• 作者： 余貴坤; 陳其揚
• 作者服務機構： 國立中央大學地球物理研究所
• 中文摘要： 本文利用台灣遙記式測震網（簡稱台網，TTSN）所收集的P波走時資料研究台灣－琉球隱沒區的P波速度構造。資料包含發生在琉球島弧下40至230公里深的95個中級地震。為探討速度的側向變化，台網的測站被分成三群，並應用延伸的Kaila解析法求取各震源深度的P波速度。結果顯示，P波速度近乎隨深度線性增加。當深度由40公里增至150公里時，分析台灣北部測站群的資料，速度由7.94公里／秒增至8.35公里／秒，分析台灣西南部及東部海岸山脈兩測站群的資料，速度由8.20公里／秒增至8.40公里／秒。此速度的差異在淺部地函尤其明顯，其原因主要來自傳播路徑的不同，即台灣北部測站收到的震波是經由大陸邊緣的弧後盆，但台灣西南部及束部海岸山脈測站收到的震波卻是沿著隱沒岩板傳上來的。同時，此淺部的速度差異亦可引申隱沒岩板的前緣至少達150公里深。此外，a值（intercept time）也可提供地殼厚度的側向變化訊息。
• 英文摘要： In this paper, the P-wave velocity structure of the Taiwan-Ryukyu subduction zone has been studiedusing the P arrival data collected by the Taiwan Telemetred Seismographic Network (TTSN). The datavolume includes 95 very accurate moderate size earthquakes with foci at depths between 40 and 230 kmbeneath the region of the Ryukyu Islands. In order to evaluate lateral variation of velocities, the TTSNstations have been divided into three groups and velocities of P-waves at depths of earthquake foci deter-mined for each group by the extended Kaila analytical method. Results show that P-wave velocitiesincrease approximately linearly 1) from 7.94 km/sec at a depth of 40 km to 8.35 km/sec at adepth of 140 km for the northern Taiwan group; 2) from 8.20 km/sec at a depth of 40 km to 8.40 km/secat a depth of 160 km for the other two groups of the east Coastal Range and southwestern Taiwan. Thevariation of velocities at shallow depths is obvious. This could be explained by different ray paths that passthrough the back-arc basin near the continental margin for northern Taiwan as well as those that propagatealong the inclined subducting slab for southern paths. Furthermore, the velocities derived from thenorthern Taiwan stations have low values at shallow depths, but approach gradually the values obtainedfrom the other two groups at depths of about 150 km. This may imply that the predestined tie of theinclined subducting slab reaches at least to a depth of about 150 km. Moreover, the‵a'-values (intercepttimes) may also provide information for crustal thickness variation along the lateral direction.
• 中文關鍵字： upper mantle; subduction zone; back-arc basin; 'a'-value
• 英文關鍵字： --