东北亚地区M_(S)5.0以上地震前后空间电场时空演化特征研究

Spatio-Temporal Evolution of Electric Field Pre-and Post-Earthquakes with Magnitude M_(S)≥5.0 in Northeast Asia

本文利用2005年1月—2009年12月DEMETER电磁卫星观测的极低频/甚低频(ELF/VLF)39 Hz~6 kHz频段电场功率谱密度(PSD)观测量,将研究频段划分为5个子频段对东北亚地区(38°N~58°N;105°E~145°E)内发生的8个M_(S)≥5.0地震前后空间电场时空演化特征进行研究。研究发现同一地震不同频段异常扰动区域并不完全在同一位置,且同一地震的不同频段地震前后扰动形态也并不一致;8个地震40次统计中有25%的统计数据虽然基本在地震前后所有时间段都超过阈值2σ,但未见明显扰动规律,其余75%的统计数据中发现其扰动特征可以归纳为3类:52%的统计数据在震前扰动幅度增大,达到最大时发震,震后持续降低;7.5%的统计数据在震前扰动幅度达到高值,而后下降过程中发震;15%的统计数据在震前扰动幅度一直在增加且绝大部分时间低于2σ,直至震后超过2σ,且出现这种类型的异常均为震例的第五频段演化特征。异常扰动区域主要集中在震中±4°以外的区域。

Five frequency bands of the power spectrum density data of the electric field in the ELF/VLF frequency band(39~6000 Hz)recorded by the microsatellite DEMETER from January 2005 to February 2009 is utilized to carry out statistical analysis about the spatio-temporal evolutions of electric field during the 8 strong earthquakes with magnitude M_(S)≥5.0 in Northeast Asia(38°N~58°N;105°E~145°E).The analysis shows the perturbations in different frequency bands of the same earthquake are not all in the same regions.And the perturbation patterns in different frequency bands of the same earthquake are not consistent during the same earthquakes.Statistical analysis of perturbation amplitude during the 8 earthquakes shows that for the 25%of these statistics shows no obvious spatial and temporal patterns,although the perturbation amplitude reached basically more than 2 times the standard deviation during the earthquakes.The remaining 75%of the statistics can be classified into three types:the perturbation amplitude of the 52%of the statistics began to increase before the earthquake,and the earthquake occurred at the high perturbation stage.For the 7.5%of the statistics,the perturbation amplitude increased to the high perturbation stage before the earthquake,and the earthquake occurred during the descent stage of the perturbation amplitude.For the 15%of the statistics,the perturbation amplitude increased and reached basically less than 2 times the standard deviation before the earthquake,and the perturbation amplitude of the fifth frequency band in these earthquakes are all in this type.The perturbations mainly appear in the places outside±4°in latitude and in longitude from theepicenter.