ML033650188
| ML033650188 | |
| Person / Time | |
|---|---|
| Site: | Humboldt Bay |
| Issue date: | 12/26/2002 |
| From: | Abrahamson N, Cluff L, Nishenko S Pacific Gas & Electric Co |
| To: | Document Control Desk, NRC/FSME |
| References | |
| +sisprbs20051109, -RFPFR GEO.HBIP.02.03, Rev 0 | |
| Download: ML033650188 (28) | |
Text
HBAP C-20.1 Rev. 7A Page of I HUMBOLDT BAY POWER PLANT CALCULATION COVER SHEET File No. :
Calculation No.:
GEO.HBIP.02.03_
E Preliminary 0 Final Department/Group:
HBPP/Geosciences Unit(s) 0 Structure, System or Component:
ISFSI Geotechnical Type or Purpose of Calculation:
Development of Maximum Credible Earthquake Magnitudes and Distances for the HBIP No. of Sheets:
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12/26/02 Hitial Issue Geosci.
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PACIFIC GAS AND ELECTRIC GEOSCIENCES DEPARTMENT CALCULATION DOCUMENT Calc Number: GEO.HBIP.02.03 Revision:
0 Date:
10/04/02 Calc Pages:
18 Verification Method:
A and B TITLE:
Development of Maximum Credible Earthquake Magnitudes and Distances for the HBIP PREPARED BY>
DATE Printed Name I
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page 1 of 18
Development of Maximum Credible Earthquake Magnitudes and Distances for the HBIP Record of Revisions Rev.
Reason for Revision Revision No.
Date 0
Initial Issue 10/04/02 I
page 2 of 18
Calc Number. GEO.HBIP.02.03 Rev Number: 0 Sheet Number. 3 of 18 Date: 10/4/02
Title:
Development of Maximum Credible Earthquake Magnitudes and Distances for the HBIP
- 2. PURPOSE The purpose of this calculation is to determine the magnitude and the closest distance to the HBIP site for the Maximum Credible Earthquake (MCE) on the Little Salmon Fault and the Cascadia interface subsources based on the Carver (2002) source characterization.
These parameters will be used in the calculation of the deterministic ground motions as described in the Work Plan (GEO 2002-01, Rev 1).
- 3. ASSUMPTIONS 3.1 Magnitude-area scaling relations for crustal earthquakes The Wells and Coppersmith (1994) magnitude-area scaling relations for all fault types is assumed to be applicable to crustal faults. The basis for this assumption is that it is a well-documented and widely used model.
3.2 Magnitude-area scaling relations for subduction zone earthquakes The Geomatrix (1994) and Abe (1981; 1984) magnitude-area scaling relations for subduction zones are assumed to be applicable to the Cascadia subduction zone. The basis for this assumption is that the relations were developed for subduction zone earthquakes.
3.3 Magnitude-fault displacement scaling relations for crustal earthquakes The Wells and Coppersmith (1994) magnitude-displacement scaling relation for all fault types is assumed to be applicable to crustal faults. The basis for this assumption is that it is a well-documented and widely used model.
3.4 Location of "Change in Fold Trends" Geomatrix (1995, p. 2-14) states that the change in fold trends is located 30 km landward of the deformation front. Later (p. 2-21) they show the downdip width of the rupture is 25 km less using the change in fold trends as compared to the deformation front. The location of the deformation front is assumed to be 30 km seaward of the change in fold trends. The basis for this assumption is that is slightly conservative but not significant.
Calc Number: GEO.HBIP.02.03 Rev Number: 0 Sheet Number: 4 of 18 Date: 10/4/02 3.5 Width of interface Carver (2002) does not give models for the downdip width of the interface. The Geomatrix (1995) model for the width of the interface is assumed to be applicable to the Carver (2002) model. The basis for this is assumption is that the Geomatrix (1995) is the most up-to-date characterization of the width of the interface.
Calc Number GEO.BIP.02.03 Rev Number: 0 Sheet Number 5 of 18 Date: 10/4/02
- 4. DESIGN INPUTS 4.1 Width Approaches for Cascadia Interface The width of the Cascadia interface depends on the location of the updip (shallowest point) and downdip (deepest point) limits of potential seismogenic rupture. Geomatrix (1995, page 2-2 1) gives two alternative models for the location of the updip limit and two alternative models for the location of the downdip limit.
The updip extent is defined by either the location of the deformation front or the location of the change in structural trends near the slope break (change in fold trends). Geomatrix (1995, p 2-21) estimates that fault width using the change in fold trends boundary is 25 km less than using the deformation front boundary. Geomatrix (1995, page 2-21) gives relative weights of 0.7 to the change in fold trends model and 0.3 to the deformation front model.
The downdip extent is defined by either the location of the zero isobase line or the midpoint of the transition zone defined by the thermal and geodetic modeling. Geomatrix (1995, page 2-21) gives relative weights of 0.6 to the zero isobase model and 0.4 to the thermal-geodetic model.
On page 2-21 of Geomatrix (1995), the width of the Cascadia interface is given for the four combinations of the locations of the updip and down-dip limits, but the values are not correct. It appears that they incorrectly used the location of the change in fold trends as the location of the deformation front and the change in the fold trends was placed 25 km east of the misplaced deformation front. The result of this error is that interface widths listed in Geomatrix (1995) are too small (see Attachment 1, R. Youngs, 2002, written communication). New calculations of the width of the interface are made in section 7 of this calculation package.
4.2 Dimensions of the Cascadia Interface 4.2.1 Rupture Lengths Carver (2002) models the Cascadia interface as a combination of the Cascadia interface, Little Salmon fault zone, and Table Bluff fault. The alternative models for the lengths of the Cascadia interface ruptures and the weights for the alternatives given by Carver (2002) are listed in Table 4-1.
f Calc Number: GEO.HBIP.02.03 Rev Number: 0 Sheet Number: 6 of 18 Date: 10/4/02 Table 4-1. Alternative segment lengths and weights for the Cascadia interface using the Carver model (Carver, 2002, page 5A-3).
Rupture Extent Segment Weight Length (km)
Eureka to the middle of 700 0.5 Washington Eureka to the Explorer plate 1050 0.5 4.2.2 Dip Cohee et al. (1991, P. 37, caption to Fig. 3) give the dip of the interface of 11 in Washington and 210 in Oregon. The average value of 160 degrees is used for the fault rupture.
4.3 Little Salmon Fault Zone 4.3.1 RuptureLength Carver (2002) defines the Little Salmon fault zone as extending from the Yager fault to the Thompson Ridge fault (PGE, Fig. 2-5). The length of the zone is 310 kn (Carver 2002, pg 5A-6).
4.3.2 Dip Carver (2002) gives three possible dips of the fault of 40, 45, and 50 degrees; weights on each are 0.2, 0.6 and 0.2, respectively.
4.3.3 Crustal Thickness The thickness of the crust in the HBIP region is given as 15 kn (Carver, 2002).
4.3.4 Displacement per Event The fault displacement is given as 7m or 9.3m (equally likely) (Carver, 2002).
4.3.5 Style of Faulting The Little Salmon fault is a reverse slip fault (Carver, 2002).
Calc Number: GEO.HBIP.02.03 Rev Number. 0 Sheet Number: 7 of 18 Date: 10/4/02
- 5. METHOD AND EQUATION
SUMMARY
5.1 Methods The magnitude of the Maximum Credible Earthquake is computed based on the mean magnitude determined for the maximum rupture area or fault displacement 5.2 Equations 5.2.1 Maznitude-Area Relations The Wells and Coppersmith (1994; Table 2A, p. 990) scaling relation for magnitude as a function of rupture area for crustal faults (using all fault types) is given by M = 0.98 Log(A) + 4.07 (5-1) where A is the rupture area in km2 and M is moment magnitude.
The Abe (1981; 1984) relation for magnitude as a function of rupture area for subduction zones is given by (Geomatrix, 1995, p. 2-29)
M = Log(A) + 3.99.
(5-2)
The Geomatrix (1993) relation for magnitude as a function of rupture area for subduction zones is given by (Geomatrix, 1995, p. 2-29)
M = 0.81 Log(A) + 4.7 (5-3) 5.2.2 Magnitude-Displacement Relations The Wells and Coppersmith (1994; Table 2B, p. 991) scaling relation for magnitude as a function of average fault displacement for crustal faults (using all fault types) is given by M = 0.82 Log(D) + 6.93 (5-4) where D is the average displacement over the rupture surface in m.
Calc Number: GEO.HBIP.02.03 Rev Number: 0 Sheet Number: 8 of 18 Date: 10/4/02 5.2.3 Downdip Width The following illustration is used for Eqns. 5-5 and 5-6.
A I
For a fault with dip Sand horizontal extentX, the downdip width, W, is given by W =
~~
(5-5) cos(5)
For a fault with dip Sand vertical extent Y, the downdip width, W, is given by We=- Y (5-6) sin(S)
Eq. (5-5) and (5-6) are well known trigonometric relations.
5.2.4 Weighted Average Given N values X, with weights wt,, the weighted mean is (Bevington, 1969, p. 73) 5 Xi wtj Mean = I (5-7) t1
. I Calc Number: GEO.HBIP.02.03 Rev Number: 0 Sheet Number 9 of 18 Date: 10/4/02
- 6. SOFTWARE No specialized computer software was used in these calculations.
- 7. BODY OF CALCULATIONS 7.1 Magnitude for the Cascadia Interface 7.1.1 Horizontal Extent of Updip Boundary The downdip widths of the interface given by Geomatrix (1995, p. 2-21) are not consistent with the plots on Fig. 2-17. To resolve this inconsistency, other sources of this information were reviewed.
The locations of the Cascadia subduction zone's Deformation Front (Geomatrix, 1995, Fig. 2-16 and Plate 1) were compared to the location of the Cascadia Subduction Zone mapped by the National Geographic Society (NGS, 1995). Geomatrix (1995, Fig. 2-16) shows locations from California to north of the Explorer plate (about 400 to 520 N);
Geomatrix (1995, Plate 1) extends only along the Oregon coast (about 42° to 460 N);
NGS (1995) plots the zone only along the U. S. coastline and ends at the Canadian border (south of Eureka to about 48.50 N)
All three sets of distances were measured as distances due west of the U. S. coastline and are shown in Table 7-1. Additionally, the location of the Change in Fold Trends (Geomatrix, 1995, Plate 1) is included in Table 7-1.
. 6 Calc Number: GEO.HBIP.02.03 Rev Number: 0 Sheet Number. 10 of 18 Date: 10/4/02 Table 7-1. Distance* (m) from U. S. coastline to 4 updip reference boundaries of the Cascadia subduction zone.
N Latitude Deformation Deformation Cascadia Change in Fold (0)
Front Front Subduction Zone Trends (Geom* Fig. 2-16)
(Geom., Plate 1)
(NGS)
(Geom., Plate 1) 41 44 N/A 73 N/A 42 61 87 85 59 43 39 63 64 37 44 67 94 97 76 45 83 113 109 76 46 94 119 116 81 47 100 N/A 135 N/A 48 94 N/A 138 N/A
- Accuracy of the distances is approximately: +/- km for Geomatrix Fig. 2-16, +/- 1 an for Geomatrix Plate 1, and +/- 2 km for NGS.
The distance to the updip subduction zone boundary measured from NGS agrees well with the deformation front boundary plotted in Geomatrix Plate 1 but not at all with the deformation front plotted in Geomatrix Fig. 2-16. The distance to the deformation front plotted in Geomatrix Fig. 2-16 agrees well with the change in fold trends plotted in Geomatrix Plate 1. Because the NGS is a data source independent of Geomatrix (1995),
the boundaries in Geomatrix Plate 1 appear correct. The boundary plotted in Geomatrix Fig. 2-16 should be labeled as the change in fold trends boundary, and not as the deformation front.
7.1.2 Width The horizontal extent of the Cascadia interface was measured from Geomatrix (1995, Fig.
2-16) using the change in fold trends boundary (identified incorrectly in Fig. 2-16 as the deformation front) as the updip margin and both the zero isobase and transition zone boundaries as the downdip margins (Table 7-2). The Transition Zone plotted in Geomatrix Fig. 2-16 is used by Geomatrix (1995) as the Thermal/Geodetic boundary (p.
2-21). The distances measured were along lines approximately normal to the updip and downdip margins and intersected the coastline at the latitudes listed in Table 7-2.
The horizontal extent using the deformation front as the updip boundary is computed by adding 30 km (assumption 3.4) to the extent using the change in fold trends as the updip boundary.
Calc Number: GEO.HBIP.02.03 Rev Number: 0 Sheet Number: 11 of 18 Date: 10/4/02 Table 7-2. Horizontal extent (lam) of the Cascadia interface using the change in fold trends (Fig. 2-16) as the updip interface boundary.
N Latitude Change in Fold Trends Deformation Front (0)
Zero Isobase Transition Zero Isobase Transition Zone Zone 41 100 65 130 95 42 100 57 130 87 43 87 52 117 82 44 83 52 113 82 45 74 57 104 87 46 78 78 108 108 47 83 117 113 147 48 70 126 100 156 49 39 83 69 113 The downdip width of the Cascadia interface between the change in fold trends and the zero isobase and the transition zone boundaries was computed from the horizontal extent (Table 7-2) using Eqn. 5-5 and the dip of 160 (input 4.2.2). The resulting downdip widths are shown in Table 7-3.
Table 7-3. Downdip width (cm) of the Cascadia interface.
N Latitude Change in Fold Trends Deformation Front (0)
Zero Isobase Transition Zone Zero Isobase Transition Zone 41 104 68 135 99 42 104 59 135 91 43 91 54 122 85 44 86 54 118 85 45 77 59 108 91 46 81 81 112 112 47 86 122 118 153 48 73 131 104 162 49 41 86 72 118 Average (41° to 47°)
90 71 121 102 Average (41° to 49°)
82 79 114 111 The interface widths were averaged over latitudes corresponding to the segment rupture length models (Table 4-2) - between Eureka and the middle of Washington (410 to 470) and between Eureka and the Explorer plate (41° to 490). These averaged values were then rounded to the nearest 5 km to reflect the accuracy of the measurements. The resulting widths are listed in Table 7-4.
Calc Number: GEO.HBIP.02.03 Rev Number: 0 Sheet Number: 12 of 18 Date: 10/4/02 Table 7-4. Maximum rupture downdip width (Cm) of the Cascadia Interface averaged along the rupture length.
Rupture Model Updip Model Downdip Model Eureka to Middle of Eureka to the Washington Explorer Plate Deformation Zero Isobase 120 115 Front Thermal/Geodetic 100 110 Change in Fold Zero Isobase 90 80 Trends Thermal/Geodetic 70 80 7.1.3 Magnitude The magnitude of the characteristic earthquake for the main Cascadia interface is estimated using the two alternative relations between magnitude and rupture area for subduction events (eq. 5-2 and 5-3) with equal weights. The rupture area is computed by multiplying the segment lengths given in input 4.2 and the downdip widths listed in Table 7-4. All possible combinations of widths and segment lengths are considered; the 16 permutations are listed in Table 7-5. The total weight is the product of the weights for the updip extent, downdip extent, length, and magnitude-area (M(A) model) relation.
The mean magnitude listed at the bottom of Table 7-5 is computed by summing the wt*Mag values (eq. 5-7).
Calc Number: GEO.HBIP.02.03 Rev Number: 0 Sheet Number: 13 of 18 Date: 10/4/02 Table 7-5 Mean Characteristic Magnitudes for the Cascadia Interface using the Carver Segmentation Model (input 4.2).
Welghts l
Updlp Downdlp Width Rupture Length M(A)
Updip Downdlp Length M(A)
Total Wt Extent Extent (km)
Model (kin)
Model Mag Exdent Exlent Model Mag Zero Eureka to 0.3 0.6 0.5 0.5 0.39 Isobase Def. Front 120 Mid Wash.
700 Geomatrx 8.69 0.045 Zero Eureka to 0.3 0.6 0.5 0.5 0.40 Isobase Del. Front 115 UN. Ple 1050 Geomalrx 8.82 I I 0.045 Zero Fold Eureka to 0.7 0.6 0.5 0.5 0.90 Isobase Trends 90 Mid Wash.
700 Geonatrix 8.59 0.105 Zero Fold Eureka to 0.7 0.6 0.5 0.5 0.91 sobase Trends 80 Expl. Plte 1050 Geomalrix 8.69 0.105 Thermal-Eureka to 0.3 0.4 0.5 0.5 0.26 geodeic Def. Front 100 Mid Wash.
700 Geomatlx 8.62 0.03 Thermal-Ewekato 0.3 0.4 0.5 0.5 0.26 geodetic _
Del. Front 110 Expl. Plate 1050 Geornatrix 8.80 0.03 Thernal-Foid Eureka to 0.7 0.4 0.5 0.5 0.60 geodetb Trends 70 Mid Wash.
700 Geomatrlx 8.50 0.07 Thermal-Fold Eureka to 0.7 0.4 0.5 0.5 0.61 aeodefic Trends 80 ExL. Plate 1050 Geornatrix 8.69 0.07 Zero Eureka to 0.3 0.6 0.5 0.5 0.40 Isobase Del. Front 120 Mid Wash.
700 Abe 8.91 0.045 Zero Eureka to 0.3 0.6 0.5 0.5 0.41 Isobase Del. Front 115 Exl. Plate 1050 Abe 9.07 0.045 Zero Fold Eureka to 0.7 0.6 0.5 0.5 0.92 Isobase Trends 90 Mid Wash.
700 Abe 8.79 0.105 Zero Fold Eureka to 0.7 0.6 0.6 0.5 0.94 Isobase Trends 80 Exl. Plate 1050 Abe 8.91 0.105 Thermal-Eureka to 0.3 0.4 0.5 0.5 0.27 geodetic Del. Front 100 Mid Wash.
700 Abe 8.84 0.03 Thermal-Eureka to 0.3 0.4 0.5 0.5 0.27 geodetic' Def. Front 110 Exl. Plate 1050 Abe 9.05 0.03 Thermal-Fold Eureka to 0.7 0.4 0.5 0.5 0.61 geodetic Trends 70 Mid Wash.
700 Abe 8.68 0.07 Thermal-Fold Eureka to 0.7 0.4 0.5 0.5 0.62 geodetic Trends 80 Expl. Plate 1050 Abe 8.91 0.07 Mean 8.76 (E
(
Calc Nunber. GEO.HBEP.02.03 Rev Number: 0 SheetNumber. 14 of 18 Date: 10/4/02 7.1.3 Distance The updip location of the Cascadia interface in the region near the HBIP, as described by Carver (2002), is given by the Table Bluff fault. Using Figure 3-3 from PGE (2001), the horizontal distance between the HBIP site and the surface expression of the Table Bluff fault is measured as 5.5 km. The Table Bluff fault has a change in dip direction as shown in Fig. 3-4 from PGE (2001). In the top 2 km, the fault has a shallow dip to the southwest, whereas below 2 km, the fault has a shallow dip to the northeast. The part of the fault below 2 km dipping to the northeast is consistent with the dip direction of the subduction zone. Therefore, the distance to the fault is measured to the part of the fault dipping to the northeast. Using the cross-section (Fig 3-4 from PGE 2001), the closest distance between the site and the northeast dipping part of the fault is measured to be 7 km.
7.2 Magnitude for the Little Salmon Fault System 7.2.1 Maenitude The magnitude of the characteristic earthquake for the Little Salmon fault zone is estimated using the relations between magnitude and rupture area for crustal faults (eq. 5-
- 1) and between magnitude and fault displacement (eq. 5-4). The two alternative approaches (area or distance) are given equal weight.
Using the dip (column #2 in Table 7-6) from input 4.3.2 and the thickness (column #4) from input 4.3.3, the downdip width (column #5) is computed using eq. 5-6. The segment length (column #6) is from input 4.3.1. The area (column #8) is computed by multiplying the downdip width and the length. The magnitude (column #11) is computed using eq. 5-1 and the area in column #8. The total weight (column#12) is the product of weights for the different approaches (column #1), the segment weight (column #7), and the dips (column #3).
Using the displacement approach, the magnitude (column #11) is computed using eq. 5-4 with the displacement per event value listed in column #9 (input 4.3.4). The total weight (column #12) is the product of the approach weight (column #1) and the displacement per event weight (column #10).
The magnitude is multiplied by the weight (column #13). The mean magnitude is computed using eq. 5-7 (sum of values in column #13). The mean weighted magnitude of 7.74 from the Table 7-6 is rounded to 7.7 for defining the mean characteristic magnitude.
Calc Number. GEO.HBIP.02.03 Rev Number: 0 Sheet Number: 15 of 18 Date: 10/4/02 Table 7-6. Mean Characteristic Magnitudes for the Little Salmon Fault System.
- 1 N2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
- 10 1I 12
- 13 Downdip Segment Approach Approach Dip Thckness Width Length Are a Disp Disp Total Wted Wt Dip Wt (m
(
Wt (km2)
()
Wt Mae Wt Me Am 0.5 40 0.2 15 23.3 310 1
7223 N/A N/A 7.85 0.10 0.79 Area 0.5 45 0.6 15 21.2 310 I
6572 N/A N/A 7.81 0.3d 2.34 Area 0.5 50 0.2 15 19.6 310 1
6076 N/A N/A 7.78 0.10 0.78 Disp.
0.5 N/A N/A 7
0.5 7.62 0.25 191 0.5 D
i m
O.S_______
NA N/A 9.3 0.5 7
.72 0.25 1.93 Mean 7.74 7.2.2 Distance The Bay Entrance fault is the closest strand of the Little Salmon fault to the HBIP site.
The approximate location of the Bay Entrance fault is shown in the cross section in PG&E (2002, Figure 4-16). Based on this Figure, the shortest distance between the HBIP site and the Bay Entrance Fault is measured to be 0.5 km.
- 8. RESULTS The Little Salmon fault zone and the Cascadia interface are assumed to rupture synchronously. The magnitude and closest distance of the maximum credible earthquakes for the two subources are listed below:
Table 8-1. MCE for Cascadia interface and Little Salmon fault subsource.
Rupture Subsource Source Type Moment Distance Magnitude (km)
Little Salmon Crustal 7.7
-0.5 Fault Zone Reverse Cascadia Interface Subduction 8.8 7
Interface I
- 9. CONCLUSIONS The source types, magnitudes, and rupture distances listed in Table 8-1 represent the MCE for these two subsources. They should be used for deterministic evaluations of the ground motion at HBIP.
Limitations:
The magnitudes andfdistances are for use in a deterministic approach only.
I I Calc Number. GEO.IBIP.02.03 Rev Number: 0 Sheet Number. 16 of 18 Date: 10/4/02
- 10. REFERENCES Abe, K. (1981). Magnitudes of large shallow earthquakes from 1904-1980, Physics of the Earth and Planetary Interiors, v. 27, 72-92.
Abe, K. (1984). Complements to " Magnitudes of large shallow earthquakes from 1904-1980", Physics of the Earth and Planetary Interiors, v. 34, 17-23.
Bevington, P. R. (1969). Data Reduction and Error Analysis for the Physical Sciences, McGraw-Hill. 336 pp.
Carver G. (2002). Seismic Source Characterization of the Cascadia Subduction Zone, Appendix 5A in Technical Report TR-HBIP-2002-01, Seismic Hazard Assessment for the Humbolt Bay ISFSI Project.
Cohee, B. P., Somerville, P. G., and N. A. Abrahamson (1991). Simulated ground motions for hypothesized Mw = 8 subduction zone earthquakes in Washington and Oregon, Bull. Seism. Soc. Am., Vol. 81, No. 1, pp. 28-56.
Geomatrix (1995). Seismic Design Mapping, State of Oregon. Report to the Oregon Department of Transportation, Contract Number 11688, January 1995.
National Geographic Society (1995). Living on the Edge, map insert within April 1995 issue.
Wells, D. L. and K. J. Coppersmith (1994). New empirical relationships among magnitude, rupture length, rupture width, rupture area, and surface displacement, Bull.
Seism. Soc. Am., 84, 974-1002.
Cale Number GEO.HBIP.02.03 Rev Number 0 Sheet Number 17 of 18 Date: 10/4/02 Attachment A 5 September 2002 Letter from R Youngs, Geomatrix to R. White, PG&E
Calc Number GEO.HBIP.02.03 Rev Number: 0 SheetNumber. 18 of 18 Z1cl w,ast u-c. 12n FP-l Date: 10/4/02 O..sz:ur-i.
CA 9Aeo1n2
=I C 683-d1
- F
- =1a6 aE41 GEOMATRPIX September 30, 2002 Project 5 117.009, Task 9 Robert K. White Pacific Gas and Electric Company Geosciences Department 245 Market Street, Room 418B Mail Code N4C P.O. Box 770000 San Francisco CA 94177
Dear Rob:
I am writing to acknowledge a potential error you may have identified in your letter dated September 11, 2002. Comparison of Plate 1 in the January 1995 report "Seismic Design Mapping, State of Oregon" with Figures 2-16 and 2-17 indicates that the Deformation Front identified in these Figures may be mislabeled and may correspond to the Change in Fold Trends line as mapped in Plate I. As a result, the interface widths listed on page 2-21 may be too small by about 25 ln.
Thank you for bringing this matter to my attention.
Sincerely, GEOMATRX CONSULTANTS, INC.
Robert R. Youngs Principal Engineer
- \\ProjeMOOos1 17OCORESPONYougs-L_093002.doc Gooamtrix Cmustents, Inc.
Airs.
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Geosciences BPP ISFSI Geotechnical Calculation Verification Report Calculation
Title:
Development of Maximum Credible Earthquake Magnitudes and Distances for the HBIP Calculation No.:
GEO.HBIP'02.03 Revision No.:
0 Calculation Author: Norman Abrahamson Calculation Date:
10/4/02 Verifier:
Stuart Nishenko Verification Date:
10/16/02 Introduction As required by Geosciences Work Plan GEO 2002-01, Rev 1 and Geosciences Calculation Procedure GEO.001, Rev. 6, have performed an independent technical review (lTR) and peer review of the above listed calculation. In addition to performing a step-by-step check of the calculation (Verification Method A), I also verified the calculations using an Excel spreadsheet program (Verification Method B). Those alternate verification files are attached to this ITR Report. This ITR report is structured with the same Section headings as the Calculation.
- 2.
Purpose I determined that the purpose of this calculation is clearly stated as per NUREG 1567 section 2.4.6.1-2.4.6.2 and NUREG 0800 section 2.5.2.
- 3.
Assumptions I reviewed the assumptions for this calculation and find them reasonable and consistent with current seismological practice and understanding of earthquake hazards in the region.
I specifically reviewed the original data cited in Geomatrix (1995, p. 2-14) for Assumption 3.4 (e.g. Goldfinger, C., et al., 1992, Neotectonic Map of the Oregon Continental Margin and Adjacent Abyssal Plain, DOGAMI Open File Rpt. 0-92-4) and agree that 30 km is a more conservative (and accurate) estimate of the location of the change in fold trends with respect to the Deformation Front.
- 4.
Data Inputs 4.1 Width Approaches for the Cascadia Interface Geomatrix (1995) is the primary reference for establishing the width of the Cascadia interface. I verified that the weights for the alternative estimates of the updip and downdip extent of the Cascadia interface were correctly cited and used in the calculations.
Page 1 of5
Verification Report GEO.HBIP.02.03 Rev. 0 The determination that p. 2-21 of Geomatrix (1995) contains an error in mapping the width of the interface resulted in the need to independently recalculate the width (see Section 7 of this calculation). Given the critical nature of this parameter for these calculations, I suggest that a letter of confirmation, as to the cause of this error (as stated in Section 4.1 of the calculation), from Geomatrix be attached to the calculation.
Resolution: A letter has been obtained from R. Youngs of Geomatrix acknowledging this issue and is attached to the Calculation Package.
4.2 /4.3 Dimensions of Cascadia Interface and Little Salmon Fault Zone I reviewed the parameters listed in these two sections based on a July 12, 2002 version of Appendix 5A [Carver (2002) [memo from L. Pulley to G. Carver, 7/12/02)). While I find them to be correctly cited, I note that these numbers are preliminary and will need to be checked against the final Appendix 5A when it is issued.
Resolution: Values used in this calculation package are consistent with those cited in Appendix 5A, Rev. 0 (September 5, 2002)
I note that rupture length for the Little Salmon Fault is listed as 310 km in the calculation (Section 4.3 and Table 7-7) and 330 km in Figure 2-5 (PGE, 2001) and Carver (2002, p.
5A-6). I measured the along-strike length of the Little Salmon fault zone from Figure 2-5 and found it to be 300 km at the center, 330 km along the western (seaward) edge and 280 km along the eastern (landward) edge. To minimize confusion, the estimates in this Calculation should be consistent with the text for Figure 2-5 and Appendix 5A.
Resolution: A rupture length of 310 km has been consistently adopted for the Little Salmon fault and is used in all calculations.
The estimate of 7 to 8 meters displacement per event on the Little Salmon fault system (Appendix 5A, Carver (2002)) needs to be clarified.
Resolution: The estimated displacements per event for the Little Salomon fault has been clarified in Appendix SA, Rev. 0 and the resultant numbers carried through the calculations.
S.
Method and Equation Summary I reviewed the equations listed in Section 5.2 for accuracy by checking the original references.
Equation 5-7 is missing a l/Ewi term (see Bevington, 1969, p. 73).
Resolution: The equation has been corrected
- 6.
Software No specialized software is required for these calculations.
- 7.
Calculations Page 2 of 5
Verification Report GEO.HBIP.02.03 Rev. 0 7.1 Magnitude for the Cascadia Interface To resolve the inconsistency in the Geomatrix (1995) estimates of the width of the Cascadia interface, an independent data source was used (Living on the Edge, the April 1995 National Geographic Society (NGS) map of the Cascadia subduction zone). While this map is an independent source, the lack of geographic coordinates makes me question the accuracy of this map for use in this calculation. I crosschecked the National Geographic map against the original scientific references that were used to compile the map (see maps attached to this ITR - Clarke, S.H., 1990, Geologic Structures, Northern California Continental Margin, USGS Map MF-210; and Goldfinger, C., et al., 1992, Neotectonic Map of the Oregon Continental Margin and Adjacent Abyssal Plain, DOGAMI Open File Rpt. 0-924). The width of the margin, defined as the distance between the Deformation Front and the coastline on the NGS map is consistent, to within a few km, with these references. I judge the NGS map to be an accurate presentation suitable for this calculation, based on this comparison.
I also checked the measurements listed in Tables 7-1 and 7-2 against the calculation computation sheets (A.M. Becker, attached), Plate 1 and Figure 2-16 (Geomatrix, 1995) and the NGS map and found them to be accurate and suitable for estimating the downdip width of the Cascadia interface. These data support the conclusion that the boundary listed in Figure 2-16 of Geomatrix (1995) is mislabeled.
I independently calculated the downdip width based on these parameters to verify the values listed in Table 7-3 (see attached Excel Spreadsheet).
I note that either Table 74 is missing or Table 7-5 (and all subsequent Tables) is (are) mislabeled.
Resolution: Table numbers have been corrected Comparison of Tables 7-3 and 7-5 show a number of discrepancies in the estimates of the maximum downdip width of the Cascadia interface. The heading for Table 7-5 should be changed to -Average Maximum Rupture Downdip Width of the Cascadia Interface to resolve this confusion.
Resolution: Table 74 title changed to indicate that down dip widths are averaged along the rupture length I independently calculated the mean characteristic magnitudes for the Cascade interface using the values from Section 4 and the equations from Section 5 to verify the values listed in Table 7-6 (see attached Excel Spreadsheet). Differences are noted in red.
Resolution: Differences noted in the ITR have been corrected and resolved.
I verified that 5.5 kn is the closest horizontal distance to the HBIP from the Table Bluff fault from Figure 3-3 (PGE, 2001) and 7 km is the closest distance (at depth) from the cross-section in Figure 3-4 (PGE, 2001). I note that these figures are preliminary and these values will need to be checked against the final figures when they are issued.
Page 3 of 5
Verification Report GEO.HBIP.02.03 Rev. 0 Resolution: These distances have been checked and verified against the final versions of Figure 3-3 and 3-4 (Rev. 0. Sept 11, 2002).
7.2 Magnitude for the Little Salmon Fault System I independently calculated the mean characteristic magnitude for Little Salmon fault system using the values from Section 4 and the equations from Section 5 to verify the values listed in Table 7-7 (see attached Excel Spreadsheet). Differences are noted in red.
While the math is correct, application of these values is subject to resolution of the length of the Little Salmon fault system (310 or 330 km - see comments for Section 4.3). Note, that in the attached spreadsheet for Table 7-7, the difference in the final weighted magnitude is 0.01 unit (7.74 vs. 7.73)
Resolution: Length of the Little Salmon fault is now consistently defined as 310 km throughout this Calculation Package as per Appendix SA, Rev. 0. The final weighted magnitude for the mean characteristic event is rounded to M 7.7.
I verified that 0.5 km is the shortest distance to the HBIP from the Bay Entrance fault from Figure 4-16 (PGE, 2002). I note that these figures are preliminary and these values will need to be checked against the final figures when they are issued.
Resolution: This distance has been checked and verified against the final version of Figure 4-16 (Rev. 0, Sept 16,2002).
- 8. & 9. Results/ Conclusions I verified that the results of this calculation are consistent with the analysis and that the conclusions of the calculation are well supported by the results, subject to resolution of the comments raised in this ITR. The purpose of the calculation (as described in the Purpose section) has been met.
- 10.
References I verified that all the references are appropriately cited and note that a reference is needed for Carver (2002).
Resolution: Reference for Carver (2002) was added.
- 11.
Attachments Verification spreadsheets, Method B, for Tables 7-3, 7-6 (revised 7-5), and 7-7 (revised 7-63.
Page 4 of 5
Verification Report GEO.HBIP.02.03 Rev. 0 c;/0 Ce4 sh;'e
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Verification Report Attachment GEO.HBIP.02.03 Rev. 0 Table 7-3 Latitude HorlIY4W D
W w
P H4WINI DWIdIOMWI ne e
"ipb I
3Dformatohi FrontOi I -
-as~
ITansZie l ohi4W Dj dltWj HartzlW. Downdi W 41 42 43 44 45 46 47 48 49 100 100 87 83 74 78 83 70 39 104 104 91 86 77 81 86 73 41 65 57 52 52 57 78 117 126 83 68 69 64 64 59 81 122 131 86 130 130 117 113 104 108 113 100 69 135 135 122 118 108 112 118 104 72 95 87 82 82 87 108 147 156 113 99 91 86 86 91 112 163 162 118 Average 41-47 41-49 90 83 71 79 121 114 102 111 I
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Verification Report Attachment GEO.HBIP.02.03 Rev. 0 Table 7-6 j(J' e D~ VdI U Width LeI¶ MA Mr Lwtt Drir ltWt Model Wti Total Wti.
tlV' Mao.; I Zero Def 120 700 Geo 8.69 0.30 0.6 0.5 0.5 0.045 0.39 Zero Def 115 1050 Geo 8.82 0.30 0.6 0.5 0.5 0.045 0.40 Zero Fold 90 700 Geo 8.59 0.70 0.6 0.5 0.5 0.105 0.90 Zero Fold 85 1050 Geo 8.71 0.70 0.6 0.5 0.5 0.105 0.91 Thermal Def 100 700 Geo 8.62 0.30 0.4 0.5 0.5 0.03 0.26 Thermal Def 110 1050 Geo 8.80 0.30 0.4 0.5 0.5 0.03 0.26 Thermal Fold 70 700 Geo 8.50 0.70 0.4 0.5 0.5 0.07 0.59 Thermal Fold 80 1050 Geo 8.69 0.70 0.4 0.5 0.5 0.07 0.61 Zero Def 120 700 Abe 8.91 0.30 0.6 0.5 0.5 0.045 0.40 Zero Def 115 1050 Abe 9.07 0.30 0.6 0.5 0.5 0.045 0.41 Zero Fold 90 700 Abe 8.79 0.70 0.6 0.5 0.5 0.105 0.92 Zero Fold 85 1050 Abe 8.94 0.70 0.6 0.5 0.5 0.105 0.94 Thermal Def 100 700 Abe 8.84 0.30 0.4 0.5 0.5 0.03 0.27 Thermal Def 110 1050 Abe 9.05 0.30 0.4 0.5 0.5 0.03 0.27 Thermal Fold 70 700 Abe 8.68 0.70 0.4 0.5 0.5 0.07 0.61 Thermal Fold 80 1050 Abe 8.91 0.70 0.4 0.5 0.5 0.07 0.62 1
8.77 Mean Page 2 of 3
Verification Rport Attachment GEO.HBIP.02.03 Rev. 0 Utt Salmon Fault Zone Table 7-7 iilm3#6 W Dl Width Pt DF;;
Dl, WI $a Ma
. Total WL~' WtMa l
Area Area Area Disp Disp 0.5 0.5 0.5 0.5 0.5 40 0.2 15 23.3 45 0.6 15 21.2 50 0.2 15 19.6 310 310 310 1
7223 1
6572 1
6078 7.85 0.1 7.81 0.3 7.78 0.1 7
0.5 7.62 0.25 9.3 0.5 7.72 0.25 7.8 Mean 1
0.79 2.34 0.78 1.91 1.93 7.74 Mag(Area) Is Eqn 5-1, Wells and Copersmlth(94)
Mag(Disp) Is Eqn 5-4, Wells and Copersmith(94) l-C"X[IWID PMI DWI.Sllh~ngtWk-ISW.;U.SM0S lPt I CAWWjj Area Area Area Disp Disp 0.5 0.5 0.5 0.5 0.5 40 0.2 15 23.3 45 0.6 15 21.2 50 0.2 15 19.6 330 330 330 1
7689 1
6996 1
6468 7.88 0.1 0.79 7.84 0.3 2.35 7.80 0.1 0.78 7
0.5 7.62 0.25 1.91 9.3 0.5 7.72 0.25 1.93 7.8 Mean 7.76 1
Mag(Area) IS Eqn 5-1, Wells and Copersmith(94)
Mag(Disp) Is Eqn 54, Wells and Copersmilh(94)
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