921集集大地震之地表破裂及地盤變形現象

Surface Rupture and Ground Deformation Associated with the Chi-Chi, Taiwan Earthquake

李錫堤(C. T. Lee) ； 康耿豪(K. H. Kang) ； 鄭錦桐(C. T. Cheng) ； 廖啟雯(C. W. Liao)

《地工技術》 81期 (2000/10) Pp. 5-16

https://doi.org/10.30140/SG.200010.0001

摘要

發生於台灣中西部地區的921集集大地震，除了提供了世界上有史以來最完整的地震記錄，並為本世紀發生在陸地上逆衝斷層活動中的最大者，亦提供了研究低角度逆衝斷層破裂及地盤變形現象的絕佳機會。此次地震斷層破裂長達近百公里，最大水平位移量達約十公尺及最大垂直位移量達約八公尺，地盤變形現象集中在斷層上盤，其變形範圍少者數公尺，多則數十公尺寬；少數特例更達數百公尺到超過一公里之情形。在變形帶內，地盤拱彎、傾斜，產生分支斷層及張裂縫，有時更有背衝斷層出現。車籠埔斷層沿線的地盤變形現象大致可分為九類，包括：（1）純逆衝變形，（2）單斜褶皺變形，（3）純拱彎變形，（4）逆衝及拱彎變形，（5）逆衝拱彎及地塹變形，（6）拱彎及正斷層變形，（7）逆衝及背扭褶變形，（8）逆衝及背衝斷層變形，及（9）逆衝及多張裂帶變形等。一般而言，純逆衝及純拱彎的變形現象較為單純，變形帶也較窄；逆衝及拱彎變形次之；餘各類則屬較複雜之變形，變形帶也較寬。無論斷層變形帶的寬窄，斷層錯動是對建築及結構物最大的破壞，所以防震設計首要避開斷層錯動面。美國加州自西元1972年後，開始有斷層帶限建之規定。921集集大地震之後，我國也開始有類似之思考。然而，對於複雜的斷層，到底應如何劃設禁限建帶，則須謹慎考量。原則上，一般建築及結構物最好能適當地避開斷層錯動帶，但對於安全性要求極高的結構物，例如：核能電廠及大型水壩等，則應有更特別之考量。

關鍵字

地震斷層 ； 地表破裂 ； 地盤變形

並列摘要

The 1999 Chi-Chi, Taiwan earthquake is the largest known onshore thrust-faulting event that has occurred in the 20th century. It provides an excellent opportunity to characterize the surface rupture and ground deformation associated with thrust faulting. The surface faulting along the Chelungpu fault produced by the earthquake extends north-south about 96 km, and has a maximum horizontal slip of about 10 m and a maximum scarp height about 8 m. Ground deformation occurred predominant on the hangingwall, ranged in width from several meters to several tens of meter. In a few cases, the deformation zone was several hundred meters wide, and it was even wider in Tsuolan area. In the deformation zone, there are secondary faults, branch faults, open cracks and/or tilted ground, which damaged existing buildings and structures.Along the length of the Chelungpu fault rupture, hangingwall deformation may be classified into 9 different styles. This includes: (1) Simple thrusting, (2) Monoclinal folding, (3) Simple warping, (4) Thrusting and warping, (5) Thrusting, warping and graben formation, (6) Warping and normal faulting, (7) Thrusting and back-kinking, (8) Thrusting and backthrusting, and (9) Thrusting with multiple zones of open crack. Simple thrusting and monoclinal folding generally represent narrower deformation; whereas more complex zones of deformation tend to be wider.Fault rupture is the direct reason to cause serious damage to engineering structures; the deformation zone away from fault tip is not so critical to common buildings and structures. One method of mitigating hazard from earthquake surface rupture, currently being used in California, is to develop setback zones along fault traces in order to restrict the location of structures for human occupancy across the trace of an active fault. After the Chi-Chi earthquake, the Taiwan Government is also developing a similar rule. However, for complicated faulting like the Chelungpu, it is not easy to draw a simple setback zone to avoid all possible damage from the next earthquake. However, the most important point for a common building or structure is to avoid it from across fault crush zone. But, for a critical facility, like a nuclear power plant or a high dam, sitting and construction on the hangingwall deformation zone should be avoided.

並列關鍵字

earthquake fault ； surface rupture ； ground deformation