ML20137Y554
| ML20137Y554 | |
| Person / Time | |
|---|---|
| Issue date: | 10/01/1985 |
| From: | Zurflueh E NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | Beratan L NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| References | |
| NUDOCS 8510080028 | |
| Download: ML20137Y554 (6) | |
Text
.. . __
t OCT 011335 improved weighting of observed data. For instance, for depth determination nearby stations are critical, whereas for location distant stations are just as good. The resulting program does, however, have less stability than the conventional HYP0 71 algorithm.
Focal mechanisms are being studied with SV/P amplitude ratios. An estimate of probabilistic reliability for the solutions will be added during the next fiscal year. The structure of the Moho is also being studied. Data from the 3-component stations suggest that the Moho has a sharp but undulating surface.
Depending on the station locations, this undulation may give the appearance of multiple layering, which has been proposed as a model for the .
Overall, Georgia Tech's research has produced valuable results, and future research topics promise to provide continued improvement in understanding the relationship between seismicity and crustal structure.
Ernst G. Zurflueh, Geophysicist Seismology Section Earth Sciences Branch, DRPES/RES DIST ESB/RDG ESB SUBJ EZURFLUEH AMURPHY ECONTI F -.. ~
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OCT 011985 MEMORANDUM FOR: Leon L. Beratan, Chief l Earth Sciences Branch, DRPES/RES THRU: Andrew J. Murphy, Section Leader Seismology Section Earth Sciences Branch, DRPES/RES FROM: Ernst G. Zurflueh, Geophysicist Seismology Section Earth Sciences Branch, DRPES/RES
SUBJECT:
REVIEW 0F PROGRAMS WITH UNIVERSITY OF SOUTH CAROLINA, LAW ENGINEERING AND GEORGIA TECH Between September 4 and 6, 1985, I traveled to Columbia, South Carolina, and Atlanta, Georgia, to review NRC-sponsored programs with contractors in these areas. On September 4, I visited with Drs. Pradeep Talwani and Don Colquhoun and some of their graduate students at the University of South Carolina. In view of Dr. Tom Schmitt's departure from the NRC, the purpose of the visit was to become familiar with the work done on the present contract and to discuss possible future work.
Dr. Colquhoun presented an outline of his stratigraphic work in South Carolina which includes a large number of shallow borings with geophysical logs. These data have been used to define details of the coastal plain stratigraphy and to construct structure contour maps. The most significant conclusion reached from the data is that there exists a graben on the coast near Charleston and that the graben is bounded by the Woodstock, Ashley River and Charleston faults.
Releveling data have shown that the graben is a region of continuing subsidence.
Dr. Talwant has collected sizable amounts of gravity data which have been analyzed together with other geophysical data to gain insight into crustal structure and.its relation to seimicity. I obtained a map of gravity coverage by the University of South Carolina and the USGS to avoid duplication with the work to be done under the Law Engineering contract.
Subjects for future research include borings and geophysical investigations along the coast north and south of the graben to establish boundaries and the uniqueness of the graben; releveling and gravity profiles across the Edisto River to determine if it is fault bounded; reprocessing of Seisdata ',ine 4 in 0FC: DRPES/ESB :DRPES/ESB : : : : :
l NAME:Zurflueh/mb :AMurphy : : : : :
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c DATE: / /85 : / /85 : : : : :
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T 01 99I order to enhance reflections below the Jurassic basalt; and analysis of travel time residuals to investigate deeper crustal structure which cannot be resolved by other methods.
On September 5, I met with representatives of Law Engineering in Marietta, Georgia, to discuss the Task 1 report. Representatives of the company and consultants included Mr. Bob White, Mr. John Dwyer, Mr. Sid Brandwein and Drs.
Tim Long of Georgia Tech and James Butler of the University of North Carolina.
Several questions resulting from the Task I report were discussed. The extent of gravity work to be done was more clearly defined based on the map obtained from Dr. Talwani. It was agreed that, although stress modeling is an important part of the project, conventional interpretation of geological and geophysical data will also be given proper weight.
The main question revolved around the magnetotelluric (MT) field work. The plan in the Task 1 report mentions 5-8 stations which is insufficient for the purpose of this work. After some discussion it was agred that 16 MT stations will be measured. As far as equipment is concerned, Law Engineering obtained proposals from Michigan Tech and LBL. LBL's proposal, although technically good, is not very responsive to the needs of this project and is also quite expensive.
Michigan Tech's proposal is more reasonable, and their equipment (similar to LBL's) includes optional remote reference and field processing capability. I explained that the NRC prefers high-quality data, and it was decided that the j remote reference station will be used, even though it will add $5000 to the survey costs. Field processing will permit an instant quality check during the field work and is also a very desirable feature of the equipment.
On September 6, I visited with Dr. Tim Long and graduate students at Georgia Tech to discuss progress on seismic network operations and related studies.
Network operations are progressing, with some stations being converted to 3-component recording. This improvement has permitted, among other things, to record reflections from the Moho. A proposal for digital recording equipment has been submitt"d *o the NRC. Digital recording would permit a substantial improvement in the capability of analyzing seismic data.
Research based on the network data has provided a crustal model for southeastern Tennessee. At present, solutions for the depths of hypoceuters are_ ambiguous because ray tracing pennits a shallow and a deep solution for a given travel time. Recent studies have led to a revised method of location using the_ velocity gradient, which changes sign for different depths, and separating computation of origin time, location and depth, which leads to 0FC: DRPES/ESB :DRPES/ESB : : : : :
NAME:Zurflueh/mb :AMurphy : : : : :
DATE: / /85 : / /85 : : : : :
improved weighting of observed data. For instance, for depth determination nearby stations are critical, whereas for location distant stations are just as good. The resulting program does, however, have less stability than the conventional HYP0 71 algorithm.
Focal mechanisms are being studied with SV/P amplitude ratios. An estimate of
, probabilistic reliability for the solutions will be added during the next i
fiscal year. The structure of the Moho is also being studied. Data from the 3-component stations suggest that the Moho has a sharp but undulating surface.
Depending on the station locations, this undulation may give the appearance of multiple layering, which has been proposed as a model for the .
Overall, Georgia Tech's research has produced valuable results, and future research topics promise to provide continued improvement in understanding the relationship between seismicity and crustal structure.
, Ernst G. Zurflueh, Geophysicist Seismology Section Earth Sciences Branch, DRPES/RES DIST E58/RDG ESB SUBJ EZURFLUEH AMURPHY ECONTI KGOLLER DROSS RMIN0GUE DCRh
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a l OCT 011985 MEMORANDUM FOR: Leon L. Beratan, Chief Earth Sciences Branch, DRPES/RES THRU: Andrew J. Murphy, Section Leader Seismology Section Earth Sciences Eranch, DRPES/RES FROM: Ernst G. Zurflueh, Geophysicist Seismology Section Earth Sciences Branch, DRPES/RES
SUBJECT:
REVIEW 0F PROGRAMS WITH UNIVERSITY OF SOUTH CAROLINA, LAW ENGINEERING AND GEORGIA TECH Between September 4 and 6, 1985, I traveled to Columbia, South Carolina, and Atlanta, Georgia, to review NRC-sponsored programs with contractors in these areas. On September 4, I visited with Drs. Pradeep Talwani and Don Colquhoun and some of their graduate students at the University of South Carolina. In view of Dr. Tom Schmitt's departure from the NRC, the purpose of the visit was to beccme familiar with the work done on the present contract and to discuss possible future work.
Dr. Colquhoun presented an outline of his stratigraphic work in South Carolina which includes a large number of shallow borings with geophysical logs. These data have been used to define details of the coastal plain stratigraphy and to construct structure contour maps. The most significant conclusion reached from the data is that there exists a graben on the coast near Charleston and that the graben is bounded by the Woodstock, Ashley River and Charleston faults.
Releveling data have shown that the graben is a region of continuing subsidence.
Dr. Talwani has collected sizable amounts of g*avity data which have been analyzed together with other geophysical data to gain insight into crustal structure and its relation to seimicity. I obtained a map of gravity coverage by the University of South Carolina and the USGS to avoid duplication with the work to be done under the Law Engineering contract.
Subjects for future research include borings and geophysical investigations along the coast north and south of the graben to establish boundaries and the uniqueness of the graben; releveling and gravity profiles across the Edisto River to determine if it is fault bounded; reprocessing of Seisdata line 4 in i 0FC: DRPES/ESB :DRPES/ESB : : : : :
NAME:Zurflueh/mb :AMurphy : : : : :
DATE: / /85 : / /85 : : : : :
a
_g_ GCT o t mg order to enhance reflections below the Jurassic basalt; and analysis of travel time residuals to investigate deeper crustal structure which cannot be resolved by other methods.
On September 5, I met with representatives of Law Engineering in Marietta, Georgia, to discuss the Task I report. Representatives of the company and consultants included Mr. Bob White, Mr. John Dwyer, Mr. Sid Brandwein and Drs.
Tim Long of Georgia Tech and James Butler of the University of North Carolina.
Several questions resulting from the Task 1 report were discussed. The extent of gravity work to be done was more clearly defined based on the map obtained from Dr. Talwani. It was agreed that, although stress modeling is an important part of the project, conventional interpretation of geological and geophysical data will also be given proper weight.
The main question revolved around the magnetotelluric (MT) field work. The plan in the Task I report mentions 5-8 staticns which is insufficient for the purpose of this work. After some discussion it was agred that 16 MT stations will be measured. As far as equipment is concerned, Law Engineering obtained proposals from Michigan Tech and LBL. LBL's proposal, although technically good, is not vary responsive to the needs of this project and is also quite expensive.
Michigan Tech's proposal is more reasonable, and their equipment (similar to LBL's) includes optional remote reference and field processing capability. I explained that the NRC prefers high-quality data, and it was decided that the remote reference station will be used, even though it will add $5000 to the survey costs. Field processing will permit an instant quality check during the field work and is also a very desirabla feature of the equipment.
On September 6, I visited with Dr. Tim Long and graduate students at Georgia Tech to discuss progress on seismic network operations and related studies.
Network operations are progressing, with some stations being converted to 3-component recording. This improvement has permitted, among other things, to record reflections from the Moho. A proposal for digital recording equipment has been submitted to the NRC. Digital recording would permit a substantial improvement in the capability of analyzing seismic data.
Research based on the network data has provided a crustal model for ,
southeastern Tennessee. At present, solutions for the depths of hypoceuters are ambiguous because ray tracing permits a shallow and a deep solution for a given travel time. Recent studies have led to a revised method of location using the velocity gradient, which changes sign for different depths, and separating computation of origin time, location and depth, which leads to 0FC: DRPES/ESB :DRPES/ESB : : : : :
l .............- ..........................__..............--............--...___ --.......
l hAPE:Zurflueh/mb :AMurphy : : : : :
DATE: / /85 : / /85 : : : : :
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