DRC-2015-001664 - 0901a0688050d785

Energy Fuels Resources
(USA) Inc.
WHITE MESA MILL
Probabilistic Seismic Hazard
Analysis
<MvMarch 20145
@) MWH
DRC-2015-001664 BUILDING A BETTER WOULD
3665 JFK Parkway
Suite 206
Fort Collins, CO USA
© MWH
Probabilistic Seismic Hazard Analysis
TABLE OF CONTENTS
1.0 INTRODUCTION 1
1.1 Background and Purpose 1
1.2 Approach 24
1.3 Design Criteria 2
2.0 GEOLOGIC SETTING 43
2.1 Regional Setting 43
2.2 Site Geology 43
3.0 SEISMOTECTONIC SETTING AND HISTORICAL SEISMICITY 54
3.1 Historical Seismicity 54
3.2 Catalogs of Earthquake Data 54
3.2.1 Petersen Catalog 54
3.2.2 ComCat 64
3.2.3 Combined Catalog and Magnitude Bias Correction 65
3.2.4 Earthquakes Attributed to Specific Faults 75
3.2.5 Artificially Induced Earthquakes 75
3.3 Magnitude Conversion 85
3.4 Developing Recurrence Parameters 85
3.4.1 Assessment of Catalog Completeness 85
3.4.2 Estimation of the Recurrence Parameters 97-
4.0 SEISMIC SOURCE CHARACTERIZATION IIS
4.1 Faults jM8
4.1.1 Capable Faults 118
4.1.2 Fault Sources 118
4.2 Seismic Sources 120
4.2.1 Colorado Plateau 1340
4.2.2 Intermountain Seismic Belt 1444
4.3 Shear Wave Velocity 1444
4.3.1 Summary of Site-Specific Vp Values 1544
4.3.2 Development of Vp/Vs Ratio 1645
4.3.3 Estimation of Site-Specific Vs Values 1844
5.0 GROUND MOTION PREDICTION EQUATIONS 1940
6.0 PROBABILISTIC SEISMIC HAZARD ANALYSIS 2047-
6.1 PSHA Code and Methodology 2047-
6.2 PSHA Inputs 2047-
6.2.1 Areal Source Zones 2J48
6.2.2 Fault Sources 2J48
6.3 Probabilistic Seismic Hazard Analysis Results 2148
7.0 RESULTS AND COMPARISON WITH PREVIOUS STUDIES 2320
8.0 REFERENCES 2424
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LIST OF TABLES
Table 1. Magnitude Conversions 8
Table 2. Time Periods for Complete Evont Reporting 9
Table 3. Minimum Criteria for Faults Considered in Soismic Investigation (NRC 10
CFR Appendix A to Part 100) 11
Table A. Envelope of Vp and Vs Values for the White Mesa Site 18
Tablo5. GMPEc usod in tho PSHA 19
Tablo6. PSHA Results 21
Table 1. Time Periods for Complete Event Reporting 9
Table 2. Colorado Plateau - Magnitude Bins and Cumulative N* Values 10
Table 3. Intermountain Seismic Belt- Magnitude Bins and Cumulative N* Values 10
Table 4. Minimum Criteria for Faults Considered in Seismic Investigation (NRC 10
CFR Appendix A to Part 100) 11
Table 5. Envelope of VP and V£ Values for the White Mesa Site 18
Table 6. GMPEs used in the PSHA 19
Table 7. PSHA Input Parameters 20
Table 8. PSHA Results 21
LIST OF FIGURES
Figure 1 Quaternary Faults Within the Study Area
Figure 2 Faults and Earthquake Events Included in PSHA
Figure 3 Artificially Induced EarthguakesCatalog Completeness Plots
Figure 4 Catalog Completeness Plots
Figure 5 Areal Source Zones
Figure 5 Gutenberg-Richter Relationship, Colorado Plateau
Figure 6 Gutenberg-Richter Relationship, Dispersed Earthquake Zone
Figure 7 Gutenberg Richter Relationship, Intermountain Seismic Belt
Figure 87 Seismic Refraction Data from Nielsons Inc. (1978)and Boring Locations
Figure 98 Fault Traces as Modeled in the PSHA
Figure 40 9 Uniform Hazard Spectra Comparison of Vs30Vs3o
Figure 41 10 Peak Ground Acceleration Seismic Source Contribution
Figure 4211 Deaggregation of PGA, 2,-175 year Return Period
Figure 13 Deaggregation of PGA, 9.900 year 10,000-Year Return Period
LIST OF ATTACHMENTS
Attachment 1 List of Earthquake Events within the White Mesa Study Area
Attachment 2 List of Faults and Fault Characteristics Included in the PSHA
Attachment 3 Summary of Individual Fault Parameters
Attachment 4 Dames & Moore Boring Logs (1978)
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1.0 INTRODUCTION
This report presents results of a site-specific probabilistic seismic hazard assessmentanalysis
(PSHA) to develop the seismic design criteria for the-reclamation of the White Mesa Mill (site).
The site is located approximately 6 miles (10 km) south of Blanding., Utah7 at approximately
37.5° N latitude and 109.5° W longitude. The siteSite facilities consist of a uranium processing
mill and five lined tailings/process solution storage cells located within an approximately 686-
acre restricted area.
The probabilistic seismic hazard assessmentanalysis is based on a seismotectonic model and
source characterization of the site and surrounding area. The study evaluated a 200-mile (322-
km) radius surrounding the site. For purposes of this report, this area is termed the "study area"
(Figure 1).
The seismotectonic model identifiesidentified three general seismic sources in the study area: 1)
seismicity of the Intermountain Seismic Belt (ISB), 2) seismicity of the Dispersed Earthquake
Zone (DEZColorado Plateau (CP), and 3) crustal faults that meet the NRC minimum criteria
discussed in Section 4.1.1. Each source zone was characterized to establish input parameters
for the seismic hazard analyses. The PSHA was performed using HAZ43 (20122014) software
developed by Dr. Norman Abrahamson. Operational and long-term design recommendations
were developed based on the results from this PSHA and previous seismic investigations at the
site.
1.1 Background and Purpose
The Utah Division of Radiation Control (DRC) reguested that Energy Fuels Resources (USA),
Inc. (EFRI) conduct a site-specific PSHA for reclamation of the site. This request was part of
DRC's February 2013 review comments (DRC, 2013) on EFRI's August 2012 responses to
DRC's Round 1 interrogatories for the White Mesa Reclamation Plan Rev. 5.0 (EFRI, 2012).
The PSHA was performed to better understand the likelihood of the potential earthquake
sources, to correlate results with previous analyses conducted for the site, and to evaluate the
contribution of the seismic sources for a given return period (e.g. deaggregation). This analysis
assessed the site-specific seismic hazard using Ground Motion Prediction Eguations (GMPEs)
to estimate seismically induced ground motion amplificationmotions at the site. Previous
seismicSeismic hazard analyses were previously conducted for the design of the Cell 4A and
4B facilities (MFG, 2006; Tetra Tech, 2010) and in response to comments by Utah DivisionDRC
review of Radiation Control (DRC) InterrogatoriesEFRI responses to interrogatories on the
Whito Mosa Reclamation Plan, Rov. 5.0 (DRC, 2013) for the sito (MWH, 2012). These roports
indicateanalvses indicated that the seismic hazard at the site is dominated by background
events in the Colorado Plateau.
This report presents a description and results of analyses conducted to respond to the DRC's
comment on ERFI's interrogatory responses (DRC, 2013) requesting a site-specific seismic
hazard evaluation be performed to develop site-specific seismic design parameters. This report
also addresses comments later provided by URS (URS, 2015) in response to a previous version
of this report. This report has been prepared by MWH Americas, Inc. (MWH) at the request of
EFRI.
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1.2 Approach
| This evaluation used data on faults and earthquakes occurring within a 200-mile (322-km)
radius of the site to develop seismic source characterization for the PSHA. An earthquake
| catalog was compiledT and the historical seismicity and information on specific faults was used
to develop the seismic source models for the three seismic sources described above. The
| PSHA considered all defined seismic sources with the goal of identifying the major contributor(s)
to the seismic hazard at the site. The hazard is defined according to GMPEs selected for the
region.
1.3 Design Criteria
Different seismic criteria were established for short-term operational and long term reclaimed
conditions of the tailings cells at the site. The projected operational lifetime of the most recently
constructed tailings cell at the Site is approximately 50 years, from construction through
dewatering and reclamation.—The design life for the reclaimed facility is required to be 1,000
years to the extent reasonably achievable, and at least 200 years, per the US Environmental
Protection Agency (EPA) (EPA 40 CFR 192) and the US Nuclear Regulatory Commission
(NRC) (NRC 10 CFR Appendix A to Part 100 AM (NRC, 2013). An event with a 10,000-vear
return period has a 2 percent probability of exceedance during a 200-year period and a less
than 10 percent probability of exceedance in a 1,000-year period. Therefore, the peak ground
acceleration (PGA) calculated using a 10,000-vear return period is conservative, but appropriate
for the reclaimed (long-term) seismic design criteria for the site.
Seismic design oritoria for operational conditions were evaluated by MFG (2006) using both
deterministic and probabilistic approaches.—MFG selected a peak ground acceleration (PGA)
with an average return period of 2,475 years as the probabilistic design earthquake. MFG used
United States Geological Survey (USGS) National Seismic Hazard Maps to estimate the
seismic event with a return period of 2,475 years. The use of this return period in formulating
the probabilistic operational design criteria is conservative, as an event with this return period
has a 2 percent probability of exceedance over the anticipated 50 year operational design life.
Tetra Tech (2010) evaluated the seismic design criteria for reclaimed tailings cells.—As
discussed above, tho reclaimed tailings cells are assumed have a design life of 200 to 1,000
years.—Tetra Tech ucod both deterministic and probabilistic approaches in evaluating the
seismic design criteria.—Tetra Tech selected an average return period of 9,900 years as
appropriate for estimating the probabilistic seismic design criteria, based on data from the
USGS 2008 National Soismic Hazard Mapping Program (NSHMP) PSHA Intoraotivo
Deaggregation website. The use of a 9,900 year return period in formulating the probabilistic
design criteria for reclaimed conditions is conservative as an event with this return period has a
2 percent probability of exceedance during a 200 year period and a less than 10 percent
probability of exceedance in a 1,000-year period.
The updated site-specific probabilistic seismic hazard analyses described in this report
incorporates the conservative return periods assumed by MFG (2006) and Tetra Tech (2010) for
operational and—long term design,—respectively, to—maintain—consistency with—previous
probabilistic seismic hazard analyses for the site.
The peak ground acceleration calculated in this PSHA will be used during reclamation design to
evaluate liquefaction potential and slope stability of the reclaimed tailings cells. These analyses
use either the PGA or a pseudostatic coefficient of 2/3 of the PGA (DOE, 1989).
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2.0 GEOLOGIC SETTING
2.1 Regional Setting
| -The Reclamation Plan for White Mesa Mill (Denison, 2011), and-the previous seismic studies
(MWH, 2006; Tetra Tech, 2010) provide information on the regional geologic setting. Only
| information specificrelevant to the PSHA will be included here.
| The Sitesite is located within the Colorado Plateau physiographic province in southeastern
Utah. The Colorado Plateau is a broad, roughly circular region of relative structural stability.
The contemporary seismicity of the Colorado Plateau was investigated by Wong and Humphrey
(1989), based on seismic monitoring. Their study characterized seismicity of the plateau as
small to moderate magnitude with a low to moderate rate of widely-distributed earthquakes with
| epicenterhypocentral depths of 9 to 12 miles (15 to 20 kmr). The area is characterized by
generally northwest-striking normal faulting.
Regional geology approximately 50 to 100 miles (80 to 161 km) north to northeast of the site is
characterized by the Uncompahgre Uplift and salt tectonics of the Paradox Valley area. The
Uncompahgre Uplift is a northwest-trending, east-tilted fault block located in southwest
Colorado. For purposes of this PSHA, faults associated with the Uncompahgre Uplift are
considered seismogenic. Faults in the area of the Paradox Valley are generally related to salt
tectonics and are considered non-seismogenic.
The western extent of the study area is bounded by the eastern extent of the Intermountain
Seismic Belt (ISB). The ISB runs from northwestern Montana south into northern Arizona and is
one of the most extensive zones of seismicity within the continental United States (Wong et al.,
1997). Much of the ISB near the site is characterized by north-trending normal faults. The two
| largest earthquakes recorded in the study area, MWmoment magnitude (MJ 6.30 and 6.5,
occurred within the ISB.
The southern and southeastern extent of the study area is a relatively stable area of the
| Colorado Plateau with no guaternaryQuaternary faults. One exception is the Northern
Nacimiento fault, located in northeastern New Mexico.
2.2 Site Geology
Information on site geology is provided in the Reclamation Plan for the White Mesa Mill
(Denison, 2011). This information is summarized below.
The site is located near the center of the White Mesa in southeastern Utah. The area is a north-
south trending mesa characterized by steep canyons formed by stream erosion. The site is
underlain by the Dakota Sandstone, predominately composed of cross-bedded, fine- to coarse-
grained, well-cemented sand (Denison, 2011). Site soils are predominantly derived from wind-
| blown sediment. In the area of the tailings cells,4he soils were removed during construction, as
discussed in Section 4.3.1.
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3.0 SEISMOTECTONIC SETTING AND HISTORICAL SEISMICITY
3.1 Historical Seismicity
The seismic hazard analysis for the site includes a review of historic earthquakes within the
study area. The historic earthquake record for the study area contains earthquakes from 1887
| through the end of 20122014 and provides a general overview of the seismicity of the study
area.
Figure 2 shows seismicity {[events with moment magnitude (Mjyy greater than or equal to 3.0
(MMjv > 3.0)) around)] within the sitestudv area. The earliest recorded event included in the final
PSHA catalog occurred in 1887. The final PSHA catalog contains two events larger than or
egual to moment magnitude 6.0 (Mw 6.0) and 2411 events with moment magnitudes greater
than or egual to 5 and less than 6 (6> > M^_> 5). The remaining events are all less than ©r-
equal to Mw 5.0 (Mw << 5). All events described in this report are given in moment magnitude
unless specified otherwise.
The following paragraphs summarize development of the earthquake catalog used in the PSHA.
I
3.2 Catalogs of Earthquake Data
3.2.1 Petersen Catalog
Catalogs from the US Geological Survey (USGS) NSHMP for the Western United States (WUS)
and Central and Eastern United States (CEUS) (Petersen et al., 20082014) were roviowodused
to compile information regarding historic earthquakes within 200 miles (322 km) of the site.
Petersen et al. (20082014) compiled the catalogs for the WUS and CEUS by reviewing and
combining other available catalogs and combining them.. Petersen et al. (20082014) used their
interpretation of catalog reliability to eliminate duplicate records when an—earthquake
wasearthguakes were listed in more than one catalog. Since attenuation relations,
completeness, and magnitude conversion rules all vary regionally, Petersen et al. (20082014)
built two cataloosr generally following the approach used by the CEUS-SSCn (NRC et al..
2012): a moment-magnitude (Mw) catalog for WUS and a body wave magnitude (Mb) catalog
for the CEUS. Petersen et al. (2014) converted both catalogs to Mw from the original magnitude
recorded.
Within the study area, the Petersen et al. (2008) used a four step algorithm to develop the new
catalogs as described in Mueller et al. (1997).
1. Original catalogs wore reformatted to include each record in a common format that
included its catalog source. For catalogs with an event with multiple magnitude ontrios
(PDE, DNAG, USHIS, and SRA), a single magnitude value was computed for that ovont
in the catalog.
3r.—Reformatted catalogs were concatenated and the full catalog was sorted into
chronological order.
3. When an earthquake was listed in more than one catalog, information regarding data
reliability in the original catalog was used to choose a single event. Earthquakos woro
considered duplicates when their origin times were within one minute.
4^(2014Potoroon ot al. (2008) removed aftershocks and foreshocks (declustering) using
the sliding time and distance window algorithm of Gardner and Knopoff (1974).
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Tho Potorsen et al. (2008) database includes historical seismic events from 1887 through 2000
with Mw > 4.02012 for the WUS and events from 49441910 through 2006 with Mb > 3.02012 for
the CEUS. The original Petersen catalog search returned 6.649 Both catalogs contain events
within the approximate area of tho study area.with Mw S 3.0. AutoCAD software was used to
delineate tbea 200-mile (322-km) radius around the site and includeto identify only those events
within the seismic study area. Further steps taken to develop the final PSHA catalog are
itsteddiscussed below. The PSHA catalog includes 420328 events from the Petersen catalog.
3.2.2 ComCat Catalog
Earthguake information from the WUS and CEUS catalogs was supplemented by a search of
the NEIC database.Advanced National Seismic System (ANSS) Comprehensive Catalog
(ComCat), also maintained by the USGS. The USGS's Global—Earthquake Search
(Beta)ComCat was used to obtain additional earthquake information from January 1, 20072013
through December 31, 2012.—This database pulls from tho new Comprehensive Catalog
(ComCat).February 7, 2015. The catalog was accessed on February 8, 2015. ComCat
contains data from networks contributingthat contribute to the Advanced National Seismic
Svstom and historicANSS database as well as historical data-is from the USGS National
Earthquake Information Center's (NEIC) Preliminary Determination of Epicenters (PDE) catalog
(http://earthquake.usgs.gov/earthquakes/eqarchives/epic/). The—original—ComCat—search
returned 122 events within the approximate area of the seismic study area. AutoCAD software
was used to delineate tbea 200-mile (322-km) radius around the site and includeto identify only
those events within the seismic study area. The final PSHA catalog includes 51 ComCat events,
including five larger magnitude events from 1973 through 2006, as described below, six
ComCat events.
The ComCat catalog was declustered for this PSHA using the Reasenberg (1985) algorithm to
remove dependent events (aftershocks and foreshocks). In order to use the independence
assumption of a Poisson model (typically assumed in PSHA analyses), events that can be
associated with other close-in-time and near-in-space events must be removed from the
catalog. Reasenberg's algorithm identifies events that occur within time and distance windows,
termed clusters. These clusters are replaced with an equivalent earthquake. In order to use the
independence assumption of a Poisson model (typically assumed in PSHA analyses) ovonts
that can be associated with other near -in time and spaco events must be removed. This
process was done following an heuristic defined for this study because algorithms like Gardner
and Knopoff (1974) had not given good results for other (larger) databases (i.e. KiK net).then
replaced with the mainshock.
3T2T3—SvnthesizedCombined Catalog
3.2.3 Rolativoly larger magnitude events from 1973 through 2006 were comparod
between the Petersen et al. (2008) and ComCat catalogs to verify that the ComCat
catalog could be used to supplement tho Peterson ot al (2008) catalog between
January 1, 2007 through December 31, 2012. Events of Mw 45 or greater were
compared to verify that both tho Potorsen et al (2008) and ComCat catalogs
contain the same large magnitude events. Of the ovonts M > 4.5 or greater, 14
ovonts were found to be duplicatos and five events wore found exclusively in the
ComCat catalog. These five events were added to tho Petersen et al. (2008)
catalog for this PSHA and tho ComCat catalog was used to supplement Petersen
ot al. (2008) catalog for events from January 1, 2007 through Docombor 31, 2012.
Additions from tho ComCat catalog wore limited to ovonts of Mw 3.0 or greater in
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order to be consistent with the CEUS catalog. Sixty-five ovonts from the ComCat
catalog were added to the Petersen et al (2008) catalog to develop a
comprehensive catalog for the seismic study area. Magnitude Bias Correction
The ComCat and Petersen catalogs were combined to create a final declustered catalog for the
PSHA. The Petersen catalog reports magnitude as expected moment magnitude EfMwl
(Petersen et al., 2014). The conversion of various magnitudes to EfMJ for events from the
ComCat was completed following the guidance presented in CEUS-SSCn (NRC et al., 2012).
This approach is identical to that used in development of the Petersen catalog.
The
The combined catalog was screened to a magnitude greater than Mw 4.0 within 200 miles of the
site. This resulted in a catalog of 209 events.
PSHA catalog includes expected magnitude EfMwl. magnitude uncertainty, and a counting
factor termed N* (or nstar) for each event. The counting factor N* was used to compute
unbiased earthguake rates following guidance presented in CEUS-SSCn (NRC et al., 2012).
Earthquake recurrence parameters were computed using the maximum likelihood approach by
using the N* factor instead of the observed counts. This approach has been shown to work well
for catalogs with variable levels of catalog completeness as a function of magnitude (CEUS-
SSCn. NRC et al.. 2012).
3.2.4 Earthquakes Attributed to Specific Faults
In order to compute areal seismicity of a given area independent from the fault sources,
earthquakes associated with movement along a fault were removed from the earthquake
catalog. Earthquakes located within 5 km of faults included in the PSHA were assumed to be
attributed to fault movement, and were removed from the earthquake catalog. This resulted in
removal of 25 earthquakes.
In order to prevent double-counting earthguakes in both the fault and areal source models,
earthquakes occurring within 3.1 miles (5 km) of faults were evaluated in detail. Within the study
area, 31 events were located within 3.1 miles (5 km) of Quaternary faults. In order to evaluate
the difference between the earthguake recurrence parameters, the recurrence was computed
with and without these events. The result was very little variation in the a and b parameters with
or without the 31 events. Additionally, the recurrence calculations for the catalog including the
31 events resulted in an exponential distribution with a better fit to the data. Therefore, given the
small variation in results, and the fact that the literature indicates most earthguakes within the
CP (Wong and Humphrey. 1989) and ISB (dePolo, 1994) are not related to surface ruptures, all
earthquake events in the areal source zones were included in the recurrence calculations.
3.2.5 Artificially Induced Earthquakes
An anomalously active low seismicity area is located in western Colorado between the general
area of Glenwood Springs and Paonia. The area experienced 31 earthguake events with Mw >
3.0, with 14 events since 2007. All but one event were in close proximity to one of three
underground coal mines in the area. The area around the underground coal mines is described
by Swanson et al. (2008) and the Colorado Geological Survey (undated) as an area of artificially
induced seismicity. Reported events within the coal mining study area are between Mw 3.0 and
3.4. These 13 earthquakes were included in the evaluation of completeness periods discussed
in Section 3.4.1 but were removed from the catalog used for the PSHA analysis, as they do not
influence the design criteria. The location of these earthquakes are shown in Figure 3.
Several areas of artificially induced seismic activity are located within the study area. These
include: 1) an area between Glenwood Springs and Paonia, Colorado (Swanson et al., 2008,
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and CGS, undated), 2) the Book Cliffs-eastern Wasatch Plateau area near Price, Utah (Arabasz
et al., 2005), and 3) the Paradox Valley area (Ake et al., 2005). The areas listed above were
examined against the Petersen catalog and were confirmed as having been removed from the
Petersen catalog. Furthermore, no events in the ComCat fall within these areas of artificially
induced seismicity.
3.3 Magnitude Conversion
All events described here are reported in moment magnitude unless specified otherwise. Body
wave magnitude (Mb)The events included in the Petersen catalog were converted to moment
magnitude (Mw) using the conversions summarized in Table 1. Local magnitude (ML) events
were assumed to be equivalent to moment magnitude. Magnitude conversions from ML to Mw
is reouired when one of the all given in My; therefore, it was only necessary to convert those
events from the ComCat. This conversion was completed by following two conditions are met:
(1) the event is larger than ML~7, or (2) the epicenter dopth is greater than 373 miles (600 km)
(Bakun & Siokin. 2002: Hanks and Kanamori, 1979). All events recordedthe approach used to
compile the Petersen catalog and guidance provided in tho study area in ML range from 3.0 to
3.7 and the deepest epicenter recorded within the study area is 30 miles (49 km) below the
ground surface. Therefore, all local magnitudes were assumed to equal moment magnitude for
purposes of this analysis.CEUS-SSCn (NRC et al.. 2012).
Table 1. Magnitude Conversions
Equation
Mw. = 0.85 m# I 1.03 (fflg < 6)
Mw. = 1.69m#—4.01 (m^ > 6)
Source
Scordilis (2006)
3.3.1 PSHA Catalog
The earthquake catalog used in the recurrence calculations for this PSHA includes the
combined Petersen et al. (2003)2014) catalog and Comcat catalogs.ComCat. The data was
declustered, screened to exclude earthquakes attributed to a nearby fault, and screened to
exclude artificially-induced earthquakes due to mining and oil and gasanthropogenic activity.
The final catalog included inused for the PSHA includes 4^4334 earthquakes. These
earthquakes are shown on Figure 2.
Earthquakes included in the final catalog for the P-SHAcomputation of recurrence parameters
generally have small magnitudes, with over 3090 percent of the earthquakes having a Mw < 5.0.
FiguresFigure 2 and 3 showshows that earthguake activity within a 200-mile (322-km) radius of
the site is diffuse, with the exception of those in the ISB located on the western edge of the
study area, and in western Colorado (the northeast corner of the study area). A list of
| historichistorical earthquakes is included in Attachment 1.
3.4 Developing Recurrence Parameters
To estimate probabilistic ground motions for the site, recurrence parameters are required to
characterize seismic activity in the study area. Two areal source zones were delineated within
the study area, as discussed in Section 4.2.
3.4.1 Assessment of Catalog Completeness
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In order to estimate a recurrence rate for earthquakes in tho aroa, an assessment of the
completeness of the earthquake catalog tswas necessary. One way to test tnts-completeness is
to plot the rate of the earthquakes (number of events greater than mta specified magnitude
divided by the time period) as a function of time, starting at present time and moving back
towards the beginning of the catalog. If the rate of earthquakes is represented by a stationary
| Poisson process (the rate -Xm- does not change with time) for the area in study area, which is
the typical assumption, then the rate of earthguakes should remain constant for the portions of
the catalog that have complete reporting.
| The evaluation was performed using the StreppStepp (1972) method, which includes generating
completeness plots to visually inspect the rate of events over the years. Plots were developed
| starting at a minimum magnitude of 3.0 and carried out for each 0.45 to 1.0 magnitude unit,
depending on the size of the magnitude bins. Based on this evaluation, the catalog is
| considered complete for the date and magnitude ranges shown in Table 2-1. Figure 43 shows
the catalog completeness plots developed for this study.
The timeframecatalog is complete for first detection ofthose events greater than Mw 5.5 for
approximately 130 years, this corresponds to several specific activities in the Colorado Plateau
region.—Events Mw > 5.5 were first recorded in the late 1890s as1880's, when settlement
became more widespread mfor southeastern Utah. -The Paradox Basin seismographic network
was installed in 1962. allowing detection of eventsfirst event in the catalog is a Mw > 4.0, and
the first long term seismographic network operated within tho Colorado Plateau was installed in
1979 by Woodward Clyde Consultants (Wong, et al., 1996), allowing detection of events Mw >
3T5.-7 which occurred in 1887.
Table 21. Time Periods for Complete Event Reporting
Magnitude Range Period of Complete
Reporting
<M<3.45
3.5—aTQ<M<4.0
20401984
4-97Q1964
2O422014
20432014
4.0—<M<4.95 40621964 20422014
4.5<M<5.0—&4
5.0<M<5—6.5
M>5.5
49421959 20422014
4S921904
1884
20422014
2014
3.4.2 Estimation of the Recurrence Parameters
As stated above, 13 earthquakes that appear to be artificially induced were removed from tho
catalog used to develop earthquake recurrence parameters. The locations of the earthquakes
that were removed from the catalog are shown in Figure 3. After the completeness intervals for
each magnitude range waewere developed and dependent events were removed, the
characterization of the freguencv of events was recurrence parameters were computed. A
common way to characterize this frequency is by using the Gutenberg-Richter relationship,
which is linear when the magnitude is plotted against the frequency of events on a semi-
logarithmic scale. The magnitude-frequency relation expressed in its cumulative form is:
logyv(M) = a-bM
where M is the magnitude and N is the cumulative frequency of earthquakes greater than
magnitude M. The calculation of cumulative freguencv of earthguakes (N) used the N* value (a
counting factor used to compute unbiased rates) instead of observed counts. Recurrence
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relationships were then estimated using the maximum likelihood procedure developed by
Weichert (1980). The maximum likelihood line is characterized by the slope of the line, or b-
value, and the activity rateloq N value at the minimum magnitude (ah magnitude of zero (a-
value). For this study, a minimum magnitude of 3.0 was used to develop the recurrence
parameters. The inputs used to calculate the recurrence parameters are summarized in Table 2
and Table 3. The recurrence parameters (a- and b-values) were developed for each seismic
source zone, as discussed in Section 4.2.
Table 2. Colorado Plateau - M aqnitude Bins and Cumulative N* Values
Magnitude Bin Cumulative N* value Cumulative Observed
Counts
3<M<3.5
3.5<M<4.0
78.59
52.65
69
46
4.0<M<4.5 18.25 16
4.5<M<5.0 8.03
5.0<M<5.5 4.82
5.5<M<6.0 1.21
Table 3. Intermountain Seismic Belt- Magnitude Bins and Cumulative N* Values
Magnitude Bins
3<M<3.5
3.5<M<4.0
4.0<M<4.5
4.5jM<5.0
5.0<M<5.5
5.5<M<6.0
6.0<M<6.5
6.5<M<7.0
Cumulative N* value
136.51
81.48
32.56
14.89
7.98
4.71
2.41
1.21
Cumulative Observed
Counts
133
78
31
14
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4.0 SEISMIC SOURCE CHARACTERIZATION
The seismic source model includes crustal fault sources, seismicity of the ISB, and seismicity of
| the PEZrColorado Plateau (CP). These sources are described below.
4.1 Faults
4.1.1 Capable Faults
A "capable fault" is defined by the Nuclear Regulatory Commission (NRC) in 10 CFR Appendix
A to Part 100, Seismic and Geologic Siting Criteria for Nuclear Power Plants, as a fault that has
exhibited one or more of the following characteristics:
1. Movement at or near the ground surface at least once within the past 35,000 years or
movement of a recurring nature within the past 500,000 years.
2. Macro-seismicity (magnitude 3.5 or greater) instrumentally determined with records of
sufficient precision to demonstrate a direct relationship with the fault.
3. A structural relationship to a capable fault according to characteristics (1) or (2) above
such that movement on one could be reasonably expected to be accompanied by
movement on the other.
Capable faults must also meet the minimum criteria for fault length and distance from the site,
| as defined by NRC 10 CFR Appendix A to Part 100, and included in Table 34. A fault that is
deemed capable by the criteria listed above, but does not meet the minimum criteria provided in
| Table 34, does not need to be considered in the seismic hazard analysis.
The term "capable fault" may be abandoned by the NRC, but this is not vet reflected in the CFR,
so the term is used in this report.
Table 34. Minimum Criteria for Faults Considered in Seismic Investigation (NRC 10 CFR
Appendix A to Part 100)
Distance from Site
(mi)
Oto 20
20 to 50
50 to 100
100 to 150
150 to 200
Minimum Length of Fault to be
Considered
(mi)
1
10
20
40
All capable faults that meet the minimum criteria presented above were considered in the
PSHA.
4.1.2 Fault Sources
The existence and location of faults with Quaternary displacement were primarily identified
using the USGS Quaternary Fault and Fold database (USGS et al., 2013). All faults identified
| with potential Quaternary-age offset that exist within a 200-mile (322-km) radius of the site are
shown in Figure 1. Those faults were further screened to those that meet the criteria listed in
| Table 34 and shown in Figure 2.
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I All faults that meet the requirements outlined in Table 34 were considered in this seismic
| investigation. This is a conservative approach,, because although the NRC defines a "capable
fault" as one having "movement at or near the ground surface at least once within the past
35,000 years or movement of a recurring nature within the past 500,000 years," including all
identifiable faults with Quaternary displacement would include fault movement over the past 1.8
million years. The 41 faults considered in the seismic hazard analysis are listed in
Attachment 2.
The USGS separates faults with Quaternary displacement into classes. These classes are
provided below, as described by USGS et al. (2013).
• For a Class A fault, geologic evidence demonstrates the existence of a Quaternary fault
of tectonic origin, whether the fault is exposed by mapping or inferred from liquefaction
or other deformational features.
• For a Class B fault, geologic evidence demonstrates the existence of Quaternary
deformation, but either 1) the fault might not extend deeply enough to be a potential
source of significant earthquakes, or 2) the currently available geologic evidence is too
strong to confidently assign the feature to Class C but not strong enough to assign it to
Class A.
• For a Class C fault, geologic evidence is insufficient to demonstrate 1) the existence of
tectonic faulting, or 2) Quaternary slip or deformation associated with the feature.
• For a Class D fault, geologic evidence demonstrates that the feature is not a tectonic
fault or feature; this category includes features such as joints, landslides, erosional or
fluvial scarps, or other landforms resembling fault scarps but of demonstrable non-
tectonic origin.
The faults with Quaternary displacement that meet the NRC minimum criteria and are included
in this analysis are either Class A or B.
Many of the faults in Colorado are attributed to the Uncompahgre Uplift. The Uncompahgre
Uplift faults are typically northwest-trending normal faults with minimal evidence to constrain the
slip rates. Faults located north of the site in the area of the Paradox Valley are associated with
salt tectonics and are therefore considered non-seismogenic. Faults in the western section of
the study area are assumed to be seismogenic. Tectonic features in this area include Basin
| and Range extension, multiple small-scale mountains and plateaus, and the southern extent of
the Wasatch Plateau in central Utah.
| Characteristics of individual faults that meet the criteria specified in Table 24, including
subsurface orientation, depth, slip rate, probability of activity, and age were obtained where
possible from USGS et al. (2013), Wong et al. (1989 and 1996), and Hecker (1993). A
comprehensive list of fault characteristics used in the PSHA is included in
AttachmentsAttachment 2 and Attachment 3. Published fault characteristics were used when
available. When there were no published sources for specific faults, a weighted range of values
were used. The probability of activity is the probability that a fault will ruptureis seismogenic.
For purposes of this analysis, non-seismogenic faults were assigned a value of probability of
activity of 0.5 or less and seismogenic faults are assigned a probability activity of 1.0.
4.2 Seismic Sources
The hazard from background events unassociated with known faults was assessed by dividing
| the area of the 200-mile (322-km) radius around the site into two areal source zones that were
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assessed independently. The first zone is a portion of the Intermountain Seismic Belt (ISB),
discussed previously in Section 2.1. This area includes the western portion of the study area,
as shown in Figure §4. The second areal source zone is the Dispersed Earthquake Zone
{DEZColorado Plateau (CP), and includes the remaining portion of the study area, as shown in
Figure §4. The PEZ-CP is characterized by a dispersed distribution of historic seismic events,
and the ISB is characterized by a denser distribution of seismic events.
Boundaries of the areal source zones were developed based on similar patterns of historical
seismicity. regional geology, tectonic regime, and similar patterns of historical seismicity. As
discussed in Section 2.1, the Colorado Plateau physiographic province extends through eastern
and southern Utah through northern Arizona. The Basin and Range province extends through
western Utah, Nevada, and southern Arizona. Within the study area, the ISB runs adjacent to
the Colorado Plateau and Basin and Range boundary (Wong and Olig, 1998 and Sbar, 1984).
The boundary presented in Figure 4, is based on observed seismicity and the delineation
provided by Sbar (1984). Catalog seismicity within each source zone was used to estimate the
Gutenberg-Richter a and b parameters. Earthquake locations within each zone are assumed to
be uniformly located within the space. Parameters for defining seismicity within each source
zone include the following: minimum and maximum depth, activity rate (number of events per
year > Mmin) and B (ln(10) times b-value) estimated from the historical seismicity catalog for
that zone, probability of activity, and parameters for rupture length estimation based on
magnitude.
4v24—Dispersed Earthquake Zono
4.2.1 Colorado Plateau
The site is located within the DEZCP, as shown on Figure §4. This zone exhibitedexhibits
relatively sparse concentrations of earthquake events. About 58Within a 200-mile (322-km)
radius, 134 events were recordedincluded in the catalog between 49421910 and 2013, with
three events February 2015 within the CP source zone. One event was of Mw > 5.5. The largest
earthquake event within the DE^-CP source zone developed for this project was a Mw 5.75
event that occurred on October 11. 1960 August 18, 1912 approximately 447131 miles (188 km)
from the site. _Based on the historical seismicity, the event closest to the project siteevent was
aan Mw 3.7 event that occurred on June 6, 2008 and was located approximately 12 miles (19
km) from the site.
As discussed previously, the a- and b-values for the Gutenberg-Richter recurrence relationship
were estimated using the maximum likelihood method developed by Weichert (1980) and the
collected seismicity for the DEgrproject-specific CP source zone. The estimated b-value for the
DEZ-CP is 0.6388 and the calculated activity rate is 0.4307 earthquake events per year greater
than Mw 5.0. The cumulative event rates with magnitude for the DEZCP are shown in Figure 5,
along with the 5 percent and 95 percent confidence intervals at each magnitude increment.
Figure 5 only shows the fit to the data and the development of the a and b parameters: the
figure does not show a representation of the truncated exponential recurrence relationship used
in the PSHA. A maximum magnitude of Mw 6.75 was used for the CP, based on Wong and Olig
(1998). A maximum magnitude of 6.0 to 6.5 is recommended in the study area and a standard
error of ± 0.25 was added for an upper estimate of M» of 6.75. The maximum magnitude value
is also eguivalent to the Intermountain Seismic Belt's maximum magnitude. The minimum and
maximum depth of events specified for the CP is 1.9 miles and 12 miles (3 km and 20 km),
respectively. The CP background source has a maximum magnitude of 6.75 and magnitudes
below 7.0 are not likely to rupture the surface, therefore the minimum depth was assigned to be
1.9 miles (3 km).
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4.2.2 Intermountain Seismic Belt
Within the study area, the ISB exhibited a denser distribution of historical earthquake events
than the CP. Within the ISB source zone, 200 events were included in the catalog between
1887 to February 2015. Four events were IvL 5.5 or greater. Of the events within the study area,
the largest earthguake event within the ISB was an M„ 6.5 that occurred on November 14. 1901
approximately 164 miles (264 km) from the site.
The estimated b-value for the ISB is 0.84 and the calculated activity rate is 0.15 earthguake
events per year greater than IVL 5.0. The cumulative event rates with magnitude for the ISB are
shown in Figure 6, along with the 5 percent and 95 percent confidence intervals at each
magnitude increment. Tho maximum recorded magnitude for an event within the seismic source
zone was assumed to be Figure 6 only shows the fit to the lower bound for data and the zone.
Therefore, development of the maximum magnitude was assumed to be 0.5 magnitude units
greater thana and b parameters; the maximum recorded value withinfigure does not show a
representation of the DEZ. For the DEZ, the maximum magnitude truncated exponential
recurrence relationship used in the analysis wasPSHA. A maximum magnitude of Mw 6.2 (tho
largest event recorded in the DEZ (75 was used for the ISB based on the recommendation of
dePolo (1994) of an Mmay 6%. Mw 5.7) plus 0.5). 6.75 is a generally-accepted maximum
magnitude within the Basin and Range Province. The minimum and maximum depth of events
specified for the DEZ-ISB is 1.9 miles and 12 miles (3 km and 20 km^ respectively. -The ISB
areal zone has a maximum magnitude of 6.75 and magnitudes below 7.0 are not likely to
rupture the surface, therefore the minimum depth was assigned to be 1.9 miles (3 km).
4.2.2—Intermountain Seismic Belt
The ISB has exhibited a denser distribution of historic oarthquake evonts than the DEZ. About
113 events were recorded between 1887 and 2013, with six events of Mw 5.5 or greater. The
largest earthquake event within the ISB was a Mw 6.5 event that occurred on November 14,
1901 approximately 164 mi from the site.
The estimated b-value for the ISB is 0.84 and the calculated activity rate is 0.13 earthquake
events per year greater than Mw 5.0. The cumulative event rates with magnitude for the ISB are
shown in Figure 7, along with the 5 percent and 95 percent confidonce intervals at each
magnitude increment. The maximum recorded magnitude for an ovont within the ISB was
assumed to be the lower bound for the zone. Therefore, the maximum magnitude was assumed
to be 0.5 magnitude units greater than the maximum recorded value within the ISB.—For the
ISB, the maximum magnitude used in the analysis was Mw 7.0 (the largest event recorded in
the ISB (Mw 6.5) plus 0.5). Tho minimum and maximum depth of evonts specified for the ISB is
3 km and 20 km, respectively.
4.3 Shear Wave Velocity
The following paragraphs summarize the method used to calculate a site-specific shear wave
velocity for use in the PSHA. The time-averaged shear-wave velocity fefin the top 30 meters at
the site (Vs30) was calculated from measured seismic refraction data. The uncertainty in the Vs30
estimation was addressed in the PSHA by calculating a lower bound, best estimate, and upper
bound Vs30, as described below.
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4.3.1 Summary of Site-Specific Vp Values
As discussed in Section 2.2, the site is underlain by the Dakota Sandstone, predominately
composed of cross-bedded, fine-to coarse-grained, well-cemented sand (Denison, 2011).
Borings were drilled across the site by Dames & Moore in 1977 to depths ranging from 6.5 to
132.4 feet (Dames & Moore, 1978). The boring locations are shown on Figure 7, and the boring
logs are provided in Attachment 4. The boring logs show sandstone underlying the site to
depths greater than 132 feet.
Site-specific compression wave velocity (Vp) data are available for the White Mesa site from
Nielsons Incorporated (1978). During site characterization for construction of the tailings cells,
| Nielsons performed 43thirteen seismic refraction surveys at several locations across the site to
estimate the compressive wave velocity and depth to bedrock, and to evaluate the excavation
characteristics of the material underlying the proposed cells. Nielsons reported Vp values for
various soils and rock to a depth of 33 feet. Locations of the seismic refraction surveys and
| measured Vp data are shown in Figure 87.
Seismic refraction survey results show unconsolidated and/or compact soil to depths ranging
from 4 to 18 feet, overlying Dakota Sandstone. This upper soil material was excavated during
grading and construction of the tailings cells, as documented in the design and construction
completion reports (D'Appolonia, 1979, 1981, 1982; Energy Fuels Nuclear, 1983; Geosyntec,
2006, 2007) and by personal communication with site personnel (Roberts, personal
| communication, 2013). SheetsSheet 7 and Sheet 8 of D'Appolonia (1979) are cross sections
through the tailings cells showing the planned excavation of the tailings cells below through the
upper soil material and into shallow bedrock.
The Nielsons report divides the Dakota Sandstone into four categories based upon compressive
wave velocity, as summarized below (with the reported range of measured Vp values):
• Soft Rippable Rock (Vp = 3,100 to 4,000 ft/s)
• Medium Soft Rippable Rock (Vp = 3,500 to 4,500 ft/s)
• Medium Hard Rippable Rock (Vp = 5,000 ft/s)
• Drill & Shoot Rock (Vp = 6,500 to 8,400 ft/s)
At all of the seismic survey locations, Vp increased with depth. At seven out of the thirteen
locations, "Drill & Shoot Rock" was encountered as the deepest material (Vp = 6,500 to 8,400
ft/s). The Vp value was less than 4,000 ft/s at the greatest depths profiled at only two of the
survey locations.
| As shown on Figure 87, two of the seismic refraction surveys (S-12 and S-13) were conducted
more than 2,000 feet north of the existing mill and impoundment area and are not considered
relevant to the tailings impoundment reclamation design. The remaining eleven seismic
locations (S-1 through S-11) are relevant to the current study because they are within or near
the footprint of the existing tailings cells, or they are in areas of potential future tailings facility
expansion. For these eleven locations, the Vp values for the Dakota Sandstone ranged from
3,100 ft/s to 8,400 ft/s at the greatest depth profiled, with an average value of 6,009 ft/s and a
median value of 6,500 ft/s.
Based on these site-specific Vp values, a Vp of 6,500 ft/s was chosen as the best estimate of the
| compression wave velocity for the upper 100 feet (30 meters) of material underlying the site.
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This value is the median value of compressive wave velocities measured at a depth of 33 feet
(10 meters) (the greatest depth profiled at each relevant location) underlying or near the cells.
Compressive wave velocities at depths greater than 33 feet (10 meters) are expected to be
equal to or greater than the velocity at 33 feetT (10 meters), since measured Vp increases with
depth at each survey location. Thus, the velocity measured at the bottom of the profile at a
depth of 33 feet (10 meters) is considered potentially conservative, but is the most
representative measurement of Vp for the entire upper 30 meters (100 feet) of material at the
site.
To account for uncertainty in the Vp data measured across the site, a lower bound and upper
bound Vp was estimated from the site data. Vp values of 4,400 ft/s to 7,400 ft/s envelope the
compression wave velocity for the site. This range of values encompasses all but three of the
Vp data measured at the site at the deepest depth profiled, and is approximately equivalent to
plus or minus one standard deviation from the average. The three values not included are the
two lowest values (3,100 ft/s and 4,000 ft/s) measured more than 300 ft from the tailings cells,
and the highest value measured at the site (8,400 ft/s).
4.3.2 Development of Vp/Vs Ratio
To estimate the shear wave velocity (Vs) from the compression wave velocity (Vp) measured at
the site, it is necessary to assume a Vp/Vs ratio. A Vn/V£ ratio can be calculated from a
Poisson's ratio, or an appropriate Vp/Vs ratio can be found in the literature. Several
sfuoiespublished references were reviewed to determine an appropriate ratio.typical Poisson's
ratios for sandstone. We also reviewed several references to determine the typical range of the
Vp/Vg ratio and the typical range of V* for sandstone. These studios are summaries
betew^references were reviewed to select the most appropriate VP/Vs ratio, and verify that the
computed values for Vs^n fall within the expected range for the material.
Poisson's ratios from select references are summarized below:
• Goodman (1989) provides a table of Poisson's ratios for various rock specimens, as
determined from laboratory unconfined compression testing. The following Poisson's
ratio values are presented for three sandstone samples: 0.38 (Mississipian Berea
Sandstone from Ohio), 0.46 (Jurassic Navajo Sandstone from Arizona), and 0.11
(Pennsylvian Tensleep Sandstone from Wyoming).
• Burger (1992) presents a table of laboratory-measured elastic properties for common
rocks. A Poisson's ratio of 0.06 is presented for a sandstone sample from Wyoming.
* Hatcher (1990) presents a table of Poisson's ratios for various rock types. A value of
0.26 is presented for Mississippian sandstone from Berea, Ohio.
* Unpublished notes by Dr. David Boore of the USGS (Boore, 2007) were
reviewed. These notes present an evaluation of Poisson's ratio calculated from Vc and
Vs data from over 300 boreholes in California which were logged using surface source,
downhole receiver method or P-S suspension logging. The notes indicate a range of
Poisson's ratio from about 0.2 to 0.48 for the various materials, including unconsolidated
sediments, with the data centered around a Poisson's ratio of about 0.3. Dr. Boore
concludes that the Poisson's ratio is generally less than 0.4 for materials above the
water table.
Several studies were also reviewed to determine typical vyv* ratios for sandstone, and to
determine the typical range of Vs values for sandstone:
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• Castagna et al. (1985) presentspresent a variety of data related to the relationship
between Vs and Vp for clastic silicate rocks. For dry sandstones, the paper reports that
both laboratory data and modeling results indicate a nearly constant VPA/S ratio of 1.4 to
1.5. The reported V£ values for dry sandstone range from approximately 500 to 3,500
m/s, with most values in the range of approximately 1,500 to 3,500 m/s.
• Wu and Liner (2011) present a case study that compares shear wave and compression
wave velocities for the Dickman field in Ness County, Kansas. For sandstones, the
paper reports VPA/S ratios ranging from 1.6 to 2.0, with most. The paper presents
estimated V* values in thethat range effrom approximately ^SJ000 to 1.7. 2,300 m/s for
depths less than 500 m.
• Lin and Heuze (1986) reviewed sonic borehole logs for boreholes drilled in Colorado and
Wyoming through shales and sandstones of the Mesaverde formation. The authors
computed in-situ Vp and Vs values from the sonic data, and a review of these results
indicates Vp/Vs ratios ranging from 1.65 to 1.8 for both shales and sandstones. The
associated Vs values (measured in-situ) range from approximately 1,800 to 2.800 m/s for
all depths evaluated in the study.
• Han et al. (1986) present Vp and Vs values measured on 75 laboratory samples of
sandstone. The samples had a variety of clay content values and were measured at
confining pressures ranging from 5 to 40 MPa. Nearly all of the computed Vp/Vs ratios
fall within the range of 1.6 to 1.9. 5 to 2.0. The reported laboratory-measured Vs values
range from approximately 1,500 to 3,600 m/s.
• TheseWillis and Clahan (2006) present mean V*™ values for a variety of California
geological units. Vs was measured at 24 sites underlain by Tertiary bedrock, and the
paper presents a mean V^ value of 515 m/s for Tertiary sandstone. V£ was measured
at 6 sites underlain by Cretaceous sandstone, and the paper presents a mean V^n of
566 m/s for this material.
The references regarding Poisson's ratio indicate that the ratio for sandstone, in particular the
laboratory-measured ratio, can have a broad range, from as low as 0.06 to as high as 0.46. Of
particular interest is the range of values presented in Boore (2007) (about 0.2 to 0.48) because
this range of values was derived from in-situ downhole data.
The studies regarding the VgA/g ratio indicate that typical Vp/Vs ratios for sandstones like the
Dakota Sandstone generally range from about 1.54e-4 to 2.0. The Vs values presented in the
studies indicate Vs values ranging from about 500 to 3,600 m/s, with most values greater than
1.9. Ratios above 2 are uncommon and are indicative of saturated conditions or very high clay
content. ,000 m/s.
Based on the literature referenced abovethis review, a VeAfePoisson's ratio of 4r70.35 was
selected ae-theto compute a best estimate for computing the Vs values from theVp/Vs ratio. The
Poisson's ratio of 0.35 falls within the range of laboratory-measured data presented by
Goodman (1989), Burger (1992) and Hatcher (1990), and is near the center of the in-situ data
presented by Boore (2007). Using a Poisson's ratio of 0.35, a Vp values measured at the
S4tev/V£ ratio of 2.1 was computed. This value is representative of a Poisson's ratio for tho
Dakota Sandstone in the range of 0.25 to 0.3, which is reasonable for the material
properties.slightly higher than the range of values discussed above, and is therefore considered
potentially conservative.
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To account for epistemic uncertainty in the VPA/S ratio used to compute Vs from the measured
Vp values, a range of values of VpA/s ratio of 1.5 to 1.9 to 2.3 was evaluated. This range of
values encompasses nearly all of the typical values published in the aforementioned
referencesVgA/s ratios is representative of a Poisson's ratio ranging from 0.31 to 0.38.
4.3.3 Estimation of Site-Specific Vs Values
Site-specific Vs30 values were computed from the upper bound, lower bound,, and best estimate
Vp values using the VpA/s ratios described in Section 4.3.2. The results envelope the Vs30 data
as follows:
• A lower bound Vs30 calculated from the lower bound Vp {of 4,400 ft/s (1,340 m/s) and a
VPA/S ratio of 402.3.
• A best estimate Vs30 calculated from the best estimate Vp {of 6,500 ft/s) and a VpA/s ratio
(1T7-,980 m/s) and a VDAA ratio 2.1.
• An upper bound Vs30 calculated from the upper bound Vp {of 7,400 ft/s (2,255 m/s) and a
VPA/S ratio of 1.69.
The resulting Vs30 values range from 706583 m/s to 1,504187 m/s, as shown in Table 45. For
purposes of the PSHA, Vs30 values of 7-00580 m/s, 4T47-O940 m/s, and 1,500190 m/s were
evaluated in the PSHA to envelope the PGA. -These values were compared to the Vs values
published in the references discussed above. The values used in the analysis fall within the low
end of the expected range of values for sandstone (500 to 3,600 m/s).
Table 45. Envelope of Vp and Vs Values for the White Mesa Site
Measured
(ft/s) (m/s)
Computed
(m/s)
Vs Used in
Analysis
(m/s)
Lower Bound 4,400 1,340 706583 580
Best Estimate 6,500 1,980 4466943 940
Upper Bound 7,400 2,255 1.504187 1,190
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5.0 GROUND MOTION PREDICTION EQUATIONS
GMPEs are applied to earthquakes to estimate the ground motion at the site. GMPEs are
mathematical expressions that define how seismic waves propagate from the source to the site.
Several factors combine to cause the decrease in amplitude or intensity as the wave travels to
the site, including refraction, reflection, diffraction, geometric spreading, and absorption.
GMPEs estimate the ground motion as a function of magnitude, distance, and site conditions
(e.g. soil, rock, or rook type-V^L The relationships are derived by fitting equations to data
obtained by strong-motion instruments for a specific region.
For the crustal faults, the following Next Generation of Attenuation (NGA) relationships were
used: Abrahamson and Silva (2008. et al. (2014). Boore and Atkinson (2008. et al. (2014),
Campbell and Bozorgnia (20082014), and Chiou and Young (2008). Youngs (2014). Idriss
(20082014) was not used because ef-the maximum applicable distance limitations ofis limited to
93 miles (150 kmh) and the areal source zones extend to a 200-mile (322-km) radius.
| Current NGA West 2 relationships were used as the GMPEs for the crustal faults and the areal
source zones. The GMPEs were egually weighted. It should be noted that the GMPEs
implemented in this study use the best available information, as these models have been shown
| to be applicable worldwide. Table 56 lists the relationships and the associated weights. The
logarithmic mean of the four NGA relationships was used.
Table 66. GMPEs used in the PSHA
GMPE Weight
0.25
Boore and Atkinson (2008, et al. (2014) 0.25
Campbell and Bozorgnia (200S2014) 0.25
Chiou and Young (2008Youngs (2014) 0.25
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6.0 PROBABILISTIC SEISMIC HAZARD ASSESSMENTANALYSIS
The following sections describe the PSHA methodology, inputs for analysis, and results.
6.1 PSHA Code and Methodology
The methodology for PSHA was developed by Cornell (1968), and is used to provide a
framework in which uncertainties in size, location, and rate of recurrence of earthquakes can be
considered to provide a probabilistic understanding of seismic hazard.
A PSHA can be described as a procedure of four steps (Kramer 1996):
• Identification and characterization of earthquake sources, along with the assignment of a
probability distribution to each source zone
• Characterization of earthquake recurrence
• Estimation of ground motion produced at the site by earthquakes of any possible size
occurring at any possible point in each source zone
• Calculation of the probability that the ground motion parameter will be exceeded during a
particular time period given uncertainties in earthquake location, earthquake size and
ground motion parameters
Calculations for this report were performed using the computer code HAZ43, developed by Dr.
Norman Abrahamson. Earlier versions of this code were verified under the PEER PSHA Code
Verification Workshop (Thomas et al., 2010).
6.2 PSHA Inputs
A PSHA uses a combination of areal sources and fault sources. Exponential relationships were
developed to characterize the seismicity of the areal source zones. Historical seismicity was
used to characterize activity based on Gutenberg-Richter relationships within each of the
seismic zones that are shown in Figure §4. Areal sources are described in Section 4.2 and the
GMPEs considered are explained in Section 5.0.
Additional input parameters fdepth to (1.0 km/s) (Z1.0) and depth to (2.5 km/s) (Z2.5)1 were
estimated from the input Vm value. Each of these values are summarized in Table 7.
Tab e 7. PSHA Input Parameters
Input Parameter Value
y^n ft/s (m/s) 1.903 ft/s
(580m/s)
3.083 ft/s
(940 m/s)
3.904 ft/s
(1.190 m/s)
Zi_n (km) 0.152 km 0.012 km 0.0 km
(km) 0.827 km 0.476 km 0.363 km
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6.2.1 Areal Source Zones
Characteristics of the two areal source zones (the PEZ-CP and the ISB) included in this analysis
are described in Section 4.2. The earthquake recurrence for the areal source zones is based on
the rate of historical seismicity within each zone. The estimation of the recurrence parameters
for each source zone was presented in Section 4.2. Although recurrence parameters were
developed considering events with magnitudes as low as Mw 3.0, a minimum magnitude of Mw
5.0 was used in the probabilistic analysis^ as events with magnitudes less than Mw 5.0 are
unlikely to generate a significant hazard at the site. The maximum magnitude assigned to the
DEZ was M 6.5 and the maximum magnitude assigned to the ISB was M 6.7. These values
were obtained by adding 0.5 magnitude units to the maximum historical event that occurred in
eaobareal source zone, as described in Section 4.2.zones was Mw 6.75.
6.2.2 Fault Sources
Quaternary faults that meet the minimum criteria presented in Table 34 were included in the
analysis. The mapped fault lineation (USGS et al., 2013) was simplified in the analysis by
tracing the mapped lineation and redrawing the faults as they appear in Figure 88.
FaultsFault recurrence were modeled as both characteristic and truncated exponential.
Characteristic events were assigned a probability of 0.7 and the exponential model was
weighted 0.3. The weighting was te-set as such to balance out the two different models. The
truncated distribution predicts a higher ratio of lower magnitudes to higher magnitudes than is
observed on a single fault. In contrast, the characteristic model, in its most simple application,
predicts fewer earthquakes on a fault than are generally observed. Additional information on
the fault parameters, including dip, slip rate, depth, type of fault, and probability of activity, is
included in Attachment 2.
6.3 Probabilistic Seismic Hazard Assessment-Analysis Results
Ground motions at the project site are calculated for the average horizontal component of
motion in terms of PGA. In order to bracket the PGA and account for uncertainty in the site-
specific Vs30, the PGA was calculated for the range of Vs30 valuesV^values presented in
Section 4.3.3. The results are summarized below in Table 8 and shown on Figure 9.
Table €8. PSHA Results
Return Period VS30
(ft/s)
VS30
(m/s)
Mean PGA
(g)
2747§4 70Q &44
10,000 1,080903 580 0.O919
4^6003.084 940 0.O815
9T9003
7Q0
3,904 1,080190
4,600
Or20
0.4614
0T46
Notos:
4—A 2,475 year return period is suitable for dosign of operational conditions.
3r.—A 9,900 yoar rotum period is suitable for design of long torm/reolamation conditions.
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| The PSHA Galculatesis used to calculate the annual frequency of exceeding a specified ground
motion level. The results of the PSHA are typically presented in terms of ground motion as a
function of annual exceedance probability. Figure 4410 shows the total hazard curve plotted for
the upperlower bound of 1,903 ft/s (580 m/s) which resulted in the highest mean PGA-and
includes the contribution from oach source to the total hazard.. At the 10,000-vear return
poriods of interest (2,475 and 9,900 years),period, the hazard is controlled by the
OEZbackground earthguake from the CP areal source zone. The ISB and crustal faults have
little effect on the total hazard due to the distance from the site.
The hazard was deaggregated to evaluate the magnitude and distance contributions to the
| wpeflower bound V^or highest mean PGA at the 2,475 year and 9,900 year return periods..
The deaggregation of the hazard allows the probability density to be calculated for selected
distance and magnitude bins. The deaggregated hazard for the two return periods is shown m
Figures 12 and 13. respectively.on Figure 11. The plots also include mean magnitude, mean
distance, and mean epsilon values. For both return periods,Figure 11 shows that the hazard is
generally dominated by earthguakes greater than Mw 5.0 located less than 19 miles (30 km}
from the site.
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7.0 RESULTS AND COMPARISON WITH PREVIOUS STUDIES
Based on the results of this PSHA, the mean PGA for operationalreclaimed (long-term)
conditions is estimated to range from 0.0814 g to 0.4419 g. This PGA is associated with an
average return period of 2,475 years and has a 2 percent chance of exceedance in tho
anticipated 50 year operational design life of the cells. The mean PGA for reclaimed conditions
is estimated to rango from 0.15 g to 0.20 g. This PGA is associated with an average return
period of 9,900 years, 10,000 years, or a probability of exceedance of 2 percent to 10 percent
for a design life of 200 to 1,000 years, respectively. The Vs30 values used for the analysis
ranged from 700tn/s to 1500m/s1.903 ft/s to 3.904 ft/s (580 m/s to 1,190 m/s). Selection of the
PGA or a pseudostatic coefficient used for reclamation design shall be performed during final
design and be based on the results presented in Table 8.
Results of this site-specific PSHA were compared to previous analyses conducted for the siter
£MWH-L_2012) ucod tho USGS 2008 NSHMP PSHA Intoractivo Doaggrogation wobsito
(https://geohazards.usgs.gov/deaggint/2008/) to evaluate the PGA at the site. The web based
PSHA program provides estimates of the deaggregated seismic hazard at specific spectral
periods for the conterminous United States. The program incorporates regional seismicity data
including background earthquakes (unassociated with faults), earthquakes associated with
faults, fault characteristics, and regionally appropriate attenuation relationships.}. Results of
MWH, 2012 indicate a PGA of 0.07 g for a return period of 2,475 years and a PGA of 0.15 g for
a return period of 9,900 years-, using an estimated Vs30 of 750m2,493 ft/s-—The PGA for
operational conditions from MWH (2012) is less than the range of PGA values estimated for this
PSHA. (760 m/s). The PGA for reclaimed conditions from MWH (2012) is equal to the tewer-
beundbest estimate PGA value estimated for this PSHA.
The U.S. Dopartment of Energy (DOE, 1989) recommends that a horizontal seismic coefficient
of two thirds of the peak acceleration be usedcalculated in pseudostatic stability analyses for
design. Selection of the PGA to use for design and calculation of the corresponding seismic
coefficient shall be performed during final design and be based on tho results presented in
Table 6. this PSHA.
Additionally, results of this site-specific PSHA were compared to USGS 2014 NSHMP gridded
hazard curves. The USGS 2014 NSHMP indicate a PGA of 0.10 g for a return period of 2,475
years, which compare well to this study's result of 0.10 g at a VS3n of 3,904 ft/s (580 m/s) for the
same return period. For a return period of 10,000 years, using an estimated Vgan of 2,493 ft/s
(760 m/s), the 2014 NSHMP PGA is about 0.23 q, which is approximately 0.04 g greater than
the highest PGA calculated in this PSHA. The USGS NSHMP methodology was developed for
return periods up to 2,475 years, meaning that estimating the 10,000-vear return period from the
2014 NSHMP is outside the intended use of the data and likely explain the differences in the
PGA.
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FIGURES
® MWH Probabilistic Seismic Hazard Analysis
ATTACHMENT 1
LIST OF EARTHQUAKE EVENTS WITHIN THE WHITE MESA STUDY AREA
MWH Probabilistic Seismic Hazard Analysis
ATTACHMENT 2
LIST OF FAULTS AND FAULT CHARACTERISTICS INCLUDED IN THE PSHA
MWH Probabilistic Seismic Hazard Analys
ATTACHMENT 3
SUMMARY OF INDIVIDUAL FAULT PARAMETERS
MWH Probabilistic Seismic Hazard Analysis
ATTACHMENT 4
DAMES & MOORE BORING LOGS (1978)