About SPUD

SPUD Version 3.0

The Searchable Product Depository (SPUD) is the IRIS DMC's primary data product management system. Complementing the DMC's SEED and assembled data archives, which contain time series recordings, the SPUD system primarily contains derivative data products of other types (images, movies, etc.) created either at the DMC or by members of the community.

For users SPUD is the query and access point for these products. The web interfaces allow users to search for products using customized queries across product and event details. Users can search across all product types at once or within specific product types. SPUD also has web service interfaces for programmatic discovery and access to the data products.

If any products from SPUD are used in your research please be sure to cite the identified author of the product and the IRIS DMS [Citation Information].

About EM_TF Products

The EMTF data product contains magnetotelluric (MT) transfer functions (TFs), which define the frequency dependent linear relationship between components of electromagnetic (EM) field variations measured at a single site. Two sorts of TF are provided for most sites: 2x2 impedance tensors, and vertical field TFs, which respectively relate horizontal electric and vertical magnetic components (the outputs in the TF relationship) to the horizontal magnetic field vectors (the corresponding inputs).

Note that for some sites only impedances are provided. All of the TFs, which can be justified if external source fields are quasi-uniform (varying over length scales that are long compared to the skin depth), provide input data for subsequent MT inversion and interpretation. They are estimated from the raw EM time series by (a) Fourier transforming data in a series of short overlapping time windows, and (b) applying robust regression methods to the resulting sequence of Fourier coefficients. For remote reference estimates data from a second site are used for noise cancellation, and to reduce bias due to noise in the predicting magnetic channels. Apparent resistivities and phases, which can be computed from the off-diagonal components of the impedance tensors, are frequently used in 2D interpretations. The EMTF data product includes estimates of the TFs for a range of periods (which may vary, depending on instrumentation and deployment time), as well as estimation error covariances.

Citing EM_TF Products

When citing this particular Magnetotelluric Transfer Function, please cite based on the "Citation Info" panel of this page. To cite the Magnetotelluric Transfer Function database at IRIS, please use the instructions at:


EM TF Help

The page displays information for individual Electromagnetic Transfer Functions.

The Transfer Function details are displayed in panels by default and optionally the XML may be viewed in the browser.

Magnetotelluric Transfer Functions (Inactive) icon
Status: Inactive
Sub Type: MT_TF
Description: Magnetotelluric Transfer Functions
Product ID: USArray.GAA56.2015
Tags: impedance,tipper

Citation Info
Survey Reference: Schultz, A., G. D. Egbert, A. Kelbert, T. Peery, V. Clote, B. Fry, S. Erofeeva and staff of the National Geoelectromagnetic Facility and their contractors (2006-2018). "USArray TA Magnetotelluric Transfer Functions". doi:10.17611/DP/EMTF/USARRAY/TA. Retrieved from the IRIS database on Aug 03, 2021
Specific Site Reference: Schultz, A., G. D. Egbert, A. Kelbert, T. Peery, V. Clote, B. Fry, S. Erofeeva and staff of the National Geoelectromagnetic Facility and their contractors (2006-2018). "USArray TA Magnetotelluric Transfer Functions: GAA56". doi:10.17611/DP/15050279. Retrieved from the IRIS database on Aug 03, 2021
Acknowledgements: USArray MT TA project was led by PI Adam Schultz and Gary Egbert. They would like to thank the Oregon State University MT team and their contractors, lab and field personnel over the years for assistance with data collection, quality control, processing and archiving. They also thank numerous districts of the U.S. Forest Service, Bureau of Land Management, the U.S. National Parks, the collected State land offices, and the many private landowners who permitted access to acquire the MT TA data. USArray TA was funded through NSF grants EAR-0323311, IRIS Subaward 478 and 489 under NSF Cooperative Agreement EAR-0350030 and EAR-0323309, IRIS Subaward 75-MT under NSF Cooperative Agreement EAR-0733069 under CFDA No. 47.050, and IRIS Subaward 05-OSU-SAGE under NSF Cooperative Agreement EAR-1261681 under CFDA No. 47.050.
Selected Publications: Schultz, A. (2009). EMScope: a continental scale magnetotelluric observatory and data discovery resource. Data Science Journal, 8, IGY6-IGY20. Meqbel, N. M., Egbert, G. D., Wannamaker, P. E., Kelbert, A., & Schultz, A. (2014). Deep electrical resistivity structure of the northwestern US derived from 3-D inversion of USArray magnetotelluric data. Earth and Planetary Science Letters, 402, 290-304. Yang, B., Egbert, G. D., Kelbert, A., & Meqbel, N. M. (2015). Three-dimensional electrical resistivity of the north-central USA from EarthScope long period magnetotelluric data. Earth and Planetary Science Letters, 422, 87-93.
Release Status: Unrestricted Release
Conditions of Use: All data and metadata for this survey are available free of charge and may be copied freely, duplicated and further distributed provided that this data set is cited as the reference, and that the author(s) contributions are acknowledged as detailed in the Acknowledgements. Any papers cited in this file are only for reference. There is no requirement to cite these papers when the data are used. Whenever possible, we ask that the author(s) are notified prior to any publication that makes use of these data. While the author(s) strive to provide data and metadata of best possible quality, neither the author(s) of this data set, nor IRIS make any claims, promises, or guarantees about the accuracy, completeness, or adequacy of this information, and expressly disclaim liability for errors and omissions in the contents of this file. Guidelines about the quality or limitations of the data and metadata, as obtained from the author(s), are included for informational purposes only.
Site Info
Project: USArray
Survey: Transportable Array
Year Collected: 2015
Name: Griffin Ridge, GA, USA
Elevation: 11.0
Latitude: 31.681602
Longitude: -81.83706
Declination: -5.4
Declination Epoch: 1995.0
Orientation: orthogonal
Angle To GG North: 0.000
Release Status: Unrestricted Release
Acquired By: National Geoelectromagnetic Facility
Data Quality Rating: 5
Data Quality Comments: great TF from 10 to 10000 secs (or longer)
Runlist: GAA56a GAA56b GAA56o GAA56p GAA56q
Start Date: 2015-08-27 14:45:00
End Date: 2015-08-31 18:50:49
Processing Info
Input Channels
Output Channels
Related URLs