Xisha Trough is arcuate in shape,42Okm long,6-14 km wide and lying at waterdepth of 1500-3400km. The bottom of the trough dips toward east. It is of negative free-air gravity anomaly of-20mgal and positive magnetic anomaly between 50 to 150 nT.

• 西沙海槽是一条水深1500－3400m、长420km的水槽，新生代沉积厚2－6km。