ANALYSIS OF VARIATIONS OF INDOOR BASE LINE AT ANQIU STATION

The research result of the indoor base line of Anqiu seismographic station in 16 years shows that the measurement precision of the indoor base line can reach 2×10^-7. A large part of the indoor base line variation is cursed by ground surface thermal deformation, with its value reaching 7×10^-5. The information of seismic activity is only about 5×10^-6, Thus decreasing and eliminating the ground surface thermal deformation is the key to improve the applied value of indoor base line.