OCGC Seminar - Water Content and Processes in Complicated Subduction Settings as Inferred with Electromagnetic Methods


Dr. Anna Kelbert  
College of Earth, Ocean and Atmospheric Sciences, Oregon State University 


Thursday, April 9th, 2015
11:30 a.m.  

233 Advanced Research Complex (ARC) 
University of Ottawa  



Natural source electromagnetic induction methods in geophysics include the local to regional scale magnetotelluric method, and the global to semi-global electromagnetics. Introduced in 1950-s, these methods have rapidly developed in the past 20 years to produce high resolution 3D images of the electrical conductivity in the Earth¹s crust and upper mantle. Electrical conductivity is most sensitive to the presence of fluids and partial melts, and therefore provides a view that¹s highly complementary to the seismic wave velocities. In this talk, I aim to introduce the methods through a tour of one of their most useful deep Earth applications: complicated subduction zone regions. I make use of the versatility of our techniques to look at subduction zones, globally, through the lens of electrical conductivity images; then zoom in to regional scales. I give an overview of electromagnetic constraints on the Philippine Sea plate subduction beneath China and Japan; the Nazca and Cocos plate subduction in South and Central Americas; and finally the younger subduction in North America, as imaged by EarthScope MT and the earlier studies. Throughout my brief global tour I try to show that electromagnetic inversion images the slabs and the associated volcanic arcs in a geophysically consistent manner that complements the seismic results, while adding independent and valuable information on the water content and the associated subduction-related processes.