Magnetotelluric characterization of a salt diapir: a case study on Bicorb–Quesa Diapir (Prebetic Zone, SE Spain)

The availability of geophysical data to determine the geometry at depth of a salt diapir and its surrounding structure is essential because of the complexity and changing geometry of these structures. For this purpose, potential field methods are commonly the first steps in subsurface exploration whereas seismic techniques are applied in later stages. However, the magnetotelluric method (MT) may fill the gap between the precision and the time that these two methods entail. To prove the usefulness of the MT method, it has been applied to the Bicorb–Quesa Diapir. This diapir is composed of evaporitic rocks piercing an overburden of carbonate rocks, providing a wide and contrasting range of electrical resistivity values. In this situation, the MT method may provide a coherent and realistic image of the subsurface. The application of the MT method has allowed us to (1) recognize a basement fault with a vertical throw of 1000 m, (2) elucidate the shape of the diapir, which is asymmetrical, with a north wall vertical and south wall dipping southwards, and (3) determine that all of the Late Triassic salt is concentrated in the diapir core.

由于盐底辟（salt diapir）及其围限构造的形态复杂且多变，获取地球物理数据以确定其深部几何形态至关重要。为此，地下勘探通常先采用位场法，后续阶段再开展地震勘探技术。然而，大地电磁法（magnetotelluric method, MT）恰好可以填补这两种方法在精度与耗时之间的缺口。为验证大地电磁法的实用性，研究团队将其应用于比科尔普-克萨盐底辟（Bicorb–Quesa Diapir）。该盐底辟由刺穿碳酸盐岩覆盖层的蒸发岩构成，其电阻率值跨度大且差异显著。在此类场景下，大地电磁法可获取连贯且贴合实际的地下结构图像。通过开展大地电磁法勘探，研究团队得以：(1) 识别出垂直落差达1000米的基底断层；(2) 阐明该盐底辟的非对称形态——北壁直立，南壁向南倾斜；(3) 确定所有晚三叠世盐岩均富集于盐底辟核部。