地震工程學家常以最大地表加速度（Peak Ground Acceleration）來估計可能的震災，但最大地表加速度只能代表作用時間極短的(最大)地震力，且一般而言，組成最大地表加速度的地震動成份的振動頻率較高，對於結構簡單且自然振動頻率較高的低矮建築物影響較大，以今日複雜的結構物環境，很難只用最大地表加速度來推估可能的震災。譜震度（Spectrum Intensity）包含地震延時、振幅和頻率內涵等與震災相關的種種特性，因此更適合做為評估地震災害的指標。雖然探討譜震度分佈時距離（在相關文獻裡距離定義為場址到震源距離或場址到地表斷層線距離）是個重要參數，但從來沒有文獻探討過不同型態地震的適用距離。本研究定義距離為場址到能量源頭的距離，並以921 地震（有明顯的斷層錯動）和嘉義地震（無明顯的斷層錯動）為對象從地震能量輻射的觀點來探討距離的選擇方式。 Nowadays, the structural environment is becoming so complicated that the originally defined intensity scale and peak ground acceleration (PGA) are not adequate to do a good job for assessing earthquake damage. Therefore, an index adequately assess earthquake damage is needed. Spectrum intensity (SI) includes the three elements affecting earthquake damage, earthquake duration, frequency content, and amplitude, and it is a more adequate intensity parameter to assessing earthquake damage. Although distance, defined as the distance from site to hypocenter or distance from site to the fault on earth surface in related literatures, is an important parameter for exploring the distribution of spectrum intensity, there is no study investigated the adequate distance for different types of earthquake. In this study, distance is defined as the distance from the energy source to site and the selection of adequate distance is discussed from the concept of energy radiation by using the data of Chi-Chi earthquake and Chia-Yi earthquake.
