汶川8.0级特大地震前的地磁垂直分量日变“双低点”异常

The "double low-points" anomaly of daily vertical component variation of geomagnetic field before the M8.0 Wenchuan earthquake

2008年5月9日,我国有13个地磁台(纳入国家地磁台网中心的台站)地磁垂直分量日变形态出现"双低点"异常.这些台站在空间上大致呈交汇的3个条带分布,其交汇处位于四川西部.异常出现3天后的5月12日,正好在四川西部的汶川发生了8.0级特大地震.地磁垂直分量日变"双低点"是客观存在的一种区域地磁异常现象.其成因可能是产生地磁静日变化Sq的外空涡旋电流体系发生变化,或可能是产生地磁静日变化的内源感应涡旋电流体系与外源涡旋电流体系产生数小时的滞后所引起.地磁垂直分量日变"双低点"异常与地震的关系,可能是前者反映了地球深部地震孕育状态的加速变化.

The ＂double low-points＂ anomaly of daily variation of the vertical geomagnetic component was observed in 13 geomagnetic observatories belonging to Geomagnetic Observatory Network Centre,China Earthquake Administration, on May 9th in 2008. These observatories distribute roughly in 3 intersected spatial belts, with the intersection located in western Sichuan. On May 12th, three days after the anomaly appearance, the great M8.0 Wenchuan earthquake occurred. The ＂double low-points＂ anomaly of daily variation of the vertical geomagnetic component is an anomalous phenomenon of regional geomagnetism, which does exist. The possible cause is the change of the extrinsic eddy current system resulting in geomagnetic daily quiet variation （Sq）, or the delay between internal and extrinsic eddy current system. The relationship between ＂double low-points＂ anomaly of daily geomagnetic variation and earthquake may be that the former reflects the accelerative alteration of earthquake gestation in deep earth.