Possible precursory anomalies of the Wenchuan earthquake (Ms8.0) based on geomagnetic data

On 12 May 2008, a major earthquake struck Wenchuan, Sichuan Province, China. Numerous scholars have published research reports. However, there are limited reports on the impending anomalies of this earthquake. In this paper, based on geomagnetic data, we calculated the cross-wavelet spectrum. The geomagnetic data were available from Chengdu station (CDP) and Chongqing station. The results demonstrate that the coherence of the vertical and the declination component (Z-D) increased one day before the earthquake at CDP. This is the expression of the synchronous change of the vertical component and declination component in the seismogenic area. We believe, based on evidence from geomagnetic data, theimpendinganomaly of the Wenchuan earthquake was gained, and it may be related to the convergence of energy by the earthquake formation.