Glossary
- Earthquake catalogue
List of earthquakes and their features (e.g., magnitude, hypocenter, time, etc.)
- Instrumental catalogue
Earthquake catalogue that only contains events recorded by seismographs.
- Historical catalogue
Earthquake catalogue that contains events occurred before the instrumental recording era, assembled from non-instrumental sources such as historical documents, and archives.
- Declustering
A data-processing technique used to identify and cull dependent or clustered events (e.g., aftershocks).
- Probabilistic Seismic Hazard Analysis (PSHA)
A methodology to compute seismic hazard by taking into account the potential contributions coming from all the sources of engineering importance for a specified site.
- Mean (average or arithmetic mean)
The average value of all data in a sample, obtained by summing all observations and dividing by the number of observations.
- Median (discrete sample)
The middle value of a dataset when the observations are ordered; if there is an even number of values, it is the average of the two middle values.
- Variance
A measure of a dataset’s dispersion, calculated as the average of the squared deviations from the mean.
- Standard deviation
The square root of the variance, representing the typical amount by which values in the dataset differ from the mean.
- Coefficient of variation (CV)
A normalized measure of variability defined as the ratio of the standard deviation to the mean.
- Magnitude completeness (Mc)
The minimum magnitude above which earthquakes in a catalogue are assumed to be reliably detected and recorded.
- Seismicity rate
Number of events per unit of time (if not better specified), the definition of a seismicity rate generally presumes a time independent.
- Mainshock
The largest earthquake in a sequence of related seismic events, typically followed by aftershocks and sometimes preceded by foreshocks.
- Aftershock
An earthquake that occurs after a larger mainshock, typically near the rupture area, as the crust adjusts to stress changes caused by the main event.
- Foreshock
A smaller earthquake that occurs before a larger mainshock in the same region and is identified as a foreshock only after the mainshock has occurred.
- Swarm-type seismicity
A sequence of earthquakes occurring closely in space and time without a single dominant mainshock.
- Magnitude–Frequency Distribution (MFD)
A statistical relationship describing how often earthquakes of different magnitudes occur within a region and time period, commonly used to characterize seismicity and estimate earthquake recurrence rates.
- Earthquake recurrence rate
The average frequency at which earthquakes of a given magnitude or greater are expected to occur in a specified region over a certain time period.
- Magnitude homogenization
The process of converting different earthquake magnitude types (e.g., Mw, ML, Mb, Ms) into a consistent magnitude scale.
- Moment magnitude (M w)
magnitude scale based on the seismic moment of an earthquake, representing the total energy released during fault rupture; it is the most widely used and physically consistent magnitude scale.
- Body-wave magnitude (m b)
A magnitude scale calculated from the amplitude of short-period body waves (primarily P-waves) recorded by seismographs, commonly used for distant and moderate-sized earthquakes.
- Surface-wave magnitude (M s)
A magnitude scale determined from the amplitude of long-period surface waves, typically Rayleigh waves, recorded by seismographs for shallow earthquakes.
- Stochastic Event Set (SES)
A simulated earthquake events generated using probabilistic models to represent the possible occurrence, magnitude, location, and frequency of earthquakes over a specified time period.
- Ground-Motion Field (GMF)
An object describing the geographic distribution around a rupture of a ground motion intensity measure.
- Logic Tree
Data structure used to systematically describe uncertainties on parameters and models used in a PSHA study.