ISO 19901-2:2022 石油および天然ガス産業—海洋構造物の特定の要件— Part 2: 耐震設計手順および基準 | ページ 6

3.1

abnormal level earthquake

ALE

intense earthquake of abnormal severity with a very low probability of occurring during the life of the structure

Note 1 to entry: The ALE event is comparable to the abnormal event in the design of fixed structures that are described in ISO 19902 and ISO 19903.

3.2

attenuation

decay of seismic waves as they travel from the earthquake source to the site under consideration

3.3

deaggregation

separation of seismic hazard contribution from different faults and seismic source zones

3.4

escape and evacuation system

system provided on the offshore structure to facilitate escape and evacuation in an emergency

3.5

extreme level earthquake

ELE

strong earthquake with a reasonable probability of occurring during the life of the structure

Note 1 to entry: The ELE event is comparable to the extreme environmental event in the design of fixed structures that are described in ISO 19902 and ISO 19903.

3.6

fault movement

movement occurring on a fault during an earthquake

3.7

ground motion

accelerations, velocities or displacements of the ground produced by seismic waves radiating away from earthquake sources

Note 1 to entry: A fixed offshore structure is founded in or on the seabed (3.17) and consequently only seabed motions are of significance. The expression"ground motions" is used rather than seabed motions for consistency of terminology with seismic design for onshore structures.

Note 2 to entry: Ground motions can be at a specific depth or over a specific region within the seabed.

3.8

liquefaction

fluidity of soil due to the increase in pore pressures caused by earthquake action under undrained conditions

3.9

modal combination

combination of response values associated with each dynamic mode of a structure

3.10

mud volcano

diapiric intrusion of plastic clay causing high pressure gas-water seepages which carry mud, fragments of rock (and occasionally oil) to the surface

Note 1 to entry: The surface expression of a mud volcano is a cone of mud with continuous or intermittent gas escaping through the mud.

3.11

probabilistic seismic hazard analysis

PSHA

framework permitting the identification, quantification and rational combination of uncertainties in earthquakes' intensity, location, rate of recurrence and variations in ground motion (3.7) characteristics

3.12

probability of exceedance

probability that a variable (or that an event) exceeds a specified reference level given exposure time

3.13

response spectrum

function representing the peak elastic response for single degree of freedom oscillators with a specific damping ratios in terms of absolute acceleration, pseudo velocity, or relative displacement values against natural frequency or period of the oscillators

3.14

safety system

systems provided on the offshore structure to detect, control and mitigate hazardous situations

3.15

sea floor

interface between the sea and the seabed (3.17)

3.16

seabed slide

failure of seabed (3.17) slopes

3.17

seabed

soil material below the sea in which a structure is founded

3.18

seismic risk category

SRC

category defined from the exposure level and the expected intensity of seismic motions

3.19

seismic hazard curve

curve showing the annual probability of exceedance (3.12) against a measure of seismic intensity

Note 1 to entry: The seismic intensity measures can include parameters such as peak ground acceleration, spectral acceleration (3.22) , or spectral velocity (3.23) .

3.20

seismic reserve capacity factor

factor indicating the structure’s ability to sustain ground motions due to earthquakes beyond the level of the extreme level earthquake (3.5)

Note 1 to entry: The seismic reserve capacity factor is a structure specific property that is used to determine the extreme level earthquake acceleration from the abnormal level earthquake (3.1) acceleration.

3.21

site response analysis

wave propagation analysis permitting the evaluation of the effect of local geological and soil conditions on the ground motions (3.7) as they propagate up from depth to the surface at the site

3.22

spectral acceleration

maximum absolute acceleration response of a single degree of freedom oscillator subjected to ground motions (3.7) due to an earthquake

3.23

spectral velocity

maximum pseudo velocity response of a single degree of freedom oscillator subjected to ground motions (3.7) due to an earthquake

Note 1 to entry: The pseudo velocity spectrum is computed by factoring the displacement or acceleration spectra by the oscillator’s circular frequency or the inverse of its frequency, respectively. The pseudo spectrum is either relative or absolute, depending on the type of response spectra that is factored.

3.24

spectral displacement

maximum relative displacement response of a single degree of freedom oscillator subjected to ground motions (3.7) due to an earthquake

3.25

static pushover analysis

application and incremental increase of a global static pattern of actions on a structure, including equivalent dynamic inertial actions, until a global failure mechanism occurs

3.26

tsunami

long period sea waves caused by rapid vertical movements of the sea floor (3.15)

Note 1 to entry: The vertical movement of the sea floor is often associated with fault rupture during earthquakes or with seabed slides (3.16) .