在暹罗湾内离越南西南海岸约150公里的土珠岛周围做了折射和连续地震反射测量。工作区域位置在东经102°4′到104°5′北纬9°15′到9°40′之间。这个地区的海洋地质情况还不太清楚。有关该区的实际地质知识只能从陆地的和几个沿海岛屿的地质资料推论。地震研究的主要目的是要进行普查,以查明可能的沉积层的存在和厚度并建立它和陆上地质的关系。在土珠岛的北、南、东、西共做4条折射剖面。前三条剖面的平均长度约50公里。西剖面延伸长达137公里,试图获得上地幔折射初至。可是没有获得结果,推测莫霍不连续面的深度超过25公里。根据计算速度和各种地层的深度,可以对这个地区的地质构造提出一些见解。根据折射资料,与邻近岛屿的地质联系起来,说明海床建造是中生界型。它复于古生界岩层和可能是花岗岩的基底上。中生界地层的平均厚度估计在3.0～3.5公里之间。古生界地层厚约3.2～4.5公里。土珠岛西南60公里有一大断裂。断裂的走向与早先航磁测量的类似,也许它是暹罗湾第三纪盆地东部边界。最重要的发现是,在该地区第三纪沉积完全缺失。基底北部和东部的形态可与已知的陆上地质很好对比。在土珠岛东边和东南边,用电火花当震源,总共做了370公里地震反射剖面。根据地震反射资料,在中生界沉积层内可以分出三套明显的地层。具体地说,这三套地层相当于侏罗系与泰国普加当群相当的三迭系和红层、以及二迭系灰岩。另一方面,由于第二第三反射层彼此很接近,后者也可能是三迭系的一部分,而二迭纪灰岩还要更深些。出露于海底的第一反射层从其形态来看,可认为是变形后地层,只在某些区域为深部的断裂所切割。从第二反射层可看出许多大小构造。特别重要的是盐丘状的底辟构造群与一个背斜,这一层也为断层所切割。对于第三反射层,要在大范围内追踪它比较困难。可以认为该层一般地亦受第二层的变形作用所影响。根据所获得的成果,认为在这里有一个厚约3～4公里的广阔沉积盆地。至于它是不是向南、向东延伸的更大盆地的一部分,还有待进一步研究。 Refraction and continuous seismic reflection measurements were made around the Tusu Island, about 150 km south-west of Vietnam, in the Gulf of Siam. The working area is between longitude 102 ° 4 ’to 104 ° 5’ and latitude 9 ° 15 ’to 9 ° 40’ north. The marine geology in this area is not yet clear. The actual geological knowledge about the area can only be deduced from the geological data on land and on several coastal islands. The main purpose of the seismic study is to conduct a census to find out the possible existence and thickness of sediments and to establish its relationship with the onshore geology. In the Tusu Island north, south, east and west to do a total of 4 refraction profiles. The average length of the first three profiles is about 50 km. The west section extends for 137 kilometers and attempts to obtain a first arrival refraction on the upper mantle. However, no results were obtained, suggesting that the depth of the Moho discontinuity exceeds 25 km. Based on the calculated velocities and the depth of various strata, some insights into the geological formations in this area can be put forward. Based on the refraction data, it is linked with the geology of the adjacent islands to show that the seabed construction is of Mesozoic type. It is complex in the Paleozoic strata and may be granite on the substrate. The average thickness of Mesozoic strata is estimated at 3.0 ~ 3.5 km. Paleozoic strata thick about 3.2 ~ 4.5 km. 60 kilometers southwest of Tuzhu Island has a large fault. The strike of the fault is similar to that of previous aeromagnetic surveys, perhaps it is the eastern boundary of the Gulf of Thailand of the Tertiary Basin. The most important finding is the complete absence of Tertiary deposits in the area. The morphology of the north and east of the basement is well comparable to known onshore geology. On the east and southeast of Tadu Island, a total of 370 km of seismic reflection profile was made using electrical sparks as a source. According to the seismic reflection data, three sets of obvious strata can be separated in the sediments of the Mesozoic. Specifically, these three sets of formations correspond to Triassic and red beds of the Jurassic equivalent to the Pachidang group of Thailand and Permian limestone. On the other hand, due to the close proximity of the second third reflecting layers to each other, the latter may also be part of the Triassic system and the Permian limestone is even deeper. The first reflecting layer exposed on the seabed can be considered as a post-deformation stratum by its shape, and it is cut only by deep faults in some areas. A number of size configurations can be seen from the second reflective layer. Of particular importance is the salt-shaped diapir structural group with an anticline, which is also cut for faults. For the third reflector, it is more difficult to track it over a wide area. It is believed that this layer is also generally affected by the deformation of the second layer. According to the results obtained, we think there is a vast sedimentary basin about 3 to 4 km thick here. As for whether it is part of a larger basin extending southwards or eastward, further study is needed.