呂宋島是一個構造活動頻繁的地區，位於兩個隱沒方向相反的系統之間——西側為巽他板塊（Sunda Plate），東側為菲律賓海板塊。在這種複雜的動力構造環境下，促成了沉積盆地、蛇綠岩套（ophiolite complexes）及火山弧的形成，並導致頻繁的地震與火山活動，對人口稠密地區構成重大威脅。為了深入了解地下結構如何影響地震波傳播與地表震動，本研究應用環境噪訊層析成像（Ambient Noise Tomography， ANT）技術，針對呂宋島地殼至上部地函的結構進行二維成像，並進一步探討地震波速度變化、地質特徵與地震災害之間的相互關係。藉由對 2022 年 3 月至 2023 年 3 月期間，46 個陸上地震測站與 9 個海底地震儀（OBS）測站所記錄之垂直分量地震資料進行互相關分析，估算基階雷利波格林函數。首先將每日連續紀錄依韋爾奇法（Welch′s method）切分為長度一小時之時間窗，並使相鄰時間窗重疊 15 分鐘，隨後再依標準環境噪訊處理流程進行前處理。本研究採用相位加權堆疊（phase-weighted stacking）以獲取堆疊後的噪訊互相關函數（NCFs）。結果顯示，藉由整合不同感測器類型與測站環境（包括陸域及海域環境）的數據，便能提取出具備可接受訊噪比（SNR）且穩定可靠的 NCFs。進一步利用 NCFs 的對稱部分提取經驗格林函數，並使用 EGFAnalysisTimeFreq 軟體獲取雷利波群速度與相速度的頻散（dispersion）觀測值。接著採用快速行進法表面波層析成像（Fast Marching Surface Wave Tomography），針對群速度 3–30 秒及相速度 3–25 秒的頻散曲線進行反演，產出與週期相關的二維速度圖。結果顯示，速度模型與呂宋島全境的主要地質及構造特徵存在高度相關性。在短週期下，低速區（LVZs）與主要沉積盆地密切對應，包括卡加延谷盆地、伊羅戈—中央谷盆地、林加延灣及民都洛盆地，以及與呂宋火山弧和比科爾火山弧相關的活躍火山區域。反之，高速區（HVZs）則與蛇綠岩套重合，包括三描禮士蛇綠岩套（Zambales Ophiolite Complex）、安加特蛇綠岩（Angat Ophiolites）、伊莎貝拉－奧羅拉蛇綠岩（Isabela–Aurora Ophiolites），以及東比科爾蛇綠岩套（East Bicol Ophiolite Complex）。在長週期下，於呂宋島西側可辨識出沿馬尼拉海溝的板塊窗（slab window），暗示可能存在板塊撕裂（slab tear）現象，同時東呂宋海槽的南北延伸範圍亦清晰可見。卡加延谷盆地與中央谷地盆地下方的低速異常，可能分別與卡瓜火山及皮納圖博火山相關的岩漿庫有關。於民都洛地區，觀測到的速度對比與巴拉望大陸地塊和菲律賓活動帶之間所提出的碰撞帶相一致，但仍需進一步研究加以驗證。識別出的低速區（LVZs）尤為重要，因其對應於沉積盆地及其他可能影響地震波放大與造成長時間地表震動的地質環境。因此，本研究所得到的二維速度模型，為理解區域地震反應差異提供重要的地球物理約束，並可作為未來地震危害潛勢評估、地震微分區（microzonation）研究及地震工程應用的基礎資料。總體而言，本研究顯示環境噪訊層析成像為解析呂宋島地殼與上部地函結構的有效工具，並突顯地震波速度模型在解釋地質特徵及支持菲律賓未來地震災害研究上的價值。;Luzon is a tectonically active region situated between two opposing subduction systems: the Sunda Plate to the west and the Philippine Sea Plate to the east. This complex geodynamic setting has led to the formation of sedimentary basins， ophiolite complexes， and volcanic arcs， and is responsible for frequent seismicity and volcanism that pose significant hazards to densely populated areas. To improve understanding of the subsurface structures that influence seismic-wave propagation and earthquake ground motion， this study applies Ambient Noise Tomography (ANT) to image the crustal to upper mantle structure of Luzon and examine the relationship between seismic velocity variations， geological features， and seismic hazards. Fundamental-mode Rayleigh-wave Green′s functions were estimated through cross-correlation of vertical-component seismic data from 46 land-based and nine ocean-bottom seismic stations recorded between March 2022 and March 2023. Continuous daily records were segmented into one-hour windows with 15-minute overlap following Welch′s method and preprocessed using standard ambient-noise procedures. Stacked noise cross-correlation functions (NCFs) were obtained using phase-weighted stacking. The results demonstrate that reliable NCFs with acceptable signal-to-noise ratios can be achieved through the integration of data from different sensor types and station environments， including both land and marine settings. Symmetric components of the NCFs were used to extract empirical Green′s functions， from which Rayleigh-wave group- and phase-velocity dispersion measurements were obtained using EGFAnalysisTimeFreq software. Dispersion curves in the period ranges of 3–30 s for group velocity and 3–25 s for phase velocity were inverted using the Fast Marching Surface Wave Tomography method to generate period-dependent two-dimensional velocity maps. The resulting velocity models reveal strong correlations with major geological and tectonic features throughout Luzon. At shorter periods， low-velocity zones (LVZs) correspond closely to major sedimentary basins， including the Cagayan Valley Basin， Ilocos–Central Valley Basin， Lingayen Gulf， and Mindoro Basin， as well as active volcanic regions associated with the Luzon and Bicol volcanic arcs. In contrast， high-velocity zones (HVZs) coincide with ophiolitic complexes， including the Zambales Ophiolite Complex， Angat Ophiolites， Isabela–Aurora Ophiolites， and East Bicol Ophiolite Complex. At longer periods， a slab window along the Manila Trench is identified on the western side of Luzon， suggesting the presence of a slab tear， while the northern and southern extent of the East Luzon Trough is clearly imaged. Low-velocity anomalies beneath the Cagayan Valley Basin and Central Valley Basin may indicate magma reservoirs associated with Cagua and Pinatubo volcanoes， respectively. In Mindoro， observed velocity contrasts are consistent with the proposed collision zone between the Palawan Continental Block and the Philippine Mobile Belt， although further investigation is required. The identified LVZs are particularly significant because they correspond to sedimentary basins and other geological environments known to influence seismic-wave amplification and prolonged ground shaking during earthquakes. As such， the resulting velocity models provide important geophysical constraints for understanding regional variations in seismic response and may serve as valuable baseline information for future seismic hazard assessment， microzonation studies， and earthquake engineering applications. Overall， this study demonstrates that ANT is an effective tool for imaging the crustal and upper mantle structure of Luzon and highlights the value of seismic velocity models for interpreting geological features and supporting future seismic hazard investigations in the Philippines.
