ML19254E001
| ML19254E001 | |
| Person / Time | |
|---|---|
| Site: | Humboldt Bay |
| Issue date: | 09/01/1979 |
| From: | WOODWARD-CLYDE CONSULTANTS, INC. |
| To: | |
| Shared Package | |
| ML19254E000 | List: |
| References | |
| NUDOCS 7910300434 | |
| Download: ML19254E001 (27) | |
Text
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FOR SUBMITTAL TO NRC
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SCOPE OF WORK GEOLOGICAL AND SEISMOLOGICAL STUDIES HUMBOLDT BAY REGION Prepared for PACIFIC GAS AND ELECTRIC COMPANY-77 Beale Street l
San Francisco, California 94106 '\\
By WOODWARD-CLYDE CONSULTANTS Three Embarcadero Center, Suite 700 San Francisco, California 94111 September 1, 1979 1236 088
[
7 9103 00 4-3 p i
2 Woodward Clyde Consultants SECTION 1 INTRODUCTION This section describes the objectives and scope of work for the geologic, seismologic, and engineering studies to address the issues pertaining to the assessment of the geologic suitability of the Humboldt Bay Nuclear Power Plant site.
These issues were identified by the NRC staff in 1976 and discussed in their written communications and discussions with PG&E and its consultants between 1976 and March 1978.
In March 1978, PG&E initiated a program of geologic and seismologic studies which is continuing at present.
The objective of the program is to address issues related to surface faulting and ground motions identified by the NRC staff.
The issues will be addressed by developing additional information on the regional-tectonics and the geologic conditions at the site, integrating the information with previously developed information, and reevaluating the combined data.
l The program of investigations started in the site reg on in March 1978 is continuing at present.
The program has focused on field and office studies to obtain additional information on the regional tectonics, the rate and style of deformation, t'. nature of f aulting in the site locality and at the site, evaluation of capability of the faults in the site vicinity, and a preliminary reevaluation of ground motions at the site.
The scope of field studies has included drilling, geologic mapping, test pits, geophysical logging of borings, laboratory tests for age dating of materials, collection of strong motion recordings, and operation of a microearthquake network in the site locality.
The office studies included reevaluation of appropriate data on regional and site geology, interpretation of the seismologic data generated by the work from March 1978 to date, and preliminary evaluations of ground motions at the site.
1236 089 l-1
Woodward Clyde Consultants The wock to date has provided useful insights into some of the issues that were sought to be addressed.
It has provided additional information on the regional tectonics and geologic structure at the site, and additional information has been obtained on'the Quaternary geology of the site region.
- However, additional work will be necessary in order to complete the investigations for a resolution of the various issues identified by the N7C staff, using the work to date as a basis fo'r the planning.
Outlined in this document is a description of the program for continuation of geologic investigations beyond September 1979.
The program description covers the activities for the next nine to twelve months.
Activities may have to continue beyond this period depending upon the outcome of the various tasks and a periodic evaluation of the objectives.
Also attached is a schedule for the various activities including the approximate times when progress reports will be submitted to the ASLB.
l The program is divided into four major activities:
\\
1.
Regional geologic studies.
2.
Site geologic and. engineering studies.
3.
Regional seismologic studies.
4.
Site ground motion and dynamic site behavior studies.
Figure 1-1 is a flow diagram of the various activities, each of which is divided into several tasks.
The description of the tasks (Section 3) is preceded by a summary of work accocplished during the period March 1978 through July 1979 (Section 2).
1236 090 1-2
Woodward Clyde Consultants SECTION 2
SUMMARY
OF WORK COMPLETED FROM MARCH 1978 THROUGH AUGUST 1979 This section presents a summary of work completed during the period March 1978 through August 1979.
The results of the completed work provide the basis for defining the scope of work in the program for continuation of investigations.
I.
REGIONAL GEOLOGIC STUDIES Regional Geologic Mapping During tne period March 1978 through August 1979, 3eologic mapping was completed along the trace of the.Little Salmon fault in the area between Yager Creek on the south and. Salmon Creek on.
the north.
Detailed and reconnaissance mapping was begun in the area of the Freshwater f ault northeast of the site; in the areas of the Elk River and Van Duzen River southeast of the site; and in cliff exposures along Centerville Beach southwest of the i
site.
In the lower Van Duzen River area and on the kacific Lumber Company property, studies were conducted to evaluate which deposits or features may be used to evaluate the capability of the Little Salmon and other faults in the Humboldt Bay area.
Samples of several ash beds that are distributed throughout the area were collected.
Analysis of these ash samples will be used to assess the ages of the deposits in the Humboldt Bay area.
Trace element analyses and radiometric age dating have been completed for several of the ash bed samples.
Paleomagnetic measurements for age dating purposes were completed on samples from Scotia Bluf fs and Carlotta formations of Ogle, as well as on certain of the ash beds and enclosing sediment.
A literature review of micropaleontology that might be useful for dating deposits in the area was also completed.
1236 091 2-1
flegional Geology s
l Geologic Structure Sur f ace at the Sete avut F aulting F ault Capatulity Potential i
i On Sete Geology eruf Engineering ii I
i I
Evaluation of l
'ieologic Site g
Suitability 1
i 1
I Seismology Sete Ground Motions
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asut Dynamic Dynaanic Motims j
Site Behevior l/..
Site Groural Motions Nu O
C.)
Figure 1-1 FLOW DIAGilAfs.
Woodward.Clyde Consultants Quaternary Geology Studies of the Quaternary geology of the site region were conducted to evaluate the ages of deposits, soils, and geomorphic features and may be useful for evaluating fault capability.
An initial search for available literature, maps, and other data was completed, and the reference list and library were established.
A reconnaissance of Quate. a.y marine terraces was made along the California coast from Punta Gorda northward to the Klamath River.
Detailed soil stratigraphic studies were conducted cn the sequence of raised marine terraces in the Trinadad area.
These studies included analysis of the clay content and degree of heavy mineral etching in the soils on the successively older marine terraces.
Preliminary age dates for the sequence of terrace soils are being developed by analyzing the fossils, by paleomagnetic measurements, and by correlation with the Quaternary sea level curves.
The soil stratigraphic sequence at Trinidad Head will be used to evaluate the ages of other Quaternary deposits and soils in the site region.
}.,
t II.
SITE GEOLOGIC AND ENGINEERING STUDIES Geologic Studies Twenty-five borings totalling approximately 20,000 f eet of drilled depth have been drilled in the site vicinity to obtain data to clarify the subsurface structure.
From these data, three new cross-sections, a structural contour map of the key horizon in the site area, and two isometric block diagrams were constructed.
Previously constructed maps were updated as new information was obtained.
Samples for paleomagnetic age dating were collected and measured to assess the age of the deposits beneath the site.
1236 093 2-2
Woodward Clyde Consultants Geophysical Studies The general quality, coverage, and usefulness of geophysical data available in the Humboldt site vicinity were reviewed.
These data included marine sparker, acoustical, and common depth point reflection profiles run in Humboldt Bay and off shore.
On land geophysical surveys included common depth point reflection profiles, vibroseis, and high resolution reflection profiles.
The land side common depth point reflection profiles, which were of much higher quality than the rest of the data, were analyzed in detail.
Oblique reflections were migrated manually using a wave-f ront chart.
The results of the analysis complemented and enhanced the structural interpretations obtained from data produced by the boring program.
Fault Formation and Propagation A literature review of reported cases of new faulting has been completed.
Included were the review of five reportkd cases of new faults occurring during historic earthquakes and(three reported cases of secondary faults.
At the present time, there is insufficient data to evaluate the factors that control the development and propagation of the new faults.
Informatica on experimental studies of fracture propagation and published data on laboratory simulations of thrust and reverse faults was also compiled and reviewed.
A review of data on the structural history of the Mendocino triple junction was started to assess the significance of the tectonic setting of the site to the potential for new faults to form at the site.
III.
SEISMOLOGIC STUDIES Regional Studies A series of underwater explosions detonated along the coast of Humboldt County were monitored with portable microearthquake 1236 094 2-3
Woodward Clyde Consultants recording stations.
Time delays for the individual recording stations were calculated.
Microearthquake monitoring by the telemetered network in the site vicinity was extended to the south with a network of portable microearthquake recording i ns truments'.
The portable network was in place for approximately 6 months.
Strong Motion Studies Eight strong motion recording stations were installed at the sites that produced the strong motion records for the 1975 Ferndale earthquake.
These stations have three component, force calanced accelerometers with the lower threshold for recording on these digital event recorders set at approximately magnitude 3.
Fourteen recorded earthquakes have been printed out on an expanded scale and peak values read for all the available components.
Several selected events have been examined spectrally as part of the preliminary spectral ratio studies.
Work was begun on attenuation studies based on hypoc,entral distance plots of peak acceleration.
Table 2-1 summd{izes the digitized accelerogram data obtained between August 1978 and February 1979.
I V.
SITE GROUND MOTIONS AND DYNAMIC SITE BEHAVIOR Previcasly completed ground motion studies were reviewed to assess the requirement for additional data.
Preliminary estimates of site peak accelerations, respcnse spectra, and durations of strong shaking for the SSE were developed based on reasonable but conservative estimates of maximum credible earthquakes that might be applicable.
A review was also completed of previous studies of liquefaction potential and soil-structure interaction to assess the need for further work in these areas.
I236 095 2-4
Table 2-1 Digitized Accelerometer Earthquake Data Latitude Longitude Depth Date Time N
W (km)
Magnitude 16 Aug.
1978 0745 40.J64 124.485 15.5 4.0 06 Oct.
2126 40.455 124.534 23.7 4.6 06 Oct.
2142 40.432 124.339 23.9 3.4 07 Oct.
0447 40.480 124.501 22.5 3.6 16 Oct.
0218 40.468 124.528 22.1 3.9 21 Oct.
0548 40.363 124.533 14.7 2.9 29 Oct.
0433 40.352 124.511 16.0 3.3 20.0 3.6 29 Oct.
0651 40.290 124.649 22 Nov.
2303 40.368 124.560 15.0 3.9 16 Dec.
1117 40.984 124.898 27.9 2.9 02 Feb.
1979 0254 40.365 124.483 95.3 3.7 g
02 Feb.
0541 40.259 124.527 20.6 3.7 03 Feb.
0958 40.885 124.387 23.9 4.8 03 Feb.
1005 40.882 124.371 23.7 3.5 1236 096
Woodward Clyde Consultants SECTION 3 PROGRAM FOR CONTINUATION OF INVESTIGATIONS This section presents an outline of the program for the continuation of investigations.
The program is divided into four parts; seve.ral major tasks are identified for each part.
I.
REGIONAL GEOLOGIC STUDIES Objective In previous discussions, the NRC staff has suggested that uncertainties as to the relationship between the Little Salmon f ault and other f aults in the Humboldt Bay region should be evaluated to assess the geologic suitability of t,he Humboldt Bay site.
Furthermore, concern was expressed regarding the possible characterization of the region as being one of " transitional tectonics" and the likely potential for surface f aulting at the site.
As a first step to address these uncertainties, the proposed program is aimed at obtaining an understandipg of the geologic and, structural evolution of the rcgion around the site.
The following tasks have been identified:
Task 1 - Regional Geologic Mapping and Age Da ting The Humboldt Bay site lies within the late Cenozoic Eel River basin.
Study of the stratigraphic and structural history of this basin can provide a link between local geologic events recorded at the site and broader regional events known to have affected northern California and adjacent areas during the late Cenozoic.
The ongoing studies of the Eel River basin include:
1.
Refining, modifying, and extending the geologic map that was compiled by earlier workers in the area.
1236 097 3-1
Woodward Clyde Consultants 2.
Age dating of the late Cenozic strata of the Eel River basin.
(This is done in conjunction with the age dating of deposits along the Little Salmon fault described above.)
3.
Synthesizing these data with previous and ongoing studies of the Eel River basin by other investigators.
Task 2 - Late Quaternary Geologic Studies one of the issues raised in the NRC evaluation of the site is that, from a theoretical viewpoint, the Humboldt Bay region lies in a zone of " transitional tectonics" (i.e., changing stress regime) near a migrating triple junction.
One approach to assessing the possibility that tha stress regime is changing with time is to compare he style of deformation and position of f aults and folds wita time in the Humboldt Bay area.
To accomplish this assessment, investigations will be made of late Quaternary terraces and associated deposits.
A prog (am of geol'ogic' mapping that will include the excavation of boil test pits and trenches at selected localities is planned that will define the distribution of terrace surfaces, their relative stratigraphic positions and ages, and the amounts of deformation or uplift of the surfaces.
In addition, the investigations to identify and date late Quaternary deposits and soils that can be used to evaluate fault capability in the Humboldt Bay region will continue.
Task 3 - Fault Cacability Evaluation The capability of a number of faults in the Humboldt Bay region requires further evaluation.
Two such faults, the Little Salmon f ault and the Bay Entrance f ault, pass near the Humboldt Bay site and are of primary interest in the fault capability evaluations.
The capability of these faults will be investigated during the proposed program, as described below.
1236 098, 3-2
Woodward Clyde Consultants Little Salmon Fault - Work to date on the Little Salmon fault has included geologic mapping and analyses of existing subsurface information.
Future work will include subsurface exploration by trenching and drilling in several areas along the fault that have a potential for revealing details of the movement history of the fault.
The data collected from this work, along with that from other tasks, will be utilized in the final analysis of the capability of the Little Salmon fault.
Bay Entrance Fault - Data useful for the capability evaluation of the Bay Entrance fault will be obtair.ed primarily from the subsurf ace investigations described below for the site geologic studies.
These data along with other data collected during the regional geologic studies, the late Quaternary geologic studies, the geophysical and geodetic studies, and the regional seismologic investigations will be synthesized for use in the analysis of capability of the Bay Entrance fault.
II.
SITE GEOLOGIC AND ENGINEERING STUDIES A
Objective Data to date have shown that a program of deep, comprehensively logged boreholes is required if faults are to be accurately located and the potential for faulting at the site is to be assessed.
Where f aults are steep, as in the Fields Landing area, seismic reflection surveys may also be required because reflection data are, in certain areas, more definitive than that from borings.
The borings and seismic surveys proposed below define a minimum program.
The results of this proposed program may indicate a broader scope of work required to resolve the issues.
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1236 099
Woodward Clyde Consultants Task 1 - Identification of Faults in the Site Locality a.
Identification of Faults South of Fields Landing This is a continuation of ongoing work to locate the Little Salmon fault south of Fields Landing and t7 determine whether a second fault, that is suggested by the available data, is also present.
Figure 3-1 shows the locations of the borings that have been drilled to date and proposed locations for borings during this program.
A new boring is planned in the vicinity of boring A-10.
Tne new boring will terminate in the Wildcat Group at an expected depth of approximately 2300 feet.
The Wildcat, however, may be as deep as approximately 2800 feet, as in AW-2 and AW-3 to the north and in the Brauner well to the south.
In the vicinity of boring P-16, the data to date loffer alternate interpretations; either two faults are present or there may be only one fault with the structure complicated by a local facies change.
A 500-feet-deep corehole is planned between borings P-16 and,A-22 to obtain additional information on near-su'eface correlations.
Also, a deeper boring of about 2000 to 3000-feet-depth is planned routheast of boring A-3 to resolve deepqf correlations.
This boring may be advanced to a repeated section of Wildcat or 2000 feet, whichever is encountered first.
b.
Relationship Between Bay Entrance and Little Salmon Faults Notable progress has been made in understanding the geologic structure in the Buhne Point and the Fields Landing areas.
However, additional information is required to resolve the location of the Little Salmon fault and its relationship to the Bay Entrance fault.
236 100 3_,
Woodward Clyde Consultants To resolve these questions, a program of several borings and seismic lines is planned.
As shown on Figure 3-2, a minimum of nine horings are planned in the triangular area bounded by A-14, RD-19, end A-15 in the Fields Landing area to determine the number and. attitudes of faults there.
Available data show this to be a structurally complex area and several different interpretations are presently possible.
A grid of seistaic lines to tie the planned and older borings together is essential, see Figure 3-2.
Approximate locations and depths of the borings are listed in the following table.
Estimated Minimum Bor ing Location (approximate)
Depth ( fee t) 1 600 f t south of RD-11 1200 2
700 ft north of B-19 500 3
700 ft north of B-19 750 4
300 ft southeast of P-12 700 5
300 ft northeast of P-11
\\l400 4
6 400 to 600 ft northwest of P-12
\\1000 7
midway between B-69 and A-15 3000 8
midway between P-12 and B-69 2500 9
4 00 to 500 f t north of A-14 2500 Three borings will be drilled north of Fields Landing to evaluate whether the faults there are the same as those at Buhne Point.
Borings 10 and 11 will be drilled to Wildcat (estimated at 2100 and 2500 feet, respectively).
Boring 12 will be drilled to a dept of 3000 feet.
Four additional borings are also designed to aid in locating the Little Salmon fault and assessing its relationship to the Bay Entrance f ault.
Two of these (13 and 14) are located on opposite sides of U.S.
101 southeast of AW-5, and the other two are on South Spit (15) and North Spit (16), north of Buhne Point.
1236 101 3-5
Woodward Clyde Consultants Boring 15 on South Spit is planned for 3000 feet; borings 13 and 14 near AW-5, for 4500 feet; and boring 16 on the North Spit, for approximately 6000 feet.
c.
North Soit Fault - Elk River Vallev A continuing evaluation is in progress to tie the site geology into the regional tectonic framework.
Part of this effort included enlarging the structure contour map of the Hookton "B Clay" (previously identified as unit F) to include outlying borings such as those on North Spit, in the Elk River Valley, and near Table Bluff.
The B Clay could not be recognized near Table Bluff, but preliminary indications suggest that it is present beneath North Spit and Elk River Valley.
The available sparse boring control in the Elk River area suggests that the B clay may be offset on the north side of the valley by the North Spit fault and also on the south side of the valley where no fault has previously been mapped.
The sense of offset suggests that the Elk River valley is a graben produced by normal or strike-clip faulting on parallel faults.
Poor quality sparker pyofiles in the bay offshore from Elk River faintly suggest disruption of bedding across this area.
A limited initial investigation of this area is proposed, including reconnaissance field mapping along the Elk River and three to eight shallow (to 500 feet) borings at some of the proposed locations in the Elk River Valley shown on Figure 3-3.
Based on the results of this work, further investigation may be planned.
Task 2 - Age Dating of Hookton Formation Extensive paleomagnetic dating work in the borings drilled to date did not locate the 700,000-year-old Matayama Reversal within 950 feet of the surface at the site.
It will be useful to locate the reversal so that offset rates can be estimated and the stratigraphy at he site area can be accurately correlated with that at Centerville Beach, along the Van Duzen River, and 1236 102 3-6
Woodward Clyde Consultants elsewhere.
Because basal Hookton and/or Carlotta and/or Scotia Bluff beds occur nearer the surface on Humboldt Hill than at the site, one or two coreholes will be drilled on Humboldt Hill.
Figure 3-4 shows, schematically, the proposed locations.
It is anticipated that the borings will penetrate a few hundred feet of Wildcat Group so that the paleomagnetic analysis can be compared to published interpretations of paleomagnetic data that place the Bruhnes-Matayama Reversal within the Wildcat Group.
Total estimated depth is 800 feet in the southern boring and 1200 feet in the northern boring.
Task 3 -
Installation of Free-Field, Embedded Strong-Motion Accelerometers Three component strong-motion accelerometers will be installed in the free field in a boring at a depth of approximately 80 feet below the finished grade.
The location of the instruments will be near the storage building where the free-field, finished-grade accelerometers is currently located.
.'\\
The purpose of the embedded accelerometers is to obtain empirical data of site response and soil-structure interaction during earthquakes.
Strong motion data recorded by the embedded accelerometers, along with data from the accelerometers located at finished grade and at the base of the reactor caisson, will be processed and analyzed.
Task 4 - Formation and Propagation of Faults The NRC staff suggested that the geologic conditions at the site should be reviewed to examine the following:
1.
The potential for the sudden appearance of new fault zones in previously unfaulted terrain, 2.
Progressive rupturing of recent faults in regions of i236 103 3-7
Woodward Clyde Consultants
" transitional tectonics", and 3.
The possible similarity of the Humboldt Bay Power Plant region to such areas.
The purpose of this task is to evaluate the potential at the site for the above events.
A conceptual framework for understanding the geologic setting of the site will be established.
One the bases for the assessment of f ault formation and propagation at the Humboldt Bay site will be the evaluation of worldwide case histories where new faulting has been reported.
A second basis will be a quantitative evaluation of the experimental studies of crack growth and rupture propagation.
As a third basis, a review will be made of the structural history and area of influence of the Mendocino triple junction and its relationship to conditions at the Humboldt Bay site.
With, the accumulation of additional site-specific an'a regional information, conceptual models of the geologic condit ons at the site will be' refined and estimates of the potential for fault formation and propagation at the site will be made.
Task 5 - Geophysical.?nd Geodetic Data Analysis The objective of this task is to obtain a comprehensive understanding of the geologic and structural evolution of the site locality.
Available and new geophysical and geodetic data will be analyzed.
This work will supplement data and analyses performed in other tasks.
It is believed that supplementary high resolution reflection data will be useful to clarify the subsurface structure in the plant vicinity.
It may be necessary to bypass the areas where existing data is of poor quality which may be due in part to localized 1236 104 3_,
Woodward Clydo Consultants near-surface conditions.
Existing geodetic leveling data will be analyzed.
The scope of this work is described below.
1.
Seismic Reflection Data a.
Record up to 7700 feet of high resolution seismic reflection data in the plant area and up to 6700 feet in the Fieldr' Landing area.
This work will be done in two phases with some preliminary control being obtained in the initial phase to test alternate areas for record quality and to define structure trends in order to define the field program for the later phases.
b.
Obtain the Chevron seismic reflection profiles in the site area.
Chevron has onshore and 6ffshore seismic reflection control and well log data that are pertinent to a more complete understanding of the geologic structure in the site vicinity.
These data have been available for brief inspectiods in the past, but may now be available for acquisition.
Obtain and interpret a portion (say about 20 percent)
.t c.
of the 1500 miles of Western Geophysical *s offshore reflection survey lines.
e 2.
Analyze data from those first-order geodetic leveling lines that have ceen resurveyed.
[ e-III.
REGIONAL SEISMOLOGIC STUDIES Objective The details of the northwest migration of the Mendocino triple junction are of concern to both the NRC and USGS staff.
A seismic network has been recording the earthquakes in the regior of the Humboldt Bay Nuclear Power Plant since 1975.
During tl 9 1236 105 2-9
-.-.-------m-
Woodward Clyda Consultants period, more than 5000 earthquakes have been located.
The results to date suggest that seismicity is occurring in two distinct depth zones separated by a seismically quiet zone.
It has been postulated that the Eel River basin is in a zone of transitional tectonics, within which the release of seismic energy is not confined to stable, well-defined plate margins.
An element in the assessment of earthquake sources is an association of the larger historic earthquakes to tectonic structures in the region.
The tectonic association of the 1922, 1923, 1934, and 1954 earthquakes, among others, will be reassessed in terms of focal depth and focal mechanism.
The proposed program includes the following tasks:
Task 1 - Analysis of Seismologic Data 1.
Complete the analysis to refine crustal velocity models.
2.
Analyze the significance of changes in the velocity models on the locations and focal mechanismsiof recorded earthquakes.
3.
Analyze source mechanisms of selected earthquakes larger than magnitude 4.
4.
Estimate strain relief rates and their differences between the upper and deeper crustal plates.
5.
Correlate seismicity with geologic structures for an overall tectonic evaluation.
i236 106 Task 2 - Site Soecific Earthquake Characteristics The assessment of the ground motion characteristics for future earthquakes expected to affect a particular site is based upon evaluations of earthquake source effects, wave propagation 3-10
Woodward Clyde Consultants effects, and site characteristics.
Limited data are available from past earthquakes in the Humboldt Bay region relating to factors that may influence the characteristics of future ground motions at the Humboldt Bay plant.
Sufficient data have been collected from the sites of strong motion recording stations to allow a better understanding of the differences of site response for the 1975 Ferndale earthquake, and these data will be analyzed.
To better understand the response of the material beneath the plant, accelerstion data will be collected from the same geologic sequence as the plant as well as f rom a limited number of bedrock sites for comparicon.
To accomplish this, some of the strong motion digital event recorders will be moved closer to the plant while leaving in place the recorders at Ferndale and at the rock site in Butler Valley.
As well as having continued recordings of larger regional earthquakes at the site, the relocated network will' give better seismic coverage of small shallow earthquakes.
These will be anal ~yzedforsourcecharacteristicsthatwillbeusehina Green's function technique for scaling of small magnitude seismic records to larger magnitudes.
This will assist in generating the wave character of the largest earthquakes expected from each of the sources.
The site response will be an aspect of this near source earthquake analysir.
Unprocessed earthquake data are available from old records at the Ferndale station.
These data will be reviewed, and selected earthquake data will be digitized and analyzed for the seismic characteristics in the two source regions.
1236 l'07 3-11
Woodward Clyde Consultants I V.
SITE GROUND MOTIONS AND DYNAMIC SITE BEHAVIOR Ob3ecti",e The objectives of these tasks are to (1) evaluate the free-field site peak decelerations, response spectra, and durations of strong shaking for the SSE; and (2) examine empirical evidence of soil-structure interaction at the plant site.
Task 1 - Assessment of Earthquake Ground Motions Recorded accelerogram data from historic earthquakes that are most pertinent to the SSE will be collated and examined.
The data include records of historic earthquakes occurring in the site region and other regions as appropriate.
Refined estimates of site ground motions will be made on the basis of:
(1) analyses of recorded (empirical) data; (2) ground response analyses to aid in assessing the modifying influence on ground motions of local soil conditions at the plant, site; and (3) *the data gathered and analyses performed during $ite specific earthquake characteristics evaluation.
Estimates of ground motions for the SSE will be for the maximum earthquakes in the site region identified in the regional seismologic investigations.
Task 2 - Assessment of Soil-Structure Interaction Currently available accelerograms recorded in the free field and at the base of the reactor caisson during higher magnitude earthquakes (M 4.5) will be compared to examine the effects of soil-structure interaction on site ground motions.
Additional accelerograms that may be obtained at the plant in the future will also be compared.
If free-field ground motions are recorded at the ground surface and at depth, one-dimensional,
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1236 108
Woodward Clyde Consultants f ree-field ground response analyses will be conducted to compare analytical predictions of ground motion variations with depth with recorded data.
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EXPLANATION
$ PROPOSEO BOalNG
^
1236 112 Figure 3-3. PROPOSED BORINCS, ELK RIVER VALLEY, TASK ll-1c
f B
2 x
c I
2 I
~;
-n-a
)
D h
t O L-3 O L-8 O
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g RD-18 O P-12 3
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(
- 4 EXPLANATION O PRE 1978 80 RING
$ PROPOSED BORING 0
,500 1000 1500 feet 0
10 0 2."C 300 400 500 meters Figure 3-4. BORING LOCATIONS, HUMBOLDT HILL AREA, TASK 11-2 2b
SCilEDULE OF ACTIVITIES Months from Steet lessumed 9/15/79) 1 2
3 4
5 6
7 8
9 10 11 12 i HEGIONAL GEOLOGIC STUDIES 1.
Regional Geologic Mapping and Age Deting 2.
Late Ouaternery Geologic Studies 3.
Fauft Capability Evolustion 11 SITE GEOLOGIC AND ENGtNEERING STUDIES l
1.
Identifketion of Faults in Site Locality la - Faultlel Sousti os Fields Landing
-===
Ib Boy Entrance - Little Salmon Faults Refetionship
..=
- -.=
fc North Spit Feuil-Elk Rhrer Valley 2.
Age Deting of Hookton Formattori 3.
Free - Fleid Strong Mottori Accelerometers 4
Fault Formation and Propogetion 5.
Geophyskel end Geodetic Stud 6es til REGIONAL SEISMOLOGICAL STUDIES 1.
Seismoloskal Date Analyslo 2.
Site Specific Earthquake Cherectoristka IV slTE GROUND MOTION AND DYNAMIC SITE SEHAVIOR j,. -
1.
Earthquake Ground Motlors
-I
= = = =.
-==== -.
a 2.
Soll Structure Interection 4
ASLB Reports 4 8 4>
4>
d8 48 48 4>
Figure 4-1. SCllEDULE