短期重现性地磁日变化感应电流集中分布与地震关系初步研究

通过分析台站之间地磁垂直分量日变化相关性,研究中国大陆南北带地区90°E～110°E,2009～2018年地磁日变化感应电流线状集中分布现象与M_S≥6.0地震关系。统计发现,我国每月平均出现约2次感应电流集中分布现象,且10天左右内有原地重复出现现象——感应电流集中分布重叠异常,原地重现的集中分布感应电流日期间隔一般在10天左右以内,原地重现日期一般不连续,重现次数一般仅有2次。研究发现,我国南北带2009～2018年共出现重叠异常23次,20次重叠异常出现后18个月内重叠段发生M_S≥6.0地震,对应率高达87%,地震基本发生在重叠段端部250km以内,重叠段发生2次M_S≥6.0地震的比例较低,约35%;重叠段2个端部均发生M_S≥6.0地震的比例极小,仅约9%。部分重叠段走向与已经发现的上地幔和地壳高导带埋深走向基本一致,推测重叠异常发生在上地幔和地壳高导带附近,是来自上地幔和地壳内高导带附近的地震异常信息。目前已知,中国大陆强地震主要发生在上地幔高导层的隆起区一带及其壳内高导层发育地区,深部电性测深结果表明,大震易于发生在电导率急剧变化的梯度带,但这些地区何时发生地震还未得知,本文发现的重叠异常解释了这些地区1～2年内是否发生地震这一问题。

A Preliminary Study on Relationship between Induced Current of Geomagnetic Diurnal Variation with Short-term Reproducibility Concentration Distribution and Earthquakes

By calculating the diurnal-variation correlation of the daily geomagnetic vertical component,we have studied the boundary(lines of centrally distributed induced currents from geomagnetic diurnal-variations)between geomagnetic stations with anti-phase variation in the North-South seismic belt of the Chinese mainland from March 1 to October 31 between 2008 and 2018. We identified 23 times of superimposed anomalies that lines of centrally distributed induced currents with superimposed lengths of more than 500km occurred within 16 days. Within 18 months after the superposition,earthquakes above magnitude M_S6 occurred in 20 superimposed sections,leading to a probability of 87% earthquake occurrence. The earthquakes mainly occurred within 250km of the end of the superimposed sections,and one or more superposition may occur before an earthquake. The strike of the superimposed sections is consistent with high-conductivity belts in the upper mantle and crust. It is speculated that these superimposed anomalies are near the high-conductivity zones in the upper mantle and crust,which provides information as earthquake precursor near the high-conductivity zones in the upper mantle and crust. Strong earthquakes in the Chinese mainland mainly occur in areas where the high-conductivity zones in the upper mantle and crust have been uplifted,even though it is still not clear when they will occur at present. It is proposed that the superimposed anomalies may be reliable precursors to strong earthquakes occurring within 1~2 years near the high-conductivity zones in the crust and upper mantle.