Cascadia Subduction Zone Earthquakes and Critical Infrastructure Workshop

Edward Perez, FERC

Background

- Part 12D Report.- Every 5 years.- Top-to-bottom review of

safety. - Accept/Supplement- Remedial Action.- Safe or not?- Seismic Load case- Stay up to speed with

latest science.- Update analyses as

needed.

2

Cascadia Subduction Zone Earthquakes and Critical Infrastructure Workshop

Edward Perez, FERC

Two significant seismic reports currently under review.-Probabilistic Hazard Analyses For Mid-Columbia Dams.-EWEB: Seismic Hazard Assessment, Carmen-Smith and Leaburg-Walterville Projects.-Ground motions higher than previous studies.- Results may affect other FERC projects.

2012 PROBABILISTIC SEISMIC HAZARD ANALYSES

PROJECT FOR THE MID-COLUMBIA DAMS

Prepared for Public Utility Districts of Chelan, Douglas, and Grant Counties February 2012

Chelan Dam Wells Dam Rocky Reach Dam Priest Rapids Dam Wanapum Dam Rock Island Dam

Also currently under FERC review:

Seismic Hazard Assessment

Carmen-Smith and Leaburg Walterville EWEB requested to conduct comprehensive seismic hazard assessment

(previous Part 12D studies indicated very low ground motions). Info needed for Part 12 Subpart D Reports and new fish passage facility

design. Consistent framework for seismic evaluation of existing and proposed

facilities. DSHA,MCE, and PSHA Located along McKenzie River east of Eugene, OR. CSZ ( interface and intraplate) and 20 crustal sources. Intraplate in Oregon? Nason McCullough, CH2M-Hill

FERC review:

Crustal Faults Use the most current mapped fault dimensions and

locations, as documented in the USGS Fault and Fold Database.

Use the USGS mapped fault length with the Wells and Coppersmith (1994) relationships to estimate maximum moment magnitude.

Use a random crustal (normal fault) event located 15 km from the project site to be consistent with recommendations in northern Oregon Cascades.

Crustal sources: Use the geometric mean of all five GMPE relationships (2008 NGA’s).

Use the median (50th percentile) motions for low activity or low slip rate sources and 84th percentile for high activity or high slip rate sources. As no crustal faults have been identified within the vicinity of EWEB facilities with high activity or slip rates, the 50th percentile motions should be used unless additional evidence of higher activity/slip rates is found.

Seismic Recomendations

Subduction Zone Interface Source Use the bottom of the transition zone as used by the USGS national

seismic hazard mapping to determine the site-to-source distance. Use a maximum MW 9.0. Use the 84th Percentile motions – given that this source has an average

recurrence interval on the order of about 500 years, it is prudent to use the 84th percentile ground motions.

Seismic Recommendations

Subduction Zone Intraplate Source Use the most recent information to determine the closest site-to-source

distance to the top of the Juan de Fuca plate. Use a maximum MW 7.2. Use the median (50th percentile) motions – given that this source has

no historical activity of engineering interest (MW greater than 5.0), an anomaly for intraplate sources worldwide.

Recommendation: There is geologic evidence that the Intraplate source may not be capable of generating earthquakes of engineering interest; therefore, use the median ground motions.

EWEB Projects Include

1. The Leaburg-Walterville Facilities considered include the:

a. Walterville Forebay

b. Leaburg Forebay

c. Leaburg Diversion

2. Carmen-Smith Facilities considered include the:

a. Carmen Diversion Dam

b. Smith Dam

a. Trail Bridge Dam

Crustal Seismic Sources

Crustal Seismic Sources

TABLE 1 Crustal Faults within the Vicinity of EWEB Facilities, as documented by USGS (2011)

Fault Name USGS Fault Number a

Fault Type b

Mapped Length (km)

Most Recent Deformation c

Slip Rate (mm/yr)

Canby-Molalla Fault 716 RL 31.1 < 15 ka < 0.2

Salem-Eola Hills homocline 719 Fold 19.9 < 1.6 Ma < 0.2

La Pine Graben Faults 838 N 46.0 < 130 ka < 0.2

Chemult Graben Fault System (west) 839a N 31.7 < 130 ka < 0.2

Unnamed Faults near Millican Valley 841 N 24.9 < 750 ka < 0.2

Unnamed Faults near Kiwa Butte 842 N 4.3 < 1.6 Ma < 0.2

Warm Springs Fault Zone 851 N 21.1 < 750 ka < 0.2

Sisters Fault Zone 852 N 53.4 < 15 ka < 0.2

Metolius Fault Zone 853abc N 92.0 < 15 ka < 0.2

Unnamed Faults NE of Diamond Lake 854 N 28.0 < 130 ka < 0.2

Unnamed Faults near Sutherlin 862 N 17.4 < 750 ka < 0.2

Upper Willamette River Fault Zone 863 RL 44.0 < 1.6 Ma < 0.2

Clackamas River Fault Zone 864 RL 18.0 < 1.6 Ma < 0.2

Corvallis Fault Zone 869 T 41.0 < 1.6Ma < 0.2

Owl Creek Fault 870 R 15.0 < 750 ka < 0.2

Mill Creek Fault 871 R 11.2 < 15 ka < 0.2

Waldo Hills Fault 872 N 7.5 < 1.6Ma < 0.2

Mount Angel Fault 873 T 18.6 < 15 ka < 0.2

Newberry Volcano Ring Faults 1806 N 5.0 < 15 ka < 0.2

White Branch Fault Zone 1809 N 18.0 < 750 ka < 0.2 a Faults are identified by number in Figure 1. b Fault type notation: R (Reverse), N (Normal), RL (Right Lateral), T (Thrust) c Deformation age notation: Ma (million years before present), ka (thousand years before present)

Interface & Intraplate Seismic Sources

Juan de Fuca Plate Distances

Leaburg-Walterville Results

TABLE 7 Peak Ground Acceleration Values (PGA) – Median Values Crustal Sources for Leaburg-Walterville

Seismic Source Walterville Forebay Leaburg Forebay Leaburg Diversion

White Branch Fault 0.03 0.03 0.04

Upper Willamette River Fault 0.10 0.10 0.09

Metolius Fault 0.03 0.04 0.04

Random, M6 R17 0.12 0.12 0.12

Crustal Source Envelope 0.12

TABLE 8 Peak Ground Acceleration Values (PGA) Cascadia Interface and Intraplate Sources for Leaburg-Walterville

Seismic Source Walterville Forebay Leaburg Forebay Leaburg Diversion

Cascadia Interface – 84th Percentile 0.27 0.25 0.24

Cascadia Intraplate – Median 0.25 0.24 0.24

Carmen-Smith Results

TABLE 9 Peak Ground Acceleration Values (PGA) – Median Values Crustal Sources for Carmen-Smith

Seismic Source Trail Bridge Dam Smith Dam Carmen Diversion

White Branch Fault 0.14 0.12 0.10

Upper Willamette River Fault 0.04 0.04 0.04

Metolius Fault 0.11 0.12 0.14

Random, M6 R17 0.12 0.12 0.12

Crustal Source Envelope 0.14

TABLE 10 Peak Ground Acceleration Values (PGA) Cascadia Interface and Intraplate Sources for Carmen-Smith

Seismic Source Trail Bridge Dam Smith Dam Carmen Diversion

Cascadia Interface – 84th Percentile 0.17 0.17 0.17

Cascadia Intraplate – Median 0.21 0.21 0.21

Earthquake Time Histories

Considered Motions: Interface:

- 1978 Miyagi-Oki- 1985 Mexico- 1985 Chile- 2010 Chile

Intraplate:- 1949 Olympia- 1965 Puget Sound- 2001 Nisqually- 1974 Peru

- 1997 Mexico

Crustal:- 1980 Irpinia, Italy- 1979 Norcia, Italy- 1975 Oroville- 1992 Little Skull Mtn,

Nevada- 1980 Mammoth Lakes- 1983 Borah Peak,

Idaho