SMART analysis of geomagnetic data observed in Taiwan

In this paper, 3-component geomagnetic fields recorded by a fluxgate magnetometer are employed in examining 181 ML ≧ 4.0 earthquakes around the Taiwan area from 2002 to 2005. To search anomalies, the singular value decomposition (SVD) is used to extract the declinations and inclinations of the principal components from the geomagnetic field every 900 s for each 5-day period and the entire four years. Six reference angles of surface magnetic anomaly reference tip (SMART) are employed to readjust the azimuth of anomalous polarizations for unifying earthquakes. A bootstrap method is further applied to find whether the anomalies are significant or not. Meanwhile, the odds proportions between the inward and outward geomagnetic field on the earth’s surface reveal the associated anomalous inclinations. With the anomalous inclinations and declinations observed 10 days before earthquakes, SMART and the polarizations of the anomalous field can be located and described, respectively.