Estimation of Q Value by SP/S Spectral Ratio

由SP/S譜比值估計Q值

謝秋雰(Chiou-Fen Shieh)

《Terrestrial, Atmospheric and Oceanic Sciences》 3卷4期 (1992/12) Pp. 469-482

摘要

S波從震傳播到高阻抗對照的邊界時，會産生轉換的波相SP。通常S波主要記錄在徑向分量，而SP波記錄在垂直分量，用三分量資料，這兩個波相可以識別並分離。而研究這兩個波相，可以得到構造上的一些訊息。沈積岩的Q值就是其中之一。本研究主要由計算SP/S的譜比值，仨計近表層和頻率無關的Q值。
藉由淺層P及S波的速度構造，SP及S波的走時可以估計，所以不同的SP波能被識別。在羅東地區，有三個從不同邊界轉換的SP波，可以被識別出來。最早到達的SP波是從更新世地層底部轉換，第二到達的SP波是從衝積層底部轉換，而最後到達的SP波則是從表層土壤底部轉換而來。從三個不同的SP/S譜比值，求出不同的Q值，顯示Q值在不同層的變化。此法估計之Q值，和實驗室內量度沈積岩之Q值符合

並列摘要

S-wave propagation from source to a high impedence contrast boundary can produce convert phase SP. Normally S-phases are recorded on radial these two phases can be identified and isolated. Some significant structure information can be studied from these two phases. The Q value of sedimentary rock is one of them. The spectral ratio of SP-and S-phases are calculated in this study for estimating frequency-independent Q value of near surface layer. By the help of P-and S-waves velocity structure, the travel times of SP-and S-phases can be estimated such that SP-phase is identified. Three SP-phases, converted from different layers in the Lotung area, can be identified. The earliest SP-phase is possibly converted from the bottom of PLEISTOCENE formation. The second SP-phase might be converted from the bottom of ALLUVIUM layer, and the last one might be converted from the bottom of surface soil layer. Each SP/S ratio gives a different Q value which shows the variation of Q in each layer. The range of Q value estimated by this method agreed with the laboratory measurement of sedimentary rock.