Glossary
Browse the IADC Lexicon alphabetically or by category. Get comprehensive definitions of drilling industry terms.
Sea Floor Slide
Definition(s)
Sea Floor Slide
Failure of sea floor slopes. Source:API RP 2EQ, Seismic Design Procedures and Criteria for Offshore Structures, First Edition, November 2014. Global StandardsSafety Systems
Definition(s)
Safety Systems
Systems provided on a platform to detect, control, and mitigate hazardous situations. NOTE Safety systems include gas detection, emergency shutdown, fire protection, and their control systems. Source:API RP 2EQ, Seismic Design Procedures and Criteria for Offshore Structures, First Edition, November 2014. Global StandardsSafety Systems
Systems, including required utilities, which are provided to prevent, detect/ warn of an accidental event/abnormal conditions and/or mitigate its effects Interpretation: The following should be considered as safety systems: — ESD, including blowdown where relevant — PSD — fire and gas detection — PA/GA — fire-fighting systems — BOP incl. control system — safety systems for essential or important services — safety systems are normally considered as “on-demand” functions. Source: Rules for Classification – Offshore units, DNVGL-OU-0101, Offshore drilling and support units, DNV GL, July 2015. Global StandardsResponse Spectrum
Definition(s)
Response Spectrum
Plot representing structural response in terms of absolute acceleration, pseudo velocity, or relative displacement values against a structural natural frequency or period. Source:API RP 2EQ, Seismic Design Procedures and Criteria for Offshore Structures, First Edition, November 2014. Global StandardsProbability of Exceedance
Definition(s)
Probability of Exceedance
Probability that a variable (or that an event) exceeds a specified reference level given exposure time. EXAMPLE Examples of probabilities of exceedance during a given exposure time are the annual probability of exceedance of a specified magnitude of ground acceleration, ground velocity, or ground displacement. Source:API RP 2EQ, Seismic Design Procedures and Criteria for Offshore Structures, First Edition, November 2014. Global StandardsProbabilistic Seismic Hazard Analysis
Definition(s)
Probabilistic Seismic Hazard Analysis
Framework permitting the identification, quantification, and rational combination of uncertainties in earthquakes' intensity, location, rate of recurrence, and variations in ground motion characteristics. Source:API RP 2EQ, Seismic Design Procedures and Criteria for Offshore Structures, First Edition, November 2014. Global StandardsPSHA
Definition(s)
PSHA
Probabilistic seismic hazard analysis. Source:API RP 2EQ, Seismic Design Procedures and Criteria for Offshore Structures, First Edition, November 2014. Global StandardsPSHA
Framework permitting the identification, quantification, and rational combination of uncertainties in earthquakes' intensity, location, rate of recurrence, and variations in ground motion characteristics. Source:API RP 2EQ, Seismic Design Procedures and Criteria for Offshore Structures, First Edition, November 2014. Global StandardsMud Volcanoes
Definition(s)
Mud Volcanoes
Diapiric intrusion of plastic clay causing high pressure gas-water seepages which carry mud, fragments of rock (and occasionally oil) to the surface. NOTE The surface expression of a mud volcano is a cone of mud with continuous or intermittent gas escaping through the mud. Source:API RP 2EQ, Seismic Design Procedures and Criteria for Offshore Structures, First Edition, November 2014. Global StandardsModal Combination
Definition(s)
Modal Combination
Combination of response values associated with each dynamic mode of a structure. Source:API RP 2EQ, Seismic Design Procedures and Criteria for Offshore Structures, First Edition, November 2014. Global StandardsLiquefaction
Definition(s)
Liquefaction
Fluidity of cohesionless soil due to the increase in pore pressures caused by earthquake action under undrained conditions. Source:API RP 2EQ, Seismic Design Procedures and Criteria for Offshore Structures, First Edition, November 2014. Global StandardsGround Motions
Definition(s)
Ground Motions
Accelerations, velocities, or displacements of the ground produced by seismic waves radiating away from earthquake sources. NOTE A fixed offshore structure is founded in or on the seabed and consequently only seabed motions are of significance. The term ground motions is used rather than seabed motions for consistency of terminology with seismic design for onshore structures. Source:API RP 2EQ, Seismic Design Procedures and Criteria for Offshore Structures, First Edition, November 2014. Global StandardsFault Movement
Definition(s)
Fault Movement
Movement occurring on a fault during an earthquake. Source:API RP 2EQ, Seismic Design Procedures and Criteria for Offshore Structures, First Edition, November 2014. Global StandardsExtreme Level Earthquake
Definition(s)
Extreme Level Earthquake
Earthquake with a severity which the structure should sustain without major damage. NOTE The ELE event is comparable to the extreme environmental event in the design of fixed structures which is described in API 2A-WSD, 22nd Edition and ISO 19903, When exposed to an ELE, a structure is supposed to retain its full capacity for all subsequent conditions. Source:API RP 2EQ, Seismic Design Procedures and Criteria for Offshore Structures, First Edition, November 2014. Global StandardsEscape and Evacuation Systems
Definition(s)
Escape and Evacuation Systems
Systems provided on a platform to facilitate escape and evacuation in an emergency. NOTE Escape and evacuation systems include passageways, chutes, ladders, life rafts, and helidecks. Source:API RP 2EQ, Seismic Design Procedures and Criteria for Offshore Structures, First Edition, November 2014. Global StandardsDirectional Combination
Definition(s)
Directional Combination
Combination of response values due to each of the three orthogonal components of an earthquake motion. Source:API RP 2EQ, Seismic Design Procedures and Criteria for Offshore Structures, First Edition, November 2014. Global StandardsAttenuation
Definition(s)
Attenuation
Decay of seismic waves as they travel from a source to the site under consideration. Source:API RP 2EQ, Seismic Design Procedures and Criteria for Offshore Structures, First Edition, November 2014. Global StandardsAbnormal Level Earthquake
Definition(s)
Abnormal Level Earthquake
Intense earthquake of abnormal severity under the action of which the structure should not suffer complete loss of integrity.- NOTE: The ALE event is comparable to the abnormal event in the design of fixed structures which are described in API 2A-WSD and ISO 19903. When exposed to the ALE, a manned structure is supposed to maintain structural and/or floatation integrity for a sufficient period of time to enable evacuation to take place.