ML20133F797
| ML20133F797 | |
| Person / Time | |
|---|---|
| Issue date: | 01/22/1982 |
| From: | Arsenault F NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | Ross D NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| Shared Package | |
| ML20132B198 | List: |
| References | |
| FOIA-85-363 NUDOCS 8508080439 | |
| Download: ML20133F797 (2) | |
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JAN 2 21982 MEMORANDUM FOR: D. Ross. Deputy Director Office of Wclear Regulatory Research FROM: Frank J. Arsenault Director Division of Health. Siting, and Waste Panagement Office of Huclear Regulatory Research
SUBJECT:
RELATIONSHIP OF NRC SEISMIC ffETJORKS AND GEOLOGIC RESEARCH TO: JAN. 9 and 11,1982 NEW BRUNSWICK EARTHQUAKES New Brunswick Earthquakes - NRC Roles - The New Brunswick earthanakes of
- January 9 and 11 were major earthquakes which were felt over most of new England and recorded by many worldwide seismic units. They were assigned Richter .
segnitudes 5.9 and 5.5 by the National Earthquake Information Center. Nr. age was slight due to the remoteness of the area. The NRC sponsored seismic networks supplied critical information necessary for evaluation of the seismic risk and understanding of the events. This inforsation includes:
- 1. Background information on seismicity of the area. This was trsportant in that it was established early that the earthouake occurred in an area of pesvious seismic activity. Consequently, while the magnitude was high. it was not a total surprise.
- 2. Detection of the events by fixed and mobile seismic stations. The "!RC seismic networks dete",ed the main events and over one thousand aftershocks.
In addition to preciaely locating the events, this seismic information yielded data that will be used in determining the source mechanism of the earthquakes. This infbreation is vital to establishing the relation-ship between geology and seismicity in the eastern U.S.: a significant open question. .
- 3. Strong motion data. Strong motion instruments were e:rplaced by MRC sponsored teams. Several accelegrams are now available from the after-shock sequences. This is 1sportant because ground motion is critical to the seismic design of nuclear power plants and there is a scarcity of ground motion data in the eastern U.S. The existing ground motion records s indicate that the vibratory ground motion from an earthquake is more
' slowly attenuated than the ground motion from a similar earthquake in the West. The cause of this is not well understood.
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- 4. Licensing Needs. Although the prieary purpose for the seismic network _.
is research on the cause, distribution and size of seismicity in the . ~i llortheast, the network provided infomation of timely importince for the NRC. Within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> of the first earthquake, cocm'unicatlon was Nestablished between RES staff and the investigators on site. ?;RR vgs completely briefed on the event at 8:30 a.m., "onday morning, January ll, and was updated constantly as new information was available.
Replatory Issues and Problems - The New England Seismic ffetworks were established to gain infomation to address regulatory issues.
The design and regulation of nuclear power plants requires knowledge of the severity of ground shaking at a site due to earthquakes. Present procedures estimate vibratory ground motion at a site in the eastern U.S. by correlation of seismicity with tectonic province. The cause of seismicity in the eastern U.S. is not under-stood, and there is significant doubt whether there is a correlation between tectonic province and seismic hazard.
The problem is that due to unknown cause of Eastern seismicity, the uncertainty in ..
the assessment of seismic risk to nuclear power plants is unknown. Of particular importance is the 183G Charleston earthquake. The cause of that event is unknown -
and it is uncertain if it could occur elsewhere in the eastern U.S.
Previous NRC sponsored geologic research in the eastern U.S. bas been largely
{- directed towards attempting to relate earthquakes +4 surface exposed pre-Cenozoic (older than 65 million years) geologic structures. The results suggest that no correlation exists. When ftands become available, future research activities in geology should be directed toward the detemination of causes of the earthquakes through analysis of the active tectonic process involved. Such analysis should include analyses of active crustal strain and stress, the structure of the crust at hypocentral depth in zones of seismicity and the detailed geology in the vicinity of earthquake activity.
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i Frank J. Arsenault, Director Division of Health, Siting, and l
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POLICY ISSUE Unformation)
FOR: The Commissioners FROM:
Executive Director for Operations
SUBJECT:
POSSIBLE RELCCATION OF DESIGN CONTROLLING EARTHQUAKES IN THE EASTERN U.S.
PURPOSE: To provide the Commissi6n'ers with in. formation ~
relating to (1)jossible modiffcation-of the U.S. Geological Survey position on the association of the 1886 Charleston, S.C. earthquake with geologic structure, and (2-)Nthe r.ecant earthquakes in New Brunswick, Canada.
DISCUSSION: In the licensing of facilities in the Southeastern U.S., the NRC has maintained the position,-based on the advice of the U.S. Geological Survey (USGS), that any reoccurrence of the 1886 Charleston, S.C. earthquake (Modified Mercalli Intensity (MMI) X, estimated Magnitude about 7) would be confined to the Charleston area. That is, the Charleston earthquake is assumed to be associated with a geologic structure in the Charleston area. Nuclear power plants in the region east of the Appalachian Mountains are, therefore, usually controlled in their seismic design, according to Appendix A to 10 CFR Part 100, by the maximum historical earthquake not associated with a geologic '
structure. This controlling earthquake._is typically an MMI VII or VIII. Since 1974, tTiE1RC .has funded an extensive research project in the Charleston area to gain further information on the causative mechanism of this event.
On January 28 and 29, the Extreme External Phenomenon Subcommittee of the ACRS convened a meeting of expert professionals in the geosciences to obtain an overview of the state of knowledge and future NRC research needs. During that meeting, we were informed by the
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\ N USGS that they had formed a working group to reassess the validity of their position on the Charleston ' earthquake. They indicated that their tentative position concluded that the reoccurrence of a Charleston-type earthquake should not be con-l sidered unique to the Charleston area. It was further indicated their recommendation would be forwarded to the USGS Director in approximately one month and that a policy decision on the treatment of the Charleston earthquake would be made at the Director's level. .
Any major modification of the former USGS position could have significant impact on many Eastern US nuclear plant sites because Appendix A to 10 CFR Part 100 could require an earthquake of this type, with its resulting high ground motion, to be assumed to occur at any location.
A meeting between the EDO and the Director, USGS, on licensing issues is planned for the near future.
Further information may be available at that time.
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- New Brunswick, Canada, Earthouaker s
On January 9-11, 1982, a series of earthquakes
. occurred in New Brunswick; Canada. The largest of these events was a Magnitude 5.7 earthquake which am occurred on January 9,1982. Because of its remote .
location, no damage was associated with this earthquake.
. In the past, however, events of such size have resulted in MMI VIII. Although all information relating to the size and location of this event is preliminary, it eventually may be concluded that this earthquake could have occurred anywhere within the New England Piedmont Tectonic Province and, in accordance with the Appendix A to 10 CFR Part 100, would represent the ,.
largest historical earthquake in that province. The previous historical maximum earthquake is MMI VII.
This could result in an increase in the size of the controlling earthquake and, therefore, the assumed earthquake ground motion and Safe Shutdown Earthquake for nuclear power plant sites in this region which includes much of New England and southern New York.
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The historical 1755 MMI VIII Cape Ann earthquake, currently used in the design of Seabrook, is related to a diff_erent tectonic province within the White Mountain region of New England. ~
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William J: Dircks Executive Director for Operations -
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