(加拿大多倫多大學(xué)物理系， Toronto, M55 1A7, Canada)
摘 要: 對(duì)近十年來發(fā)展起來的海底電磁法作了綜述，重點(diǎn)放在可控源時(shí)間域上。類似于航空電磁法可對(duì)陸地上的經(jīng)濟(jì)帶進(jìn)行電導(dǎo)率填圖一樣，可控源海底電磁法也可在數(shù)十米的范圍內(nèi)對(duì)海底進(jìn)行電導(dǎo)率填圖。海底的電導(dǎo)率通常遠(yuǎn)小于海水的電導(dǎo)率，理論研究表明可控源時(shí)域水平電偶極子及水平磁偶極子系統(tǒng)能用來精確地確定海底的電導(dǎo)率。這兩種裝置對(duì)兩個(gè)半空間的響應(yīng)會(huì)在時(shí)間軸上出現(xiàn)兩個(gè)峰值。早期的第一個(gè)峰值在時(shí)間軸上的位置可以直接用來確定海底的電導(dǎo)率，代表了電磁波在海底的傳播；而晚期的第二個(gè)峰值代表電磁波在海水中的傳播，亦可用來確定海水的電導(dǎo)率。該文概述了可控源時(shí)域海底電磁法理論方面的主要研究成果， 同時(shí)也討論了海底電磁法的儀器設(shè)備，特別介紹了多倫多大學(xué)物理系研制的時(shí)域水平磁偶極子及水平電偶極子海底觀測(cè)系統(tǒng)。這些設(shè)備在淺海及洋中脊附近深海中的試驗(yàn)結(jié)果也在文中作了討論。
關(guān)鍵字: 可控源 時(shí)間域 電磁系統(tǒng) 海底電導(dǎo)率填圖
（Department of Physics, University of Toronto, Toronto, Ontario, M5S 1A7, Canada）
Abstract:A review of recently developed marine electromagnetic methods with special attention focused on the time-domain has been made. The objective of the methods is to map the electrical conductivity of the sea floor over scale of several tens of meters. The methods are to the sea floor what the airborne EM methods are to the economic zone of the continental crust . The electrical conductivity of the sea floor is usually much less than that of the seawater above it. A theoretical study of the transient step-on responses of some common controlled-source, electromagnetic systems to adjoining conductive half-dipole and horizontal, in-line, electric dipole-dipole, are capable of accurately measuring the relatively low conductivity of the sea floor. The step response of those two systems to a double half-space model has two distinct parts. The position in time of the initial transient, due to diffusion of EM field in the sea-floor, is indicative of the conductivity of the sea floor, while at distinctly later times, a second characteristic of the transient is a measure of the seawater conductivity, implying the propagation of EM wave in the seawater. Major results of theoretical studies on the time-domain marine EM methods are summarized. Marine EM instrumentation, especially the time-domain horizontal magnetic dipole-dipole system and horizontal electric dipole-dipole system which were designed and constructed in the Department of Physics of the University of Toronto, is given with applications to geotechnical studies on the shelf and deep ocean surveys near the mid ocean ridges.
Key words: controlled source time-domain EM systems sea-floor conductivity mapping
