ML24198A105
| ML24198A105 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 07/17/2024 |
| From: | Bird P Environmental Working Group, Friends of the Earth, San Luis Obispo Mothers for Peace |
| To: | Perry Buckberg NRC/NRR/DORL/LPL2-2 |
| Lee S, 301-415-3158 | |
| Shared Package | |
| ML24074A328 | List: |
| References | |
| EPID L-2024-CRS-0000, OEDO-24-00083 | |
| Download: ML24198A105 (27) | |
Text
Correcting 4 False Assumptions in PG&Es Seismic Source Characterization [2015]
and Update [2024] that Caused PG&E to Seriously Underestimate Seismic Hazard at Diablo Canyon Nuclear Power Plant 2024.07.17 presentation to the Petition Review Board of the U.S. Nuclear Regulatory Commission
by Peter Bird, Professor Emeritus, UCLA consulting to San Luis Obispo Mothers for Peace, Friends of the Earth, & Environmental Working Group 4 False Assumptions
- 1. The Irish Hills are uplifting as a rigid block, with no internal deformation.
- 2. Active thrust faults may dip at any angle.
- 3. Geologic structures older than ~0.33 Ma are irrelevant to seismic hazard estimation.
- 4. GPS geodetic velocities are not useful for site-specific seismic hazard estimation.
- 1. The Irish Hills are uplifting (at ~0.2 mm/year, stipulated) as a rigid block, with no internal deformation.
Therefore, thrust faulting occurs only at the margins (Los Osos thrust, San Luis Bay thrust,
?Inferred Coastline thrust? ) with fault throw (vertical) rates of ~0.2 mm/year.
HOWEVER:
Ø The geologic map shows tight folding of Late Miocene sedimentary rocks has occurred since 6~5 Ma. Therefore, the Irish Hills are not rigid, and additional blind thrust faults are active in the interior.
Ø Rigid-body uplift does not produce crustal thickening. Therefore, if the Irish Hills were a rigid block, they would have a positive isostatic gravity anomaly.However, data shows a negative isostatic gravity anomaly, indicating more than simple Airy compensation by crustal roots (more than the typical Airy ratio of 6:1).
THEREFORE:
A simple isostatic model for the total rate of thrust-fault slip under the Irish Hills is at least:
(0.2 mm/year uplift) x 6 / sin(25°dips) = 2.8 mm/year This is the 1 st of 3 independent analytic estimates developed in this presentation.
- 1. The Irish Hills are uplifting (at ~0.2 mm/year, stipulated) as a rigid block, with no internal deformation.
Therefore, thrust faulting occurs only at the margins (Los Osos thrust, San Luis Bay thrust,
?Inferred Coastline thrust? ) with fault throw (vertical) rates of ~0.2 mm/year.
HOWEVER:
Ø The geologic map shows tight folding of Late Miocene sedimentary rocks has occurred since 5 Ma. Therefore, the Irish Hills are not rigid, and additional blind thrust faults are active in the interior.
Ø Rigid-body uplift does not produce crustal thickening. Therefore, if the Irish Hills were a rigid block, they would have a positive isostatic gravity anomaly.However, data shows a negative isostatic gravity anomaly, indicating more than simple Airy compensation by crustal roots (more than the typical Airy ratio of 6:1).
THEREFORE:
A simple isostatic model for the total rate of thrust-fault slip under the Irish Hills is at least:
(0.2 mm/year uplift) x 6 / sin(25°dips) = 2.8 mm/year This is the 1 st of 3 independent analytic estimates developed in this presentation.
The geologic map of the Irish Hills demonstrates large internal deformation since 5 Ma, especially in the Pismo Syncline.
PG&E [2014]
- 1. The Irish Hills are uplifting (at ~0.2 mm/year, stipulated) as a rigid block, with no internal deformation.
Therefore, thrust faulting occurs only at the margins (Los Osos thrust, San Luis Bay thrust,
?Inferred Coastline thrust? ) with fault throw (vertical) rates of ~0.2 mm/year.
HOWEVER:
Ø The geologic map shows tight folding of Late Miocene sedimentary rocks has occurred since 5 Ma. Therefore, the Irish Hills are not rigid, and additional blind thrust faults are active in the interior.
Ø Rigid-body uplift does not produce crustal thickening. Therefore, if the Irish Hills were a rigid block, they would have a positive isostatic gravity anomaly.However, data shows a negative isostatic gravity anomaly, indicating more than simple Airy compensation by crustal roots (more than the typical Airy ratio of 6:1).
THEREFORE:
A simple isostatic model for the total rate of thrust-fault slip under the Irish Hills is at least:
(0.2 mm/year uplift) x 6 / sin(25°dips) = 2.8 mm/year This is the 1 st of 3 independent analytic estimates developed in this presentation.
The negative isostatic gravity anomaly here means that:
The topography of the Irish Hills is not just isostatically compensated, it is OVER -
compensated by crustal thickening.
PG&E [2024]
- 1. The Irish Hills are uplifting (at ~0.2 mm/year, stipulated) as a rigid block, with no internal deformation.
Therefore, thrust faulting occurs only at the margins (Los Osos thrust, San Luis Bay thrust,
?Inferred Coastline thrust? ) with fault throw (vertical) rates of ~0.2 mm/year.
HOWEVER:
Ø The geologic map shows tight folding of Late Miocene sedimentary rocks has occurred since 6~5 Ma. Therefore, the Irish Hills are not rigid, and additional blind thrust faults are active in the interior.
Ø Rigid-body uplift does not produce crustal thickening. Therefore, if the Irish Hills were a rigid block, they would have a positive isostatic gravity anomaly. However, data shows a negative isostatic gravity anomaly, indicating more than simple Airy compensation by crustal roots (more than the typical Airy ratio of 6:1).
THEREFORE:
A simple isostatic model for the total rate of thrust-fault slip under the Irish Hills is at least:
(0.2 mm/year uplift) x 6 / sin(25°dips) = 2.8 mm/year This is the 1 st of 3 independent analytic estimates developed in this presentation.
- 2. Active thrust faults may dip at any angle (measured from the horizontal). dip
PG&E assigned alternative model dips of 30 °, 50 °, and 80 ° for the Los Osos thrust fault, and 45 ° to 75 ° for the San Luis Bay thrust fault.
HOWEVER:
125 -year -old Mohr/Coulomb friction theory shows that thrusts never form at dips steeper than 45 °, and most commonly dip at ~25 ° [for rock friction coefficient of 0.85; Byerlee, 1978].
THEREFORE:
Seismic potency rate (per m of fault trace) is defined as = (slip rate) x (down -dip width).
This important measure of earthquake generation varies as 1/sin 2 (dip) when throw -rate is held constant (as in these 2 SSC studies).
Compared to reasonable estimates (obtained with dip of 25 °), an assignment of 50 ° dip reduces seismic potency rate by a factor of 3.3 x. An assignment of 80 ° dip reduces seismic potency rate by factor of 5.4 x.
Thus, PG&E underestimated seismic potency of these 2 thrusts (which were the only ones they recognized ) by large factors.
- 2. Active thrust faults may dip at any angle (measured from the horizontal). dip
PG&E assigned alternative model dips of 30 °, 50 °, and 80 ° for the Los Osos thrust fault, and 45 ° to 75 ° for the San Luis Bay thrust fault.
HOWEVER:
125 -year -old Mohr/Coulomb friction theory shows that thrusts never form at dips steeper than 45 °, and most commonly dip at ~25 ° [for rock friction coefficient of 0.85; Byerlee, 1978].
THEREFORE:
Seismic potency rate (per m of fault trace) is defined as = (slip rate) x (down -dip width).
This important measure of earthquake generation varies as 1/sin 2 (dip) when throw -rate is held constant (as in these 2 SSC studies).
Compared to reasonable estimates (obtained with dip of 25 °), an assignment of 50 ° dip reduces seismic potency rate by a factor of 3.3 x. An assignment of 80 ° dip reduces seismic potency rate by factor of 5.4 x.
Thus, PG&E underestimated seismic potency of these 2 thrusts (which were the only ones they recognized ) by large factors.
- 3. Geologic structures older than ~0.33 Ma are irrelevant to seismic hazard estimation.
PG&E based the throw-rates of the San Luis Bay thrust fault and the Los Osos thrust fault on vertical offsets of marine & fluvial terraces with Upper Pleistocene ages, typically ~0.12 Ma.
PG&E never attempted to model the uplift and folding of sedimentary rocks in the Irish Hills which occurred since 5 Ma.
HOWEVER:
A statistical study of all dated fault offsets in California by Bird [2007] showed that the risk of inapplicability to neotectonics is constant for offset features with ages of to 3 Ma, and then rises only modestly for features of 5 Ma age [his Figure 8].
Bird [2007] also showed that a well-constrained fault offset rate requires 4~7 offset features, not just 1 or 2
[his Figure 9].
THEREFORE:
Therefore, all the structures in the Irish Hills, which formed since 5 Ma, should have been studied and modeled to provide geologic constraints on the rates of thrust-faulting.
I provided one example in Figure 1 of my March 2024 Declaration: Throw of the Obispo Formation at the San Luis Bay-Inferred Coastline thrust fault is 1.6~2.2 km since 5 Ma, implying throw-rate of 0.32~0.44 mm/year, and fault slip rate of 0.76~1.04 mm/year.
If thrusting in the Irish Hills has been symmetrical(?), then a minimum total thrust slip-rate by this method would be 1.52~2.08 mm/year. (However, this neglects any internal blind thrusts.)
Bird [2007, Geosphere ]
It takes more than 1 (or 2) offset features to give a well-constrained fault slip rate; actually it takes more than 4!
In California, inapplicability to neotectonics is only a problem for offset features older than 5 Ma. All younger features are equally relevant.
- 3. Geologic structures older than ~0.33 Ma are irrelevant to seismic hazard estimation.
PG&E based the throw-rates of the San Luis Bay thrust fault and the Los Osos thrust fault on vertical offsets of marine & fluvial terraces with Upper Pleistocene ages, typically ~0.12 Ma.
PG&E never attempted to model the uplift and folding of sedimentary rocks in the Irish Hills which occurred since 5 Ma.
HOWEVER:
A statistical study of all dated fault offsets in California by Bird [2007] showed that the risk of inapplicability to neotectonics is constant for offset features with ages of to 3 Ma, and then rises only modestly for features of 5 Ma age [his Figure 8].
Bird [2007] also showed that a well-constrained fault offset rate requires 4~7 offset features, not just 1 or 2
[his Figure 9].
THEREFORE:
Therefore, all the structures in the Irish Hills, which formed since 5 Ma, should have been studied and modeled to provide geologic constraints on the rates of thrust-faulting.
I provided one example in Figure 1 of my March 2024 Declaration: Throw of the Obispo Formation at the San Luis Bay-Inferred Coastline thrust fault is 1.6~2.2 km since 5 Ma, implying throw-rate of 0.32~0.44 mm/year, and fault slip rate of 0.76~1.04 mm/year.
If thrusting in the Irish Hills has been symmetrical(?), then a minimum total thrust slip-rate by this method would be 1.52~2.08 mm/year. (However, this neglects any internal blind thrusts.)
Figure 1. Revised geologic section through the Irish Hills near DCPP. The base for this figure is Figure 13-17 of the Seismic Source Characterization for DCPP (PG&E, 2015). Note that the fault dips suggested by black lines in their figure were not based on data, but were constrained by PG&Es (2015) a priori assumption that only strike-slip tectonics is active in the area. In red, I have suggested more plausible 25° dips for the Los Osos thrust (at right/North) and the Inferred Coastline thrust (at left/South).
The upper -left portion of this figure is also edited to show the throw (vertical offset) of map unit Tmo across the Inferred Coastline thrust, discussed in my text paragraph IV.B.25(b).
- 3. Geologic structures older than ~0.33 Ma are irrelevant to seismic hazard estimation.
PG&E based the throw-rates of the San Luis Bay thrust fault and the Los Osos thrust fault on vertical offsets of marine & fluvial terraces with Upper Pleistocene ages, typically ~0.12 Ma.
PG&E never attempted to model the uplift and folding of sedimentary rocks in the Irish Hills which occurred since 5 Ma.
HOWEVER:
A statistical study of all dated fault offsets in California by Bird [2007] showed that the risk of inapplicability to neotectonics is constant for offset features with ages of to 3 Ma, and then rises only modestly for features of 5 Ma age [his Figure 8].
Bird [2007] also showed that a well-constrained fault offset rate requires 4~7 offset features, not just 1 or 2
[his Figure 9].
THEREFORE:
Therefore, all the structures in the Irish Hills, which formed since 5 Ma, should have been studied and modeled to provide geologic constraints on the rates of thrust-faulting.
I provided one example in Figure 1 of my March 2024 Declaration: Throw of the Obispo Formation at the San Luis Bay-Inferred Coastline thrust fault is 1.6~2.2 km since 5 Ma, implying throw-rate of 0.32~0.44 mm/year, and fault slip rate of 0.76~1.04 mm/year.
If thrusting in the Irish Hills has been symmetrical(?), then a minimum total thrust slip-rate by this method would be 1.52~2.08 mm/year. (However, this neglects any internal blind thrusts.)
- 4. GPS geodetic velocities are not useful for site -specific seismic hazard estimation.
PG&E operated a GPS receiver at DCPP, and PG&E[2015] reported the shortening direction across the Irish Hills (~N15° E), but notthe rate. The PG&E[2024] update adds no new geodetic information !
HOWEVER:
Seismicity has been successfully forecast using only GPS data, both in southern California [Shen et al., 2007] and globally [Bird et al., 2010; Bird & Kreemer, 2015].
Therefore, GPS data are useful. Any deformation model used in SSC should fit GPS strain-rate constraints (within their uncertainties).
THEREFORE:
Our two NeoKinemamodels of neotectonics in the western US [Field et al., 2013; Shen & Bird, 2022] had low-resolution F -E grids in the Irish Hills region, but:
Both showed ~2 mm/year shortening across the Irish Hills, implying total thrust fault slip rate of (~2 mm/year) / cos(25°) = ~2.2 mm/year.
This is the 3 rd of 3 independent analytic estimates developed here.
Bird & Kreemer
[2015, BSSA]
global forecast based on strain -ra t e s measured by GPS geodesy.
Historic earthquakes (black dots) were not used in creating this forecast.
- 4. GPS geodetic velocities are not useful for site -specific seismic hazard estimation.
PG&E operated a GPS receiver at DCPP, and PG&E[2015] reported the shortening direction across the Irish Hills (~N15° E), but notthe rate. The PG&E[2024] update adds no new geodetic information !
HOWEVER:
Seismicity has been successfully forecast using only GPS data, both in California
[Shen et al., 2007] and globally [Bird et al., 2010; Bird & Kreemer, 2015].
Therefore, GPS data are useful. Any deformation model used in SSC should fit GPS strain-rate constraints (within their uncertainties).
THEREFORE:
Our two NeoKinemamodels of neotectonics in the western US [Field et al., 2013; Shen & Bird, 2022] had low-resolution F -E grids in the Irish Hills region, but:
Both showed ~2 mm/year shortening across the Irish Hills, implying total thrust fault slip rate of (~2 mm/year) / cos(25°) = ~2.2 mm/year.
This is the 3 rd of 3 independent analytic estimates developed here.
- 4. GPS geodetic velocities are not useful for site -specific seismic hazard estimation.
PG&E operated a GPS receiver at DCPP, and PG&E[2015] reported the shortening direction across the Irish Hills (~N15° E), but notthe rate. The PG&E[2024] update adds no new geodetic information !
HOWEVER:
Seismicity has been successfully forecast using only GPS data, both in California
[Shen, 2007] and globally [Bird et al., 2010; Bird & Kreemer, 2015]. Therefore, GPS data are useful. Any deformation model used in SSC should fit GPS strain-rate constraints (within their uncertainties).
THEREFORE:
Our two NeoKinemamodels of neotectonics in the western US [Field et al., 2013; Shen & Bird, 2022] had low-resolution F -E grids in the Irish Hills region, but:
Both showed ~2 mm/year shortening across the Irish Hills, implying total thrust fault slip rate of (~2 mm/year) / cos(25°) = ~2.2 mm/year.
This is the 3 rd of 3 independent analytic estimates developed here.
- Each time a fa l s e a s s u m p t i o n was removed, thrust - fa u l t i n g a c t i v i t y (seismic potency rate) in the Irish Hills went up by a large factor.
- It is important to estimate how these factors combine, and how much seismic hazard (and SCDF) is increased at DCPP.
- This could be done with a new SSC study and a new SPRA study, except that we cannot afford years of time and millions of $.
- Instead, we will use a much simpler method to show that the lower limit on seismic hazard (and SCDF) due to thrust - fa u l t i n g alone is much higher than the total hazard claimed by PG&E.
- We w i l l d o t h i s b y a d o p t i n g a c h a ra c t e r i s t i c g r e a t t h r u s t e a r t h q u a ke f o r this tectonic setting, and then estimating its frequency in the Irish Hills.
A CHARACTERISTIC GREAT THRUST EARTHQUAKE?
The Noto Peninsula on the northwest coast of Japan is tectonically analogous to the Irish Hills:
a block of crust now being uplifted between two conjugate intraplate thrust faults.
We learned 2 essential facts from the 2024.01.01 m7.5 earthquake there:
§ Mean slip on the seismogenic part of the thrust was 2 m [USGS finite-fault solution].
§ Peak ground accelerations (PGA) at 5 strong-motion seismometers were 1.0~2.3 g.
To d a Stein
[2024]
CONCLUSIONS:
Ø The two SSC studies by PG&E[2015; 2024] seriously underestimated the seismic hazard from thrust - faulting under the Irish Hills because they relied on 4 demonstrably false assumptions.
Ø Three independent analytic methods give values for the total slip-rate on all shallow - dipping thrust faults under the Irish Hills:
2.8 mm/year, ~2.0 mm/year, or 2.2 mm/year.
Ø Using the 2024.01.01 Noto Peninsula earthquake as a characteristic great thrust earthquake (with its 2 m of mean slip) yields recurrence times for great thrust earthquakes under the Irish Hills of 715 years, 1000 years, or 910 years, respectively.
Ø Because such a great thrusting earthquake would cause seismic core damage at DCPP, its seismic core damage frequency (SCDF) is at least
1.4x 10 - 3 /year, or 1.0x 10 - 3 /year, or 1.1x 10 - 3 /year, respectively.
[This is before the hazard contribution from strike-slip faults like the Hosgri is added.]
REFERENCES CITED Bird, P. [2007] Uncertainties in long-term geologic offset rates of faults: General principles illustrated with data from California and other western states, Geosphere, 3(6), 577-595; doi:10.1130/GES00127.1, + 9 digital file appendices.
Bird, P., and C. Kreemer [2015] Revised tectonic forecast of global shallow seismicity based on version 2.1 of the Global Strain Rate Map, Bull. Seismol. Soc. Am., 105(1), 152-166, doi: 10.1785/0120140129.
Byerlee, J. [1978] Friction in rocks, Pure Appl. Geophys., 116, 615-626.
Field, E. H., G. P. Biasi, P. Bird, T. E. Dawson, K. R. Felzer, D. D. Jackson, K. M. Johnson, T. H. Jordan, C.
Madden, A. J. Michael, K. R. Milner, M. T. Page, T. Parsons, P. M. Powers, B. E. Shaw, W. R. Thatcher, R. J.
Weldon, II, and Y. Zeng [2013] Unified California Earthquake Rupture Forecast, version 3 (UCERF3) -The time-independent model, U.S. Geol. Surv. Open-File Rep., 2013-1165(and Cal. Geol. Surv. Spec. Rep. 228, and Southern California Earthquake Center Pub. 1792), 97 pages (main report) + 20 Appendices; http://pubs.usgs.gov/of/2013/1165/ ; including:
Parsons, T., K. M. Johnson, P. Bird, J. Bormann, T. E. Dawson, E. H. Field, W. C. Hammond, T. A. Herring, R.
McCaffrey, Z.-K. Shen, W. R. Thatcher, R. J. Weldon, II, and Y. Zeng [2013] Appendix CDeformation Models for UCERF3. 66 pages.
Pacific Gas and Electric Company [2014] Geologic Map of the Irish Hills and Adjacent Area, 1:32,000, DCPP Geologic Mapping Project, Ch9.GEO.DCPP.TR.14.01 R0, https://www.pge.com/includes/docs/pdfs/safety/systemworks/dcpp/report/Ch9.GEO.DCPP.TR.14.01_R0_Plates.pdf,
NRC ADAMS Accession No. ML14260A068.
Pacific Gas and Electric Company (PG&E) [2015] Seismic Source Characterization for the Diablo Canyon Power Plant, San Luis Obispo County, California; report on the results of SSHAC level 3 study, Rev. A, March; 652 pages plus Appendices. Available online at http://www.pge.com/dcpp-ltsp; downloaded 2023.05.11.
Pacific Gas and Electric Company (PG&E) [2024] Diablo Canyon Updated Seismic Assessment: Response to Senate Bill 846, 1 February 2024, 392 pages.
Shen, Z.-K., and P. Bird [2022] NeoKinema deformation model for the 2023 update to the U.S. National Seismic Hazard Model, Seismol. Res. Lett., 93, 3037-33052, doi: 10.1785/0220220179.
Shen, Z.-K., D. D. Jackson, and Y. Y. Kagan [2007] Implications of geodetic strain rate for future earthquakes, with a 5 -
year forecast of M5 earthquakes in southern California, Seismol. Res. Lett., 78(1), 116-120.
Toda, S., and Stein, R. S. [2024] Intense seismic swarm punctuated by a magnitude 7.5 Japan shock, Temblor, http://doi.org/10.32858/temblor.333