Re: Re: [geonet] Depth to source methods

[edcunion <edcun...@yahoo.com>]

Some examples of usgs  mag-grav depth determination results are illustrated  from a handful of Jeff Phillips papers on these methods. These are available as pdfs from different web sources. I've used older manual graphical rule of thumb methods as crosschecks on these using a profile or two usually for larger aeromag datasets.   Ed Cunion    Sent from my T-Mobile 4G LTE device     ------ Original message------ From: Dhananjay Ravat Date: Fri, 5/1/2015 11:21 AM To: Geosoft Oasis montaj and Target; Subject:Re: [geonet] Depth to source methods   Hi,  I presume all the potential field books have been looked into for methodological details and a lot of useful advice. This article below, and references therein, is a good place to start for the Euler method, if not already read.  For inclined contacts 2D analytical signal, carefully paying attention to Misac Nabighian’s (1972, 1974 Geophysics) use for thin sheets and trapezoids expressions and when to use anomaly and when to use its gradient will be helpful, and also the bell-shaped 2D analytic signal and their depth relationships will be helpful in determining parameters of interest. I know those papers have a lot of math, but I have found it very worthwhile struggling through that to understand what and why. Finally, in window based methods, there will always be a tradeoff between the size of the window, resolution, and noise in the data.  Similarly, noise in the data vs the use of methods that require higher order derivatives should be a consideration as I am sure you know.  I have found it useful to compare results from compatible methods as you are doing.   I hope this is useful. Best wishes, -tiku   GEOPHYSICS, VOL. 79, NO. 4 (JULY-AUGUST 2014); P. J61–J66, 3 FIGS., 1 TABLE. 10.1190/GEO2013-0235.1 The structural index in gravity and magnetic interpretation: Errors, uses, and abuses by Alan B. Reid1 and Jeffrey B. Thurston2  _____________________________ D. Ravat | Professor of Geophysics  Earth & Environmental Sciences | Physics & Astronomy University of Kentucky 101 Slone Research Building | Lexington, KY  40506-0053 fax: +1 859 323 1938  Web:  http://ees.as.uky.edu/users/drava2 https://www.researchgate.net/profile/Dhananjay_Ravat/ https://ees.as.uky.edu/gravity-magnetics-heat-flow-tectonics https://ees.as.uky.edu/near-surface-geophysics _____________________________ On May 1, 2015, at 12:25 PM, Doug Perkin <doug.j.per...@gmail.com> <geonet@lyris.geosoft.com> wrote: Hi I have been trying various source depth estimation methods for grids of potential field data and wanted to start a discussion on which methods tend to provide better solutions for gravity vs aeromag.  I am usually interested in sub vertical or dipping contacts, so for magnetics I have tried a structural index of 0 or 1 and for Gravity I have tried 0 and -1 using the USGS special function depth analysis GX.  I have also tried Euler with various window sizes. The local wavenumber method using the USGS GX was interesting because it actually provides estimates of the structural index for various anomalies; however that method tended to give a lot more noise and was in places giving me a structural index of 3 when the RTP grid clearly did not look like a magnetic dipole source. Does anyone have experience with these depth estimation methods?  Which methods tend to give more reliable solutions for a vertical or dipping contact using aeromag?  And which methods tend to provide better solutions for a vertical or dipping contact using gravity?  Any advice or discussion on these methods would be much appreciated Regards, Doug     --- Forum archives can be accessed here: http://lyris.geosoft.com/read/?forum=geonet You are currently subscribed to geonet as: dhananjay.ra...@uky.edu. To subscribe or unsubscribe from any of our forums, select the User Forum selection on the Geosoft Community page: http://www.geosoft.com/support/community/forums/register/ --- Forum archives can be accessed here: http://lyris.geosoft.com/read/?forum=geonet You are currently subscribed to geonet as: edcun...@yahoo.com. To subscribe or unsubscribe from any of our forums, select the User Forum selection on the Geosoft Community page: http://www.geosoft.com/support/community/forums/register/ --- Forum archives can be accessed here: http://lyris.geosoft.com/read/?forum=geonet You are currently subscribed to geonet as: arch...@mail-archive.com. To subscribe or unsubscribe from any of our forums, select the User Forum selection on the Geosoft Community page: http://www.geosoft.com/support/community/forums/register/