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:

http://ds.iris.edu/ds/products/emtf/#citation


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.
Imnaging the Clear Lake Volcanic System icon
Identification
Sub Type: MT_TF
Description: Imnaging the Clear Lake Volcanic System
Product ID: USGS-GMEG.2022.cl306
Tags: impedance, tipper


Citation Info
Survey Reference: J. Peacock, M. Mitchell, B. Dean, S. Burgess (2022). "Magnetotelluric data for investigating the Clear Lake Volcanic Field, northern California". doi:10.17611/DP/EMTF/GMEG/Clearlake. Retrieved from the IRIS database on May 13, 2026
Specific Site Reference: J. Peacock, M. Mitchell, B. Dean, S. Burgess (2022). "Magnetotelluric data for investigating the Clear Lake Volcanic Field, northern California: cl306". doi:10.17611/DP/22141343. Retrieved from the IRIS database on May 13, 2026
Acknowledgements: This project was funded by the U.S. Geological Survey Volcano Hazards Program.
Selected Publications:
Release Status: Data Citation Required
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 this data set is cited as the reference. While the author(s) strive to provide data and metadata of best possible quality, neither the author(s) of this data set, not 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: USGS-GMEG
Survey: Clearlake
Year Collected: 2022
ID: cl306
Name: Clearlake, CA, USA
Elevation: 400.143
Latitude: 39.083637
Longitude: -122.68393
Declination: 13.48
Declination Epoch: 2020
Orientation: orthogonal
Angle To GG North: 0.000
Release Status: Data Citation Required
Acquired By: U.S. Geological Survey
Data Quality Rating: 4
Data Quality Comments: Power lines
Runlist: cl306a
Start Date: 2022-07-12 00:00:00
End Date: 2022-07-13 16:05:09
Processing Info
Input Channels
Output Channels
Data
Attachments
Contributions