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(Components)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。由於譜震度（Spectrum Intensity, SI）包含地震延時、振幅強弱、頻率內涵等，Housner建議譜震度可作為地震危險度的指標。
本研究分析1993~2008年期間台灣中部地區(彰化縣、台中市、台中縣、雲林縣、南投縣、苗栗縣)芮氏規模 4、深度在35公里內之淺層地震資料。總共分析586筆的淺層地震，共7657筆的紀錄資料。
最後應用基因演算法(Genetic Algorithm)迴歸得到短週期平均譜震度SIa、中週期平均譜震度SIv和長週期平均譜震度SId之衰減模式並探討這三組衰減模式的特性，以利結構耐震評估之用。 Earthquake engineers usually use peak ground acceleration (PGA) to assess possible earthquake damage. Since PGA can only represent the earthquake force during a very short time (or maximum earthquake force) and is composed of higher vibration frequencies, PGA influences low-rise buildings with simple structure and higher natural frequency larger. Nowadays, the structural environment is becoming so complicated that the originally defined intensity scale and PGA are not adequate to do a good job for assessing earthquake damage.
Housner suggested that spectrum intensity (SI) can be risk index of an earthquake since it involves duration, amplitude and frequency content of seismic wave.
Earthquake data of central Taiwan (Changhua County, Taichung City, Taichung County, Yunlin County, Nantou County, and Miaoli conuty) collected from TSMIP (Taiwan Strong Motion Instrumentation Program) system were used in this study to develop the empirical attenuation form of SI. The database consists of 7657 recordings collected from 586 shallow earthquake events of depth d≤35 km and Richter magnitude scale 4 from 1993 to 2008. Finally, genetic algorithm (GA) is employed as a nonlinear regression method to find the global optimal solution of parameters in attenuation models of acceleration controlled spectrum intensity SIa, velocity controlled spectrum intensity SIv, and displacement controlled spectrum intensity SId. The three spectrum attenuation models can be applied to earthquake resistant evaluation of structures.
