地震斷層作用造成的近地表變形為地震災害中人工建物損毀主因之一，利用受損建物的分布與地表變形特徵，將可有效地提供地震斷層的相關資訊。甲仙地震(MW=6.4)於嘉義、台南和高雄地區引起地表破裂、建築物損毀等災害，本研究蒐集甲仙地震造成的破壞及前人野外調查的資料加以統整，依破壞形式分類成地表破裂、建築物損壞與土壤液化三種，其中地表破裂主要集中在高雄市美濃區一帶，以一系列具方向性的開張型地表裂隙形式出現；地表裂隙出現地點可分成五個區域，約呈西北東南向破壞帶。依地表裂隙走向及性質，將其分成三組，其中一組裂隙走向為230°± 30°，判斷其成因明顯與人造建物的結構無關，推測可能與斷層作用相關。建築物損壞與土壤液化現象多與震波、地質條件及建物本身強度有關，本研究不多加以討論。 透過尖峰地動應變(peak ground strain)分析和彈性半無限空間斷層錯位模擬，探討地表裂隙的成因。結果顯示震波引致的地動應變雖已達地表破裂門檻，但無法佐證破壞具方向性；據地球物理及本研究彙整的地表破裂資料，作為模擬的參考依據，模擬所得的近地表變形之大小及可能的破裂形式皆與美濃區之地表裂隙相符，故本研究推論這組地表裂隙與斷層錯動有密切關聯，其破壞帶分布反映該處地震斷層雖未穿破地表但已極接近地表面(數公尺或數百公尺)，其位置及走向可粗略的反映斷層空間幾何形貌。 活動斷層錯動具週期性，且引致地表變形也具重複性，本研究結果指出甲仙地震其觸發地震之盲斷層的可能空間幾何位置及其可能造成近地表變形範圍，提供該區未來地震防災相關之參考。 Near-surface deformation induced by earthquake faulting is one of main causes to the damage of engineering structures during earthquakes. In return, the information of distribution of damaged engineering structures and features of surface deformation can reveal important characteristics of the earthquake fault. The 4 March 2010 Jaishian, southwestern Taiwan, earthquake (MW6.4) caused moderate damage in Chiayi, Tainan and Kaohsiung including ground surface fractures, engineering structure damage and soil liquefaction. This study collects and collates all the data from the reports of the earthquake-induced engineering structure damage by earthquake engineers and field fracture investigation by geologists. The collated result shows there were dense open-type surface fractures locally distributed within an northwest-trending rupture zone at Meinong in Kaohsiung. The surface fractures can be divided into three sets according to their characteristics. The formation of one set of the fractures which oriented in azimuth of 230°± 30° likely resulted from the earthquake faulting because of no evidence connected with the weakness of engineering structures. The locations of densely damaged buildings may reflect the information of the hanging wall of the earthquake fault. The phenomenon of soil liquefaction is usually related to seismic shaking and the property of geomaterial at sites. The formation mechanisms of these fractures will be studied via analyzing dynamic (peak ground) strains derived from peak ground velocities and static strains produced from an elastic half-space dislocation model. The result of the dynamic strain analysis shows that the cause of fracturing due to the seismic shaking cannot be ruled out because the magnitude of the strains could reach the threshold of ground failure but there is no evidence for the directional characteristic. On the contrary, open-type fractures and their orientation of 230°± 30° in azimuth produced from the near-surface modeled static strains are consistent with those discovered in field investigations. Thus, this study suggests the set of surface fractures is closely associated with the Jaishian earthquake faulting. Furthermore, the fracture-distributed rupture zone may infer that the earthquake fault might almost reach the ground surface (tens or hundreds of meters beneath)；its location and orientation roughly reflects the same properties of the fault. The activation of an active fault is repeating and probably cyclical. So is its induced ground deformation. This study highlights the accuracy of location of a blind fault associated with Jaishian earthquake and extent of its activation-resultant near-surface deformation. These results shall provide valuable information for mitigating earthquake hazard in southwestern Taiwan.
