地震、屋毀與傷亡：集集地震風險的因果分析

Earthquake, Housing Damage, and Fatality: A Causal-effect Analysis of Seismic Risk in Chi-Chi Earthquake

在聯合國國際減災辦公室及政府間氣候變遷小組的風險分析架構上，本研究將地震風險視為地震危害度（hazard）、人口與建物暴露性（exposure）與脆弱性（vulnerability）三項風險（risk）因素的總體函數。我們以集集地震為分析案例，整合危害度、暴露性與脆弱性三類因素對房屋倒塌與人員死亡進行兩步驟的因果分析，以Poisson迴歸模型進行估計。結果顯示，地震危害度、人口與建物暴露性與社會經濟脆弱性對集合式住宅倒塌棟數與全倒戶數皆有影響，即使在控制集合式住宅倒塌棟數與房屋全倒戶數之後，前述三項風險因素對地震死亡人數仍具統計顯著效應。其中地震的災害變量與人口建物暴露變量的效果最顯著，震動強度、斷層經過與集合式住宅倒塌三者加上其交互作用，是造成集集地震死亡的首要因素。相較之下社會脆弱性變量（性別比、幼年人口、家戶所得、所得標準差）雖然較弱但仍有顯著效應，會擴大集合式住宅棟數、全倒戶數與死亡人數。在學術上，本研究突顯跨領域理論與數據整合對分析與理解地震災難風險的重要性。在實務上，本研究建議應強化都市規劃、區域計畫、建築法規與社會扶助等機制，以降低對地震災害的暴險率與社會脆弱性。

Based on the disaster risk framework proposed by the United Nations Office for Disaster Risk Reduction and the Intergovernmental Panel on Climate Change, this study defines seismic risk as a function of seismic hazard, population-building exposure and vulnerability. The Chi-Chi, Taiwan, earthquake was used as a case study of a two-step cause and effect (housing damage and fatalities) analysis. Data (mostly at village scale) from various governmental and academic sources, including data for demographics, housing tax, family income tax, seismology, housing damage, and fatality, were used to construct four statistical models to examine the physical and social determinants underlying the seismic risk. The Poisson regression model was used to estimate the impacts of these factors on housing collapses and fatalities. The regression models showed that all factors significantly affected housing collapseand fatality. Seismic hazard and population-building exposure are the most key factors. Earthquake intensity, passage of the Chelungpu Fault, collapse of condominium and their intersectional effects explained most earthquake fatalities. Compared with those factors, social vulnerability variables (gender-female, young population, low family income, and income inequality) have a weaker influence; however these variables have a significant marginal effect on enlarging the fatalities. The contribution of this study is the use of an interdisciplinary approach that integrates theories and data across seismology, geology, geography and sociology to enrich seismic risk study. Regarding social implications, this study demonstrates the important role of national institutions, such as urban planning, regional planning, building regulation, and social welfare mechanisms, in minimizing exposure and social vulnerability to seismic risk.