【摘要】 "九五"以来,国内布设了地震地电场观测网,目前有100多个台正式投入观测,部分台站至今已积累了近十年的资料.期间发生了2008年5月12日汶川8.0级地震和2010年4月14日玉树7.1级等强烈地震,这对检验大地电场前兆方法的监测效果具有非常重要的意义.本文收集了汶川、玉树地震区附近的39个地电场观测台自投入运行以来的观测资料,并对全部资料的观测质量和映震情况进行了检查和分析,发现观测资料中存在不规则的与地磁场或固体潮汐变化相关的扰动变化,很难从中识别出地震前兆信息.为突出地震前兆信息,作者采用同台地电场观测的同一测向长、短极距测值的比值方法进行了分析处理.结果发现在地震前,多数台站的地电场观测资料存在不同形态的比值异常变化.研究结果表明,汶川、玉树地震前震源区附近的地电场观测资料中有较为丰富的地震前兆信息,只是由于这些信息混杂于正常大地电场变化的背景中,从原始观测数据中或使用常规的分析方法无法识别和提取.而使用本文的数据处理方法能有效地排除资料中来自大地电场的正常变化以及自然电场的远场变化,突出了近场的变化信息,使得地震前源自孕震区一定范围内的地电场异常信号容易识别.由图4可见,2002年的玉门5.9地震和2003年的山丹-民乐6.1地震前震源区的电场观测也出现了比值异常变化,而其他时段的比值曲线近似直线变化,因此表明本文地电场观测资料的分析处理方法是识别和提取观测资料中地震前兆信息的有效方法之一.分析结果还表明地电场前兆的不同形态可能与观测台的台址条件有关.更多还原

【Abstract】 Geoelectric filed network has been established for inland seismic monitoring since the ninth five-year plan.More than 100 stations have been observing and some of them have accumulated data about ten years.On May 12,2008 an earthquake with MS 8.0 struck Wenchuan,Sichuan Province and on April 14,2010 an earthquake with MS 7.1 struck Yushu,Qinghai Province.The earthquakes verified the monitoring effect of geoelectric field network.In this paper,the data set from39 stations near Wenchuan and Yushu area,have been collected and analyzed for their observation quality and earthquake-reflecting ability.It is found that seismic precursor could not identify due to the anomalous disturbance in observation data set related with geomagnetic field and solid tide.In order to highlight the seismic precursor information,a ratio method is used between the long and short dipole distance observation data in the same direction of the same station.The result indicates most of the stations appear ratio anomaly with different shape before an earthquake. The research also indicates that the geoelectric data,accumulated from stations around Wenchuan and Yushu area near the epicenter,contain plenty of seismic precursor information.Such information is hardly distinguished and extracted from original observation data or using ordinary methods,hided by the normal geoelectric change background.The ratio method used in this paper can effectively eliminate the disturbance from the normal geoelectric change and the far-field change of the natural electric field and simultaneously highlight the near-field geoelectric information,finally make it easy to identify the geoelectric abnormal information before earthquake around epicenter area.As figure 4 shows,geoelectirc data ratios in epicenter area appear anomaly before Yumen earthquake with magnitude of 5.9 in 2009 and Shandan-Minle earthquake with magnitude of 6.1 in 2003.Besides,ratio curve in other period is nearly straight with no anomaly,which also proves that it is effective to distinguish and extract geoelectric precursor information using ratio method.At last,it is indicated that different forms of geoelectric precursor are likely related with the location of the earthquake stations.更多还原