Based on the geothermal anornaly and pore pressure distribution in Yinggehai Basin

South China Sea

a 2D mathematical model is established and applied to analyze the transient variation process of fluid flow and fluid pressure within paralle opening fractures and in the connected permeable formations.A characteristic time constent was obtained to illustrate the influences of stratigraphic and hydrodynamic factors on the process.The fluid transmisson coefficient of the fracture surfaces and the hydraulic conductivity of the fracture surfaces control the peak flow and the time duration keeping this flow through the fracture respectively.The vertical flow of underground thermal fluid resulted from the opening fracture is the important cause of geothermal anomaly.However

the existences of high abnormal thermal indexes

such as the smectite lillite transformation and vitrinite reflectivity observed in Yinggehai Basin

should be the results of a large flow of hot fluid along the vertical fractures during a long period.