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长周期大地电磁(LMT)是基于常规MT理论发展起来的电磁测深技术,青藏高原东部岩石圈较厚、视电阻率较低,应用LMT方法能够弥补常规MT仪器对低频信号响应的不足,获得有用的深部信息。文中概述了LMT的数据采集、处理及反演解释,并介绍了将LMT应用于东喜马拉雅构造结及其周围地区完成的长周期观测剖面——下察隅—玉树LMT剖面的岩石圈结构探测实例。实际观测表明,在重叠频段内LMT结果与常规MT具有良好的一致性;LMT数据处理实现的阻抗和倾子估计,在深部信息上具有更高的分辨率。LMT剖面结果揭示了青藏高原东部普遍存在地下低阻体,为局部地区部分熔融和地下流体存在的可能性提供了依据。LMT测深较好地弥补了常规MT方法在巨厚岩石圈和遇到低阻体时探测深度的局限性。
The long-period earth magnetotelluric (LMT) is an electromagnetic sounding technique developed based on the conventional MT theory. The lithosphere is thick and the apparent resistivity is low in the eastern part of the Qinghai-Tibetan Plateau. Applying the LMT method can make up for the shortcomings of conventional MT instruments in response to low frequency signals. Useful deep information. In this paper, the data acquisition, processing and inversion interpretation of LMT are summarized. The application of LMT to the long-period observation section completed in East Himalayan structural knot and its surroundings . The actual observations show that LMT results are in good agreement with conventional MTs in overlapping bands and that the impedance and pips estimates achieved by LMT data processing have higher resolution in deep information. The results of LMT reveal that underground low resistivity bodies are common in the eastern Tibetan Plateau, which provides a basis for the possibility of partial melting and subsurface fluid in some areas. LMT sounding better make up for the limitations of the conventional MT method in detecting the depth of thick lithosphere and low resistance body encountered.