Abstract: In this paper, we studied the Gaoliying earthquake with M_s 4.0 occurred on 16 Decem-ber 1996,Beijing. First, by using the spatial correlation method we analyze the vertical component Z of proton magnetometer records near the epicenter, and have found that the coefficient of correlation Rz goes down 3 months before the earthquake. It shows that the linearity of the local geomagnetic field has been damaged,and the damage became stronger until the energy released (the earthquake occurred), and the anomaly quickly recovered af-ter the event, indicating that linearity of geomagnetic field has been recovered before the earthquake. Meanwhile, by using the weighted difference method we revealed the immi-gration of the anomaly before the earthquake.

Key words: Seismo-magnetic effect, Fracture zone, Weighted difference