利用周遭雜訊逆推沖繩海槽地下構造

Abstract

摘要 我們利用周遭雜訊法研究沖繩海槽淺部岩圈，因為此法不受地震與測站之間時空幾何分布的限制，只在乎測站之間分布的位置。我們計算由BATS、F-net和IES-OBS提供之共19個寬頻地震記錄站所記錄垂直方向上之長時間連續記錄的交互相關函數，得到測站間表面波傳遞的格林函數。把所有天數資料的疊加訊號與每20天疊加一次的訊號做相關係數的計算，挑選出較好品質的格林函數重新疊加，以不同的頻段(10~50秒之間)對其做窄頻濾波並計算其群速度值。利用得到的頻散曲線以三種不同的逆推的方法得到此區的層析成像、模型解析矩陣與模型變異數，並且比較其不同。最後我們佈放虛擬的海底地震儀，觀察其解析函數以及模型變異的空間變化，來探討如何佈放可使我們最能有效的描繪波速構造。

Abstract We use ambient noise technique(ANT) to study the shallow lithosphere of Okinawa Trough, because ANT would not be limited by the distribution of earthquakes and stations. It depends only critically on the geometrical spread of stations. Vertical-component time-series recorded from 19 broad-band stations have been correlated with one another to yield estimated Green’s functions. We sort out data if the coefficient correlation between all-stacked and per 20 days-stacked record that are over an a prior assigned threshold. We then stack again to get higher quality Green’s function. We filter them by a narrow band that is concentrated within 10 to 50 s period to compute the group velocity maps in order to execute the tomography, and obtain the inverse model, the model resolution, and the model covariance matrix by three ways of inversion. In the end, we discuss the ideal pattern of OBSs deployment enhance our understanding of the Okinawa Trough.