Joint Inversion Of Electromagnetic Data Research Articles

Joint Inversion of Daily and Long‐Period Geomagnetic Transfer Functions Reveals Lateral Variations in Mantle Water Content

AbstractWe present a novel approach to investigate variations in upper mantle and transition zone (MTZ) water content based on the joint analysis of electromagnetic (EM) signals originating in the ionosphere and magnetosphere. We invert EM signals (period range 6 hr to 85 days) to probe the electrical conductivity structure underneath 20 geomagnetic observatories, accounting for the complex spatial structure of the ionospheric and magnetospheric sources. The joint inversion of EM data for the daily and long‐period bands leads to significantly improved resolution in the upper mantle and MTZ. The conductivity profiles reveal significant lateral variability, which we interpret in terms of mantle water content by coupling electrical conductivity with constrains on mantle thermochemical structure derived from the analysis of seismic data. Our results suggest the existence of a relatively dry MTZ beneath Europe and a water‐enriched MTZ underneath North America and northern Asia.

Potential to map soil salinity using inversion modelling of EM38 sensor data

Soil salinization limits agricultural productivity and can ultimately cause desertification and land abandonment. Traditionally soil salinity is assessed using soil sampling methods for laboratory determinations. These are not representative of soil properties at management scales and are highly time and work consuming, resulting in costly surveys. Recent research is revolutionizing how soil information can be obtained quickly and cheaply by using a state-of-the-art electromagnetic (EM) instrument and inversion techniques in conjunction with soil sampling results to generate high-resolution effective conductivity models and soil salinity maps. In this study, located in Leziria Grande, Portugal, an EM survey was performed at an experimental site to map the spatial variability of soil salinity. EM data were collected using an EM38 instrument deployed at different heights and orientations. The conductivity model obtained from joint inversion of EM data shows a high correlation with conductivity data from soil sampling. This has permitted the rapid development of a model of soil salinity.

New geoelectrical characterization of a continental collision zone in the Central – Eastern Pyrenees: Constraints from 3-D joint inversion of electromagnetic data

Continent-continent collisions are responsible for the formation of large mountain ranges like the Himalayas and the Alps and play a primary role in the development of the continents. The continental collision between the Iberian and European plates during the Alpine Orogeny resulted in the formation of the Pyrenees. In this study new electromagnetic data from the Eastern Pyrenees were complemented with older data from the Central Pyrenees, constraining the physical and geological processes at the eastern end of the Pyrenean mountain range. The electrical resistivity distribution beneath the Central-Eastern Pyrenees was characterized by means of three-dimensional (3-D) joint inversion of three electromagnetic datasets: (1) the MT impedance tensor (Z), (2) the geomagnetic transfer function (T), and (3) the inter-station horizontal magnetic transfer function (H). The main finding was the non-continuity to the east of the major conductive anomaly observed previously beneath the Central and West-Central Pyrenees related to partial melting of the Iberian subducted lower crust. Lower amounts of water (related to the presence of muscovite and biotite) in the subducted lower crust beneath the Eastern Pyrenees were suggested to explain the lack of partial melting in this part of the mountain range. The electrical resistivity model also revealed higher electrical resistivity values for the lithospheric mantle beneath the Eastern Pyrenees than beneath the Central Pyrenees, thus supporting the hypothesis of an heterogeneous Iberian plate inherited from the Variscan Orogeny. A less clear signature was the lateral variation along the strike direction of the lithosphere-asthenosphere boundary beneath the Eastern Pyrenees (relatively flat, between 110 km and 140 km depth) and the Central Pyrenees (north dipping, between 80 km and 120 km depth beneath the Iberian Plate and between 110 km and 160 km depth beneath the European plate), supporting the hypothesis of a missing lithospheric root beneath the Eastern Pyrenees.