台灣島座落在菲律賓海板塊與歐亞大陸板塊的聚合區域，是呂宋島弧碰撞大陸邊緣所產生的島嶼。在這高聳且陡峭的島嶼東邊以及南邊各有一個隱沒系統存在，分別是琉球隱沒系統和呂宋隱沒系統。在此區域裡，地震主要是分布在台灣島東部的碰撞帶或者沿著兩個隱沒系統延伸，並且呈現逆衝型和拉張型的震源機制型態。然而，在西菲律賓海盆上卻有不少的走向滑移型地震出現，甚至已經遠離了板塊隱沒的邊界。除此之外，從2009年8月到2010年2月的七個月期間，耶雅瑪增積楔形體底下的海洋板塊也發生四起規模大於5.0的走向滑移型地震，而其中的兩起還分別達到了6.3和6.7。因為受限於現有的地震測站較遠，或者觀測網無法完全地包覆這些地區，所以仍然無法確定造成這些地震的斷層走向，遑論是形成原因。2010年4月26日，加瓜海脊東邊發生一起Mw= 6.5的走向滑移型地震，而它的震源機制型態與先前提到的地震相當類似。為了對這種類型的地震有更進一步地了解，甚至希望能夠得知它們背後代表的意義，所以我們在主震發生後的一個星期於震央周圍佈設16顆海底地震儀，並利用記錄到的餘震資料來做分析。
　　由海底地震儀組成的臨時觀測網持續地記錄22天，期間共有1476個地震事件被記錄到並成功地定出震源位置。經過地震資料品質的篩選以及雙差分地震定位演算法的重新定位後，主震震央周圍的地震群排列出西北－東南向的線形，指示這次的事件是由左移型的走向滑移斷層所引發的。此外，這條斷層的走向大致上與菲律賓海板塊和歐亞大陸板塊間的相對移動方向平行，所以本次主震與板塊間的運動應該有密切的關係。台灣周圍磁力異常圖顯示台灣東邊有兩條互相平行且呈現西北－東南向的構造邊界存在。其中，西南邊的構造邊界正好將呂宋島弧撞擊台灣島所引發的地震和一系列發生在隱沒板塊上的地震分隔開來，暗示著此構造邊界兩側受到的應力作用狀態並不相同。另外，本次主震的震央位置就正好落在西南邊的構造邊界延伸方向上，且餘震分布指示的斷層走向和構造邊界的方向完全一致。根據上述的所有現象，我們推測這些發生在海洋板塊上的走向滑移型地震是因為菲律賓海板塊持續地朝西北方向移動時，高凸在板塊西邊的呂宋島弧阻礙了板塊繼續向前的移動；另一方面，一系列典型的隱沒帶地震顯示海洋板塊正順利地沿著北邊邊界－琉球海溝朝西北方向隱沒到歐亞大陸板塊之下。當同一個板塊卻受到不同的應力作用邊界時，就在應力轉換的區域形成一系列左移型的走向滑移地震。

　　　　Taiwan, located on the boundary between the Eurasia plate (EU) and the Philippine Sea plate (PSP), is an orogenic belt formed by the collision between the Luzon Arc and the continental margin. Most earthquakes occur around Taiwan and along the Ryukyu subduction system with thrusting mechanism. However, there are some events which are associated with strike-slip faulting on the Philippine Sea plate and away from the subduction zone. On 26 April 2010, a strike-slip type of earthquake (Mw = 6.5) occurred on the east of the Gagua Ridge. We deployed 14 OBSs to record its aftershocks in order to acquire more information regarding these strike-slip earthquakes on the oceanic plate. Most aftershocks are clustered and aligned to the NW-SE direction. It indicates that the area is dominated by a sinistral strike-slip mechanism. In West Philippine Basin, two main geological structures, oriented NE-SW and NW-SE, were recognized from bathymetry map. The two features are associated with the spreading event in West Philippine Basin and an old oceanic fracture zone. Since the trending of the cluster in our study is different from the strikes of the two features in the West Philippine Basin, the seismicity seems not to be linked to the reactivation of the former structures. Finally, the aftershock distribution is sparse from 11 to 13 km depth, indicating the presence of Moho discontinuity where the lithospheric strength is weak relatively. This result is consistent with the Moho depth obtaining from the gravity model.

Basile, C., and P. Allemand (2002), Erosion and flexural uplift along transform faults, Geophysical Journal International, 151(2), 646-653.
Deschamps, A., and S. Lallemand (2002), The West Philippine Basin: An Eocene to early Oligocene back arc basin opened between two opposed subduction zones, J. Geophys. Res., 107(B12), 2322.
Deschamps, A., P. Monié, S. Lallemand, S. K. Hsu, and K. Y. Yeh (2000), Evidence for Early Cretaceous oceanic crust trapped in the Philippine Sea Plate, Earth and Planetary Science Letters, 179(3–4), 503-516.
Deschamps, A. E., S. E. Lallemand, and J.-Y. Collot (1998), A detailed study of the Gagua Ridge: A fracture zone uplifted during a plate reorganisation in the Mid-Eocene, Marine Geophysical Research, 20(5), 403-423.
Escartín, J., G. Hirth, and B. Evans (1997), Nondilatant brittle deformation of serpentinites: Implications for Mohr-Coulomb theory and the strength of faults, J. Geophys. Res., 102(B2), 2897-2913.
Escartín, J., G. Hirth, and B. Evans (2001), Strength of slightly serpentinized peridotites: Implications for the tectonics of oceanic lithosphere, Geology, 29(11), 1023-1026.
Fabbri, O., and M. Fournier (1999), Extension in the southern Ryukyu arc (Japan): Link with oblique subduction and back arc rifting, Tectonics, 18(3), 486-497.
Fournier, M., O. Fabbri, J. Angelier, and J.-P. Cadet (2001), Regional seismicity and on-land deformation in the Ryukyu arc: Implications for the kinematics of opening of the Okinawa Trough, J. Geophys. Res., 106(B7), 13751-13768.
Gomberg, J. S., K. M. Shedlock, and S. W. Roecker (1990), The effect of S-wave arrival times on the accuracy of hypocenter estimation, Bulletin of the Seismological Society of America, 80(6A), 1605-1628.
Hayes, G. P., et al. (2010), Complex rupture during the 12 January 2010 Haiti earthquake, Nature Geosci, 3(11), 800-805.
Hilde, T. W. C., and L. Chao-Shing (1984), Origin and evolution of the West Philippine Basin: A new interpretation, Tectonophysics, 102(1-4), 85-104.
Hsu, S.-K., C.-S. Liu, C.-T. Shyu, S.-Y. Liu, J.-C. Sibuet, S. Lallemand, C. Wang, and D. Reed (1998), New Gravity and Magnetic Anomaly Maps in the Taiwan-Luzon Region and Their Preliminary Interpretation, TAO, 9(3), 509-532.
Kao, H. (1998), Can Great Earthquakes Occur in the Southermost Ryukyu Arc-Taiwan Region?, TAO, 9(3), 487-508.
Kao, H., and R.-J. Rau (1999), Detailed structures of the subducted Philippine Sea plate beneath northeast Taiwan: A new type of double seismic zone, J. Geophys. Res., 104(B1), 1015-1033.
Kao, H., S.-s. J. Shen, and K.-F. Ma (1998), Transition from oblique subduction to collision: Earthquakes in the southernmost Ryukyu arc-Taiwan region, J. Geophys. Res., 103(B4), 7211-7229.
Kao, H., G.-C. Huang, and C.-S. Liu (2000), Transition from oblique subduction to collision in the northern Luzon arc-Taiwan region: Constraints from bathymetry and seismic observations, J. Geophys. Res., 105(B2), 3059-3079.
Kennett, B. L. N., and E. R. Engdahl (1991), Traveltimes for global earthquake location and phase identification, Geophysical Journal International, 105(2), 429-465.
Kissling, E., W. L. Ellsworth, D. Eberhart-Phillips, and U. Kradolfer (1994), Initial reference models in local earthquake tomography, J. Geophys. Res., 99(B10), 19635-19646.
Kubo, A., and E. Fukuyama (2003), Stress field along the Ryukyu Arc and the Okinawa Trough inferred from moment tensors of shallow earthquakes, Earth and Planetary Science Letters, 210(1–2), 305-316.
Kuo, B.-Y., W.-C. Chi, C.-R. Lin, E. T.-Y. Chang, J. Collins, and C.-S. Liu (2009), Two-station measurement of Rayleigh-wave phase velocities for the Huatung basin, the westernmost Philippine Sea, with OBS: implications for regional tectonics, Geophysical Journal International, 179(3), 1859-1869.
Kurt Stuwe, Geodynamics of the Lithosphere: An Introduction, Second Edition, Springer Berlin Heidelberg, New York, 2007.
Lallemand, S., C.-S. Liu, S. Dominguez, P. Schnürle, J. Malavieille, and A. C. T. S. C. The (1999), Trench-parallel stretching and folding of forearc basins and lateral migration of the accretionary wedge in the southern Ryukyus: A case of strain partition caused by oblique convergence, Tectonics, 18(2), 231-247.
Nettles, M., and V. Hjörleifsdóttir (2010), Earthquake source parameters for the 2010 January Haiti main shock and aftershock sequence, Geophysical Journal International, 183(1), 375-380.
Pavlis, G. L. (1986), Appraising earthquake hypocenter location errors: A complete, practical approach for single-event locations, Bulletin of the Seismological Society of America, 76(6), 1699-1717.
Ranalli, G., and D. C. Murphy (1987), Rheological stratification of the lithosphere, Tectonophysics, 132(4), 281-295.
Schnurle, P., C.-S. Liu, S. Lallemand, and D. Reed (1998), Structural Controls of the Taitung Canyon in the Huatung Basin East of Taiwan, TAO, 9(3), 453-472.
Sibuet, J.-C., S.-K. Hsu, and A. Normand (2004), Tectonic Significance of the Taitung Canyon, Huatung Basin, East of Taiwan, Marine Geophysical Research, 25(1), 95-107.
Trnkoczy, A., Understanding and parameter setting of STA/LTA trigger algorithmm, 2(IS 8.1), DEU: GeoForschungsZentrum Potsdam, Potsdam, 2002.
Waldhauser, F., and W. L. Ellsworth (2000), A Double-Difference Earthquake Location Algorithm: Method and Application to the Northern Hayward Fault, California, Bulletin of the Seismological Society of America, 90(6), 1353-1368.
Wessel, P., and W. F. Haxby (1990), Thermal Stresses, Differential Subsidence, and Flexure at Oceanic Fracture Zones, J. Geophys. Res., 95(B1), 375-391.
Yu, S.-B., H.-Y. Chen, and L.-C. Kuo (1997), Velocity field of GPS stations in the Taiwan area, Tectonophysics, 274(1-3), 41-59.
卓彥宇，「利用2009石垣島餘震資料探討琉球隱沒帶的地體構造」，國立臺灣海洋大學，碩士論文，民國101年。
張晉銘，「西菲律賓海盆西部的海床構造分析」，國立中央大學，碩士論文，民國97年。
陳鼎仁，「從海底地震儀資料探討加瓜海脊東西兩側的地殼速度構造」，國立臺灣海洋大學，碩士論文，民國98年。