Anna Kelbert

Global electromagnetic induction constraints on transition-zone water content variations.

Small amounts of water can significantly affect the physical properties of mantle materials, including lowering of the solidus, and reducing effective viscosity and seismic velocity. The amount and distribution of water within the mantle thus has profound implications for the dynamics and geochemical evolution of the Earth. Electrical conductivity is also highly sensitive to the presence of hydrogen in mantle minerals. The mantle transition zone minerals wadsleyite and ringwoodite in particular have high water solubility, and recent high pressure experiments show that the electrical conductivity of these minerals is very sensitive to water content. Thus estimates of the electrical conductivity of the mantle transition zone derived from electromagnetic induction studies have the potential to constrain the water content of this region. Here we invert long period geomagnetic response functions to derive a global-scale three-dimensional model of electrical conductivity variations in the Earth’s mantle, revealing variations in the electrical conductivity of the transition zone of approximately one order of magnitude. Conductivities are high in cold, seismically fast, areas where slabs have subducted into or through the transition zone. Significant variations in water content throughout the transition zone provide a plausible explanation for the observed patterns. Our results support the view that at least some of the water in the transition zone has been carried into that region by cold subducting slabs.

ModEM: A modular system for inversion of electromagnetic geophysical data

Abstract We describe implementation of a modular system of computer codes for inversion of electromagnetic geophysical data, referred to as ModEM. The system is constructed with a fine level of modular granularity, with basic components of the inversion – forward modeling, sensitivity computations, inversion search algorithms, model parametrization and regularization, data functionals – interchangeable, reusable and readily extensible. Modular sensitivity computations and generic interfaces to parallelized inversion algorithms provide a ready framework for rapid implementation of new applications or inversion algorithms. We illustrate the code׳s versatility and capabilities for code reuse through implementation of 3D magnetotelluric (MT) and controlled-source EM (CSEM) inversions, using essentially the same components.

Methodology for time-domain estimation of storm time geoelectric fields using the 3-D magnetotelluric response tensors

Geoelectric fields at the Earths surface caused by magnetic storms constitute a hazard to the operation of electric-power grids and related infrastructure. The ability to estimate these geoelectric fields in close to real time and provide local predictions would better equip the industry to mitigate negative impacts on their operations. Here, we report progress towards this goal: development of robust algorithms that convolve a magnetic storm time series with a frequency domain impedance for a realistic three-dimensional (3D) Earth, to estimate the local, storm-time geoelectric field. Both frequency domain and time domain approaches are presented, and validated against storm-time geoelectric field data measured in Japan. The methods are then compared in the context of a real-time application.

Science and Cyberinfrastructure: The Chicken and Egg Problem

In September, I participated in a general scientific discussion regarding the U.S. National Science Foundation Directorate for Geosciences (NSF GEO) Priorities and Frontiers 2015–2020 document. One of the key issues raised in conjunction with this document was the issue of science versus infrastructure. Although there was overwhelming agreement on the need for infrastructure to do our science, there was much concern about the corresponding balance of investment.