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<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US">Dear Josh,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US">Thanks for your response. I take on board the caveats around this data and will consequently treat it with caution.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US">Best wishes,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US">Edward<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> Rigler, Erin (Josh) [mailto:erigler@usgs.gov]
<br>
<b>Sent:</b> 23 February 2016 21:05<br>
<b>To:</b> geomag-data@geohazards.usgs.gov<br>
<b>Cc:</b> Edward Oughton <e.oughton@jbs.cam.ac.uk><br>
<b>Subject:</b> Regional Resistivity<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-family:"Courier New"">Edward,<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-family:"Courier New"">Your recent inquiry to the USGS geomagnetism program was forwarded to me. We are currently transitioning to an email list-serve to help field questions about our operations
and data products, so I hope you won't mind if I CC your question, and my response, to this server. If you want to continue this conversation, or think you may have reason to receive very occasional future emails related to our data products, you might consider
registering yourself: </span><a href="https://geohazards.usgs.gov/mailman/listinfo/geomag-data"><span style="font-family:"Courier New"">https://geohazards.usgs.gov/mailman/listinfo/geomag-data</span></a><span style="font-family:"Courier New"">.<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-family:"Courier New"">With that out of the way, here is my response to your inquiry (copied below):<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-family:"Courier New"">Short answer: we don't have conductivity data available for the regions you mentioned below; for reasons unknown they were not included in the report from which these
data were extracted (i.e., P. Fernberg 2012, </span><a href="http://www.epri.com/abstracts/Pages/ProductAbstract.aspx?ProductId=000000000001026430" target="_blank"><span style="font-family:"Courier New"">One-Dimensional Earth Resistivity Models for Selected
Areas of Continental United States and Alaska</span></a><span style="font-family:"Courier New"">, EPRI Technical Update 1026430, Palo Alto, CA).<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-family:"Courier New"">Longer answer: the data we *do* have are hypothetical 1-D models of conductivity constructed from geological/geophysical research articles published in the past. They
are organized by physiographic provinces that only roughly approximate the geographic bounds of conductivity ("physiographic" pertaining to surface features, *not* the actual underlying geology). Some of the depth-dependent conductivities are measured (e.g.,
using magnetotelluric or magnetic sounding techniques), but most are estimated from knowledge of the underlying geology, and laboratory measurements of the conductivity of similar rock types. These 1-D conductivities, with large uncertainty bounds, should
be considered representative of their region, and not necessarily accurate for any particular location. For this reason, it is not unreasonable to choose a nearby region that *does* have conductivity data to serve as a proxy for a region where it is missing,
especially if there is reason to believe the two regions have similar underlying geology.<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-family:"Courier New"">Long-term plans: We are working to convert magnetotelluric measurements made in the United States' NSF Earthscope program into a self-consistent, and much more physically
realistic, 3-D model of conductivity. There is no firm delivery date for this, but it is probably safe to say it will go public within a 1-2 year time frame, with beta releases somewhat earlier, and regular updates following on.
<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-family:"Courier New"">Thanks for your interest in the USGS Geomagnetism Program.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">Kind Regards,<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-family:"Courier New"">Josh Rigler<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-family:"Courier New""><br>
---------- Forwarded message ----------<br>
From: <b>Edward Oughton</b> <</span><a href="mailto:e.oughton@jbs.cam.ac.uk" target="_blank"><span style="font-family:"Courier New"">e.oughton@jbs.cam.ac.uk</span></a><span style="font-family:"Courier New"">><br>
Date: Sun, Feb 21, 2016 at 10:41 AM<br>
Subject: Regional Resistivity<br>
To: "</span><a href="mailto:geomagdata@usgs.gov" target="_blank"><span style="font-family:"Courier New"">geomagdata@usgs.gov</span></a><span style="font-family:"Courier New"">" <</span><a href="mailto:geomagdata@usgs.gov" target="_blank"><span style="font-family:"Courier New"">geomagdata@usgs.gov</span></a><span style="font-family:"Courier New"">><br>
<br>
<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Dear Sir/Madam,<br>
<br>
I noticed a couple of regional gaps in this data with no model being assigned. This includes:<o:p></o:p></p>
<ul type="disc">
<li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo3">
Northern Rocky Mountains<span style="font-family:"Courier New""><o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo3">
Middle Rocky Mountains<span style="font-family:"Courier New""><o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo3">
Wyoming Basin<span style="font-family:"Courier New""><o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo3">
Southern Rocky Mountains<span style="font-family:"Courier New""><o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo3">
Ozark Plateaus<span style="font-family:"Courier New""><o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo3">
Ouachita<span style="font-family:"Courier New""><o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo3">
Interior low plateaus<span style="font-family:"Courier New""><o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo3">
Eastern Maryland, Delaware and New Jersey<span style="font-family:"Courier New""><o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo3">
Northwest Massachusetts, Vermont, New Hampshire and Northern Maine<span style="font-family:"Courier New""><o:p></o:p></span></li></ul>
<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:12.0pt">Is this because we don't have data available for these locations, or do they serve some sort of baseline?
<br>
<br>
Any help would be very much appreciated. <br>
<br>
Thanks and best wishes,<br>
<br>
<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:10.0pt;font-family:"Courier New"">Edward</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:10.0pt;font-family:"Courier New""> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:10.0pt;font-family:"Courier New"">--
</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:10.0pt;font-family:"Courier New"">Dr Edward J. Oughton
</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:10.0pt;font-family:"Courier New"">Senior Risk Researcher</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:10.0pt;font-family:"Courier New"">Centre for Risk Studies</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:10.0pt;font-family:"Courier New"">Judge Business School</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:10.0pt;font-family:"Courier New"">University of Cambridge</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New"">T: +44 (0) 7920 401 571</span><span style="font-family:"Courier New""><o:p></o:p></span></p>
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-- <o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">E. Joshua Rigler</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">Research Geophysicist</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">Geomagnetism Program</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">U.S. Geological Survey</span><o:p></o:p></p>
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