Skip Links

USGS - science for a changing world

Data Series 901


Southerly view into the crater of Mount St. Helens

Mount St. Helens: Controlled-Source Audio-Frequency Magnetotelluric (CSAMT) Data and Inversions


Skip past contents information
Cover
Introduction
Data Acquisition
GPS Data
EDI Data
Data Processing
Occam Inversions
Fischer Inversions
Marquardt Inversions
References
Index page

Occam Inversions

An Occam inversion generates a smooth model from CSAMT data—one different depth-conductivity value for each frequency (Constable and others, 1987). It is a fast and simple way to get a first look at the conductivity structure beneath a station, but requires a starting layer thickness and conductivity, and it cannot provide a least-squares error or other quantification of the fit. An Occam inversion of CSAMT data is shown in figure 3.

All Occam inversions were done for the TE = XY orientation. Station MSH-1001 is identical to station MSH-1002, and station MSH-1003 is identical to station MSH-1004 (two sets of repeated measurements).

(NOTE: each line is a link to a PDF image).

MSH-1002-OccamInversion

MSH-1003-OccamInversion

MSH-1102-OccamInversion

MSH-1103-OccamInversion

MSH-1104-OccamInversion

MSH-1105-OccamInversion

MSH-1106-OccamInversion

MSH-1107-OccamInversion

MSH-1108-OccamInversion

MSH-1109-OccamInversion

MSH-1110-OccamInversion

Example of an Occam inversion of controlled-source audio-frequency magnetotelluric (CSAMT) data. A, The computer inversion of the data into a resistivity versus depth vertical profile for station MSH-1105. B, The original resistivity data and the inversion model fit for resistivity as a function of measurement frequency. C, The original phase data and the inversion model fit for phase as a function of measurement frequency.

Figure 3. Example of an Occam inversion of controlled-source audio-frequency magnetotelluric (CSAMT) data. A, The computer inversion of the data into a resistivity versus depth vertical profile for station MSH-1105. B, The original resistivity data and the inversion model fit for resistivity as a function of measurement frequency. C, The original phase data and the inversion model fit for phase as a function of measurement frequency.

 

 

 

Accessibility FOIA Privacy Policies and Notices

USA.gov logo U.S. Department of the Interior | U.S. Geological Survey
URL: https://pubs.usgs.gov/ds/0901/occam_inversions.html
Page Contact Information: Contact USGS
Page Last Modified: Monday, November 28, 2016, 08:31:50 PM