| 摘要: | 本研究之目的在於探討台東縱谷(瑞穗至池上地區)地層的電性地層構造，並嘗試利用所測得之地電阻剖面資料，分析縱谷地層與中央山脈及海岸山脈岩層間之接觸關係。 本研究在瑞穗、玉里及池上三個地區，使用直流電阻法進行施測，應用雙偶極法與二極排列法共蒐集六條剖面，分別是瑞穗地區的AA’測線、玉里地區的BB’、CC’和DD’測線、池上地區的EE’、FF’測線。 測勘資料經二維逆推處理結果顯示，縱谷的沖積層在中央最厚，往兩側遞減，沖積層的厚度從幾十公尺到三、四百公尺不等。 而在沖積層之下，則為一低電阻層，推測可能是跟海岸山脈有關的沉積物混入，厚度從大約三百公尺到六、七百公尺變化。 在此低電阻層之下，則有一高電阻層出現，研判此一高電阻層可能反應出縱谷底下之基盤，縱谷下方之基盤面大約在深度500~700公尺之間。 在縱谷東側存在一電性不連續面，在瑞穗地區，此一不整合面位於距離海岸山脈西緣約1600~1800公尺處，而在池上地區，不整合面則位於距離海岸山脈西緣約200公尺左右，研判此一兩側岩性不同的界面，即為海岸山脈斷層的位置所在。 In this study , the electric formations between Rui-sui and Chi-shang of the Taitung Longitudinal Valley are studied . The geological structures and the situations of the strata of the Central Range and the Costal Range under the Taitung Longitudinal Valley are studied also . The DC resistivity method was used to investigate three area : Rui-sui , Yu-li and Chi-shang , with six geoelectric sounding profiles across the Taitung Longitudinal Valley . The sounding date were interpreted with 2-D inversion . The geoelectric sounding profile AA’situated at the Rui-sui area , and profile BB’, CC’, DD’ situated at the Yu-li area , and profile EE’, FF’ situated at the Chi-shang area . The dipole-dipole array is used for profile AA’, EE’,and pole-pole array is used for profile BB’, CC’, DD’and FF’. All of the geoelectric sounding profiles are almost vertical to the straight of the Taitung Longitudinal Valley . Several conclusions can be drawn as follows : ( 1 ) The results indicate that the alluvium in the middle of the valley is the thickest , and it is about few tens meters to 300 meters thick and has a resistivity ranging from 500 to 800 ohm-m . In three area , the alluvium of Rui-sui is about 100 to 200 meters thick and has a resistivity ranging from 500 to 800 ohm-m . The alluvium of Yu-li is about 200 to 350 meters thick and has a resistivity ranging from 500 to 1000 ohm-m . The alluvium of Chi-shang is about 250 to 350 meters thick and has a resistivity ranging from 500 to 800 ohm-m . ( 2 ) Under the alluvium , the second layer is a low resistitity layer . The second geoelectric layer is composed of debris , which come from the coastal Range for the east . The second geoelectric layer of Rui-sui is more than 600 meters thick and has a resistivity ranging from 30 to 60 ohm-m , and the second geoelectric layer of Chi-shang is about 300 to 400 meters thick and has a resistivity ranging from 30 to 100 ohm-m . ( 3 ) Under the second geoelectric layer , the third geoelectric layer is a high resistitity layer . It is presumed of the basement of the valley , which are composed of slate and schist . For the Rui-sui area ,the depth of the top of the basement varies from 500 to 600 meters and has a resistivity ranging from 200 to 700 ohm-m . For the Chi-shang area , the depth of the top of the basement varies from 500 to 700 meters and the resistivity of Chi-shang is more than 500 ohm-m . ( 4 ) According to the result of geoelectric sounding profiles , there are discontinuities exist in the east part of the valley , which are presumed to be the places of the Costal Range fault . |
