| OpendTect User Documentation version 4.2 |
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Name
Event -- Attribute that quantifies an event's shape or distance relative to a next event
Description
It is a very useful tool to quantify the quality of a horizon in seismic data which can also be applied to any inline, crossline, or timeslice element. A sketch of several event attributes has been shown here first to show the basics architecture of the Event attributes.
In the single event mode, the algorithm searches for an extremum and quantifies the shape around the event in terms of either Peakedness, Steepness, or Asymmetry.
- Peakedness: It is the ratio between the Extremum value and distance between next and previous zero crossings (ZC).
- Steepness: It is the slope of tangent to the seismic trace at a zero crossing.
- Asymmetry: Defines the asymmetry of event. Mathematically it can be written as:
(L-R)/(L+R) where L is the distance between previous ZC and extremum and R is distance between next ZC and extremum.
In the multiple event mode, the event type needs to be specified. For the event types Extremum, Maximum, Minimum, Zero Crossing, Negative to Positive Zero Crossing and Positive to Negative Zero Crossing, the output is the distance between the chosen event and either the next or previous like event.
Single event mode
For the event types Maximum within the gate and Minimum within the gate, a time-gate in milliseconds needs to be specified. The algorithm computes the distance, within the specified time-gate, from the current point, e.g. on a horizon, to the nearest maximum or minimum.
Multiple event mode
The Event attribute is, for example, useful when doing a quality check for a horizon. It can also helpful for users to find the distance between two events and using it as an estimate of relative thickness changes between two events. The adaptive use of Volume Statistics along with Event attribute can also bring relative changes to derive meaningful geological aspects.