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October 25, 1977 Mr. Edson G. Caso, Acting Director Scrlal No. 463 Office of Nuclear Reactor Regulation PSECC/l!UBJ r:bcb Attention:
Mr. J. F. Stolz, Chief Dockot Hos: 50-330 Light 11ater Reactors Dranch llo.1 50-339 Division of Project Manageront 50-404 U. S. huclear Regulatory Commission 50-405 Washington, D. C.
20555
Dear Mr. Case:
This letter is in rcsponse to a telephonc request by Dr. Reiter on Septenber 26, 1977 for additional Information pertaining to a report titled "A SEISMIC P.0:ilTORING FROGRAM AT THE t10RTil Alit:A SITE 111 CENTRAL VIRGilll A - JAilVARY 21,.1974 Tt! ROUGH AUGUST 1,1977," which was forwarded to you on September 13, 1977 !,y our letter Scrial No. 393.
Dr. Rei ter requested two items of additional Inforo.ation:
1.
Hypocentor location error.. estimates, and 2.
A composite figure showing all events recorded on a map which also showed the geology.
As explained to Dr. Reiter, hypocenter error estimates are pro-vided in chapters 11 and til of the report in Tables 1-11, 2-11, 3-11, 5-11, 6-11, 1, 2, 3, 5, 6, and 7 under the colunns noted "tRH/ERZ." These values of standard error are calculated by the "IlYPD-71" computer program.
Forty (40) copics of a floure titled " REGIONAL EPICEtiTER MAP, PERIOD: JANUARY 21,1974, T;ll'.0VCil AUGUST 1,1977" arc enclosed for your This figure shows the geology and all locatable events recorded uso.
within tac prescribed five second S-P Intcryal
(-451,m of station no.1).
!!ont toring of events outsido the 45 len radius has never been a notwork requirencnt.
Some locatable events in the 45 to 100 kn rango fron stration number 1 were recorded by our network as well as others.
Theso events are shown only to give a comparison of regional activity.
8500220518 850722 FOIA PDR PDR BELL 85-363
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Mr. Edson G. Casa 2
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As shown on Figure 5 In Chapter 111 of the above referenced report, the outermost network stations are approximately ten (10) miles frora the power station.
Locatability of events diminishes beyond these stations. This is rest notable in lower 1cvel activity (it<1.0).
Thus you will notice the lack of lesser nagnitude events with Increased illstance from the site. This should neither be construed as a lack of activity beyond the network boundary, nor a confineraent of activlty with-f in the network.
The location of these very low icyc1 events where possible has been shown voluntarily by Vepco, and has not been a requirenont of the-NRC.
If we can be of any further assistance In your review of this Infonution, please contact us.
Very truly yours, cc.ui S,:-s v,!
S, C. EROWN JK.
Sam C. Brown, Jr.
Vice President
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. Power S tation Engineering and Construction e
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