` and :term:`S waves~~`, which shake
the ground in different ways, are examples.
body wave magnitude
see :term:`magnitude, body-wave (mb)`
calibration
The process of determining the response function (distortion of the input signal) and
sensitivity of an instrument or its derived component.
CAV
cumulated absolute velocity
CI
Characteristic Intensity
channel code
Description of characteristics of data related to the recording sensor and
data logger as well as instrument responses, sampling frequencies, etc.
The standard codes are defined in the
`SEED manual ~~

~~` and :term:`S waves~~~~`.
EDA
Effective Design Acceleration
EIDA
European Integrated Data Archive: http://www.orfeus-eu.org/data/eida/
epicenter
Vertical projection of the hypocenter to the surface.
event
a) General term used for a localized disturbance (earthquake, explosion, etc.) which generates seismic waves.
b) QuakeML object. The event is the parent object of several :term:`origins ~~~~` and/or to measure amplitude
ratios between different phase types. Further inferences can be made from these data concerning the
principal axes of stress in the region of the earthquake. The principal stress axes determined by this
method are the compressional axis (also called the P-axis, i.e. the axis of greatest compression, or s1),
the tensional axis (also known as the T-axis, i.e., the axis of least compression, or s3), and the
intermediate axis (s2).
filter(ing)
A filter attenuates certain frequencies of a (seismic) signal and amplifies others. The process of
filtering can be accomplished electronically while recording or numerically in a computer. Filtering also
occurs naturally as seismic energy passes through the Earth.
The available and integrated filters in SeisComP are documented in :ref:`filter-grammar`.
first motion
The first noticeable displacement in a seismogram caused by the arrival of a P wave at the seismometer.
Upward motion of the ground at the seismometer indicates a dilatation at the source, downward motion
indicates a compression. Due to the presence of seismic noise the proper polarity of the first motion
may be difficult to recognize.
F-K
F-K refers to a 2-D :term:`Fourier analysis` where the base functions
are defined, e.g. by ranges of :term:`frequency` and :term:`wave number`.
F-K analysis is applied for signal detection by transforming time series
recorded at several sensors, e.g. seismic or infrasound :term:`array`
stations to the time and space domain.
The equivalent to F-K analysis in the time domain is :term:`beam packing`.
focal mechanism
see :term:`fault-plane solution`
foreshocks
Earthquakes that occur in a series of earthquakes before the largest earthquake, termed the mainshock.
Foreshocks may precede the mainshock by seconds to weeks and usually originate at or near the focus
of the larger earthquake. Not all mainshocks have foreshocks.
Fourier spectrum
The relative amplitudes (and phase angles) at different frequencies that are derived from a time series
by Fourier analysis.
Fourier analysis
The mathematical operation that resolves a time series (for example, a recording of ground motion)
into a series of numbers that characterize the relative amplitude and phase components of the signal
as a function of frequency.
frequency
Number of cycles of a repeating signal per unit time, typically per second.
frequency domain
The transformation of a seismic signal from the time domain (as a seismogram) to the frequency
domain is conducted by a :term:`Fourier analysis`. The signal is represented in the frequency domain by
the amplitude and phase components as a function of frequency (see spectrum). The representations of
a seismic signal in the time and in the frequency domain are equivalent in a mathematical sense.
For some procedures of data analysis the time-domain representation of a seismic record is more
suitable while for others the frequency-domain approach is more appropriate and efficient.
gempa GmbH
`gempa GmbH ~~~~` drops from
about 7.3 km/s to 0 km/s. The CMB reflects the change from the solid mantle material to the
fluid outer core.
GUI
Graphical use interface, e.g. :ref:`scolv`.
hypocenter
Coordinates of an earthquake point source. Hypocenters based on :term:`P~~

~~` and :term:`S wave`
first arrivals point to the place where the rupture process starts. For large earthquakes the
source location determined by :term:`P wave` first arrivals can differ significantly from the location of
maximum energy release.
Ia
Arias Intensity
infrasound array
An :term:`array` of barometers measuring infrasound signals.
intensity
A measure of the effects of an earthquake at a particular place at the Earth's surface on humans
and (or) structures. The intensity at a point depends not only upon the strength of the earthquake
(magnitude) but also upon the distance from the earthquake, the depth of the hypocenter and the
local geology at that point. Several scales exist, most of them giving the intensity in 12 degrees,
usually written as Roman numerals. Most frequently used are at present the European Macroseismic
Scale (EMS-98), and in the United States the Modified Mercalli scale and the Rossi-Forel scale.
There are many different intensity values for one earthquake, depending on how far you are away
from the epicenter; this is unlike the magnitude value, which is one number for each earthquake
as a measure of the amount of seismic wave energy released by it.
interplate/intraplate
Intraplate pertains to processes within the Earth's crustal plates. Interplate pertains to
processes between the plates.
interplate coupling
The qualitative ability of a subduction thrust fault to lock and accumulate stress. Strong
interplate coupling implies that the fault is locked and capable of accumulation stress whereas
weak coupling implies that the fault is unlocked or only capable of accumulating low stress.
A fault with weak interplate coupling could be aseismic or could slip by creep.
inventory
The inventory is the collection of all available meta data related to :term:`network`,
:term:`station`, :term:`location code`, station :term:`channel code`,
characteristics of sensors and data loggers, etc. More details are given in
the concepts section :ref:`concepts_inventory`.
latency
The time difference between the current time and the arrival time of the record (SeisComP).
The latency can be computed by :ref:`scqc`.
lithosphere
The outer solid part of the Earth, including crust and uppermost mantle. The lithosphere is
about 100 km thick, although its thickness is age-dependent (older lithosphere is thicker).
At some locations the lithosphere below the crust is brittle enough to produce earthquakes by
faulting, such as within a subducted oceanic plate.
location code
Description of particular sensor location associated to a station. The standard
location codes are defined in the `SEED manual ~~

~~` and :term:`S waves~~~~` on the direction and take-off
angle under which their seismic rays have left the seismic source. It is controlled
by the type of source mechanism, e.g., the orientation of the earthquake fault plane
and slip direction in space.
Rayleigh wave
A seismic surface wave causing a retrograde, elliptical motion of a particle at the free
surface, with no transverse motion. It is named after Lord Rayleigh (1842-1919), who
predicted its existence.
ray theory
Theoretical approach, which treats wave propagation as the propagation of seismic rays.
It is an approximation, which yields good results for short wave length (high-frequency
approximation) and allows easy calculations of travel times.
ray-tracing method
Computational method of calculating ground-shaking estimates that assumes that the
ground motion is composed of multiple arrivals of seismic rays and related energy
bundles (Gauss beams) that leave the source and are reflected or refracted at velocity
boundaries according to Snell's Law. The amplitudes of reflected and refracted waves
at each boundary are recalculated according to the Law of Conservation of Energy.
RecordStream
Interface to access data records from data processing modules.
:term:`SeisComP` applications access waveform data through the
`RecordStream ~~

~~` or :term:`S waves~~~~`, recorded at different
points as a function of distance
from the seismic source. Seismic velocities within the Earth can be computed
from the slopes of the resulting curves.
XXL event
An event based on :term:`XXL picks~~