利用周遭噪迅雷利波層析成像法研究台灣北部地區淺層速度構造

Ambient Seismic Noise Rayleigh Wave Tomography across Northern Taiwan

尤水輝(Shuei-Huei You)

指導教授 ： 龔源成

共同指導教授 ： 林正洪(Cheng-Horng Lin)

國立臺灣大學/理學院/地質科學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.00966

摘要

我們將周遭噪訊雷利波層析成像法應用在三個地震觀測網垂直向連續紀錄，包括中央氣象局地震觀測網、陽明山微震觀測網，與新竹微震監測網。藉由計算測站連續紀錄的交互相關函數，得到測站之間的格林函數，此結果主要反應在雷利波的能量上。我們針對週期為0.35hz的訊號，量測測站之間雷利波的群速度值，並經過適當的資料品質篩選，剩餘的資料配合多重尺度有限參數法反演台灣北部地區的淺層速度構造，得到的群速度模型與地表的地質構造吻合度相當高。除此之外，我們還發現測站連續紀錄之間的交互相關函數的強度，隨著時間、測站間的距離以及測站之間的相對位置有所變化，藉此我們發現台灣北部地區的噪訊主要來源可能來自於台灣北部以及西北部沿海地區。除了應用在速度模型反演以及噪訊來源的研究上，藉由測站連續紀錄之間的交互相關函數，我們還發現兩項測站儀器的誤差，並在其它分析之前予以修正，包含地震儀垂直向感應極性的反轉，以及記錄器時間偏移誤差，避免這種誤差對我們的結果造成影響。由此發現，周遭噪訊雷利波層析成像法不僅可以應用在速度模型反演的研究上，對於測站誤差的修正也能有所貢獻。

關鍵字

周遭噪訊 ； 雷利波層析成像法 ； 多重尺度有限參數法

並列摘要

We apply the ambient noise cross-correlation technique to the vertical component of the continuous short-period waveforms recorded by three seismic arrays, including Tatun Volcanic Area (TVA) array, Hsinchu array and stations in the northern portion of Central Weather Bureau Seismic Network (CWBSN). The noise-derived Green’s functions are treated as fundamental mode Rayleigh waves. With adequate data selection and quality control, the group velocity of each traces is analyzed, and the qualified results at about 0.35Hz are used to invert for a tomographic map of short period Rayleigh wave group velocity in northern Taiwan with multi-scale parameterization. The main feature of the tomographic result shows very good fit to the surface geological units. In addition to tomographic study, we demonstrate how the retrieved surface waves are affected by various factors, such as seasonal change, site location, and path azimuth. In particular, we notice an evident path-azimuth-dependent asymmetry between causal and acausal signals in most paths. The asymmetric properties imply the correlated ambient noise in northern Taiwan is mainly contributed from the north. Two unexpected while useful by-products are observed, the waveform polarity reversal and time shift of the stations, both present typical features on the retrieved surface waves. Thus, the ambient noise cross-correlation technique provides an alternative method to examine the station condition and secure the data quality from instrument errors.

並列關鍵字

ambient noise ； Rayleigh wave tomography ； multiscale parameterization

參考文獻

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