Seismic risk assessment of water supply systems - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 668

system risk curve with 24-hour running tanks plots to the right of the fi rst
curve, indicating much lower SSI values for the same annual exceedance
frequency. The linear portion of the curve, with lower SSI values, is app-
roximately parallel to the system risk curve without 24-hour period of
running tanks. The difference between the curve without 24-hour period of
running tanks and its parallel portion in the curve with 24-hour period
of running tanks signifi es the effects of running tanks. After 24-hour period
of running tanks, the system deteriorates rapidly and the SSI decreases
signifi cantly. The system risk curve with a 24-hour period of running tanks
provides an estimate of LADWP system performance after earthquakes
that refl ects the deteriorating capacity of local tanks and reservoirs, where
water levels drop because of pipeline damage after earthquakes.
24.7 Economicandsocialconsequences
Economists and social scientists have contributed to a growing body of
research and applications associated with the economic and social conse-
quences of lifeline damage and loss of functionality. It is well recognized
that lifeline disruption has a direct effect on business losses and social con-
sequences. Consider, for example, water supply disruption, which adversely
affects fi re protection, the loss of which may trigger serious economic and
social consequences. One catastrophic example is the 1906 San Francisco
earthquake in which most of the City of San Francisco was burned down
by the fi res following the earthquake because of the water supply disruption
and loss of fi re-fi ghting capability (Gilbert et al. 1907).
The direct regional economic consequences of lifeline loss often set off
a chain reaction of further production cutbacks among successive rounds
of customers and suppliers that spread through the entire regional economy,
which is described as 'ripple effect' or 'multiplier effect'. Some well-
established analysis methodologies in economics, such as input-output
(I-O) analysis and computable general equilibrium (CGE) analysis, have
been successfully utilized to assess the indirect economic effects of lifeline
disruption.
The social and economic consequence evaluations have been performed
for the LADWP water supply system. CGE models have been developed
to assess the economic impacts caused by earthquake-induced losses of
water supply (e.g., Rose and Guha, 2003; Rose and Liao, 2003, 2005; Rose
et al. 2011). The community impacts of the seismic-induced lifeline loss have
also been evaluated by other researchers (e.g., Chang and Miles 2003;
Chang and Chamberlin 2004; Chang et al. 2008). Davidson and Cagnan
(2004), Cagnan (2005), and Brink et al. (2010) modeled lifeline system res-
torations after earthquakes and simulated system repair and recovery