# Presentation: 497781

##  Development of Seismic Basis Draft FERC Guidelines A Case History

- April 2006

## Our Interpretation!Draft FERC Guidelines

- _STEP 1_ - Use USGS Maps for a PSHA
- Modern Approach – Consensus Based
- Uniformity across the USA
- Too Costly to perform a site-specific PSHA
- 2500 year results are conservative
- EPRI 1980’s
- LLNL 1980’s
- 2500 yr vs.1000 yr or MCE
- USGS keeps the Maps Current
- May need to enhance if dam is adjacent major active fault
- May need to perform Site Response analysis for soil site

## Our Interpretation!Draft FERC Guidelines

- _STEP 2_ – Perform a deterministic analysis
- Use USGS Source Map
- Use USGS Recurrence Relationships
- Use Recent Ground Motion Models
- May need to enhance if near active fault
- May need to consider Site Response if not a rock site

## Our Interpretation!Draft FERC Guidelines

- _STEP 3_ – Envelop the results of two analyses
- If USGS PSHA governs design, consider Site-Specific PSHA
- Choose Real Time histories carefully
- At least two for linear analysis, more for non-linear
- Consider source mechanisms, distance, magnitude, and recording station media
- Consider duration, frequency contribution, scale factors
- Consider natural frequency of the dam

##  Case History for a New Dam

- Three Step Process
- Our Approach:
- Perform _Two_ Independent Analysis
- (a) the USGS _2500_ year event, and
- (b) the ground motion as calculated from a deterministic analysis based on events having a recurrence interval of _2500_ years
- Check impact of a local fault postulated to be active
- Use “Worst Case”

## Slide 6

## Slide 7

## USGS 2500 Yr Return Period For Site

|  Site | 2% PE in 50 yrs |
| --- | --- |
| 1 Hz (Sd1) | 0.1987 |
| 5Hz (Sds) | 0.6716 |
| PGA | 0.3276 |

- Based on USGS Hazard Maps

- To=0.2*Sd1/Sds

- Ts=Sd1/Sds

| To | 0.059 sec |
| --- | --- |
| Ts | 0.2959 sec |

## Slide 9

## Deterministic Analysis

- Use 2500 yr events (low slip rate faults) for background events
- Use MCE for New Madrid & Wabash Valley Zones
- Use USGS Recurrence Periods
- Use Multiple Attenuation Relationships

## Site Deterministic Seismic Hazard Evaluation

## Local and Regional Geology

## Site Deterministic Seismic Hazard Evaluation

| Source | T=2500  | MCE |
| --- | --- | --- |
| Local. Seismicity | 5.8 | - |
| Wabash Valley | 6.5 | 7.5 |

- Log(N)=a-b*Mw

- For New Madrid
- MCE= 7.7 (Mw) for a period of 1000 years (Tuttle et al., 2002)

- Mw values for Different Sources

## Site  Deterministic Seismic Hazard Evaluation

- Attenuation relationships
- Atkinson & Boore (1997)
- Toro et al. (1997)
- Frankel et al. (1997)
- Somerville et al. (2001)
- Campbell (2003)

-      Moment Magnitudes and Distances for earthquakes
- _New Madrid MCE_
-        Mw= 7.7    D=110 km
- _Wabash Valley MCE_
-        Mw=7.5     D=88 km
- _Background Seismicity (T=2500 yrs)_
-        Mw=5.8     D=20 km

## Site Deterministic Seismic Hazard Evaluation

| Ground Motion Model | Weight |
| --- | --- |
| Atkinson & Boore (1997) | 0.25 |
| Toro et al. (1997) | 0.25 |
| Frankel et al. (1997) | 0.25 |
| Somerville et al. (2001) | 0.125 |
| Campbell (2003) | 0.125 |

| Ground Motion Model | Weight |
| --- | --- |
| Atkinson & Boore (1997) | 0.286 |
| Toro et al. (1997) | 0.286 |
| Frankel et al. (1997) | 0.286 |
| Somerville et al. (2001) | 0 |
| Campbell (2003) | 0.143 |

** ****New Madrid**

**Wabash Valley & Background Seismicity**

- Weight tables above are based on USGS

## Site Deterministic Seismic Hazard Evaluation

## Site  Deterministic Seismic Hazard Evaluation

## Site Deterministic Seismic Hazard Evaluation

- T(sec)

##  Deterministic Seismic Hazard EvaluationConsideration of the Black Fault

- Mw = 5.8 assuming 10km subsurface rupture length (Wells and Coppersmith, 1994)
- Closest Approach to site = 8 km.
- USGS includes potential activity in this Fault system ad Background Seismicity, with Mw 5.8.
- Site Site specific analysis also assumes a Mw 5.8 allowing fault segmentation.

##  Deterministic Seismic Hazard Evaluation

| Subsurface Rupture Length (km) | Subsurface Rupture (%) | Mw |
| --- | --- | --- |
| 40 | 100 | 6.8 |
| 30 | 75 | 6.6 |
| 20 | 50 | 6.3 |
| 10 | 25 | 5.8 |

- Subsurface Rupture Length vs Mw correlation for Black Fault
- (Wells and Coppersmith, 1994)

## Response Spectra for Real Time Histories

## Time History Summary

## Mammoth Lakes Earthquake

- Accel. TH (g)

- Vel. TH (cm/s)

- Displ. TH (cm)

- Arias Intensity (%)

- Fourier Ampl. (cm/s)

## Morgan Hill Earthquake

- Accel. TH (g)

- Vel. TH (cm/s)

- Displ. TH (cm)

- Arias Intensity (%)

- Fourier Ampl. (cm/s)

## Saguenay Earthquake

- Accel. TH (g)

- Vel. TH (cm/s)

- Displ. TH (cm)

- Arias Intensity (%)

- Fourier Ampl. (cm/s)

## Factored Time Histories

## Slide 27

## Slide 28

## Strong Motion Duration Based on Husid Plots

- The Selected Time Histories capture strong motion durations from expected Deterministic Scenario Events.

## Slide 30

## FERC Consultant A Comments

- “...major departure from FERC Draft Guidelines.”
- “The use of NUREG 0098 Spectra...”
- Local Event
- RIZZO used Mag 5.8 @20 km
-  Mag 5.8 is “too precise” –Use 6.0
-  “more reasonable to use 15 km

## FERC Consultant B Comments

- Upgrade Local Event
- “...RIZZO Design Spectrum is significantly above median spectral ordinates...”
- “...for frequencies below 25 Hz, RIZZO Design Spectrum is much more conservative...”
- “...Local earthquake controls the design for frequencies greater than 25 Hz

## Consultant B Conclusions

- Conservative design can be made with Landers and Gilroy #6 (not necessary to use Saguenay Record)
- Adjusted records selected by RIZZO will result in a conservative design

## RIZZO Design Spectra vs. Adjusted Local Event Spectra

## Time History Spectra and Design Spectra