HR: 10:50h
AN: GP32A-03    [Abstracts]
TI: Analysis and 3-D inversion of EarthScope magnetotelluric data : some preliminary results
AU: * Patro, P K
EM: patro@coas.oregonstate.edu
AF: National Geophysical Research Institute, Uppal Road, Hyderabad, AP 500007, India
AU: * Patro, P K
EM: patro@coas.oregonstate.edu
AF: Oregon State University, 104 COAS Administration Building, Corvallis, OR 97331, United States
AU: Egbert, G D
EM: egbert@coas.oregonstate.edu
AF: Oregon State University, 104 COAS Administration Building, Corvallis, OR 97331, United States
AU: Kelbert, A
EM: anya@coas.oregonstate.edu
AF: Oregon State University, 104 COAS Administration Building, Corvallis, OR 97331, United States
AB: As part of the EarthScope project in 2006-07 approximately 100 long period (5-15000 s) magnetotelluric (MT) sites were occupied covering Oregon and Washington. In contrast to traditional MT surveys where sites are concentrated along one or a few profiles, in the EarthScope project sites have been occupied on a quasi-uniform 75 km grid. Both the site distribution, and the wide station spacing covering a wide range of geologic environments such as subduction zone at the coast, cascade volcanoes, columbia plateau, high desert into the basin and range demand three-dimensional (3D) inversion and interpretation. Here we present preliminary efforts in this direction. The MT data, which were collected in a series of overlapping arrays, were processed using robust remote reference and multi-station codes to derive MT impedances, along with vertical and interstation transfer functions. We present maps of these transfer functions (i.e., hypothetical events, induction vectors), along with results from distortion, dimensionality, and phase tensor analysis. We also present results from initial 3D inversions of all the four measured tensor components, carried out using the data-space Occam inversion code of Siripunvaraporn et al. (2004). This inversion poses a challenge in terms of the substantial computational resources required for inversion of a data set of this size. One strategy we are trying, and will discuss, is to focus on inversion of data from a reduced number of frequencies, chosen from studying the frequency dependence of induction vectors. Higher error floor was assigned to the static shifted apparent resistivities compared to their phases. This helps in downweighting the apparent resistivities with respect to the phases which in turn reduce the influence of static shifts. Preliminary interpretations based on the inversion results, together with the hypothetical event, induction vector, and phase tensor maps, and results from previous experiments in this area will be presented.
DE: 0600 ELECTROMAGNETICS
DE: 0905 Continental structures (8109, 8110)
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 9350 North America
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting