How do I locate the contents of Chapter 17 Annualized Losses?
The HAZUS MR3 Technical Manual is missing Chapter 17 Annualized Losses. It has been included with this FAQ and will be made permanently part of the Technical Manual with HAZUS-MH MR4.
Chapter 17 Annualized Losses
The U.S. Geological Survey (USGS) provided the probabilistic seismic hazard data for the entire United States. A three-step process was used to convert the data into a HAZUS compatible format.
Step 1: Compute the PGA, SA @ 0.3, and SA @ 1.0 at each grid point for the eight return periods.
The USGS provided the hazard data as a set of 18 (or 20) intensity-probability pairs for each of the approximately 150,000 grid points used to cover the United States. For each grid point, a linear interpolation of the data was used to calculate the ground motion values corresponding to each of the eight return periods used in this study (100, 250, 500, 750, 1000, 1500, 2000, and 2500 years).
Table 17-1 below shows an example of USGS hazard data for an individual grid point.
Table 17-1. Example of the USGS Hazard Data
* AFE = Annual Frequency of Exceedence = approximately 1 / Return Period
Step 2: Compute the PGA, SA @ 0.3 and SA @ 1.0 at each census tract centroid for the eight return periods.
For estimating losses to the building inventory, HAZUS uses the ground shaking values calculated at the centroid of the census tract. To incorporate the USGS data into HAZUS, the ground shaking values at the centroid were calculated from the grid-based data developed in Step 1.
Two rules were used to calculate the census-tract-based ground shaking values:
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For census tracts that contain one or more grid points, the average values of the points are assigned to the census tract.
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For census tracts that do not contain any grid points, the average value of the four nearest grid points is assigned to the census tract.
Using this method, census-tract-based ground motion maps are generated for all eight return periods.
Step 3: Modifying the PGA, SA @ 0.3 and SA @ 1.0 at each census tract centroid to represent site-soil conditions for a NEHRP soil class type D.
The USGS data were based on a National Earthquake Hazard Reduction Program (NEHRP) soil class B/C (medium rock / very dense soil). For this study, NEHRP soil class type D (stiff soil) was assumed for all analyses. To account for the difference in soil class types, the data developed in Step 2 were modified. The procedure described in Chapter 4 of the HAZUS Technical Manual was used for the modification of the ground-shaking values.
Average Annualized Earthquake Loss Computation
After the hazard data is processed, an internal analysis module in HAZUS is used to transform the losses from all eight scenarios into an Annualized Earthquake Loss (AEL). Figure 17-1 illustrates schematically a HAZUS example of eight loss-numbers plotted against the exceedence probabilities for the ground motions used to calculate these losses.
Figure 17-1. Probabilistic Loss Curve
HAZUS computes the AEL by estimating the shaded area under the loss-probability curve shown in Figure 17-1. This area represents an approximation to the AEL and is equivalent to taking the summation of the losses multiplied by their annual probability of occurrence.
The choice for the number of return periods was important for evaluating average annual losses, so that a representative curve could be connected through the points and the area under the probabilistic loss curve be a good approximation. The constraint on the upper bound of the number was computational efficiency versus improved marginal accuracy. To determine the appropriate number of return periods, a sensitivity study was completed that compared the stability of the AEL results to the number of return periods for 10 metropolitan regions using 5, 8, 12, 15 and 20 return periods was negligible.
Last Modified: Wednesday, 20-Feb-2008 11:18:05 EST