ANOMALIES OF SHORT-PERIOD GEOMAGNETIC VARIATIONS AND DISTRlBUTION OF HIGH CONDUCTIVITY LAYER IN THE

• 作 者: 祁贵仲 詹志佳 侯作中 范国华 王志刚 白彤霞
• 机 构: Institute of Geophysics, State Seismological Bureaurrrrrrrrn,Institute of Geophysics, State
• 出 处: Science in China,Ser.B
• 发表日期: 1982年02期
• 关键词: Bohai uplift generating mantle minutes margin sudden attempt quake disturbed

In this paper, analyses of short-period geomagnetic events such as sudden commencementand geomagnetic bay, together with some quiet day, disturbed day and geoinagnetic stormvariations, recorded at 25 repeat stations in the Bohai Sea area during the years 1973--1979are presented. It is found that there are anomalies of short-period variations in this areaincluding the Tangshan earthquake region, and that local anomalies with periods rangingfrom 5 minutes to 2 hours along the Changli- Tangshan-Ninghe-Baodi belt (positive △Z ) andat Yantai (negative △Z) are most obvious. By applying the numerical theory of three-dimensional electromagnetic induction, an attempt is made to fit these anomalies to the struc-ture of high electrical conductivity in the upper mantle. The result brings to light an upliftof high conductivity layer, at the northern margin of which the Tangshan earthquake islocated. The additional thermal stress due to such an uplift calculated to amount to a thou-sand of bars may be an important possible source of generating force for the Tangshan earth-quake.

In this paper, analyzes of short-period geomagnetic events such as sudden commencement and geomagnetic bay, together with some quiet day, disturbed day and geoinagnetic stormvariations, recorded at 25 repeat stations in the Bohai Sea area during the years 1973--1979 have presented. It is found that there an anomalies of short-period variations in this are ancillary to the Tangshan earthquake region, and that anomalies with periods ranging ranging from 5 minutes to 2 hours along the Changli- Tangshan-Ninghe-Baodi belt (positive △ Z) andat Yantai △ Z) are most obvious. By applying the numerical theory of three-dimensional electromagnetic induction, an attempt is made to fit these anomalies to the struc-ture of high electrical conductivity in the upper mantle. The result brings to light an uplift of high conductivity layer, at the northern margin of which the Tangshan earthquake islocated. The additional thermal stress due to such an uplift calculated to amount to a thou-sand of bars may be an important possible source of generating force for the Tangshan earth-quake.