ML20140C296

Discusses Review of Seismic Reflection Data for Facility. Data & Applicant Interpretation Described in Harding Lawson Assoc 851030 Rept, Interpretation of Geophysical Data.... Interpretation Correct & Only Faults a & I May Surface

ML20140C296
Person / Time
Site:	South Texas
Issue date:	03/11/1986
From:	Zurflueh E NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES)
To:	Brocoum S Office of Nuclear Reactor Regulation
References
NUDOCS 8603250315
Download: ML20140C296 (6)

Text

.. - . -- _ . . ..- -

~

, GAR 11 1333 4 MEMORANDUM FOR: Stephan J. Brocoum i Senior Reliability and Risk Analyst Reliability and Risk Assessment Branch Division of Safety Review & Oversight, NRR FROM: Ernst G. Zurflueh, Geophysicist Earth Sciences Branch Division of Radiation Programs &

Earth Sciences, RES

SUBJECT:

REVIEW 0F SEISMIC REFLECTION DATA FOR THE SOUTH TEXAS PROJECT i

! In accordance with your request, I have reviewed seismic reflection data for j '

the South Texas Project. The data and the applicant's interpretation are described in a report by Harding Lawson Associates (HLA) - issued on October l 30, 1985, and entitled " Interpretation of Geophysical Data, South Texas Project, Houston Lighting and Power."

! The description given in the HLA report seems to be correct in general, except l for minor differences in interpretation that could be postulated. A j significant conclusion of the report is that there are two faults, designated A

and I, that come close to the surface. Although the report only lists the shallowest fault picks and does not describe the possible extent of these faults towards the surface, the applicant stated during a meeting on October 23, 1985 that, for the purposes of the FSAR, it will be assumed that those two faults extend to the surface.

It is my conclusion that the shallowest fault picks given by HLA for faults A i

and I are indeed correct. However, suggestions of even shallower faulting can be found on the seismic records, and the assumption that they may go through to the surface should definitely be used in considering the site. In this respect I would like to remark, although this is not the central theme of this rev!ew, that I cannot disagree with the assumption stated by the applicant in the October meeting, that a magnitude 4 earthquake is the maximum hazard that can be expected from movement on one of these faults. This is based on the observed seismicity of the gulf coast, which has produced only two earthquakes with a magnitude of 3.5.

A second form of hazard that results from the presence of these faults is

surface displacement. For instance, fault I crosses the area proposed for the l l cooling pond. However, given an approximate surface trace of the fault from l the seismic data, it should not be difficult to design the embankments of the  !

l I

' 8603250315 860311 PDR ADOCK 05000498

A PDR

- . - - - _ . . - . _ - - - - . . , . . ~ - . - , , . __ _ _ , . - _ _ . . . . _ . _ - _ . - - - _ ~ - . . .

,,,.-.=

l Stephan J. Brocoum 2 g ;J pond so that they will safely accommodate both anticipated seismic motion and a small vertical offset along the fault (if loss of coolant is critical). For comparison, several earth- or rockfill dams of considerable height have been designed and built to accommodate such hazards.

The next shallowest fault, J, appears to be capped at about 3850' as stated in the HLA report. There are indications of possible additional faults not shown on the HLA interpretations, but all of those faults would also be capped at considerable depth, if indeed they exist. Therefore, these possible additional faults do not pose a hazard to the plant.

Following are some more detailed comments on the analysis of the seismic data:

Fault A is most clearly seen on lines Jaecon 2M, 4M and GUS-A. The shallowest clear indication of faulting is at 0.16s or 490' depth as described in the HLA report. Indications of possible faulting can be found as shallow as 0.11s or at a depth of 310', and on the GUS-A line there are suggestions that the fault may continue upward towards the surface. Given the applicant's position that the fault is assumed to go through to the surface, this interpretation does not affect the status of the site.

Fault I is found on lines Jaecon 2M and Conoco 3. On line 2M clear fault indications are visible up to about 0.3s or 915' depth. No capping layers can be found, and possible changes in layering along the fault trace can be seen closer to the surface. Therefore, the assumption that fault I may continue to the surface seems reasonable.

A fault that is subparallel to fault I and about one mile north of it can also be seen on lines Jaecon 2M and Conoco 3. The fault may be designated fault I';

it has an ESE trend and extends to approximately 1.45s or 5450' depth. Line 2M shows that the fault is capped at this level, and the fault must be considered inactive. Conoco line 3 shows less definite information on capping of this fault, but this line does not have good shallow data.

Other faults can be inferred at various locations, but none of these possible faults are significant in that, if they exist, they all terminate at depths of several thousand feet.

In sumary, the HLA interpretation is essentially correct, and faults A and I are the only ones that may continue to the surface. The fault locations, shallowest picks and offsets identified by HLA are approximately correct; minor variations in interpretation are possible. Indications of possible faults in

r "t Y Stephan J. Brocoum 3 MAR 11 195 addition to those interpreted by HLA can be found, but these faults do not extend to the surface, are clearly inactive, and therefore pose no hazard to the site.

Ernst G. Zurflueh, Geophysicist Earth Sciences Branch Division of Radiation Programs &

Earth Sciences, RES cc: F. Congel J. Rosenstiel G. Giese-Koch P. Kadambi Distribution /R-2811:

Circ /Chron RMinogue Econti DCS/PDR Dross LBeratan ESB Sbj/Rd KGoller AMurphy EZurflueh

'~ ~ - . ~ . _ . , .

1 # 1. . ~ '4 f

.k I_

~

~

~

5 i ii ._y;,, .

G -..._..__._$

~..

~ ~

~

ESB:RES:pf ESB:RES ESB:RES g l EZurflueh AMurphy LBeratan ld[J..i j"] 'I -

h__ j

'? / // /86 S At 86 3 //l /86 -

-l gr n

g;T 11 G 3 MEMORANDUM FOR: Stephan J. Erocoum Senior Reliability and Risk Analyst Reliability ed Risk Assessment Branch Division of Safety Review & Oversight, NRR FROM: Ernst G. Zurflueh,-Geophysicist Earth Sciences Branch Division of Radiation Programs &

Earth Sciences, RES

SUBJECT:

REVIEW 0F SEISMIC REFLECTION DATA FOR THE SOUTH TEXAS PROJECT In accordance with your request, I have reviewed seismic reflection data for the South Texas Project. The data and the applicant's interpretation are described in a report by Harding Lawson Associates (HLA) - issued on October 30, 1985, and entitled " Interpretation of Geophysical Data, South Texas Project, Houston Lighting and Power."

The description given in the tiLA report seems to be correct in general, except for minor differences in interpretation that could be postulated. A significant conclusion of the report is that there are two faults, designated A and I, that come close to the surface. Although the report only lists the shallowest fault picks and does not describe the possible extent of these faults towards the surface, the applicant stated during a meeting on October 23, 1985 that, for the purposes of the FSAR, it will be assumed that those two faults extend to the surface.

It is my conclusion that the shallowest fault picks given by HLA for faults A and I are indeed correct. However, suggestions of even shallower faulting can be found on the seismic records, and the assumption that they may go through to the surface should definitely be used in considering the site. In this respect I would like to remark, although this is not the central theme of this review, that I cannot disagree with the assumption stated by the applicant in the October meeting, that a magnitude 4 earthquake is the maximum hazard that can be expected from movement on one of these faults. This is based on the observed seismicity of the gulf coast, which has produced only two earthquakes with a magnitude of 3.5.

A second form of hazard that results from the presence of these faults is surface displacement. For instance, fault I crosses the area proposed for the cooling pond. However, given an approximate surface trace of the fault from .

the seismic data, it should not be difficult to design the embankments of the l l

l 1

Stephan J. Brocoum 2 g6 ;i i

pond so that they will safely accommodate both anticipated seismic motion and a small vertical offset along the fault (if loss of coolant is critical). For comparison, several earth- or rockfill dams of considerable height have been designed and built to accommodate such hazards.

The next shallowest fault, J, appears to be capped at about 3850' as stated in the HLA report. There are indications of possible additional faults not shown on the HLA interpretations, but all of those faults would also be capped at considerable depth, if indeed they exist. Therefore, these possible additional faults do not pose a hazard to the plant.

Following are some more detailed comments on the analysis of the seismic data:

Fault A is most clearly seen on lines Jaecon 2M, 4M and GUS-A. The shallowest l clear indication of faulting is at 0.16s or 490' depth as described.in the HLA report. Indications of possible faulting can be found as shallow aC 0.11s or at a depth of 310', and on the GUS-A line there are suggestions that the fault may continue upward towards the surface. Given the applicant's position that the fault is assumed to go through to the surface, this interpretation does not affect the status of the site.

Fault I is found on lines Jaecon 2M and Conoco 3. On line 2M clear fault indications are visible up to about 0.3s or 915' depth. No capping layers can be found, and possible changes in layering along the fault trace can be seen closer to the surface. Therefore, the assumption that fault I may continue to the surface seems reasonable.

A fault that is subparallel to fault I and about one mile north of it can also be seen on lines Jaecon 2M and Conoco 3. The fault may be designated fault I';

it has an ESE trend and extends to approximately 1.45s or 5450' depth. Line 2M shows that the fault is capped at this level, arid the fault must be considered ,

inactive. Conoco line 3 shows less definits information on capping of this fault, but this line does not have good shallow data.

Other faults can be inferred at various locations, but none of these possible "

faults are significant in that, if they exist, they all terminate at depths of several thousand feet. <

x In summary, the HLA interpretation is essentially correct, and faults A and I are the only ones that may continue to the surface. The fault locations, shallowest picks and offsets identified by HLA are approximately correct; minor variations in interpretation are possible. Indications of possible faults in

.w Stephan J. Brocoum 3 g,qg 1 7 jgg3 J

addition to those interpreted by HLA can be found, but these faults do not extend to the surface, are clearly inactive, and therefore pose no hazard to the site.

Ernst G. Zurflueh, Geophysicist Earth Sciences Branch Division of Radiation Programs &

Earth Sciences, RES cc: F. Congel J. Rosenstiel G. Giese-Koch P. Kadambi Distribution /R-2811:

Circ /,Chron RMinogue Econti DCS/RQ3) Dross LBeratan ESB Sbj/Rd KGoller AMurphy EZurflueh i

1 l

l l

ESB:RES:pf ESB:RES ESB:RES EZurflueh AMurphy LBeratan$

7 / // /86 3 /il /86 SAlf86 i;p<e' est

. . . .