Attenuation Relationship
This is a type of Intensity Measure Relationship that assumes the IMLs (or logarithm thereof) exhibit a Gaussian distribution. Therefore, in addition to providing the probability that an IMT will exceed a specified IML for a given Site and Earthquake Rupture, an Attenuation Relationship can also provide the mean and/or standard deviation of the Gaussian distribution.
The mean and standard deviation are computed from a variety of independent Parameters, categorized as follows:
In addition to giving the probability that an IML will be exceeded, an Attenuation Relationship can also provide the IML that has a specified probability of exceedance.Earthquake-Rupture Parameters (obtained or computed from the given Earthquake Rupture) such as:
- Magnitude
- Average Rake
- Average Dip
- Rupture Top Depth
Site Parameters (from the given Site) such as:
Propagation-Effect Parameters (computed from the given Site and Earthquake Rupture) such as:
- Distance Parameter
- Hanging-Wall Parameter
- Directivity Parameter
Other Parameters such as:
Furthermore, an Attenuation Relationship can declare exactly which Parameters the mean, standard deviation, and exceedance probability depend upon (e.g., to designate the case where the standard deviation, for example, depends on relatively few parameters). This allows an application to hide any irrelevant parameters from a user without having to know any details of the model (i.e., no hard coding of options).
Currently implemented Attenuation Relationships include: