are no values exposed to natural hazard. The quantification of the risk due to different perils R_i can be carried out for selected elements of risk RE_j or for one or more loss indicators. The risk R_i is described with the following formula


where SR is the specific risk and C the value of elements at risk (e.g. economical costs, value of property, number of persons at risk, level of economic activity etc.)

The specific risk SR is the expected degree of loss of an i^th structure due to a specific natural phenomenon j (e.g. the specific risk due to earthquakes) which is connected with the hazard H_i expressed as the probability of occurrence of a certain ground motion. It is the product of hazard and vulnerability:


Seismic source region
An area or line where, in connection with probabilistic assessment of earthquake hazard, a uniform distribution of the seismicity ca be adopted. The delineation of seismic source regions results from the observed seismicity, the regional tectonics, the tectonic regime of crustal deformations and the observed crustal stress field, and from zones of weakness in the earth's crust.
A line source follows the geometry of a seismically active fault.
The depth distribution of the earthquake activity in the source regions is described by distribution functions.

Tectonics
The science of the constitution, as well as the movements and deformation, of the earth's crust and solid parts of the earth mantle. The tectonics cover global, regional, and local aspects. The neotectonics give attention to the tectonics of the recent geologic time, i.e., depending on the area of investigation, of the last 15 to 35 million years.

Uncertainty, aleatory
Denotes the uncertainty inherently connected to stochastic phenomena or processes. In principal, this type of uncertainty cannot be reduced by additional data or information.

Uncertainty, epistemic
Denotes the uncertainty due to incomplete knowledge of models or parameters. This type of uncertainty can be reduced by additional data or improved models.

The vulnerability V describes the degree of loss (0<V<1) resulting from a natural phenomenon; 0: no damage, 1: total damage or total loss.

The total of elements at risk within a specified sector, e.g., number of people, value of property (personal and corporate), level of economic activity (including official services) are the risk elements RE.

The cumulative risk CR is the expected summary loss as a result of different potential natural disasters, e.g., earthquakes, storms, floods, vulcanic eruptions, landslides, droughts etc.