U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2007-1152

Earthquake Hazards Geophysical Investigations

Miscellaneous High-Resolution Seismic

Imaging Investigations in Salt Lake and

Utah Valleys for Earthquake Hazards
Miscellaneous High-Resolution Seismic 

Imaging Investigations in Salt Lake and 

Utah Valleys for Earthquake Hazards

By W.J. Stephenson, R.A. Williams, J.K. Odum, and D.M. Worley

Earthquake Hazards Geophysical Investigations

Open-File Report 2007-1152

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

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Suggested citation:

Stephenson, W.J., Williams, R.A., Odum, J.K., and Worley, D.M., 2007, Miscellaneous high-resolution seismic

imaging investigations in Salt Lake and Utah Valleys for earthquake hazards: U.S. Geological Survey

Open-File Report 2007-1152, 29 p.
iii

Contents

Introduction.....................................................................................................................................................1

Proof-of-Concept Minivib P-Wave Imaging Profile in South-Central Salt Lake Valley......................1

Deep S-wave Minivib Reflection/Refraction Soundings in Salt Lake and Utah Valleys....................3

Interpretation Methodology................................................................................................................3

Saltair 4

Siesta Drive............................................................................................................................................6

River Oaks ..............................................................................................................................................9

Fire Training Tower.............................................................................................................................10

North Oquirrh Mountains ..................................................................................................................10

Provo Airport........................................................................................................................................10

Exchange Park.....................................................................................................................................10

Summary...............................................................................................................................................10

Vs30 (and Vp30) Surface Investigations in Utah Valley.........................................................................10

Downhole Vs Measurements in Utah Valley..................................................................................11

Data Processing..................................................................................................................................12

Provo Airport........................................................................................................................................14

Spanish Fork Airport...........................................................................................................................15

Youd Farm.............................................................................................................................................16

K-96 Radio Tower................................................................................................................................16

Discussion and Synopsis of Vs Results ...................................................................................................17

Combined FTT Interpretation ............................................................................................................17

Combined NOQ Interpretation ..........................................................................................................19

Summary of Vs30 and Vs100 Values ................................................................................................20

References Cited..........................................................................................................................................29

Figures

1. Investigated sites in Salt Lake and Utah Valleys.....................................................................5

2. Line location of minivib P-wave seismic imaging profile along 3200 W. in

South Jordan, Utah.......................................................................................................................6

3. Photos of minivib during acquisition along 3200 W. in South Jordan, Utah........................7

4. Typical field records along 3200 W. in South Jordan, Utah ...................................................7

5. Depth-converted P-wave seismic reflection profiles.............................................................8

6. Schematic of general acquisition geometry used at seven minivib

S-wave investigation sites. .........................................................................................................9

7A. Traces from combined Saltair (SA) minivib S-wave seismic records used for

refraction interpretation, sorted by source-sensor offset distance ..................................11

7B. Common midpoint (CMP) reflection stack at site SA overlain by “best”

refraction model..........................................................................................................................12

8. Final hybrid S-velocity models for the seven minivib S-wave soundings in

Salt Lake and Utah Valleys........................................................................................................13
iv

9A. Traces from combined Siesta Drive (SD) minivib S-wave seismic records

used for refraction interpretation sorted by source-sensor offset....................................14

9B. CMP reflection stack at site SD overlain by “best” refraction

model ............................................................................................................................................15

10. Traces from two minivib records sorted by offset ................................................................16

11. Traces from combined fire training tower (FTT) S-wave minivib seismic

records used for refraction interpretation sorted by source-sensor offset.....................17

12. (A) Traces from combined S-wave minivib seismic records near

Advanced National Seismic System seismograph station NOQ.

(B) NOQ refraction picks and results from robust linear least-squares

regression analysis ....................................................................................................................18

13A. Traces from combined S-wave minivib seismic records at Provo Airport (PA)

site sorted by source-sensor offset.........................................................................................19

13B. CMP reflection stack at site PA overlain by “best” refraction model ...............................20

14. Traces from combined Exchange Park (EP) S-wave minivib seismic records

used for refraction interpretation, sorted by source-sensor offset...................................21

15. Spanish Oaks (SOGC) shear-timber Vs and sledgehammer Vp site ..................................22

16. Spanish Fork Canyon Elementary School (SFCE) shear-timber Vs and

sledgehammer Vp site ...............................................................................................................23

17. Spanish Fork Clark Park (SFCP) shear-timber Vs and sledgehammer Vp site .................24

18. Spanish Fork Airport (SFA) shear-timber Vs and sledgehammer Vp site..........................25

19. S-velocity models for the four downhole S-wave soundings in Utah Valley

are shown as solid lines on graph ...........................................................................................26

20. Fire training tower (FTT) comparison of minivib, shear-timber, and SASW results ........27

21. (A) Shear-timber data acquired at site NOQ and interpreted velocity-depth

structure. (B) Comparison of minivib and shea .....................................................................28

Tables

1. Geographic locations of study sites and estimated Vs30 and Vs100 values ......................2

2. Processing parameters for P-wave seismic profile in South Jordan, Utah .......................4

3. Generalized processing parameters for S-wave common mid-point (CMP)

seismic reflection profiles in Salt Lake and Utah Valleys, Utah............................................9
Introduction

In support of earthquake hazards and ground motion 

studies by researchers at the Utah Geological Survey, University of Utah, Utah State University, Brigham Young University, and San Diego State University, the U.S. Geological 

Survey Geologic Hazards Team Intermountain West Project 

conducted three high-resolution seismic imaging investigations along the Wasatch Front between September 2003 and 

September 2005. These three investigations include: (1) a 

proof-of-concept P-wave minivib reflection imaging profile in 

south-central Salt Lake Valley, (2) a series of seven deep (as 

deep as 400 m) S-wave reflection/refraction soundings using 

an S-wave minivib in both Salt Lake and Utah Valleys, and 

(3) an S-wave (and P-wave) investigation to 30 m at four sites 

in Utah Valley and at two previously investigated S-wave (Vs) 

minivib sites. In addition, we present results from a previously unpublished downhole S-wave investigation conducted 

at four sites in Utah Valley.

The locations for each of these investigations are shown 

in figure 1. Coordinates for the investigation sites are listed 

in Table 1. With the exception of the P-wave common midpoint (CMP) reflection profile, whose end points are listed, 

these coordinates are for the midpoint of each velocity sounding. Vs30 and Vs100, also shown in Table 1, are defined as 

the average shear-wave velocities to depths of 30 and 100 m, 

respectively, and details of their calculation can be found in 

Stephenson and others (2005). The information from these 

studies will be incorporated into components of the urban 

hazards maps along the Wasatch Front being developed by 

the U.S. Geological Survey, Utah Geological Survey, and 

numerous collaborating research institutions.

Proof-of-Concept Minivib P-Wave 

Imaging Profile in South-Central Salt 

Lake Valley

We acquired approximately 2.7 km of P-wave seismicreflection CMP data along 3200 West in South Jordan, Utah, 

in the south-central Salt Lake Valley (fig. 2), with a 6,370-kg 

minivib II source truck. Our goals for this study were to: (1) 

assess the effectiveness of using the minivib II in an urbanized 

portion of Salt Lake Valley, and (2) image the R1, R2, and R3 

reflectors beneath this section of the valley. These reflectors in 

the Salt Lake Basin are important seismic boundaries separating unconsolidated and semiconsolidated sediments, semiconsolidated and consolidated sediments, and consolidated sediments and basement rock, respectively, as summarized by Hill 

and others (1990). In particular, the R2 boundary is believed 

to be a major earthquake ground motion amplifier within the 

valley (Olsen and others, 1995).

The profile (fig. 2) was along a north-south arterial 

roadway with significant automobile traffic. The data were 

acquired using both a 10-m source and receiver spacing and 

single 8-Hz vertical geophones. Four 14-second seismic 

sweeps between 10 and 200 Hz were stacked for each source 

location. We recorded between 72 and 159 channels per field 

record, dictated by field logistics along the profile, with the 

majority of records having 120 channels. Photographs of the 

6,370-kg minivib II in action along 3200 West are shown in 

figure 3. The profile, acquired north-to-south, benefited from a 

well-maintained grass strip for sensor planting and wide roads 

for more than one-half of the profile’s length. Typical field 

records from the northern, middle, and southern portions of 

the profile are shown in figure 4. The variable number of channels per source point is evident in each of the records. Sourcegenerated surface waves and significant urban noise are also 

evident throughout these records.

Data processing was conventional, and the processing 

steps are listed sequentially in table 2. Analyzing the surface waves for S-velocity structure (results not shown) was 

unsuccessful to depths greater than about 10 m because of the 

limited bandwidth governed by both the 10- to 200-Hz source 

sweep and 8-Hz sensors. Stacking these data using S-wave 

velocities was also not successful at delineating S-velocity 

structure because of the high ambient noise prevalent throughout the records. An interpreted P-wave depth-converted stack 

and its post-stack migrated counterpart are shown in figure 5.

We interpret four main reflections beneath the northern 

end of the profile. Of these, only the shallowest reflection 

is traceable to the profile’s southern end (fig. 5). The three 

Miscellaneous High-Resolution Seismic Imaging 

Investigations in Salt Lake and Utah Valleys for 

Earthquake Hazards

By W.J. Stephenson, R.A. Williams, J.K. Odum, and D.M. Worley
Table 1. Geographic locations of study sites and estimated Vs30 and Vs100 values. 

Site Data Type 

Latitude,

N°

Longitude,

W°

Vs30, Vs100,

m/s

Surface

Unit*

South Jordan (SJ) 

profile, north end 

P-wave CMP 40.5797† 111.9675† -------- --------

South Jordan (SJ) 

profile, south end 

P-wave CMP 40.5556† 111.9675† -------- --------

Saltair (SA) S-wave minivib 40.82370 112.06784 180, 270 Q01

Siesta Drive (SD) S-wave minivib 40.61099 111.83996 280, 435 Q02

River Oaks (RO) S-wave minivib 40.58449 111.91534 245, 400 Q02

Fire Training 

Tower (FTT) 

S-wave minivib 

S-wave timber 

40.68656

40.68653

112.08576

112.08698

480, 620

690

Q03

North Oquirrh 

Mountains (NOQ) 

S-wave minivib 

S-wave timber 

40.6519†

40.65270

112.1211†

112.12080

620, 1,100

660

P

Provo Airport 

(PA)

S-wave minivib 40.22649 111.71094 160, 235 Q01

Exchange Park, 

Provo (EP) 

S-wave minivib 40.2475† 111.6711† 190, 310 Q02

Spanish Oaks Golf 

Course (SOGC) 

S-wave timber 40.08766 111.59842 370 Q03

Spanish Fork 

Airport (SFA) 

S-wave timber 40.14518 111.67367 200 Q01

Clark Park, 

Spanish Fork 

(SFCP)

S-wave timber 40.12281 111.64675 230 Q01

Canyon

Elementary, 

Spanish Fork 

(SFCE)

S-wave timber 40.09278 111.62613 350 Q02

Provo Airport 

(DPA)

Downhole 40.223 111.721 161 Q01

K96 radio tower, 

Provo (K96) 

Downhole 40.212 111.671 202 Q01

Spanish Fork 

Airport (DSFA) 

Downhole 40.135 111.661 223 Q01

Youd Farm (YF) Downhole 40.133 111.730 223 Q01

* Mapped surface unit from Solomon and others (2004). 

† Coordinates estimated using GoogleEarth®.

deeper reflections are probably not traceable across the entire 

section because of both lower data coverage, caused by 

acquisition logistics, and higher urban noise caused by heavier 

automobile traffic as acquisition proceeded south. With only 

limited information from nearby boreholes that penetrate to 

these interpreted horizons, we speculate the shallowest and 

strongest reflection represents the R1 interface. A borehole 

near the profile location documents the R1 reflector at a depth 

of 98 m (G. McDonald, Utah Geological Survey, written commun., 2006), which coincides with the approximate depth of 

the shallowest strong reflector (red horizon in fig. 5); however, 

previous studies document the R2 as being a higher impedance contrast and therefore a stronger reflection than R1 (Hill 

and others, 1990; Olsen and others, 1995). By inspection, the 

 Miscellaneous High-Resolution Seismic Imaging Investigations in Salt Lake and Utah Valleys for Earthquake Hazards
highest impedance contrast of the depth section would appear 

to be the red horizon, leaving open the possibility that it may, 

in fact, be the R2 interface.

If both R1 and R2 are not distinctly imaged in these data, 

then we suggest several possibilities to explain this observation. 

It is possible the semi-consolidated sediments between the R1 

and R2 reflectors have either pinched out beneath this portion 

of the valley, or this sediment package is too thin to be resolved 

by these data. Alternately, gravity modeling of Radkins (1990) 

resolved “bedrock,” generally correlated with R2, in the 

300–400 m depth range beneath the seismic profile. A semicontinuous reflector (magenta in fig. 5) does mark a change in 

reflection character in this depth range, although this reflector 

is not as laterally coherent as the overlying red horizon. The 

next most distinct laterally coherent reflector is imaged until 

a depth of nearly 650 m. This reflector (cyan horizon in fig. 

5) may be the R2 reflector, but we consider this scenario as 

less likely. Finally, a reflector at approximately 900 m (green 

horizon in fig. 5) is near the expected depth for the R3 interface 

based on a recently developed basin model (H. Magistrale, San 

Diego State University, written commun., 2006).

In summary, the minivib II is a viable source for P-wave 

acquisition in at least this part of Salt Lake Valley, although 

future imaging investigations would possibly need to be run 

at night for less urban noise, with a more powerful source 

and (or) with multiple source vehicles. Regardless of whether 

the approximately 100-m-deep high-impedance reflection 

boundary is R1 or R2, this horizon, gently dipping south, will 

most likely act as a seismic wave amplifier in the investigated 

region of the southwestern Salt Lake Valley.

Deep S-wave Minivib Reflection/

Refraction Soundings in Salt Lake and 

Utah Valleys

The goal of our second investigation was to obtain Svelocity structure to at least a 100-m depth at selected sites 

throughout Salt Lake and Utah Valleys using minivib S-wave 

reflection/refraction data (fig. 1). Because the focus of this 

investigation was to image as deep as possible with this source, 

the resulting S-velocity structures represent coarse proxies of the subsurface. The site locations were guided in part 

by the mapped Quaternary surface geologic units within the 

valleys: Q01, Q02, and Q03 (finer-to-coarser grain size; for 

example, Ashand and McDonald,2003; Solomon and others 

2004). The minivib I S-wave source, mounted on an identical 

vehicle but (at 5,194 kg) lighter than the P-wave minivib II (fig. 

3), coupled sufficiently well to asphalt, concrete, and compacted gravel surfaces in this study; however, source coupling 

undoubtedly introduced noise in some instances in these data.

Data were acquired at seven sites within or along the 

edge of these urbanized sedimentary basins along the Wasatch 

Front, with five in Salt Lake Valley and two in Utah Valley. 

At each site, a 290-m sensor array was laid out with a source 

point at each end (fig. 6). Where possible, source points were 

also positioned every 100 m out to a 300-m distance from each 

end of the sensor array. These source points offset the farthest 

provide redundancy for deeper imaging, but they were not 

always used in data analysis if the respective 300-m source 

records had a high signal-to-noise ratio. At four of the sites, 

where it was logistically practical, intra-array source points 

(records) were collected for CMP profiling at every second or 

third sensor location. Sensor stations were spaced 5 m apart; 

to enhance signal-to-noise two 4.5-Hz single-component horizontal sensors aligned perpendicular to the line azimuth were 

summed in series at each location.

Interpretation Methodology

The first step for refraction analysis was to pick the first 

arrivals on data based on visual inspection of refraction-phase 

signal at available offsets. Not all data were incorporated if 

signal-to-noise was deemed low. Additionally, only the best 

data trace at a given source-sensor offset was used because 

offset-stacking tended to distort refraction phases. The firstarrival picks were next assigned to subsurface seismic layers in 

an initial refraction model based on traveltime-offset analysis. 

A robust least-squares linear regression algorithm in Matlab®

was then used to estimate intercept time and apparent refraction velocity for each picked layer. Finally, these intercept 

times and apparent velocities were forward-modeled using 

the refraction code of Mooney (1984) to develop a “best” 1D 

refraction velocity model at each site.

Reflection analysis was conducted on data at four sites 

using ProMAX® processing software. Processing of the 

S-wave field data to derive final stacked sections was conventional and generally followed the steps in table 3. Poststack migration was not attempted on these data because of 

both high noise levels at later arrival times and the generally 

flat-lying nature of the imaged strata. The “best” reflection 

velocity model was derived by first converting the best stacking velocity field to a smoothed interval velocity field using a 

ProMAX® proprietary algorithm. This interval velocity field 

was then averaged between strong reflection horizons to get a 

single velocity for each interpreted layer.

After processing and analyzing the reflection and refraction phases independently as described previously, our interpretation methodology next involved merging the “best” reflection 

and refraction models into the final velocity model for each 

site through both inspection and additional iterative modeling. 

Refraction model results were preferred over those of the reflection model in the shallowest section where reflection velocity 

control is poorest. Reflection model results were preferred 

over refraction results at depths greater than 100 m and in poor 

refraction signal areas. When the reflection and refraction models differed markedly in regions with good signal for both (layer 

depths and (or) velocities varied by greater than 10 percent), we 

iteratively adjusted the reflection and refraction models within 

the constraints of the data to converge to a final hybrid model.

Deep S-wave Minivib Reflection/Refraction Soundings in Salt Lake and Utah Valleys 
Table 2. Processing parameters for P-wave seismic profile in South Jordan, Utah. 

Processing Step Parameters/comments 

Data reformat SEG 2 to Promax® internal format 

Geometry installation Associate cartesian coordinates with data 

Trace editing Delete bad/unusable data traces 

Coherent noise attenuation Attenuate coherent noise caused by urban 

environment 

Surgical mute Zero amplitudes within the surface wave noise zone 

Bandpass filter Zero-phase Ormsby bandpass, 15–200 Hz 

Automatic gain correction 400 ms operator length 

DSN filter FX-domain signal-to-noise enhancement 

Elevation statics Correct for variations in elevation along line 

Normal moveout correction Use best velocity function estimated from constantvelocity stack analysis 

CMP Stacking Stack data by common midpoint (CMP) 

Post-stack coherent noise attenuation Attenuate additional coherent noise 

Post-stack migration Reverse-time TK implementation 

Predictive deconvolution Adaptive L2 norm, 40-ms prediction distance 

Eigenvector filter (migrated data only) Attenuate migration tails 

Time-to-depth conversion Use best-estimate velocity function for conversion 

Velocity inversions did not appear to be a significant 

problem in these data, but by incorporating the reflection 

information with the refraction results, velocity inversion and 

thin layer errors should be minimized (e.g., Williams and 

others, 2003). Additional error in the velocity-depth estimates from these minivib S-wave data are primarily from: (1) 

acquisition geometry error and variations in topography, (2) 

refraction picking error that can be as much as 15 milliseconds 

per source-offset distance, (3) root-mean-square misfit error in 

the refraction velocity analysis, (4) refraction modeling error 

caused by averaging over a 290-m array, where non-horizontal 

bedding is represented by a single 1D structure, and (5) reflection-velocity analysis error caused by limited source-array 

aperture, limited seismic bandwidth, and random noise. These 

error sources map into time-to-depth conversion error.

Saltair

The S-wave sounding at Saltair was on the mapped 

Q01 Quaternary unit (for example, Ashland and McDonald, 

2003; Solomon and others, 2004) in Salt Lake Valley, near 

the location of an industry P-wave profile and several deep 

boreholes (for example, Hill and others, 1990). The site was 

generally west of the Salt Lake City Airport in undeveloped 

ranch land, which gave an excellent opportunity for deep 

S-wave imaging (SA in fig. 1). Data quality was generally 

very high, as shown by the interpreted seismic refraction 

records in figure 7a. First-arrival traveltime picks are shown in 

red with their assigned refracting layer shown by blue lines on 

negative-offset traces only. We collected a source-point record 

at every third station along the sensor array and processed 

these data following the general procedures detailed in table 

3 to obtain the subsurface image in figure 7b. Subsurface 

layering is horizontal to sub-horizontal across the reflection 

depth section. The initial refraction and reflection models are 

remarkably similar and required little modification to integrate 

into a hybrid model for the site. We do not believe these data 

image sufficiently deep for the R1, R2, or R3 boundaries; 

however, based on correlation with a nearby industry borehole, 

the R1 boundary may be present at a 150-m depth (Hill and 

others, 1990). The final velocity model is interpreted to about 

a 225-m depth, as shown in figure 8.

 Miscellaneous High-Resolution Seismic Imaging Investigations in Salt Lake and Utah Valleys for Earthquake Hazards
41¡

40.5¡

112¡ 111.5¡

T

Pz

Q03

Q02

Q01

Q05

Mz

Q04

Station with minivib and hammer S-wave data

Station with hammer S-wave data

Station with minivib S-wave data

P-wave seismic reflection profile

Downhole S-wave

SA

FTT NOQ

RO

SD

SJ

EP

PA

Great

Salt

Lake

Utah

Lake

Figure 1. Map of investigated sites in Salt Lake and Utah Valleys. P-wave reflection profile for South 

Jordan is abbreviated SJ. S-wave minivib sites are SA (Saltair), FTT (Advanced National Seismic System 

(ANSS) instrument site Fire training tower), RO (River Oaks), SD (Siesta Drive), EP (Exchange Park), PA 

(Provo Airport), and NOQ (ANSS instrument site). Hammer S- and P-wave sites are SFA (Spanish Fork 

Airport), SFCP (Spanish Fork Clark Park), SFCE (Spanish Fork Canyon Elementary), SOGC (Spanish Oaks 

Golf Course), NOQ, and FTT. Downhole sites are DPA (Provo Airport), DSFA (Spanish Fork Airport), YF 

(Youd Farm), and K96 (K96 radio towers). Map modified from Solomon and others (2004).

Deep S-wave Minivib Reflection/Refraction Soundings in Salt Lake and Utah Valleys 
Siesta Drive

The Siesta Drive sounding (SD, fig. 1) was acquired on 

the eastern side of Salt Lake Valley on mapped Q02 sediments. Figure 9a shows the interpreted refraction data sorted 

by source-receiver offset. Data quality is good, although 

the refraction interpretation is more difficult than at Saltair 

because of prominent “steps” observed on the first arrivals. 

These steps suggest a complex wavefield arrival pattern (for 

example caused by possible velocity inversions, reflected 

waveforms overprinting refractions, survey geometry). 

Because the modeling undertaken here cannot accurately 

handle such complexity, the steps are treated as noise, and 

picks across them are incorporated into a single layer. These 

are especially prominent in layer-3 positive-offset picks (inset, 

fig. 9a). The stacked reflection section shown in figure 9b 

does not support the refraction steps being caused by velocity 

inversions. The reflection data strongly suggest the presence 

of two layers between depths of 30 and 100 m and, given the 

uncertainties in the refraction interpretation in this depth range 

due to the “steps,” the final model is interpreted as having 5 

layers (fig. 8). These data do not image to a depth sufficient 

for observing the R1, R2, or R3 reflectors.

400 m

N

Figure 2. Line location of minivib P-wave seismic imaging profile along 3200 W. in South Jordan, Utah. Profile location 

shown by red line.

 Miscellaneous High-Resolution Seismic Imaging Investigations in Salt Lake and Utah Valleys for Earthquake Hazards
Figure 3. Photos of minivib during acquisition along 3200 W. in South Jordan, Utah. Left: view east toward Wasatch Range; right: 

view south showing seismic cabling along curb and minivib base plate in contact with asphalt. Similar source vehicle was used 

during S-wave minivib acquisition in Salt Lake and Utah Valleys during field investigations described in this report.

North Middle South

0

1

2

CHANNEL NUMBERS

Figure 4. Typical field records along 3200 W. in South Jordan, Utah. Records from northern, middle and southern portion of profile displayed 

after 400 ms Automatic Gain Correction and 15–200 Hz bandpass filter. Arrows indicate location of minivib during acquisition. The effect of 

urban noise is prevalent throughout records.

Deep S-wave Minivib Reflection/Refraction Soundings in Salt Lake and Utah Valleys 
S. Jordan Parkway

(10400 S)

150 200 250 300 350

0

500

1,000

1,500

500 m

South Jordan Unmigrated Depth Section

Sta.150

S. Jordan Parkway

(10400 S)

200 250 300 350

500 m

South Jordan Migrated Depth Section

9400 S

Sta.

9800 S

9400 S 9800 S

North South

0

500

1,000

1,500

R3?

R2?

a)

b)

R1?

R3?

R2?

R1?

Figure 5. Depth-converted P-wave seismic reflection profiles. Upper: unmigrated; Lower: 

migrated. Four reflectors (red, magenta, cyan, green) are interpreted on each section.

 Miscellaneous High-Resolution Seismic Imaging Investigations in Salt Lake and Utah Valleys for Earthquake Hazards
Vibe points (all stars) 290-m sensor array

Vibe points used for negative

offset arrivals

100 m

Figure 6. Schematic of general acquisition geometry used at seven minivib S-wave investigation sites. At 

four of the sites, vibration points were also acquired at every second or third station within the array.

River Oaks

This S-wave sounding was at the River Oaks Golf Course 

(RO, fig. 1) on mapped Q02 sediments along the Jordan River. 

Figure 10 shows the interpreted refraction data sorted by 

source-receiver offset. Refraction signal quality is lower than 

for the soundings at Saltair and Siesta Drive. No reflections 

are clearly evident in these data, as lower-frequency surface 

waves dominate the records. Limited space prevented reversing the spread at offsets beyond the ends of the sensor array. 

The refraction picks support a general three-layer interpretation (inset, fig. 10). The final interpreted refraction model is 

generally faster than either Saltair or Siesta Drive to a 100-m 

depth (fig. 8). Arnow and others (1970) suggest the depth to 

R1 at the River Oaks site is greater that 150-m depth, thus R1 

would not be imaged by these S-wave seismic data.

Table 3. Generalized processing parameters for S-wave common mid-point (CMP) seismic reflection 

profiles in Salt Lake and Utah Valleys, Utah. 

Processing Step Parameters/comments 

Data reformat SEG 2 to ProMAX® internal format 

Geometry installation Associate cartesian coordinates with data 

Trace editing Delete bad/unusable data traces 

Bandpass filter Zero-phase Ormsby bandpass, 5–60 Hz 

Automatic gain correction 300 ms operator length 

Coherent noise attenuation Attenuate coherent noise caused by urban 

environment using fan filter 

Top mute Zero amplitudes above direct arrival 

Elevation statics Correct for variations in elevation along line 

Normal moveout correction Use best velocity function estimated from constant 

velocity stack analysis 

Residual statics Refine corrections for variations in elevation 

Dip moveout correction Prestack partial migration 

CMP stacking Stack data by common midpoint 

Time-to-depth conversion Use best-estimate velocity function for conversion 

Deep S-wave Minivib Reflection/Refraction Soundings in Salt Lake and Utah Valleys 
Fire Training Tower

The S-wave sounding at the fire training tower was near 

the Advanced National Seismic System (ANSS) seismograph 

station FTT on mapped Q03 sediments (fig. 1; in this study, 

the abbreviation FTT will denote our site, not the ANSS 

station site). Figure 11 shows the interpreted seismic refraction data, sorted by source-sensor offset. Limited space at 

the site prevented full reversed-spread refraction shooting at 

far offsets, akin to River Oaks, thus depth of investigation 

is less than 100 m. The site appears seismically complex 

and proved initially difficult both to pick and to interpret. 

Although we attempted reflection processing at this site with 

field records recorded with the source at every third sensor, 

no interpretable reflections emerged and are therefore not 

presented here. These minivib refraction data required amplitude-squared gain adjustment and no filtering, as opposed to 

automatic gain correction and bandpass filtering used on all 

other minivib data sets. The refraction data are most confidently interpreted as a two-layer subsurface, although limited 

far-offset picks do suggest a third high-velocity layer below 

a 30-m depth. This third layer, at a depth of about 75 m, is 

consistent with the R2 layer depth of approximately 70 m in 

Radkins (1990).

North Oquirrh Mountains

This S-wave sounding location, as shown in figure 1, 

was near ANSS seismograph station NOQ, which is installed 

on a mapped Paleozoic bedrock outcrop (e.g., Ashland and 

McDonald, 2003; Solomon and others, 2004). Because the 

station is at a topographically remote location, we were 

unable to acquire data directly at the seismograph station 

with the minivib. Instead, acquisition was along a sinuous dirt 

road approximately 100 m downslope of and 30 m lower than 

NOQ. Refraction arrival times were significantly complicated 

by line geometry, topography, and possible heterogeneity in 

underlying bedrock (fig. 12a). The most conservative interpretation of these data is as a two-layer model, as shown in 

figure 8.

Provo Airport

The minivib S-wave sounding near the Provo Airport 

(PA, fig. 1) was acquired on the Q01-mapped sediments in 

Utah Valley. Both refraction and reflection information at this 

location was among the best acquired of the seven sites. Figure 

13a shows the interpreted seismic refraction data, sorted by 

source-sensor offset. Strong refraction arrivals are visible to 

about -600 m offset, but the shooting geometry is unreversed 

because of permitting logistics. This record section consists of 

data from three source locations: from offsets 0 to 290 m, -295 

to 0 m, and -595 to -300 m. The pre-refraction noise in these 

three offset ranges differs markedly and is probably related to 

source coupling variations.

Reflection imaging was exceptional at this site, allowing 

the velocity model interpretation to extend to a depth of about 

420 m. Reflections and reverberations are visible throughout 

much of the field data (fig. 13a). The combined reflection and 

refraction “best” models are shown in figure 13b. The top of 

refraction-model layer 4 (Vs of about 340 m/s) correlates with 

a reflection at a depth of about 55 m. The final hybrid model 

for the Provo Airport data is shown in figure 8. This site has 

the lowest S-velocity structure (130–340 m/s) in the upper 100 

m of any of the investigated minivib sites.

Exchange Park

Exchange Park (EP, fig. 1) was the second minivib Swave site acquired in Utah Valley and is within the city limits 

of Provo on mapped Q02 sediments. Refraction arrivals are 

generally clear in these data, and reflections are also visible 

(fig. 14). Field logistics allowed a fully reversed refraction 

acquisition geometry to an almost 600-m offset. This aperture 

permitted modeling of as many as five layers during refraction 

analysis (see inset, fig. 14). Reflections were not stacked into 

a depth section but did provide control on the final velocity 

model, shown in figure 8.

Summary

The minivib S-wave source successfully generated sufficient energy to obtain S-velocity structure images to depths 

of more than 200 m at several of the sites along the Wasatch 

Front. A more robust solution was determined by combining 

independent reflection and refraction interpretations. These 

interpreted velocity-depth models should be considered a 

coarse representation of Vs at each investigated site, with 2-m 

vertical resolution on average at the 20-m depth and 6-m vertical resolution on average at the 100-m depth.

Vs30 (and Vp30) Surface Investigations 

in Utah Valley

We acquired shallow seismic Vs30 (and Vp30) data at 

four sites in southern Utah Valley along a transect from highest (Q03) to lowest (Q01) S-wave velocity lacustrine deposits 

mapped at the surface (fig. 1). In addition, we occupied locations near ANSS stations NOQ and FTT because of uncertainty in the earlier interpretations from the minivib S-wave 

studies done near these sites. Both P- and S-wave reflection/

refraction data were acquired at all six sites, although in this 

report we emphasize the S-wave results. The source for these 

data was a sledgehammer impacted on either a shear-timber 

(S-wave) or a metal plate on the ground (P-wave). Interpretation of these data also utilized the refraction modeling code of 

Mooney (1984) and incorporated reflection information. The 

Matlab® robust linear regression algorithm was not used in the 

analysis of the refraction picks for these data.

10 Miscellaneous High-Resolution Seismic Imaging Investigations in Salt Lake and Utah Valleys for Earthquake Hazards
1

2

3 4 5

0

1.0

2.0

3.0

4.0

200 m

SOURCE-SENSOR OFFSET, IN METERS -680 m 0 680 m

Figure 7 (A). Traces from combined Saltair (SA) minivib S-wave seismic records used for refraction interpretation, sorted 

by source-sensor offset distance. Refraction picks (red lines) and 5-layer interpretation (blue lines) are shown. Reflection 

labeled at 1.4 s. Processing on refraction records included geometric sorting of selected records, gain correction (AGC), and 

bandpass filter 5–60 Hz.

The four Vs30 and Vp30 sites acquired with a sledgehammer source in Utah Valley are presented in figures 15 to 

18. Data acquired at each of these sites were of very good 

quality, lending confidence to the interpreted results. A representative S-velocity record, a table of Vs and Vp models, and 

a graphical presentation of Vs and Vp are shown for each site 

in each of the respective figures 15 to 18. Data acquired near 

Spanish Oaks Golf Course (SOGC, figs. 1, 15) are on mapped 

Q03 deposits, although this site will likely be changed to 

Q02 in future updated maps (G. McDonald, Utah Geological 

Survey, written commun., 2006); those acquired near Spanish 

Fork Canyon Elementary (SFCE, figs. 1, 16) were on mapped 

Q02 deposits. Progressing northwestward, data acquired near 

both Clark Park (SFCP, figs. 1, 17) and the Spanish Fork 

Airport (SFA, figs. 1, 18) were on mapped Q01 deposits. The 

Vs30 values for these shear-timber sites are listed in Table 1.

Downhole Vs Measurements in Utah Valley

This section presents previously unpublished borehole 

data acquired in Utah Valley as part of the investigation 

presented in Tinsley and others (1991). We have been unable 

to recover lithologic logs for these boreholes. The borehole 

acquisition equipment used in this investigation consisted of a 

portable digital seismograph and a single downhole geophone. 

The shear-wave seismic source, which was offset about 1.8 

m from the borehole, was a sledgehammer and shear-timber 

device similar to the “horizontal traction” source described by 

Kobayashi (1959). The S-wave polarity reversal produced with 

this method facilitates identification of the shear-wave onset. 

The start signal, generated by the hammer impact against the 

timber, served as the origin time. The timing for the source 

pulse origin time varies slightly (probably less than 0.001 s) 

Vs30 (and Vp30) Surface Investigations in Utah Valley 11
Vs~220 m/s

Vs~530 m/s

Vs~600? m/s

Vs~375 m/s {

Interval velocities from

stacking velocities

(reflection model)

stacking velocities

(reflection model)

157

m/ 219s

m/s 330

m/s

403

m/s

530

m/s

460

m/s

0

100

200

300

400

50 m

Refraction model,

in m/s

Saltair Reflection Section and Refraction Model

Figure 7 (B). Common midpoint (CMP) reflection stack at site SA overlain by “best” refraction model. Colored 

areas on both reflection and refraction interpretations represent geologic layers.

due to variable delays in the trigger switch and instrument 

response. We assume that there will be a reasonably constant 

time delay in the data that does not significantly affect the 

derived velocities.

The 15.2-cm diameter boreholes were cased with 

10.2-cm diameter plastic pipe and grouted in place. The 

boreholes were sampled at 2-m vertical intervals using a 

three-component 28-Hz resonant-frequency geophone. A 

magnetic declinometer on the geophone was used to orient 

the geophone at each new depth so that the horizontal S-wave 

(SH) component was aligned with the shear timber. Because 

it was difficult to achieve the same orientation at each depth, 

especially below 30 m, there was a variation of about ±5° in 

the SH component orientation in some cases. This variation in 

geophone orientation relative to the SH source may account 

for some of the small arrival time and amplitude differences 

observed in the data.

Data Processing

A 180° wavelet phase reversal identifies the S-wave onset 

time recorded at each depth. Depending on the record signal 

quality and the timing scale, time-pick accuracy varies from 

about 0.001 to 0.003 s for S waves. Greater errors in picking 

wavelet first arrivals occurred on records from greater borehole depths for several reasons: (1) these signals are longer in 

duration and required a coarser digital time-sampling interval 

to fit them in the limited seismograph memory space, (2) 

signal-to-noise ratios tended to decrease with depth, making it sometimes difficult to select the SH-wave first arrival, 

or (3) some boreholes may have sections of the casing that 

are poorly coupled to the borehole wall, which could create 

anomalously low signal amplitude or spurious signals. The 

greatest impediment to accurate first arrival picks was caused 

by seismic noise (possibly tube waves) arriving before and 

12  Miscellaneous High-Resolution Seismic Imaging Investigations in Salt Lake and Utah Valleys for Earthquake Hazards
Figure 8. Final hybrid S-velocity models for the seven minivib S-wave soundings in Salt Lake and Utah Valleys. Red lines 

represent soundings on Q01 deposits, green lines are for soundings on Q02, magenta lines are for soundings on Q03, and blue 

lines are for sounding on “bedrock” at site NOQ. Solid lines represent soundings in Salt Lake Valley while dashed lines represent 

soundings in Utah Valley. Velocity-depth models in table form are listed to right of diagram.

0 130

11 130

11 185

29 185

29 240

55 240

55 340

115 340

115 435

295 435

295 695

420 695

Provo Airport (PA)

Depth Vs

Exchange Park (EP)

0 135

8 135

8 200

24 200

24 340

62 340

62 540

102 540

102 665

Depth Vs

Saltair (SA)

0 160

16 160

16 220

36 220

36 330

70 330

70 400

110 400

110 460

135 460

135 530

225 530

Depth Vs

Siesta Drive (SD)

Depth Vs

0 210

10 210

10 340

30 340

30 480

95 480

95 515

138 515

138 914

200 914

River Oaks (RO)

Depth Vs

0 195

20 195

20 550

150 550

FTT

Depth Vs

0 430

19 430

19 600

75 600

75 1040

NOQ

Depth Vs

0 550

25 550

25 1675

150 1675

Units for all tables:

Depth, in meters

Vs, in meters per second

SHEAR-WAVE VELOCITY (VS),

IN METERS PER SECOND

250

200

150

100

50

0

300

350

400

SA

FTT

NOQ

RO

SD

PA

EP

Salt Lake and Utah Valley

Minivib Final Vs Velocity Models

Q01

Q02

Q03

Rock

Vs30 (and Vp30) Surface Investigations in Utah Valley 13
simultaneously with the SH arrival. Usually this noise could be 

separated from the SH-wave arrival through a comparison of 

amplitude and polarity; in most cases, the noise was of lower 

amplitude and did not exhibit a polarity reversal. This report’s 

second author (R.A. Williams) independently analyzed these 

downhole data.

Intervals of constant seismic velocity within the borehole 

were determined by visual inspection of the time-depth plots 

(not shown). Depth intervals on the time-depth plot where 

consecutive data points display a relatively constant slope (fit 

by a linear least-squares method) define a constant-velocity 

interval in a manner similar to the refraction analysis described 

previously. In all borehole data the linear fits have correlation 

coefficients of 0.98 to 0.99.

Provo Airport

The S-wave downhole data from Provo Airport (DPA, 

fig. 1), which is located about 1 km southwest of the Provo 

Airport S-wave minivib site PA (fig. 1), are quite similar to the 

minivib data from the 0 to 28-m depth (the maximum downhole data reading) as shown in figure 19. In the layer from 0 

to 11 m, there is a 20 m/s S-velocity difference (150 to 130 

m/s) between the two sites, and in the layer from 14 to 28 m 

the results are essentially identical at about 185 m/s. These 

two sites are located on the Q01 Salt Lake Valley equivalent 

unit. The geologic log from the downhole site indicates that 

the depth interval from 0 to 28 m consists mostly of very soft 

clay in the upper 11 m (J. Tinsley, U.S. Geological Survey, 

Figure 9 (A). Traces from combined Siesta Drive (SD) minivib S-wave seismic records used for refraction 

interpretation sorted by source-sensor offset. Refraction picks are shown as red lines and reflection is labeled 

at about 0.65 seconds. Processing on refraction records included geometric sorting of selected records, gain 

correction (AGC), and bandpass filter 5–60 Hz. Inset: results of 4-layer interpretation showing picks used for the 

linear regression as black (layer 1), blue (layer 2), magenta (layer 3), and green (layer 4) circles.

0

1.0

2.0

3.0

4.0

100 m

-595 m 0 590 m

SOURCE-SENSOR OFFSET, IN METERS

-600 -400 -200 0 200 400 600

0.2

0.4

0.6

0.8

1

1.2

1.4

layer 1

layer 2

layer 3

layer 4

SOURCE-SENSOR OFFSET, IN METERS

ÒstepÓ

14  Miscellaneous High-Resolution Seismic Imaging Investigations in Salt Lake and Utah Valleys for Earthquake Hazards
Siesta Drive Reflection Section and Refraction Model 208

341

515

m/s

914

m/s

~322 m/s

~480 m/s

~513 m/s

0

100

200

300

400

Refraction model

50 m

Refraction model,

in m/s

Figure 9 (B). CMP reflection stack at site SD overlain by “best” refraction model.

written commun., 1986). An increase in sand content at about 

11 m appears to be the cause of the jump in Vs from about 130 

m/s to 185 m/s. Note that the Vs30 value in table 1 assumes a 

constant Vs between the last measurement point at 28 m and 

the 30-m depth.

Spanish Fork Airport

In the vicinity of the Spanish Fork Airport (DSFA, fig. 

1), we find some differences between the S-wave downhole 

data and the S-wave hammer refraction/reflection survey in 

the upper 55 m. The hammer and downhole data sites, which 

are separated by about 1.5 km, have similar low velocities 

in the upper 10 m, ranging from 80 to 210 m/s (fig. 19). The 

geologic log from the borehole indicates a change from soft 

clayey silt to sand at a 4-m depth, which corresponds to the 

jump from 114 to 212 m/s in the downhole data (J. Tinsley, 

U.S. Geological Survey, written commun., 1986). Another 

change in Vs occurs at a 10-m depth where the deposits 

change from sand to stiffer clay. Below about 10 m, however, 

the downhole record shows three velocity inversions in the 

10- to 50-m depth range that are not observed in the refraction/reflection profile. In this depth interval, the downhole Vs 

oscillates between about 220 and 320 m/s while the refraction/reflection data interpretation for this interval is a constant 

370 m/s. Though it was not recognized in the original refraction data interpretation, there is evidence for the presence of at 

least one low velocity zone below an 11-m depth in the form 

of a time delay or step in the refraction first arrivals.

Vs30 (and Vp30) Surface Investigations in Utah Valley 15
Youd Farm

The downhole data at Youd Farm (YF, fig. 1) reveal 

another soft soil site with S-velocity in the range of 230 to 325 

m/s to a depth of almost 60 m. The Vs30 at this site is 231 m/s 

and the Vs66 (bottom of the hole) is 279 m/s. In contrast to 

the downhole data at the Provo and Spanish Fork airports, no 

velocity inversions were interpreted. The Vs maximum of 390 

m/s is reached at 58 m and extends to at least the bottom of the 

hole at a 66-m depth.

K-96 Radio Tower

This site (K96, fig. 1), which is located near Interstate 15 

about 4 km east-southeast of the Provo Airport downhole site, 

also has a Vs structure that is characteristic of soft sediments. 

The downhole data reach a 46-m depth with an average Vs 

to that depth of only 217 m/s, which is not much of a change 

from the Vs30 for this site (202 m/s). The Vs maximum is 

297 m/s, which is detected in the 40- to 46-m depth range 

(fig. 19).

Figure 10. Traces from two minivib records sorted by offset (no room for additional farther-offset minivib source 

points) at River Oaks (RO) S-wave site. Refraction picks shown as red lines; no reflections are clearly evident in 

field records. Inset: results of 3-layer interpretation showing first-arrival picks used for the linear regression as 

black (layer 1), blue (layer 2), and magenta (layer 3) circles.

0

1.0

2.0

3.0

4.0

150 m

-300 m 0 295 m

SOURCE-SENSOR OFFSET, IN METERS

-300 -200 -100 0 100 200 300

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

layer 1

layer 2

layer 3

SOURCE-SENSOR OFFSET, IN METERS

16  Miscellaneous High-Resolution Seismic Imaging Investigations in Salt Lake and Utah Valleys for Earthquake Hazards
Discussion and Synopsis of Vs Results

Combined FTT Interpretation

Because the minivib S-velocity data at FTT were complex and an initial interpretation attempt yielded ambiguous 

results, shear-timber data were acquired in 2005 to better 

characterize the shallow subsurface and constrain the minivib 

interpretation. The shear-timber and the minivib data were not 

acquired at the exact same location. The minivib array location was based on road access and the need for 290 m of array 

distance. The shear-timber array location was established the 

following year along a portion of the minivib array; however, 

interim land reworking at the investigated site forced the later 

shear-timber array center to be offset from the minivib array 

center. The sensor array locations overlapped but their midpoints are separated by about 100 m (fig. 20a).

Spectral Analysis of Surface Wave (SASW) data were 

acquired at two sites near FTT (J. Berry, Utah State University, 

written commun., 2006). Results from the second acquisition 

study (SASW2) are shown in figure 20b (analysis by J. Berry 

and J. Bay, Utah State University, written commun., 2006). 

The site SASW1 Vs30 result was 422 m/s versus the SASW2 

result of 432 m/s, and both velocity-depth models are comparable (J. Berry, Utah State University, written commun., 2006). 

The SASW2 array center is approximately 250 m east of the 

shear-timber array center and about 150 m east of the minivib 

center. Because of the minivib array length, the SASW2 array 

midpoint is roughly on the eastern end of the minivib array. 

The SASW2 model velocities are consistently lower in the 

upper 10 m than either the shear-timber or minivib models.

With higher velocity layers (greater than 500 m/s) getting 

deeper as the array centers progress eastward, one possibility 

for the differences between the three models is that bedrock 

Figure 11. Traces from combined fire training tower (FTT) S-wave minivib seismic records used for refraction 

interpretation sorted by source-sensor offset. Refraction picks shown as red lines; no reflections are clearly 

evident in field records. Low refraction signal return (weak arrivals) was probably caused by poor source/

receiver coupling and (or) complex near-surface geologic conditions. Results at this site from the minivib data 

are problematic. See text for discussion. Inset: results of 3-layer interpretation showing first-arrival picks used 

for the linear regression as black (layer 1), blue (layer 2), and green (layer 3) circles.

0

0.5

1.0

150 m

-290 m 0 410 m

SOURCE-SENSOR OFFSET, IN METERS

layer 1

-400 -300 -200 -100 0 100 200 300 400

0

100

200

300

400

500

600

layer 2

layer 3?

SOURCE-SENSOR OFFSET, IN METERS

Discussion and Synopsis of Vs Results 17
Figure 12. (A) Traces from combined S-wave minivib seismic records near Advanced National Seismic System seismograph station 

NOQ used for refraction interpretation sorted by source-sensor offset. Refraction picks shown as red lines; no reflections observed. 

Inset: schematic diagram of source-sensor acquisition geometry used to obtain these data about 150 m south of NOQ along curvy dirt 

road. The very complex first-arrival pattern is caused in part by acquisition geometry along the narrow dirt road. (B) NOQ refraction picks 

and results from robust linear least-squares regression analysis. Inset: yellow and blue areas are velocity model derived from regression.

0

0.2

0.4

0.6

0.8

A

150 m

-450 m 0 450 m

SOURCE-SENSOR OFFSET, IN METERS

vibe point 150-m sensor array

Shots used for negative

offset arrivals

550 m/s

1675

m/s

~150 m

Depth?

25 m

layer 1

layer 2

layer 1

layer 2

0 50 100 150 200 250 300 350 400 450

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

NOQ positive offsets

0 50 100 150 200 250 300 350 400

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

NOQ negative offsets

SOURCE-SENSOR OFFSET, IN METERS SOURCE-SENSOR OFFSET, IN METERS

B

18  Miscellaneous High-Resolution Seismic Imaging Investigations in Salt Lake and Utah Valleys for Earthquake Hazards
0

1.0

2.0

3.0

4.0

SOURCE-SENSOR OFFSET, IN METERS

-595 m -295 m 0 290 m

-400 -300 -200 -100 0 100 200 300 0

200

400

600

800

1000

1200

1400

layer 2

layer 1

layer 3

layer 4

SOURCE-SENSOR OFFSET, IN METERS

Figure 13 (A). Traces from combined S-wave minivib seismic records at Provo Airport (PA) site sorted by sourcesensor offset. Refraction picks shown by red lines. Reflections and reverberations are visible throughout record 

section. Refraction arrivals are visible to an offset of about -600 m, but the profile is unreversed because of permitting 

logistics. Inset: results of 4-layer interpretation showing first-arrival picks used for the linear regression as black (layer 

1), blue (layer 2), magenta (layer 3), and green (layer 4) circles.

complexity such as a dipping sediment-bedrock contact is 

being mapped by the different methods. Depending on how 

layers are correlated between the S-timb, SASW2, and S-vibe 

results shown in figure 20b, bedrock or high-velocity soil layers would only need to dip 5°–30° east in plane-dipping scenario. Within the uncertainties of these acquisition methods, 

the minivib and SASW results are consistent in the upper 30 m 

near the FTT station location, as evidenced by the Vs30 values 

of 480 m/s and 432 m/s, respectively. Additionally, assuming 

the interface at about 13 m depth in the shear-timber result 

is the base of the soil column, the Vs13 for this site is about 

481 m/s as well (as noted by G. McDonald, Utah Geological 

Survey, written commun., 2006).

Combined NOQ Interpretation

Shear-timber data were acquired within several meters 

of ANSS seismograph station NOQ, crossing from limestone 

outcrop onto an inferred thin veneer of alluvium/colluvium. 

These shear-timber data are very high quality, as demonstrated 

by the clean first breaks in the reverse-polarity plot in figure 

21a. These data suggest layer boundaries at 10 and 17 m. 

The minivib Vs30 value of 620 m/s is lower than the sheartimber Vs30 of 660 m/s, which is not surprising given that the 

minivib acquisition was along a gravel road near the stream 

channel, with presumably more alluvial cover and weathered 

material than at station NOQ, while the shear-timber data were 

Discussion and Synopsis of Vs Results 19
0

100

200

300

400

50 m

~230 m/s

~295 m/s

~435 m/s

~695 m/s

~800? m/s

130

185

240

340

m/s

Provo Airport Reflection Section and Refraction Model

Refraction model,

in m/s

Figure 13 (B). CMP reflection stack at site PA overlain by “best” refraction model.

acquired on or near bedrock. The shear-timber Vs30 is similar 

to that of a linear velocity gradient model from 300 to 1675 

m/s between depths of 0 and 38 m, as used in the weak-motion 

analysis of Pankow and Pechmann (2004). An alternative theoretical exponential function (J. Pechmann, written commun., 

2004) is also shown in figure 21b and has a still higher Vs30 

of 760 m/s. The shear-timber model is undoubtedly most representative of the NOQ site when compared with the minivib 

model. The final Vp and Vs models for site NOQ are shown in 

figure 21c.

Summary of Vs30 and Vs100 Values

The Vs30 values for the minivib, shear-timber and downhole sites are listed in table 1. Minivib Vs30 values in Salt 

Lake Valley are near the logarithmic means for Vs30 of the 

representative “non-rock” surface units in the Utah Geological Survey database (Ashland and McDonald, 2003). Minivib 

Vs30 values in Utah Valley are both on the low end for unit 

Q01 according to the statistics of Ashland and McDonald 

(2003) derived for the Salt Lake City metropolitan area. The 

Vs30 values for the shear-timber data on the southern side of 

Utah Valley decreased from 370 m/s to 200 m/s as sites proceeded to finer-grained deposits into the basin. These values 

are all within ranges for the representative site-condition units 

one would infer based on Ashland and McDonald (2003).

The Vs30 values from downhole results compare well 

to Vs30 values from the surface methods. The Vs30 for the 

Saltair site, listed in table 1, differs by only 2 percent from a 

Vs30 downhole measurement reported by Williams and others 

(1993) at a site roughly 2 km south of the minivib sounding 

location. The Vs30 value at a site along the Jordan River 

20 Miscellaneous High-Resolution Seismic Imaging Investigations in Salt Lake and Utah Valleys for Earthquake Hazards
approximately 4 km north of the River Oaks sounding site, 

from Williams and others (1993), is 278 m/s. The difference is 

approximately 13 percent. The S-wave downhole data near the 

Provo Airport are approximately 1 km southwest of the Provo 

Airport minivib site. The Vs30 values for these are 161 m/s 

and 160 m/s, respectively.

Because of their greater depth of penetration, Vs100 

values were calculated for the seven minivib acquisition sites 

only. Sites acquired on mapped Q01 deposits in Salt Lake and 

Utah Valleys are qualitatively similar down to a depth of over 

150-m (fig. 8). Site EP on mapped Q02 deposits in Utah Valley 

is more similar to Q01 sites in the upper 50 m than to the other 

Q02 sites RO and SD. In general, Q03 sites are consistently 

higher in velocity than Q01 sites, but are not markedly different 

from Q02 sites at depths below approximately 30 m. Comparing the Vs100 calculations in table 1, these qualitative observations are consistent with this mean value. At depths of 100 m 

or greater, site similarity apparently becomes more related to 

site-location/basin-edge distance and basin geometry than to 

the surface unit mapped at a given site. While Vs100 is not a 

standard implemented in building codes (International Building 

Council, 2006), it is perhaps a more meaningful value when 

analyzing ground motions at 1 Hz and less.

Figure 14. Traces from combined Exchange Park (EP) S-wave minivib seismic records used for refraction 

interpretation, sorted by source-sensor offset. Refraction picks shown by red lines. Clear reflections observed in 

upper 1 s are consistent with refraction-only model, shown in inset.

0

0.5

1.0

1.5

2.0

reflection

-590 m 0 570 m

150 m

SOURCE-SENSOR OFFSET, IN METERS

-600 -400 -200 0 200 400 600

0.5

1.0

1.5

layer 1

layer 2

layer 3

layer 4

layer 5

SOURCE-SENSOR OFFSET, IN METERS

Discussion and Synopsis of Vs Results  21
Site: Spanish Oaks Golf Course, Spanish Fork, Utah

S-vel (m/s) Depth (m) P-vel (m/s) Depth (m)

325 0.0 325 0.0

325 13.0 325 3.0

410 13.0 535 3.0

410 43.0 535 20.0

955 43.0 2,275 20.0

955 50.0 2,275 30.0

Vs30 = 370 m/s NEHRP class C

A

B

0

10

20

30

40

50

60

500 1,000 1,500 2,000 2,500

VELOCITY, IN METERS PER SECOND

S-wave

P-wave

South North

218 ms

294 ms

48 ms

240 ms

C

400

200

600

-10 -70 -130 135 75 15

OFFSET, IN METERS

Figure 15. Spanish Oaks (SOGC) shear-timber Vs and sledgehammer Vp site. (A) Graphical display of Vs and Vp velocity structures; 

(B) Interpreted velocity structures in table format; (C) Representative Vs field records. Interpreted reflections and refractions are 

shown by red lines.

22  Miscellaneous High-Resolution Seismic Imaging Investigations in Salt Lake and Utah Valleys for Earthquake Hazards
Figure 16. Spanish Fork Canyon Elementary School (SFCE) shear-timber Vs and sledgehammer Vp site. (A) Graphical display of Vs and 

Vp velocity structures; (B) Interpreted velocity structures in table format; (C) Representative Vs field records. Interpreted reflections and 

refractions are shown by red lines.

S-vel (m/s) Depth (m) P-vel (m/s) Depth (m)

250 0.0 480 0.0

250 3.0 480 5.0

340 3.0 615 5.0

340 9.0 615 26.0

445 9.0 1,945 26.0

445 20.0 30.0

325 20.0

325 80.0

1,325 80.0

Vs30 = 350 m/s NEHRP class D

85.0

Possible strong site resonance

at about 1.0 Hz (based on

reflection time from rock)

S-wave velocity estimated - no control and assuming it

is “bedrock”

S-wave velocity estimated by assuming a velocity that fits

with reflection velocity from an 80-m deep layer

South North

480 ms

58 ms

20 ms

A

C

B

0

10

20

30

40

50

60

70

80

90

100

500 1,000 1,500 2,000 2,500

S-wave

P-wave

VELOCITY, IN METERS PER SECOND

Site: Canyon Elementary, Spanish Fork, Utah

1,325

1,945

495 m/s 348 m/s

252 m/s

330 m/s

400

200

600

90 60 30

OFFSET, IN METERS

800

150 120

Discussion and Synopsis of Vs Results  23
Figure 17. Spanish Fork Clark Park (SFCP) shear-timber Vs and sledgehammer Vp site. (A) Graphical display of Vs and Vp velocity 

structures; (B) Interpreted velocity structures in table format; (C) Representative Vs field records. Interpreted reflections and refractions 

are shown by red lines.

0

10

20

30

40

50

60

70

80

90

100

500 1,000 1,500 2,000 2,500

S-wave

P-wave

A

C

B

Site: Clark Park, Spanish Fork, Utah

S-vel (m/s) Depth (m) P-vel (m/s) Depth (m)

85 0.0 260 0.0

85 0.5 260 2.0

140 0.5 1,510 2.0

140 2.0 10.0

185 2.0 1,600 50.0

185 5.5 1,700 70.0

240 5.5

240 18.0

275 18.0 Vs30 = 230 m/s NEHRP

275 35.0 class D

340 35.0

340 50.0 Data from reflections only

380 50.0

380 95.0

Suggested by reflection data

West East

25 ms

424 ms

183 ms

OFFSET, IN METERS

Site: Clark Park, Spanish Fork, Utah

VELOCITY, IN METERS PER SECOND

400

200

600

30 60 90

800

120 150

298 ms

56 ms

7 ms

100 m/s

188 m/s

243 m/s

245 m/s

203 m/s

1,510

268 m/s

144 m/s

24  Miscellaneous High-Resolution Seismic Imaging Investigations in Salt Lake and Utah Valleys for Earthquake Hazards
Figure 18. Spanish Fork Airport (SFA) shear-timber Vs and sledgehammer Vp site. (A) Graphical display of Vs and Vp velocity 

structures; (B) Interpreted velocity structures in table format; (C) Representative Vs field records. Interpreted reflections and 

refractions are shown by red lines.

South North

353 ms

C OFFSET, IN METERS

400

200

600

90 60 30

800

150 120

193 ms

79 ms

415 m/s

183 m/s

384 m/s

78 m/s

0

20

40

60

80

100

500 1,000 1,500 2,000

S-vel (m/s) Depth (m) P-vel (m/s) Depth (m)

78 0.0 285 0.0

78 4.0 285 2.0

160 4.0 1,670 2.0

160 12.0 20.0

370 12.0 1,800 20.0

370 82.0 1,900 95.0

410 82.0

410 95.0

Vs30 = 200 m/s NEHRP class D

Unreversed profile

Layer not observed from south end

A

B

Site: Spanish Fork Airport, Spanish Fork, Utah

VELOCITY, IN METERS PER SECOND

S-wave

P-wave

1,670

Discussion and Synopsis of Vs Results  25
Figure 19. S-velocity models for the four downhole S-wave soundings in Utah Valley are shown as solid lines on graph. Dashed 

pink line is Provo Airport S-minivib result for comparison with Provo Airport downhole result. Dashed blue line is S-timber 

Spanish Fork Airport result for comparison with nearby downhole result. Velocity-depth models, in table form, are listed to right of 

diagram.

Spanish Fork

Airport

K96 Radio

Towers

Youd Farm

Provo Airport

Spanish Fork

Airport S-timber

Provo airport

S-minivib

SHEAR-WAVE VELOCITY (VS), IN METERS

PER SECOND

Utah Valley Downhole Vs Velocity Models Depth Vs

0

20

20

40

40

46

192

192

227

227

297

297

K96

Depth Vs

Spanish Fork Airport

0

4

4

10

10

18

18

26

26

30

30

38

38

44

44

48

48

56.6

114

114

212

212

314

314

237

237

330

330

223

223

306

306

266

266

579

579

Depth Vs

0

10

10

14

14

28

150

150

124

124

184

184

Provo Airport

Depth Vs

0

6

6

30

30

58

58

65.8

187

187

234

234

326

326

388

388

Youd Farm

Units for all tables:

Depth, in meters

Vs, in meters per second

26  Miscellaneous High-Resolution Seismic Imaging Investigations in Salt Lake and Utah Valleys for Earthquake Hazards
Figure 20. Fire training tower (FTT) comparison of minivib, shear-timber, and SASW results. (A) Locations of 

array midpoints for shear-timber (S-timb), minivib (S-vibe), first SASW (SASW1), and second SASW (SASW2) 

investigations. SASW results from J. Berry and J. Bay (Utah State University, written commun., 2006). (B) Vsdepth models from shear-timber (red), minivib (green), and SASW2 (blue) investigations. Dashed lines indicate 

a decreased confidence in the interpretation.

200 400 600 800 1,000

80

70

60

50

40

30

20

10

0

Method Vs30(m/s)

S-timb 690

S-vibe 480

SASW2 432

S-timb

S-vibe

SASW2

S-vel (m/s)

430

430

535

535

1035

1035

Depth (m)

0.0

6.0

6.0

13.0

13.0

30.0

FTT S-timber model

SHEAR-WAVE VELOCITY (VS),

IN METERS PER SECOND

B

A

FTT

Discussion and Synopsis of Vs Results  27
Figure 21. (A) Shear-timber data acquired at site NOQ and interpreted velocity-depth structure. Data are shown as reversedpolarity overlay to emphasize clean first arrival times. Red lines show refraction interpretation. (B) Comparison of minivib and 

shear-timber results with theoretical linear and exponential velocity functions. Vs30s of shear-timber and linear velocity-depth 

model are very similar at 660–670 m/s. (C) Graph showing Vs and Vp result from respective sledgehammer-source data. NOQ 

shear-timber velocity-depth model and P-wave velocity-depth model are shown in table format to right of figure.

C

500 1,500 2,500

S-vel (m/s)

450

450

535

535

1,290

Depth (m)

0.0

10.0

10.0

17.0

17.0

30.0

NOQ S-timber model

1,290

VELOCITY (VS AND VP),

IN METERS PER SECOND

10

20

30

Depth (m) P-vel (m/s)

0.0 650

4.0 650

4.0 970

12.0 970

12.0 2,950

30.0 2,950

NOQ P-wave model

S-wave

P-wave

red: S-timber

Vs30=660 m/s

green: S-minivib

Vs30=620 m/s

blue: theoretical exponential

Vs30=760 m/s

blue dash: theoretical linear

Vs30=670 m/s

B

-60

-50

-40

-30

-20

-10

0

SHEAR-WAVE VELOCITY (VS),

IN METERS PER SECOND

A OFFSET, IN METERS

100

200

300

0 -30 0 30

481 m/s

421 m/s 521 m/s

350 m/s

1202 m/s 1399 m/s

28  Miscellaneous High-Resolution Seismic Imaging Investigations in Salt Lake and Utah Valleys for Earthquake Hazards
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