Seismic risk assessment for oil and gas pipelines - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 686

Ground movements due to landslides
Signifi cant ground movements could occur due to landslides triggered
(without soil liquefaction) during earthquake shaking. This would become
a concern in areas of steep terrain and saturated slopes with soft soils, or
in areas where there is ongoing relatively slow moving landslide activity.
25.4.3 Volcanichazards
In terms of volcanic hazards, exposure to the hazard is generally related to
the type and nature of the volcano (e.g. impact of volcanic hazards tends
to be greater for andesitic volcanoes than for basaltic volcanoes) and to the
proximity to the volcano edifi ce, as well as to whether it is on a drainage
that emanates from the edifi ce. The potential volcanic hazards that may be
present along the pipeline routes include tephra (ash) fall, pyroclastic fl ow/
surge, blast surge, lava fl ow, mud fl ow, debris fl ow, ground deformations, and
volcanic earthquakes.
25.5 Determininghazardlikelihood
To be technically complete, seismic risk assessment should consider the
integrated likelihood of exceeding a specifi c acceptance criterion from the
total range of earthquake hazards. Such an approach accounts for the cumu-
lative likelihood associated with a large number of frequently occurring
earthquakes with a small probability of producing a vulnerability. In prac-
tice, the process is often simplifi ed by assuming a single earthquake fre-
quency that is acceptable for a particular level of vulnerability. For example,
if an acceptable level of risk an annual probability that the pipeline will lose
pressure integrity less than 0.5%, it is common practice to only address
earthquake hazards that have an annual chance of being exceeded of 0.5%.
This simplifi cation allows the results of the risk assessment to be viewed in
the context of other components such as buildings, dams, and bridges that
are typically designed and evaluated for a single level of earthquake hazard.
The severity of earthquake ground shaking is commonly defi ned using
probabilistic methods that include consideration of the variability in the
size, recurrence interval, and location of earthquakes within a region. The
other induced seismic hazards are typically defi ned based upon determin-
istic or empirical methods that may rely upon the probabilistic ground
shaking estimate as an input parameter. It needs to be recognized that there
is considerable uncertainty in any seismic hazard defi nition.
The range of uncertainty can be gauged by examining the typical uncer-
tainty in estimating ground shaking. Considering only the uncertainty in
attenuation and adopting the range of standard deviations in ground motion