2009-08-012024-05-16https://scholars.lib.ntu.edu.tw/handle/123456789/667264摘要：沖繩海槽一直被認為是琉球隱沒系統的弧後張裂系統，且其弧後張裂的動力機制甚至影響到台灣的東北緣。然而最近的GPS以及地震觀察顯示，台灣東北部以及蘭陽平原的構造應力在水平方向有明顯的側向旋轉 ;此外地球化學的分析認為，沖繩海槽的西南端到台灣一帶的岩漿有多次分化熔融的特性，顯示沖繩海槽西南端的構造演化情形可能並不單純。本研究將進行地震接收函數以及折射地震分析，解析沖繩海槽西南端由淺到深的地震散射訊號構造。地震散射面主要反應不同物理性質的地層或構造幾何的空間分佈，地震波通過這些層面時會反射折射，甚至產生轉換波相。我們希望藉由這些分析，確實描述西南沖繩海槽地震莫氏面以及地幔楔形體的幾何形狀。本研究將佈放寬頻以及短週期地震儀於西南沖繩海槽，我們將匯整該地區的地震紀錄，研究該區的地震發震特性。由於收集到的地震波路徑將有部分穿過琉球隱沒帶最西南緣的地慢楔形體，我們可以進一步探討地幔楔形體的震波特性，對西南沖繩海槽的岩石圈結構以及地幔楔形體的速度模型，將會有更進一步的了解。本研究將進行三年，除了上述的科學研究議題外，也希望藉由本項研究工作陸續開發海底地震儀系統，更進ㄧ步了解海底地震儀的訊號內容。<br> Abstract: The Okinawa Trough is used to be considered as the back-arc rifting in the Ryukyu subduction system. Such a back-arc extension is further considered to propagate westernward causing the tectonic basin in the northeast Taiwan. Nevertheless, recent GPS and seismic observation reveal significant deviations of displacement vectors which should correspond with the changes of the tectonic horizontal stresses in the northeast Taiwan and the Ilan plain. The geochemical analyses further depicts that there exist various degrees of melting within an ascending region of the asthenospheric mantle, which are triggered by extensional collapse of the northern Taiwan mountain belt. In this study, we set out the study in figuring the shallow seismic discontinuities in the southwestern Okinawa Trough (SOT). In general, seismic scattering reflects the distribution and geometry of layers in varied seismic velocity. The means of receiver function and seismic refraction are adopted to release the main velocity contrasts within the southwest Okinawa subduction system. The seismic refraction surveying method used seismic energy that returns to the surface after travelling through the ground along refracted ray paths. On the other side, a receiver function is defined as the response of the velocity structure beneath a seismic receiver (station) to an impulsive plane wave generated by an earthquake at teleseismic distance. These two approaches can reveal the main seismic discontinuities in different scales. 5 board-band OBS and a few short-period OBS will be correspondingly deployed in the SOT within this study. The in situ OBS data can provide the information about not only the local seismic parameter but also the mantle-wedge velocity structure revealed by intermediate-to-deep subducting earthquakes and teleseismic waveforms. Here we set our study on the main velocity contrasts beneath the SOT, which could correspond to the Moho, subducting slab, and other density variations along the depth. We will combine all the seismic records in the studied area to model the seismic discontinuities and 2D, 3D seismic tomography in the SOT. This project is scheduled in three years, from the beginning of August in 2009 to the end of August in 2012. In addition to procuring the scientific purpose described as above by means of ocean-bottom seismology, execution of this project also renders opportunities of examination of the current OBS development policy.地震散射訊號沖繩海槽地震接收函數折射地震分析seismic scatteringOkinawa Troughreceiver functionseismic refraction survey.