HR: 1340h
AN: GP33B-1258    [Abstracts]
TI: Insights into signal and noise in long period MT data from multi-station processing of EarthScope arrays
AU: * Egbert, G
EM: egbert@coas.oregonstate.edu
AF: Oregon State University, College of Oceanic and Atmospheric Sciences, 104 COAS Admin Bldg, Oregon State University, Corvallis, OR 97331-5503, United States
AB: During 2006-2007 long period (10-10000 s) MT data were collected at approximately 100 sites covering Washington and Oregon as part of the EarthScope transportable array experiment. Site occupations in a series of overlapping two dimensional arrays, and the relatively large spacing (75 km) make this a unique data set for studies of signal and noise characteristics in long period MT data, and to explore novel data processing and interpretation strategies. I will present results from applying multiple station array processing methods based on principal component (SDM eigenvector) analysis to a series of small overlapping arrays, each consisting of 5-10 sites operating for 10-15 days. Data quality was exceptional in 2006, and poorer in 2007. Causes of this decline in quality will be explored. Very short spatial scales associated with PC3 pulsations are clearly evident in data from all arrays near a period of 30 s; source effects in MT impedances (but not always in vertical field TFs) are generally negligible at this period. At longer periods (> 1000 s) gradients in the magnetic field, and associated "normal Hz" can be associated with smaller significant coherent signal components. In addition, there are large scale coherent electric fields clearly evident in essentially all arrays at the longest periods. These electric fields scale with the plane wave impedance, and probably reflect galvanic current flows induced at some distance from the local site, and hence not always coherent with local magnetic fields. We will also present results of initial efforts to compute 3D spatial gradient transfer functions, and to construct hypothetical events of the full EM surface fields.
DE: 0910 Data processing
DE: 1515 Geomagnetic induction
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting