Arden Valley: Prioritising Earthquake Risk Reduction
Arden Valley is a rapidly growing city of 520,000 people built across a fault-bounded valley. A shallow fault lies 12 km from the city centre and last ruptured 140 years ago. About 38% of buildings are unreinforced masonry, including two hospitals, 14 schools and a stadium used as an emergency shelter. The fastest-growing informal settlement, home to 70,000 people, sits on reclaimed land with a high water table and liquefaction risk. The main road to the airport and the only trauma hospital crosses a narrow bridge. The city's disaster plan assumes outside help within 72 hours, but a recent simulation found the bridge unusable and the hospitals at 60% capacity. The city has $40 million for disaster risk reduction and strong pressure to spend it on a high-profile river flood defence instead.
1. Assess the earthquake disaster risk in Arden Valley using hazard, exposure and vulnerability. [8]
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Hazard: shallow fault 12 km away, last rupture 140 years ago, so stress may be accumulating; a shallow rupture would cause strong shaking. Exposure: 520,000 people; 38% unreinforced masonry; two hospitals, 14 schools, stadium shelter; 70,000 in informal settlement on reclaimed land; bridge on the only route to trauma hospital. Vulnerability: unreinforced masonry collapses; liquefaction on reclaimed land; hospitals at 60% capacity; plan assumes 72-hour outside help but bridge may fail; political pressure to spend on flood defence instead of earthquake risk. Risk is high because exposure and vulnerability are concentrated in critical facilities. The flood defence may be useful but does not reduce earthquake risk. The highest risk is not the fault itself but the built environment and emergency access.
2. Evaluate how the $40 million should be prioritised to reduce risk before the next earthquake. [12]
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Priority 1: retrofit the trauma hospital and the bridge, because they are lifelines; without them, casualties rise even if other buildings survive. Priority 2: retrofit schools and the stadium shelter, because they are used by vulnerable people and as shelters. Priority 3: enforce building codes and provide low-cost retrofitting in the informal settlement, plus liquefaction mitigation such as drainage and foundations. Not the river flood defence unless it also protects critical infrastructure; it addresses a different hazard. Cost: $40m is unlikely to cover all; phased spending with matching funds and code enforcement can multiply impact. Equity: the informal settlement has the least capacity to recover, so investment there is justified. Judgement: the portfolio should be lifeline-first, not visibility-first. A high-profile flood defence may be politically attractive but leaves the earthquake risk unchanged.
3. Explain why a 'zero casualties' target may be unrealistic and what indicator would be more useful. [6]
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Zero casualties is unrealistic because residual risk remains after any affordable mitigation; earthquakes are uncertain in timing and magnitude; some exposed people may not be reached; and critical facilities may fail. A target of zero can also encourage blame avoidance and false confidence. Better indicators: expected annual loss, percentage of population in earthquake-resistant shelter, hospital functionality after a scenario event, bridge access time, percentage of schools retrofitted, and recovery time for water and power. These measure risk reduction and resilience, not just deaths. They allow the council to compare the flood defence with earthquake measures on a consistent basis.