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Geographic Area Covered 

The report covers the Lower Hutt area in the Wellington Region, including Wainuiomata, Eastbourne, and the Lower Hutt Valley. 

Summary of the Report 

This report is part of a seismic hazard mapping initiative by the Wellington Regional Council, aimed at understanding and mitigating earthquake risks in the region. It focuses on ground shaking hazards in Lower Hutt and divides the area into four zones based on geological conditions and expected seismic response. 
 
Zone 1 consists of bedrock and is the least hazardous, with very low to low amplification of seismic waves. Zone 2 includes firm materials like compact gravel and stiff clay, showing low to moderate amplification. Zone 3–4 contains 5–10 meters of soft or loose material, leading to moderate to high amplification. Zone 5, the most hazardous, has over 10 meters of soft or loose material and experiences high to very high amplification. 
 
Two earthquake scenarios were considered. Scenario 1 involves a large, distant earthquake (Magnitude 7), producing Modified Mercalli (MM) intensities from V–VI in Zone 1 to VIII–IX in Zone 5. Peak ground acceleration ranges from 0.02g to 0.3g, with shaking durations from under 5 seconds in Zone 1 to over 15 seconds in Zone 5. Scenario 2 simulates a local rupture of the Wellington Fault (Magnitude 7.5), with MM intensities from IX near the fault to XI in Zone 5. Peak ground acceleration could reach up to 0.8g, and shaking may last up to 40 seconds. 
 
The report uses data from 850 drillhole logs, microearthquake and strong motion records, cone penetrometer tests, and gravity surveys. It highlights the importance of site-specific studies due to geological variability and limitations in data resolution. The findings are intended to support planning, engineering, and civil defence efforts by identifying areas most at risk from earthquake-induced ground shaking.