Guam Hazard Mitigation Plan - Western States Seismic Policy Council

SECTIONFIVERisk AssessmentAdditionally, similar to the findings in earlier versions of the Guam HMP, Dededo has the mostand highest-valued exposed GBS structures, with 7,339 structures (74.2 percent), worth $117.1million. Yigo has the second-highest number of exposed structures with the second-highest value,with 4,905 structures (99.9 percent) worth $450.0 million. Mangilao has the third highest value ofexposed structures, with 1,502 structures (47.4 percent) worth $222.5 million.Slope Failure: LandslideSimilar to earlier versions of the Guam HMP, 26.5 percent of the landmass on Guam has a veryhigh or high susceptibility to landslides (see Tables 5-20 and 5-21. Likewise, in 2008, 11,574people (6.6 percent) on the island were exposed to this hazard while in 2011, 11,893 (6.6 percent)are exposed to this hazard. The number of exposed 2011 EFMUTS is 31 Essential Facilities worth$17.3 million, 53 Major Utilities (worth $132.6 million), and 23 Transportation Systems (worth$5.1 million). Of the GBS, 1,730 structures (worth $165.8 million) are exposed.In terms of village-level population were found to be exposed to very high and high landslidehazard, as shown in Tables F-21 to F-24 (Appendix F [Vulnerability and Potential Loss Resultsby Village]), Inarajan and Merizo have the largest two vulnerable populations with 2,593 (72.8percent of the village population) and 2,413 (95.6 percent of the village population) exposedpeople, respectively.Exposure of the EFMUTS is concentrated in Merizo and Umatac, with 9 Essential Facilities inMerizo that are worth $3.9 million and 9 Essential Facilities in Umatac that are worth $3.1million. Likewise, 13 Major Utilities are located in the exposed area of Merizo (worth $11.5million) and 19 Major Utilities are located in the exposed area of Umatac (worth $46.1 million).Similar to the analyses in earlier versions of the Guam HMP, 100 percent of GBS structures (264structures) in Umatac are exposed to a very high or high landslide hazard (worth $17.3 million).However, Merizo has the greatest number of exposed GBS, with 613 structures (worth $50.5million).TsunamiA relatively low proportion of Guam’s population (8,883 people or 4.9 percent) is exposed totsunami, as shown in Tables 5-20 and 5-21. In 2008, approximately 7,330 people or 4.2 percentof the total population were found to be exposed to tsunami inundation. The number of exposedEFMUTS is 93 Essential Facilities (26.2 percent, with a value of $173.3 million), 46 MajorUtilities (12.7 percent, with a value of $282.4 million), and 52 Transportation Systems (39.1percent, with a value of $88.5 million). Of the GBS, 3,270 structures (8.2 percent), worth $555.8million are exposed.As noted previously, the lands adjacent to Apra Harbor are likely to be almost completelyinundated by a tsunami with a 16-foot run-up. This area includes several port and utility facilities.If permanent damage from a tsunami occurs to port facilities, the movement of goods on and offGuam would also be affected. A value for the normal and daily functions of these facilities hasnot been assessed for this analysis, but disruption to these functions would be a secondarypotential effect of this hazard event. A substantial secondary hazard of a tsunami can occur due toits impact on the functioning of certain utilities, particularly water treatment plants and potablewater distribution facilities, which in turn may expose large portions of the population to hazardssuch as drought and disease.5-69