An analysis for the attenuation properties of the uppermost inner core by using Taiwan seismic array data

• Main Authors: Tseng, Tai-Lin, 曾泰琳
• Other Authors: Bor-Shouh Huang, Byau-Heng Chin
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/61116815011983268678

碩士 === 國立中央大學 === 地球物理研究所 === 86 === Inner core attenuation properties from two spots were examined in detail scale using PKIKP and PKP(BC) phases with distance range between 147 and 155 degrees recorded by both of the short- period regional seismic array in Taiwan and the broadband stations of the German Regional Seismic Network. Six earthquakes from the Northern South America and one from Fiji Islands regionwere investigated in this study. The ray path of South America to Taiwan samples the inner core region beneath the east of northern Pacific Ocean and the ray path of Fiji to Europe reflects the inner core boundary under the west of northern Pacific Ocean. The Qp values of inner core were estimated using Fourier spectrum ratios of core phases PKIKP and PKP(BC) on the short-periodfrequency band around 1 Hz. The multiple taper method was adopted to reduce the leakage effect due to the short duration of these two phases. Within the depth range of 160~340 km under the inner core boundary (ICB), the weighted means of Qp estimated from east Pacific Ocean are 246±19 (frequency band appropriate) and 305±25.4 (frequency band fixed). The average Qp is 192±28(appropriate) and 241±21.8 (fixed) in depth shallower than 210 km from ICB. In contrast, the average Qp obviously higher at depths more than 270km as a range from 31±15.7 (appropriate) to 337±46.5 (fixed). Our study demonstrated that Qp is increasing with depths and the gradient might probably be 1/km in this region. We observed a few of anomaly spectral characteristics during analysis, but there are not enough evidences to understand the primary causes. The average Qp calculated from west Pacific Ocean is 160±33.5 ( frequency band at 0.5~1.5Hz) within depth range from 178 to 265 km, and the value is much lower than that of east Pacific Ocean. The discrepancy of attenuation property between these two regions doesn't result from anisotropyof inner core, and might be related to the regional variation in the uppermost inner core.